Electrophysiological Analysis of Error Monitoring in Schizophrenia
Sarah E. Morris, Cindy M. Yee, and Keith H. Nuechterlein
University of California, Los Angeles
In this study, the authors sought to determine whether abnormalities exhibited by schizophrenia patients
in event-related potentials associated with self-monitoring—the error-related negativity (ERN) and the
correct response negativity (CRN)—persist under conditions that maximize ERN amplitude and to
examine relationships between the ERN and behavior in schizophrenia. Participants performed a flanker
task under 2 contingencies: one encouraging accuracy and another emphasizing speed. Compared with
healthy participants, in schizophrenia patients the ERN was reduced in the accuracy condition, and the
CRN was enhanced in the speed condition. The amplitude of a later ERP component, the error positivity,
did not differ between groups in either task condition. Reduced self-correction and increased accuracy
following errors were associated with larger ERNs in both groups. Thus, ERN generation appears to be
abnormal in schizophrenia patients even under conditions demonstrated to maximize ERN amplitude;
however, functional characteristics of the ERN appear to be intact.
Keywords: self-monitoring, schizophrenia, error-related negativity
Accurate and rapid online monitoring of one’s thoughts and
actions is essential for the completion of goal-directed behavior
and for maintaining the internal organization of intentions, infor-
mation, and reasoning. Investigators have hypothesized that failure
of this internal monitoring process may contribute to the clinical
symptoms experienced by schizophrenia patients. It has been sug-
gested, for example, that misattribution of internally generated
thoughts may result in auditory hallucinations (Frith, 1987). Sim-
ilarly, failure to detect one’s intention to execute a behavior may
lead to the experience that these behaviors are under external
control (e.g., Frith & Done, 1989), and faulty self-monitoring of
speech may contribute to formal thought disorder (McGrath,
1991). Detection of behavioral errors is another important form of
internal monitoring, allowing an individual to adjust his or her
behavior in the absence of external feedback. In light of the
possible disruption of self-monitoring in schizophrenia, examina-
tion of error detection provides an empirical basis for testing
hypotheses regarding these internal processes.
Accordingly, researchers have examined the ability of schizo-
phrenia patients to monitor their own behavior. Malenka, Angel,
Hampton, and Berger (1982) reported that schizophrenia inpatients
were less likely than nonpsychiatric participants to correct incor-
rect responses and more likely to reverse correct moves on a motor
tracking task. In addition, medicated (Turken, Vuilleumier, Matha-
lon, Swick, & Ford, 2003) and unmedicated (Frith & Done, 1989)
schizophrenia patients showed reduced rates of spontaneous error
correction compared with nonpatients when visual feedback con-
cerning their performance was not available. Schizophrenia pa-
tients also appear to be impaired in discriminating their own
movements from those made by others (Daprati et al., 1997). In
other studies, however, schizophrenia patients have not exhibited
impairment in self-monitoring (e.g., Fourneret, Franck, Slachev-
sky, & Jeannerod, 2001; Kopp & Rist, 1994). Thus, there is
intriguing but inconsistent behavioral evidence of impaired self-
monitoring in schizophrenia.
The present study relied on a component of the event-related
brain potential (ERP), the error-related negativity (ERN; Gehring,
Goss, Coles, Meyer, & Donchin, 1993), which is theorized to be
related to self-monitoring. The ERN peaks approximately 60–100
ms after the execution of incorrect responses and is a robust signal
that has been elicited in a variety of paradigms (e.g., Bernstein,
Scheffers, & Coles, 1995; Nieuwenhuis, Ridderinkhof, Blom,
Band, & Kok, 2001; Scheffers, Coles, Bernstein, Gehring, &
Donchin, 1996). Efforts to localize the neural generators of the
ERN using electroencephalography (EEG; Dehaene, Posner, &
Tucker, 1994; Holroyd, Dien, & Coles, 1998; Luu, Flaisch, &
Tucker, 2000) and magnetoencephalography (Miltner et al., 1997)
have converged on the anterior cingulate cortex (ACC). Functional
Sarah E. Morris, Department of Psychology, University of California,
Los Angeles; Cindy M. Yee and Keith H. Nuechterlein, Department of
Psychology and Department of Psychiatry and Biobehavioral Sciences,
University of California, Los Angeles.
Sarah E. Morris is now at the Veterans Administration Capitol Health
Care Network (VISN 5) Mental Illness Research, Education, and Clinical
Center (MIRECC), Baltimore, Maryland; and the Department of Psychia-
try, University of Maryland School of Medicine.
This research was completed as part of a doctoral dissertation submitted
by Sarah E. Morris under the supervision of Cindy M. Yee-Bradbury.
Preliminary results were presented at the International Congress on Schizo-
phrenia Research, April 2001, and at the annual meeting of the Society for
Psychophysiological Research, October 2001. This research was supported
by National Institute of Mental Health Grants MH-12534, MH-14584, and
MH-37705; the Veterans Administration Capitol Health Care Network
(VISN 5) MIRECC; and an Associate Investigator grant from the Depart-
ment of Veterans Affairs, Veterans Health Administration, Rehabilitation
Research and Development Service to Sarah E. Morris. We thank William
Gehring for his consultation regarding the implementation of the experi-
Correspondence concerning this article should be addressed to Sarah E.
Morris, MIRECC, Suite 6A, Veterans Administration Medical Center, 10
North Greene Street, Baltimore, MD 21201. E-mail: sarah.morris2@
Journal of Abnormal Psychology
2006, Vol. 115, No. 2, 239–250
Copyright 2006 by the American Psychological Association
MRI studies provide further evidence of the involvement of the
ACC in self-monitoring (e.g., Carter et al., 1998; Holroyd et al.,
2004; MacDonald, Cohen, Stenger, & Carter, 2000). This region of
the brain is activated during tasks that require selective attention,
working memory, language generation, and controlled information
processing (Cabeza & Nyberg, 1997). It also has been suggested
that the ACC is involved in the executive control of cognition
(D’Esposito et al., 1995; Posner & Dehaene, 1994). Of importance,
there is evidence suggesting that the ACC may be compromised in
schizophrenia (e.g., Benes, Majocha, Bird, & Marotta, 1987;
Benes, McSparren, Bird, SanGiovanni, & Vincent, 1991; Gabriel
et al., 1997).
Several research groups have observed diminished ERN ampli-
tude in patients with schizophrenia. Kopp and Rist (1999) reported
that paranoid patients exhibited reduced ERNs compared with
nonparanoid schizophrenia patients and healthy comparison par-
ticipants during performance of a flanker task. Mathalon et al.
(2002) examined response-related ERPs during a picture–word
matching task and similarly found that schizophrenia patients
exhibited reductions in ERN amplitude, with paranoid patients
showing smaller ERNs than nonparanoid patients. In addition,
ERN-like activity following correct responses, the correct response
negativity (CRN), was larger in patients than in healthy compar-
ison participants. Alain and colleagues (Alain, McNeely, He,
Christensen, & West, 2002) reported a similar pattern of a dimin-
ished ERN and an enhanced CRN among schizophrenia patients
during performance of a Stroop task. Using a go/no-go paradigm,
Bates and colleagues (Bates, Kiehl, Laurens, & Liddle, 2002) also
observed ERN reductions in schizophrenia patients. In contrast to
Mathalon et al., patients did not show enhancement of the CRN,
possibly because patients were less confident in the accuracy of
their responses while associating words with pictures than while
discriminating letters (Bates et al., 2002). Recently, Bates, Liddle,
Kiehl, and Ngan (2004) reported that although the ERN increased
in schizophrenia patients tested following 6 weeks of antipsychotic
treatment, patients’ ERN was diminished relative to that of healthy
comparison participants regardless of medication status. In con-
trast to Bates et al. (2002), Bates et al. (2004) observed a CRN in
patients and healthy participants, although the magnitude of the
activity was not substantial. Taken together, reductions in ERN
activity have been observed reliably in schizophrenia patients
across a variety of paradigms, whereas enhanced CRN amplitude
was found in only a subset of studies.
In considering its functional significance, the ERN was initially
theorized to reflect the activity of an error-detection system, with
heightened responses indicative of a mismatch between the in-
tended and actual response (e.g., Bernstein et al., 1995; Coles,
Scheffers, & Holroyd, 2001; Gehring et al., 1993). An alternate
theory proposes that the ERN arises from the presence of response
conflict rather than the detection of an error (Botvinick, Braver,
Barch, Carter, & Cohen, 2001; Carter et al., 1998). More recently,
Yeung, Botvinick, and Cohen (2004) modeled various conflict and
response parameters and demonstrated that the ERN arises during
continued processing of the stimulus and activation of the correct
response even following the commission of errors. They further
showed that the appearance of an ERN on correct trials (e.g.,
Falkenstein, Hoormann, Christ, & Hohnsbein, 2000; Luu, Flaisch,
& Tucker, 2000) may reflect conflict that is resolved prior to the
execution of a correct response and is better characterized as an N2
(van Veen & Carter, 2002a). They proposed that conflict monitor-
ing and error detection are not mutually exclusive but that conflict
monitoring serves as a computationally simple method for detect-
ing errors. This theory, however, does not account for the presence
of ERN-like activity following correct responses appearing in
response-locked averages (Vidal, Hasbroucq, Grapperon, & Bon-
net, 2000). It is possible that such activity reflects error processing
due to the presence of some aspect(s) of erroneous responding
even on correct responses, such as a slow reaction time (RT)
during a task with an RT cutoff (Coles et al., 2001). Thus, it
appears that the ERN may reflect a comparison of intended and
actual responses, simultaneous activation of correct and incorrect
responses, processing of a response in which one aspect is erro-
neous, or a combination of these factors.
Both error monitoring and response conflict detection can be
expected to be affected by task context, which is governed by
factors that include reward and penalty contingencies, instructions,
difficulty, and recent and remote task-related experience (Cohen &
Servan-Schreiber, 1992). These factors determine, at least in part,
the significance of errors and the strength of activation (and
potential coactivation) of responses. Among nonpsychiatric par-
ticipants, for example, ERN amplitude appears to be highly sen-
sitive to differences in task context and is largest when participants
are instructed to focus on responding accurately, smaller when
accuracy and speed of responding are emphasized equally, and
smallest when participants are instructed to respond quickly
(Gehring et al., 1993). Similarly, ERN is reduced under high
compared with moderate time pressure (Falkenstein et al., 2000).
These findings are consistent with recent evidence that the ERN is
also modulated by affective or motivational factors (Luu, Collins,
& Tucker, 2000) and demonstrate the critical importance of task
instructions in studies of response-related ERPs.
One aim of the present study was to investigate the scope of
error monitoring difficulties in schizophrenia patients by using a
task devised to optimize ERN amplitude and by varying the
motivational significance of errors. Specifically, performance de-
mands were introduced to examine whether ERN activity is intact
when schizophrenia patients are provided with a task context that
enhances response monitoring in healthy individuals. In prior
studies, participants were instructed either to respond quickly at
the expense of accuracy (Kopp & Rist, 1999) or to respond quickly
but without sacrificing accuracy (Alain et al., 2002; Bates et al.,
2002, 2004; Mathalon et al., 2002). A key question is whether
ERN activity in schizophrenia patients can be optimized when
accuracy of performance is emphasized. It was hypothesized that
compared with healthy participants, schizophrenia patients would
exhibit a diminished ERN and an enhanced CRN across task
conditions. Given prior reports of disruption in the representation
and maintenance of task context in schizophrenia patients (e.g.,
Barch, Carter, MacDonald, Braver, & Cohen, 2003; Cohen, Barch,
Carter, & Servan-Schreiber, 1999; MacDonald & Carter, 2003), it
also was expected that any impact of instructional context on the
ERN would be reduced in schizophrenia patients compared with
healthy comparison participants. Among healthy participants, the
ERN was predicted to be larger when task instructions and con-
tingencies favored accurate responding than when they favored
fast responding. In contrast, it was anticipated that schizophrenia
patients would have difficulty sustaining the task context and
would have a weakened representation of task-appropriate re-
MORRIS, YEE, AND NUECHTERLEIN
sponses, such that the ERN in these participants would not differ
between instruction conditions.
To examine whether abnormalities observed in schizophrenia
patients are specific to the ERN, we compared the error positivity
(Pe) between the two groups. The Pe is a positively deflected ERP
that appears approximately 160–500 ms after the execution of a
response and is more prominent following errors than correct
responses (Falkenstein, Hohnsbein, & Hoormann, 1991; Falken-
stein et al., 2000). Dipole modeling of the Pe suggests that its
neural source lies in the rostral ACC (van Veen & Carter, 2002b),
consistent with the theory that it is related to subjective assessment
of errors (Bush, Luu, & Posner, 2000; Falkenstein et al., 2000). In
prior studies that did not emphasize accuracy of performance,
schizophrenia patients have not shown differences from healthy
comparison participants in Pe amplitude (Alain et al., 2002; Bates
et al., 2004; Mathalon et al., 2002). Thus, we hypothesized that
group differences would be limited to the ERN and not extend to
Another aim of this research was to evaluate the relationship
between the ERN and response-related behaviors such as error
correction and posterror slowing in schizophrenia patients. In-
creased error correction and slowing of RTs on trials following
errors have been associated with a larger ERN in some studies
(Gehring et al., 1993; Nieuwenhuis et al., 2001; Scheffers & Coles,
2000) but not in others (Gehring & Fencsik, 2001; Hajcak, Mc-
Donald, & Simons, 2003). Investigations conducted with schizo-
phrenia patients (Alain et al., 2002; Mathalon et al., 2002) also
have failed to find a relationship between the ERN and posterror
slowing. It is possible that the impact of differences in experimen-
tal tasks, instructions to participants, analytic methods, and statis-
tical power may be obscuring what might be only moderate rela-
tionships between the ERN and response behaviors. Because the
methods used in the present study were most similar to those of
Gehring et al. (1993), similar ERN-behavior relationships were
predicted. Specifically, it was expected that in healthy participants,
larger ERNs would be associated with greater posterror slowing,
improved accuracy on trials following errors, and increased prob-
ability of error correction. Given evidence for normal posterror
slowing (Alain et al., 2002; Laurens, Ngan, Bates, Kiehl, & Liddle,
2003; Mathalon et al., 2002) and self-correction (Kopp & Rist,
1994) in schizophrenia, it was hypothesized that the relationship
between the ERN and response-related behaviors would not differ
between patients and healthy comparison participants.
The association between ERP amplitude and response-related
behaviors also was examined for the Pe. There is some suggestion
that Pe amplitude does not differ between corrected and uncor-
rected errors (Falkenstein, Hohnsbein, & Hoormann, 1996). In
contrast, Pe amplitude and posterror slowing have been found to be
greater for perceived errors compared with those that are unper-
ceived (Nieuwenhuis et al., 2001). Older participants, however,
exhibit a reduced Pe but increased posterror slowing compared
with younger participants (Falkenstein et al., 2000), suggesting a
possible uncoupling as a function of aging. To our knowledge, the
present study is the first to examine the relationship between Pe
and behavior in schizophrenia. On the basis of similarities in
experimental tasks between the present study and that of Falken-
stein et al. (2000), we hypothesized that Pe amplitude would not be
related to error-related behaviors in healthy participants. A normal
pattern of relationships also was anticipated among schizophrenia
patients, assuming that the disjunction between Pe and posterror
slowing is restricted to older persons.
A total of 19 schizophrenia patients and 11 healthy comparison partic-
ipants participated in the study. Data from 3 patients were excluded
because of equipment problems (n ? 2) or excessive artifact from move-
ment (n ? 1), yielding a final sample of 16 patients. The groups did not
differ in age, F(1, 25) ? 0.01, p ? .92; years of education, F(1, 25) ? 3.74,
p ? .06; years of parental education, F(1, 25) ? 0.00, p ? .99; gender,
?2(1, N ? 27) ? .08, p ? .78, or ethnicity, ?2(5, N ? 27) ? 3.24, p ? .66.
Demographic characteristics of the groups are summarized in Table 1.
Outpatients were recruited from a longitudinal study of recent-onset
schizophrenia (see Nuechterlein et al., 1992). They were assessed with the
Structured Clinical Interview for the DSM–IV (SCID; First, Spitzer, Gib-
bon, & Williams, 1994) and diagnosed with schizophrenia (n ? 11;
subtypes: 7 undifferentiated, 3 paranoid, 1 disorganized), schizoaffective
disorder, depressive type (n ? 2), or schizophreniform disorder (n ? 3).
Subsequently, diagnoses of schizophrenia (n ? 2) and schizoaffective
disorder, depressed type (n ? 1) were assigned to the schizophreniform
patients. Patients were treated with atypical antipsychotics (risperidone: 9,
olanzapine: 4, clozapine: 2), except for 1 patient who received fluphena-
zine decanoate. The mean number of years between the onset of psychotic
symptoms and participation in this study was 7.38 (SD ? 6.57).
All healthy comparison participants were screened with the SCID to
exclude for any personal history of schizophrenia, schizoaffective disorder
or other major psychopathology, and any alcohol or substance abuse in the
last 3 months. Individuals were excluded if they reported serious medical
conditions (e.g., neurological disorders, history of major head trauma, more
than a 5-min loss of consciousness) or a family history of schizophrenia or
schizoaffective disorder. Except for 1 healthy comparison participant, all
participants reported that they were right-handed. All participants were
fluent in English and provided written informed consent.
Demographic and Clinical Status Data for Schizophrenia
Patients and Healthy Comparison Participants
(n ? 11)
(n ? 16)
Parent’s highest education (years)
BPRS 18-item total score
SANS total score
Assessment of Negative Symptoms.
an ? 13.
BPRS ? Brief Psychiatric Rating Scale; SANS ? Scale for the
bn ? 15.
ERROR MONITORING IN SCHIZOPHRENIA
Participants performed a flanker task similar to that used by Kopp and
Rist (1999). Each trial began with a 1-cm fixation cross displayed for 500
ms in the center of the screen, followed by the onset of the flanker stimuli,
which were two equilateral triangles or squares arranged in a vertical array.
The length of each side of the triangles was 21 mm, and the squares were
15-mm high. Flanker stimuli were displayed for 100 ms before the middle
triangle, the target, appeared. The entire array was displayed for 50 ms.
Participants were instructed to respond with the hand that corresponded
with the direction in which the target was pointing. RT was determined
relative to the onset of the target stimulus. Response feedback (see below)
was displayed for 500 ms, beginning 1400 ms after the response. The delay
between the offset of the target (or feedback when provided) and the onset
of the subsequent fixation cross ranged within 1 to 2 s. The flanking
triangles were oriented either in the same (facilitation condition) or oppo-
site (interference condition) direction as the target. On some trials, flanking
squares were used instead of triangles (neutral condition). Flanker stimuli
were positioned either close (2 cm) or far (6.3 cm) from the target. The
facilitating and interfering effects of the flankers on performance have been
shown to be related to the distance of the flankers from the target (Eriksen
& Eriksen, 1974). The array subtended 1oof vertical visual angle in the
close condition and 3oin the far condition. The six different types of trials
were presented with equal probability in random order. All stimuli were
gray and presented on a black background with a 24-cm ? 32-cm monitor
placed 1.5 m from the participant’s face. The response device consisted of
two 3.1-cm buttons mounted on a lapboard, with a minimum force of 2 N
(.45 lb) required to make a response.
EEG recordings were obtained from a 128-channel electrode cap (Neu-
roscan, El Paso, TX) with Quick-gel applied to the sensors. Only data from
primary midline sites are reported. The first 10 participants (7 patients and
3 comparison participants) were tested in a semidarkened, sound-
attenuated room, and the remaining participants were tested with the same
equipment but in a soundproof chamber. No differences in ERPs were
observed between the two rooms.
Before testing, participants were informed they could win a bonus of up
to $10 (beyond the payment given for their participation) depending on
their task performance. Feedback was provided to reinforce the task con-
tingencies, as indicated below in parentheses. In the accuracy condition,
participants were instructed to respond as accurately as possible and were
penalized 5¢ for incorrect responses regardless of RT (Incorrect ? 5¢) and
rewarded 1¢ for correct responses made within 300 ms of target onset (Fast
response ? 1¢). These contingencies had the effect of encouraging correct
responding while also introducing a modest time pressure that elicited
errors sufficient for computation of the ERN and Pe. In the speed condi-
tion, participants were instructed to perform the task as quickly as possible
and were given a bonus of 4¢ for responding within 270 ms regardless of
the accuracy of their response (Fast response ? 4¢). If participants
responded after the deadline, they were penalized 1¢ if their response was
incorrect (Incorrect ? 1¢). This contingency had the effect of encouraging
rapid responding, and because participants inevitably missed the RT dead-
line on a subset of trials, the contingencies also minimized purely random
responding that would, in effect, introduce a fundamental difference in the
nature of the task between the two instruction conditions.
Task instructions and information regarding reward contingencies were
displayed on the video monitor. Participants were questioned prior to
beginning the task to ensure comprehension. The order of the speed and
accuracy conditions was counterbalanced across participants. Participants
completed 60 practice trials at the beginning of each instruction condition.
Each task was then administered in 60-trial blocks with brief rest periods
between blocks. The experimenter reminded participants of the perfor-
mance emphasis at the beginning of each trial block. Participants per-
formed 7 blocks of trials for a total of 420 trials in the speed condition and
14 blocks for a total of 840 trials in the accuracy condition. The entire
testing session lasted approximately 90 min. At the end of the session,
participants were debriefed about the nature of the study and given the
entire $10 bonus, regardless of task performance.
Ratings of patients’ symptoms during the 2-week (n ? 12) or 3-week
(n ? 4) period preceding the date of testing were obtained by a clinic staff
member from the expanded version of the Brief Psychiatric Rating Scale
(Ventura et al., 1993) and the Scale for the Assessment of Negative
Symptoms (Andreasen, 1982).
Psychophysiological Recording, Data Reduction, and
EEG and electrooculogram (EOG) were recorded with Synamps ampli-
fiers and Scan 4.1 software (Neuroscan, El Paso, TX). All physiological
data were recorded at a rate of 1000 Hz. EEG was filtered online at .05 and
100 Hz with a gain of 1000. To identify eye movement artifact in the EEG,
EOG activity was recorded from electrodes placed above and below the left
eye, filtered online at .05 and 200 Hz with a gain of 500. EOG artifact was
removed from the EEG with singular value decomposition (see Picton et
al., 2000). In data in which cardiac activity was visible, the same method
was used to minimize this artifact. Epochs contaminated by participant
movement were excluded. Response-locked epochs beginning 1000 ms
before and extending 1000 ms beyond the response were then created for
each trial. A 1–10 Hz, 96 dB filter was applied, and a 50-ms preresponse
baseline was subtracted. Four averages were computed for each participant:
correct and incorrect responses in the two instruction conditions.
The amplitude of the ERN and CRN was scored at Fz, FCz, Cz, and Pz
with the use of methods similar to those of Gehring et al. (1993) and Luu,
Flaisch, and Tucker (2000). The latency of the most negative point from 40
to 160 ms after the response was determined from the FCz channel, relying
on the average waveform derived from incorrect trials during the accuracy
condition. The average amplitude in a 50-ms period centered on this
latency was then computed for each of the four averages for each channel
and participant. This method eliminates the opportunity to analyze latency
differences but permits measurement of the CRN, which is typically a
positive deflection. The Pe was scored at the same sites as the ERN and
was computed as the mean amplitude from 170 to 400 ms after the
To assess the relationships between ERP amplitude and response char-
acteristics, averages characterized by small, medium, and large ERNs and
Pes were created for each participant (see Gehring et al., 1993). All error
trials from the accuracy condition and an equal number of correct trials
with the same range of RTs from the same task were used. Trials with a
missing response on the next trial were excluded. Data from the FCz site
(where the ERN and Pe were observed to be maximal) were entered into a
stepwise discriminant analysis (SWDA) using SPSS Version 11. The
SWDA was performed once for the ERN data and again for the Pe data. For
the ERN analysis, the SWDA included data from 20 to 180 ms following
the response. For the Pe analysis, data from 170 to 410 ms following the
response were used. The SWDA procedure produced a probability value
for each trial that indicated the likelihood of the trial being an error. Error
trials were sorted on the basis of these probabilities into three bins con-
taining an equal number of trials for each participant (M number of trials
per bin per ERP for each participant ? 25.9, SD ? 11.9, range ? 5–60).
Epochs were averaged within bins to create small, medium, and large
ERNs and Pes. Four additional variables were computed for each size
category for the ERN and Pe: RT, probability of error correction, and RT
and accuracy on the next trial. An error correction was defined as a
response occurring with the opposite hand after an error at any time before
the onset of the trial feedback or, on trials in which no feedback occurred
(e.g., a correct trial not fast enough to earn the bonus for fast responding),
before the onset of the fixation cross. The probability of error correction
MORRIS, YEE, AND NUECHTERLEIN
was computed by dividing the number of error corrections for each ERN
size by the total number of error corrections for each participant. Data from
participants who made fewer than three response corrections (2 patients
and 1 comparison participant) were excluded from these analyses.
An alpha level of .05 was adopted, and the Greenhouse–Geisser method
was used to adjust for repeated measures. Simple effects analyses of
variances (ANOVAs) with the Bonferroni correction were used for post
hoc comparisons on between-groups measures.
Flanker Task Performance
of maximizing correct responding in the accuracy instruction con-
dition. A Group ? Instruction ANOVA performed on the percent-
age of correct responses indicated a main effect for instruction
condition. Both schizophrenia patients and comparison partici-
pants responded more accurately during the accuracy condition
(M ? 89% correct, SD ? 5%) than the speed condition (M ? 68%
correct, SD ? 13%), F(1, 25) ? 84.53, p ? .00, ?p
was no group difference in response accuracy, F(1, 25) ? 0.21,
p ? .65, which is consistent with prior studies using the flanker
task (e.g., Kopp & Rist, 1999).
The effects of the type of flanker and distance of the flankers
from the target on performance accuracy were examined sepa-
rately for the two instruction conditions with Group ? Flanker
Type ? Distance ANOVAs. Accuracy data are shown in Table 2.
In the speed instruction condition, a Group ? Flanker Type inter-
action was observed, F(2, 50) ? 4.22, p ? .04, ?p
The manipulation had the intended effect
2? .77. There
2? .14, in
addition to a Distance ? Flanker Type interaction, F(2, 50) ?
8.79, p ? .001, ?p
7.94, p ? .009, ?p
flanker distance and group were significant only in the interference
condition, such that accuracy was reduced when flankers were
close compared with far from the target, F(1, 25) ? 19.59, p ? .00,
rate than comparison participants when speed of performance was
emphasized, regardless of flanker distance, F(1, 25) ? 5.65, p ?
In the accuracy instruction condition, main effects of flanker
type and distance were modified by an interaction between these
variables, F(2, 50) ? 116.43, p ? .00, ?p
distance conditions, accuracy was reduced in the interference
compared with the neutral conditions: close, F(1, 25) ? 124.30,
p ? .00, ?p
and with the facilitation conditions: close, F(1, 25) ? 118.11, p ?
Accuracy was also reduced in the neutral compared with the
facilitation conditions: close, F(1, 25) ? 15.34, p ? .001, ?p
.38, and far, F(1, 25) ? 8.07, p ? .01, ?p
interference, F(1, 25) ? 148.29, p ? .00, ?p
F(1, 25) ? 4.65, p ? .04, ?p
facilitation condition, F(1, 25) ? .145, p ? .71, the effect of
flanker distance was significant, with reduced accuracy when
flankers were closer to the target compared with when they were
A Group ? Instruction Condition ? Response Accuracy
ANOVA on RT revealed an Instruction Condition ? Response
Accuracy interaction, F(1, 25) ? 7.39, p ? .012, ?p
performance during the two instruction conditions was examined
separately, main effects for response accuracy (i.e., faster respond-
ing on error than on correct trials) were observed for both the
speed, F(1, 25) ? 85.22, p ? .000, ?p
25) ? 317.96, p ? .000, ?p
magnitude of the effect was larger in the accuracy (correct: M ?
357 ms, SD ? 9 ms; incorrect: M ? 272 ms, SD ? 8 ms) than in
the speed (correct: M ? 277 ms, SD ? 15 ms; incorrect: M ? 213
ms, SD ? 10 ms) condition. In addition, a main effect of group
indicated that schizophrenia patients (M ? 303 ms, SD ? 11 ms)
responded more slowly than healthy comparison participants (M ?
256 ms, SD ? 13 ms), F(1, 25) ? 7.95, p ? .009, ?p
There were group differences in the rates at which participants
received bonuses and penalties in the speed instruction condition,
results that are consistent with this RT slowing. Although a re-
peated measures ANOVA comparing the proportion of trials on
which the groups obtained bonus, penalty, or neither feedback did
not show a significant Group ? Feedback Type interaction, F(2,
50) ? 3.93, p ? .057, ?p
bonuses for fast responses on fewer trials: patients, M ? 49%,
SD ? 28%, and comparison participants, M ? 69%, SD ? 19%;
F(1, 25) ? 4.45, p ? .045, ?p
for slow erroneous responses on more trials than did comparison
participants: patients, M ? 7%, SD ? 4%, and comparison par-
ticipants, M ? 3%, SD ? 3%; F(1, 25) ? 5.17, p ? .032, ?p
.18. In the accuracy instruction condition, there was no Group ?
Feedback Type interaction, F(2, 50) ? 2.25, p ? .15, and no
significant differences between groups in the rates at which the
2? .26, and main effects of distance, F(1, 50) ?
2? .24, and flanker type, F(2, 50) ? 60.70, p ?
2? .71. Post hoc analyses revealed that the effects of
2? .44. Unexpectedly, schizophrenia patients were more accu-
2? .82. In both flanker
2? .83, and far, F(1, 25) ? 39.79, p ? .00, ?p
2? .82, and far, F(1, 25) ? 42.22, p ? .00, ?p
2? .24. In the
2? .86, and neutral,
2? .16, conditions, but not the
2? .74. When
2? .77, and accuracy, F(1,
2? .93, conditions. However, the
2? .14, schizophrenia patients earned
2? .15; and they received penalties
Task Performance Data as a Function of Instructional
Emphasis, Flanker Type, and Flanker Distance
Flanker type and distance
(n ? 11)
patients (n ? 16)
RT% CorrectRT% Correct
Accuracy instruction condition
Speed instruction condition
deviations are in parentheses.
Mean reaction times are presented in milliseconds and standard
ERROR MONITORING IN SCHIZOPHRENIA
different types of feedback were obtained: bonus, F(1, 25) ? 3.91,
p ? .06; penalty, F(1, 25) ? 1.71, p ? .20; and none, F(1, 25) ?
1.32, p ? .26. Comparison participants earned a larger total bonus
across instruction conditions (M ? $9.07, SD ? $3.38) than did
schizophrenia patients (M ? $3.68, SD ? $3.51), F(1, 25) ?
15.84, p ? .001, ?p
The effects of group, flanker type, and distance on RT were
examined for correct responses in the speed and accuracy instruc-
tion conditions separately. In the speed instruction condition, a
main effect of flanker type was observed, F(2, 50) ? 19.98, p ?
condition than in the neutral, F(1, 25) ? 10.88, p ? .003, ?p
.30, and facilitation, F(1, 25) ? 24.14, p ? .000, ?p
conditions and in the neutral compared with the facilitation con-
dition, F(1, 25) ? 26.16, p ? .000, ?p
instruction condition, a main effect of group was observed, F(1,
25) ? 6.42, p ? .02, ?p
ing among schizophrenia patients. In addition, a Flanker Type ?
Distance interaction modified the main effects of these variables,
F(2, 50) ? 27.22, p ? .000, ?p
neutral flanker conditions, RTs were slower when the flankers
were closer to the target than when they were further away, F(1,
25) ? 48.38, p ? .000, ?p
there was no effect of flanker distance on RT, F(1, 25) ? 2.45, p ?
reports of an enhanced impact of flankers that are closer to the
target (Eriksen & Eriksen, 1974) and of normal or reduced inter-
ference effects in schizophrenia patients (Elkins & Cromwell,
1994; Kopp, Mattler, & Rist, 1994).
2? .44. As expected, RTs were slower in the interference
2? .51. In the accuracy
2? .20, characterized by slower respond-
2? .52. In the interference and
2? .66; and F(1, 25) ? 14.63, p ? .001,
2? .37, respectively. In the facilitation condition, however,
2? .09. These effects are generally consistent with previous
Midline Distribution of the ERN and Pe
To confirm that the midline distribution of the ERN in the
current study was consistent with that of previous reports, we
compared ERN amplitude in the accuracy instruction condition at
four midline sites (Fz, FCz, Cz, and Pz). One patient was excluded
from these analyses because of missing data from the Cz site. A
Group ? Site ANOVA revealed a main effect for site, F(3, 72) ?
28.19, p ? .000, ?p
as expected. Pe amplitude also was found to be maximal at FCz,
F(1, 24) ? 6.81, p ? .004, ?p
al., 2004), although more anterior than the central–parietal maxi-
mum reported by others (e.g., Falkenstein et al., 2000; Leuthold &
Sommer, 1999). Because prior studies have not detected qualita-
tive topographical differences in the ERN or Pe between schizo-
phrenia patients and healthy comparison participants (Alain et al.,
2002; Bates et al., 2004; Mathalon et al., 2002), we conducted all
further analyses using only data from the FCz site.
2? .54, such that the ERN was maximal at FCz
2? .22 (as in the study by Bates et
ERN Amplitude, Response Accuracy, and Task Context
Grand average waveforms are presented in Figure 1, and mean
ERN–CRN and Pe amplitudes are shown in Figure 2. The hypoth-
esis that schizophrenia patients would exhibit a reduced ERN and
enhanced CRN was supported by a Group ? Response Accuracy
interaction, F(1, 25) ? 16.30, p ? .000, ?p
remained significant when patients with a schizoaffective or
2? .39. This interaction
schizophreniform diagnosis were omitted, F(1, 20) ? 11.13, p ?
were examined, F(1, 18) ? 9.84, p ? .006, ?p
analyses compared the ERN and CRN separately in the two groups
during the two instruction conditions. Consistent with previous
reports were our findings that the schizophrenia patients’ ERN was
diminished relative to that of comparison participants during the
accuracy condition, F(1, 25) ? 4.24, p ? .05, ?p
to our expectations, there were no group differences in ERN during
the speed condition, F(1, 25) ? 1.42, ns. As hypothesized, schizo-
phrenia patients also showed a larger CRN than healthy compar-
ison participants during the speed instruction condition, F(1, 25) ?
9.25, p ? .005, ?p
schizophrenia patients relative to healthy comparison participants
was observed during the accuracy instruction condition, although
this difference did not reach statistical significance, F(1, 25) ?
4.10, p ? .054.
To test the hypothesis that the ERN would be larger during the
accuracy than the speed instruction condition for healthy partici-
pants but not schizophrenia patients, we compared the ERN during
the two conditions and conducted post hoc analyses addressing
within-group differences. A Group ? Instruction interaction in this
analysis, F(1, 25) ? 7.50, p ? .01, ?p
effect of instruction condition, F(1, 25) ? 34.67, p ? .000, ?p
.58. Healthy comparison participants’ ERN was larger following
errors during the accuracy condition than during the speed condi-
tion, F(1, 10) ? 24.43, p ? .001, ?p
consistent with our hypothesis. Unexpectedly, schizophrenia pa-
tients’ ERN also exhibited sensitivity to task context; the ERN in
the accuracy condition was larger than in the speed condition,
although the difference was much smaller than that observed in
healthy comparison participants, F(1, 15) ? 7.51, p ? .015, ?p
In comparison to previous reports (Alain et al., 2002; Bates et
al., 2004; Bush et al., 2000; Falkenstein et al., 1991, 2000; Matha-
lon et al., 2002; van Veen & Carter, 2002b), the Pe component in
both groups was generally smaller and negative in amplitude,
although positively deflected. The broad, centrally maximal dis-
tribution and sensitivity of the component to response accuracy,
however, suggested that the Pe had been correctly identified and
scored. No group differences were observed in either the speed,
F(1, 25) ? 1.35, p ? .25, or accuracy, F(1, 25) ? 0.33, p ? .57,
instruction conditions, results consistent with the hypothesis that
Pe would not discriminate between schizophrenia patients and
comparison participants. Main effects of response accuracy were
significant in both the speed, F(1, 25) ? 30.91, p ? .000, ?p
.55, and accuracy, F(1, 25) ? 23.72, p ? .000, ?p
conditions, with larger Pes occurring on error trials compared with
correct trials. Pe also was sensitive to task context, with greater
amplitude occurring following errors in the speed instruction con-
dition, F(1, 25) ? 12.10, p ? .002, ?p
group differences were significant in these Pe analyses. Taken
together, results of the ERN and Pe analyses are largely consistent
with the hypothesis that schizophrenia patients’ ERN is reduced
and CRN is enhanced relative to healthy comparison participants
and that these group differences have some specificity relative to
2? .36, and when only patients treated with risperidone
2? .35. Post hoc
2? .14. Contrary
2? .27. A similar pattern of enhanced CRN in
2? .23, modified the main
2? .71, results that were
2? .33. No effects involving
MORRIS, YEE, AND NUECHTERLEIN
The discriminant analysis procedure produced three distinct
ERN waveforms for each group. As shown in Figure 3A, a small,
medium, and large ERN is apparent for the healthy comparison
participants. Among healthy participants, it appears that the activ-
ity that best distinguished errors from correct trials occurred in the
early portion of the segment included in the analysis, as the
greatest discrimination is apparent in the 60–100 ms latency range.
For schizophrenia patients, a similar pattern is present, although
the medium and small waveforms are distinguished from each
other more by temporal characteristics than by amplitude. This
may indicate that error-related activation associated with medium
and especially small ERNs occurred over a more extended or
variable time period for patients than for comparison participants.
To examine the relationships between the ERN and error-related
behaviors, we performed Group ? ERN Size ANOVAs on RT, RT
on the next trial, response accuracy on the next trial, and probability
of error correction. RT did not differ between the three ERN size
categories, F(2, 50) ? 1.83, p ? .17, although responses of schizo-
phrenia patients were slower than those of comparison participants,
F(1, 25) ? 6.33, p ? .019, ?p
size on RT on trials following errors, F(2, 50) ? 2.19, p ? .49. In
analyses including all trials (not only those used in the discriminant
analysis), a Group ? Instruction Condition repeated measures
ANOVA revealed a main effect of instruction condition on posterror
2? .2. There also was no effect of ERN
slowing, F(1, 25) ? 15.46, p ? .001, ?p
between the groups, F(1, 25) ? 0.48, p ? .49. Specifically, RTs
following errors were an average of only 6 ms slower than those
following correct responses in the accuracy condition, whereas RTs
following errors in the speed condition were an average of 23 ms
faster than RTs following correct responses.
Consistent with the hypothesis that schizophrenia patients and
healthy comparison participants would exhibit similar ERN-
behavior relationships, the ERN was associated with posterror
accuracy and error correction in both groups. As shown in Figure
4A, the hypothesized relationship between ERN size and accuracy
on trials following errors was observed, in which accuracy was
improved following larger ERNs, F(2, 50) ? 3.13, p ? .05, ?p
.11. A main effect of group revealed that schizophrenia patients
were generally less accurate following errors than were healthy
comparison participants, F(1, 25) ? 6.65, p ? .02, ?p
Error correction data are presented in Figure 4B. A main effect of
ERN size on the probability of error correction was observed, F(2,
44) ? 4.10, p ? .02, ?p
however, was the reverse of the hypothesized relationship with
corrections more likely following smaller ERNs than larger ERNs.
The overall percentage of errors corrected by schizophrenia pa-
tients (M ? 27%, SD ? 15%) did not differ from that of healthy
comparison participants (M ? 31%, SD ? 18%), F(1, 23) ? 0.29,
p ? .54.
2? .38, but no difference
2? .16. The direction of this relationship,
Accuracy Instruction Condition
Speed Instruction Condition
(n = 16)
Healthy Comparison Participants
(n = 11)
accuracy and speed instruction conditions. Data displayed are from the FCz site. ERN ? error-related negativity;
Pe ? error positivity.
Grand average waveforms for healthy comparison participants and schizophrenia patients during
ERROR MONITORING IN SCHIZOPHRENIA
Examination of relationships between Pe size and response-
related behaviors showed some similarities with those observed in
the ERN analyses. Waveforms showing small, medium, and large
Pes are presented in Figure 3B. Similar to the relationship ob-
served with ERN size, error correction rates also differed between
the three Pe size categories, F(2, 44) ? 6.45, p ? .005, ?p
with more frequent error correction following smaller Pes (see
Figure 4C). There were no differences between the three Pe sizes
in RT on trials following errors, F(2, 50) ? 2.16, p ? .13, or
accuracy on trials following errors, F(2, 50) ? 0.16, p ? .80, and
no effects involving group.
The aims of this study were to compare the amplitude of
response-related ERPs under varying task demands in schizophre-
nia patients and healthy comparison participants and to examine
the relationships between ERN amplitude and behavioral variables
in these groups. As predicted, the ERN was reduced in schizo-
phrenia patients but maximized in healthy comparison participants
when performance accuracy was emphasized. Somewhat unex-
pectedly, ERN amplitude did not differ between patients and
comparison participants when speed of responding was rewarded.
The CRN was larger in schizophrenia patients than in healthy
comparison participants during the speed instruction condition
and, to a lesser extent, when contingencies favored accurate re-
sponding. These results largely replicate and extend previous find-
ings of reduced ERN amplitude in schizophrenia by demonstrating
that this impairment is observed even under task demands that
have been shown to potentiate the component. In addition, the
findings are consistent with other reports of enhanced CRN in
schizophrenia patients (Alain et al., 2002; Mathalon et al., 2002).
The picture that emerges, therefore, is not so much one of a lack
of monitoring in schizophrenia but of imprecise monitoring, char-
acterized by enhanced activity when it is not appropriate and
diminished activity when an erroneous response is executed under
conditions in which errors are most costly. This interpretation,
however, depends upon the still-controversial assumption that the
ERN and CRN reflect the same underlying process. Until the
precise nature of the CRN and its properties are fully understood,
conclusions regarding its significance must remain tentative.
The theoretical import of these findings differs depending upon
the model that is adopted regarding the generation of the ERN.
Considered within the framework of error detection theory (e.g.,
Bernstein et al., 1995; Coles et al., 2001; Scheffers & Coles, 2000),
the present results suggest that schizophrenia patients have diffi-
culty distinguishing between correct and incorrect responses, per-
haps because of disruptions in phasic dopamine (DA) activity that
render the ACC unable to detect changes in the success or failure
of ongoing events (Holroyd & Coles, 2002). This interpretation is
consistent with long-standing theories of the involvement of DA in
schizophrenia (for a review, see Davis, Kahn, Ko, & Davidson,
1991) and reports of abnormal DA transmission in the ACC of
schizophrenia patients (Benes, 2000; Suhara et al., 2002). Chal-
lenging this idea, however, is the absence of group differences in
response accuracy rates despite the ERN abnormalities observed in
this and other studies of schizophrenia (Alain et al., 2002; Bates et
al., 2004; Kopp & Rist, 1999; Mathalon et al., 2002) and essen-
tially normal modulation of the Pe according to response accuracy
(Alain et al., 2002; Bates et al., 2004; Mathalon et al., 2002). It
appears improbable that schizophrenia patients could perform ex-
perimental tasks with essentially normal rates of accuracy if their
ability to discriminate correct from incorrect responses is funda-
mentally disrupted. One possibility is that error monitoring diffi-
culties in schizophrenia manifest themselves in general slowing of
responses rather than increased error rates. Given the sensitivity of
the ACC to the loss of reward, it is also possible that group
differences in ERN amplitude in the face of normal response
accuracy might point to insensitivity to reward and loss of reward
(see Holroyd & Coles, 2002).
Within the conflict detection model of ERN generation (Botvin-
ick et al., 2001; Carter et al., 1998; MacDonald et al., 2000; Yeung
et al., 2004), results of the current study suggest that schizophrenia
patients experience diminished response competition compared
with healthy participants during trials on which accuracy of per-
formance is emphasized and an incorrect response is executed.
This may be due to premature selection of a response and, thus, the
absence of concurrently activated responses. In contrast, during
trials on which a correct response is made, it appears that schizo-
phrenia patients experience enhanced response competition com-
pared with healthy comparison participants and that simultaneous
(n = 16)
(n = 11)
(A) and error positivity (B) amplitudes for healthy comparison participants
and schizophrenia patients during accuracy and speed instruction condi-
tions. Data displayed are from the FCz site. Error bars represent standard
Mean error-related negativity and correct response negativity
MORRIS, YEE, AND NUECHTERLEIN
coactivation of response units persists even though a correct re-
sponse is executed. If enhanced CRN amplitude in schizophrenia
patients is due to increased response competition, however, slower
RTs and higher error rates would be expected in patients than in
healthy comparison participants. Although increased RTs were
observed among schizophrenia patients as compared with healthy
participants, it is difficult to discern if this was due to increased
response competition or the psychomotor slowing that is consis-
tently observed in schizophrenia patients (for a review, see
Nuechterlein, 1977). The absence of group differences in perfor-
mance accuracy and greater response accuracy in schizophrenia
patients than in healthy comparison participants on interference
trials during the speed instruction condition argues against the
possibility of heightened response competition in patients.
The observed pattern of results also could be explained by
failures of context maintenance in schizophrenia (Barch et al.,
2003; Braver, Barch, & Cohen, 1999; Cohen et al., 1999; Mac-
Donald & Carter, 2003). Failure by schizophrenia patients to
accurately hold online response representations of task demands
and appropriate responses could result in disruption in the gener-
ation of the ERN, as a result of either the unpredictable occurrence
of response competition according to the conflict detection model
or failure to accurately discriminate errors from correct responses,
consistent with the error detection model. Contrary to this notion,
however, results from the present study suggest that the ERN in
schizophrenia patients is sensitive to task instruction condition,
showing increased amplitude when accuracy of responding is
emphasized compared with when speed of responding is encour-
aged. Results of the flanker task manipulation could be interpreted
as providing further evidence of appropriate context maintenance
in schizophrenia given that patients performed even more accu-
rately than comparison participants on interference trials during
the speed condition. It may be that schizophrenia patients adopted
a response strategy of emphasizing accuracy to compensate for
their slower RTs and to avoid the penalty for slow incorrect
responses, thus demonstrating sensitivity to task context. Alter-
nately, the performance difference between groups on interference
trials could be interpreted as reflecting failure on the part of
schizophrenia patients to understand task contingencies or an
inability to modify their behavior by responding quickly without
regard to response accuracy.
Although it is apparent that the present investigation does not
lend overwhelming support for one theoretical model over the
others, the results do suggest various interesting possibilities. The
discussion above also underscores the range and complexity of
issues associated with evaluating self-monitoring in schizophrenia
patients. Yet another factor to consider is the possible effects of
antipsychotic medications on DA activity and, according to the
Holroyd and Coles (2002) model, the generation of the ERN. With
the exception of a small subset of patients who were tested while
Healthy Comparison Participants
(n = 11)
(n = 16)
-1000 100200 300400
instruction condition grouped according to size for healthy comparison participants and schizophrenia patients.
Data displayed are from the FCz site.
Error-related negativity (A) and error positivity (B) waveforms on error trials in the accuracy
ERROR MONITORING IN SCHIZOPHRENIA
unmedicated (Alain et al., 2002) or while their medication status
was uncertain (Bates et al., 2004), ERN studies of schizophrenia
have included only patients receiving antipsychotic medications.
Because these medications act to block DA receptors, they may
diminish the effects of phasic DA release, resulting in an attenu-
ation of the ERN. Experimental evidence for this hypothesized
effect of antipsychotic medication on the ERN is mixed. Acute
administration of haloperidol to healthy participants has been
shown to diminish ERN amplitude (Zirnheld et al., 2004), although
Kopp and Rist (1999) found medication dose not to be related to
ERN amplitude in schizophrenia patients. Moreover, it is unclear
how antipsychotic medications could account for the finding of
increased CRN amplitude detected in the current and prior studies
(Alain et al., 2002; Mathalon et al., 2002).
Another factor that may have resulted in the appearance of a
diminished ERN in schizophrenia patients is differential variability
in the latency of the response-related brain activity between the
two groups. If the variability of the ERN latency from trial to trial
(i.e., “latency jitter”) is greater in schizophrenia patients than in
healthy comparison participants, it would have the effect of
“smearing” the component and reducing the amplitude of the peak
that is observed in averaged data. The differences in ERN latency
observable in the waveforms resulting from the SWDA suggest
that there may indeed have been latency jitter or shift among
schizophrenia patients, particularly on trials associated with
smaller ERNs. It is difficult to conclude, however, that diminished
ERN amplitude in schizophrenia patients is due predominantly to
shifts or jitter in latency when these participants also exhibited
enhanced CRN activity. These issues require careful further study,
perhaps using techniques that allow for adjustment of latency
differences on a single trial basis, before it can be concluded that
the ERN is diminished in schizophrenia as a result of heightened
In contrast to the ERN and consistent with previous findings
(Alain et al., 2002; Bates et al., 2004; Mathalon et al., 2002), the
Pe did not differ between schizophrenia patients and healthy
comparison participants. The observation of greater Pe amplitude
in the speed condition relative to the accuracy condition was
somewhat unexpected. Considering the theorized relationships be-
tween Pe amplitude and subjective evaluation of error significance
(Bush et al., 2000; Falkenstein et al., 2000), it would be reasonable
to expect Pe to be larger in the accuracy instruction condition
because of the importance of minimizing errors for successful task
performance. In the speed condition, however, an additional eval-
uative component may have been present, reflecting reinterpreta-
tion of the meaning of an error within a task context in which the
prepotent behavioral tendency (i.e., to respond correctly) is of
reduced relevance compared with the less dominant tendency to
respond quickly. This additional level of processing may be re-
flected in the increased Pe amplitude observed in the speed in-
Examination of relationships between ERP measures and error-
related behaviors supported the hypothesis that these associations
would be similar in the two groups. Specifically, both schizophre-
nia patients and healthy comparison participants showed increased
rates of error correction following smaller ERNs and Pes and
increased accuracy on trials that followed larger ERNs, although
patients were generally less accurate following errors than were
comparison participants. The overall similarity of the relationships
between the ERN and response-related variables suggests that the
functional significance of the ERN does not differ between the two
groups. It may be that despite weaker error-related activation
detected at the scalp for schizophrenia patients, the neural response
to errors is adequate to engage systems involved in error correction
and response selection. In contrast to our findings, however,
Gehring et al. (1993) reported increased error correction with
larger ERNs as well as a relationship between ERN amplitude and
posterror RT, which was not present for either group in the current
study. In the earlier paper, however, corrected responses were
determined on the basis of forearm flexor electromyography ac-
tivity rather than overt responses used in the present study to
define error correction. This methodological difference likely ac-
counts for the large difference in error correction rates between the
two studies (70% in Gehring et al., 1993, vs. 27% for schizophre-
nia patients and 31% for healthy comparison participants in the
present study) and suggests that partial or weak error corrections,
occurring in the present study but not included in the analyses,
could account for the inconsistency between the findings. The
relationships observed in the current study, nonetheless, are help-
(n = 16)
(n = 11)
% correct on next trial
% of corrected errors
(n = 141)
(n = 101)
% of corrected errors
(n = 101)
(n = 141)
error correction (B) for healthy comparison participants and schizophrenia
patients for small, medium, and large error-related negativities. Error
correction rates for small, medium, and large error positivities (C) for
healthy comparison participants and schizophrenia patients. Error bars
represent standard error.1Data from 2 schizophrenia patients and 1 normal
comparison subject who made fewer than 3 error corrections are excluded.
Rates of response accuracy on trials following errors (A) and
MORRIS, YEE, AND NUECHTERLEIN
ful in understanding the potential significance of ERN reduction in
schizophrenia, suggesting that the effects of diminished ERN and
the associated decrease in posterror accuracy might be apparent in
failures of executive control in schizophrenia.
The possibility of overlap between stimulus-related ERP com-
ponents and the ERN cannot be definitively ruled out by the
analyses conducted in the present research. It should be noted,
however, that ERN size was not associated with RT in either
participant group. If stimulus-locked activity was co-occurring
with the ERN, larger ERNs would be expected on trials with
relatively faster RTs, resulting from the combined N2–ERN. This
pattern was not detected, suggesting that the ERN in the present
study was largely independent of stimulus-related activity.
In sum, results of the present study advance research in the area
of self-monitoring in schizophrenia by demonstrating that schizo-
phrenia patients show diminished differentiation in response-
related ERPs between correct and incorrect responses and that this
pattern persists across task contexts varying in response demand
and reward contingencies. Such anomalies may be a manifestation
of neuroanatomical abnormalities found in the ACC in schizophre-
nia patients as well as disruptions in DA signals to the ACC that
may reflect insensitivity to the state of ongoing events. This deficit
appears to demonstrate some specificity, as Pe amplitude did not
differ between the groups. Despite these abnormalities in ERN
generation, schizophrenia patients exhibited normal modulation of
both the ERN and the Pe in response to alterations in task context.
In addition, ERP-behavior relationships did not differ between the
groups, suggesting that the functional characteristics of these com-
ponents are intact in schizophrenia.
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Received May 6, 2004
Revision received March 3, 2005
Accepted July 27, 2005 ?
MORRIS, YEE, AND NUECHTERLEIN