Short-term memory for a pure-tone stimulus among mentally retarded and nonretarded persons

Two studies were conducted to determine whether short-term memory performance differences between mentally retarded and nonretarded persons can be attrubuted to the operation of structural features, as contrasted with strategic control processes. The task—discrimination of intensity differences between two pure tones—was selected as one which would minimize specific strategy utilization. In the first experiment normal children, normal adults, and retarded adults were presented with a standard tone and then a comparison tone after an interval of 1, 5 or 10s. Difference limens and constant errors were computed over a substantial number of trials. Measures of intra-individual variability were also obtained. Clear age and IQ-related threshold differences were obtained. Difference thresholds increased over intervals for all groups. However, the critical interaction that would support a theory of differential decay of the memory trace was not obtained. A second experiment, procedurally similar to the first, was conducted using signal detection methodology. The major findings were: (a) groups differed in sensitivity (d′); (b) d′ decreased with increasing separation of standard and comparison tones; (c) d′ increased as the intensity differences between standard and comparison tones increased; and (d) retarded subjects did not alter response bias to changing task requirements Again, however, the interaction of groups and retention interval was not significant. Intelligence and age-related differences in the task occur early in the information processing sequence and appear to be of a perceptual nature.