Short term memory for numerousness in schizophrenic young adults.

The short term memory of schizophrenics for random dot patterns was examined by a delayed comparison procedure. In experiment 1, the 10 schizophrenics and 10 normals compared a fixed dot pattern (standard) with a variable dot pattern (compairson) appearing 2 or 8 seconds later and decided whether the comparison stimulus had "more" or "less" dots than the standard. Memory strength, indexed by the d' value of signal-detection theory, showed neither group difference nor decay over time. In experiment 2, the interstimulus interval was filled with an unjudged dot pattern (storage interference), and the standard stimulus followed the variable comparison stimulus (encoding difficulty). The memory strength of 17 schizophrenics and 17 normals was severely impaired, and their memory strength weakened over time, but again, no group differences were found. In both experiments, the two groups showed a strong bias (beta) in underestimating the first (to-be-remembered) stimulus. It was concluded that schizophrenics' short term perceptual memory for nonverbal stimuli remains good.