5aSC21. Effects of amplitude on voicing contrast may not be explained by VIIIth nerve synchrony capture.

Session: Friday Morning, May 17

Author: Andrew J. Lotto
Author: Keith R. Kluender
Location: Dept. of Psych., Univ. of Wisconsin, 1202 W. Johnson St., Madison, WI 53706


Kluender, Lotto, and Jenison [J. Acoust. Soc. Am. 97, 2552--2567 (1995)] reported that overall stimulus amplitude can affect perception of the voicing contrast in syllable-initial stops. Their results supported an hypothesis that a shift in the temporal pattern of neural firing from frequencies near F2 and F3 to F1 and f0 could signal voicelessness. The results of the current study undermine this ``synchrony capture hypothesis.'' The effect of amplitude (increased voiceless identifications with higher amplitude) maintains when there is no cutback in F1 during the quasiperiodic portion of the syllable and when stimuli are high-pass filtered above the frequency of F1. In a further test of the hypothesis, two ten-step series (/ba/--/pa/ and /ga/--/ka/) were created which maintained period voicing throughout the syllable (with F1 cutback signaling voicelessness). The energy just below the frequency of F2 and the energy above F1 were presented dichotically. Thus, at the periphery, there was no competition between frequencies near F2 and lower frequencies and, as a result, no chance for a change in neural temporal patterns. Subjects continued to label voicelessness as a function of overall amplitude. Alternative models of the encoding of voicelessness will be considered. [Work supported by NIDCD and NSF.]

from ASA 131st Meeting, Indianapolis, May 1996