Stimulus persistence in retarded and nonretarded children: a signal detection analysis

Nine institutionalized EMR and 9 equal-CA nonretarded children were tested on a visual backward masking task. Signal detection analysis was used to separate the sensory and nonsensory aspects of behavior, and the presentation of stimuli was randomized to minimize the formation of effective strategies. Two sets of instructions, strict and lenient, and two stimulus durations, 10 and 30 msec, were used in a repeated measure design. No differences were found between the intelligence groups on interstimulus interval threshold or measures of stimulus sensitivity, criterion placement, and false positive rate. Retarded subjects showed significantly greater intersubject variability in criterion placement but failed to raise their criterion in response to strict instructions. The results suggest that (a) stimulus-trace concepts of retardation have been confounded by retarded subjects' inability to compete effectively with nonretarded subjects in the experimental situation, and (b) signal detection procedures are a useful alternative to traditional psychophysical techniques in such comparative research.