Rebecca Scarborough

Optical Phonetics and Visual Perception of Lexical and Phrasal Stress in English

In a study of optical cues to the visual perception of stress, three American English talkers spoke words that differed in lexical stress and sentences that differed in phrasal stress, while video and movements of the face were recorded. The production of stressed and unstressed syllables from these utterances was analyzed along many measures of facial movement, which were generally larger and faster in the stressed condition. In a visual perception experiment, 16 perceivers identified the location of stress in forced-choice judgments of video clips of these utterances (without audio). Phrasal stress was better perceived than lexical stress. The relation of the visual intelligibility of the prosody of these utterances to the optical characteristics of their production was analyzed to determine which cues are associated with successful visual perception. While most optical measures were correlated with perception performance, chin measures, especially Chin Opening Displacement, contributed the most to correct perception independently of the other measures. Thus, our results indicate that the information for visual stress perception is mainly associated with mouth opening movements.

Neighborhood-conditioned patterns in phonetic detail: Relating coarticulation and hyperarticulation

Abstract The experiments presented here provide a careful phonetic description of the effects of phonological neighborhood density (operationalized as relative neighborhood frequency) on speech production: not only on hyperarticulation (which has been described elsewhere as well (e.g., Wright, 2004a , Wright, 2004b ), but also on two types of coarticulation. Acoustic analysis of elicited American English data with varying neighborhood properties reveals an increased degree of coarticulation in words with a high neighborhood frequency (i.e., many neighbors with high summed frequencies), as well as increased hyperarticulation. Both nasal coarticulation (measured as degree of vowel nasality) and vowel-to-vowel coarticulation (measured as F1/F2 deviation from canonical vowel quality) display this pattern in both coarticulatory directions (anticipatory and carryover). These findings extend the current descriptions of lexically-conditioned phonetic effects to new phonetic features and new lexical structures, as well as speak to the relationship between hyperarticulation and coarticulation. The pattern of co-occurrence of hyperarticulation and coarticulation demonstrates that these two phonetic phenomena are confluent (rather than inversely occurrent) but independent, facts which inform both articulatory and functional models of coarticulation. Finally, various accounts of these neighborhood-conditioned effects on production, both those relating the effects to neighborhood influences in lexical perception and those that do not, are discussed.

An acoustic study of real and imagined foreigner‐directed speech

Foreigner‐directed speech is a much cited speech style, but its acoustic properties are surprisingly under‐studied, and many existing studies evoke imagined interlocutors to elicit foreigner‐directed speech. This study provides an acoustic comparison of foreigner‐directed and native‐directed speech in real and imaginary conditions. Ten native English speakers described the path between landmarks on a map to each of two confederate listeners (one native English speaker and one native Mandarin speaker) and to two imagined listeners (one described as a native English speaker and the other as a non‐native speaker). Vowel duration, rate of speech, and vowel centralization were examined across native‐foreigner and real‐imagined conditions in 22 target words. Stressed vowels were longer and rate of speech was slower in foreigner‐directed than in native‐directed speech. Additionally, /ae/ was more peripheral in the vowel space in the foreigner‐directed condition. These effects were consistent across real and imag...

Imitability of contextual vowel nasalization and interactions with lexical neighborhood density

This study investigates the imitability of contextual vowel nasalization in English. Unlike other phonetic features reported to be imitable [e.g., vowel formants (Babel, 2012), VOT (Nielsen, 2011)], vowel nasality is non-contrastive in English. Nasality is, however, systematically variable: words from dense lexical neighborhoods (high-ND words) are produced with greater nasality than words from sparse neighborhoods [Scarborough (2004), (2012)]. Two experiments were conducted to test (1) whether (experimentally manipulated) nasality can be imitated in a shadowing task, and (2) whether direction of manipulation (more or less nasality, enhancing or countering natural neighborhood-conditioned patterns) affects shadowing behavior. Subjects shadowed 16 high-ND words (which are naturally more nasal) containing a vowel-nasal sequence and modified by spectral mixing to exhibit either greater-than-natural (experiment 1) or less-than-natural (experiment 2) nasality. Both the increase and the decrease in nasality were imitated (though not overall degree of nasality, as our imitation model was more nasal in both conditions than any of our subjects). This change persisted into a post-shadowing task for just the less-nasal condition. These results indicate that speakers are sensitive to non-contrastive phonetic detail in nasality, affecting their subsequent production. Further, the naturalness of nasality (reflecting neighborhood-conditioned variation) may affect the pattern of imitation.

Phonetic imitation of coarticulatory vowel nasalization

This study investigates the spontaneous phonetic imitation of coarticulatory vowel nasalization. Speakers produced monosyllabic words with a vowel-nasal sequence either from dense or sparse phonological neighborhoods in shadowing and word-naming tasks. During shadowing, they were exposed to target words that were modified to have either an artificially increased or decreased degree of coarticulatory vowel nasality. Increased nasality, which is communicatively more facilitative in that it provides robust predictive information about the upcoming nasal segment, was imitated more strongly during shadowing than decreased nasality. An effect of neighborhood density was also observed only in the increased nasality condition, where high neighborhood density words were imitated more robustly in early shadowing repetition. An effect of exposure to decreased nasality was observed during post-shadowing word-naming only. The observed imitation of coarticulatory nasality provides evidence that speakers and listeners are sensitive to the details of coarticulatory realization, and that imitation need not be mediated by abstract phonological representations. Neither a communicative account nor a representational account could single-handedly predict these observed patterns of imitation. As such, it is argued that these findings support both communicative and representational accounts of phonetic imitation.

Lexically conditioned phonetic variation in motherese: age-of-acquisition and other word-specific factors in infant- and adult-directed speech

Abstract Words produced to infants exhibit phonetic modifications relative to speech to adult interlocutors, such as longer, more canonical segments and prosodic enhancement. Meanwhile, within speech directed towards adults, phonetic variation is conditioned by word properties: lower word frequency and higher phonological neighborhood density (ND) correlate with increased hyperarticulation and degree of coarticulation. Both of these types of findings have interpretations that recruit listener-directed motivations, suggesting that talkers modify their speech in an effort to enhance the perceptibility of the speech signal. In that vein, the present study examines lexically-conditioned variation in infant-directed speech. Specifically, we predict that the adult-reported age at which a word was learned – lexical age-of-acquisition (AoA) – conditions phonetic variation in infant-directed speech. This prediction is indeed borne out in spontaneous infant-directed speech: later-acquired words are produced with more hyperarticulated vowels and a greater degree of nasal coarticulation. Meanwhile, ND predicts phonetic variation in data from spontaneous adult-directed speech, while AoA does not independently influence production. The patterns of findings in the current study support the stance that evaluation of the need for clarity is tuned to the listener. Lexical difficulty is evaluated by AoA in infant-directed speech, while ND is most relevant in adult-directed speech.

Phonetic and phonological patterns of nasality in Lakota vowels

Lakota (Siouan) has both contrastive and coarticulatory vowel nasality, and both nasal and oral vowels can occur before or after a nasal consonant. This study examines the timing and degree patterns of acoustic vowel nasality across contrastive and coarticulatory contexts in Lakota, based on data from six Lakota native speakers. There is clear evidence of both anticipatory and carryover nasal coarticulation across oral and nasal vowels, with a greater degree of carryover than anticipatory nasalization. Nasality in carryover contexts is nonetheless restricted: the oral–nasal contrast is neutralized for high back vowels in this context and realized for three of the six speakers in low vowels. In the absence of nasal consonant context, contrastive vowel nasalization is generally greatest late in the vowel. Low nasal vowels in carryover contexts parallel this pattern (despite the location of the nasal consonant before the vowel), and low nasal vowels in anticipatory contexts are most nasal at the start of the vowel. We relate the synchronic patterns of coarticulation in Lakota to both its system of contrast and diachronic processes in the evolution of nasality in Lakota. These data reflect that coarticulatory patterns, as well as contrastive patterns, are grammatical and controlled by speakers.

Use of waveform mixing to synthesize a continuum of vowel nasality in natural speech

Studies of the perception of vowel nasality often use synthesized stimuli to produce controlled gradience in nasality. To investigate the perception of nasality in natural speech, a method was developed wherein vowels differing naturally in nasality (e.g., from CVC and NVN words) are mixed to yield tokens with various degrees of nasality. First, monosyllables (e.g., CVC, NVC, CVN, NVN) matched for vowel quality and consonant place of articulation were recorded. The vowels from two tokens were excised, matched for amplitude, duration and pitch contour, and then overlaid sample-by-sample according to a specified ratio. The resulting vowel was spliced back into the desired consonantal context. Iterating this process over a series of ratios produced natural-sounding tokens along a continuum of vowel nasality. Acoustic measurements of the nasality of output tokens [using A1-P0 (Chen, 1997)] confirmed a relation between the ratio used and the nasality of the output. Stimuli created in this manner were used in a...

Optical phonetics and visual perception of lexical and phrasal boundaries in English

Detection of lexical and phrasal boundaries in the speech signal is crucial to successful comprehension. Several suprasegmental acoustic cues have been identified for boundary detection in speech (e.g., stress pattern, duration, and pitch). However, the corresponding optical cues have not been described in detail, and it is not known to which optical cues to boundaries speechreaders are attuned. In a production study, three male American English talkers spoke two repetitions each of eight pairs of sentences in two boundary conditions (one‐word versus two‐word sequences, one‐phrase versus two‐phrase sequences). Sentence pairs were constructed such that they differed minimally in the presence of a boundary. Audio, video, and 3D‐movements of the face were recorded. Sentence pairs in both boundary conditions differed on both optical and acoustic duration measurements. A subset of the sentence pairs was also presented in a visual perception study. Pairs were chosen a priori because they differed or did not dif...

Neighborhood-conditioned coarticulation effects in French listener-directed speech

Words from dense phonological neighborhoods (Hi-ND words) are realized with greater vowel hyperarticulation and increased coarticulation in English, relative to words from sparser neighborhoods (Lo-ND words) [e.g., Wright 2004]. Here, the relation between coarticulation and neighborhood density is investigated for French by looking at patterns for anticipatory and carryover nasal coarticulation, coronal and uvular CV coarticulation, and V-to-C rounding coarticulation. Twelve native French speakers (northern France) produced 82 disyllabic words of French containing a context for one of these 5 types of coarticulation in phonetically similar high-low ND pairs. Test words were produced to a real listener who had to transcribe them in the instructed positions on a grid. F1, F2, and A1-P0 (a spectral measure of nasality) were measured at 5 timepoints across each test vowel. In addition to having more hyperarticulated (peripheral) vowel midpoints, Hi-ND words showed greater anticipatory nasality and stronger coronal transitions in appropriate contexts than Lo-ND words. Carryover nasality and uvular and rounding coarticulation did not differ across NDs. These results can be interpreted in light of the relation between coarticulation and contrast and the role these effects may serve in making Hi-ND words, which are subject to greater lexical competition, easier to perceive.