Decision processes and the slowing of simple choices in schizophrenia

Individuals diagnosed with schizophrenia have slowed response times (RT). We examined the role of decision processes in the slowing of simple choice responses. We updated Schatz's (1998) meta-analysis of deficits in speed and extend it to systematically examine the effects of schizophrenia on choice accuracy. We then report an experiment requiring decisions about motion direction, which we analyzed using an evidence accumulation model of choice, the linear ballistic accumulator (LBA; Brown & Heathcote, 2008). By simultaneously taking into account all aspects of behavior, the LBA was more sensitive to deficits than mean RT or accuracy alone. It also identified the 2 underlying causes of slowing: more cautious decisions (i.e., requiring more evidence before making a decision) and perceptual deficits. The schizophrenia group displayed strong sequential effects that were captured by the response on the previous trial affecting the relative amount of evidence required for choice in the LBA. These results illustrate that evidence accumulation models provide a sensitive tool that can be used to identify the cognitive mechanisms causing slowing in schizophrenia.