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Social feedback is a driving force for speech development. A recent study provided a key finding to explain how contingent responses influence developmental change: infant speech-related vocalizations are contingent on responses to prior speech-related vocalizations (Warlaumont et al., 2014). However, the study did not distinguish between different speech-related vocalizations, vowel-like (V) and consonant-vowel (CV) vocalizations, which is important because CV vocalizations are a precursor to words. The present study explored parents' responses to infants' vocalizations and infants' subsequent vocal production at a point when vocalizations become more like adult speech. The relative proportion of CVs following contingent responses to CV did not differ between 10- and 12-months-olds; however, there was only a significant contingent relationship between responses to CV and subsequent CV production in 12-month-olds. Results suggest a developmental transition and a social feedback loop for the production of more developmentally advanced sounds when infants are learning their first words.

Previous research shows that listeners are sensitive to talker differences in phonetic properties of speech, including voice-onset-time (VOT) in word-initial voiceless stop consonants, and that learning how a talker produces one voiceless stop transfers to another word with the same voiceless stop [Allen, J. S., and Miller, J. L. (2004). J. Acoust. Soc. Am. 115, 3171-3183]. The present experiments examined whether transfer extends to words that begin with different voiceless stops. During training, listeners heard two talkers produce a given voiceless-initial word (e.g., pain). VOTs were manipulated such that one talker produced the voiceless stop with relatively short VOTs and the other with relatively long VOTs. At test, listeners heard a short- and long-VOT variant of the same word (e.g., pain) or a word beginning with a different voiceless stop (e.g., cane or coal), and were asked to select which of the two VOT variants was most representative of a given talker. In all conditions, which variant was selected at test was in line with listeners' exposure during training, and the effect was equally strong for the novel word and the training word. These findings suggest that accommodating talker-specific phonetic detail does not require exposure to each individual phonetic segment.

Two experiments were conducted to determine whether listeners' ability to use allophonic variation to identify word boundaries is influenced by speaking rate. Listeners in both experiments were presented two-word sequences (such as great eyes) spoken by naturally fast and naturally slow talkers; in one experiment the sequences were presented in quiet and in the other they were presented in noise. The listeners' task was to identify the intended sequence from among four choices with alternative segmentations (e.g. great eyes, gray ties, great ties, gray eyes). In both experiments performance was worse for the sequences produced by the naturally fast talkers than for those produced by the naturally slow talkers. This finding suggests that the extent to which allophonic variation contributes to the identification of word boundaries may depend on the rate at which the speech was produced., ((c) 2008 S. Karger AG, Basel)

Recent findings in the domains of word and talker recognition reveal that listeners use previous experience with an individual talker's voice to facilitate subsequent perceptual processing of that talker's speech. These findings raise the possibility that listeners are sensitive to talker-specific acoustic-phonetic properties. The present study tested this possibility directly by examining listeners' sensitivity to talker differences in the voice-onset-time (VOT) associated with a word-initial voiceless stop consonant. Listeners were trained on the speech of two talkers. Speech synthesis was used to manipulate the VOTs of these talkers so that one had short VOTs and the other had long VOTs (counterbalanced across listeners). The results of two experiments using a paired-comparison task revealed that, when presented with a short- versus long-VOT variant of a given talker's speech, listeners could select the variant consistent with their experience of that talker's speech during training. This was true when listeners were tested on the same word heard during training and when they were tested on a different word spoken by the same talker, indicating that listeners generalized talker-specific VOT information to a novel word. Such sensitivity to talker-specific acoustic-phonetic properties may subserve at least in part listeners' capacity to benefit from talker-specific experience.

Previous work has demonstrated that the graded internal structure of phonetic categories is sensitive to a variety of contextual factors. One such factor is place of articulation: The best exemplars of voiceless stop consonants along auditory bilabial and velar voice onset time (VOT) continua occur over different ranges of VOTs (Volaitis & Miller, 1992). In the present study, we exploited the McGurk effect to examine whether visual information for place of articulation also shifts the best exemplar range for voiceless consonants, following Green and Kuhl's (1989) demonstration of effects of visual place of articulation on the location of voicing boundaries. In Experiment 1, we established that /p/ and /t/ have different best exemplar ranges along auditory bilabial and alveolar VOT continua. We then found, in Experiment 2, a similar shift in the best-exemplar range for /t/ relative to that for /p/ when there was a change in visual place of articulation, with auditory place of articulation held constant. These findings indicate that the perceptual mechanisms that determine internal phonetic category structure are sensitive to visual, as well as to auditory, information.

Individual talkers differ in the acoustic properties of their speech, and at least some of these differences are in acoustic properties relevant for phonetic perception. Recent findings from studies of speech perception have shown that listeners can exploit such differences to facilitate both the recognition of talkers' voices and the recognition of words spoken by familiar talkers. These findings motivate the current study, whose aim is to examine individual talker variation in a particular phonetically-relevant acoustic property, voice-onset-time (VOT). VOT is a temporal property that robustly specifies voicing in stop consonants. From the broad literature involving VOT, it appears that individual talkers differ from one another in their VOT productions. The current study confirmed this finding for eight talkers producing monosyllabic words beginning with voiceless stop consonants. Moreover, when differences in VOT due to variability in speaking rate across the talkers were factored out using hierarchical linear modeling, individual talkers still differed from one another in VOT, though these differences were attenuated. These findings provide evidence that VOT varies systematically from talker to talker and may therefore be one phonetically-relevant acoustic property underlying listeners' capacity to benefit from talker-specific experience.

Previous research has shown that phonetic categories have a graded internal structure that is highly dependent on acoustic-phonetic contextual factors, such as speaking rate; these factors alter not only the location of phonetic category boundaries, but also the location of a category's best exemplars. The purpose of the present investigation, which focused on the voiceless category as specified by voice onset time (VOT), was to determine whether a higher order linguistic contextual factor, lexical status, which is known to alter the location of the voiced-voiceless phonetic category boundary, also alters the location of the best exemplars of the voiceless category. The results indicated that lexical status has a more limited and qualitatively different effect on the category's best exemplars than does the acoustic-phonetic factor of speaking rate. This dissociation is discussed in terms of a production-based account in which perceived best exemplars of a category track contextual variation in speech production.

The importance of vowel duration for specifying vowel contrasts differs across languages. In English, for example, a number of vowel pairs are acoustically differentiated by both temporal and spectral information, whereas in standard French temporal information plays a much more minor role. Gottfried and Beddor (1988) reported that the effectiveness of vowel duration in perception varies accordingly: For native speakers of English, but not native speakers of standard French, a change in vowel duration affected the perceptual identity of a vowel contrast. We tested the hypothesis that the relative prominence of vowel duration within different dialects of a given language also has perceptual consequences. Vowel duration plays a much more important role in the phonological system of Swiss French than standard French. Given this, we predicted that native speakers of Swiss French, unlike native speakers of standard French, would use temporal information when identifying vowels. Our prediction was confirmed. These findings indicate that just as there are cross-language differences in fundamental aspects of speech perception, so too are there cross-dialect differences, and they support the view that the perceptual mapping between acoustic signal and vowel category is sensitive to global aspects of the listener's phonological system.

Many studies have shown that listeners process speech in a rate-dependent manner, altering the location of phonetic category boundaries in accord with the acoustic consequences of a change in rate during speech production. In a recent series of papers that focused on a voicing contrast, we reported that the perceptual adjustment for rate is not limited to the region of the category boundary, but extends to well within the category, producing a change in which stimuli are perceived to be the best category exemplars. In the current paper, we provide evidence for the generality of this effect by showing analogous results for a /b/-/w/ contrast, specified by transition duration. The implications of these findings for models of rate-dependent processing are discussed.

It is well established that young infants process speech in terms of perceptual categories that closely correspond to the phonetic categories of adult language users. Recently, Kuhl (1991) has provided evidence that this correspondence is not limited to the region of category boundaries: At least by 6-7 months of age, vowel categories of infants, like those of adults, have an internal perceptual structure. In the current experiments, which focused on a consonantal contrast, we found evidence of internally structured categories in even younger infants-3-4 months of age. The implications of these findings for the nature of the infant's earliest language-universal categories are discussed, as is the role of exposure to the native language in shaping these categories over the course of development.

In the experiments reported in this paper we compared the effects of syllable-level and sentence-level speaking rate on phonetic perception. In an earlier set of experiments, we found that syllable-level rate influences the internal perceptual structure of phonetic categories [Miller and Volaitis, Percept. Psychophys. 46, 505-512 (1989); Volaitis and Miller, J. Acoust. Soc. Am. 92, 723-735 (1992)]. Specifically, a change in target-syllable rate altered the location of the stimuli judged to be the best category exemplars, as well as the width of this best-exemplar range. In the present investigation, it was asked whether sentence-level rate has the same influence. It was found that slowing sentence rate shifted the location of the best-exemplar range, but did not alter its width. These findings are discussed in terms of timing mechanisms that may operate during speech perception.

There is growing evidence that phonetic categories have a rich internal structure, with category members varying systematically in category goodness. Our recent findings on this issue, which are summarized in this paper, underscore the existence and robustness of this structure and indicate further that the mapping between acoustic signal and internal category structure is complex: just as in the case of category boundaries, the best exemplars of a given category are highly dependent on acoustic-phonetic context and are specified by multiple properties of the speech signal. These findings suggest that the listener's representation of phonetic form preserves not only categorical information, but also fine-grained information about the detailed acoustic-phonetic characteristics of the language.

We investigated the conditions under which the [b]-[w] contrast is processed in a context-dependent manner, specifically in relation to syllable duration. In an earlier paper, Miller and Liberman (1979) demonstrated that when listeners use transition duration to differentiate [b] from [w], they treat it in relation to the duration of the syllable: As syllables from a [ba]-[wa] series varying in transition duration become longer, so, too, does the transition duration at the [b]-[w] perceptual boundary. In a subsequent paper, Shinn, Blumstein, and Jongman (1985) questioned the generality of this finding by showing that the effect of syllable duration is eliminated for [ba]-[wa] stimuli that are less schematic than those used by Miller and Liberman. In the present investigation, we demonstrated that when these "more natural" stimuli are presented in a multi-talker babble noise instead of in quiet (as was done by Shinn et al.), the syllable-duration effect emerges. Our findings suggest that the syllable-duration effect in particular, and context effects in general, may play a more important role in speech perception than Shinn et al. suggested.

In this investigation, the effects of context on the perception of voicing contrasts specified by voice-onset-time (VOT) in syllable-initial stop consonants were examined. In an earlier paper [J.L. Miller and L.E. Volaitis, Percept. Psychophys. 46, 505-512 (1989)], it was reported that the listener's adjustment for one contextual variable, speaking rate, was not confined to the region of the phonetic category boundary, but extended throughout the phonetic category. The current investigation examines whether this type of perceptual remapping also occurs for another contextual variable, the place of articulation of the syllable-initial consonant. In a preliminary experiment that involved acoustic measurement of natural speech, it was confirmed that as place of articulation moves from labial to velar, VOT increases, and it was established that this occurs across a range of speaking rates (syllable durations). In the main experiments, which focused on the voiceless category, it was found that this acoustic change was reflected in perception not only as a shift in the location of the voiced-voiceless category boundary, but also a change in both the specific range of stimuli identified as members of the voiceless category and the set of stimuli judged to be the best exemplars, or prototypes, of the category. These findings extend earlier research by showing that a change in place of articulation, like a change in speaking rate, systematically alters the internal perceptual structure of voicing categories.

Three- and four-month-old infants were tested on their ability to discriminate the third-formant transitions sufficient to signal the syllable-medial stops [t] and [k]. The stimulus patterns consisted of an initial fricative [s], 20 or 100 msec of silence, and the vowel [a], whose initial formant transitions were appropriate for [t] or [k]. Discrimination only occurred when the duration of silence was 100 msec. This constraint on discrimination is discussed in terms of a psychoacoustic explanation based on forward masking and in terms of the hypothesis that the processing of speech signals involves a species-specific system dedicated to deriving a phonetic message.

Three experiments examined the conditions under which the speaking rate of a context sentence affects vowel identification. In these experiments, listeners identified the vowel in synthetic /b/-vowel-/t/ syllables that varied systematically in the duration (temporal), the formant frequencies (spectral), or both the duration and formant frequencies (temporal-spectral) of the steady-state portion of the syllable. These syllables were embedded in two synthetic sentence frames, one with the temporal characteristics of a natural fast sentence and one with those of a slow sentence. For two vowel distinctions that are specified in natural speech by both temporal and spectral characteristics, /I/-/i/ and /e/-/ae/, listeners adjusted their identification of the vowels according to the sentence rate in all three conditions. Although there was a trend for the rate effect to be reduced in the temporal-spectral condition, the influence of sentential rate was never eliminated. By contrast, for a vowel distinction that is naturally specified primarily by spectral characteristics, /e/-/I/, there was no effect of sentence rate in any of the conditions. We conclude that when vowels are differentiated in natural speech by both temporal and spectral information, listeners obligatorily use the duration of the vowel to identify it and do so in relation to the rate of the sentence in which the vowel occurs.

We used a selective adaptation procedure to investigate the possibility that differences in the degree to which stimuli within a phonetic category are considered to be good exemplars of the category--that is, differences in perceived category goodness--have a basis at a prephonetic, auditory level of processing. For three different phonetic contrasts (/b-p/, /d-g/, /b-w/), we assessed the relative magnitude of adaptation along a stimulus continuum produced by a variety of stimuli from the continuum belonging to a given phonetic category. For all three phonetic contrasts, nonmonotonic adaptation functions were obtained: As the adaptor moved away from the category boundary, there was an initial increase in adaptation, followed by a subsequent decrease. On the assumption that selective adaptation taps a prephonetic, auditory level of processing, these findings permit the following conclusions. First, at an auditory level there is a limit on the range of stimuli along a continuum that is treated as relevant to a given contrast; that is, the stimuli along a continuum are effectively grouped into auditory categories. Second, stimuli within an auditory category vary in their effectiveness as category members, providing an internal structure to the categories. Finally, this internal category structure at the auditory level, revealed by the adaptation procedure, may provide a basis for differences in perceived category goodness at the phonetic level.

Among the contextual factors known to play a role in segmental perception are the rate at which the speech was produced and the lexical status of the item, that is, whether it is a meaningful word of the language. In a series of experiments on the word-initial /b/-/p/ voicing distinction, we investigated the conditions under which these factors operate during speech processing. The results indicated that under instructions of speeded responding, listeners could, on some trials, ignore some later occurring contextual information within the word that specified rate and lexical status. Importantly, however, they could not ignore speaking rate entirely. Although they could base their decision on only the early portion of the word, when doing so they treated the word as if it were physically short--that is to say, as if there were no later occurring information specifying a slower rate. This suggests that listeners always take account of rate when identifying the voicing value of a consonant, but precisely which information within the word is used to specify rate can vary with task demands.

In a series of experiments a selective adaptation technique was used to examine the dependencies that arise in processing phonetically relevant acoustic information in syllable-initial consonants. The pattern of results, identical across two vowel contexts, indicated that voice-onset-time specifying a voicing contrast and the spectral form of the initial transitions specifying a place of articulation contrast are processed in a mutually dependent fashion. A different pattern was revealed, however, for the processing of the spectral form of the transitions specifying a place contrast and the duration of the transitions specifying a manner contrast. Specifically, the data indicated that transition duration is processed independently of the spectral characteristics of the transitions, even though the processing of the spectral characteristics of the transitions is dependent on their duration. On the basis of these findings, the following conclusions were drawn: First, there are distinct patterns of interaction during speech processing; second, the system does not operate entirely in a context-conditioned fashion; and third, at early stages of processing the speech signal is not treated holistically, but rather undergoes analysis in terms of those acoustic dimensions that provide information about phonetic distinctions.

This paper reviews a series of studies on the effects of variation in speaking rate on phonetic perception, in particular, on the identification of /b/ and /w/ in syllable-initial position. The major finding of these studies was that in a variety of tasks listeners adjusted for speaking rate when using the duration of the initial formant transitions to distinguish between /b/ and /w/: At slower rates of speech, a longer transition was needed to hear /w/ rather than /b/, and conversely at faster rates of speech. This effect occurred when rate was specified by the duration and acoustic-phonetic structure of the syllable containing the target consonant and, to a more limited extent, when it was specified by the duration of a subsequent syllable. Moreover, the influence of syllable duration on the processing of transition duration was also evident in young, prearticulate infants, suggesting that at least the rudiments of a system that provides perceptual constancy across rate is part of the linguistic endowment of the infant.

One of the acoustic properties distinguishing the syllable-initial stop consonant /b/ from the semivowel /w/ is the duration of the initial formant transitions; syllables beginning with /b/ have shorter transitions than those beginning with /w/. This experiment investigated the way in which the transition durations of /b/ and /w/ change as a function of speaking rate by examining tokens of /ba/ and /wa/ produced by four male speakers. At any given speaking rate the /wa/ transitions were, on average, longer than the /ba/ transitions, although pooled across rates, the distributions of transition duration for /ba/ and /wa/ were overlapping. In addition, the magnitude of the difference between average /ba/ and /wa/ transition durations increased with decreases in speaking rate. This is because as rate of speech decreased so that syllable duration increased, there was little change in the initial transition duration of /ba/, but a considerable increase in the initial transition duration of /wa/. Given the overall pattern of results, the transition duration that could optimally distinguish /ba/ from /wa/ was not constant, but increased with syllable duration. This is in accord with Miller and Liberman's (1979) finding that when listeners identify /ba/ and /wa/ on the basis of transition duration, they do so in relation to the duration of the syllable.

When listeners process temporal properties of speech that convey information about the phonetic segments of the language, they do so in a rate-dependent manner. This is seen as a shift in the location of the phonetic category boundary along a temporal continuum toward longer values of the acoustic property in question, as speech is slowed. In a series of experiments, we found that the adjustment for rate is not confined to the region of the category boundary, but extends throughout the phonetic category. Specifically, a change in rate modified the range of stimuli identified as members of a phonetic category, as well as which stimuli were overtly judged to be good exemplars of the category. These findings suggest that the listener's adjustment for speaking rate entails a comprehensive perceptual remapping between acoustic signal and phonetic structure.

In two studies we investigated the way in which the components of speaking rate, articulation rate and pause rate, combine to influence processing of the silence-duration cue for the voicing distinction in medial stop consonants. First, we replicated the finding that the articulation rate of a carrier sentence, that is, the rate at which the speech itself is produced, influences how the duration information is used to assign voicing values. Second, and more importantly, the assignment of voicing values was also influenced by the pause rate of the sentence. Thus, the listener adjusts for both articulation rate and pause rate when processing the phonetically relevant information. Finally, the two rate components did not function in an equivalent manner, since changes in articulation rate had considerably more effect on phonetic judgments than did changes in pause rate. Alternative explanations fo the relative weighting of the two variables are discussed.

Mutual dependence in the processing of manner and place of articulation was investigated in two experiments. The first study assessed the location of the voiced-voiceless boundary as a function of place of articulation, and the second investigated the location of the labial-alveolar boundary as a function of manner class. In both experiments, the location of the phonetic boundary systematically varied as a function of the nontarget feature value. These results indicate that the processing of phonetic feature information occurs in parallel, with decisions about one feature influencing the particular value assigned to another feature.