Detection of interaural delay in high-frequency sinusoidally amplitude-modulated tones, two-tone complexes, and bands...

Listeners' ability to detect interaural temporal disparities (ITDs) was investigated for 160-ms, sinusoidally amplitude modulated (SAM) tones, two-tone complexes, and bands of noise at center frequencies of 4, 8, or 12 kHz. Rates of modulation for the 100%-modulated SAM tones and frequency separation for the equal-amplitude, two-tone complexes ranged from 32-768 Hz, depending on center frequency. Noise bandwidths ranged from 50-2000 Hz, also depending on center frequency. The data indicate, consistent with previous results, that sensitivity to ITD with the SAM and two-tone complexes decreases as the rate of envelope fluctuation increases beyond about 400 Hz. The decline in performance is not due simply to reduced depths of modulation produced by critical-band-like filtering, but is consistent with an inability to "follow" or encode high rates of modulation. For bands of noise, sensitivity to ITD was relatively constant as a function of bandwidth. Generally, sensitivity to ITD decreased as center frequency was increased from 4 to 8 kHz, but the relations among the data were essentially unchanged. Increasing the center frequency to 12 kHz resulted in very poor performance.