Temporal extrapolation of unimodal and multimodal stimulus sequences in retarded and nonretarded persons.

Retarded adolescents, CA-matched nonretarded adolescents, and MA-matched nonretarded children attempted to match the repetition rate of 10-second stimulus sequences presented under four modality switching conditions and at two pusle frequencies. Error magnitudes were least for the CA-matched subjects and under the faster pulse rate increased from the no-switching to maximum-switching condition in all groups. Error increases from the no-switching to maximum-switching condition were preponderantly underestimations. No differences between groups were obtained for a switching condition in which the modality-sequence pattern was aperiodic. A hypothesis of longer psycholoical refractory periods in retarded adolescents was rejected in favor of one explaining their inferior performance on sequential enumeration and tracking tasks in terms of inefficient organizational abilities.