Pupillary dilation to simple vs. complex tasks and its relationship to thought disturbance in schizophrenia patients

Task-evoked pupil dilation is a measure of attentional allocation. Schizophrenia patients have pupil dilation deficits during high cognitive load tasks, which have been attributed to attentional resource deficits. Moreover, this attentional impairment is thought to be linked to cognitive fragmentation and thought disturbance. Previous attempts to associate attentional deficits to thought disturbance have typically measured these domains at distinct times, incorrectly assuming that both are static variables. In this study, we compared the pupil dilation of 24 schizophrenia patients to 15 non-patients during complex (Rorschach blots) vs. simple visual (line drawings) processing tasks while simultaneously assessing their verbal responses for thought disturbance. Schizophrenia patients' dilation to the simple stimuli was similar to the non-patients; however, they demonstrated significantly less dilation to the complex stimuli. Reduced dilation was also significantly correlated with reduced response complexity and more severe thought disorder. The results suggest that, in the face of complex problem-solving situations, greater attentional impairment and cognitive overload in schizophrenia is associated with higher levels of disturbed and impoverished thinking. These findings support the 'resource limitations hypothesis' of schizophrenia and underscore the utility of a simultaneous paradigm when studying the relationship between attentional deficits and thought disturbance.