Prepreparatory interval effects on redundancy deficit reaction time patterns in schizophrenic and normal subjects using the embedded-set procedure.

The relative influence of genuine "redundancy deficit" and the artifactual effects of prepreparatory interval on measures of the redundancy deficit reaction time pattern (faster reaction time on trials with long preparatory intervals when the interval is of predictable vs. unpredictable length) was investigated in a study using the "embedded-set" procedure. Twenty normal and 20 schizophrenic subjects received two series of reaction time trials containing embedded sets (blocks) of four isotemporal 1-, 3-, and 7-second trials. The 7-second blocks (the blocks of interest for the calculation of redundancy deficit) were preceded by long prepreparatory intervals in one condition and by short intervals for the second. Each subject received both conditions, with the orders counterbalanced. The results indicated redundancy deficit for both schizophrenics and normals with short prepreparatory intervals, but in neither group with long prepreparatory intervals. This suggests that redundancy deficit in the embedded-set procedure (which is normally heavily biased with short prepreparatory intervals) may be more related to the enhancing effect of short prepreparatory intervals on the first (unpredictable) trial of the set than to impaired performance on the fourth (predictable) trial. The finding of similar effects in both schizophrenic and normal subjects raises questions about the specificity of redundancy deficit to schizophrenic reaction time performance. The results were discussed with reference to the original "long run" reaction time procedure for studying the same phenomenon, and theoretical issues related to the interpretation of results from the two procedures were considered.