Detectability of a pulsed tone in the presence of a masker with time-varying interaural correlation

Abstract

Detectability of a filtered probe tone (250, 500 or 1000 Hz) was measured in the presence of a narrowband Gaussian masker centered at the signal frequency. The signal was interaurally phase-reversed (S .pi.), and the masker''s interaural correlation varied sinusoidally between +1.00 (NO) and -1.00 (N .pi.) at a variable rate (fm = 0-4 Hz). The signal was presented at various points on the masker''s modulation cycle. For 0 Hz modulation (fixed interaural correlation) signal threshold decreased monotonically as the masker''s interaural correlation was changed from -1.00 to +1.00 (by a total of about 20, 16 and 8 dB, respectively, for 250, 500 and 1000 Hz signals). For fm > 0 the function relating signal threshold to the masker''s interaural correlation at the moment of signal presentation became progressively flatter with increasing fm for all signal frequencies. For fm = 4 Hz the function was flat; there was no measurable effect of masker interaural correlation on signal detectability. Estimates of minimum binaural integration time based on these data ranged from 44-243 ms, supporting previous studies which have noted the binaural system''s relative insensitivity to dynamic stimulation. The estimated time constants were approximately twice at large at 250 Hz as at 500 Hz, indicating human observers could follow binaural fluctuations better at 500 Hz. The time-constant estimates at 1000 Hz were not sufficiently reliable to permit comparisons with the lower-frequency data.