Certain attributes of a syllable-final liquid can influence the perceived place of articulation of a following stop consonant. To demonstrate this perceptual context effect, the CV portions of natural tokens of [al-da], [al-ga], [ar-da], [ar-ga] were excised and replaced with closely matched synthetic stimuli drawn from a [daj-lga] continuum. The resulting hybrid disyllables were then presented to listeners who labeled both liquids and stops. The natural CV portions had two different effects on perception of the synthetic CVs. First, there was an effect of liquid category: Listeners perceived "g" more often in the context of [al] than in that of [ar], Second, there was an effect due to tokens of [al] and [ar] having been produced before [da] or [gaJ: More "g" percepts occurred when stops followed liquids that had been produced before [gJ. A hypothesis that each of these perceptual effects finds a parallel in speech production is supported by spectrograms of the original utterances. Here, it seems, is another instance in which findings in speech perception reflect compensation for coarticulation during speech production.When an utterance is articulated, the gestures for adjacent phonemes overlap and become interwoven. One consequence of this coarticulation of adjacent phonemes is that stop consonants may have different places of occlusion when they occur in different phonetic sequences. To date, the best known illustration of this point concerns the shift in place of occlusion that is consequent upon a change in the preceding or following vowel. Velar stops receive a more forward place of occlusion when they are adjacent to a front vowel such as [i] than when they are adjacent to a back vowel such as [a] (Ohman, 1966; Gay, Note 1). Another example, which has recently emerged from Repp and Mann's (in press) perceptual and acoustic observations of stops in fricative-stop clusters, is that when [t] or [k] follow lsI, these stops can receive a relatively more forward place of articulation than when they follow [fl.Insofar as coarticulation with adjacent phones causes shifts in the place of stop occlusion and, correspondingly, changes in the acoustic signal that reflects stop production, we should suppose that perception of a stop consonant must often require the integration of acoustic cues that are numerous, diverse, and context sensitive. That listeners do, in fact, integrate such cues in the process of stop perception can be seen in the existence of two perceptual "context
When synthetic fricative noises from a [f]-[s] continuum are followed by [a] or [u] (with appropriate formant transitions), listeners perceive more instances of [s] in the context of [u] than in the context of [a]. Presumably, this reflects a perceptual adjustment for the coarticulatory effect of rounded vowels on preceding fricatives. In Experiment 1, we found that varying the duration of the fricative noise leaves the perceptual context effect unchanged, whereas insertion of a silent interval following the noise reduces the effect substantially. Experiment 2 suggested that it is temporal separation rather than the perception of an intervening stop consonant that is responsible for this reduction, in agreement with recent, analogous observations on anticipatory coarticulation. In Experiment 3, we showed that the vowel context effect disappears when the periodic stimulus portion is synthesized so as to contain no formant transitions. To dissociate the contribution of formant transitions from contextual effects due to vowel quality per se, Experiment 4 employed synthetic fricative noises followed by periodic portions excerpted from naturally produced [Ja], [sa], [Ju], and [su]. The results showed strong and largely independent effects of formant transitions and vowel quality on fricative perception. In addition, we found a strong speaker (male vs. female) normalization effect. All three influences on fricative perception were reduced by temporal separation of noise and periodic stimulus portions. Although no single hypothesis can explain all of our results, they are generally supportive of the view that some knowledge of the dynamics of speech production has a role in speech perception. In other words, the phoneme boundary shifted toward lower noise frequencies in the context of rounded vowels, in conformity with the analogous effect of anticipatory lip rounding on fricative noise spectra. Thus, the Japanese listeners seemed to take account in perception of contextual changes characteristic of fricative production, as if their phonetic perception were guided by an intrinsic knowledge of articulatory dynamics. EXPERIMENT 1The purpose of our first experiment was to replicate the basic finding of Kunisaki and Fujisaki (Note 3) that the phonetic perception of a fricative noise depends on the nature of the following vowel. This experiment also addressed the question of how the magnitude of that perceptual context effect changes as a function of two variables: the duration of the fricative noise and the presence or absence of a silent interval between the noise and the periodic portion.It is important to note that changes in noise duration (within the range employed by us) have no gross effect on phonetic perception, whereas insertion of a silent interval induces perception of a stop consonant
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