TEMPORAL-ORDER DISCRIMINATION FOR SELECTED AUDITORY AND VISUAL STIMULUS DIMENSIONS

Thresholds for the discrimination of temporal order were determined fa r selected auditory and visual stimulus dimensions in 10 normal-adult volunteers. Auditory stimuli consisted of binary pure tones varying in frequency or sound pressure level, and visual stimuli consisted of bi nary geometric forms varying in size, orientation, or color. We determ ined the effect of psychophysical method and the reliability of perfor mance across stimulus dimensions. Using a single-track adaptive proced ure, Experiment 1 showed that temporal-order thresholds (TOTs) varied with stimulus dimension, being lowest for auditory frequency, intermed iate for size, orientation, and auditory level, and longest for color. Test performance improved over sessions and the profile of thresholds across stimulus dimensions had a modest reliability Experiment 2 used a double-interleaved adaptive procedure and TOTs were similarly order ed as in Experiment 1. However, TOTs were significantly tower for init ially ascending versus descending tracks. With this method, the reliab ility of the profile across stimulus dimensions and tracks was relativ ely law. in Experiment 3, psychometric functions were obtained for eac h of the stimulus dimensions and thresholds were defined as the interp olated 70.7% correct point. The relative ordering of TOTs was similar to those obtained in the first two experiments. Non-monotonicities wer e found in some of the psychometric functions, with the most prominent being for the color dimension. A cross-experiment comparison of resul ts demonstrates that TOTs and their reliability are significantly infl uenced by the psychophysical method. Taken together, these results sup port the notion that the temporal resolution of ordered stimuli involv es perceptual mechanisms specific to a given sensory modality or submo dality.