Abstract:
Thresholds were measured for a 6-kHz sinusoid, temporally centered in a 500-ms masker which was either a bandpass Gaussian noise (20 dB SPL spectrum level) or a 6-kHz sinusoid (40 dB SPL). A notched noise centered on 6 kHz prevented the use of off-frequency cues. The signal, gated with 2-ms ramps, ranged in half-amplitude duration from 2 to 300 ms. The noise bandwidth was arithmetically centered on 6 kHz and was varied from 60 Hz to 12 kHz. For masker bandwidths below 300 Hz, the slope of integration for signal durations between 2 and 20 ms decreased with decreasing masker bandwidth. For the tonal masker, increasing signal duration from 2 to 20 ms had no effect on threshold. These results cannot be accounted for by lowpass-filter or temporal-window models of temporal integration or resolution. Instead, it is proposed that the auditory system performs a spectral analysis of the stimulus envelope, so that the rapid fluctuations (high modulation frequencies) introduced by gating the signal can be used as a cue for brief signals in narrowband noise and tones. For broadband maskers, this cue is not available due to the masker's inherent rapid envelope fluctuations. [Work supported by the Wellcome Trust.]