Lack of asymmetrical transfer for linguistic stimuli
in schizophrenia: an ERP study
Kylie J. Barnett*, Ian J. Kirk
Department of Psychology, Trinity College, Dublin 2, Ireland; Research Centre for Cognitive Neuroscience,
University of Auckland, Private Bag 92019, Auckland, New Zealand
Accepted 9 December 2004
Available online 25 January 2005
Objective: To assess the mechanisms underlying lack of speeded information transfer asymmetry (faster right to left) for verbal
information in schizophrenia.
Methods: Interhemispheric transfer times (IHTT) between the hemispheres were assessed using a lateralized lexical-decision task in
males with schizophrenia (NZ12) and matched controls (NZ12). Words were presented to the left visual field (LVF), right visual field
(RVF), or bilaterally (BVF) while 128-channel EEG was recorded continuously. A direct measure of IHTT in each direction was obtained by
comparing the latencies of the N160 evoked potential (EP) component in the hemispheres contralateral and ipsilateral to stimulation.
Results: Controls showed faster information transfer from the right to left hemisphere (R-to-L) for linguistic stimuli. The two groups did
notdiffer for IHTTs L-to-R. Lack ofIHTT asymmetryin the schizophrenia groups was associated withan overall concomitant decrease inthe
amplitude of the N160 in the right hemisphere.
Conclusions: Differences in IHTT asymmetry may be attributed to lack of right hemisphere activation and not callosal dysfunction as has
been previously suggested.
Significance: It is suggested that a relative excess of myelinated axons in the right hemisphere speeds IHTT faster R-to-L, findings are
discussed with reference to differences in right hemisphere white matter connectivity in schizophrenia.
q 2005 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.
Keywords: Schizophrenia; EEG; Interhemispheric transfer time (IHTT); Right hemisphere; Corpus callosum; Language.
Differences in the structural asymmetry of language
regions, especially lack of asymmetry of the planum
temporale are often cited in schizophrenia (Barta et al.,
1997; Petty et al., 1995; Saugstad, 1999; Shapleske et al.,
1999). In accordance, behavioural studies commonly cite
loss of the normal RVF/left hemisphere advantage for
language in schizophrenia (Gur, 1978; Sommer et al., 2001).
Characteristic language disturbances in schizophrenia
include poverty of speech, poverty of content, repetition,
illogicality, derailment, perseveration, and the use of
neologisms (invented words) (Andreasen and Grove, 1986;
Maher, 1991). Yet, while left hemisphere dysfunction may
provide a parsimonious explanation for language symptoms
in schizophrenia there are reports of normal left hemisphere
lateralization of language in this population (Mohr et al.,
2000, 2001; Endrass et al., 2002).
Further evidence suggests that individuals with schizo-
phrenia have difficulty integrating information between the
hemispheres. There are reports of deficits when either the
same (Mohr et al., 2000) or different stimuli (Beaumont and
Dimond, 1973; Eaton et al., 1979) are presented to both
hemispheres simultaneously. The accuracy advantage
usually reported when stimuli are presented to both
hemispheres simultaneously (bilateral gain) is not observed
in schizophrenia (Mohr et al., 2000). (paragraph shortened).
Finally there is evidence to suggest that interhemispheric
1388-2457/$30.00 q 2005 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.
Clinical Neurophysiology 116 (2005) 1019–1027
* Corresponding author. Tel.: C353 0 1 6082971; fax: C353 0 6172006.
E-mail address: firstname.lastname@example.org (K.J. Barnett).
both reaction time studies (Marzi et al., 1991) and visual
evoked potentials (EPs) (Brown and Jeeves, 1993; Brown
et al., 1994) finds that, in healthy controls, information
than from the left to the right (L-to-R). There has been one
previous study of IHTT in schizophrenia using a direct EP
method. Endrass et al. (2002) used a lateralized lexical-
or RVF, and measured IHTT using 65-channel EEG. While
controls had significantly faster IHTT from the R-to-L
hemisphere for words, this directional asymmetry was not
present in the schizophrenia group. The lack of bilateral
et al., 2002) in schizophrenia have been attributed to
dysfunctional information transfer via the corpus
callosum. In accordance meta-analysis finds an overall
reductioninthe area of the corpus callosum in schizophrenia
(Woodruff et al., 1995).
Because callosal dysfunction should influence infor-
mation transfer in both directions we suggest that impair-
ments in callosal transfer may not provide the best
explanation for differences interhemispheric transfer in
schizophrenia. We suggest that asymmetry of transfer
results from increased activation in the hemisphere that is
the source of the faster transfer. Since most of the evidence
suggests faster R-to-L transfer, this implies greater acti-
vation in the right hemisphere than the left. For this reason
we suggest that right hemisphere dysfunction may give rise
to differences in asymmetry of IHTT (faster R-to-L) in
Miller (1996) argues that the right hemisphere has more
myelinated axons specialised for rapid conduction and the
processing of gestalts. Following Miller (1996), we suggest
that the presence of more rapidly conducting cortico-
cortical myelinated axons in the right hemisphere increases
the likelihood of neural summation in that hemisphere, so
increasing the speed of transfer from the R-to-L hemisphere
relative to that from L-to-R. White matter enables
corticocortical connectivity and information transfer and
there is substantial evidence for white matter differences in
schizophrenia. In fact, it has been suggested that myelina-
tion and white matter abnormalities may indicate a genetic
marker for schizophrenia (Hakak et al., 2001; Hulshoff Pol
et al., 2004a). White matter differences have been found in
the right hemisphere of males with schizophrenia (Bullmore
et al., 1995), especially those with negative symptoms
(Wible et al., 2001).
We used 128-channel EEG to assess information transfer
between the hemispheres in males with negative-symptom
schizophrenia and hypothesise differences in IHTT asym-
metry and right hemisphere activation. This study is
basically a replication of that done by Endrass et al.
(2002) with the specific aim of investigating the association
between slowing of information transfer R-to-L and right
hemisphere dysfunction. Participants performed a latera-
lized lexical-decision task while EEG was recorded
continuously. Like Endrass et al. (2002) we recorded the
N160 component from parietal regions, however, while they
only assessed latency differences we also assessed ampli-
tude differences between the groups. Previous reports have
found the N160 to be pronounced in parietal regions (Brown
and Jeeves, 1993; Brown et al., 1994; Endrass et al., 2002)
and the N160 has previously been used to estimate IHTT in
both letter-matching and linguistic tasks (Brown et al.,
1994; Endrass et al., 2002).
Two groups (all males) were tested. Controls (NZ12)
had a mean age of 30.8 years (SDZ6.9) and the
schizophrenia group (NZ12) a mean age of 31.8 years
(SDZ8.5). The Auckland District Health Board Ethics
Committee approved this study and written informed
consent was obtained. Controls were recruited from the
University of Auckland and had no history of mental
illness, neurological disorder, or drug and alcohol abuse.
No control participant had a first-degree relative with
schizophrenia. Participants with schizophrenia were
recruited via notices in mental health outpatient units.
Each underwent a semi-structured interview that took
approximately 1 h. Diagnosis was confirmed with DSM-IV
criteria and the Positive and Negative Symptoms Scale
(PANSS) was used to assess whether symptoms were
predominantly positive or negative (Kay et al., 1987).
According to composite PANSS scores all schizophrenia
participants were characterised by predominantly negative
symptoms (mean negativeZ22.1, SDZ2.9; mean positi-
veZ16.1, SDZ3.3). All schizophrenia participants were
on standard atypical antipsychotics (Clozapine equivalent
400 mg) at the time of testing, and mean duration of illness
was 8.6 years (SDZ3.9). We controlled for laterality
quotient as individuals with schizophrenia are more likely
have mixed or ambiguous patterns of handedness (Green
et al., 1989; Orr et al., 1999; Sommer et al., 2001), which
may affect lateralization. According to the Edinburgh
Handedness Inventory (Oldfield, 1971), the control group
consisted of 4 left-handers, one mixed-hander, and 8 right-
handers and the schizophrenia group of two left-handers
and 10 right-handers. One-way analysis of variance
(ANOVA) found no differences between groups for age
(PZ.755) or laterality quotient (PZ.354).
The stimuli consisted of 4-letter strings presented in
Courier New 24 font. They were .58 of visual angle in height
with a diameter of 38 of visual angle. The letters represented
either words or non-words and were presented against a
white background. They appeared for 120 ms at 48 of visual
K.J. Barnett, I.J. Kirk / Clinical Neurophysiology 116 (2005) 1019–10271020
angle to the left (LVF), right (RVF) or both (BVF) sides of a
central fixation cross. One hundred and sixty stimuli were
each randomly presented twice (NZ320 trials). Each letter
string was one syllable long and comprised 4 letters
presented in upper case. There were a total of 320 trials
excluding practise. A total of 160 English words and 160
non-words were presented. Half of the real words were
content words (i.e. GIRL) and half were function words
(i.e. THIS). Half of the non-words were pseudohomophones
(i.e. WATE) and half were pronounceable non-words (i.e.
YODE). Words all had a high frequency of occurrence and
were obtained from the list developed by Kucera and
The experiment was conducted in a quiet, electrically-
shielded Faraday chamber and participants were monitored
via a closed-circuit camera. Participants sat 57 cm from the
screen so that 1 cm corresponded to 18 of visual angle.
Stimuli were presented on a 15” SVGA monitor (640!480
pixel resolution). Participants were instructed to avoid
movement in order to limit non-cognitive artefacts. The
experiment contained 4 blocks; two were performed with
the right hand and two with the left in a randomly assigned
counterbalanced order (i.e. R–L–L–R or L–R–R–L). Each
block of trials was initiated using the space bar and there
was a brief practice with each hand. Each block contained
20 LVF, 20 RVF, and 40 BVF presentations. A randomised
trial list was generated for every participant and a brief
break separated each block. Prior to the stimulus a blank
screen was presented (500 ms), followed by a central
fixation cross (1000 ms), which signalled that the stimulus
was about to appear. Participants made word or non-word
judgments using computer keys, with ‘1’ representing
‘word’ and ‘2’ representing ‘non-word’. They were given
3 s to respond before that trial was scored as incorrect. The
experiment took approximately 20 m to complete.
EEG was recorded continuously (250 Hz sampling rate)
with Electrical Geodesics amplifiers (200 kU input impe-
dance) using a 128-channel Ag/AgCl electrode net and the
data was amplified (100 MU input impedance). The
software used to acquire data was run on Macintosh GA
with 16-bit analogue to digital conversion card. The average
impedance of electrodes was 43 kU. EEG data were
acquired using a common vertex (Cz) reference and later
re-referenced to the average reference off-line. Data were
segmented using a program that rejected data contaminated
by eye movements. The rejection criterion was 70 mV
activity recorded in eye channels. Data for correct responses
were segmented and averaged to create 6 conditions for
each participant: word (LVF, RVF, BVF), and non-word
(LVF, RVF, BVF).
2.5. Statistical analysis
To assess behavioural performance mean accuracy and
RT data were subjected to ANOVA. The within-subjects
factors were field (LVF, BVF, RVF), word (content,
function, pseudoword, pronounceable non-word), and
response hand (right, left) and the between-subjects factor
was group (control, schizophrenia). Interactions were
evaluated using paired samples t-tests with Bonferroni
adjusted alpha level (0.05/3). For each participant EP
latencies and amplitudes were recorded from electrodes
according to the standard 10–20 system. The N160 latency
for words and non-words was recorded from a posterior
parietal pair (PO3, PO4). The N160 was recorded form this
region as previous reports have found the N160 to be
pronounced in parietal regions (Brown and Jeeves, 1993;
Brown et al., 1994). This was also the region Endrass et al.
(2002) recorded from.
The N160 was defined as the greatest negative amplitude
wave that occurred between 140 and 220 ms post-stimulus
onset (Nowicka and Fersten, 2001). IHTT latencies were
calculated by comparing latencies recorded in the hemi-
sphere contralateral to stimulation to those in the hemi-
sphere ipsilateral to stimulation. Contralateral and
ipsilateral EP latencies to words and non-words were then
used to calculate directional asymmetries. That is, LVF/
right hemisphereKLVF/left hemisphere provided the
measure of R-to-L transfer, while RVF/left hemisphere
minus RVF/right hemisphere provided the measure of
L-to-R transfer. To avoid the assumptions associated with
normal distribution of data we used non-parametric (Mann–
Whitney rank/Wilcoxon signed-rank) tests to assess differ-
ences between the groups for unilateral and bilateral stimuli
and directional asymmetry of IHTT.
Differences in N160 amplitude (mV) were assessed using
data from each condition from the time window
140–220 ms post-stimulus onset. Each time window was
based on averaged group Global Field Power estimates. For
each participant, amplitude data were exported from 4
electrode pairs for each condition (word LVF, RVF, BVF,
and non-word LVF, RVF, BVF). Electrodes of interest
included the central parietal electrode pair (PO3, PO4) and
the 3 adjacent electrodes (P5, P6, P7, P8, PO7, PO8). In
order to compare groups in each condition a t-test was
performed at each electrode. A Bonferroni correction factor
(0.05/2) was derived to correct for multiple comparisons
using the principle-components analysis method described
by Hopf and Mangun (2000).
3.1. Behavioural results: accuracy
There was no difference in accuracy between the two
groups (PZ.276) and no interactions involving group.
K.J. Barnett, I.J. Kirk / Clinical Neurophysiology 116 (2005) 1019–10271021
Mean accuracy for controls was 75.4% (SDZ8.9) and for
the schizophrenia group 78.8% (SDZ5.5). There was no
main effect of visual field (PZ.130), word (PZ.299),
however, there was a main effect of response hand (t(23)Z
2.772, PZ.011) with participants making more correct
responses when responding with the left hand (80%) than
the right hand (77%). There was no interaction betweenfield
and group (P Z .246), or hand and group (PZ.077). The
interaction between word and group approached signifi-
cance (F(3,66)Z2.486, PZ.068), as surprisingly the
schizophrenia group were slightly more accurate than
controls in the pronounceable non-word condition.
Table 1 shows the mean and SD accuracies for each word
type in each visual field.
There was a significant interaction between field and word
(F(6,132)Z3.463, PZ.003). This was attributed to more
efficient processing of pseudowords in the RVF than the LVF
(t(23)Z4.424, PZ!.001) and the BVF than the LVF
(t(23)Z3.325, PZ.003). This suggests a LVF/right hemi-
3.2. Behavioural results: reaction time
Controls had a mean RT of 806.74 ms (SDZ120.15),
and the schizophrenia group a mean RT of 964.47 ms
(SDZ183.69). The schizophrenia group were significantly
slower than controls (F(1,22)Z6.197, PZ.021). There was
no main effect of response hand (PZ.715). The main effect
of field approached significance (PZ.070) as subjects were
slightly faster in the RVF (872.55) in contrast to the BVF
(877.35) or LVF (906.91) conditions, but there were no
interactions between field and group (PZ.790), field and
word (PZ.225), word and group (PZ.877), or hand
and group (.358). There was a main effect of word
(F(3,66)Z8,363, PZ!.001). Participants had faster RTs
to words than non-words (t(23)ZK3.638, PZ.001).
Table 2 displays mean and SD ‘RTs for each word type.
3.2.1. EEG latency
A Mann–Whitney rank test showed that controls had
significantly shorter transfer times than the schizophrenia
group when words were transferred R-to-L (UZ2.832,
P!.004), but not when transfer was L-to-R (UZ1.483,
PZ.143). These findings held for non-words as again
controls had significantly shorter transfer times when non-
words were transferred R-to-L (UZ2.580, PZ.010), but not
when the transfer was L-to-R (UZ0.726, PZ.478).
Conversely, Wilcoxon signed-rank tests carried out for
each group showed the control group had significantly faster
IHTT when words were transferred R-to-L compared to
when information transfer was L-to-R (ZZ2.988, PZ.003).
There was also a significant difference in the schizophrenia
group (ZZ1.967, PZ.049). However, they actually had a
faster transfer for words from the L-to-R hemisphere than
from the R-to-L. The same analysis done for non-words
showed the control group had significantly faster IHTT
when words were transferred R-to-L compared to when
information transfer was L-to-R (ZZ2.361, PZ.018).
There was no significant difference for the schizophrenia
group (ZZ0.515, PZ.607) who had similar transfer times
R-to-L and L-to-R for non-words. Fig. 1 shows the mean
and standard error of directional asymmetry of N160
transfer speed each group for both types of words. Figs. 2
and 3 show the N160 IHTT components for each group
(both word types are combined) after stimulation in each
visual field (LVF, RVF).
3.2.2. EEG bilateral gain results
We also assessed EP latency differences in response to
words and non-words and unilateral and bilateral presenta-
tions. Average EP latencies were calculated for words
and non-words presented unilaterally and bilaterally. A
Mann–Whitney rank test found that participants had
significantly faster EP latencies for words in contrast to
non-words (UZ4.287, PZ!.001) (mean differenceZ
36 ms). There were also latency differences related to
presentation. Participants had shorter EP latencies when
words were presented bilaterally (UZ4.289, PZ!.001)
(mean difference Z18 ms). Somewhat unexpectedly the EP
latencies for non-words were faster when presentation was
unilateral (UZ4.287, PZ!.001) (Mean difference Z
71 ms). Wilcoxon signed-rank tests carried out for each
group found no differences between the groups for words
presented unilaterally (PZ.932) or bilaterally (PZ.671) or
non-words presented unilaterally (PZ.078) or bilaterally
(PZ.932) (Fig. 3).
3.2.3. EEG amplitude results
There were significant differences in amplitude between
the groups when stimuli (all conditions combined) were
presented to the LVF (right hemisphere) or bilaterally.
The differences were due to smaller N160 EPs in the right
hemisphere in the schizophrenia group. There were no
amplitude differences between the groups when stimuli
Accuracy (% correct): mean for each word type (content, function,
pseudohomophone, pronounceable non-word) in each visual field (LVF,
BVF, RVF). Standard deviations are shown in brackets
Reaction time (ms): mean and standard deviations (SD) for each word type
(content, function, pseudohomophone, pronounceable non-word)
Word TypeMean SD
K.J. Barnett, I.J. Kirk / Clinical Neurophysiology 116 (2005) 1019–10271022
were presented to the RVF (left hemisphere). Table 3 plots
the statistical results (PZ!.025). These results were more
complex when broken down into conditions as specifically
the RVF presentation of words to the left hemisphere was
associated with a decrease hemispheric activation
suggesting that the differences are not only restricted to
the right hemisphere. The statistical results and amplitude
differences for each condition are plotted in Tables 4 and 5.
Bilateral gain and IHTT were assessed in males with
schizophrenia and controls matched for age and handedness.
A lexical-decision task was used and words and non-words
were presented to the LVF, RVF, or bilaterally, while
128-channel EEG was recorded. This was a complex task
and while the schizophrenia group were not less accurate
than controls, they were slower. Absence of bilateral gain
for accuracy has been previously reported in schizophrenia
using a RT task (Mohr et al., 2000). In contrast, the current
study used a direct electrophysiological measure and finds
no differences between the groups for any measures of
bilateral gain. In fact, there was evidence for a decrease in
EP latency for all participants when words were presented
IHTTs were estimated using the N160 EP component and
comparing ipsilateral and contralateral latencies in each
visual field. Data from the control group for both words and
non-words supports previous reports of faster IHTT R-to-L.
The finding of faster IHTT R-to-L in controls has been
confirmed using meta-analysis (Brown et al., 1994) and
has been found using the N160 (Brown et al., 1994;
Endrass et al., 2002). The two groups did not differ when
words and non-words were transferred from the L-to-R
Fig. 1. IHTT directional asymmetry for words and non-words for each
group. Error bars show one SE of the mean.
Fig. 2. Grand average N160 ERPs (PO3, PO4) in the left and right
hemisphere after LVF presentation for the schizophrenia and control group.
K.J. Barnett, I.J. Kirk / Clinical Neurophysiology 116 (2005) 1019–10271023
hemisphere. In contrast the schizophrenia group did not
show the speeded R-to-L transfer asymmetry evident in
controls, in fact they actually had faster L-to-R transfer for
words and symmetry of transfer for non-words (i.e. IHTTs
were almost identical for in either direction).
We also report an overall concomitant decrease in
the N160 amplitude in the right hemisphere of
the schizophrenia group, while amplitude in the left-
hemisphere did not differ between the two groups. While
there were some left hemispheric differences (specifically
for the presentation of words) we suggest that right
hemisphere dysfunction is responsible for the lack of
speeded R-to-L of information transfer rather than callosal
dysfunction. The fact that IHTTs may be virtually normal
in individuals with partial callosal agenesis provides some
evidence for equipotentiality of the corpus callosum
(Berlucchi et al., 1995). This suggests that even if there
are callosal differences in schizophrenia that are of a
neurodevelopmental origin, normal IHTTs could still
occur. In addition, if we attributed the differences in R-
to-L transfer to callosal dysfunction we might also expect
that L-to-R transfer would differ between the groups yet we
found no evidence for this. Rather we suggest that in
controls that greater activation of the right hemisphere
speeds R-to-L transfer, while this is absent in the
schizophrenia group who show symmetry of transfer in
association with smaller overall N160 amplitudes in the
The right hemisphere has been implicated in some of the
language related phenomena in schizophrenia, for example
deficits in the comprehension of emotional prosody
(Murphy and Cutting, 1990). Functional imaging (fMRI)
has found a decrease in the activation of right superior
temporal gyral regions during a word generation task in
individuals with thought disorder (Kircher et al., 2001). It is
not implausible to suggest that right hemisphere dysfunction
in schizophrenia leads to a deficit in the transfer of verbal
information from the right hemisphere to the dominant left
hemisphere. Indeed Crow (1998) argues that lateralization
of the hemispheres means that the phonological properties
of language are lateralized to the left hemisphere while the
associational properties are lateralized to the right.
The right hemisphere may be involved disturbances of
affect, which is a key feature of schizophrenia and refers to a
dulling or blunting in the range of normal expressions and
feelings (Bleuler, 1911/1950; Kraepelin, 1899/1989). Indi-
viduals with schizophrenia have a deficit in the perception
of their own emotions and in their ability to perceive
the emotions of others (Edwards et al., 2002). Deficits in
Amplitude (mV): amplitude data for each group at electrodes of interest (nZ8) for the N160 component
Visual FieldGroup Electrode
Left hemisphere Right hemisphere
P5P7 PO3PO7 PO8 PO4P8P6
LVF LVF Control
Data shown for each visual field (LVF, RVF, BVF) for all word conditions. Statistics in bold, significant group differences, PZ!.025.
Fig. 3. Grand average N160 ERPs (PO3, PO4) in the left and right
hemisphere after RVF presentation for the schizophrenia and control group.
K.J. Barnett, I.J. Kirk / Clinical Neurophysiology 116 (2005) 1019–10271024
Amplitude (mV): statistical differences between groups at electrodes of interest (nZ8) for the N160 component
HemisphereElectrode Word Non-word
LVF RVFBVFLVF RVFBVF
t valueSig.t valueSig.t valueSig.t value Sig.t valueSig.t valueSig.
t Values and significance (two-tailed, Bonferroni correction factor 0.05/2) are shown for data at each electrode for each condition. Statistics in bold PZ!.025.
Amplitude (mV): amplitude data for each group at electrodes of interest (nZ8) for the N160 component. Data shown for each visual field (LVF, RVF, BVF) for all word conditions (word LVF, RVF, BVF, non-
word LVF, RVF, BVF)
Condition Group Electrode
Left hemisphere Right hemisphere
P5P7 PO3PO7 PO8 PO4P8P6
Statistics in bold, significant group differences, PZ!.025.
K.J. Barnett, I.J. Kirk / Clinical Neurophysiology 116 (2005) 1019–1027
face processing are commonly reported in schizophrenia
(Borod et al., 1989; Edwards et al., 2002; Oepen et al., 1987;
Shaw et al., 1996). Although structural differences in the
right hemisphere are less commonly reported in schizo-
phrenia (Gur and Chin, 1999), differences in white matter in
the right hemisphere have been found. For example
reductions in prefrontal white matter in the right hemisphere
have been reported in males with negative symptoms (Wible
et al., 2001). Similarly there are reports of a loss of white
matter volume in the right internal capsule (Hulshoff Pol
et al., 2004b; Velakoulis et al., 2002), right anterior
commissure (Hulshoff Pol et al., 2004b), right thalamus
(Andreasen et al., 1994), and reduction in white matter
along anterior–posterior frontal tracts in the right hemi-
sphere in schizophrenia (Shapleske et al., 2002). A decrease
in oligodendrocyte numbers in schizophrenia provides a
quantitative correlate of changes in white matter in
schizophrenia (Hof et al., 2003), and the development of
3-dimensional tracking of axonal pathways, using diffusion
tensor imaging may provide a more reliable way of
assessing white matter connectivity in vivo (Amodei
et al., 2000).
A decrease in white matter may reduce right-hemisphere
activation and therefore prevent speeded asymmetry of
information transfer (faster R-to-L) in schizophrenia. It
could be argued that the N160 is only involved in basic
visual perception of a stimulus’ features and is not involved
in linguistic processing. Yet a lack of the normal speeded
asymmetry (faster R-to-L) has previously been reported in
schizophrenia using lexical stimuli (Endrass et al., 2002). In
addition the schizophrenia group in this study showed
differential transfer asymmetries for words and non-words
suggesting that early components may be involved in
linguistic processing. Reductions in interhemispheric coher-
ence have previously been reported in schizophrenia
(Winterer et al., 2001) and an analysis of coherence data
in each hemisphere may enable better differentiation
between competing hypotheses re hemispheric or callosal
dysfunction. The current findings may be specific to males
with negative symptoms, but do suggest that revision of the
dominant left hemisphere hypothesis in schizophrenia may
This study was supported by a research grant from the
Schizophrenia Fellowship of New Zealand.
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