Discrimination of the rate of filtered impulses.

Abstract

When subjects detect changes in interaural differences of time or level in the envelope of a complex waveform, the accuracy of the detection depends on the stimulus’s duration. The change in threshold with duration, in turn, depends on the rate of modulation of the waveform’s envelope. As the envelope rate increases beyond about 85 Hz, detectability relies increasingly on information derived from the early portion of the signal. The purpose of the present experiment was to determine whether a similar reliance on onset information might affect the detection of changes in envelope rate per se. The stimuli were trains of high-frequency, filtered clicks that differed only in their click rates. Control conditions included low-frequency noise intended to interfere with nonlinear distortion and a roving carrier technique designed to discourage comparisons between individual harmonic components. Unlike the case for lateralization, rate-discrimination thresholds for click rates as high as 400 Hz declined with the square root of duration, indicating that listeners derived information from throughout the stimulus. From these data it is suggested that separate channels may be used to convey envelope information for spatial hearing and for the discrimination of pitch.