Phonological decoding involves left posterior fusiform gyrus.

Abstract

Aloud reading of novel words is achieved by phonological decoding, a process in which grapheme-to-phoneme conversion rules are applied to "sound out" a word's spoken representation. Numerous brain imaging studies have examined the neural bases of phonological decoding by contrasting pseudoword (pronounceable nonwords) to real word reading. However, only a few investigations have examined pseudoword reading under both aloud and silent conditions, task parameters that are likely to significantly alter the functional anatomy of phonological decoding. Subjects participated in an fMRI study of aloud pseudoword, aloud real word, silent pseudoword, and silent real word reading. Using this two-by-two design, we examined effects of word-type (real words vs. pseudowords) and response-modality (silent vs. aloud) and their interactions. We found 1) four regions to be invariantly active across the four reading conditions: the anterior aspect of the left precentral gyrus (Brodmann's Area (BA) 6), and three areas within the left ventral occipitotemporal cortex; 2) a main effect of word-type (pseudowords > words) in left inferior frontal gyrus and left intraparietal sulcus; 3) a main effect of response-modality (aloud > silent) that included bilateral motor, auditory, and extrastriate cortex; and 4) a single left hemisphere extrastriate region showing a word-type by response-modality interaction effect. This region, within the posterior fusiform cortex at BA 19, was uniquely modulated by varying phonological processing demands. This result suggests that when reading, word forms are subject to phonological analysis at the point they are first recognized as alphabetic stimuli and BA 19 is involved in processing the phonological properties of words.

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Phonological Decoding Involves Left Posterior
Fusiform Gyrus
Nicole A.E. Dietz,1Karen M. Jones,1Lynn Gareau,1Thomas A. Zeffiro,2
and Guinevere F. Eden1*
1Center for the Study of Learning and Department of Pediatrics, Georgetown University Medical
Center, Washington, DC
2Center for Functional and Molecular Imaging and Department of Neurology, Georgetown
University Medical Center, Washington, DC
?
?
Abstract: Aloud reading of novel words is achieved by phonological decoding, a process in which
grapheme-to-phoneme conversion rules are applied to “sound out” a word’s spoken representation.
Numerous brain imaging studies have examined the neural bases of phonological decoding by contrast-
ing pseudoword (pronounceable nonwords) to real word reading. However, only a few investigations
have examined pseudoword reading under both aloud and silent conditions, task parameters that are
likely to significantly alter the functional anatomy of phonological decoding. Subjects participated in an
fMRI study of aloud pseudoword, aloud real word, silent pseudoword, and silent real word reading.
Using this two-by-two design, we examined effects of word-type (real words vs. pseudowords) and
response-modality (silent vs. aloud) and their interactions. We found (1) four regions to be invariantly
active across the four reading conditions: the anterior aspect of the left precentral gyrus (Brodmann’s Area
(BA) 6), and three areas within the left ventral occipitotemporal cortex; (2) a main effect of word-type
(pseudowords ? words) in left inferior frontal gyrus and left intraparietal sulcus; (3) a main effect of
response-modality (aloud ? silent) that included bilateral motor, auditory, and extrastriate cortex; and 4)
a single left hemisphere extrastriate region showing a word-type by response-modality interaction effect.
This region, within the posterior fusiform cortex at BA 19, was uniquely modulated by varying phono-
logical processing demands. This result suggests that when reading, word forms are subject to phono-
logical analysis at the point they are first recognized as alphabetic stimuli and BA 19 is involved in
processing the phonological properties of words. Hum Brain Mapp 26:81–93, 2005.
© 2005 Wiley-Liss, Inc.
Key words: reading; phonological processing; decoding; words; pseudowords; fMRI
?
?
INTRODUCTION
Functional neuroimaging studies of pseudoword (pro-
nounceable nonword) reading are a prominent part of on-
going efforts to understand the neural basis of reading
[Cappa Perani et al., 1998; Fiebach et al., 2002; Fiez et al.,
1999; Hagoort et al., 1999; Jobard et al., 2003; Joubert et al.,
2004; Mechelli et al., 2003; Petersen et al., 1990; Price et al.,
1996; Rumsey et al., 1997a] and its disorders [Brunswick et
al., 1999; Rumsey et al., 1997b]. Decoding of unfamiliar
nonwords necessitates sublexical phonological processing,
whereby the conversion of the visual word representation
into its abstract phonological code is accomplished by the
use of grapheme-to-phoneme correspondence rules. Rela-
tive to reading familiar words, pseudoword reading places a
greater demand on the phonological processing system;
even though real words can be read via assembled phonol-
ogy, pseudoword reading can only be accomplished via this
Contract grant sponsor: National Institute of Child Health and
HumanDevelopment;Contract
HD40095; Contract grant sponsor: General Clinical Research Center
Program of the National Center for Research Resources; Contract
grant number: MO1-RR13297; Contract grant sponsor: National In-
stitutes of Health.
*Correspondence to: Guinevere Eden, Center for Study of Learning,
Georgetown University Medical Center, Building D, Suite 150, Box
571406, 4000 Reservoir Rd., NW, Washington, D.C. 20057-1406.
E-mail: edeng@georgetown.edu
Received for publication 26 April 2004; Accepted 17 December 2004
DOI: 10.1002/hbm.20122
Published online 31 May 2005 in Wiley InterScience (www.
interscience.wiley.com).
grantnumbers:HD36461,
? Human Brain Mapping 26:81–93(2005) ?
© 2005 Wiley-Liss, Inc.

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indirect/sublexical
problems, especially those requiring sublexical analyses, are
the hallmark of some cases of acquired reading disorders
[Friedman et al., 1993; Leff et al., 2001] and account for many
of the difficulties encountered by children and adults with
the reading disability developmental dyslexia [Vellutino et
al., 2004]. Better knowledge of the neural bases of reading
and sublexical phonological processing could facilitate the
early identification of reading disabilities and the develop-
ment of effective reading remediation strategies.
Various models and theories of word recognition offer
accounts of the neural mechanisms that may underlie the
transformation of orthography to phonology in reading.
These theories were largely introduced to explain the differ-
ent patterns of reading disabilities observed among patients
with acquired dyslexias [Warrington and Shallice, 1980].
Some patients had intact word reading (regular and excep-
tion words) accompanied
pseudowords (phonological dyslexia), while others could
read pseudowords and regular real words, but were unable
to read exception words (surface dyslexia). The dual-route
model of word reading arose to explain this double dissoci-
ation [Coltheart et al., 1993]. According to this model,
known words have stored lexical representations that can be
very quickly accessed via a memory-based lexical route of
reading, whereas pseudowords must undergo a more me-
thodical process of grapheme-to-phoneme conversion (GPC)
using a rule-based sublexical route. A model with three
routes for reading was developed based on the observation
of a patient who could correctly read regular words, excep-
tion words, and pseudowords, but whose comprehension
was poor [Gerhand, 2001; Southwood and Chatterjee, 2000].
Alternatively, a computational approach in the form of par-
allel distributed processes (PDP) describes a system of inter-
connected word processing units linked together in parallel
[Seidenberg and McClelland, 1989]. Consequently, the same
neural network is used for reading whether or not the word
is familiar. Word exposure modulates the connection
strengths between phonological and orthographic units such
that frequently encountered words are phonologically de-
coded more rapidly and accurately than unknown words.
Neuroanatomical correlates of these reading models have
been examined and tested using functional imaging tech-
niques including positron emission tomography (PET), mag-
netoencephalography (MEG), and functional magnetic res-
onance imaging (fMRI). The contrast of pseudoword with
real word reading differs in phonological demands and
elicits an increase in activity in left posterior superior (“dor-
sal stream”) cortical areas including the lateral inferior pa-
rietal and posterior superior temporal cortices [Hagoort et
al., 1999; Herbster et al., 1997; Price et al., 1996; Pugh et al.,
1996; Rumsey et al., 1997a; Simos et al., 2002]. Dyslexic
readers, having impaired phonological processing abilities,
show underactivation of these regions relative to typical
readers during phonological processing tasks [Brunswick et
al., 1999; Eden et al., 2004; Rumsey et al., 1997a; Shaywitz et
al., 1998]. Based on these findings, the left inferior parietal/
procedure.Phonological processing
by difficultyin reading
posterior superior temporal cortex has been purported to be
the substrate subserving the assembled, sublexical, or indi-
rect route of the dual-route model, where GPC rules are
applied to decode words. In addition, the dorsal left inferior
frontal cortex has also been implicated in supporting pho-
nological processing. This finding appears to be most con-
sistent in studies of aloud reading [Brunswick et al., 1999;
Fiez et al., 1999; Hagoort et al., 1999; Herbster et al., 1997;
Poldrack et al., 1999; Pugh et al., 1996; Rumsey et al., 1997a;
Zurowski et al., 2002]. The exact role of the inferior frontal
cortex is likely to be more complex as semantic processing
also invokes activity here, but in regions ventral and poste-
rior to those found during phonological processing [Fiez et
al., 1999; Gabrieli et al., 1998].
Familiar, frequently encountered words and irregularly
spelled “sight” words that make little demand on sublexical
phonological processing have been shown to activate left
posterior inferior areas (inferior occipitotemporal cortex and
fusiform gyrus), suggesting perhaps that this ventral stream
houses the direct, lexical route of reading [Cohen et al., 2000;
Fiez et al., 1999; Kiehl et al., 1999; Paulesu et al., 2000].
However, not all brain imaging studies support the idea of
two routes. For example, contrary to predictions from a
dual-route model, multiple studies have shown activation of
this ventral region when processing pseudowords [Bruns-
wick et al., 1999; Paulesu et al., 2000; Price et al., 1996; Xu
et al., 2001]. Consequently, it has been argued that these
findings of simultaneous activity in multiple brain regions
are more consistent with either a connectionist parallel
distributed processing (PDP) model of reading [Seiden-
berg and McClelland, 1989] or other more extensive serial
models.
Some of the inconsistencies reported among neuroimag-
ing studies have been attributed to experimental parameters
or statistical limitations [Mechelli et al., 2003]. Specifically,
opinions regarding which cognitive model provides the best
description of the neural representation have been divided,
with some claiming evidence for the dual-route model [Fie-
bach et al., 2002; Jobard et al., 2003; Joubert et al., 2004] and
others for connectionist models [Herbster et al., 1997; Rum-
sey et al., 1997a]. However, in this debate surprisingly little
attention has been given to the importance of aloud reading.
Instead, silent and aloud reading are often assumed to be
interchangeable when making cognitive inferences about
the neural basis of reading or phonological processing. Fur-
ther, the advent of fMRI technology has prompted a dispro-
portionate use of tasks that avoid spoken paradigms, favor-
ing manual responses during lexical decision or silent
reading tasks because of technical constraints. As a result,
silent reading studies greatly outnumber aloud reading
studies due to the concern that speech-induced movements
are not compatible with the need to minimize motion-re-
lated artifacts.
However, it has been demonstrated that neural activity
underlying aloud word reading is not the equivalent of
silent reading activity with the addition of related motor and
auditory activity [Bookheimer et al., 1995; Huang et al.,
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2001]. In fact, when reading aloud vocalization is not initi-
ated until the computation of phonology is complete [Rastle
et al., 2000; Seidenberg and McClelland, 1989]. Hence, read-
ing aloud maximally elicits activation of the phonological
processing system in a way that silent reading does not
[Barch et al., 1999; Huang et al., 2001]. As a consequence, the
use of different response modalities (silent vs. aloud read-
ing) will draw on different neural substrates subserving
reading [Price et al., 1994; Rumsey et al., 1997a]. These
findings from PET studies demonstrate the necessity to in-
clude both conditions in future brain imaging studies of
reading and phonological processing. To date, only three
neuroimaging studies have incorporated both aloud and
silent reading to investigate phonological processing [Bruns-
wick et al., 1999; Hagoort et al., 1999; Rumsey et al., 1997a].
Two of these studies involved overt pronunciation of single
words, but the comparison task entailed decision-making
(phonological or feature) and hence did not allow for a
direct comparison. A PET study by Hagoort et al. [1999]
employed the same reading tasks for both the aloud and
silent conditions. Native German speakers were scanned as
they read real German words and pseudowords aloud and
silently, but an interaction analysis of response-type (aloud
and silent) and lexicality (real words and pseudowords) was
not provided. Further, the German language has a relatively
transparent orthography (a regular one-to-one correspon-
dence between words’ spellings and their pronunciations),
whereas English has an opaque (or deep) orthography. Gen-
eralization of these results from German to English may
therefore be limited and underscores the need for further
studies that directly address reading English words and
pseudowords aloud.
Taken together, there is a need to examine brain mecha-
nisms related to aloud and silent reading in the English
language. To address this question in the context of the
neural mechanisms underlying phonological processing in
reading, we employed a two-by-two experimental paradigm
that placed differential demands on phonological decoding
under overt and covert reading conditions in order to elicit
differential activation of their corresponding neural sub-
strates. Pseudoword decoding puts more stress on phono-
logical processing than real word reading, as nonwords can
only be decoded using addressed phonology, whereas real
words can be read either via addressed phonology or the use
of the direct lexico-semantic route. Aloud reading also puts
greater demands on phonological processing than reading
silently, as the phonological codes need to be represented in
their entirety in order to pronounce the word. We used fMRI
to detect task-related signal changes while adult monolin-
gual English speakers read words and pseudowords aloud
and silently. An interleaved data acquisition technique was
used to minimize magnetic susceptibility and motion arti-
facts caused by aloud word reading [Eden et al., 1999]. The
aim of our study was not to verify any particular model of
reading but to develop a more comprehensive understand-
ing of the neural mechanisms of phonological processing
under conditions of aloud and silent reading.
SUBJECTS AND METHODS
Subjects
Sixteen subjects (nine female, seven male; mean age 31.1
years; age range, 20.9–39.5) participated in this study. Sub-
jects were right-handed as determined by the Edinburgh
Handedness Inventory [Oldfield, 1971] and were native
speakers of English. Subject exclusion criteria included bi-
lingualism, claustrophobia, nicotine or other drug use, a
history of head injury, a known family history of psychiatric,
neurological, or developmental disorders involving first-
degree relatives, presence of metal fragments in the body, or
pregnancy. Subjects had normal or corrected vision, normal
local and global stereopsis, and normal color vision [Ishi-
hara, 1996]. Attention Deficit/Hyperactivity Disorder was
excluded using the abbreviated Wender Utah Rating Scale
[Ward et al., 1993]. Reading was evaluated by a comprehen-
sive battery of neuropsychological tests that included real
word and pseudoword reading as well as phonological
awareness skills. Results of these behavioral measures were
normal or above for all subjects. Subjects were paid for their
participation and gave written informed consent in accor-
dance with the Georgetown University Medical Center In-
stitutional Review Board.
Experimental Tasks and Design
Subjects participated in two 12-min experimental runs
during which they read 1) silently (without moving the lips,
tongue, or jaw), and 2) aloud. Both runs contained alternat-
ing blocks of real words and pseudowords and consisted of
10 48-s task periods and 10 24-s rest (fixation) periods. The
two runs were pseudorandomized in order of presentation
with two additional runs collected for the purpose of a
different study.
To minimize any magnetic susceptibility artifacts caused
by potential head and jaw movements associated with read-
ing [Birn et al., 1998], task performance (reading) coincided
with a time during the block when the gradients were
turned off [Eden et al., 1999]. These trials were interleaved
with periods of image acquisition, with the assumption that
the 4–8-s delay in the hemodynamic response [Bandettini et
al., 1992; Kwong et al., 1992; Logothetis, 2001] would allow
detection of the blood oxygenation-level dependent (BOLD)
contrast generated by the previously performed task. In this
way, the use of a TR (repetition time) of 12 s yielded four
brain volumes (time points) during each 48-s task block (see
Fig. 1). Withina word
pseudowords were presented for 200 ms and followed by a
2450 ms response interval during which subjects viewed a
fixation crosshair. Three words were presented within a
trial, each trial lasting 8 s. The epoch was completed after the
fixation crosshair was displayed for 4,050 ms, while a whole-
brain volume was acquired, hence resulting in each epoch
lasting 12 s (equal to the TR). Three more epochs occurred,
so that a total of four brain volumes were acquired within
48 s, before a 24-s fixation block ensued, wherein subjects
viewed a crosshair while two brain volumes were acquired.
reading epoch,words or
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A total of 60 data points were collected during each 12-min
experimental run: 20 each for the word task, pseudoword
task, and fixation condition.
Real words were regularly spelled, single-syllable En-
glish nouns of midrange frequency (three to five letters in
length, median of four letters; mean MRC Psycholinguis-
tic Database ratings: concreteness, 574.4 (range 270–642);
familiarity, 552.1 (range 446–645); Kucera-Francis written
frequency, 60.6 (range 20–431)). Words were matched for
concreteness, familiarity, and frequency across word lists.
Pseudowords were generated from the real words by
changing one or more letters until novel words were
formed (e.g., norp, saff, janth, and kig), and were matched
with real words for letter length and number of syllables.
Pseudowords were reviewed by three native speakers of
English and were discarded from the list if determined to
be unpronounceable, were pseudohomophones of real
words, or had a close orthographic resemblance to a real
word. Sixty words and 60 pseudowords were presented in
each experimental run. No word or pseudoword was
repeated throughout the course of the entire experiment.
The stimuli were displayed in white lower-case Arial font
on a black background.
fMRI Data Acquisition
All MRI data were acquired on a 1.5 T Siemens Magnetom
Vision system with a circularly polarized head coil. The visual
stimuli were projected onto a screen mounted on the top of the
head coil. An angled mirror affixed to the head coil allowed a
clear view of the screen and stimuli. Each whole-head volume
was acquired in four seconds with echo planar imaging (EPI)
acquisition parameters as follows: 40 ms echo time (TE), 12-s
repetition time (TR), 64 ? 64 matrix, 230 mm field of view
(FOV), 46 axial slices, 3.0 mm slice thickness, 0.6 mm gap,
resulting in 3.6 mm cubic voxels. For both of the runs a total of
63frames(brainvolumes)wereacquired.Thefirstthreeframes
for each experimental run were discarded to achieve equilib-
rium in longitudinal relaxation.
Data Analysis
Image analysis was carried out using MEDx (Sensor Sys-
tems, Sterling, VA) and custom scripts. Image time series
were motion-corrected to the mean intensity image using
the Automated Image Registration (v. 3.08) rigid body re-
alignment algorithm [Woods et al., 1998a,b]. Gaussian spa-
tial smoothing was applied using a low-pass filter with a
full-width at half-maximum of 7.2 mm (two times the voxel
size) and a 9 ? 9 mm convolution kernel. Global spatial
variations in global image intensity were corrected with
ratio normalization. To remove local low frequency signal
drift, each time series was processed with a high-pass tem-
poral Butterworth filter with a period of 144 s (equal to two
times the task period). For each subject the mean image was
calculated for each task condition (word aloud, word silent,
pseudoword aloud, pseudoword silent, fixation) and mean
difference images were generated by subtracting the fixation
condition from each task condition.
To determine regions of increased task-related signal
change for each condition relative to fixation at the group
level, single-group t-tests were performed. These analyses
resulted in t-statistic maps that were then converted to Z-
score images and thresholded at Z ? 3.1 (P ? 0.001, uncor-
rected). The transformation matrix obtained when trans-
forming the mean EPI image from a specific run to the EPI
template (provided within Statistical Parametric Mapping,
SPM96, Wellcome Department of Cognitive Neurology,
London) was saved and used to shadow transform the sta-
tistical maps of various contrasts (e.g., pseudoword minus
fixation) into the MNI 305 atlas space. The coordinates of the
significant foci were converted from MNI space to a coordi-
nate system corresponding with the stereotaxic atlas of Ta-
lairach and Tournoux [1988], using equations derived by
Brett [1999]. For all figures displayed in the Results section,
images are portrayed in the radiological convention, with
the left side of the brain (L) represented on the right side of
the figure and anterior towards the top of the figure. Using
the GLM module within MEDx, an analysis of variance
(ANOVA) was performed between the mean difference im-
ages of the four contrasts in order to identify the main effects
of word-type (pseudowords ? real words) and response-
modality (aloud ? silent), and the interaction of word-type
with response-modality. The significance threshold em-
ployed was Z ? 3.1 (P ? 0.001).
Figure 1.
Experimental paradigm. Subjects underwent two experimental
runs: reading single words (nonwords and real words) aloud and
silently. No stimuli were repeated across the two runs. Each run
consisted of blocks during which subjects read words (48 s) or
blocks during which they only fixated (24 s). During the reading
blocks three words (or nonwords) were presented during an 8-s
trial, followed by a 4-s acquisition period. Each block contained
four epochs (trial plus acquisitions) each epoch lasting 12 s, the
duration of the TR. Real word or pseudoword trials consisted of
a 200 ms word presentations, followed by a pause of 2450 ms in
which a crosshair was presented and the subjects responded aloud
or silently.
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RESULTS
Behavioral Performance
Accuracy of the pronunciation of real words and
pseudowords was determined for the overt condition.
Pseudowords were judged as correct if the pronunciation
corresponded to English grapheme-to-phoneme rules; some
pseudowords had more than one acceptable pronunciation.
As expected, the mean accuracy for real words for the 15
subjects analyzed was 99.5%, significantly greater than the
mean pseudoword accuracy of 94.5% (P ? 0.003).
Functional MRI Results
Several contrasts were carried out in this study. We
present results from: (1) the contrasts of each individual task
(i.e., aloud pseudoword reading, aloud real word reading,
silent pseudoword reading, and silent real word reading)
relative to the viewing of a fixation point; (2) the conjunction
of these four reading contrasts to reveal areas of activity
common to all tasks; (3) the main effect of pseudoword vs.
real word reading, when collapsing the aloud and silent
conditions (main effect of word-type); (4) the main effect of
aloud vs. silent reading, when collapsing pseudoword and
real word reading (main effect of response-modality); and
(5) the interaction of word-type with response-modality.
1. All Tasks vs. Fixation
We first subtracted viewing of a fixation point from each
reading condition to visualize the global pattern of neural
activity elicited by each reading task. Figure 2 displays
representative transverse sections of the results of the single-
group t-tests showing regions of increased task-related sig-
nal for each condition (aloud pseudoword, aloud real word,
silent pseudoword, and silent real word reading) relative to
fixation. Visual inspection of the activation maps reveals the
two aloud reading tasks elicited considerably more activity,
both in intensity and extent, than the silent tasks, particu-
larly in the primary motor (Brodmann’s Area (BA) 4) and
auditory cortices (BA 38, 21/22). Not surprisingly, for each
task the overall intensity and extent of activity tended to be
left hemisphere lateralized.
2. Effects Common to All Reading Conditions:
Aloud Pseudoword, Aloud Real Word, Silent
Pseudoword, and Silent Real Word
The statistical maps generated as described above were
submitted to a conjunction analysis to identify regions that
showed increased task-related signal change across all four
reading conditions relative to their respective fixation base-
line: the left anterior precentral gyrus in BA 6, and three
regions within the left fusiform gyrus, one located within
anterior BA 37, another in the mid-fusiform region of BA 37,
and the third posteriorly in BA 19. These are depicted in
Figure 2, and Table I provides the corresponding spatial
coordinates of the center of mass for each region.
3. Main Effect of Word-Type:
Pseudowords > Real Words
The main effect of lexicality was determined by collapsing
across aloud and silent conditions. A main effect of
pseudoword reading relative to reading real words was
observed in two regions within the left inferior frontal gyrus
(BA 44/6 and BA44) and an area in the left intraparietal
sulcus (IPS, BA 7). As can be seen in Figure 3, the left IPS
region demonstrated an especially prominent effect (with
corresponding spatial coordinates provided in Table II).
4. Main Effect of Response-Modality:
Aloud > Silent
Table III and Figure 4 show the main effect of reading
aloud relative to silent reading (with word-type col-
lapsed). Reading aloud elicited large increases in the
BOLD-contrast response bilaterally within the primary
motor (BA 4), premotor (BA 6), presupplementary motor
areas (BA 6, in the medial superior frontal gyrus), bilateral
auditory cortex within the superior temporal gyri (BA
42/22), and bilateral posterior fusiform cortex (BA 19).
The main effect of aloud reading also included two re-
gions of the left hippocampal cortex (BA 36, 28), midline
thalamus, and the left putamen.
5. Interaction of Word-Type With
Response-Modality
Using the mean difference images of the four contrasts
generated as described above, an ANOVA was performed
to reveal regions demonstrating an interaction effect of
word-type (pseudowords vs. real words) and response-
modality (aloud vs. silent reading). The interaction re-
vealed a single significant locus (see Fig. 5), in the left
posterior fusiform gyrus (BA 19, peak voxel –22, –73, –13;
peak Z-score ? 3.59, P ? 0.0002). A post-hoc analysis
showed that the activity here for aloud pseudoword read-
ing was greater than for aloud real word reading, silent
pseudoword reading, and silent real word reading (P
? 0.05). We confirmed that the area was located in the
extrastriate/fusiform cortex by first registering and then
overlaying each individual subjects’ statistical maps with
their own anatomical T1-weighted image.
DISCUSSION
In this study we investigated the neural mechanisms of
phonological decoding in the context of aloud and silent
single word reading. Four reading conditions were used,
each of which varied from the other in the demands
placed on phonological processing: silent real word read-
ing, silent pseudoword reading, aloud real word reading,
and aloud pseudoword reading. The lexical unfamiliarity
of pseudowords invokes addressed phonology. Phonolog-
ical processing is also invoked by aloud reading, as pro-
nunciation obligates access to the complete phonological
word form. Hence, the reading of real words and reading
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Figure 2.
Transverse sections illustrating areas of significant activity for
the four task conditions relative to the fixation baseline. From
left to right: aloud pseudoword reading; aloud real word read-
ing; silent pseudoword reading; silent real word reading; and
the conjunction of all four tasks showing regions of activity
common to all tasks. For all figures the z-coordinate given is in
the coordinate space of the atlas of Talairach and Tournoux
[1988]. Images are portrayed in the radiological convention,
with the left side of the brain (L) represented on the right side
of the figure and anterior is towards to top of the figure. For
visualization purposes, activity is displayed at a critical thresh-
old of Z ? 2.33 (P ? 0.01, uncorrected).
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silently served as contrasts for reading pseudowords and
reading aloud, respectively. We examined 1) task-related
signal change common to the four reading conditions, 2)
the main effects of word-type and response-modality, and
3) their interaction. Our central finding was derived from
the interaction analysis and revealed a region within the
left posterior fusiform cortex (ventral BA 19) that was
modulated by increased stress on phonological process-
ing. Hence, this region appears to serve a role in detecting
the phonological demands associated with words. It is
sensitive to a variety of aspects of phonological process-
ing, including addressed phonology (applying sound-
correspondence rules) necessary to decode novel words
intheabsence ofrecognition-based
(pseudowords), and to conditions that necessitate the
computation of a complete phonological representation
(pronunciation). It is likely that this functional specializa-
tion for the phonological attributes of word processing is
the end result of reading acquisition, much like the emer-
gence of the “visual word form area” [McCandliss et al.,
2003], a region tuned to orthographically legal word
forms [Polk and Farah, 2002].
experience
Effects Common to All Reading Conditions
Four cortical regions were active consistently across all read-
ing conditions: the anterior aspect of the left precentral gyrus
(BA 6), and three areas within the left ventral occipitotemporal
cortex. This consistency, regardless of word-type or response-
modality, suggests that these four regions play important roles
in reading of regular letter combinations. The ubiquitous pres-
ence of activity within the anterior aspect of the left precentral
gyrus (i.e., premotor cortex) implies that word reading in gen-
eralentailssomeamountofsubvocalization,orinternalspeech.
Activation was observed here even for the silent reading task,
for which subjects were instructed to read the words to them-
selves without moving their tongue or jaw, suggesting motor
preparation activity regardless of whether or not the words are
overtly pronounced.
Also active for all reading conditions were three regions of
the left ventral occipitotemporal cortex, situated in an anterior-
posterior line along the fusiform gyrus. The most posterior
region was located in the extrastriate cortex, within BA 19.
Despite its early placement within the visual processing
stream, this region has been shown to demonstrate a preferen-
tial response to alphabetic stimuli (words and consonant
strings) over checkerboards [Cohen et al., 2003]. The second
locus was within the mid fusiform gyrus at BA 37, the location
of the putative visual word form area (VWFA) described by
Cohen and others who have taken note of its very reliable
response to orthographically legal word forms invariant of
font, case, size, or position [Cohen et al., 2000, 2002]. The
VWFA has been shown to respond to pseudowords and real
words alike, signifying that its representation of word forms is
at a prelexical level. Recent work suggests that the role of the
VWFA may be quite sophisticated, serving as a repository for
visual-orthographic patterns which serve as recognition units
in subsequent encounters of words [Kronbichler et al., 2004]. A
region specifically sensitive to letters has been found adjacent
(lateral and anterior) to this region and suggests that letters
acquire a special object category with respect to BA 37 [Flowers
et al., 2004]. The third fusiform region identified in the present
study was located anterior to the VWFA. This area may receive
afferent information from the more posterior regions of BA 37
and have a role in initiation of more complex, higher-level
word processing such as semantic access [Moore and Price,
1999].
Main Effect of Word-Type: Pseudowords > Words
The contrast of pseudowords with words, independent of
response-modality, was performed to identify areas of the
brain in which activity can be attributed to addressed pho-
nology (necessary to decode words that cannot be read by
relying on context or recall). Two foci within the left inferior
frontal gyrus and an area in the left intraparietal sulcus were
activated by this contrast. A great deal of evidence impli-
cates the left inferior frontal cortex as playing a key role in
phonological processing [Bookheimer et al., 1995; Burton et
al., 2000; Fiez et al., 1999; Fiez and Petersen, 1998; Hagoort et
al., 1999; Herbster et al., 1997; Huang et al., 2001; Newman,
2001; Rumsey et al., 1997a; Xu et al., 2001; Zatorre et al.,
1996]. More in-depth investigations of this region have led to
the proposal that it has two anatomically distinct functions
in reading: the ventral aspect of the inferior frontal gyrus
(BA 47/45) appears to be involved with semantic process-
ing, while the dorsal (opercular) inferior frontal gyrus (IFG,
BA 44 and 46) aspect is recruited for phonologically effortful
tasks [Bokde et al., 2001; Fiebach et al., 2002; Paulesu et al.,
1997; Poldrack et al., 1999]. The inferior frontal cortex activ-
ity in the present study is located in BA 44, congruent with
the putative phonological area. The left IFG has also been
implicated in verbal working memory as the possible locus
of the rehearsal loop [Paulesu et al., 1993], which could be
another source of the activity we see here.
The activity observed in BA 44 for pseudowords (rela-
tive to real words) also expanded into BA 6. As noted
above, left BA 6 was active during all of our reading tasks,
likely reflecting the occurrence of subvocalization activity.
The greater activity here for pseudowords relative to
words supports the notion that motor planning is in-
volved in the decoding of unfamiliar word forms and
TABLE I. Regions of activity common to all reading
tasks (vs. fixation): aloud pseudoword, aloud real word,
silent pseudoword, silent real word
BA
Cluster Center*
Cluster
size
(mm3)xyz
L precentral gyrus
L fusiform gyrus
6
?54,
?39,
?45,
?38,
1,36
?20
?15
?12
224
368
384
56
37
37
?44,
?58,
?77,19/18
* Data are given in Talairach coordinates.
?Phonological Decoding in Fusiform Gyrus?
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Page 8

increases in response to heightened phonological demands.
Other studies have reported increases in left precentral
gyrus activity with increasing phonological demands [Ha-
goort et al., 1999], and cognitive models have implicated
the motor system in the perception and production of the
phonological features of language [Liberman and Mattingly,
1985].
Motor planning could also be a possible interpretation of
the observed activity in the left intraparietal sulcus (BA 7),
the third region to demonstrate a main effect of lexicality.
The anterior inferior parietal lobule and posterior superior
parietal lobule of the left hemisphere contribute to covert
motor movement preparation or “motor attention” [Rush-
worth et al., 2003]. Reading of pseudowords might invoke
planning of articulatory sequence movements that corre-
spond to the pronunciation of the word. Alternatively, the
greater activation of left IPS for pseudowords (relative to
words) could be attributed to the increased demands unfa-
miliar words put on the phonological store of verbal work-
ing memory. Several PET studies have identified the left
parietal cortex, including the intraparietal sulcus, as the
locus of the phonological store [Becker et al., 1999; Paulesu et
al., 1993; Ravizza et al., 2004] and parietal cortex has been
shown to be underactivated in individuals with develop-
mental dyslexia [Eden and Zeffiro, 1998].
Based on previous studies of phonological processing and
phonological assembly, we anticipated activity in posterior
aspects of the superior and middle temporal gyri [Bookhei-
mer et al., 1995; Herbster et al., 1997; Price et al., 1996; Pugh
et al., 2000; Rumsey et al., 1997a; Simos et al., 2002]. Indeed,
dyslexics show a characteristic pattern of reduced activity
within these regions [Brunswick et al., 1999; Paulesu et al.,
1996; Rumsey et al., 1997b]. The lack of left posterior tem-
poral activity in this study may have been due to the nature
of our stimuli; perhaps our pseudowords were not challeng-
ing enough to elicit activation here. Greater discrepancy in
Figure 3.
Transverse slices of the three cortical
regions showing a main effect of lexicality
(pseudowords ? real words, collapsed
across aloud and silent modalities). The
z-coordinate of each slice matches those
in Table II.
Figure 4.
Transverse slices showing a main effect of response-modality (aloud ? silent, collapsed across
pseudoword and real word-types). The maxima of these areas are presented in Table III.
?Dietz et al.?
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Page 9

phonological difficulty between the pseudowords and real
words, such as by using polysyllabic pseudowords with
infrequent letter combinations, might have revealed activity
in this area. Also, as subjects were reading covertly in the
silent condition, it was not possible to obtain performance
accuracy. This provides some uncertainty about the de-
mands made by this condition and future studies might
address this (at least in part) by using a post-scanning test in
which subjects are asked to identify words from a list to
indicate how many items they recognize from the scanning
session [Turkeltaub et al., 2003]. In any case, reports of
activity in the left posterior middle temporal gyrus tend to
be intermittent, with some studies, including ours, reporting
little or no responses here [Hagoort et al., 1999; Xu et al.,
2001]. These variations across different studies raise ques-
tions about these regions’ precise role in phonological pro-
cessing and merits further investigation.
Main Effect of Response-Type:
Aloud Reading > Silent Reading
The analysis focusing on aloud vs. silent reading (inde-
pendent of word type) revealed findings that were consis-
tent with earlier studies of aloud word reading [Bookheimer
et al., 1995; Hagoort et al., 1999; Turkeltaub et al., 2002]. We
found increased activity in bilateral motor, auditory, and
extrastriate visual cortices. The expansive activity underly-
ing aloud reading attests to the fact that reading aloud
involves more complex participation of multiple regions
other than motor and auditory cortex, and that studies in-
volving silent word reading cannot be substituted for aloud
word reading. Our results also demonstrate the utility of
interleaved fMRI data acquisition for tasks involving overt
speech production to distinguish differences contributed by
aloud vs. silent reading.
Interaction Effect of Word and Response Types
The interaction analysis of word-type and response-mode
revealed a single locus in the left ventral extrastriate cortex
located in posterior fusiform cortex at BA 19. This region
was uniquely modulated by increased phonological process-
ing demands invoked by a need for phonological assembly
and access to the words’ entire phonological code. This
finding indicates a special role for left ventral BA 19 in
phonological processing.
Ideas and controversies regarding the functional role of
the left ventral extrastriate cortex have been evolving with a
progression of neuroimaging studies of word form process-
ing. In an early PET study by Petersen et al. [1990], activation
in the left medial extrastriate cortex was detected during
silent viewing of real words and pseudowords but not con-
sonant letter or false font strings. It was concluded that this
region was tuned to orthographically legitimate word forms.
Although ventral extrastriate cortex had traditionally been
associated with relatively low-level visual processing such
as color and form detection, this study and others that
ensued supported the idea that the functions of extrastriate
cortex are not limited to basic early visual processing. Spe-
cifically, left BA 19 and nearby regions have been shown to
be more responsive to pseudoword compared to real word
TABLE II. Main effect of lexicality (word-type):
pseudowords > real words
BA
Peak voxel
Peak Zxyz
L inferior frontal gyrus
L inferior frontal gyrus
L intraparietal sulcus
44/6
44
7
?57,
?44,
?28,
15,
7,
?54,
27
24
47
3.24
3.34
4.05
TABLE III. Main effect of response-modality: aloud > silent
BA
Peak voxel
Peak Zxyz
R medial superior frontal gyrus
L precentral gyrus
6
6
4
8,13,
?3,
?6,
?1,
?4,
15,
?15,
?27,
6,
?27,
?6,
?28,
?63,
?67,
?19,
8,
60
13
28
13
28
?11
3
7
?4
3
?33
?10
?19
?13
6
?2
5.41
7.25
7.84
7.59
7.76
4.85
6.94
7.02
6.18
6.71
6.20
5.88
6.81
7.34
5.23
4.26
?59,
?51,
57,
51,
?51,
?62,
?61,
55,
57,
?18,
?12,
?34,
16,
4,
?20,
R precentral gyrus 4/6
4
38
22/42
22/42
22
22
36
28
19
18/19
L superior temporal gyrus
R superior temporal gyrus
L hippocampal
L fusiform
R fusiform
Midline Thalamus (DM nucleus)
L putamen
?Phonological Decoding in Fusiform Gyrus?
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Page 10

reading [Hagoort et al., 1999], pseudoword rhyming [Xu et
al., 2001], and phonological working memory [Zurowski et
al., 2002]. For example, Hagoort et al. [1999] report on a
focus (BA 19/37; –34, –55, –11) slightly more anterior to ours
that was more active during the reading of pseudowords
when contrasted to real words, and more active for aloud
compared to silent reading of real words (although this
comparison wasnot significant
pseudowords). Paulesu et al. [2000] reported a similar result
in a sample of English and Italian readers (their coordinates
were –48, –68, –6); and Xu et al. [2001] also report a region,
more lateral and anterior than the one described in the
present study (46, –66, –10), which they identified when
subtracting real word rhyming from pseudoword rhyming.
whenrepeated for
These authors discuss the possibility of this area in mapping
orthographic forms to sublexical phonological codes as the
result of phonological assembly.
Taken together, these studies not only implicate the left
ventral fusiform in an early process where alphabetic stimuli
are distinguished from nonalphabetic stimuli [McCandliss et
al., 2003; Polk and Farah, 2002], but our results go so far as
to suggest the involvement of posterior areas of extrastriate
cortex in the initial phonological analysis of written words.
The posterior aspect of fusiform gyrus identified in the
present study is 20 mm posterior and medial to the visual
word form area located in mid-fusiform cortex at BA 37
[McCandliss et al., 2003]. It has been suggested that the
VWFA groups letters into “integrated perceptual units” and
Figure 5.
Transverse (a), sagittal (b), and coronal (c) views of the single region,
located in the left posterior fusiform gyrus (BA 19), revealed by the
interaction between word-type (lexicality) and response-modality.
The bar graph illustrates the relative contribution (mean voxel inten-
sity given in arbitrary units) of each of the four task conditions to the
142-voxel region revealed by the interaction analysis. Post-hoc paired
t-tests showed significantly greater activation for the aloud
pseudoword reading condition relative to the aloud real word, silent
pseudoword, and silent real word reading conditions (P ? 0.05).
There were no significant differences between the aloud and silent
real word reading conditions, or between the silent pseudoword and
silent real word conditions.
?Dietz et al.?
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Page 11

is sensitive to abstract information even for newly encoun-
tered words [McCandliss et al., 2003; Polk and Farah, 2002;
however, see Price and Devlin, 2003]. By analogy, it seems
that during aloud reading BA19 is tuned to the phonological
properties of words much like the VWFA is tuned to the
orthographic properties. The implication of this finding is
that phonological analysis of word forms coincides with the
early process of recognition of alphabetic stimuli. Our find-
ings build on previous studies that considered phonological
processing as a possible explanation for extrastriate cortex
activity during reading [Buchel et al., 1998; Polk and Farah,
2002] and rhyming [Xu et al., 2001] tasks. Future studies will
be necessary to elucidate the mechanisms that control left
ventral BA 19 activity in response to varying levels of pho-
nological demands. One alternative possibility to early pro-
cessing of phonological information could be a top-down
mechanism from regions more directly involved in phono-
logical processing or regions such as the prefrontal cortex
(PFC) responsible for implementing task instructions (e.g.,
“read the presented words aloud”) [Chelazzi et al., 1993;
Miller and Cohen, 2001; Wallis et al., 2001]. This scenario
cannot be substantiated by the results of this study since no
activity was seen within the PFC in the interaction analysis
or in the comparisons of reading tasks to fixation. Temporal
limitations of fMRI block design studies limit the utility of
fMRI in addressing these types of questions, but magnetoen-
cephelography (MEG) can shed more light on this matter.
Studies using MEG to investigate pseudoword reading do
report early activation if visual and visual association areas,
although the nature of the tasks and statistical comparisons
do not allow an exact interpretation with regards to the
specific region of BA 19 described here [Simos et al., 2002].
CONCLUSIONS
Demands on phonological processing were modulated
using a two-by-two design with tasks that had different
phonological processing demands with reference to word-
type and response-modality. The anterior aspect of the left
precentral gyrus (BA 6) and three areas within the left ven-
tral occipitotemporal cortex were found to be active across
all reading conditions. The left inferior frontal gyrus and left
intraparietal sulcus demonstrated sensitivity to word-type,
while bilateral motor, auditory, and extrastriate cortex were
modulated by response mode. Activity underlying word
reading in BA 19 in the left posterior fusiform cortex dem-
onstrated a word-type by response-modality interaction ef-
fect, indicating that phonological processing during reading
begins early in the processing stream, at the point at which
words are first recognized as alphabetic stimuli.
ACKNOWLEDGMENTS
We thank J. Agnew, P. Turkeltaub, and J. VanMeter for
their help. We also thank L. Cutting, C. Vaidya, D. Howard,
D.L. Flowers, two anonymous reviewers who provided con-
structive comments, and our subjects for their participation.
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