The use of temporal and amplitude cues by schizophrenics, psychiatric controls, and aged normals in auditory lateralization.

The present study investigated the ability of paranoid and nonparanoid schizophrenics, psychiatric controls, and aged controls to use temporal and amplitude cues to make judgments about the direction of auditory stimuli on an auditory lateralization task. Twelve subjects in each group were tested on three lateralization conditions: temporal--fixed, temporal--shifted, and amplitude. The subjects' task was to identify the apparent direction (left or right) of a train of clicks presented binaurally through headphones. In the temporal conditions interaural click onset differences provided the lateralization cues, while in the amplitude condition interaural amplitude differences provided the cues. In the temporal--fixed condition, onset asynchrony was constant for the duration of each stimulus. In the temporal--shifted condition, onset asynchrony was introduced midway through each stimulus presentation. A forced-choice random staircase method was used to determine each subject's 70 per cent correct response threshold. Results indicated that paranoids had particular difficulty with the temporal--fixed condition relative to the temporal--shifted condition. The opposite was true for the nonparanoids. Both control groups showed no significant difference in performance on the two temporal conditions. Psychiatric controls performed significantly better than aged controls in both the fixed and shifted conditions. There were no significant differences among groups on the amplitude condition. The data were discussed in terms of schizophrenics' clinical symptoms and previous perceptual research with schizophrenics.