Synchrony capture hypothesis fails to account for effects of amplitude on voicing perception

Kluender et al. [J. Acoust. Soc. Am. 97, 2552-2567 (1995)] reported that overall stimulus amplitude affects perception of the voicing contrast in syllable-initial stops as a function of frequency separation between the first formant (F1) and higher formants (F2, F3). These results were offered as support for a hypothesis that [-voice] could be signaled by a shift in the temporal pattern of neural firing from synchronizing to energy at frequencies of F2 and F3 to synchronizing to energy near F1. Several predictions from this "synchrony capture hypothesis" were tested in the current study. In all cases the hypothesis was not supported. Effect of stimulus amplitude (increased voiceless responses with higher amplitude) was maintained when there was no cutback in F1 or when F2 and F1 energy bands were presented dichotically. In further tests of the hypothesis, voice-voiceless series were created that maintained periodic energy throughout the syllable (with F1 cutback signaling voicing). Energy just below the frequency of F2 and energy above F1 were presented dichotically. Thus, at the periphery there was no competition between frequencies near F2 and lower frequencies. In contrast to predictions of the "synchrony capture hypothesis," overall amplitude still had an effect on voice-voiceless identifications.