Visual Deficits in Contrast and Depth Perception in Psychotic Disorders: Implications for a Neural Hierarchy.

Background: A key challenge in understanding the neurobehavioral mechanisms of psychotic disorders (PD) is identifying the level and interactions of the affected brain regions. The early visual system, with its hierarchical structure, offers a model for studying such mechanisms. Specifically, variations in visual contrast are detected as early as in the retina, whereas binocular depth perception emerges at a higher level, in visual cortex. Comparing these processes within individuals can provide insights into the mechanisms and progression of perceptual deficits in PD.

Methods: Psychophysical sensitivity to stimulus contrast and binocular disparity were assessed in 53 PD subjects and 58 demographically-matched healthy control (HC) subjects. Across the two tasks, the physical features of the stimuli were matched except for the primary variable of interest. Psychometric functions were fitted to the performance of each subject, and the normalized area under the psychometric curves quantified the average performance across stimulus strengths.

Results: The PD group showed significantly impaired performance in both visual contrast detection (p<0.007) and binocular depth perception (p<0.021), compared to the HC group. In the PD but not the HC group, the performance across the two tasks were correlated with each other. A direct comparison revealed a more pronounced deficit in depth perception compared to contrast detection in the PD group. Differences in psychometric parameters (i.e. threshold, flatness, and lapse rate) revealed additional cognitive and attentional dysfunctions in the PD group.

Conclusion: These findings provide evidence for a progressive accumulation of deficits through the visual hierarchy in psychosis.