Detectability of varying interaural temporal differencesa)

Abstract

Detectability and salience of time-varying interaural temporal differences (IATD) were measured in 3 experiments by determining observers'' ability to follow the temporal fluctuations of a moving stimulus, a 3000 Hz low-pass computer-generated noise presented binaurally with a sinusodially varying IATD. In the first 2 experiments the peak IATD (.DELTA.t, the extent of movement) was manipulated to determine, for different rates of interaural variation (fm), threshold discriminability of the moving stimulus from a reference (2-interval forced-choice paradigm). The nonmoving reference was either a dichotic noise stimulus (experiment 1) or a dichotic noise stimulus whose image width matched that of the excursions traced by the moving stimulus (experiment 2). Threshold .DELTA.t in the 2 experiments were similar, increasing from 30 .mu.s at fm = 0 Hz to 90 .mu.s at fm = 20 Hz, indicating a low-pass characteristic for the binaural system. Thresholds decreased again for fm > 50 Hz, apparently because at these high rates of movement observers used other cues than the varying IATD to perform the task. The 3rd experiment measured the threshold of a binaural click in the presence of a moving noise masker as a function of fm and of the instantaneous IATD of the masker when the click was presented. As fm increased, click threshold gradually became independent of the masker''s instantaneous IATD, again suggesting a low-pass characteristic for the binaural system; there was some evidence for a lag in the system''s response for fm < 5 Hz. The data from the 3 experiments were discussed in terms of results from other studies which investigated temporal aspects of the binaural system. The existence of movement detectors in the auditory system was discussed.