Gradient Effects of Fundamental Frequency on Stop Consonant Voicing Judgments

Abstract

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.