Detecting pitch-pulse asynchronies and differences in fundamental frequency.

Abstract

A series of experiments investigated the detection of pitch-pulse asynchronies (PPAs) and of differences in fundamental frequency (delta F0's) between two simultaneous "formants," each of which consisted of a group of sinusoidal components spaced sufficiently closely in frequency to be incompletely resolved by the peripheral auditory system. For such stimuli, introducing a delta F0 caused the pitch pulses of the two groups to become progressively more asynchronous at later and later parts of the stimulus. A comparison of the psychometric functions for the detection of delta F0's and of (constant) PPAs suggested that listeners could, under some circumstances, detect delta F0's from the resulting asynchrony. Using an adaptive procedure, it was also shown that, for a range of F0's from 20 to 125 Hz, the threshold PPA was constant at about 2.5 ms. This relationship between PPA threshold and F0 differs from that previously reported for the detection of envelope asynchronies between pairs of sinusoidally modulated tones [e.g., Strickland et al., J. Acoust. Soc. Am. 86, 2160-2166 (1989)], which remain constant in degrees, rather than in ms. Further experiments investigated the role of onset asynchronies in the detection of PPAs and showed that, although an asynchrony between the first pitch pulse in each formant was sufficient for near-asymptotic performance, listeners could still do the task when this cue was removed. For the detection of delta F0's, onset asynchronies also aided, but were not necessary for, discrimination.