Kanizsa in  Psychosis

A Kanizsa illusory contour (or subjective contour) is a visual phenomenon where the brain perceives a sharp, distinct edge or boundary despite there being no actual change in luminance, color, or texture across that boundary

Deficits in illusory contour perception (i.e. resistance to illusions) are known in chronic schizophrenia. However, evidence for impairments in Clinical High Risk for Psychosis (CHR-P) and First Episode Psychosis (FEP) patients groups is less explored. 

In this work, we examined / recorded neuromagnetic responses to Kanizsa squares to establish whether illusory contour responses are impaired during early stage psychosis. 

This work is still in progress. 

Executive Summary: Perceptual organization is disrupted in schizophrenia, but whether abnormalities arise during early illusory-contour formation or later global integration remains unclear. We reviewed Kanizsa illusory-contour processing in schizophrenia, emphasizing evidence from early-stage illness. Evidence does not support a uniform failure of illusory-contour formation. Patients can retain sensitivity to contour formation while showing impaired use of completed contours for global shape discrimination. Critically, shape-completion deficits are already pronounced at first episode and comparable to later-stage schizophrenia. Schizophrenia may involve a hierarchical perceptual-organization deficit: early neural processing is altered but remains sufficient for contour formation, whereas abnormalities become prominent during global integration and higher-order utilization. Longitudinal studies are needed to determine whether this deficit precedes psychosis onset.

Title: "When Does Perceptual Completion Break Down in Schizophrenia? A Review of Kanizsa Illusory-Contour Processing Across Illness Stages"

Background

Perceptual organization is disrupted in schizophrenia, but it remains unclear whether abnormalities in Kanizsa illusory-contour perception reflect impaired early contour formation or later integration of contours into coherent object representations, and whether these abnormalities are already present near illness onset. Kanizsa stimuli provide a useful means of dissociating local contour interpolation from subsequent global shape completion. We reviewed behavioural and neurobiological studies of Kanizsa/illusory-contour processing in schizophrenia to determine the processing stage at which abnormalities emerge and evaluate evidence for their presence in early-stage illness.

Methods

Studies investigating Kanizsa illusory contours or closely related perceptual-closure processes in schizophrenia were identified from the published literature. Studies using behavioural psychophysics, EEG/ERP, oscillatory electrophysiology, fMRI, or causal neural perturbation were included. Genetic association studies using perceptual-organization performance primarily as a phenotype were excluded. Ten studies met these criteria. Findings were synthesized according to illness stage and processing level, distinguishing early contour formation from later global shape integration and higher-order attentional processing.

Results

Across studies, the evidence did not indicate a uniform failure to generate illusory contours. Behavioural psychophysics demonstrated relatively preserved sensitivity to illusory-contour formation but impaired discrimination and completion of global shapes. Critically, first-episode patients showed shape-completion deficits comparable to those observed in later-episode schizophrenia, suggesting that this impairment is already established near illness onset. Electrophysiological findings qualified this behavioural preservation: early visual responses showed abnormalities in timing and spatial modulation, while EEG studies identified reduced or altered gamma-band synchronization during later integrative or response-related processing. Neuroimaging implicated abnormal dorsal-attention-network engagement and disrupted interactions between attentional and visual systems. Causal perturbation of the dorsal visual pathway in healthy participants produced schizophrenia-like impairment of perceptual closure without disrupting illusory-contour discrimination.

Discussion

The literature supports a hierarchical rather than unitary account of perceptual-organization dysfunction in schizophrenia. Initial interpolation of Kanizsa contours can remain sufficiently intact to support contour perception, whereas subsequent integration and effective use of these representations for global shape perception are disproportionately compromised. Importantly, behavioural evidence indicates that this higher-order deficit is already prominent at first episode. Abnormal neural timing, synchronization, and dorsal attention–visual interactions may provide candidate mechanisms linking relatively preserved contour formation to impaired global perceptual organization. Longitudinal EEG/MEG and neuroimaging studies in clinical-high-risk and first-episode populations are needed to establish when these abnormalities emerge relative to psychosis onset.

Here is my poster summarising this literature review