Temporal order identification for tone/noise stimuli with onset transitions.

Abstract

Temporal order of onset identification boundaries and difference thresholds (DLs) were measured for stimuli modeled after two formant speech stimuli that varied in voice onset time (VOT). The stimuli had dynamic onset transitions and consisted of a tone pair that varied in onset relative to a noise whose center frequency matched the higher frequency tone. DLs were measured relative to 0- and 7-msec onset delays (as well as 49- and 56-msec onset delays) by using a method of constant stimuli with a two-interval temporal forced choice psychophysical procedure. Discrete thresholds were found for noise lead conditions, but tone lead conditions were very difficult for most subjects. With rising-onset stimuli, evidence was found for long DLs based upon a fixed threshold location at 32–38 msec, and thus independent of the standard stimulus. With falling-onset stimuli, the short (5- to 20-msec) DLs were roughly proportional to the standard (0- or 7-msec) onset difference, although there was evidence for an additional fixed perceptual boundary at a longer (30- to 40-msec) onset difference. A noise burst at stimulus onset seemed to act as a type of masking stimulus, causing a shift in temporal order threshold to longer onset differences. The 30- to 40-msec fixed threshold location is similar in magnitude to those typical of VOT voicing boundaries for stop consonants of English.