The impact of context processing deficits on task-switching performance in schizophrenia.

The prefrontal cortex (PFC) has been described as important for maintaining and implementing contextual information in the service of goal-oriented behavior. Accordingly, impairments in context processing are thought to underlie cognitive deficits associated with schizophrenia, a clinical disorder that has been linked to PFC dysfunction (Servan-Schreiber et al., 1996). However, task switching, a cognitive ability linked to PFC function, has not been consistently impaired in schizophrenia. In this experiment, we assessed whether task-switching performance would be selectively impaired for patients when context demands were high. In the rule-switching condition, a switch required the updating of the relevant task response rules whereas perceptual switching did not entail a switching of contextual information. Instead, a perceptual switch entailed a shift of visuospatial attention to the relevant feature. A second goal was to determine whether potential deficits in context switching would be observed in schizophrenia even in situations when these patients do not need to overcome a prepotent response. Studies of context processing have typically required patients with schizophrenia to use contextual rules to overcome prepotent response tendencies whereas our switching paradigm did not require the inhibition of a competing response. Patients were much slower to switch tasks than controls when contextual rules switched from one trial to the next whereas their performance was intact when the switch occurred between different feature sets and contextual demands were low. Our results demonstrate that context processing deficits are observable in schizophrenia even when there is no prepotent response tendency to inhibit. Moreover, our results suggest that PFC impairments influence performance primarily when patients are required to switch the application of one explicit rule to another.