The clinical translation of a measure of gain control: the contrast-contrast effect task

Abstract

The goal of the current project was to further develop a measure of gain control--the Contrast-Contrast Effect (CCE)--for use in clinical studies of schizophrenia. The CCE is based on an illusion in which presenting a medium contrast patch surrounded by a high-contrast patch induces individuals to perceive that center patch as having lower contrast than when the patch is presented in isolation. Thus, in the CCE, impaired gain control should lead to more accurate perceptions of the center patch. We tested 132 individuals with Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, schizophrenia or schizoaffective disorder and 130 demographically similar healthy controls. The results indicated that the CCE effect can be obtained with standard equipment, simplified scoring, and a short interstimulus interval (100 ms), revealing a robust suppression of perceived contrast of the center patch when surrounded by a high-contrast annulus. Furthermore, we found a significant reduction in the effect of the high-contrast surround among individuals with schizophrenia, though the effect size was smaller than original reported by Dakin. However, when we eliminated subjects who performed poorly on "catch" trials that controlled for off-task performance, the reduced surround effect among patients was no longer significant in the main analyses. Importantly, this suggests that at least part of the reduced surround effect (if not all) in schizophrenia could be attributable to impaired attentional mechanisms that contribute to off-task performance. Additional analyses suggested that the length of the task could be shortened without losing power to detect surround effects in healthy individuals.

Fig. 1.

Illustration of the Contrast-Contrast Effect (CCE) paradigm. On each trial, participants are presented with a patch, either in isolation (left bottom patch) or surrounded by a high-contrast annulus (95% contrast, left top patch) for 500 ms. After either 1000 or 100 ms, participants were then presented with a single patch in isolation (example patches on right) and asked to decide whether the first or second patch had higher contrast. When the first patch was presented with the high-contrast surround, it was made clear to participants that the comparison was between the center patch and the subsequent patch.

Fig. 2.

Graph illustrating the mean contrast of the comparison patch on the last 10 trials of each stream, averaged across the 4 streams, separately for each task condition. Error bars are SEs.