To investigate possible auditory factors in the perception of stops and glides (e.g., /b/ vs /w/), a two-category labeling performance was compared on several series of /ba/-/wa/ stimuli and on corresponding nonspeech stimulus series that modeled the first-formant trajectories and amplitude rise times of the speech items. In most respects, performance on the speech and nonspeech stimuli was closely parallel. Transition duration proved to be an effective cue for both the stop/glide distinction and the nonspeech distinction between abrupt and gradual onsets, and the category boundaries along the transition-duration dimension did not differ significantly in the two cases. When the stop/glide distinction was signaled by variation in transition duration, there was a reliable stimulus-length effect: A longer vowel shifted the category boundary toward greater transition durations. A similar effect was observed for the corresponding nonspeech stimuli. Variation in rise time had only a small effect in signaling both the stop/glide distinction and the nonspeech distinction between abrupt and gradual onsets. There was, however, one discrepancy between the speech and nonspeech performance. When the stop/glide distinction was cued by rise-time variation, there was a stimulus-length effect, but no such effect occurred for the corresponding nonspeech stimuli. On balance, the results suggest that there are significant auditory commonalities between the perception of stops and glides and the perception of acoustically analogous nonspeech stimuli.

There is some disagreement in the literature about the relative contribution of formant transition duration and amplitude rise time in signalling the contrast between stops and glides. In this study, listeners identified sets of /ba/ and /wa/ stimuli in which transition duration and rise time varied orthogonally. Both variables affected labelling performance in the expected direction (i.e. the proportion of /b/ responses increased with shorter transition durations and shorter rise times). However, transition duration served as the primary cue to the stop/glide distinction, whereas rise time played a secondary, contrast-enhancing role. A qualitatively similar pattern of results was obtained when listeners made abrupt-onset/gradual-onset judgements of single sine-wave stimuli that modelled the rise times, frequency trajectories, and durations of the first formant in the /ba/-/wa/ stimuli. The similarities between the speech and non-speech conditions suggest that significant auditory commonalities underlie performance in the two cases.

Variation of amplitude envelope at stimulus onset has been considered to be of primary importance for distinguishing voiceless affricates from fricatives (e.g., ItII and IIf). In earlier perceptual experiments, however, variation in amplitude rise time was confounded with variation in frication duration. In two experiments, these variables were independently manipulated, and their individual and combined effects for perception of Itf/ and III were examined. Variation in amplitude rise time alone was not sufficient to signal the voiceless affricate/fricative contrast in these experiments, but variation in frication duration alone was sufficient.The first acoustic and perceptual analyses involving the affricate/fricative distinction were carried out at Haskins Laboratories over 30 years ago. Perhaps the most complete and informative of these early studies was the dissertation of L. J. Gerstman (1957). His acoustic measurements showed that the production of the affricates Itfl and Id'!J, as in chop and job, results in shorter amplitude rise times and shorter durations of fricative noise than does the production of the fricatives IfI and 131, as in sJwp and azure. Gerstman also evaluated the effects of rise time and frication duration on perception of affricates and fricatives. His results led him to conclude that "the fricativeaffricate distinction appears to depend upon the rate at which the frictional energy grows. An abrupt onset is heard as an affricate, a smooth onset is heard as a fricative" (p. 118). Although this dissertation was never published, it has served as the predecessor to a number of studies on the production and perception of voiceless affricates and fricatives, and the perceptual salience of other acoustic properties such as preceding closure silence and release burst have also been demonstrated (e

Fowler [J. Acoust. Soc. Am. 88, 1236-1249 (1990)] makes a set of claims on the basis of which she denies the general interpretability of experiments that compare the perception of speech sounds to the perception of acoustically analogous nonspeech sound. She also challenges a specific auditory hypothesis offered by Diehl and Walsh [J. Acoust. Soc. Am. 85, 2154-2164 (1989)] to explain the stimulus-length effect in the perception of stops and glides. It will be argued that her conclusions are unwarranted.

The duration of an adjacent vowel has been demonstrated to affect the judgment of consonant duration and, hence, phonetic identity. For example, syllable-initial stops can be distinguished from glides on the basis of transition duration and, when the following vowel is relatively long, longer transitions are required in order for a glide to be perceived. Apparently, the vowel provides a source of durational contrast, whereby a longer vowel makes the adjacent consonant seem shorter. This effect has been demonstrated for both speech and nonspeech signals [L. Diehl and M. A. Walsh, J. Acoust. Soc. Am. Suppl. 1 80, S125 (1986)], and is presumably grounded in a general auditory mechanism. In this study, the effect of vowel duration on perception of syllable-initial consonants is also demonstrated for fricatives and affricates. Frication duration is an important cue to this distinction, with longer durations yielding more /∫/ responses. Two series of edited natural tokens of /∫a/ and /t∫a/ were created in which frication duration varied from 100 to 210 ms. The duration of the following vowel was 204 ms for one series, and 358 ms for the other. With the longer vowel context, significantly longer frication was required to yield a /∫/ percept. Consistent with earlier findings for other consonantal distinctions, durational contrast occurred between the vowel and fricative. [Work supported by NINCDS.]