Gradient effects of fundamental frequency on stop consonant voicing judgments.

The post-stop-release rise or fall of fundamental frequency (F0) is known to affect voicing judgments of syllables with ambiguous voice onset times (VOTs). In 1986, Silverman claimed that the critical factor was not direction of F0 change but rather its direction relative to the intonational contour. He further claimed that only F0s that start above and fall to the contour have an effect proportional to the size of the frequency change; F0s that rise to the contour by different amounts were claimed to be equivalent. In our first experiment, we examined the effect on voicing judgments of five onset F0s preceding a single, flat contour. Only falling F0s were differentiated in the first set of judgments, but after increased exposure to the syllables, even F0s below the contour differentially affected the voicing judgment. In a second experiment, the contour of the final part of the syllable was flat, rising or falling. F0 contour affected the judgments, as did onset F0s, but the two factors did not interact, indicating that the onset values were not being judged by reference to the contours. However, the contour which was predicted to result in more voiceless judgments also ended at a higher F0 in the vowel, and another effect of voicing is that the F0 is higher throughout the vowel after voiceless stops. In a third experiment, F0 contours were created to contrast contour and mean F0. The effect of the F0 during the vocalic segment appeared to be attributable to the average F0 rather than the contour. In all three experiments, the F0 onset values contributed to the voicing judgment whether they were above or below the putative intonation contour. The contribution of the lower F0s, while significant, was not as great as that of the higher F0s, which argues for a noncategorical contribution of intonation.