Abstract:
Data are presented on experiments that compare binaural sensitivity to sinusoidal amplitude and frequency modulation (SAM and SFM). Among the stimulus parameters examined are carrier frequency (3--8 kHz), modulation rate (25--800 Hz), and depth ((beta)=0.1--2). Observers are most sensitive to interaural delays in SAM tones at rates of about 50 to 300 Hz, while for SFM tones, best sensitivity occurs at rates of 200 to 400 Hz. Interaural-delay thresholds for SFM tones are quantitatively predicted from a stochastic AM-envelope model whose parameters are uniquely determined from data on SAM tones. The model uses short-term cross-correlation analysis of Hilbert envelopes at the outputs of a bank of peripheral bandpass filters. The envelopes are subsequently convolved with the impulse response of a low-pass FIR filter, followed by additive noise, and a decision device whose output is a position estimate. The expected value and variance of estimates are stochastically approximated, from which the model adaptively tracks the 0.707 probability of a correct response (d[sup ']=0.78) on the observer's forced-choice psychometric function. [Work supported by NIH.]