Event-Related Potential Component Analyses of the Illusory Contour Task in Patients with Psychosis
Background: Perceptual organization, the process of deriving meaningful patterns and object representations based on complex visual information supplied by the eyes, has been demonstrated to be impaired in patients with schizophrenia. The ability to visually complete shapes in the absence of complete stimuli can be assessed by the illusory contour task, which employs Kanizsa shape stimuli.
Methods: Behavioral and electrophysiological data during the task were obtained from three diagnostic groups of individuals with psychosis; schizophrenia (SCZ, n = 13), schizoaffective (SZa, n = 14), and bipolar (BP, n =14). Of the 41 patients who provided data in the behavioral task, 28 participants were eligible for EEG collection. Event-related potential (ERP) component analyses were conducted for two early components, P1 (85-130 ms) and N1 (130-230 ms), and a later component thought to be implicated in closure processes, Ncl (260-330 ms).
Results: Patients performed poorly in the illusory condition compared with the fragmented (control) condition. SCZ and SZa, but not BP, had significantly diminished Ncl responses. In all three ERP components, amplitude and shape completion predicted scores in the SAPS Reality Distortion symptom domain, but not in the SAPS Formal Thought Disorder or SANS Negative domain.
Discussion: patients with psychosis demonstrate impaired visual shape completion. Differences in Ncl amplitude between diagnostic groups suggest specific impairments unique to SCZ and SZa patients. Diminished brain responses and poor task performance may be associated with increased symptoms of reality distortion, such as hallucinations and delusions.