Auditory temporal acuity for dynamic signals

Abstract

Previous reports of auditory temporal acuity have generally used static, rather than dynamic, signals; that is, the charactersitics of the signal did not change within its brief duration. Temporal acuity is defined as in Green [Psychol. Rev. 78, 540–551 (1971)]: the shortest time interval within which a listener cannot detect a change in the sound. Auditory temporal acuity is determined using frequency‐modulated (FM) sinusoids. The two FM signals used in each block of trial always began at the same initial frequency and moved to the same final frequency. Only the trajectory, the path from initial to final frequency, differed. One trajectory, the glide, moved linearly from initial to final freqency; the other proceeded in a series of discrete steps. As the number of steps increased, the size and duration of an individual step decreased, and the multiple‐stepped transition more closely approximated the glide. Four well‐practiced listeners were asked to identify the interval containing the glide in a 2‐Q, 2AFC task. Frequency transitions of 100‐, 200‐, and 403‐Hz durations of 25, 50, and 100 ms were centered on octave frequencies from 250 to 4 kHz. Signals were presented at 50 dB SL for each subject. Results for the four listeners were remarkably consistent, with the 75% discrimination point falling at 7 to 10 ms for all conditions except for signals centered at 4 kHz. Poorer performance at 4 kHz may reflect the loss of synchrony in the frequency region; however, there are some difficulties with that explanation. [Work supported by a grant from AFOSR.]