Personal neglect-a disorder of body representation?

Abstract

The cognitive mechanisms underlying personal neglect are not well known. One theory postulates that personal neglect is due to a disorder of contralesional body representation. In the present study, we have investigated whether personal neglect is best explained by impairments in the representation of the contralesional side of the body, in particular, or a dysfunction of the mental representation of the contralesional space in general. For this, 22 patients with right hemisphere cerebral lesions (7 with personal neglect, 15 without personal neglect) and 13 healthy controls have been studied using two experimental tasks measuring representation of the body and extrapersonal space. In the tasks, photographs of left and right hands as well as left and right rear-view mirrors presented from the front and the back had to be judged as left or right. Our results show that patients with personal neglect made more errors when asked to judge stimuli of left hands and left rear-view mirrors than either patients without personal neglect or healthy controls. Furthermore, regression analyses indicated that errors in interpreting left hands were the best predictor of personal neglect, while other variables such as extrapersonal neglect, somatosensory or motor impairments, or deficits in left extrapersonal space representation had no predictive value of personal neglect. These findings suggest that deficient body representation is the major mechanism underlying personal neglect.

Full text

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Neuropsychologia 49 (2011) 898–905
Contents lists available at ScienceDirect
Neuropsychologia
journal homepage: www.elsevier.com/locate/neuropsychologia
Personal neglect—A disorder of body representation?
Ulrike Baasa, Bianca de Haand, Tanja Grässlia,c, Hans-Otto Karnathd, René Mueria,c,
Walter J. Perrigb, Pascal Wurtzc, Klemens Gutbroda,∗
aDivision of Cognitive and Restorative Neurology, Department of Neurology, Inselspital, Bern University Hospital, and University of Bern, CH-3010 Bern, Switzerland
bDepartment of Psychology, University of Bern, Switzerland
cPerception and Eye Movement Laboratory, Department of Neurology, Inselspital, Bern University Hospital, and University of Bern, Switzerland
dDivision of Neuropsychology, Centre for Neurology, Hertie-Institute for Clinical Brain Research, University of Tuebingen, Germany
a r t i c l e i n f o
Article history:
Received 9 May 2010
Received in revised form 28 January 2011
Accepted 28 January 2011
Available online 15 February 2011
Keywords:
Personal neglect
Body representation
Temporo-parietal junction
a b s t r a c t
The cognitive mechanisms underlying personal neglect are not well known. One theory postulates that
personal neglect is due to a disorder of contralesional body representation. In the present study, we have
investigated whether personal neglect is best explained by impairments in the representation of the
contralesional side of the body, in particular, or a dysfunction of the mental representation of the con-
tralesional space in general. For this, 22 patients with right hemisphere cerebral lesions (7 with personal
neglect, 15 without personal neglect) and 13 healthy controls have been studied using two experimental
tasks measuring representation of the body and extrapersonal space. In the tasks, photographs of left and
right hands as well as left and right rear-view mirrors presented from the front and the back had to be
judgedasleftorright.Ourresultsshowthatpatientswithpersonalneglectmademoreerrorswhenasked
to judge stimuli of left hands and left rear-view mirrors than either patients without personal neglect or
healthy controls. Furthermore, regression analyses indicated that errors in interpreting left hands were
the best predictor of personal neglect, while other variables such as extrapersonal neglect, somatosen-
sory or motor impairments, or deficits in left extrapersonal space representation had no predictive value
of personal neglect. These findings suggest that deficient body representation is the major mechanism
underlying personal neglect.
© 2011 Elsevier Ltd. All rights reserved.
1. Introduction
Unilateral neglect is defined as a “failure to report, respond, or
orient to novel or meaningful stimuli presented to the side oppo-
site the brain lesion when this failure cannot be attributed to either
sensory or motor defects” (Heilman, Watson, & Valenstein, 1993, p.
268). It may affect personal space, i.e. one’s own body, as well as
extrapersonal space. In personal neglect, the contralesional half of
the body is disregarded, less explored or underused by the patient.
This means that in activities of daily living, patients with personal
neglect seem to “forget” the contralesional side of their body. They
tend to groom it to a lesser degree (e.g. they do not shave the left
side of their face or forget to lace up their left shoe). They ignore
contralesional somatosensory stimuli (e.g. they insert the specta-
cle’s earpiece incorrectly, or below the contralesional ear), or they
do not use the extremities of the contralesional side of their bodies
(e.g.theydressusingtheipsilesionalarmonly,despiteintactmotor
functions of the contralesional side).
∗Corresponding author. Tel.: +41 31 632 83 91; fax: +41 31 632 97 70.
E-mail address: klemens.gutbrod@insel.ch (K. Gutbrod).
Personal neglect was first described by Zingerle in 1913 almost
as early as extrapersonal neglect (Anton, 1896). At that time,
personal neglect was explained as a loss of somatosensory func-
tions (Pierre Marie, 1918 in Babinski, 1918). However, others
subsequently suggested that in addition to somatosensory defects,
cognitive deficits had to be present (Battersby, Bender, Pollack,
& Kahn, 1956). While these authors still considered elementary
somatosensory deficits to be a basic prerequisite for personal
neglect,researcherslaterhypothesizedthatpersonalneglectrepre-
sentsahighersomatosensoryintegrationdefectthatcanalsooccur
in the absence of somatosensory deficits (Denny-Brown & Banker,
1954; Denny-Brown, Meyer, & Horenstein, 1952). Specifically, they
postulated that personal (and extrapersonal) neglect is caused by
impairments in integrating afferent input from the contralesional
side into a spatial concept.
In the second half of the last century, experimental research
almost exclusively focussed on extrapersonal neglect. Due to the
common co-occurrence of personal and extrapersonal neglect
(Brain, 1941) and the absence of appropriate diagnostic tools to
assesspersonalneglect,personalneglectwassubsumedinthecon-
cept of unilateral neglect and both phenomena were explained by
the same underlying cognitive mechanisms. Unilateral neglect was
consideredeitheraunilateralattentiondisorder(Kinsbourne,1987,
0028-3932/$ – see front matter © 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.neuropsychologia.2011.01.043

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U. Baas et al. / Neuropsychologia 49 (2011) 898–905
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1993; Mesulam, 1981; Posner, Walker, Friedrich, & Rafal, 1987),
a systematic failure in transforming multiple sensory inputs into
spatial representations, i.e. into non-retinal egocentric frames of
reference (Karnath, 1997), or a dysfunction of the cerebral repre-
sentation of contralesional body and space (Bisiach & Berti, 1995;
Bisiach & Luzzatti, 1978).
Recently, however, diagnostic tools for the assessment of per-
sonal neglect such as the Fluff-Test (Cocchini, Beschin, & Jehkonen,
2001) and the Comb-and-Razor-Test (Beschin & Robertson, 1997)
have been developed. Interestingly, these tests have shown that
personal and extrapersonal neglect dissociate more often than
previously assumed: for example, using the Comb-and-Razor-Test
McIntosh, Brodie, Beschin, and Robertson (2000) found personal
neglect without extrapersonal neglect in six of 44 brain dam-
aged patients, i.e. 13.6%. A similar percentage was discovered by
Bowen, Gardener, Cross, Tyrrell, and Graham (2005) with the Fluff-
Test: eight of 42 patients with right-sided brain lesions showed
personal neglect without extrapersonal neglect, i.e. 19.0%. These
dissociations between personal and extrapersonal neglect suggest
that different underlying mechanisms and anatomies might be
involved.
The current study aims at examining the critical mechanisms
and anatomy underlying personal neglect. Specifically, we focus on
whether the representational hypothesis put forward by Bisiach
and Berti (1995)and Bisiach and Luzzatti (1978) is valid for per-
sonal neglect, i.e. if a contralesional body representation defect is
the underlying cause.
Body representation is not a unitary concept. It can be divided
into various components. For example, Coslett, Saffran, and
Schwoebel (2002) proposed three main aspects of body repre-
sentations: the lexical-semantic knowledge of the body and its
functions (body image), the knowledge of spatial relationships
(body structure description), and a dynamic online-representation
of the body in space, which is the result of a computation of multi-
ple afferent somatosensory stimuli (body schema). Thus, according
to Coslett et al. (2002) a body schema can be understood as a
purely somatosensory representation. Other authors have how-
ever additionally emphasized the role of action intention and
subsequent motor components of the body schema (Gallagher,
2002). According to Trepel (1999) body representations can also
be classified by modalities. Research here suggests that there are
elementary motor representations in the precentral gyrus and
elementary sensory representations in the postcentral gyrus (e.g.
Trepel, 1999), visual representations in the lateral occipitotempo-
ral cortex (the so-called extrastriate body area, Downing, Jiang,
Shuman, & Kanwisher, 2001), movement representations in dif-
ferent higher order brain regions (Parsons, Gabrieli, Phelps, &
Gazzaniga, 1998), spatial representations in the posterior parietal
cortex (Stein, 1992) and conscious-affective representations in the
insula (Craig, 2002, 2003; Karnath, Baier, & Nagele, 2005).
Thelinkbetweenpersonalneglectanddefectivebodyrepresen-
tationswasfirstexaminedbyGuarigliaandAntonucci(1992).They
examined a patient with severe personal – but no extrapersonal –
neglect using three tests, measuring different forms of body rep-
resentations. Their study showed that the patient had more left-
than right-sided difficulties in dealing with visuotactile informa-
tioncomingfromthebody(recognizingtouchedfingers;indicating
partsofthebodyafterverbal,visualortactilerequest).Additionally,
he had a generally impaired body concept with bilateral difficulties
inreconstructingabodyandfaceusingpre-cutpuzzlepieces,while
no visuoconstructive deficits were present. These results indicate
that personal neglect can be associated with different body repre-
sentation deficits.
To operationalize body representation, we decided to focus on
a task that assesses proprioceptive and movement representations
of the body. In the so-called hand laterality task (Parsons, 1987a,
1987b), subjects have to evaluate if centrally presented pictures
of left and right hands presented from the front (prototypical) or
back (non-prototypical) view correspond to their covered left or
right hand. This task is an elegant method of measuring the propri-
oceptive and motor imagery of one’s own hand. The reason being
that, as Parsons (1987a, 1987b) showed earlier in intensive stud-
ies with normal subjects, one has to compare the presented hand
picture with the mental (proprioceptive) representation of one’s
own hand in order to make an appropriate judgement (see also
Shenton, Schwoebel, & Coslett, 2004 for the role of proprioception
in motor imagery). Parsons’ experiments demonstrated that sub-
jects mentally moved their hand representation, naturally of their
own accord, to bring it into the corresponding orientation with the
visual hand stimulus if the orientation of the visual hand stimulus
andthehandrepresentationwerenotidentical(1987b).Theresults
from Parsons’ study furthermore showed that it is not the stimu-
lus itself which is mentally rotated, since reaction times increased
withimplicitawkwardnessofstimulusorientation(anatomicalcon-
straints on movements to the stimulus orientation). If subjects
would have performed a mental rotation on the stimulus itself,
reaction times would have increased with the orientation differ-
ence (Cooper & Shepard, 1973), which they did not.
Variants of the hand laterality task have also been applied in the
contextofotherbodydisturbances.Forexample,ithasbeenshown
thatarmamputations(Nico,Daprati,Rigal,Parsons,&Sirigu,2004),
focal hand dystonia (Fiorio, Tinazzi, & Aglioti, 2006) or chronic arm
pain (Schwoebel, Friedman, Duda, & Coslett, 2001) are linked to
impaired body representation, while hemiparesis after stroke was
not associated with a deficient representation of the paralyzed arm
(Johnson, Sprehn, & Saykin, 2002). The hand laterality task was
also used in the context of extrapersonal neglect: Coslett (1998),
for example, examined six right-brain-damaged patients, three of
whom showed extrapersonal neglect. The latter patients showed
significantly more errors with left hand stimuli than with right
hand stimuli. The three patients without extrapersonal neglect did
not exhibit significant differences. Coslett (1998) therefore con-
cluded that neglect may be associated with a disorder in left body
representation.
In the present study we want to find out if personal neglect is
linked to defective body representation to a greater extent than
extrapersonal neglect. Moreover, we want to know whether these
deficits in representation are body-specific (i.e. whether only body
representations are affected in personal neglect) or whether there
is a dysfunction of the mental representation of the contralesional
space in general.
To assess body representations we used an adapted form of the
hand laterality task designed by Parsons (Parsons, 1987a, 1987b).
Toassessextrapersonalrepresentationofvisualstimuli,ataskcom-
parable to the hand laterality task – termed the mirror laterality
task–wasdeveloped:imaginingtheviewofamotor-cyclist,partic-
ipants had to judge photographs of left and right rear-view mirrors
of a motor cycle – presented from the front (prototypical view) or
back(non-prototypicalview)–asleftorright.Ifageneralrepresen-
tationdeficitistheunderlyingcauseforpersonalneglect,weexpect
patients with personal neglect to perform significantly worse with
left stimuli than patients without personal neglect, both on the
handlateralitytaskandthemirrorlateralitytask.Ifpersonalneglect
isduetoaspecificdeficitinbodyrepresentation,patientswithper-
sonal neglect should be particularly impaired with left stimuli in
the hand laterality task. Furthermore, we were interested in find-
ing patient characteristics that would best predict the occurrence
of personal neglect. For this purpose, additional measures were
included, such as measures of somatosensory and motor deficits
as well as measures of extrapersonal neglect.
So far, few studies have dealt with the neuroanatomical basis
of personal neglect. In a post-mortem autopsy of five patients

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U. Baas et al. / Neuropsychologia 49 (2011) 898–905
Table 1
Demographic and clinical data for patients with (PN+) and without (PN−) personal neglect and healthy controls (M=means; SD=standard deviation).
PN+ (N=7) PN− (N=15)
61.29
7.89
6
1
13.50
3.35
6
1
35.57
17.92
6.71
3.77
28.14
5.68
2
5
1.57
2.94
21.55
20.99
0.09
0.13
Controls (N=13)Statistics
Age
M
SD
Female
Male
M
SD
Vascular
Other
M
SD
M
SD
M
SD
Yes
No
M
SD
M
SD
M
SD
51.47
13.62
11
4
12.77
3.11
14
1
37.73
21.57
5.87
4.52
30.79
13.81
3
12
.27
.59
10.42
12.39
0.16
0.15
60.08
6.91
6
7
13.58
2.52
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
H(2)=4.13a
p=.13
chi2(2)=3.84
p=.15
H(2)=.47a
p=.79
chi2(1)=.34
p=.56
z=−1.8b
p=.86
z=−1.10b
p=.27
z=−1.49b
p=.14
chi2(1)=.20
p=.66
z=−1.26b
p=.33
z=−1.09b
p=.28
z=−0.95b
p=.34
Sex
Education
Aetiology
Days post onset
Motoricity
Sensibility
Hemianopia
Extrapersonal neglect: line bisection (omissions)c
Extrapersonal neglect: line bisection (deviation)d
Extrapersonal neglect: Bells Test (centre of cancellation)e
aKruskal–Wallis one-way variance analysis (H-test).
bz-Scores based on Mann–Whitney U tests.
cNumber of omissions of left-sided lines.
dPercentual deviation to the right in left-sided lines.
ecf. Rorden and Karnath (2010) and text.
with personal neglect symptoms, Nielsen (1938) found that all of
them showed lesions of thalamoparietal projection fibres. He sug-
gested that in patients with personal neglect these lesions prevent
somatosensory stimuli from reaching the supramarginal gyrus in
theinferiorparietalcortexresultingindiminishedconsciousnessof
the left side of the body. In a population of 118 patients with right-
sidedlesionsHécaenandAngelergues(1961)showedthatpersonal
neglect symptoms occurred after parietal lesions in 39%, after pari-
etotemporooccipital lesions in 47% and after temporal lesions in
16% of the cases. However, the first and only study exploring the
neural bases of personal neglect in eight patients with modern
lesion analysis methods stems from Committeri et al. (2007). Their
results suggested that the inferior parietal lobe, in particular the
supramarginal and the postcentral gyrus as well as the underlying
white matter were the critical brain structure for personal neglect.
2. Materials and Methods
2.1. Participants
Twenty-two right-handed patients with subacute right hemisphere stroke
(mean time since stroke-onset: 37 days) and without evidence of diffuse or bilateral
lesionsaswellas13right-handedhealthycontrolsubjectsparticipatedinthestudy.
The presence of personal neglect was assessed with a modified version of the Fluff
Test (Cocchini et al., 2001). In this test, 24 targets (felt stickers, 22mm in diameter)
were attached to the clothes of the blindfolded subjects by the examiner (six targets
to the left and right leg, the left arm, and the trunk). No targets were placed on the
right arm, as the task was performed using this arm. The subjects were then asked
to remove the targets as quickly as possible. The number of targets omitted on the
left half of the body after a time limit of 2min was recorded. Controls never omitted
more than three targets on the left side of the body (mean±SD: 1.15±0.90). Thus,
personal neglect was presumed if more than three left targets were omitted. Seven
patients showed personal neglect (PN+; 6.57±2.07), while 15 patients presented
no left personal neglect (PN−; 0.73±0.88).
To control potentially co-varying or confounding variables (motor and
somatosensory impairment as well as extrapersonal neglect) and to investigate the
patient characteristics that would best predict the occurrence of personal neglect,
an additional test battery was administered. Motor impairment of the upper left
limb (hand and arm) was measured with parts of the Chedoke-McMaster Stroke
Assessment (Gowland et al., 1993), which consists of 7 levels of motoricity with
level 7 representing intact motoricity and level 1 representing absent or minimal
motor function. Summing up the scores for arm and hand, the maximum total score
attained was 14 (seven for the left arm and hand respectively). Somatosensory
deficits of the contralesional arm and hand were evaluated with a clinical screen-
ing test used by our occupational therapists for pain perception, touch perception,
detection of texture and proprioception. In the test, a maximum score of 12 could be
attained for both pain and touch perception, a score of 9 for recognition of texture,
and a score of 12 for proprioception. Adding up the scores, the maximum total score
attained was 45, indicating intact somatosensory functions. The presence of extrap-
ersonal neglect was assessed by the Line Bisection Test (Schenkenberg, Bradford, &
Ajax, 1980) and the Bells Test (Gauthier, Dehaut, & Joanette, 1989). The dependent
variables of the Line Bisection Test were left or right deviations from the centre of
the lines. For the Bells Test we calculated the Centre of Cancellation (CoC), using the
procedure and software by Rorden and Karnath (2010, www.mricro.com/cancel/).
This value indicates the centre of mass for all the detected items, so that identifying
allthetargetswouldgenerateascoreofzerowhereasidentifyingonlytherightmost
item would provide a score of one. This measure is sensitive to both the number of
omissions and the location of these omissions. CoC scores higher than 0.09 in the
Bells Test were regarded as an indication of extrapersonal neglect behaviour (cf.
Rorden & Karnath).
Demographic and clinical data are provided in Table 1. As illustrated in the
table, patients and healthy controls were comparable with respect to age, sex and
educational level. Statistically, PN+ patients and PN− patients were comparable
with regard to aetiology, days post-onset of their illness, measures of sensibility,
motoricity, visual field defects, and extrapersonal neglect.
MRI scans were available for 20 patients and CT scans for the remaining two
patients. In line with the procedure used by Karnath, Fruhmann Berger, Kuker, and
Rorden (2004) and Karnath, Himmelbach, and Rorden (2002), diffusion-weighted
scans were used when an MRI was conducted within the first 48h post-stroke and
T2-weighted scans were used when an MRI was conducted later than 48h after
the stroke. Mapping of lesions was carried out by one of the authors (K.G.) with-
out knowledge of the patients’ test results and clinical features. For the 20 patients
with available MRI scans the boundary of the lesions was delineated directly on
the individual MRI image for every single transversal slice using MRIcron software
(Rorden, Karnath, & Bonilha, 2007; www.mricro.com/mricron). Both the scan and
lesion shape were then mapped into approximate Talairach space using the spa-
tial normalization algorithm provided by SPM5 (http://www.fil.ion.ucl.ac.uk/spm/).
For determination of the transformation parameters, cost-function masking was
employed (Brett, Leff, Rorden, & Ashburner, 2001). For the two patients with CT
scans lesions were mapped directly – also using MRIcron – on the T1-weighted MNI
single subject template implemented in MRIcron (Rorden & Brett, 2000) with a slice
distance of 1mm using the closest matching transversal slice of each individual.
To identify the anatomical structures commonly damaged in PN+ patients but
typically intact in PN− patients subtraction analysis was performed (Rorden &
Karnath, 2004). Considering the low number of subjects, a conservative threshold
of 50% was employed, highlighting those brain areas that were lesioned at least 50%
more frequently in PN+ compared to PN− patients.

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Fig. 1. (A) Stimuli of the hand laterality task to evaluate body representation. Left and right hands are presented from the prototypical (palm-down) or non-prototypical
(palm-up) view. (B) Stimuli of the mirror laterality task to assess extrapersonal representation. Left and right rear-view mirrors of a motor cycle are presented from the
driver’s perspective (prototypical view) or from the back (non-prototypical view).
2.2. Stimuli
For the hand laterality task, photographs of a left or right hand were shown cen-
trally in an upright position from a prototypical (palm-down) or non-prototypical
(palm-up) view, resulting in four different stimuli (left prototypical vs. left non-
prototypical stimulus, right prototypical vs. right non-prototypical stimulus; see
Fig. 1). Palm-down view was considered prototypical because this view was consis-
tent with the position of the participants’ hands during the experiment. The mirror
lateralitytaskconsistedofcentrallypresentedpicturesofleftorrightrear-viewmir-
rorsofamotorcycle,alsoshownfromprototypical(front)ornon-prototypical(back)
view,thusalsoresultinginfourtypesofstimuli.Here,thefrontviewwasconsidered
prototypical because subjects had to assume the perspective of a motor-cyclist dur-
ing the experiment. In this task, motor cycle rear-view mirrors were used instead of
the more common car rear-view mirrors as a preliminary evaluation revealed these
stimuli to be more distinctly left or right-sided compared to the rear-view mirrors
of a car.
2.3. Procedure
Every hand and mirror stimulus was presented 15 times during the experiment.
The 60 (15×4) hand and mirror laterality task stimuli were presented centrally on
a computer screen in a pseudo-randomized order to prevent an immediate repeti-
tion of the same stimulus. Stimuli were separated by a blank screen with a central
fixation cross. E-Prime (Psychology Software Tools) was used to program and con-
duct the experiment and record the response times. A microphone voice key device
was used to measure vocal reaction times of participants. Errors were logged by
the experimenter. To check for sequence effects, half of the participants performed
the hand laterality task first, while the other half started with the mirror lateral-
ity task. In the hand laterality task, subjects were asked to determine whether the
visually presented hand stimulus corresponded to a left or right hand. In the mirror
laterality task, participants had to evaluate rear-view mirrors from the perspec-
tive of the cyclist as left or right. Both tasks were preceded by a practice test in
which the four stimuli were displayed three times in a pseudo-randomized order
without a time restriction. In the practice test of the hand laterality task, partic-
ipants were allowed to look at their hands while moving them into the required
position. Whenever wrong answers were given, the experimenter pointed out the
solution (by moving his/her hand into the position of the presented stimulus). In
the practice test of the mirror laterality task, photographs of single motor cycle
mirrors and photos of the driver’s perspective were shown. This was done to
facilitate the subject’s task of mentally assuming the perspective of the motor-
cyclist. Again the correct answers were given by the experimenter in the case of
wrong answers. Before starting the experiment, participants had to place their
hands out of sight palm down in their laps under the computer table. They were
instructed to avoid any hand movement and give the answer as quickly as possi-
ble by saying “left” or “right” into the microphone to record reaction time (“voice
onset”). The stimulus disappeared when a response was given, and a blank screen
with a fixation cross appeared. The display of the next stimulus was presented by
the experimenter to adapt the experiment to the patient’s individual processing
speed.
3. Results
3.1. Group analyses
Since our hypotheses focussed on testing interactions, we
used variance analytical procedures. First of all, we tested the
assumptions of normal distribution and variance homogene-
ity, which were partially violated. Therefore, we preliminarily
applied non-parametric tests as well as analyses of variance
(ANOVA) without and with different variance stabilizing pro-
cedures (Winer, 1972) including transformations (Conover &
Imam, 1981). Non-parametric tests included Kruskal–Wallis-tests
and Mann–Whitney-U-tests to evaluate group differences, and
Friedman-tests and Wilcoxon-tests to evaluate differences of the
tasks within groups.
As the directions of the results remained the same – indicating
the robustness of our data – and one can assume that ANOVA is
a robust procedure against violations of normal distribution and
variance homogeneity (Bortz, 1989, p. 347), we decided to show
non-transformed data using parametric ANOVAs here.
A mixed four-way repeated measures ANOVA with Group (PN+
vs. PN− patients vs. controls) as between subject factor, and Stimu-
lus (hand vs. mirror), View (prototypical vs. non-prototypical) and
Side (left vs. right) as within subject factor was performed. The
percentages of errors and reaction times (RTs) were analyzed sep-
arately. Analyses of RTs only included data for correct responses.
With specific hypotheses, significant effects were further ana-
lyzed with planned comparisons. Without specific hypotheses,
unplanned post hoc comparisons (Newman–Keuls) were per-
formed.
3.1.1. Errors
Means and standard errors of the mean (SEM) for accuracy data
(errors in %) for every stimulus type and group are presented in
Table 2.
There was a significant main effect of Group (F(2,32)=5.25;
p=.01). Subsequent post hoc comparisons revealed that PN+
patients (25±5) showed significantly more errors than PN−
patients (14±3; p=.07). Additionally, the two patient groups
committed significantly more errors than controls (5±3; p<.01).
Table 2
Means and standard error of the mean (SEM) for accuracy data (errors in %).
Stimulus PN+PN−
7 (4)
5 (3)
9 (4)
14 (4)
19 (7)
15 (7)
18 (5)
25 (5)
Controls
Hand prototypical left
Hand prototypical right
Hand non-prototypical left
Hand non-prototypical right
Mirror prototypical left
Mirror prototypical right
Mirror non-prototypical left
Mirror non-prototypical right
23 (6)
15 (4)
19 (6)
13 (5)
43 (11)
39 (10)
30 (8)
18 (7)
2 (4)
2 (3)
7 (4)
9 (4)
2 (8)
3 (7)
8 (6)
7 (5)

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U. Baas et al. / Neuropsychologia 49 (2011) 898–905
Table 3
Means and standard errors of the mean (SEM) for reaction times (in ms).
Stimulus PN+ PN−
1898 (215)
1516 (148)
2085 (335)
1875 (187)
1569 (229)
1557 (273)
1980 (234)
2194 (272)
Controls
Hand prototypical left
Hand prototypical right
Hand non-prototypical left
Hand non-prototypical right
Mirror prototypical left
Mirror prototypical right
Mirror non-prototypical left
Mirror non-prototypical right
2305 (304)
1891 (209)
2245 (473)
1858 (264)
1701 (324)
1583 (385)
2090 (331)
1782 (385)
1042 (233)
885 (154)
1189 (347)
1320 (194)
1025 (238)
1000 (283)
1312 (243)
1244 (283)
There was also a significant main effect of Stimulus (F(2,32)=9.88;
p<.01). Generally, more errors were made in the mirror (19±3)
than in the hand laterality task (10±2). Furthermore, the interac-
tion View×Group was significant (F(2,32)=3.31; p<.05). That is,
while PN+ patients made significantly more errors with prototyp-
ical stimuli than with non-prototypical stimuli, PN− patients and
controlsmadesignificantlymoreerrorswithnon-prototypicalthan
with prototypical stimuli (PN+: non-prototypical stimuli: 20±5;
prototypicalstimuli:30±6;PN−:non-prototypicalstimuli:16±4;
prototypical stimuli: 11±4; controls: non-prototypical stimuli:
8±4; prototypical stimuli: 2±4). More importantly, there was
a significant interaction Group×Side (F(2,32)=4.62; p=.02; see
Fig. 2) indicating that PN+ patients made significantly more errors
with left stimuli than with right stimuli (left stimuli: 29±6; right
stimuli: 21±5; p<.01). This was not the case in PN− patients and
controls (PN−: left stimuli: 13±4, right stimuli: 15±3; controls:
left stimuli: 4±4, right stimuli: 5±4). Additionally, compared to
PN− patients PN+ patients made significantly more errors with
left stimuli (p<.03), while no such difference was found between
the two patient groups with respect to the right-sided stimuli.
In comparison to healthy controls, the two patient groups made
significantly more errors both with the left and the right stimuli
(p<0.1). All other comparisons, in particular the three way inter-
action Group×Stimulus×Side, did not achieve any significance.
It should be noted that PN+ patients did not differ statistically
from PN− patients with regard to extrapersonal neglect. Yet, PN+
patients showed a higher CoC score and/or deviations in measures
of extrapersonal neglect, as Table 1 shows. To analyze whether this
numerical difference contributed to the significant effects, an anal-
ysis of covariance with the three extrapersonal neglect variables as
covariates was performed. This analysis of covariance did not show
any changes in the reported effects.
3.1.2. Reaction times
Reaction times (means and SEM) for every stimulus type and
group are presented in Table 3. There were three significant
main effects: Group (F(2,31)=4.02; p=.03), View (F(2,31)=13.46;
p<.01) and Side (F(2,31)=8.77; p<.01). Generally, RTs in healthy
controls were significantly shorter than RTs in PN+ patients (con-
Fig. 2. Percentage of errors (mean and SEM) for left and right stimuli for patients
with (PN+) and without (PN−) personal neglect and healthy controls.
trols: 1127±206; PN+: 1932±281; p<.05) and PN− patients:
(1834±199; p=.05). No significant difference was observed
between the two patient groups (p=.65). The significant effect of
View was due to a significant increase in RTs for non-prototypical
views (non-prototypical stimuli: 1764±152; prototypical stimuli:
1498±124). Finally, as shown by the Side effect, RTs were gen-
erally longer for left stimuli (photographs of left hands and left
rearview mirrors) than for right stimuli (left stimuli: 1703±144,
right stimuli: 1559±127). All other effects, in particular, the inter-
actions of interest (Group×Side, Group×Side×Stimulus), were
non-significant.
As before, the potential influence of extrapersonal neglect was
controlled by an additional analysis of variance with covariables
of extrapersonal neglect as covariates. No relevant changes in the
results were observed.
3.2. Prediction of personal neglect
To explore whether personal neglect can be predicted by defec-
tive somatosensory or motor functions, extrapersonal neglect,
deficits in body-specific representations or a general (non-body-
specific) impairment in the representation of the left extrapersonal
stimuli, multiple regression analyses were conducted (forward-
selection, inclusion criterion F>8.90 with p<.05). The independent
variables were: total score of somatosensory deficits, motoricity
index,totalscoreofextrapersonalneglect(BellsTest:CentreofCan-
cellation; Line Bisection: percentual deviation to the right in left
lines; number of left line omissions), total score of extrapersonal
space representation impairment (difference of errors in percent
betweenphotographsofleftandrightrear-viewmirrors;difference
in RTs (medians) for left and right mirror stimuli) and total score
of defects in the representation of the body (difference of errors in
percent between photographs of left and right hands; difference in
RTs (medians) for left and right hand stimuli). For the prediction of
the extent of personal neglect, the number of left omissions in the
Fluff-Test was used as the dependent variable. The only significant
predictor (R2=.31. p<.01) for personal neglect was a deficit in the
representation of the body. Neither primary sensory impairment,
motor deficits, extrapersonal neglect nor impairments in the rep-
resentation of the left extrapersonal space significantly predicted
personal neglect.
3.3. Lesion analyses
The results of the lesion analyses are presented in Fig. 3. The
subtraction analysis revealed a centre of lesion location in the
temporo-parietal junction and underlying white matter that was
damaged at least 50% more frequently in patients with personal
neglect than in patients without personal neglect. Additionally,
there was also a smaller right frontal focus.
4. Discussion
The aim of the present study was to explore whether personal
neglect can best be explained by a specific disorder of contrale-
sional body representation in particular or a dysfunction of the
representation of contralesional space in general.
Our results show that patients with left personal neglect made
more errors with left stimuli than with right stimuli, regardless
of the type of stimulus (hand or mirror, i.e. body or extrapersonal
stimulus). Patients without personal neglect and controls did not
show any difference in results between the left and right stimuli.
Moreover,errorswithleftstimulioccurredsignificantlymoreoften
in patients with personal neglect than in patients without personal
neglect. Between the patient groups, no significant difference in
errors for right stimuli was observed.

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U. Baas et al. / Neuropsychologia 49 (2011) 898–905
903
Fig. 3. (A) Overlap map showing the degree of involvement of each voxel in the lesions of patients with (PN+) and without (PN−) personal neglect normalized to the
MNI template. The map is presented as 2D axial renderings on the MNI ‘representative’ brain, in 4mm ascending steps. The z-position of each axial slice in the Talairach
stereotaxic space is presented at the foot of the figure. (B) Contrast map in PN+ patients and PN− patients showing those regions which are 50–100% more frequently lesioned
in PN+ patients than PN− patients. (C) Centre of lesion location (x-, y-, z-coordinates) of the lesion of the contrast map in PN+ patients and PN− patients, showing that the
temporo-parietal junction is more often affected in PN+ than PN− patients.
Our results cannot be due to elementary disorders such as
somatosensory or motor deficits of the left side of the body, as
the respective variables were held constant in both patient groups.
Moreover, taking extrapersonal neglect variables as covariates did
not affect the results. The results cannot be explained by a general
problem of mental imagery either. If this were the case, then not
only left stimuli but also right stimuli should have been affected.
Furthermore, if the results were solely due to a problem with
mental rotation, then the effects should be present particularly
with non-prototypical stimuli. The reason for this is that sub-
jects need to make mental rotations with these stimuli in order
to compare the visual stimulus with the actual position of their
hands. Therefore in prototypical stimuli, where no mental-motor
rotations are required, difficulties in evaluation should not have
occurred.However,themissingeffectsofprototypicalityshowthat
patients with personal neglect also have difficulties in evaluat-
ing the side of prototypical left hands. This means that Parson’s
hand laterality task is not only a task of mental rotation, but also
a task requiring proprioceptive comparisons with one’s own hand
representation.
One might further argue that the left-right effect is due to
the position of recognition relevant cues (thumb of the hand and
stem of the mirror). Theoretically this could be true for the non-
prototypical stimuli, where the hands were presented in palm-up
position and the mirrors from the back: here, the recognition rele-
vant cue (thumb or stem) is on the left side of the left stimulus and
on the right side of the right stimulus. This could mislead neglect
patients into “ignoring” left recognition relevant cues and being
more “susceptible” to right recognition relevant cues (which is
why an increase in errors with non-prototypical left stimuli and
the opposite results for the prototypical stimuli should result).
However, as the interactions with the corresponding factor View

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U. Baas et al. / Neuropsychologia 49 (2011) 898–905
(Side×View, Group×Side×View, etc.) were non-significant, this
could not be confirmed. Additionally, if our data were due to an
unilateral attention disorder (Kinsbourne, 1987, 1993; Mesulam,
1981; Posner et al., 1987) not only higher error rates in evaluating
left (body related) stimuli should have resulted. In addition to this,
in order to orient to the left body, there should have been primarily
longer reaction times, reflecting a longer attention process. Again,
corresponding effects confirming this hypothesis were not found.
So far, the inability of personal neglect patients to reliably
identify left stimuli regardless of the type of stimulus is best inter-
preted as difficulties with contralesional body and extrapersonal
space representation. This suggests a general dysfunction in con-
tralesional representations, as postulated in the representational
hypothesis of Bisiach and colleagues (Bisiach & Berti, 1995; Bisiach
&Rusconi,1990;Bisiach&Vallar,2000).Fromourresultsitseemsas
if our patients with personal neglect systematically misinterpreted
left body and left extrapersonal space stimuli as right ones. As a
possible explanation for this behaviour, we suggest that patients
with personal neglect suffer from a deficit known as “allochiria”.
Allochoria is described as a deficit in which stimuli belonging to
one side of the body or space are interpreted as occurring on (or
belonging to) the other side. This deficit was first described by
Obersteiner (1882) for the tactile modality. He had observed this
“confusion of sides” (p. 153) in patients with spinal cord injury
andhysteriaduringtactilestimulation:thesepatientswerereason-
ably capable of localizing the place where they were touched with
the exception of the body side, despite more or less intact tactile
sensibility. Later, in the context of hemispatial neglect, allochiria
was interpreted as a unilateral disorder in which contralesional
stimuli of different modalities were interpreted as occurring ipsile-
sionally (Halligan, Marshall, & Wade, 1992). With regard to this,
Joanette and Brouchon (1984) observed that visual stimuli pre-
sented in the left hemifield of neglect patients were interpreted
as emerging in the right hemifield. Additionally, Bisiach, Capitani,
Luzzati, and Perani (1981) noted that some patients describing a
visual scene from imagery reported objects on the neglected side
as being present on the intact side. Hereby attention was drawn
to the occurrence of “these transpositions” in purely “imaginal”
tasks. The mechanism proposed for this was a defect in neural
mechanismsandstructuresprocessingincomingsensorystimuli.It
was assumed that due to brain damage contralesional stimuli were
not processed by the corresponding brain side. Instead they were
assigned to the ipsilesional side, resulting in a conscious misinter-
pretation of a contralesional stimulus as occurring ipsilesionally
(Bisiach & Berti, 1995). Or as Brain (1941) wrote: “It appears that
severe damage to the body scheme for one half of the body causes
eventsoccurringonthathalf,ifperceivedatall,toberelatedincon-
sciousness to the surviving scheme representing the normal half”
(p. 265). Other authors suggested that not only the contralesional
butalsotheipsilesionalbrainsideisdefective(Mijovic,1991).They
proposed that ipsilesional representations become more “recep-
tive” (p. 1589) to contralesional stimuli, resulting in left stimuli
being accepted as fitting the right mental representation (Mijovic,
1991). This could again explain why patients with left personal
neglect identify a left hand as a right hand without realizing the
mismatchbetweentheperceivedleftandthementallyrepresented
right hand.
Nevertheless, one might wonder why it is that performance for
both body- and non-body stimuli (i.e. hands and rear-view mir-
rors) is impaired and why the hand task is not more difficult for
patients with personal neglect, especially since we assume that a
bodyrepresentationdisorderistheunderlyingcause.Therearesev-
eralpossibleexplanationsfortheseobservations:firstly,ourresults
could be attributed to the mirror task being more difficult per se,
even in control subjects as the results (main effect of Stimulus
combined with absence of significant interaction between Stim-
ulus and Group for errors) have shown. Secondly, it could be that
body and space representations share overlapping brain structures
in the posterior parietal cortex (Andersen, Snyder, Bradley, & Xing,
1997; Brain, 1941; Dijkerman & de Haan, 2007). Finally, there is the
possibility that we use our hands mentally (i.e. our body represen-
tation) to mentally tilt non-prototypical rear-view mirrors into the
prototypical position. Hence we also activate body representations
to solve this object task.
According to the data, our personal neglect patients suffered
from impairments both in body-specific and extrapersonal space
representations. Yet our regression analyses showed that per-
sonal neglect could only be predicted by body-specific deficits.
In contrast, deficits in extrapersonal space representation had no
predictive value. This suggests that a disturbance in body-specific
representations plays a central – perhaps even causal – role in
personal neglect. So how can we then reconcile the observations
that a disorder of body representation appears critical in personal
neglect when considering that both body-specific and extraper-
sonal space representations are impaired in these patients? As
evidence shows that body and space representations share some
of the same brain areas, we explain this co-existence of impaired
bodyandextrapersonalspacerepresentationsinneglectpatientsin
terms of overlapping brain structures. Consistent with our expla-
nation, research points out that body and space representations
are processed by structures in the posterior parietal cortex (e.g.
Andersen et al., 1997; Brain, 1941; Dijkerman & de Haan, 2007).
Moreover, it seems that input from both body and extrapersonal
space is integrated in the temporoparietal junction (Blanke, Landis,
Spinelli, & Seeck, 2004). The observation that disorders of body
and extrapersonal space representation derive from lesions in this
region – especially the supramarginal (BA 40) and postcentral gyri,
the underlying white matter, and the posterior superior temporal
gyrus – is a further argument supporting the assumption of over-
lapping neural circuits (Committeri et al., 2007). In other words,
a co-occurrence of deficits in body and extrapersonal space rep-
resentation seems quite common after postcentral brain lesions,
especially when lesions are extensive, as was the case in our
patients.
The co-occurrence of impairments in body and extrapersonal
representations could, of course, also be explained by features of
the experimental tasks, as both the hand laterality task and the
mirror laterality task had to be solved from an egocentric perspec-
tive (i.e. the own body midline was the point of reference for all
decisions during the experiment). Thus, the two tasks share the
same egocentric reference system, but they diverge with respect to
the object of reference (hand and body part vs. mirror as object in
external space).
Finally, the results from our lesion analysis show that the
temporo-parietal junction, i.e. the junction of the white matter
underlyingthesuperiortemporalandthesupramarginalgyri,isthe
critical anatomical area for personal neglect. These results are con-
sistent with the findings by Committeri et al. (2007) who recently
investigated the neural basis of personal neglect by using modern
lesion analyses techniques. Our results thus provide further evi-
dence from an independent dataset that personal neglect is linked
to a dysfunction of the temporoparietal junction.
In conclusion, our findings point to the role of body represen-
tation as a critical mechanism in personal neglect. They especially
emphasise proprioceptive and motor aspects of body representa-
tion. Together with the results of Guariglia and Antonucci (1992),
who also showed a link between personal neglect and disor-
ders in body representation, our results strengthen the view
that personal neglect can be understood as a disorder of “body
schema”. Furthermore, our results imply that this “body schema”
exceeds a purely higher somatosensory representation (Coslett
et al., 2002).

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905
Althoughpersonalandextrapersonalneglectarecloselyrelated,
theresultsofthisstudysupporttheviewthatbothformsofneglect
are independent disorders that can have distinct underlying causal
mechanisms. Personal neglect should therefore be assessed sepa-
rately from extrapersonal neglect.
Acknowledgements
This work was supported by Swiss National Foundation Grant
No. 3020030-108146, the Deutsche Forschungsgemeinschaft (KA
1258/10-1),andtheBundesministeriumfürBildungundForschung
(BMBF-Verbund 01GW0641 “Räumliche Orientierung”).
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