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Neuropsychologia 190 (2023) 108666
Available online 25 August 2023
0028-3932/© 2023 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
A review of the impairments, preserved visual functions, and
neuropathology in 21 patients with visual form agnosia – A unique defect
with line drawings
Hayden J. Peel , Philippe A. Chouinard
*
Department of Psychology, Counselling and Therapy, School of Psychology and Public Health, La Trobe University, Victoria, Australia
ARTICLE INFO
Keywords:
Visual form agnosia
Apperceptive agnosia
Brain damage
Disorder of perception
Object recognition
Shape perception
Form perception
ABSTRACT
We present a comprehensive review of the rare syndrome visual form agnosia (VFA). We begin by documenting
its history, including the origins of the term, and the rst case study labelled as VFA. The dening characteristics
of the syndrome, as others have previously dened it, are then described. The impairments, preserved aspects of
visual perception, and areas of brain damage in 21 patients who meet these dening characteristics are described
in detail, including which tests were used to verify the presence or absence of key symptoms. From this, we note
important similarities along with notable areas of divergence between patients. Damage to the occipital lobe (20/
21), an inability to recognise line drawings (19/21), preserved colour vision (14/21), and visual eld defects
(16/21) were areas of consistency across most cases. We found it useful to distinguish between shape and form as
distinct constructs when examining perceptual abilities in VFA patients. Our observations suggest that these
patients often exhibit difculties in processing simplied versions of form. Decits in processing orientation and
size were uncommon. Motion perception and visual imagery were not widely tested for despite being typically
cited as dening features of the syndrome – although in the sample described, motion perception was never
found to be a decit. Moreover, problems with vision (e.g., poor visual acuity and the presence of hemianopias/
scotomas in the visual elds) are more common than we would have thought and may also contribute to
perceptual impairments in patients with VFA. We conclude that VFA is a perceptual disorder where the visual
system has a reduced ability to synthesise lines together for the purposes of making sense of what images
represent holistically.
1. Introduction
Sensory agnosia refers to a selective, modality-specic disorder of
perception that cannot be attributed to a primary sensory decit, inat-
tention, or general mental impairment (for a review on a general history
of sensory agnosia, see Coslett, 2011). The aim of the present review was
to provide a synthesis of all reported cases of “visual form agnosia”
(VFA). The term was rst used by Benson and Greenberg (1969) to
describe a patient who had a “unique defect in visual shape perception”
(pg. 82). The label has since been applied to several other patients who
presented with similar symptoms. However, there is some disagreement
about the exact nature of these symptoms, including which patients have
the syndrome. This review documents the reported features of the syn-
drome and discusses the case studies in the literature who meet those
criteria. We begin with a brief history of VFA. This is followed by a
discussion of how VFA has been conceptualised in other articles. In this
discussion, we propose that it is useful to draw a distinction between
‘shape’ and ‘form’
1
in understanding the nature of VFA as a perceptual
disorder – which is something that has not really been considered
before. Individual case studies are then described, including how
symptoms were tested for. We conclude with a discussion on broad
similarities, notable areas of divergence, and considerations for future
* Corresponding author. George Singer Building, Room 460, Department of Psychology, Counselling, and Therapy, La Trobe University, Melbourne, Victoria, 3086,
Australia
E-mail address: p.chouinard@latrobe.edu.au (P.A. Chouinard).
1
According to denitions from authoritative sources, such as the Webster and Oxford dictionaries, shape and form can be used inter-changeably. However, if one
reads their denitions in their entirety, there is more focus on shape to mean contours and outlines, and form to mean a global arrangement of parts. In this paper, we
use shape to denote a structure composed of contours and outlines, and form to denote a structure with additional real or apparent three-dimensional features. As we
discuss later, this distinction is often made in the visual arts. We think it is also useful to make a similar distinction for understanding VFA.
Contents lists available at ScienceDirect
Neuropsychologia
journal homepage: www.elsevier.com/locate/neuropsychologia
https://doi.org/10.1016/j.neuropsychologia.2023.108666
Received 21 April 2023; Received in revised form 14 August 2023; Accepted 18 August 2023
Neuropsychologia 190 (2023) 108666
2
research.
1.1. Brief history
VFA is conceptualised as a type of apperceptive agnosia. The origins
of this term can be traced to the end of the 1800s, when some re-
searchers were actively trying to identify and describe visual impair-
ments. Hughlings Jackson’s work on imperception (1876), Munk’s work
(1881) on seelenblindheit (‘mindblindness’) in dogs, and Freud’s (1891)
introduction of the term agnosia were all important contributions to the
eld. However, it was the work of Lissauer in 1890, dubbed the father of
agnosia, which stood the test of time (Riddoch and Humphreys, 2003).
Lissauer wrote about a patient, Gottlieb L., who presented with a strange
perceptual complaint. Although this person could still clearly see, in that
they could copy gures presented to them, and describe their general
features and congurations, they were completely unable to identify the
same gures. For example, Lissauer writes the following regarding
Gottlieb’s reaction when shown a pocket watch:
“A lamp”, after a bit “a lighter”. On request draws the watch clearly.
The watch is then put to his ear. He recognises it at once: “Oh, it’s a
watch” (pg. 175, Lissauer and Jackson, 2007; Lissauer, 1890).
Thus, despite being able to see and draw the pocket watch, only after
hearing the ticking could he correctly identify it. Lissauer labelled this
impairment associative agnosia – the person was unable to associate their
prior knowledge with intact visual perception. Other types of visual
agnosia specic to other sensory modalities (e.g., audition) were
considered possible. Lissauer speculated on theoretical grounds that
there could be another form of visual agnosia, one where the structural
encoding of the sensory stimulus is disrupted with a resulting failure to
perceive objects. This he termed apperceptive agnosia, which remained
a theoretical possibility until 1918, when Goldstein and Gelb published
their case study on patient Johann Schneider.
At 24 years old, Schneider suffered a head injury after a mine-
splinter exploded. Schneider displayed several neuropsychological im-
pairments following this damage and became a controversial case in
neurology. Schneider could identify images and words slowly but only
when allowed to trace them with his head and hand. Otherwise, they
were unidentiable. His visual elds were constricted but visual acuity
and other visual functions were adequate, including colour vision with
only a slight red/green anomaly. This pattern of symptoms led Goldstein
and Gelb to conclude that Schneider’s decits were an example of
apperceptive agnosia and a striking example of defective Gestalt
perception, i.e., the inability to group single elements of a composite
visual image and segregate gure from ground in static visual displays
(Heider, 2000). Due to the apparent strangeness of Schneider’s symp-
toms, he appeared in more than a dozen works in the years after, pre-
senting with “alexia, form agnosia, loss of movement vision, loss of
visual imagery, tactile agnosia, loss of body schema, loss of position
sense, acalculia, and loss of abstract reasoning” (pg., 633, Marotta and
Behrmann, 2003). Questions were then raised about the legitimacy of
Schneider’s symptoms, as one person displaying all these symptoms at
once is remarkable (for a detailed discussion, see Landis et al., 1982).
For example, Jung (1949) saw the patient and noted that the stereo-
typical head tracing movements were present but were overstressed
during replication of the Goldstein and Gelb tests and disappeared with
increasing interest in the material. Thus, Jung suggested that some of the
abnormal responses that made Schneider’s case study interesting may
have been overlearned or exaggerated. Nevertheless, Schneider was the
rst example of apperceptive agnosia, and thereafter, more case studies
were described wherein there were clear visual impairments not
attributable to a low-level sensory decit.
It soon became clear that there were distinct types of apperceptive
agnosia, and that Lissauer’s two-category scheme appeared to be too
narrow to capture the nuanced differences between patients and the
different kinds of apperceptive agnosia. The highly specic agnosia for
shape or form did not appear, or was not labelled, until 1969 by Benson
and Greenberg, when they described Mr S. As described below, Mr S
appeared to have profound problems with the recognition of basic
shapes and line drawings, despite sufciently near normal visual acuity
and visual elds. The label was then retroactively applied to one other
case, HC (Adler, 1944), and there have been several more cases reported
since. Note that although Benson and Greenberg were the rst to use the
label in its current form, Nielsen (1936) appears to have predated this
when he discussed the most fundamental of visual agnosias in a
comprehensive review. Nielsen termed it geometric-optic agnosia. “In this
difculty, the patient has lost sense of direction of lines so that he fails to
recognise objects because of their distortion … In geometric-optic
agnosia other mental disturbances are usually present.” (pg. 52).
There are many individuals who appear to meet this criterion, as we will
discuss later.
It deserves passing mention that some people have questioned if form
impairments, like those exhibited by patients with VFA, can be classied
as part of the agnosia continuum or should be considered a low-level
sensory problem (Bay, 1953; Warrington and James, 1988). Indeed,
this led some authors, such as Warrington and James (1988), to argue
that cases like Mr S cannot be considered examples of apperceptive
agnosia as described initially by Lissauer for two key reasons: (1) it is
difcult in cases of visual agnosia to unequivocally establish that visual
functions (e.g., visual acuity, visual elds etc.) are normal or sufciently
near normal, and (2) the term agnosia ought to be reserved for problems
with knowledge – after all, the Greek term from which agnosia is derived
translates roughly to ‘lack of knowledge’. In other words, instead of a
conceptual problem, or the imposition of meaning onto sensory data, as
in Lissauer’s case of associative agnosia, the symptoms of VFA may
represent more of a pseudo-agnosia, laying somewhere between
low-level sensory problems and higher-order aspects of agnosia. This
scepticism has contributed to confusion as to how one can operationally
dene apperceptive agnosia and by extension VFA. In the present paper,
we adopt Farah’s (2004) more general denition of apperceptive
agnosia and consider VFA as an example of it. Namely, apperceptive
agnosia is a broad category referring to “any failure of object recognition
in which perceptual impairments seem clearly at fault, despite relatively
preserved sensory functions such as acuity, brightness discrimination,
and colour vision” (pg. 11). VFA is a specic instance of this where shape
or form perception is disrupted.
1.2. What are the dening features of the syndrome?
VFA is primarily characterised by decits in the perception of shape
or form. Indeed, coinage of the term ‘form agnosia’ by Benson and
Greenberg was intended to capture decits in both shape and form,
given they never made a distinction between the two. In the visual arts,
the former is not the same as the latter (Art in Context, 2022). After
careful consideration, we believe making this distinction is helpful for
discussing patient symptoms and evaluating how the brain processes
visual information. Unfortunately, as evidenced from conducting this
review, the word ‘form’, as in everyday parlance, has been used in a
variety of ways when discussing VFA and rarely operationally dened,
which seems to have contributed to some confusion and a lack of
consensus as to what the syndrome could be.
The visual arts are careful to draw a distinction between shape and
form (Art in Context, 2022; Arnheim, 1974). For a stimulus to have
form, it must have a global conguration (e.g., an outline or boundary of
some kind) and an arrangement of local features within that boundary to
give an impression of a three-dimensional structure. The most common
type of stimulus shown to patients when they are being examined to
assess form perception are line drawings. Form in a 2D drawing simu-
lates structure as it is encountered in the real world. This structure is
conveyed by the addition of pictorial depth cues, such as occlusion,
shading, and texture. Hence, a 2D image can be thought of as a shape
when it comprises only outlines, whereas a 2D image has form when it
H.J. Peel and P.A. Chouinard
Neuropsychologia 190 (2023) 108666
3
gives the illusory impression of having a third dimension. For example, a
square in a picture has shape – having height and width. Conversely, a
cube has form – having length, width, and height (see Fig. 1). In
everyday parlance, there is little distinction between shape and form,
with the two often being used interchangeably. We believe it is useful to
differentiate between the two to help understand the nature of decits in
VFA.
From a phenomenological perspective, reports from VFA patients
range from “everything blurs together” (DF, in Milner et al., 1991) to “I
can’t tell what an object is because I don’t see it clearly” (Mr S, in Efron,
1969). This qualitative account of perception can help explain why there
are profound decits in shape or form perception (Heider, 2000). VFA
patients experience seeing objects that lack denable form and are un-
able to perceive their gural properties or their ‘traits and lines’ (Mar-
tinaud, 2017). This has led some to posit that they are also unable to
perceive the metric features of objects, such as their size (e.g., lengths
and distances) and orientation (Riddoch and Humphreys, 2003; Marti-
naud, 2017). These decits are usually demonstrated by patients being
unable to discriminate between basic shapes, such as a square from a
circle, and copying and identifying drawings successfully.
Typical tasks used to assess difculties in shape or form perception
include the Efron task (Efron, 1969) and the Boston Naming Test
(Kaplan et al., 2001). The Efron shape matching task was originally
designed to determine if Mr S was able to discriminate between two
objects that differed only by shape whilst matching for volume. In this
task, the patient is presented with two objects at once – a black square
and a black rectangle with identical volume and reectance. Within the
pair, the shape of one of the objects is progressively elongated (see
Fig. 2). The task requires the participant to determine if the two are the
same or different. The Boston Naming Test (Kaplan et al., 2001) consists
of 60 black-and-white line drawings of objects that must be named.
Successful naming is assumed to necessitate shape and form processing.
Although these are some of the typical tests used, it is more common for
researchers to develop their own tasks for evaluating form perception.
Doing so often yields interesting experimental ndings but makes it
difcult to directly compare task performance across studies. Finally,
the recognition of real objects is generally better than line drawings
(Farah, 2004). This is thought to be due to patients focusing on what
they can still see, such as colour and texture, in images.
VFA patients retain several visual functions. However, it is
misleading to say that they are usually normal. Rather, it may be more
prudent to say that these functions might not be sufciently affected to
explain the agnosia. Visual elds are largely intact, or, if there are any
visual eld defects (e.g., scotomas), they do not seem responsible for the
perceptual problems (Farah, 2004). When measured, visual acuity is
often reported to be within the normal range. As discussed in the pro-
ceeding sections, however, this is not entirely accurate in many cases.
Often, the reported metrics of visual acuity deviate considerably from
what most people would consider normal (i.e., 20/20), even though the
authors purport otherwise.
Measuring visual acuity is made difcult by the fact that some pa-
tients cannot recognise letters, making the Snellen chart an inappro-
priate test for measuring visual acuity. Instead, the testing of visual
acuity sometimes involves assessing the patient’s ability to differentiate
small dot patterns. For example, in patient DF, her visual acuity seemed
intact as she could distinguish between a grey patch and a ne dot
pattern (26 dots per cm) that is equivalent to a resolution of 1.7 min arc
(Milner et al., 1991). So, despite subjectively stating that things might
blur together, a wide range of ophthalmological tests in patient DF
suggest there is no defect that would be sufcient to account for her
complaints of unclear vision.
In most VFA patients, the ability to maintain xation, colour
perception, stereopsis, motion, and brightness perception are considered
sufciently intact (Farah, 2004). Thus, it is through compensatory
processing strategies, like processing colour and texture in objects, that
patients can display better recognition for real objects in pictures
compared to line drawings (Mapelli and Behrmann, 1997). For example,
a patient’s explanation when asked how they correctly identied a lion
was: “I can see it’s yellow and furry, so I just guessed.” This is not to say
that their perception of gures is normal, as they often make decisions
with great difculty and take much longer than the average observer.
So, while they can still see some things and have normal or near-normal
vision, without the capacity to perceive form or shape conguration,
profound problems with visual recognition occur. Finally, although not
Fig. 1. These illustrations provide an example of how internal features can
convey structure. To the left, we have a cube with shading cues. To the right, we
have the shading cues removed from the cube, which leaves the impression of a
at shape.
Fig. 2. These illustrations depict the Efron task, which consist of presenting
pairs of rectangles that differ in dimensions but not in surface area. Sizes are
adapted from the LEA Rectangles Game (https://www.leatest.com/catalog/
cognitive-vision/lea-rectangles-game%C2%AE). VFA patients are often unable
to perform better than chance when discriminating whether the pairs are same
or different.
H.J. Peel and P.A. Chouinard
Neuropsychologia 190 (2023) 108666
4
a visual function per se, Farah (2004) observed that some VFA patients
can utilise kinaesthetic cues to facilitate object recognition, such as
tracing a gure with their ngers or head.
There appears to be a variety of causes for VFA. Heider’s review
(2000) included only patients who suffered from carbon monoxide
poisoning, where all individuals had extended lesions in the extrastriate
cortex, particularly the lateral occipital complex (LOC). However, this
only comprises a subset of patients with VFA. Farah (2004) notes that
the neuropathology in cases of VFA is fairly homogenous. She describes
ve patients who suffered from carbon monoxide poisoning, one from
mercury poisoning, and another from a penetrating head wound.
2
Neurological signs and neuroimaging techniques suggest that brain
damage in most patients is primarily located in the occipital lobe and
surrounding regions. However, brain damage tends to be diffuse rather
than focal – particularly in cases with carbon monoxide poisoning,
which is known to also damage subcortical white matter and the cortex
diffusely (Farah, 2004).
Even Farah’s detailed investigation overlooked some existing cases
in the literature, and some new cases have since been published, which
further complicates the question of what brain regions might be impli-
cated. As such, a revisiting of the literature is necessary. Below, in Ta-
bles 1 and 2, we detail all cases post 1940 which either have been
classied as VFA patients or, who upon reading their reported symp-
toms, display one or several of the dening features for VFA. These cases
were identied by an initial search in PubMed with the search terms
“visual form agnosia”, which returned 12 unique cases from 77 results,
and “apperceptive agnosia”, which returned 9 unique cases from 33
results. The remaining cases were identied through reading review
articles and case study papers that refer to other cases of VFA. In total,
we identied 31 cases with symptoms of VFA, 10 of which were
excluded for various reasons, including comorbid diagnoses or insuf-
cient details on the presence of symptoms to conrm the possible
presence of VFA. More information on excluded cases can be found in
the Appendix.
2. Review of patients
Existing works on VFA and the criteria detailed in them paints a
relatively coherent picture of the syndrome. However, upon reading
case study papers directly, reported decits and patterns of brain dam-
age have sometimes been described in unhelpful ways for the purposes
of drawing similarities across studies. For example, possible nuanced
comparisons between patients are lost when authors provide gross as
opposed to detailed descriptions. Nuances are important because they
can lead one to better characterise the nature of the syndrome. It is our
opinion that there needs to be a single place where all cases are
described in enough detail to evaluate their similarities and disparities,
as well as the tests that were administered to evaluate their symptoms.
Therefore, this review aims to document how well the 21 case studies
that we found meet the dening criteria for VFA. They are presented
below in the order in which they were published. In addressing this aim,
we comprehensively describe decits, intact capabilities, and neuropa-
thology on a case-by-case basis, including how they were examined. It
should be noted that many original papers do not mention the specic
tests or measures used. We have included this information whenever
possible. We place emphasis on addressing the following questions:
Where, if mentioned, is the site of brain damage? How was the brain
damage acquired? Do patients have intact visual elds and visual acu-
ity? Are patients able to discriminate between objects based on shape or
form or both? Are patients able to perceive orientation, size, colour, and
motion? Can patients copy gures? Is imagery preserved? Can patients
still read? Tablea 1 and 2 lists each VFA patient that we review along
with their demographics, descriptions of brain damage, and presence
and absence of visual abilities. Figs. 3 and 4 provide illustrated tallies of
this same information.
2.1. HC in Adler (1944) and Sparr et al. (1991)
HC sustained carbon monoxide poisoning in a nightclub re at the
age of 22. She was rst described by Adler (1944) and is considered the
rst genuine case of VFA to appear in the literature after Schneider. As
such, she has been foundational to the study of VFA. HC was tested again
nearly 50 years later by Sparr et al. (1991). She provides unique insight
into how symptoms can progress and change over an extended period.
2.1.1. Impaired abilities
In the rst month after brain damage, HC was unable to recognise
simple shapes (“What is this?” [a circle] “Looks like an alphabetical A.“).
She did not recognise any objects from pictures (e.g., she called a comb a
fountain pen and a little toy elephant a pencil). Although severely
affected to begin with, she gradually developed the ability to copy
simple shapes (e.g., circles, triangles, and squares). She had greater
difculty copying gures with curved lines. Pictures were harder to
recognise than real objects. Three months after brain damage, HC
became more adept at recognising one part of an image to infer what the
whole image represented. For example, when shown a green 4-inch-long
toy battleship through a tachistoscope, she gave the following responses
for different viewing presentation times: 1 s – “a fountain pen”; 2 s – “a
knife, green”; 3 s – “a boat”. She explained her method as the following:
“First I saw the front part. It looked like a fountain pen because it was
shaped like a fountain pen. Then it looked like a knife because it was so
sharp … Then I saw the spokes and thought it was shaped like a boat.”
Forty years later, HC had no difculty identifying common objects. It
was only upon formal testing that her agnosia became evident. HC could
only truly perceive a small portion of any image. From those smaller
portions, she inferred what the image represented using a ‘sum-of-parts’
strategy. This strategy was conrmed by her inability to recognise g-
ures in the Poppelreuter test, shown in Fig. 5. Synthesising small stimuli,
complex details, and curves seemed more affected than straight lines.
Regarding imagery, in 1944 the visual component of her dreams was
diminished, but she had not lost the ability to visualise or form new
images as evidenced by her drawing ability. In 1991, imagery was re-
ported to be defective, as free drawing remained crude, she was unable
to describe objects adequately, and topographical imagery was reported
as impaired.
2.1.2. Intact abilities
In 1944, visual acuity was 20/70 in each eye, as inferred by the
Snellen chart. Despite a slight constriction of the right lower visual eld,
her visual elds were deemed normal. It was reported that her colour
perception was intact, though slightly perturbed. HC could provide good
estimates of object length, reecting intact size perception, and read
arrows, like those posted at her hospital, reecting intact orientation
perception. More rigorous tests of orientation and size perception were
not performed. In 1991, HC’s corrected visual acuity was 20/30 in each
eye, as inferred by the Snellen chart. Goldmann perimetry was per-
formed and was deemed normal aside from a small homonymous sco-
toma subtending the midline of the lower visual eld, which encroached
the central 10◦of vision inferiorly. It was reported that HC performed
normally on colour naming and matching tasks.
2.1.3. Brain damage
Sparr et al. (1991) performed electroencephalography (EEG) and
magnetic resonance imaging (MRI) on HC, which revealed bilateral
occipital atrophy. No other pathology was reported.
2
Note that Farah appears to be alone in considering the latter patient,
Schneider, as a case of VFA because of the wide array of decits.
H.J. Peel and P.A. Chouinard
Neuropsychologia 190 (2023) 108666
5
Table 1
Individuals labelled as having VFA in chronological order of reporting including the aetiology, areas of damage including neuroimaging data (if available), and the presence and absence of visual abilities.
Patient Demographics Aetiology Location of brain damage Visual
acuity
Visual elds Shape
perception
Form
perception
Real object
advantage
HC F, 22 CO •Generalised bilateral occipital atrophy
•Scans suggest damage was primarily in posterior regions (see Fig 2 in Sparr et al., 1991).
•Imaging was done with MRI.
Preserved Inconclusive Inconclusive Impaired Preserved
Mr S M, 25 CO •Persistent bilateral slow wave patterns in parietooccipital areas as revealed by EEG.
•Bilateral posterior ventricular dilation as revealed by pneumoencephalogram.
Impaired Inconclusive Impaired Impaired Preserved
RC M, 39 CO •Diffuse lesion in left calcarine sulcus, encompassing the striate and extra-striate.
•Lesion to the extra-striate cortex in the right hemisphere.
•Imaging was done with CT.
Preserved Inconclusive Impaired Impaired Preserved
X M, 30 Mercury poisoning •Unavailable other than the authors reporting that the CT, EEG, and EMG were normal. Preserved Inconclusive Inconclusive Impaired Impaired
ES M, 33 CO •Widespread damage including occipital lobes.
•Imagine was done with EEG and CT.
Inconclusive Preserved Impaired Impaired Impaired
DF F, 34 CO •Bilateral LOC damage.
•Left occipitoparietal damage, in and surrounding the intraparietal sulcus.
•Imaging was done with MRI.
Preserved Inconclusive Impaired Impaired Preserved
SMK M, 21 Anoxia •Unavailable other than the authors speculating there may be V4 damage. Preserved Preserved Inconclusive Impaired Inconclusive
FWT M, 66 Stroke •Bilateral inferior temporal lobes lesions, which were more severe in the left hemisphere
and encompassed the fusiform and lingual gyri.
•Imaging was done with CT and PET.
Impaired Inconclusive Inconclusive Impaired Inconclusive
KK F, 56 Multiple sclerosis •Bilateral occipital lobe lesions, which were anterior to the occipitotemporal junction.
•Bilateral frontal lobe white matter damage.
•Corpus callosum damage.
•Imaging was done with MRI.
Inconclusive Inconclusive Inconclusive Impaired Preserved
PG M, 27 Trauma •Bilateral frontal lobe lesions.
•Cortical-subcortical right hemisphere lesion in the occipital and parietal lobes.
•Imaging was done with MRI.
Preserved Inconclusive Impaired Impaired Preserved
JW M, 38 Anoxia •Bilateral lesions in ventral occipital lobes, including V1 and V2.
•Imaging was done with CT and MRI.
Impaired Inconclusive Inconclusive Impaired Preserved
SZ M, 54 Stroke •Lesions to the middle and inferior temporooccipital cortex with sparing of V1.
•Imaging was done with PET.
Preserved Inconclusive Inconclusive Impaired Preserved
Not
Named
M, 65 Stroke •Bilateral occipitotemporal lesions.
•Imaging was done with MRI.
Preserved Inconclusive Inconclusive Impaired Impaired
SF M, 46 Anoxia •Bilateral occipital lobe atrophy with damage primarily in posterior regions with sparing
of V1 (see Fig 1 in Aglioti et al., 1999).
•Imaging was done with MRI.
Inconclusive Inconclusive Impaired Impaired Impaired
AM M, 46 Anoxia •No damage evident from MRI scans. Inconclusive Preserved Inconclusive Inconclusive Preserved
SB M, 30 Meningoencephalitis •Partial/complete damage in V2, V3, V4, and V5 in the right hemisphere.
•Lesions in the ventral part of occipitotemporal junction in the left hemisphere.
•Imaging was done with MRI.
Impaired Inconclusive Impaired Impaired Impaired
006 M, 50 Oligodendroglioma •Right lingual and fusiform gyri lesions.
•Imaging was done with MRI.
Preserved Inconclusive Inconclusive Preserved Inconclusive
XF F, 42 CO •Bilateral occipitotemporal damage including damage to LOC and the posterior part of the
fusiform gyrus.
•Left posterior parietal cortex damage.
•Enlarged ventricles.
•Bilateral anterior frontal lobe damage
•Imaging was done with MRI.
Inconclusive Preserved Impaired Impaired Inconclusive
SA F, 50 Stroke •Bilateral damage to the dorsal extra-striate cortex, including damage surrounding the
right intraparietal sulcus.
•Imaging was done with MRI.
Preserved Inconclusive Impaired Impaired Inconclusive
JS M, 74 Stroke •Bilateral fusiform and lingual gyri lesions, extending into the posterior cingulate gyrus.
•Lesions extending into the para-hippocampal gyrus and cuneus in the right hemisphere.
•Imaging was done with MRI.
Inconclusive Preserved Impaired Impaired Impaired
SDV M, 44 Anoxia •Enlarged ventricles.
•Bilateral damage to BA 17-18 and 30-31, including partial damage in BA 19 and 7.
•Imaging was done with MRI.
Preserved Impaired Inconclusive Impaired Inconclusive
Age denotes the age of the patient when they were rst examined. Abbreviations other than patient initials: BA =Brodmann area, CO =carbon monoxide, CT =computer tomography, EEG =encephalography, F =female,
LOC =lateral occipital complex, M =male, MRI =magnetic resonance imaging, and PET =position emission tomography. V1, V2, V3, V4, and V5 are different visual areas.
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2.2. Mr S in Benson and Greenberg (1969) and Efron (1969)
At 25 years of age, Mr S was found unconscious after being exposed
to leaking carbon monoxide fumes while showering. This was the case
study where the term visual form agnosia was coined and is perhaps the
most severe case of VFA in this review.
Table 2
Individuals labelled as having VFA in chronological order of reporting including demographics and the presence and absence of visual abilities.
Patient Orientation perception Size perception Colour perception Motion perception Copying gures Imagery Reading
HC Preserved Inconclusive Preserved Inconclusive Preserved Impaired Preserved
Mr S Inconclusive Preserved Preserved Preserved Impaired Impaired Inconclusive
RC Impaired Inconclusive Impaired Inconclusive Impaired Inconclusive Inconclusive
X Inconclusive Preserved Preserved Preserved Inconclusive Impaired Preserved
ES Inconclusive Inconclusive Preserved Inconclusive Impaired Inconclusive Inconclusive
DF Impaired Impaired Preserved Inconclusive Impaired Preserved Preserved
SMK Preserved Impaired Preserved Inconclusive Impaired Inconclusive Inconclusive
FWT Inconclusive Preserved Impaired Inconclusive Preserved Preserved Preserved
KK Inconclusive Inconclusive Impaired Inconclusive Preserved Preserved Inconclusive
PG Impaired Impaired Inconclusive Inconclusive Impaired Inconclusive Inconclusive
JW Preserved Inconclusive Preserved Inconclusive Inconclusive Preserved Inconclusive
SZ Impaired Inconclusive Preserved Inconclusive Impaired Preserved Decit
Not Named Preserved Inconclusive Preserved Inconclusive Preserved Inconclusive Inconclusive
SF Inconclusive Inconclusive Preserved Preserved Impaired Preserved Decit
AM Preserved Impaired Preserved Inconclusive Preserved Inconclusive Preserved
SB Impaired Preserved Preserved Preserved Preserved Preserved Decit
006 Impaired Inconclusive Preserved Inconclusive Inconclusive Inconclusive Decit
XF Impaired Impaired Preserved Preserved Inconclusive Inconclusive Decit
SA Preserved Preserved Inconclusive Inconclusive Preserved Inconclusive Preserved
JS Impaired Impaired Preserved Inconclusive Preserved Inconclusive Inconclusive
SDV Impaired Impaired Preserved Preserved Preserved Preserved Decit
Fig. 3. The gures represent tallies of cases with different types of brain damage and visual impairments. Panel A depicts the number of cases with damage to a
particular lobe in the brain. Panel B depicts the laterality of damage either being bilateral, right hemisphere (RH) only, left hemisphere (LH) only, or inconclusive
(IC). Panels C to G depict the presence and absences of various visual abilities. For the latter panels, green denotes the number of cases with preserved abilities, red
denotes the number of cases with impaired abilities, and yellow denotes where the information provided was too inconclusive for us to decide whether these abilities
were preserved or impaired.
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2.2.1. Impaired abilities
Mr S could not identify objects by sight alone – this included physical
objects, pictures of objects, body parts, letters, numbers, and geomet-
rical gures. For example, he consistently failed to identify, copy, and
match simple gures and letters. He also maintained that he experienced
no dreams, or if there were dreams, they were devoid of visual content,
suggesting abnormal visual imagery.
2.2.2. Intact abilities
Mr S could successfully name colours. He could use colour and size
information to try to identify stimuli. For example, when he was shown a
set of keys, he said that he could see “it” while pointing in its general
direction but was only able to report it as “shiny like silver”. When the
experimenter jingled the keys, however, he snapped out “keys” (Efron,
1969). Visual acuity was estimated to be 20/100 in each eye, as assessed
by his ability to reach for objects or point to small pieces of white
cardboard on a black background. Performance on other physiological
tests of vision, like spatial summation and icker fusion, was reported to
deviate from normal only slightly (Efron, 1969). Some bilateral inferior
visual eld constriction was reported.
2.2.3. Brain damage
An EEG revealed a persistent bilateral slow wave pattern in the
parietooccipital areas, while a pneumoencephalogram revealed poste-
rior ventricular dilation bilaterally – suggesting damage to both the
Fig. 4. The gures represent tallies of cases with different types of visual impairments. Namely, panels A to G depict the presence and absences of various visual
abilities. For the latter panels, green denotes the number of cases with preserved abilities, red denotes the number of cases with impaired abilities, and yellow denotes
where the information provided was too inconclusive for us to decide whether these abilities were preserved or impaired.
Fig. 5. Example of a Poppelreuter (1917) overlapping gure.
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striate cortex and non-primary visual cortex in the occipital and parietal
lobes. Benson and Greenberg posited that “the isolated loss of form
discrimination suggests malfunction at a higher (cortical) level, a
premise consistent with the recognised pathology of carbon monoxide
intoxication” (1969, pg. 87). They noted that the presence of other
problems, like gait disturbance and the inability to recognise orally
spelled words, indicated that brain damage was likely more extensive
than damage conned to visual regions in the occipital and parietal
lobes.
2.3. RC in Adabi (2000) and Campion and Latto (1985)
RC suffered carbon monoxide poisoning from being trapped inside a
chimney. He was examined on several occasions between 1979 and
1985. Campion and Latto (1985) posited the “peppery mask hypothe-
sis”. They argued that VFA in RC was the result of ‘peppery’ scotomas
throughout his visual eld, resulting in disproportionate effects on form
perception over other kinds of perception. Note this explanation can
only apply to RC and other VFA patients with ‘peppery’ scotomas. It
cannot account for VFA in patients with intact visual elds or other
forms of scotomas.
2.3.1. Impaired abilities
RC was unable to recognise and copy simple shapes or trace their
outline with his nger. He was unable to name these items, describe
their function, or make same/different judgements between them when
presented with pairs. He could also not recognise the orientation of lines
and grating patterns. When asked to name 30 line-drawings of objects
from the Boston Naming Test and 27 real world equivalents of the
drawings, he scored 5/30 for the line drawings and 17/27 for the real
objects. Discriminating line length was impossible. RC performed poorly
when asked to detect differences in luminance and desaturated colours –
demonstrating that colour and brightness perception was also impaired.
2.3.2. Intact abilities
It was reported that RC’s visual elds were intact aside from a right
lower homonymous quadrantanopia. Sensory visual functions were re-
ported to be intact, although more specic details were not reported.
2.3.3. Brain damage
Computed tomography (CT) revealed a diffuse lesion located in and
above the left calcarine sulcus, encompassing the striate and extrastriate
cortex. There was also some damage in the extrastriate cortex in the
right hemisphere.
2.4. Mr X in Landis et al. (1982)
Mr X was exposed to inorganic mercury vapour in a laboratory job.
Landis et al. (1982) note the high correspondence between the symptom
prole of Mr X and patient Schneider, including their use of kinaesthetic
tracing to facilitate recognition.
2.4.1. Impaired abilities
When allowed to trace, Mr X could recognise simple shapes, such as
circles and triangles. However, with more complex gures, he would
give different answers for the same drawing depending on where he
started to trace. Recognition of detailed pictures was easier than line
drawings. He could not draw, copy, and recognise forms, even when he
was allowed to trace them and was given unlimited time. Visual elds
were reported to be restricted but normal within 2◦radius, as assessed
using tachistocopic perimetry testing. Mr X was said to have decits
with visual imagery – although what tests were used to determine this
was not reported.
2.4.2. Intact abilities
Colour vision was reported to be normal as assessed by the 100 Hue
Farnsworth Test and Ishihara Isochromatic Plates. Stereoscopic vision
was also considered normal using random dot stereograms. Ample evi-
dence of being able to detect motion was also provided. It was reported
that Mr X’s visual acuity was 20/20 in each eye.
2.4.3. Brain damage
The following was reported: “computerized tomography of the head,
electroencephalography and electromyography/nerve conduction
studies were all within normal limits” (Landis et al., 1982). Although no
brain damage appeared from these examinations, Landis et al. (1982)
speculated that Mr X could have had a considerable degree of posterior
white matter and callosal destruction. The authors reasoned that inor-
ganic mercury vapour is known to poison cellular function in the brain
(Bernhoft, 2012) and discussed the results from a brain autopsy of a
different patient who suffered from mercury poisoning (Hay et al.,
1963). In this patient, there was a porous appearance of white matter in
several brain regions, most notably subcortical white matter tracts in the
temporal and occipital lobes, as well as the corpus callosum. According
to Landis et al. (1982), Mr X could have had similar brain damage.
2.5. ES in Alexander and Albert (1983)
ES was found unconscious from carbon monoxide inhalation in a
burning home and remained unconscious for 2 days after the incident.
Although ES was rst described by Alexander and Albert (1983), he was
not considered a VFA patient until Farah (2004) suggested that he might
be. There is little detail about which tests were used to assess his
perceptual abilities.
2.5.1. Impaired abilities
Performance was reduced on many tasks, including reading letters
and numbers, identifying faces, and recognising geometric gures and
complex gures. He could not draw or copy any of the line drawings
presented to him.
2.5.2. Intact abilities
Visual acuity could not be measured by conventional means due to
ES’ problems with letter recognition. Nonetheless, he could see small
objects, suggesting that visual acuity was somewhat intact. ES’ visual
elds and extraocular movements were reported to be normal –
although he had difculties maintaining xation. He could no longer see
objects when xation was lost. He could name colours and real objects
presented physically in front of him.
2.5.3. Brain damage
EEG was reported to be normal. A CT scan revealed moderate
enlargement of cortical sulci. From this scan, Alexander and Albert
(1983) concluded that ES had widespread cortical damage, including
damage throughout the occipital lobes.
2.6. DF in Milner et al. (1991) and others
At 34-years-old, DF suffered from carbon monoxide toxicity due to a
leaking gas water heater while showering. She is the most studied of all
VFA patients, appearing in over 58 publications by Melvyn Goodale,
David Milner, and their colleagues. Her brain damage has been docu-
mented thoroughly by James et al. (2003) and Bridge et al. (2013).
2.6.1. Impaired abilities
DF has reduced abilities in object recognition. As discussed by Milner
et al. (1991), she cannot recognise pictures of some objects but can
identify others based on their colour, texture, and size (e.g., she can
identify a screwdriver by rst recognising it as being ‘long, black, thin,
and metallic’). She cannot identify Snodgrass and Vanderwart (1980)
line drawings at all. DF also performs poorly on the Efron task. Namely,
she cannot perceptually discriminate between two different rectangular
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stimuli with the same surface area. DF was described as partly impaired
with motion processing.
2.6.2. Intact abilities
Although she cannot perceptually discriminate between two stimuli
in the Efron task, she can calibrate her peak grip aperture in ight during
reach-to-grasp actions with high-levels of precision to match the width
of Efron blocks (Goodale et al., 1991). In other words, processing the
form of these objects for the purposes of perception is impaired but not
for the purposes of grasping them. Importantly, this behaviour cannot be
explained by compensatory mechanisms given that the calibration of her
peak grip aperture always occurs in ight before she touches the objects
and can still occur with the rest of her body remaining immobile. This
led Goodale and Milner (1992) to propose their two visual streams hy-
pothesis (TVSH) where vision for processing the form of stimuli is car-
ried out independently by the ventral and dorsal visual streams for the
purposes of perception and action, respectively. This dissociation has
been replicated multiple times with other stimuli (e.g., posting a letter in
a slot that can be oriented in different orientations, Milner et al., 1991;
grasping Blake shapes with stable versus unstable grasp points, Goodale
et al., 1994) in controlled settings with appropriate control conditions to
rule out alternative explanations than TVSH. DF’s visual elds are intact
except for some constrictions in her upper right quadrant. Other aspects
of vision, such as luminance, brightness judgements, acuity, stereoscopic
depth, and colour perception, are normal as assessed by computerized
psychophysics and ophthalmological examination. In terms of visual
imagery, DF could draw reasonably well from memory, which is
sometimes taken as evidence of intact imagery capabilities.
2.6.3. Brain damage
James et al. (2003) showed there was a concentration of bilateral
damage in the lateral occipital complex (LOC) in the ventral stream,
with sparing of the fusiform gyrus and primary visual cortex in the two
hemispheres. A later study by Bridge et al. (2013), built on the earlier
work of James et al. (2003), provides a more in-depth structural account
of her brain. Bridge et al. (2013) showed that there was a substantial loss
in cortical thickness in LOC as well as reduced white matter connections
between LOC and other areas. Areas that were minimally damaged in DF
include V1, MT/V5, and the ventromedial cortex in the temporal lobes.
Both James et al. (2003) and Bridge et al. (2013) noted some damage in
the left parietal-occipital cortex.
2.7. SMK in Davidoff and Warrington (1993)
SMK was assaulted at 21 years of age and suffered anoxia for an
extended period. SMK is not considered by some to be a case of VFA,
given that he retains the ability to recognise a range of visual stimuli.
2.7.1. Impaired abilities
On informal tests, Davidoff and Warrington (1993) reported that
SMK “totally misidentied many objects in his immediate environment
and he failed to recognise familiar faces. He was able to identify only one
(chair) of the rst six of the Oldeld pictures. He had considerable dif-
culty in identifying simple clear silhouette drawings of common ob-
jects (3/12 correct) (pg. 84).” Reading abilities could not be assessed.
SMK had specic problems with shape discrimination, performing
poorly on a modied version of the Efron task examining his ability to
discriminate between solid objects and collinear segments. Size
discrimination was also impaired, where he performed at chance when
asked to point to the larger of two stimuli when they differed by only
10% in area.
2.7.2. Intact abilities
SMK’s visual acuity was within the normal range on the Ffooks
symbols test (1965). His subtle problems with shape perception did not
permeate all aspects of visual recognition: surface characteristics were
accurately recognised (e.g., colour, brightness, and shading), gures
occluded with visual noise were detected, and he could perceive Gestalt
laws of proximity, continuity, and closure. Despite displaying some
difculties with shape processing, he performed perfectly when asked to
point to the square or triangle in a forced choice task that involved
judging the position of a Kanizsa illusory shape presented randomly on
either the left or right visual elds. SMK could also recognise geometric
forms (e.g., cubes) but line drawings of objects (e.g., Snodgrass stimuli)
were not tested.
2.7.3. Brain damage
The authors conjectured that SMK had a lesion in and around the
human homologue of V4, as they reasoned that a similar pattern of
impaired discrimination abilities had been reported in monkeys after
large lesions to V4 (Heywood and Cowey, 1987). There is no neuro-
imaging data available to conrm this speculation.
2.8. FWT in Shelton et al. (1994)
FWT had a stroke at 66 years old. He was initially blind. His vision
gradually improved, as assessed by examination, even though he stated
that he could not see because everything seemed to “run together”.
2.8.1. Impaired abilities
FWT had bilateral superior quadrantanopia for moving and station-
ary targets but could consistently identify the on and off-set of a light
ash in all visual elds. The patient failed to name, point to, or match
items of a specic colour. Simple shapes could not be named (0/9 cor-
rect), pointed to (0/9 correct), or copied (0/9 items initially correct and
3/9 items correct at a 9-month follow up) but could be matched to a
sample (10/12 correct). Snodgrass and Vanderwart (1980)
line-drawings could not be named (0/30 correct) or copied (0/30 cor-
rect) but the majority could be matched (28/40 correct).
2.8.2. Intact abilities
Snellen charts could not be used to assess visual acuity due to letter
recognition failure. However, he was able to indicate that all 14-point
numbers on the Snellen chart were different, suggesting visual acuity
at 20/100 in each eye. Initially, he was unable to discriminate between
line orientations that differed less than 90◦. At a follow-up evaluation,
he scored 75% correct on a task requiring him to make same-different
judgements for lines differing in orientations by 18◦–90◦. FWT consis-
tently discriminated between black dots that differed by 2-mm in
diameter. FWT could trace simple forms except for their upper portion,
which is in line with his visual eld defects. He could trace the missing
parts of the stimuli when they were inverted vertically. FWT was
reasonably good at describing objects visual features from memory,
suggesting intact visual imagery. Interestingly, FWT was reported to also
use a tracing technique, like Mr X, to facilitate recognition (Shelton
et al., 1990).
2.8.3. Brain damage
A CT scan showed a lesion in the inferior temporal lobes bilaterally.
The lesion was more severe in the left hemisphere and encompassed the
fusiform and lingual gyri. The primary visual cortex was spared. A
positron emission tomography (PET) scan was also performed. This scan
corroborated the ndings of the CT scan.
2.9. KK in Okuda et al. (1996)
KK was admitted to hospital at 56-years-old because of a transverse
myelitis after receiving a clinical diagnosis of multiple sclerosis at 23. KK
is the only organic case study with VFA where symptoms did not develop
because of trauma.
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2.9.1. Impaired abilities
KK’s accuracy ranged from 60 to 80% when asked to identify 15 real
objects on three separate occasions. Her perception of line drawings was
more severely impaired than real objects, with KK correctly identifying
38% of eight line drawings. Recognition was poor in overlapping Pop-
pelreuter gures (1/4 correct) and photographs of objects (0/12 cor-
rect). KK’s ability to name colours was also poor, averaging scores of 2/8
and 5/8 correct on the rst and second testing sessions, respectively.
2.9.2. Intact abilities
KK had a right-sided homonymous hemianopia. Visual acuity was
reported to be 20/60 in the right eye and 20/100 in the left eye when
corrected with reading glasses. KK could copy simple gures such as a
cross, circle, and triangle. Compared to her decits with object recog-
nition, KK performed better at reading letters and words in her native
Japanese language. She could correctly read 80% of Kanji letters and
65% of Kana letters. Like FWT, KK could describe objects reasonably
well from memory, suggesting intact visual imagery.
2.9.3. Brain damage
MRI showed white matter damage in the frontal and occipital lobes
in the two hemispheres, as well as in the corpus callosum. Her lesions in
the occipital lobe extended anteriorly to the occipitotemporal junction.
KK also had a frontal-lobe biopsy, which revealed demyelination and
gliosis.
2.10. PG in Charnallet et al. (1996)
PG sustained head trauma at 27 years of age and was in a coma for
three weeks. PG has perceptual problems that are specic to elementary
shape recognition.
2.10.1. Impaired abilities
PG could not copy lines presented at different orientations. He could
not trace or describe them either. He was unable to compare the length
of lines or the size of circles, as assessed by the Birmingham Object
Recognition Battery (BORB) subtests 2–3 (Riddoch and Humphreys,
2022), identify fragmented letters, or discriminate between basic shapes
on the Efron task. PG also performed poorly with recognition of Snod-
grass and Vanderwart (1980) line drawings (196/258 correct) and sil-
houettes (0/20 correct).
2.10.2. Intact abilities
Although PG performed poorly on tasks that required him to perceive
lines, shapes, and line drawings, he performed much better on recog-
nition tasks involving real objects (30/30 correct) and detailed images
(photographs: 32/32 correct; realistic drawings: 127/152 correct). Vi-
sual testing revealed a partial left homonymous hemianopia. It was re-
ported that PG had perfect central vision, normal visual acuity, normal
ocular movement control, and showed no signs of ocular ataxia.
2.10.3. Brain damage
An MRI showed bilateral frontal lobe lesions, diffuse lesions of the
white matter, and a large cortical-subcortical lesion in the occipital and
parietal lobes in the right hemisphere.
2.11. JW in Vecera and Gilds (1997) and others
JW suffered a cardiac event while exercising, which led to a state of
anoxic encephalopathy. For whatever reason, JW is not widely cited as a
case of VFA, despite there being clear evidence of decits in shape
processing.
2.11.1. Impaired abilities
JW recognised 21 of 39 real objects presented to him visually. He
could recognise 38 of 39 of them when they were presented to him by
touch or sound. His recognition of black-and-white drawings was worse,
naming 2 of 34 randomly selected Snodgrass and Vanderwart (1980)
drawings. He was unable to perform simple visual image segmentation,
the Efron task, and shape detection tasks consisting of objects presented
against a background of visual noise. He reported being a ‘poor reader’ –
although no formal testing of reading was mentioned.
2.11.2. Intact abilities
Tests of his vision were normal aside from the presence of an upper
left quadrantanopsia detected with Goldmann perimetry. His visual
acuity was poor, estimated to be 20/200 in each eye (Mapelli and
Behrmann, 1997). His colour vision was intact as inferred by the
Farnsworth-Munsell 100-hue test. Mapelli and Behrmann (1997) noted
that JW could reliably differentiate between basic shapes with gross
differences (e.g., a square from a circle) but struggled to differentiate
between shapes that differed more nely (e.g., a circle vs. an oval). His
struggles on the Efron task described earlier could relate to difculties
differentiating minor differences between shapes. Unpublished results
from Mapelli and Behrmann are cited stating that imagery was intact in
JW.
2.11.3. Brain damage
CT scans obtained shortly after his incident revealed V1 and V2
injury. Rosenthal and Behrmann (2006) further reported that he had
bilateral lesions in the ventral occipital lobes, areas that provide inputs
to LOC.
2.12. SZ in Grossman et al. (1997)
At 54, a massive myocardial infarction resulted in SZ being admitted
to hospital. Like JW, SZ does not appear in any previous review papers
on VFA.
2.12.1. Impaired abilities
SZ could not read any words at all (0/15 correct). When asked to
name black-and-white drawings from the Boston Naming Test, SZ
accurately named 5 of 60 pictures. On a match-to-sample paradigm, SZ
was unable to judge if two partially overlapping shapes were the same or
different, being accurate 31% of the time. When asked to match simple
designs composed of shapes (e.g., a square with a line extending
perpendicularly from the middle of one side) according to orientation,
SZ could match 43% of items differing in orientation by 90◦or less, and
50% of items rotated 180◦. Objects in colour photographs were never
correctly identied and attempts at identication typically focused on
colour cues. For example, when shown a picture of a room, SZ responded
by saying: “I can see orange, I can see black: it must be a Halloween
picture.’’ The colours were correct, but the picture was not a Halloween
scene” (pg. 323, Grossman et al., 1997). Real objects were recognised
somewhat better – although still poorly. When shown 20 real objects, SZ
was accurate on only 4 trials.
2.12.2. Intact abilities
Simple shapes (e.g., circles, squares, rectangles) could be discrimi-
nated with 80% accuracy in a match-to-sample paradigm. Although this
is not normal performance, it is still well above chance. The ability to
name objects by touch or sound was 100% accurate. Colour perception
was intact. SZ was 100% accurate judging colours in a match-to-sample
task. Identifying colour blobs was used to assess SZ’s visual acuity,
which was estimated to be 20/40 (presumably in each eye, although this
is not stated). SZ’s visual imagery is reported as being better than their
visual perception, as he could draw well from memory, and verbal
description of object features were considered good.
2.12.3. Brain damage
An MRI scan 1 month after his accident was normal. However, a 6-
month follow-up MRI scan revealed an abnormally high signal
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intensity in the occipital association regions in the two hemispheres. A
PET scan at this same time “revealed extensive hypoperfusion bilaterally
in middle and inferior temporooccipital cortices that spared primary
visual cortex" (Grossman, et al., 1996).
2.13. Not named in Ferreira et al. (1998)
The patient was a 65-year-old retired engineer who had a left occi-
pitotemporal haemorrhage in 1981 and a right occipitotemporal hae-
morrhage 1991.
2.13.1. Impaired abilities
The patient exhibited achromatopsia, as assessed by the Ishihara test
(specic scores were not provided). Additionally, it was reported that
visual eld testing revealed a bilateral quadrantanopia in the right
inferior and left superior quadrants. The patient’s ability to name
Snodgrass and Vanderwart (1980) line drawings was impaired (3/122
correct) and their performance in determining whether line drawings
corresponded to real objects or non-objects was also decient (31/40
correct) and did not improve with the use of silhouettes of the same
stimuli (26/40 correct). Furthermore, the patient’s ability to recognise
real objects was impaired when presented statically (7/30 correct) or in
motion (3/30 correct).
2.13.2. Intact abilities
It was reported that visual acuity was normal in the preserved visual
elds. Pupillary responses were also considered normal. The patient
could produce accurate copies of Snodgrass and Vanderwart line
drawings and performed normally on Benton’s line orientation test (23/
30 correct). The patient could identify real objects by touch and could
describe and pantomime their use, conrming that they knew what they
were.
2.13.3. Brain damage
MRI images are provided in the case report demonstrating damage to
the occipitotemporal cortex in the two hemispheres. No other damage is
reported.
2.14. SF in Aglioti et al. (1999)
At 40 years old, SF suffered cardio-respiratory arrest during surgery.
Consequently, he developed bilateral posterior brain atrophy. This is
another case that has been overlooked in the literature. This may be
because, like ES, there are few details about the tests employed to verify
impairments.
2.14.1. Impaired abilities
It was reported that SF could not identify or discriminate simple
visual shapes or objects. SF was acutely aware of this impairment. It was
reported that he consistently failed at standard clinical tests of reading
and visual form recognition, and that he could not recognise single black
letters on a white background.
2.14.2. Intact abilities
SF could name colour stimuli without difculty. He could recognise
the direction of motion and judge the distance of visual targets based on
binocular and monocular vision. Visual imagery was largely normal.
There is no mention of visual acuity or visual elds being assessed.
2.14.3. Brain damage
MRI performed six months after his trauma showed posterior brain
atrophy that was most marked in the occipital and parietal lobes.
2.15. SB in Lˆ
e et al. (2002)
SB developed visual agnosia at 3 years old following
meningoencephalitis. He was examined by Lˆ
e et al. (2002) much later in
life, at the age of 30.
2.15.1. Impaired abilities
Orientation perception was reported to be disrupted. This impair-
ment was inferred from his performance on two tasks. The rst assessed
his abilities to detect an oddly oriented line amongst a matrix of many
lines and the second consisted of a BORB subtest that assessed line
orientation perception. His performance on the latter comprised 18/30
items correct. It was also reported that SB was achromatopsic. He could
not discriminate, order, or name colours, and he failed the Farnsworth-
Munsell 16-Hue test. Standard drawings of common objects could not be
identied, as assessed by the BORB. Although SB made several errors
recognising real everyday objects, he was able to make intelligent
guesses based on the features of the objects presented to him. Real ob-
jects were recognised better than photographs, achieving accuracy
scores of 35/45 and 8/45, respectively. SB’s shape perception tests
showed abnormal results, but the abnormality was due to his slower
speed of processing rather than any issues with accuracy. He performed
at chance levels when discriminating between overlapping gures.
Goldmann perimetry revealed a left lateral homonymous hemianopia,
which spared the macular. The authors noted that this examination was
difcult to administer because SB had trouble maintaining central x-
ation. Common clinical tests of visual acuity could not be performed due
to SB being unable to read letters. Instead, the authors administered a
same/different test where letters or shapes were presented at different
retinal sizes. From this test, acuity was estimated to be 4/10 with both
eyes without correction.
2.15.2. Intact abilities
Stereopsis, brightness judgements, luminance detection, and motion
processing were all reported to be normal. Despite being unable to
recognise drawings, SB was able to copy them well – for example, he
could copy the Rey-Osterrieth gure. SB performed well on BORB sub-
tests assessing his abilities to match line lengths (23/30 correct) and
stimulus sizes (27/30 correct). Like DF, SB was able to use vision for
action and performed similarly to DF on tests of visuomotor control. For
example, the slot test (Milner et al., 1991), and grasping Blake shapes
(Goodale et al., 1994). Finally, in terms of imagery, SB was normal on
several tests including mentally comparing the size of different objects,
and mentally comparing a series of items and nding a similarity be-
tween them based on some visual property (e.g., global shape). Drawing
from memory, as well as describing objects from memory was also
relatively good. Finally, motion processing was deemed largely normal
with an extensive battery (opto-kinetic nystagmus, moving dots dis-
plays, moving sine wave gratings). SB reported no difculty in everyday
motion processing like estimating the speed of walking persons or
moving cars.
2.15.3. Brain damage
MRI revealed lesions in the occipitoparietal and occipitotemporal
regions in the right hemisphere, and in the occipitotemporal junction in
the left hemisphere. Right hemisphere lesions included partial or com-
plete damage to V2, V3, V4 and V5 (MT), with a sparing of V1. In the left
hemisphere, lesions comprised the ventral part of the occipitotemporal
junction. In short, the left and right ventral streams, as well as the right
dorsal stream, were damaged.
2.16. AM in Hildebrandt et al. (2004)
AM had heart arrest at 46 years old. He was in a coma for three days
after the incident. AM does not appear in any other discussion of VFA
other than the Hildebrandt et al. (2004) paper – despite the authors
describing the patient as having ‘visual form agnosia’.
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2.16.1. Impaired abilities
The authors administered the Visual Object and Space Perception
(VOSP) battery and the BORB. In doing so, they found impaired per-
formance on the identication of line drawings (14/40 correct). AM was
below the cut-off for normal performance on tasks assessing his abilities
in length matching (18/30 correct), size matching (22/30 correct),
silhouette recognition (recognising only 4 items correctly, cut-off for
normal performance being 16), and object recognition (recognising only
2 items correctly, cut-off for normal performance being 15). Some as-
pects of motion processing were impaired, as inferred by moving dot
displays.
2.16.2. Intact abilities
The Goldmann perimetry test did not reveal any visual eld defects.
AM could identify illusory contours, Kanizsa gures, and colour. Using
piecemeal strategies, AM could copy the Rey-Osterrieth gure. He made
only a few errors on the Gailinger copy test, which required him to
connect dots to draw a shape. AM could perform the orientation
matching task in the BORB. In addition, he could read single letters
provided they were sufciently spatially apart and read words provided
they were in fonts that lacked serifs (e.g., in ‘Arial’ as opposed to ‘Times
Roman’) and were sufciently large (i.e., >16 pt).
2.16.3. Brain damage
There was no structural damage evident on an MRI taken two months
after his heart attack.
2.17. Patient 006 in Barton et al. (2004)
Patient 006 was a 52-year-old man when he was examined 7 months
after a right medial occipito-temporal haemorrhage. His haemorrhage
occurred during a surgical resection of an oligodendroglioma. The pa-
per’s primary focus was on patient 006’s prosopagnosia. Later, Karnath
et al. (2009) referred to the patient as also having visual form agnosia
based on his difculties perceiving non-face stimuli, as reported by
Barton et al. (2004).
2.17.1. Impaired abilities
In addition to patient 006’s difculties recognising faces, patient 006
performed poorly on the Benton orientation task that required him to
match line segments varying in spatial orientation – achieving a score of
13/30 correct. Patient 006 also had difculties with silhouettes on the
VOSP object perception tasks. Issues with curvature perception were
also reported.
2.17.2. Intact abilities
Snellen acuity was 20/25 in each eye. Goldmann perimetry revealed
a complete left homonymous hemianopia. He correctly identied 12 of
14 Ishihara pseudoisochromatic plates. Eye movements were reported to
be normal. On the Ghent overlapping gures test, patient 006 achieved a
score of 55/57 correct, demonstrating an ability to recognise line
drawings. Patient 006 could also read, achieving a score of 49/50 cor-
rect on the Warrington word task (Warrington, 1984).
2.17.3. Brain damage
MRI showed damage to the right medial occipital cortex comprising
the lingual and fusiform gyri.
2.18. XF in Yang et al. (2006)
XF was 42 years old when she was examined by Yang et al. (2006).
She suffered from carbon monoxide poisoning due to a re and regained
consciousness 20 days after the incident. XF has not appeared in any
discussions of VFA other than in Yang et al. (2006).
2.18.1. Impaired abilities
XF had difculty reporting the correct orientation of sinusoidal
gratings presented in either horizontal, vertical, or diagonal positions.
She reported all of them as being in the vertical orientation. XF was also
impaired in discriminating object size. In addition, she was unable to
perform Gestalt grouping tasks based on similarity, proximity, conti-
nuity, or symmetry. XF performed poorly when tasked to name shapes
(scoring 30% correct) or indicate whether two shapes were the same or
different (scoring 56% correct). She could not copy these same shapes.
When presented with Snodgrass and Vanderwart line drawings, XF
correctly named 11% of coloured objects and 2% of black-and-white line
drawings.
2.18.2. Intact abilities
Static perimetry revealed normal visual elds. Acuity could not be
assessed through letter reading but was reported to be normal as
assessed using contrast sensitivity functions. Brightness perception was
reported to be relatively preserved. XF was 95% accurate on a colour
naming task. In terms of motion perception, XF was able to judge the
direction of a moving target correctly ~90% of the time.
2.18.3. Brain damage
MRI revealed enlarged ventricles and damage to the occipito-
temporal and anterior frontal cortex in the two hemispheres. Occipito-
temporal lesions in the two hemispheres included LO and the posterior
part of the fusiform gyrus. Her early visual cortex, including the primary
visual cortex, was reported to be relatively intact. Her MRI also revealed
damage in the left posterior parietal cortex. Other parts of the parietal
cortex were spared.
2.19. SA in Riddoch et al. (2008)
SA suffered a stroke at 50-years old. The trauma left her with dif-
culties in object recognition and reading. She appears in Riddoch et al.
(2008) where her symptom prole was compared to one with a patient
with integrative agnosia.
3
SA has not appeared in any subsequent review
articles on VFA despite the authors reporting that she had VFA.
2.19.1. Impaired abilities
Object recognition was assessed using Snodgrass and Vanderwart
(1980) images. She correctly named 155/260 (60%) images. Addition-
ally, she named 10/15 animate and 3/15 inanimate images of coloured
objects. Shorter exposure times exacerbated her recognition abilities.
There was some evidence of decreased contrast sensitivity, especially for
higher contrasts. On a modied Efron task, she scored 10/10 correct for
the easiest discrimination level, 9/10 correct for the next level of dif-
culty, and 5/10 correct for the hardest level of difculty. SA performed
worse naming overlapping compared to non-overlapping gures.
2.19.2. Intact abilities
Judgements of line length, line orientation, and circle size on the
BORB exam were all within the normal range based on established
norms. Visual acuity with correction was normal, as assessed with the
typical Snellen chart. SA was able to read quite well, scoring 46/50 on
the Warrington Recognition Test (Warrington, 1984). SA appeared to be
able to copy drawings, albeit poorly (see Fig. 3a in Riddoch et al., 2008;
pg., 64). In addition, she could discriminate gure-from-ground. Like
AM, she could reproduce a decent copy of the Rey-Osterrieth Figure (see
Fig. 3b in Riddoch et al., 2008; pg., 64).
3
Dened as “a case of apperceptive agnosia who succeeded on shape
discrimination and shape-copying tasks, but who failed on more stringent tests
of visual perception (such as distinguishing the individual items in an over-
lapping gures test, or detecting targets embedded in displays of homogenous
distractors)” (Humphreys et al., 2008).
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13
2.19.3. Brain damage
MRI revealed a lesion encompassing the dorsal extrastriate cortex,
including the intraparietal sulcus, in the right hemisphere. The lateral
occipital region and the striate cortex were spared.
2.20. JS in Karnath et al. (2009)
JS suffered an ischemic stroke during a coronary angiography. After
the procedure, he complained that he could not see, despite being able to
safely navigate in his environment. For instance, he could not recognise
objects, watch TV, or read newspapers, but he could take regular walks,
frequenting his local grocery store for shopping. Many of the experi-
ments performed by Karnath et al. (2009) were adopted from previous
experiments performed by Melvyn Goodale, David Milner, and col-
leagues in DF. This was done to evaluate JS’s abilities to process form for
the purposes of action as well as for the purposes of perception.
2.20.1. Impaired abilities
JS was severely impaired at the recognition of objects. He recognised
only 3 out of 12 real objects, even without time constraints. He also
failed to recognise any of the fragmented and completed line drawings
from the Fragmented Picture Test (Kessler et al., 1993). Again, this poor
performance was measured without time limits. Similar results were
found on the Boston Naming Test. He could identify only 2 of 15 line
drawings. Copying shapes (e.g., circle, square) but not simple line
drawings (e.g., comb, racket) was good. Perceptual matching of two
slots (like DF in Milner et al., 1991) in an orientation judgement task was
poor relative to controls. Perceptual discrimination of Blake shapes was
again inferior to healthy controls too (like DF in Goodale et al., 1994) -
although his responses were 73% correct, which was above chance
levels.
2.20.2. Intact abilities
Tests used to assess basic visual function were not specied. How-
ever, the authors reported that there were no visual eld defects. Colour
perception was reported to be largely normal based on JS only making 2
errors on a colour discrimination task. Like DF, JS showed normal vision
for action on the slot task and grasping irregular Blake shapes.
2.20.3. Brain damage
MRI revealed a bilateral lesion to the fusiform and lingual gyri,
extending into the adjacent posterior cingulate gyrus. In the right
hemisphere, the lesion also extended into the parahippocampal gyrus
and cuneus. Lateral cortical structures of the occipital and temporal
lobes were intact, which differs from DF with extensive damage to LOC.
2.21. SDV in Serino et al. (2014)
SDV suffered an electrocution-induced heart-attack. As a result, he
acquired brain damage that left him completely blind for almost 10
months. His vision progressively improved but he never regained his
abilities to recognise common objects, faces, and words. Serino et al.
(2014) evaluated SDV 3 years after his heart attack.
2.21.1. Impaired abilities
Copying forms, such as a cube, was impaired. On BORB subtests, SDV
performed poorly (53% correct) on the size matching task. He was un-
able to perform the line-matching and gure recognition tests either. He
was impaired recognising overlapping shapes. SDV was unable to read
strings of letters, including real words and non-words. SDV had a central
visual eld decit with relative sparing of the periphery. Specically, he
was blind in most of the fovea (i.e., within 5◦of eccentricity) but could
progressively see closer to 10◦of eccentricity. Namely, SDV could
roughly discriminate between vertical versus horizontal line orienta-
tions at different locations in his periphery – albeit his performance was
worse compared to healthy controls.
2.21.2. Intact abilities
SDV could copy simple shapes (5/7 correct) and draw basic shapes
from memory (3/3 correct). SDV accurately named 10 colours presented
as solid rectangles. SDV’s performance assessing hue discrimination
between two colours did not differ from healthy controls. His perfor-
mance on modied random dot kinematograms also did not differ from
healthy controls. Visual imagery was reported to be normal as evidenced
by his abilities to recall perceptual details of common stimuli correctly.
For example, he could indicate correctly whether a particular animal
had a long or short tail (17/17 correct) and whether they had upward or
downward ears (13/13 correct). He could also indicate correctly
whether a letter had curved or straight lines (11/11 correct). Visual
acuity could not be assessed by normal measures, so a contrast sensi-
tivity task was used instead to assess his spatial acuity. SDV’s contrast
sensitivity proles were identical to those obtained in control partici-
pants after correcting for decits with orientation perception – indi-
cating that he had good visual acuity.
2.21.3. Brain damage
MRI revealed enlarged ventricles and two lesions in the occipital lobe
bilaterally. Specically, there was evidence of brain damage in Brod-
mann areas (BA) 17 and 18, and partial damage in BA 19. SDV’s brain
damage also extended rostrally to the superior parietal lobes, corre-
sponding to brain damage in BA 30–31 and partial brain damage in BA 7.
3. Discussion
The present review aimed to document the impairments, intact
abilities, and neuropathology of all patients with VFA that we could nd.
This was done to collate all cases in one place and provide a compre-
hensive overview of how symptoms were tested. We now provide a
discussion on similarities and disparities between patients. We then note
broader methodological lessons learned from this exercise. A retro-
spective analysis on this kind of historical data is challenging because
the data are relatively sparse and there is no way to include additional
clarifying information. Nevertheless, having the information presented
in a single location affords the researcher their own reading and
comprehension of the source material. The key takeaways from our re-
view are: (1) damage often occurs in multiple areas, with damage more
often occurring in the ventral visual stream; and (2) impairments are
relatively specic to line drawings of objects, and this likely reects a
processing problem associated with the synthesis of lines in complex
stimuli, causing a break down in perception. We build upon key ndings
in the following sections of the discussion.
3.1. Location of brain damage
All patients had damage to the occipital lobes, aside from AM. This is
not surprising given the visual nature of the symptoms. Interestingly, the
primary visual cortex seemed preserved in most patients. Only Mr S, RC,
JW, and SDV were reported to have damage to this region – although
some additional cases were described as having generalised atrophy of
the occipital lobe, which may have included damage to the primary
visual cortex. Nonetheless, strong arguments could be made that LOC is
critical for form processing and that bilateral damage to this region leads
to VFA. There exists an abundance of neuroimaging evidence demon-
strating that LOC is strongly and usually activated when neurologically
intact participants visually process shape, line drawings, and other
forms (Grill-Spector et al., 1999; Kourtzi and Kanwisher, 2001; Denys
et al., 2004; Sayim and Cavanagh, 2011; Chouinard et al., 2008; Peel
and Chouinard, 2022). In addition, DF has bilateral damage to LOC and
has profound decits perceiving the shape and form of objects. How-
ever, conclusions of damage to LOC as the sole cause of VFA cannot be
made for multiple reasons.
First, conclusions that can be made about the precise areas of damage
in the patients we reviewed are limited. Although it is noteworthy that
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most patients had bilateral lesions (17/21), many did not have detailed
structural or functional neuroimaging data available. Therefore, it is
unclear how many of them had damage to LOC. Second, LOC appears to
have been spared in some cases. For example, JS had a profound VFA,
yet it was reported that his LOC was intact in both hemispheres –
although there was bilateral damage to his adjacent fusiform gyrus
(Karnath et al., 2009). Finally, the aetiology leading to brain damage
and VFA varied considerably across patients, further complicating
matters for localising a particular brain region that could underpin the
disorder. These aetiologies comprise carbon monoxide poisoning (6),
mercury poisoning (1), anoxia (5), stroke (5), organic development with
multiple sclerosis (1), head trauma (1), meningoencephalitis (1), and
oligodendroglioma (1) – typically varying in the degree of focalised
brain damage. For example, carbon monoxide toxicity typically results
in diffuse patterns of brain damage (Farah, 2004). Therefore, it is un-
likely that damage to LOC is the sole cause of VFA. What is perhaps more
likely is that VFA arises from a disruption in the ow of information
through the ventral visual stream from the primary visual cortex to LOC
and other higher-order areas implicated in form processing (Tanaka,
1996). A similar idea was put forth by Karnath et al. (2009) based on
their evaluation of JS. Alternatively, LOC is the most critical area in the
brain for form processing and any damage to its inputs or outputs or
other areas that LOC depends on for it to process form will result in VFA.
3.2. Visual acuity and visual elds
Many case reports asserted that basic vision was either normal or
that any problems with basic vision, such as reductions in visual acuity
or visual-eld defects, could not be the cause of perceptual decits in
their VFA patients. In terms of the latter, Bender and Feldman (1972),
and more recently Serino et al. (2014), have argued that accompanying
alterations in basic vision are not always inconsequential to shape and
form perception. We share their concerns. In this review, we noted that
there were signicant problems in visual acuity in 3 patients (Mr S, JW,
and FWT) and inconclusive reports of visual acuity in 7 patients (JS, ES,
KK, SF, AM, XF, and SB). Hence, only half of the VFA patients we
reviewed can be considered as having normal visual acuity.
In terms of visual elds, normal visual eld perimetry was only found
in 5 patients (Mr X, ES, SMK, AM, and JS) (24%). The other 16 patients
(76%) were reported to have defects in their visual elds, such as a
scotoma or a hemianopia. The presence of normal visual eld perimetry
in the 5 patients with VFA is not explained by a common factor. These
patients had different aetiologies, including mercury poisoning, carbon
monoxide poisoning, anoxia, and trauma. Therefore, it is challenging to
pinpoint a specic mechanism of action that can explain why these 5
patients and not the others had intact basic vision. Similarly, among the
16 patients with reported abnormalities, 8 displayed unilateral decits,
while the remaining 8 had bilateral decits. Again, the variety of dam-
age patterns and aetiologies make it difcult to establish a precise
mechanism of action as to why these 16 patients had problems with
basic vision.
Hence, the widely held notion that VFA patients have intact basic
vision is simply not true. Most have problems. This is an important
consideration. In a case study of a patient with a quadrantanopia, it was
observed that their scotoma was affecting how visual stimuli were
perceived in their intact and inside their missing visual eld (Dilks et al.,
2007). Namely, the patient perceived shapes as being elongated near
and inside their scotoma. Specically, the patient reported seeing a
rectangle and an ellipse when a square and a circle were actually pre-
sented to them, respectively. Consider how a problem like this (i.e., the
perceived elongation of a visual stimulus near and inside a scotoma)
might impact a patient’s ability to perform the Efron task, which re-
quires making same or different judgements about a progressively
elongated shape relative to another. Subtle distortions in size would
have profound consequences when differentiating pairs of objects in the
Efron task, such as those shown in Fig. 2. It could be the case that some of
the patients in this review could have had low-level visual problems
mimicking VFA and may not actually have had VFA. For this reason,
patients like DF, which have been examined extensively and whose basic
visual functions remained largely intact, provides critical validation to
VFA.
3.3. Shape and form perception
The most common symptom appears to be poor recognition of line
drawings of objects. SMK was not assessed in recognising line drawings
of objects and only patient 006 demonstrated intact abilities in this
domain. All other patients demonstrated impairments either copying,
matching, or naming line drawings. Stimuli used to evaluate these
abilities varied considerably, comprising Snodgrass and Vanderwart
(1980) images, images from the Boston Naming Test, images from the
Poppelreuter and Ghent overlapping gures, images from VOSP sub-
tests, images from the Fragmented Picture Test, and stimuli created by
the researchers. A potential explanation for patient 006’s preserved
abilities could be that he was the only patient whose damage was
conned to one hemisphere. It was reported that patient 006 had
damage in the right but not the left hemisphere. In this situation, visual
areas in the intact hemisphere could stand in for homologous areas that
are damaged in the affected hemisphere. Nonetheless, patient 006 did
have difculties identifying silhouettes, demonstrating problems in
global shape processing.
Line drawings can sometimes require both shape and form process-
ing given that form can be conveyed by occlusion depth cues (e.g., the
wings of an airplane shown in front or behind its fuselage when the
stimulus is viewed sideways). An interesting lesson from our review is
that we cannot condently say whether shape processing was impaired
in many patients when this processing was properly examined in isola-
tion by the Efron task, the VOSP subtests, or the use of line drawings
conned to simple shapes. This is surprising when one considers that the
term ‘form agnosia’ was originally intended to describe shape processing
decits by Benson and Greenberg (1969). We can only condently say
that 10 of the 21 cases had impaired shape processing abilities – namely,
Mr S, RC, ES, DF, PG, SF, XF, SA, JS, and SB.
We deemed the remaining 11 cases as inconclusive. HC displayed
impairments in shape processing for only the rst month after brain
damage, but the patient showed normal performance in subsequent
testing sessions. Mr X could recognise shapes when given an unlimited
exposure time and allowed to trace them, but his performance dropped
when tracing was disallowed. SMK performed poorly on the Efron task
but could recognise Kanizsa shapes, overlapping shapes, and simple
geometric forms. FWT could copy basic shapes but not more compli-
cated ones. KK could copy shapes but could not identify them. JW could
reliably differentiate between line drawings of shapes (e.g., a square
from a circle) but performed poorly on the Efron Task. SZ was 80%
accurate at identifying line drawings of simple shapes but fell to 31%
accuracy when an additional line was introduced into the images. “Not
named” was not tested on basic shape processing. AM struggled to
recognise silhouettes but could copy the Rey-Osterrieth gure and
recognise Kanizsa gures, overlapping, and simple geometric forms.
Patient 006 struggled to identify silhouettes but could successfully
recognise Ghent overlapping gures. SDV and KK could copy simple
shapes but struggled copying more complicated ones.
Thus, simple shape processing impairments do not appear to be
ubiquitous across VFA patients. A decit with more complex line
drawings is more common. Why might this be the case? As raised in the
Introduction, it might help to consider shape and form as conceptually
different in a similar way as artists do. From an artistic perspective, a 2D
image of a shape comprises an outline devoid of apparent depth whereas
a 2D image of a form comprises a shape with additional cues giving it an
apparent 3D structure. A square is an example of a shape. It is at and
restricted to two dimensions (i.e., height and width). Conversely, a cube
is an example of a form. It has three dimensions (i.e., length, width, and
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15
height) (see Fig. 1). Indeed, equating shape and form as the same has led
some to refer to VFA as “impaired shape processing (form agnosia)”
(Gerlach and Robotham, 2021; Benson and Greenberg, 1969) – which
highlights how previous research in this space has not considered them
different. Differentiating shape and form, as we are doing here, is
important given this historical context. Finding that only half or so pa-
tients displayed decits with processing basic shapes suggests that
statements to the effect of ‘participants cannot differentiate a square
from a circle’ may be inaccurate or even overstated. Our main conten-
tion therefore is that there is a qualitative difference conveyed between
shapes and forms in 2D images, where shapes are basic, and forms are
more complex.
Functional neuroimaging provides evidence that shape and form,
when conceptualised as different constructs, could be processed by
different neural substrates. Although Kourtzi and Kanwisher (2001)
demonstrate that the LOC processes both shape and form, other studies
examining other areas in the brain provide evidence for different pop-
ulations of neurons in nearby regions (e.g., V3A) that full a greater role
processing shapes than forms (Denys et al., 2004; Grill-Spector et al.,
1998). This difference in neural substrates could explain why shape
processing is disrupted in some but not all patients. More widespread
brain damage might result in decits with both shape and form pro-
cessing while less widespread brain damage may result in decits that
affect shape or form processing more than the other.
Thinking of form from an artistic perspective can also clarify why
processing line drawings seems consistently affected in VFA. Depictions
of form simulates three-dimensional structure more than depictions of
shape. In the case of the former, the impression of three-dimensional
structure is achieved through processing global and local properties of
stimuli that are dened by edges and lines. In the real world, there are no
lines around objects. Instead, the structure of objects is conveyed
through discontinuities in brightness, textures, colours, and other visual
qualities. In drawings, lines are congured to convey structure in 2D
space – some simulating three-dimensional structure, or form, more
effectively than others. This pictorial form can range from what we call
simple to complex – as illustrated in Fig. 6. The star (a) does not have any
pictorial form. It is a shape. The bananas (b) comprise mostly of outlines,
but they also have other lines and occlusion cues to provide apparent
depth to simulate more three-dimensional structure. The bananas can be
said to have simple pictorial form. The early workings of the portrait (c)
give a richer impression of three-dimensional structure than the bananas
(b) with the addition of even more types of depth cues. The portrait can
be said to have complex pictorial form. Line drawings from the Boston
Naming Test and the Snodgrass and Vanderwart (1980) set lie some-
where in between these simple and complex pictorial forms, and pa-
tients with VFA perform poorly on recognition tasks involving these
stimuli that have a limited impression of three-dimensional structure but
are at a higher level of complexity compared to basic shapes. Therefore,
we think it is useful to conceptually differentiate shape and form,
although it is not something that is typically done.
How does this perspective fare with contemporary theories of shape
processing? We suggest that contemporary theories of shape are largely
synonymous with our denition of form. Namely, “global shape repre-
sentations are achieved by describing objects via the spatial arrange-
ment of their local features rather than by the appearance of the features
themselves” (Ayzenberg and Behrmann, 2022). From this perspective,
shape encompasses local features and their spatial arrangement which
are key to conveying an object’s structure. Such descriptions typically do
not draw a distinction between shape and form in 2D images, but we feel
the importance of processing local cues in addition to global ones is
demonstrated as being decient in the VFA patients we reviewed.
Indeed, one quibble that we have with this perspective which largely
equates shape and form (e.g., Ayzenberg and Behrmann, 2022) is that it
somewhat overlooks the importance of local feature appearances to
structure. This is best exemplied in one aspect of shape within this
framework, which is of the shape skeleton (Blum and Nagel, 1978;
Ayzenberg et al., 2022). The shape skeleton models object structure by
describing the spatial arrangement of contours and component parts via
internal symmetry axes. It has been demonstrated that this description
can help determine an object’s structure even with noisy or incomplete
contour information (Ayzenberg et al., 2019). While this approach
seems reasonable for basic 2D shapes, we suggest that when dealing with
more complex forms, processing the appearance of internal features
within the boundary is important and can lead to qualitatively different
perceptions (see Fig. 1). The limitations of the shape skeleton metaphor,
especially when applied to complex images, have been discussed by
Arnheim (1974) with the famous duck-rabbit image. This image pre-
sents a drawing that can be perceived as either the head of a duck facing
left or a rabbit facing right. Although the image possesses only one
quantitative structure and, consequently, one shape skeleton, the pro-
cessing of internal features within the boundary can result in two
equally valid structural interpretations. This example emphasises the
signicance of processing internal features alongside global structure
and highlights the potential for qualitatively different perceptual
outcomes.
All this discussion concerns at two-dimensional images. A reason-
able question then follows: How does this problem with form relate to
abilities in recognising objects in the real world? Consider the following
studies that examined the recognition of both line drawings and real
objects in VFA patients. Mapelli and Behrmann (1997) aimed to address
why JW’s identication decits were more pronounced with
black-and-white (B/W) line drawings compared to real objects. To this
end, they created two versions of line drawings of 39 common objects:
one in B/W and the other in colour. Abilities to recognise these drawings
were compared to the real versions of the same objects. JW recognised
the real versions (21/39 correct) better than either the B/W (7/39 cor-
rect) or coloured (12/39 correct) line drawings, which demonstrates
that he could recognise stimuli better when they provide more
Fig. 6. Three line drawings of varying complexity with no (A), simple (B), and complex (C) form. Panel (A) shows a basic star, panel (B) is a sketch of a bunch of
bananas, and panel (C) is the early sketching of a portrait of one of the authors. Artwork of the author is courtesy of Wang Xiao Jing and reproduced with permission.
H.J. Peel and P.A. Chouinard
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16
information about structure. Drawings that are richer in apparent
structure achieved from the addition of shading and textures seem to be
recognised better in VFA patients. Indeed, PG was better at recognising
more realistic drawings (i.e., like the one in panel c of Fig. 6) compared
to more basic ones from the Snodgrass and Vanderwart (1980) set (i.e.,
like the one in panel b of Fig. 6) (84% and 76%, respectively).
However, these results are not always apparent in VFA patients.
Holler et al. (2019) found that images of complex pictorial forms are not
recognised efciently in DF and JW. Holler and colleagues examined
object recognition in the following display formats: real objects in both
DF and JW, high-resolution images of the same objects in both DF and
JW, and stereoscopic images of the same objects with a virtual third
dimension in JW only. For the latter, active shutter glasses were used to
present two images of an object from two slightly different viewpoints to
the left and right eyes to create stereoscopic depth. Both patients per-
formed poorly recognising the high-resolution images and JW per-
formed poorly recognising the stereoscopic images. Recognition
performance improved modestly in both patients with the real objects.
The authors of the study referred to this latter effect as a ‘real object
advantage’ (Holler et al., 2019). Nonetheless, one should keep in mind
that the real object advantage was modest. The patients’ performance
with the real objects remained worse than control participants, as evi-
denced by higher error rates and longer response times. Interestingly,
JW performed worse in recognising both the high-resolution images and
the 3D stereoscopic images compared to the real objects, which suggests
that articially creating stereoscopic depth does not completely simu-
late three-dimensional structure as in the real world.
In the patients that we cover in our review, we found real object
advantage in 9 patients (HC, RC, ES, DF, KK, PG, JW, SZ, SB) (43% of
patients), a real object decit in 6 patients (Mr S, Mr X, NN, SF, AM, JS)
(29% of patients), and inconclusive real object advantage in 6 patients
(SMK, FWT, 006, XF, SA, SDV) (29% of patients). Real object advantage
is a promising avenue for further research that could potentially by
informative. The ecological validity of line drawings is questionable
given they vary in the degree to which they simulate structure. One can
even argue that images of any kind cannot fully simulate structure.
Pictorial cues that artists apply to produce apparent depth, such as
shading, occlusion, and texture gradients, conict with other cues telling
the brain that the eyes are looking at a at surface, such as stereopsis,
vergence, motion parallax, and accommodation. Virtual three-
dimensional space created by stereoscopic images reduces but does
not eliminate this conict. Conicting depth information from a
mismatch in vergence and accommodation is an issue in virtual reality
(Hoffman et al., 2008). Other differences in processing real objects
versus images have been demonstrated by Snow and colleagues (e.g.,
Snow et al., 2011; Snow and Culham, 2021) and our research group (e.
g., Kithu et al., 2021). However, this issue not new. Notably, James
Gibson (1979) seriously questioned the ecological validity of presenting
stimuli as images in his book The Ecological Approach to Visual Perception.
In short, we suggest that decits in processing and synthesising local
and global features for the purposes of perceiving structure might
contribute to symptoms of VFA. The proposed denition of VFA dis-
tinguishes itself from conditions like simultanagnosia and integrative
agnosia in terms of the underlying difculties in processing local and
global elements in stimuli. Simultanagnosia, as discussed by Baugh et al.
(2016), refers to a condition where patients have difculty perceiving
the overall meaning or conguration of complex stimuli. However, they
typically retain the ability to perceive isolated elements or details within
the stimulus. In integrative agnosia, patients struggle with integrating
different elements of a stimulus, resulting in difculties in recognition.
In both cases, the sensory input itself is not degraded, and the impair-
ments are more related to the integration and overall perception of the
stimuli.
In contrast, VFA, as proposed here, involves a problem in accurately
processing both the local and global elements in stimuli, potentially due
to their degradation in quality. In this regard, Nielsen’s (1936) key
criterion for dening the agnosia is apt: “In this difculty, the patient
has lost sense of direction of lines so that he fails to recognise objects
because of their distortion.” (pg. 52). In the context of other models of
object recognition, such as Marr’s model (1982) (as discussed by War-
rington and James (1988) with regards to apperceptive agnosia, and
Okuda et al. (1996) with regards to patient KK), it might be that VFA
patients are only processing visual information up to the level of a 2½-D
sketch, where the visible surfaces and contours of discontinuities are
present, but they fail to derive a 3-D model of the object in which the
geometry (axes and volumetric properties) is fully specied. Indeed, the
subjective experiences reported in VFA patients seem to point to a
warped phenomenology in structure. In the real world, it is conceivable
that some VFA patients use visual cues other than lines and edges to aid
object recognition as evidenced by their improved performance with
real objects.
At a phenomenological level, we have much to learn about how VFA
patients perceive the world, presumably because of the challenges
measuring subjective experiences. Nonetheless, Vecera and Gilds (1997)
have considered this question. They applied Nagel’s (1974) seminal
thought experiment of “what is it like to be a bat?” to VFA patients by
positing “what is it like to be a patient with apperceptive agnosia?” Nagel’s
exercise highlights how difcult it is to imagine the subjective sensory
awareness that bats may have (if they do experience consciousness)
considering they primarily use echolocation to navigate their environ-
ment. The exercise is also difcult to apply to VFA patients, but it is
perhaps more approachable given they have human brains, albeit
damaged ones. Perturb and measure approaches, such as transcranial
magnetic stimulation (TMS), could explore this question in neurologi-
cally intact individuals (Paus, 2005). Once could use such techniques to
transiently disrupt LOC function in both hemispheres and evaluate the
consequences that this may have on subjective experiences. As far as we
know, this has never been done before.
Nonetheless, previous studies have used TMS to disrupt LOC have
demonstrated that it is indeed critical for form processing (Chouinard
et al., 2017). But these studies have presented visual stimuli on
atscreens. With good reason, this method of presentation has been the
norm in psychophysical experiments for many decades. They have
excellent internal validity – enabling researchers to tightly control for
many confounding variables. However, their ecological validity is
limited. One possibility to better understand the role of LOC in form
processing in day-to-day perception is to use TMS in conjunction with
VR. VR provides the means to better simulate how size and depth
operate in the real world by using a virtual three-dimensional space. It
reduces (but does not eliminate, as discussed previously) the problem of
conicting depth cues by enabling a more effective simulation of ste-
reopsis and motion parallax while potentially allowing researchers to
achieve the same high levels of internal validity as experiments using
atscreens. Using VR may lead to a better understanding of how
neurologically intact individuals and VFA patients process and visually
perceive the structure of objects in the real world, which has three
dimensions.
3.4. Orientation and size perception
It is typically assumed that VFA patients have impairments in
orientation and size perception (Martinaud, 2017). Thus, one key
question we sought to address was: Can patients perceive orientation and
size? Not all patients in this review were impaired. Orientation decits
were reported in 9 (43%) cases (RC, DF, PG, SZ, 006, XF, JS, SDV, and
SB). We deemed orientation perception to be intact in 6 (29%) cases
(HC, SMK, JW, SA, Not Named, and AM) and inconclusive in the
remaining 6 (29%) cases. Concerning size processing abilities, 7 (33%)
cases displayed evidence of a decit (DF, SMK, PG, AM, XF, JS, and SDV)
while 5 (24%) did not (Mr S, Mr X, FWT, SA, and SB). There was a lack of
information to conclude whether abilities were intact or not in the
remaining 9 (43%) cases. Given this lack of convergence, problems in
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17
orientation or size perception are not always comorbid with problems in
shape and form perception. In some patients, there is a dissociation.
The reverse dissociation can be seen in other types of visual agnosia.
In some cases of orientation agnosia, recognising objects based on their
shape or form is intact but discriminating between the same object
presented in different orientations is disrupted (Davidoff and Warring-
ton, 1999; Harris et al., 2001; Martinaud et al., 2016). Although rare, a
few cases of dysmetropsia have been reported. In this disorder, objects
appear either shrunk (miscropsia) or enlarged (macropsia) compared to
their actual size. One case study (Frassinetti et al., 1999) was observed
following right occipital ischaemic infarction, which resulted in a per-
manent left miscropsia. The patient consistently judged the size of ob-
jects presented in the left hemield as smaller than those presented in
the right hemield. In contrast, the patient performed awlessly when
naming objects, faces, and colours. Taken together, orientation and size
can be processed independently of form – suggesting that different
neural substrates might underlie their perceptual analysis.
3.5. Colour perception
Only ve patients (24%) demonstrated decits in colour processing.
RC showed impairments when making red/blue judgments. FWT per-
formed poorly at bedside testing where he failed to point to, name, and
match items of a specic colour. KK was initially poor at identifying
colours, achieving 25% accuracy, when she was rst tested. Her per-
formance improved to 60% accuracy at a follow-up testing session. “Not
named” and SB performed poorly on several tests of colour vision and
were reported to have achromatopsia. In the remaining patients, we
deemed colour vision as either normal or inconclusive. Most patients
were reported to have normal colour perception as inferred by their
performance on the Ishihara Colour Plates, the Farnsworth-Munsell 100-
Hue Discrimination Test, and naming visually presented colours.
There is substantial evidence to suggest that form and colour are
processed independently from each other. This evidence comes from
behavioural studies using the Garner Interference paradigm (Cant et al.,
2008; Algom and Fitousi, 2016), electrophysiological studies in
non-human primates (Zeki, 1993), and fMRI experiments in humans
(Cant and Goodale, 2007). The latter two have identied the involve-
ment of specic brain regions in processing form and colour, namely the
LOC for form processing and area V4 for colour processing. In the case of
VFA, it is possible that the impairment in colour vision is observed only
in a subset of patients whose brain damage extends to regions such as V4
that are crucial for colour processing. This could explain why some VFA
patients show decits in colour perception while others do not. Overall,
these ndings support the notion that form and colour processing
operate independently from each other.
In the seminal study by Milner and Heywood (1989); Milner et al.
(1991)on patient DF, a dissociation between preserved colour discrim-
ination and impaired brightness discrimination was observed. This
contrasts with ndings in achromatopsic patients, where the opposite
pattern is typically observed. These results suggest the presence of
separate processing channels for colour and brightness discrimination,
further supporting the potential independence of colour processing from
other aspects of perceptual processing. However, it is important to note
that in certain circumstances, colour has been shown to be diagnosti-
cally relevant in object recognition. Research has demonstrated that
colour can facilitate the recognition of objects (Chouinard and Goodale,
2012; Bram˜
ao et al., 2011). This may partly explain the improved per-
formance observed in some patients when identifying solid objects that
provide both colour and texture cues. Nevertheless, as mentioned
earlier, further research is necessary to gain a better understanding of
the factors contributing to the real object advantage observed in some
patients. Investigating the underlying mechanisms could help elucidate
why and how some patients display this modest advantage. Under-
standing these processes in patients with VFA and related conditions
requires further investigation.
3.6. Motion perception
Benson and Greenberg (1969) and Efron (1969) emphasised how
motion was important for Mr S’ residual abilities in perception. He could
point to an object in front of him only if it moved. In addition, he could
recognise orientation and size with the assistance of motion cues. For
example, when shown two discs of light which differed in hue, lumi-
nance, and size, he could readily point to the deeper red, brighter, or
larger one but only if the two objects were moving. Moreover, when
asked if two black sticks of tape on white paper shared the same or
different orientation, he carefully followed the contours of each one by
moving his head and frequently gave correct answers using this
compensatory strategy. He could no longer perform this task when his
head remained stationary.
As mentioned in the Introduction, preserved motion perception is
typically considered as a feature of VFA. Upon reviewing the case
studies, this appears to be largely accurate, although there are some
caveats. Although explicit decits in this domain were not found in any
of the reported cases, it is important to note that most patients were not
specically tested on motion perception. Only 6/21 (29%) cases were
reported to have preserved motion perception when tested. For the
remaining cases, the information was inconclusive or not mentioned.
Therefore, it is challenging to draw rm conclusions about the preva-
lence of preserved motion perception in VFA patients. It is possible that
the statistic of approximately 30% preservation may be underestimated
due to the lack of explicit testing in many cases and thus some incor-
poration of such testing in the future may be useful. The cases with
preserved motion perception were somewhat varied (Mr S, Mr X, SF, SB,
XF, and SDV). Mr S and Mr X both relied heavily on motion for accurate
perceptual reporting. For example, Mr S was only able to make judge-
ments about some items if they were drawn in front of him, and Mr X
was only successful with recognising some stimuli if he could trace
images with his head and hand. Similarly, Mr X, SF, XF, and SDV could
judge the direction of moving stimuli. The most in-depth patient tested
on motion was SB, whose motion processing was deemed largely normal
with an extensive battery (opto-kinetic nystagmus, moving dots dis-
plays, moving sine wave gratings), and, in everyday settings, SB re-
ported no difculty in estimating the speed of walking people or moving
cars.
This result is remarkable given the proximity of area V5 (MT) to LOC.
No patients aside from SB were reported to have lesions to MT. Inter-
estingly, SB was the patient who had the most extensive motion
perception testing, where it was found to be largely normal. One
possible explanation for this preserved motion processing in SB despite a
notable MT lesion was that this damage was conned to the right
hemisphere. As in the case of 006 who still perceived some line drawings
successfully potentially due to his unilateral brain damage, it could be
the case that the MT in the intact hemisphere was processing motion
successfully in SB. Given MT has long been found to be active during
motion perception tasks (Zeki, 2015), it is logical that motion processing
would be preserved in patients with an intact MT in either hemisphere.
3.7. Copying gures
Lissauer (1890) posited that the ability to copy gures is a key
distinction point for differentiating between apperceptive and associa-
tive agnosia, with the former not being able to do it. This perspective has
persisted today with many researchers still stating that VFA patients
cannot copy gures and suggesting that this inability should remain a
diagnostic feature (Heider, 2000; Farah, 2004; Behrmann and Nishi-
mura, 2010; Martinaud, 2017). Therefore, we asked: Can VFA patients
trace or copy gures?
Upon reviewing the case studies for this paper, nine (43%) patients
(HC, FWT, SA, AM, KK, NN, JS, SDV, and SB) were able to copy gures.
Another case (Mr X) could draw objects comprised of basic geometric
shapes when allowed to use his tracing technique. Thus, the inability to
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Neuropsychologia 190 (2023) 108666
18
copy gures is not consistently present in all patients with VFA. Nearly
half can do this. In 6/9 patients who were able to produce some copies,
these were limited to basic shapes and copying more complex forms
were severely disturbed. Only ‘Not Named’ could copy some line
drawings of objects, although this was a long and laborious process. For
example, he took 8 min to produce a copy of a comb. On the other hand,
SB and AM made some errors with copying line drawings of objects yet
produced quite good copies of the Rey-Osterrieth gure. Thus, Lissauer
(1890), distinction between apperceptive and associative agnosia as
dened by the absence or presence of abilities to copy gures, respec-
tively, seems out of date. We suggest that this sharp distinction between
being able to copy or not copy be updated to specify that there is an
inability to copy complex, sophisticated gures in most instances. This
distinction strengthens our conclusions that there exists a distinction
between basic shape and more complex form.
3.8. Imagery
Imagery, like motion, is another feature typically cited as being
preserved in cases of VFA. Upon review, this assertion is somewhat
unclear, mainly owing to most cases not being explicitly tested on this
ability. Three cases had notable decits in imagery. HC reported
diminished visual components in her dreams, Mr X was reported to be
decient without formal testing mentioned, and Mr S claimed to have no
dreams or dreams devoid of visual content. However, for most other
cases (10/21), the information on imagery was inconclusive or not
mentioned, while eight cases (DF, FWT, KK, JW, SZ, SF, SB, and SDV)
were reported to have preserved imagery. Testing for imagery was
varied – in cases with preserved imagery, this was sometimes inferred by
their drawing objects from memory, describing objects’ physical prop-
erties from memory, or mentally comparing different objects according
to some physical property to differentiate them. For instance, DF was
reported to produce drawings from memory. While SB was normal on
several tests including mentally comparing the size of different objects,
and mentally comparing a series of items and nding a similarity be-
tween them based on some physical property (e.g., global shape). Most
cases being inconclusive, along with 3 having notable decits in imag-
ery, is our main reason behind not concluding that it is typically intact.
Incorporating comprehensive testing of imagery is necessary before rm
conclusion can be made.
Indeed, the mechanism of imagery is a topic of some controversy.
Specically, the format underlying representations that are engaged and
required for imagery has been a point of contention for over 50 years,
which continues today. In this debate, Kosslyn et al. (2001) argued that
imagery engages the same pictorial representations that are engaged
when we experience sight. He argued that the same areas in the brain
that are engaged in vision are also engaged in imagery. Pylyshyn (1973)
had a different point of view. He argued that imagery is language based,
engages symbolic as opposed to pictorial representations, and is pro-
cessed outside of the visual system.
Recently, this debate has resurfaced in the context of research related
to aphantasia (Pearson, 2019). By denition, a person with aphantasia
lacks the ability to perceptually imagine visual pictures. However, like
many of the patients with VFA that we reviewed, aphants can perform
imagery tasks – undermining Kosslyn’s original views as to what im-
agery is and what is required to perform imagery tasks. There is growing
evidence that early visual areas may actually not be required for imag-
ery. It is of note that VFA patient JW had damage to V1 yet retained
imagery. Indeed, this perspective concerning the importance of early
visual areas to imagery has been further challenged by Bartolomeo and
colleagues (e.g., Bartolomeo et al., 2020). In a comprehensive review of
visual agnosia and imagery, Bartolomeo (2021) notes some patients
with acquired aphantasia following more anterior lesions in the tem-
poral lobe show decits of imagery despite intact early visual areas.
3.9. Reading
Paradoxically, when you consider that reading might depend on
shape and form processing, there have been reports of VFA patients who
have retained some reading abilities. For example, HC could write but
with many errors (Adler, 1944; Sparr et al., 1991). Counterintuitively,
she was better able to read long words compared to shorter ones. This
alexia was reported by both Adler (1944) and Sparr et al. (1991) and
seemed unchanged between the two series of testing sessions. At the
single word level, she regularly misidentied individual letters. While
she would read ‘front’ as ‘rst’ and ‘soapy’ as ‘sorry’, she could more
accurately read and comprehend longer words such as ‘jeopardise’,
‘physician’, and ‘sapphire’. Occasionally, when she had difculty
discerning a word, her performance would improve if she used her index
nger to trace one or more letters. Likewise, Landis et al. (1982) re-
ported that Mr X was able to read but that this ability was contingent on
tracing the letters with his nger. To aid recognition, he developed his
own alphabetical code for individual letters (e.g., a ‘P’ is “a pole and a
basketball hoop”) and was much quicker at identifying words written in
a font saliently abiding to his code compared to other fonts. In addition,
despite not having good visual acuity, KK could also demonstrate some
abilities in reading. The fact that she could read yet could not recognise
line drawings highlights how decits in visual form agnosia could be
specic to non-lexical shapes. This is a point for consideration in future.
In many cases, reading abilities were not assessed due to patients
initially failing with individual letter recognition. Perhaps more detailed
testing of word reading is warranted given cases like HC who could
effectively read longer words but struggled with shorter ones.
Our review highlights that 6/21 (29%) retained some abilities to
read. HC and DF were similar. Both had more difculty reading short
words (e.g., go, up) than longer ones (e.g., environment). In addition,
font type and font size can also affect how easily words could be read in
some cases, such as AM (Hildebrandt et al., 2004). Finally, although no
qualitative descriptions are available, SA performed well on formal tests
of reading like the Warrington reading task (46/50). DF’s reading
abilities have been carefully examined by Cavina-Pratesi et al. (2015).
The authors of this study provide insight into how it was possible for DF
to still read words although she cannot perceive shapes or line drawings.
This relates to difference in how the two are processed by the brain –
mechanisms that are intact in DF for the former but not the latter.
DF could read words when presented in a conventional horizontal
but not in an unconventional vertical orientation. In addition, she can
recognise full words but not individual letters. As it turns out, the visual
word form area (VWFA) activates more strongly when people read full
words presented in a conventional horizontal orientation (Dehaene and
Cohen, 2011). Cavina-Pratesi et al. (2015) demonstrated with fMRI that
DF still has an intact VWFA, which is distinct from LOC. It could be the
case that basic visual features of words (i.e., line orientations, relative
positions, lengths, line-intersections, etc) are processed in DF’s intact
early visual areas and her intact VWFA can further process this infor-
mation for word recognition. In contrast, DF has no LOC in either
hemisphere to further process visual information for the purposes of
recognising non-word shapes.
3.10. Recovery in vision
Another point to discuss is the presence of recovery over time. This is
not something that is typically considered. It was interesting to observe
that a minority of cases were reported to be initially blind (HC, Mr S, DF,
FWT, PG, SZ, SB, and SDV). The reason for this is unclear given there is
no shared aetiology, although HC, Mr S, and DF all suffered carbon
monoxide toxicity. Other kinds of improvement have been observed too.
Most cases were only seen on one occasion, but there were a few cases of
repeated testing that demonstrate that patients with VFA can show
various degrees of recovery. HC was rst seen by Adler in 1944. Her
impairments then were severe. At a follow-up session nearly 50 years
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19
later, Sparr et al. (1991) observed signicant improvements. Her im-
pairments only became evident on highly specic tasks (e.g., identifying
Poppelreuter gures). FWT was seen shortly after his trauma and nine
months later. Some improvements were observed at the second testing
session, such as copying gures (3/9 correct from 0/9 correct) and
pointing to objects (20/40 correct from 0/30 correct). On the other
hand, DF displayed more consistency in her impairments since the late
1980s (Cavina-Pratesi et al., 2015). The reasons for these differences in
recovery are unclear. The recovery in FWT could be spontaneous, i.e.,
abilities return as the brain nds new ways to perform them or naturally
repairs some of the damage it sustained. The recovery in HC could partly
be spontaneous and partly the result of learning compensatory strate-
gies. In the case of DF, it could be the case that her damage implicated
areas such as LOC that are more critical in shape and form processing,
enabling her less opportunities to develop strategies to compensate for
her decits.
3.11. Recommendations
Based on our review, we have three methodological recommenda-
tions for researchers who plan to examine a VFA patient. First, to allow
for comparisons across studies, researchers could consider using well-
established perceptual tests, at least to establish the presence of VFA.
For example, some combination of the Snodgrass and Vanderwart im-
ages or the BORB for line drawings, along with the Efron task and a
simple matching/copying task for shapes, could be considered to verify
the presence of difculties in perceiving shape and form. Second, more
detailed structural and functional data on their patient’s brain over a
period would be informative. Many patients in this review were seen
before the emergence of the neuroimaging techniques that we have
readily accessible today. DF is the only patient whose brain has been
extensively examined over a period with decent resolution imaging. We
would have a clearer picture of what brain damage causes VFA and how
it progresses over time if more patients were examined in this way.
Third, we recommend more thorough testing and disclosure of basic
visual function, such as visual acuity and visual eld perimetry. We
suspect that some previous claims of intact basic visual function or
defective basic visual function not accounting for VFA may not be
entirely accurate. In some cases, defective basic visual function could
have accounted for the agnosia, which is not necessarily problematic.
3.12. Conclusions
The ndings of the present review have implications for under-
standing the localisation of brain function. The observation that one site
of damage is not common to all patients beyond damage to the occipital
lobe provides contradictory evidence for a model of the visual system
that exclusively prescribes specic functions to discrete brain areas (e.g.,
Broca’s area being exclusively responsible for language production).
Instead, it favours a more hybrid model that considers an associationist
view of brain organisation (Weis et al., 2019; Deacon, 2018). Briey,
associationism views the brain as organised in parallel distributed net-
works around cortical epicentres. In the intact brain, a particular func-
tion can be relatively well-localised to a specic area or a set of specic
areas. However, a lesion anywhere in the brain could result in a partial
dysfunction of other regions that would otherwise be normally con-
nected to the lesioned area. Thus, damage in areas that normally operate
with LOC during shape and form processing could equally result in VFA
symptoms. Ultimately, more detailed structural and functional data are
needed from VFA patients to understand more precisely what neural
substrates might be critical.
In sum, VFA is a rare perceptual disorder with a variety of aetio-
logical causes, including carbon monoxide toxicity, stroke, and mercury
poisoning. Some clear consistencies exist between patients, such as
damage to the occipital lobes in the two hemispheres, impairments
recognising line drawings, and intact colour vision. However, as the
reader can appreciate, there is no perfect overlap in symptomatology
between cases either. As aptly stated by Adler (1944, pg., 243), “the
complexity of the process of optic recognition is such that no two patients
suffering from the disorder called visual agnosia have identical derangements
in function.” In our review, we clarify the important distinction between
shape and form, the most common perceptual decits in VFA patients,
and note key areas of divergence. Doing this has put into question some
widely held diagnostic features, such as intact basic visual function and
an inability to copy gures.
CRediT authorship contribution statement
Hayden J. Peel: Conceptualization, Writing – original draft, Writing
– review & editing. Philippe A. Chouinard: Conceptualization, Writing
– review & editing, Supervision.
Data availability
No data was used for the research described in the article.
Acknowledgements
We thank Professor Pauleen Bennett for her valuable feedback on the
manuscript.
Appendix
Some cases were cited by other authors as being examples of VFA. Upon review, we were unable to nd enough detail on their damage/symptoms
to condently conclude that they were genuine cases of VFA. Therefore, we include them here for the readers reference, should they choose to read
them. Similarly, a number of cases were identied from our literature search that we feel for reasons listed below are difcult to interpret.
Case Study Appears in Aetiology Rationale for exclusion
JAF and RBC Warrington and James (1988);
Warrington (1985)
Stroke These papers are mentioned by Milner et al. (1991) but there is insufcient detail in the chapter they
appear to conclude that the patients have VFA
Schneider Goldstein and Gelb (1918) Mine splinter in
head
Schneider is mentioned in the body of work, but was shown to have many perceptual decits in
addition to form agnosia
8-year-old girl Kaga and Shindo (2012) Trauma There is not enough detail on form agnosia in the only entry where she appears.
LG Gilae-Dotan (2016); Ariel and Sadeh
(1996)
Congenital We believe this represents integrative agnosia, not form agnosia.
AP Grossman et al. (1997) Alzheimer’s
Disease
Due to the neurodegenerative nature of the condition, we felt it necessary to exclude this person
(continued on next page)
H.J. Peel and P.A. Chouinard
Neuropsychologia 190 (2023) 108666
20
(continued)
Case Study Appears in Aetiology Rationale for exclusion
Unnamed
woman
Kertesz (1979) Car accident Patient presents with both apperceptive and associative kinds of agnosia
CK Behrmann et al. (1992) Head trauma Patients appears to have associative agnosia instead of apperceptive agnosia
Annalisa De Renzi and Lucchelli (1993 Head trauma Decits outside of just vision
13-year-old
girl
James et al. (2003); Jambaqu´
e et al.
(1998)
Congenital Comorbid diagnosis of seizures and autism
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