Detection of temporal gaps in sinusoids: effects of frequency and level

Thresholds for the detection of gaps in sinusoidal signals were measured as a function of frequency (100-2000 Hz) and level (25-85 dB SPL) in 11 normally hearing subjects. The sinusoids were presented in a background noise intended to mask spectral splatter associated with the gap. In a separate experiment, auditory filter shapes and detection efficiency were estimated for the same 11 subjects using the notched-noise method, at center frequencies of 100, 200, 400, and 800 Hz. Gap thresholds varied only slightly with frequency over the range 400-2000 Hz, but increased markedly at 200 and 100 Hz. At all center frequencies, gap thresholds were almost invariant with level for levels above 55 dB SPL. Gap thresholds increased at low levels, reaching values about 50% greater than their asymptotic values at a sensation level of about 20 dB. The decrease in auditory filter bandwidth with decreasing center frequency does not seem sufficient to account for the increase in gap thresholds. Also, individual gap thresholds at a given center frequency were not significantly correlated with the bandwidth of the auditory filter at that center frequency, as would be expected if the auditory filter played a role in limiting gap detection. Detection efficiency decreased with decreasing center frequency. Individual differences in detection efficiency were significantly correlated with gap thresholds. However, changes in detection efficiency with frequency do not seem to be of the right form to account for the increase in gap thresholds at low frequencies. It seems likely that there is a central sliding temporal integrator which integrates over longer times at lower center frequencies.