Previous research suggests that infant speech perception reorganizes in the first year: young infants discriminate both native and non-native phonetic contrasts, but by 10-12 months difficult non-native contrasts are less discriminable whereas performance improves on native contrasts. In the current study, four experiments tested the hypothesis that, in addition to the influence of native language experience, acoustic salience also affects the perceptual reorganization that takes place in infancy. Using a visual habituation paradigm, two nasal place distinctions that differ in relative acoustic salience, acoustically robust labial-alveolar [ma]-[na] and acoustically less salient alveolar-velar [na]-[ enga], were presented to infants in a cross-language design. English-learning infants at 6-8 and 10-12 months showed discrimination of the native and acoustically robust [ma]-[na] (Experiment 1), but not the non-native (in initial position) and acoustically less salient [na]-[ enga] (Experiment 2). Very young (4-5-month-old) English-learning infants tested on the same native and non-native contrasts also showed discrimination of only the [ma]-[na] distinction (Experiment 3). Filipino-learning infants, whose ambient language includes the syllable-initial alveolar (/n/)-velar (/ eng/) contrast, showed discrimination of native [na]-[ enga] at 10-12 months, but not at 6-8 months (Experiment 4). These results support the hypothesis that acoustic salience affects speech perception in infancy, with native language experience facilitating discrimination of an acoustically similar phonetic distinction [na]-[ enga]. We discuss the implications of this developmental profile for a comprehensive theory of speech perception in infancy.

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The perception of coarticulated speech as it unfolds over time was investigated by monitoring eye movements of participants as they listened to words with oral vowels or with late or early onset of anticipatory vowel nasalization. When listeners heard [CṼNC] and had visual choices of images of CVNC (e.g., send) and CVC (said) words, they fixated more quickly and more often on the CVNC image when onset of nasalization began early in the vowel compared to when the coarticulatory information occurred later. Moreover, when a standard eye movement programming delay is factored in, fixations on the CVNC image began to occur before listeners heard the nasal consonant. Listeners' attention to coarticulatory cues for velum lowering was selective in two respects: (a) listeners assigned greater perceptual weight to coarticulatory information in phonetic contexts in which [Ṽ] but not N is an especially robust property, and (b) individual listeners differed in their perceptual weights. Overall, the time course of perception of velum lowering in American English indicates that the dynamics of perception parallel the dynamics of the gestural information encoded in the acoustic signal. In real-time processing, listeners closely track unfolding coarticulatory information in ways that speed lexical activation.

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The conditions under which listeners do and do not compensate for coarticulatory vowel nasalization were examined through a series of experiments of listeners' perception of naturally produced American English oral and nasal vowels spliced into three contexts: oral (C_C), nasal (N_N), and isolation. Two perceptual paradigms, a rating task in which listeners judged the relative nasality of stimulus pairs and a 4IAX discrimination task in which listeners judged vowel similarity, were used with two listener groups, native English speakers and native Thai speakers. Thai and English speakers were chosen because their languages differ in the temporal extent of anticipatory vowel nasalization. Listeners' responses were highly context dependent. For both perceptual paradigms and both language groups, listeners were less accurate at judging vowels in nasal than in non-nasal (oral or isolation) contexts; nasal vowels in nasal contexts were the most difficult to judge. Response patterns were generally consistent with the hypothesis that, given an appropriate and detectable nasal consonant context, listeners compensate for contextual vowel nasalization and attribute the acoustic effects of the nasal context to their coarticulatory source. However, the results also indicated that listeners do not hear nasal vowels in nasal contexts as oral; listeners retained some sensitivity to vowel nasalization in all contexts, indicating partial compensation for coarticulatory vowel nasalization. Moreover, there were small but systematic differences between the native Thai- and native English-speaking groups. These differences are as expected if perceptual compensation is partial and the extent of compensation is linked to patterns of coarticulatory nasalization in the listeners' native language.

Although coarticulatory variation is largely systematic, and serves as useful information for listeners, such variation is nonetheless linked to sound change. This article explores the articulatory and perceptual interactions between a coarticulatory source and its effects, and how these interactions likely contribute to change. The focus is on the historical change VN (phonetically, Ṽ N) Ͼ Ṽ , but with more general attention to how a gesture associated with a source segment comes to be reinterpreted as distinctively, rather than coarticulatorily, associated with a nearby vowel or consonant. Two synchronic factors are hypothesized to contribute to reinterpretation: (i) articulatory covariation between the duration of the coarticulatory source (here, N) and the temporal extent of its effects (Ṽ ), and (ii) perceived equivalence between source and effect. Experimental support for both hypotheses is provided. Additionally, the experimental data are linked to the historical situation by showing that the contextual conditions that trigger (i) and (ii) parallel the conditions that historically influence phonologization of vowel nasalization.*

Certain of the complex spectral effects of vowel nasalization bear a resemblance to the effects of modifying the tongue or jaw position with which the vowel is produced. Perceptual evidence suggests that listener misperceptions of nasal vowel height arise as a result of this resemblance. Whereas previous studies examined isolated nasal vowels, this research focused on the role of phonetic context in shaping listeners' judgments of nasal vowel height. Identification data obtained from native American English speakers indicated that nasal coupling does not necessarily lead to listener misperceptions of vowel quality when the vowel's nasality is coarticulatory in nature. The perceived height of contextually nasalized vowels (in a [bVnd] environment) did not differ from that of oral vowels (in a [bVd] environment) produced with the same tongue-jaw configuration. In contrast, corresponding noncontextually nasalized vowels (in a [bVd] environment) were perceived as lower in quality than vowels in the other two conditions. Presumably the listeners' lack of experience with distinctive vowel nasalization prompted them to resolve the spectral effects of noncontextual nasalization in terms of tongue or jaw height, rather than velic height. The implications of these findings with respect to sound changes affecting nasal vowel height are also discussed.