Perception of sine-wave analogs of voice onset time stimuli

It has been argued that perception of stop consonant voicing contrasts is based on auditory mechanisms responsible for the resolution of temporal order. As one source of evidence, category boundaries for nonspeech stimuli whose components vary in relative onset time are reasonably close to the labeling boundary for a labial stop voiced-voiceless continuum. However, voicing boundaries change considerably when the onset frequency of the first formant (F1) is varied--either directly or as a side effect of a change in F1 transition duration. Stimuli consisted of a midfrequency sinusoid that was initiated 0-50 ms prior to the onset of a low-frequency sinusoid. Results showed that the labeling boundary for relative onset time increased for longer durations of a low-frequency tone sweep. This effect is analogous to the F1 transition duration effect with synthetic speech. Further, the discrimination of differences in relative onset time was poorer for stimuli with longer frequency sweeps. However, unlike synthetic speech, there were no systematic effects when the frequency of a transitionless lower sinusoid was varied. These findings are discussed in relation to the potential contributions of auditory mechanisms and speech-specific processes in the perception of the voicing contrast.