The time course of visuospatial processing deficits in schizophrenia: An event-related brain potential study.

Event-related brain potentials (ERPs) were recorded during a dot enumeration task so as to investigate electrophysiologic correlates of early visuospatial processing in schizophrenia. Twenty-eight patients having a diagnosis of schizophrenia (n?=?19) or schizoaffective disorder (n?=?9) and 28 controls were tested. Patients showed poorer dot enumeration than did controls and also had markedly reduced early negative ERPs, which began about 150 ms after stimulus onset at the peak of the N1 potential and reached its maximum about 275 ms at the N2 peak. The N1 reduction in patients was greatest over left parietal sites for stimuli in the right visual field. The marked N1 and N2 reductions in patients are supportive of models postulating deficits in early visuospatial attention and allocation of conceptual resources in schizophrenia. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The impact of prestimulus EEG frequency on auditory evoked potentials during sleep onset.

Assessed stimulus relevance vs rarity effects by investigating the N550 to stimuli identified as targets during wakefulness compared to the N550 in response to deviant stimuli with the same probability of occurrence without the target identification. Five Ss (mean age of 22.3 yrs) had their auditory evoked potentials recorded during wakefulness, Stage 1, and Stage 2 non-REM sleep using a 3-tone auditory oddball paradigm. Stage 1 sleep was divided into trials preceded by alpha and those preceded by theta. Results indicate that a negative wave peaking at about 100 ms, N1, displayed a significant decrease in amplitude with the onset of Stage 2 sleep. A later N2 peaked at about 250 ms in the waking state. This changed into a sleep-specific negative wave peaking at 300 ms (N300) at the alpha-theta transition within Stage 1. The P300 displayed a similar shift to become a P450 in Stage 2 sleep. N550 was specific to Stage 2, and was larger in response to rare, rather than frequent stimuli. There was no evidence of any enhancement to relevant rare stimuli compared with irrelevant rare stimuli. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The effects of antipsychotic medication on sequential inhibitory processes.

The authors used a Stroop negative priming paradigm to examine the effects of antipsychotic medication on selective attentional processes. The performance of 14 patients with schizophrenia who were withdrawn from neuroleptic medication was compared with that of 10 medicated patients and 16 matched controls. Results demonstrated an increase in negative priming to normal levels with neuroleptic therapy. In contrast, within-trial interference and facilitation effects appeared to be less sensitive to medication therapy. The sustainment of inhibitory processes over time may differentiate the inhibitory mechanisms of the medication-withdrawn patients from both the medicated patients and the matched controls. The study of sequential inhibitory processes and their response to neuroleptic treatment could be important methods for understanding the temporal parameters associated with inhibition in schizophrenia. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Event-Related fMRI Study of Context Processing in Dorsolateral Prefrontal Cortex of Patients With Schizophrenia.

Context processing is conceptualized as an executive function involved in voluntary, complex actions such as overcoming automatic responses. The present study tested the hypothesis that context-processing deficits in patients with schizophrenia are associated with a dysfunction of left dorsolateral prefrontal cortex (DLPFC). Using event-related functional magnetic resonance imaging (fMRI), 17 controls and 17 medicated patients performed a version of the AX task in which a learned, automatic response had to be inhibited. In controls, left DLPFC activity increased when preparing to overcome an automatic response, whereas patients with schizophrenia showed no differential activation. In controls, context processing appeared to be associated with the differential representation of cues associated with the need to provide top-down support for overcoming automatic responses. This mechanism appeared to be impaired in patients with schizophrenia. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Electrophysiological correlates of emotional responding in schizophrenia.

People with schizophrenia consistently report normal levels of pleasant emotion when exposed to evocative stimuli, suggesting intact consummatory pleasure. However, little is known about the neural correlates and time course of emotion in schizophrenia. This study used a well-validated affective picture viewing task that elicits a characteristic pattern of event-related potentials (ERPs) from early to later processing stages (i.e., P1, P2, P3, and late positive potentials [LPPs]). Thirty-eight stabilized outpatients with schizophrenia and 36 healthy controls viewed standardized pleasant, unpleasant, and neutral pictures while ERPs were recorded and subsequently rated their emotional responses to the stimuli. Patients and controls responded to the pictures similarly in terms of their valence ratings, as well as the initial ERP components (P1, P2, and P3). However, at the later LPP component (500–1,000 ms), patients displayed diminished electrophysiological discrimination between pleasant versus neutral stimuli. This pattern suggests that patients demonstrated normal self-reported emotional experience and intact initial sensory processing of and resource allocation to emotional stimuli. However, they showed a disruption in a later component associated with sustained attentional processing of emotional stimuli. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Emotional valence and reference disturbance in schizophrenia.

The authors examined the impact of emotional valence on reference disturbance in patients with schizophrenia and identified factors that moderate individual differences in this relationship. Thirty-nine patients with schizophrenia were given an interview that elicited speech samples in response to 10 neutral and 6 negatively valenced emotional questions. Speech samples were analyzed using the Communication Disturbances Index (N. M. Docherty, M. DeRosa, & N. C. Andreasen, 1996). Participants were also assessed with the Positive and Negative Symptom Scale (S. Kay, 1991) and a single-trial Stroop task (Stroop, 1935). Group analyses indicated that negative questions elicited more unclear references than neutral questions. Both the severity of disorganization symptoms and selective attention deficits predicted increased reference errors in response to emotional questions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A fair test of the spreading activation hypothesis: a study of affective congruency effects in the Stroop test

It is argued that the Stroop color-naming task is especially suited to investigate affective priming effects in the sense of an automatic spreading of activation to other concepts of the same valence, because (a) the Stroop task is not prone to an explanation of affective congruency effects on the basis of reaction priming or reaction interference, and (b) it is possible to detect specific (fast and efficient stimulus processing due to heightened accessibility) as well as nonspecific (cognitive interference, triggering of global action tendencies) effects of an activation of valenced concepts in the Stroop task. Two experiments were conducted to investigate associative and affective priming effects with the Stroop task. In a first experiment (N = 36, SOA = 300 ms) a standard priming procedure was chosen; the primes were presented without any processing instructions. In a second experiment (N = 48, SOA = 500ms) the primes had to be reproduced after naming the color of the target. In both experiments significant association effects were found for the associative material. For the valenced material no affective congruency effects were found in either experiment. The present results are not compatible with the hypothesis of an automatic affective spreading of activation that was given as an explanation of affective congruency effects in previous studies using different tasks.     

Functional network differences in schizophrenia: a rCBF study of semantic processing

Studies of regional cerebral blood flow in patients with schizophrenia have led to the idea that dysfunctional neurocircuitry may play a role in patients' cognitive deficits. The present PET study was designed to explore this idea by comparing the functional neural networks associated with semantic processing for patients and normal controls through structural equation modeling (path analysis). The patients showed significantly different neural interactions among frontal regions, between the frontal and temporal cortices, and between the frontal lobe and anterior cingulate than controls. These discrepancies were especially striking given there were minimal group differences in task performance. Results suggest that schizophrenia involves a neural abnormality that is evident in functional networks during cognitive performance.     

A time course analysis of Stroop interference and facilitation: Comparing normal individuals and individuals with schizophrenia.

Using randomized stimulus onset asynchrony (SOAs), the authors traced the time course of Stroop interference and facilitation in normal participants and participants with schizophrenia. Unlike earlier findings using blocked SOAs, singular peaks in interference, facilitation, or both occurred at particular SOAs. The peaks of normal participants and participants with schizophrenia differed. Findings are congruent with a model of Stroop performance that posits individual differences in processing speeds of target and nontarget stimulus dimensions, coupled with critical points in response selection. Participants with schizophrenia also showed more overall interference than normal control participants. A second experiment that added a temporal gap between the distractor word and target color obliterated Stroop effects only for individuals with schizophrenia. These findings provide a new empirical basis for models of Stroop effects. They are also consistent with hypotheses about the importance of the prefrontal cortex for working memory and prefrontal dysfunction in schizophrenia. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Inhibitory tagging in inhibition of return is affected in schizophrenia: Evidence from the Stroop task.

L. J. Fuentes, A. B. Vivas, and G. W. Humphreys (see record 1999-10305-007) showed that stimulus processing is affected when stimuli are presented to locations subject to inhibition of return. They argued that activated representations of stimuli presented at inhibited locations are disconnected from their associated responses through an "inhibitory tagging" mechanism occurring in inhibition of return. In the present research, the authors asked whether such a mechanism is affected in people with schizophrenia. Healthy adults and patients with schizophrenia performed a Stroop task in an inhibition of return paradigm. Healthy adults showed a reduction in the Stroop interference when stimuli were presented at inhibited locations, a result that agrees with the inhibitory tagging mechanism hypothesis and replicates previous findings. However, patients with schizophrenia did not show such a reduction, a result suggesting that they have a deficit in inhibitory processing occurring in inhibition of return. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Increased semantic and repetition priming in schizophrenic patients.

Positive and negative priming (PP and NP) in schizophrenia were studied with a lexical-decision task. Probe words, presented 800 ms after the response to the prime (containing a word and a nonword), were either identical to, semantically related to, or unrelated to the prime target word (PP) or to the prime distractor word (NP). Schizophrenic patients displayed stronger semantic and repetition PP than controls after controlling for their slower responses. Significant NP was observed in both groups for word repetition only. The PP findings contrast with results from studies with similar prime-probe intervals but without prime responses. It is proposed that schizophrenic patients, because of impaired (controlled) processes of response selection, strongly benefit from (or rely on) the automatic retrieval of processing episodes containing response information. Related findings indicating automatic response facilitation in schizophrenia are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Context-processing deficits in schizophrenia: Converging evidence from three theoretically motivated cognitive tasks.

To test the hypothesis that the ability to actively represent and maintain context information is a central function of working memory and that a disturbance in this function contributes to cognitive deficits in schizophrenia, the authors modified 3 tasks—the AX version of the Continuous Performance Test Stroop, and a lexical disambiguation task—and administered them to patients with schizophrenia as well as to depressed and healthy controls. The results suggest an accentuation of deficits in patients with schizophrenia in context-sensitive conditions and cross-task correlations of performance in these conditions. However, the results do not definitively eliminate the possibility of a generalized deficit. The significance of these findings is discussed with regard to the specificity of deficits in schizophrenia and the hypothesis concerning the neural and cognitive mechanisms that underlie these deficits. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Fast and slow reaction times and associated ERPs in patients with schizophrenia and controls

A number of studies have examined across-trial averaged late component. Event Related Potentials (EPR) and Reaction Times (RT) in response to multiple target stimuli. In this study, within-trial relatively fast and slow sub averages are additionally examined, in 20 patients with schizophrenia and 20 age and sex matched controls. A conventional auditory oddball paradigm. Across-trial ERP average analysis showed smaller N200 amplitude and delayed latency (but larger P200 amplitude) in patients with schizophrenia compared with controls. Within-trial ERP analysis revealed a number of additional findings. Controls showed distinctive differences in fast compared with slow ERP sub averages (smaller P200 amplitude, increased N200/P300 amplitudes and earlier latencies). The schizophrenic group on the other hand, showed relatively similar fast versus slow subaverages (no differences in P200 amplitude and N200 latency). In addition, between-group (within-trial) analyses highlighted significant differences in earlier stages of processing (compared with across-trial averages) in both fast and slow subaverages (increased N100 amplitude in controls). The complementary within-trial (compared with across-trial) data are interpreted with respect to a possible disturbance in inhibitory function in patients with schizophrenia.     

Distinguishing response conflict and task conflict in the Stroop task: Evidence from ex-Gaussian distribution analysis.

It has been suggested that performance in the Stroop task is influenced by response conflict as well as task conflict. The present study investigated the idea that both conflict types can be isolated by applying ex-Gaussian distribution analysis which decomposes response time into a Gaussian and an exponential component. Two experiments were conducted in which manual versions of a standard Stroop task (Experiment 1) and a separated Stroop task (Experiment 2) were performed under task-switching conditions. Effects of response congruency and stimulus bivalency were used to measure response conflict and task conflict, respectively. Ex-Gaussian analysis revealed that response conflict was mainly observed in the Gaussian component, whereas task conflict was stronger in the exponential component. Moreover, task conflict in the exponential component was selectively enhanced under task-switching conditions. The results suggest that ex-Gaussian analysis can be used as a tool to isolate different conflict types in the Stroop task. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The Stroop task and attention deficits in schizophrenia: A critical evaluation of card and single-trial Stroop methodologies.

The Stroop task, considered by many to be a paradigmatic measure of selective attention, has often been employed to investigate attention deficits in schizophrenia. Card and single-trial versions of this task have yielded different results. In this study both card and single-trial versions were administered to healthy controls (n?=?24) and patients with schizophrenia (n?=?55). No differences in reaction time (RT) interference were found on either version. On the single-trial version, patients showed greater RT facilitation and error rate interference, evidence for a deficit in selective attention. Methodologic and analytic issues that account for the mixed results from earlier card Stroop studies are addressed. It is concluded that single-trial versions provide greater sensitivity to selective attention pathology in schizophrenia. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Iodine-131-MIBG scintigraphy in adults: interpretation revisited?

Functional reorganization of auditory attention was studied in 12 congenitally blind subjects and 12 controls using high-density event-related potentials during a highly focused dichotic listening task. Reaction times for the attend-ear intensity-deviant targets were markedly faster for the blind. Brain activity associated with sustained attention (N1 effect, Nd), and with the automatic detection of deviants in an unattended channel (MMN), did not exhibit reorganization. In contrast, marked plasticity changes were reflected in late auditory attentional processing (attend-ear targets), in the form of a prolonged negativity (200-450 ms post-stimulus) that was absent in the sighted subjects. The plasticity changes in the blind had a time course indicating progressive recruitment of parietal and then occipital regions, providing new evidence for cross-modal sensory reorganization in the blind.     

Anterior cingulate activity and level of cognitive conflict: Explicit comparisons.

The role of anterior cingulate cortex (ACC) in attention is a matter of debate. One hypothesis suggests that its role is to monitor response-level conflict, but explicit evidence is somewhat lacking. In this study, the activation of ACC was compared in (a) color and number standard Stroop tasks in which response preparation and interference shared modality (response-level conflict) and (b) color and number matching Stroop tasks in which response preparation and interference did not share modality (non-response-level conflict). In the congruent conditions, there was no effect of task type. In the interference conditions, anterior cingulate activity in the matching tasks was less than that in the standard tasks. These results support the hypothesis that ACC specifically mediates generalized modality-independent selection processes invoked by response competition. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Is the donut in front of the car? An electrophysiological study examining spatial reference frame processing.

Notes that the process of describing an object's location relative to another object results in ambiguity. How do people handle this ambiguity? The present 3 studies, using a total of 88 undergraduates, examined spatial language processing when use of different reference frames results in ambiguity. This study investigated whether electrophysiological measures of cognitive processing may elucidate underlying reference frame processing; in particular, the authors were interested in semantic integration. Electrophysiological results show a larger N400, peaking between 300 and 375 ms, when the intrinsic frame was not used. Behavioral results mirrored this finding, indicating a reduced cognitive processing requirement for the intrinsic reference frame. Previous work has not definitively tied spatial reference frame processing to specific electrophysiological components and their associated cognitive processes. Although the N400 peak seen in this data is early, additional work supports the N400 interpretation, thereby linking spatial frame processing to semantic integration. Results are discussed within the larger context of spatial reference frame processing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The backward masking red light effect in schizophrenia: Relationship to clinical features and neurocognitive performance.

The “backward masking red light effect” involves a change in visual backward masking performance with a red (compared with a green or gray) background that is in the opposite direction relative to nonpsychiatric controls. This effect has been previously reported in individuals with schizophrenia, their first-degree relatives, and a schizotypy sample. The current study provides the first examination of the relationship of this effect with clinical and neurocognitive measures in a new sample of higher functioning patients with schizophrenia. A location backward masking by pattern task was administered to 16 outpatients with schizophrenia and 21 nonpsychiatric controls. The task was presented on red, green, and gray backgrounds. There was a significant group by color interaction at the 60-ms stimulus onset asynchrony: Participants with schizophrenia tended to decrease accuracy with a red (compared with a gray) background, whereas controls tended to increase accuracy. This interaction remained significant after covarying for baseline (gray) backward masking accuracy. In the schizophrenia patients, a decrease in backward masking accuracy to the red background was correlated with more negative symptoms, lower estimated premorbid IQ, and greater color–word Stroop interference but was not related to positive or disorganized symptoms, age of onset, duration of illness, digit symbol coding performance, or baseline (gray) backward masking accuracy. In contrast, there was no relationship between the red light change score and any of the neurocognitive variables in the control group. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Making sense of sentences in schizophrenia: Electrophysiological evidence for abnormal interactions between semantic and syntactic processing.

Event-related potentials to critical verbs were measured as patients with schizophrenia and healthy controls read sentences word by word. Relative to their preceding context, critical verbs were (a) congruous, (b) incongruous and semantically unrelated to individual preceding words (pragmatic-semantic violations), (c) incongruous but semantically related to individual preceding words (animacy-semantic violations), or (d) syntactically anomalous. The N400 was modulated normally in patients, suggesting that semantic integration between individual words within sentences was normal in schizophrenia. The amplitude of the P600 to both syntactic and animacy-semantic violations was reduced in patients relative to controls. The authors suggest that, in schizophrenia, an abnormality in combining semantic and syntactic information online to build up propositional meaning leaves sentence processing to be primarily driven by semantic relationships between individual words. (PsycINFO Database Record (c) 2010 APA, all rights reserved)