Event-related potential study of illusory contour perception in schizophrenia

Systematic review of visual illusions in schizophrenia

Visual illusions have long been used as tools to investigate sensory-perceptual deficits in schizophrenia. Recent conflicting accounts have called into question the assumption of abnormal illusion perception in patients and, therefore, the validity of this approach. Here, we present a systematic review of the current evidence regarding visual illusion perception abnormalities in patients with schizophrenia. Relevant publications were identified by a systematic search of PubMed, Literatura LILACS, PsycINFO, Embase, Scopus, Cochrane Central Register of Controlled Trials (CENTRAL), IBECS, BIOSIS, and Web of Science. Forty-five studies were selected which included illusions classified as 'Motion illusions', 'Geometric-optical illusions', 'Illusory contours', 'Depth inversion illusion', and 'Non-specific'. There is concordant evidence of abnormal processing of illusions in patients for most categories, especially in facial Depth Inversion and Müller-Lyer illusions. There were significant methodological disparities and shortcomings, but risk of bias was overall low for individual studies. The usefulness of visual illusions as tools in clinical settings as well as in basic research may be contingent on significant methodological refinements.

EEG findings of reduced neural synchronization during visual integration in schizophrenia

Schizophrenia patients exhibit well-documented visual processing deficits. One area of disruption is visual integration, the ability to form global objects from local elements. However, most studies of visual integration in schizophrenia have been conducted in the context of an active attention task, which may influence the findings. In this study we examined visual integration using electroencephalography (EEG) in a passive task to elucidate neural mechanisms associated with poor visual integration. Forty-six schizophrenia patients and 30 healthy controls had EEG recorded while passively viewing figures comprised of real, illusory, or no contours. We examined visual P100, N100, and P200 event-related potential (ERP) components, as well as neural synchronization in the gamma (30-60 Hz) band assessed by the EEG phase locking factor (PLF). The N100 was significantly larger to illusory vs. no contour, and illusory vs. real contour stimuli while the P200 was larger only to real vs. illusory stimuli; there were no significant interactions with group. Compared to controls, patients failed to show increased phase locking to illusory versus no contours between 40-60 Hz. Also, controls, but not patients, had larger PLF between 30-40 Hz when viewing real vs. illusory contours. Finally, the positive symptom factor of the BPRS was negatively correlated with PLF values between 40-60 Hz to illusory stimuli, and with PLF between 30-40 Hz to real contour stimuli. These results suggest that the pattern of results across visual processing conditions is similar in patients and controls. However, patients have deficits in neural synchronization in the gamma range during basic processing of illusory contours when attentional demand is limited.

Classification of schizophrenia patients and healthy controls using p100 event-related potentials for visual processing

The study of event-related potentials (ERPs) is capable of elucidating the abnormalities in brain network dynamics relevant to the information-processing deficits in schizophrenia patients. In contrast to P50 and P300 ERPs, however, the results of P100 ERP studies in schizophrenia patients are less consistent. We have previously reported that P100 amplitudes did not differ significantly between patients with schizophrenia and healthy subjects. This result raised a question as to whether P100 ERPs carry information on brain network dynamics in schizophrenia patients that is distinct from normal controls. To answer this question, in this study we performed discrimination analysis on the P100 data. The rate of correct classification of patients and controls was high (80-90% depending on stimulus categories), indicating that patients have spatial patterns of P100 amplitudes that are distinguishable from those in healthy subjects. To further explore this possibility, we performed principal component analysis on the P100 data. For the patients, the first principal component represented global activity, the second component represented the reciprocal anterior-posterior activation, and the third component represented the hemispheric reciprocity in activity. The first and second components were similar to those of the control group; however, the third component in control subjects showed activation of the center versus anterior and posterior regions. This result is consistent with the notion of abnormalities in hemispheric asymmetries during the processing of sensory information in schizophrenia. In conclusion, this ERP study demonstrated that P100 amplitudes have information that can successfully classify patients and controls.

Neurophysiological correlates of configural face processing in schizotypy

BACKGROUND

Face processing impairment in schizophrenia appears to be underpinned by poor configural (as opposed to feature-based) processing; however, few studies have sought to characterize this impairment electrophysiologically. Given the sensitivity of event-related potentials to antipsychotic medications, and the potential for neurophysiological abnormalities to serve as vulnerability markers for schizophrenia, a handful of studies have investigated early visual P100 and face-selective N170 in "at risk" populations. However, this is the first known neurophysiological investigation of configural face processing in a non-clinical schizotypal sample.

METHODS

Using stimuli designed to engage configural processing in face perception (upright and inverted Mooney and photographic faces), P100 and N170 components were recorded in healthy individuals characterized by high (N = 14) and low (N = 14) schizotypal traits according to the Oxford-Liverpool Inventory of Feelings and Experiences.

RESULTS

High schizotypes showed significantly reduced N170 amplitudes to inverted photographic faces. Typical N170 latency and amplitude inversion effects (delayed and enhanced N170 to inverted relative to upright photographic faces, and enhanced amplitude to upright versus inverted Mooney faces), were demonstrated by low, but not high, schizotypes. No group differences were shown for P100 analyses.

CONCLUSIONS

The findings suggest that neurophysiological deficits in processing facial configurations (N170) are apparent in schizotypy, while the early sensory processing (P100) of faces appears intact. This work adds to the mounting evidence for analogous neural processing anomalies at the healthy end of the psychosis continuum.