DETECTION OF ANTIPHASIC SINUSOIDS ADDED TO THE ENVELOPES OF HIGH-FREQUENCY BANDS OF NOISE

Listeners' sensitivities to antiphasic sinusoids added to the envelopes of high-frequency bands of noise were measured as a function of the frequency of the sinusoid and the bandwidth of the masking noise. The stimuli were constructed such that the added sinusoid produced interaural intensitive differences (IIDs) that fluctuated at a rate that was equal to the frequency of the sinusoid and was independent of the bandwidth of the masking noise. The data indicated that performance was relatively unaffected by the rate of modulation for rates between 5 and 160 Hz. Greater rates of modulation resulted in substantial degradations of performance. The results are pertinent to Zurek and Durlach's (1987) suggestions concerning the relatively small binaural masking-level differences typically measured with high-frequency signals and broadband maskers in the N0S(pi) configuration. Specifically, it appears that listeners' performance is greatly affected by an insensitivity to rapidly fluctuating IIDs but is relatively unaffected by any 'spectral interference' produced by masking energy beyond the monaural critical band. Interestingly, the data corroborate Grantham's (1984) insightful proposal that the binaural system may possess two independent averaging mechanisms, one for the processing of interaural temporal disparities (ITDs) and the other for the processing of IIDs.