Meghan Clayards

Tracking the time course of phonetic cue integration during spoken word recognition

Speech perception requires listeners to integrate multiple cues that each contribute to judgments about a phonetic category. Classic studies of trading relations assessed the weights attached to each cue but did not explore the time course of cue integration. Here, we provide the first direct evidence that asynchronous cues to voicing (/b/ vs. /p/) and manner (/b/ vs. /w/) contrasts become available to the listener at different times during spoken word recognition. Using the visual world paradigm, we show that the probability of eye movements to pictures of target and of competitor objects diverge at different points in time after the onset of the target word. These points of divergence correspond to the availability of early (voice onset time or formant transition slope) and late (vowel length) cues to voicing and manner contrasts. These results support a model of cue integration in which phonetic cues are used for lexical access as soon as they are available.

On place assimilation in sibilant sequences: Comparing French and English

Abstract Two parallel acoustic analyses were performed for French and English sibilant sequences, based on comparably structured read-speech corpora. They comprised all sequences of voiced and voiceless alveolar and postalveolar sibilants that can occur across word boundaries in the two languages, as well as the individual alveolar and postalveolar sibilants, combined with preceding or following labial consonants across word boundaries. The individual sibilants provide references in order to determine type and degree of place assimilation in the sequences. Based on duration and centre-of-gravity measurements that were taken for each sibilant and sibilant sequence, we found clear evidence for place assimilation not only for English, but also for French. In both languages the assimilation manifested itself gradually in the time as well as in the frequency domain. However, while in English assimilation occurred strictly regressively and primarily towards postalveolar, French assimilation was solely towards postalveolar, but in both regressive and progressive directions. Apart from these basic differences, the degree of assimilation in French and English was independent of simultaneous voice assimilation but varied considerably between the individual speakers. Overall, the context-dependent and speaker-specific assimilation patterns match well with previous findings.

High or Low? Comparing high- and low-variability phonetic training in adult and child second language learners

Background High talker variability (i.e., multiple voices in the input) has been found effective in training nonnative phonetic contrasts in adults. A small number of studies suggest that children also benefit from high-variability phonetic training with some evidence that they show greater learning (more plasticity) than adults given matched input, although results are mixed. However, no study has directly compared the effectiveness of high versus low talker variability in children. Methods Native Greek-speaking eight-year-olds (N = 52), and adults (N = 41) were exposed to the English /i/-/ɪ/ contrast in 10 training sessions through a computerized word-learning game. Pre- and post-training tests examined discrimination of the contrast as well as lexical learning. Participants were randomly assigned to high (four talkers) or low (one talker) variability training conditions. Results Both age groups improved during training, and both improved more while trained with a single talker. Results of a three-interval oddity discrimination test did not show the predicted benefit of high-variability training in either age group. Instead, children showed an effect in the reverse direction—i.e., reliably greater improvements in discrimination following single talker training, even for untrained generalization items, although the result is qualified by (accidental) differences between participant groups at pre-test. Adults showed a numeric advantage for high-variability but were inconsistent with respect to voice and word novelty. In addition, no effect of variability was found for lexical learning. There was no evidence of greater plasticity for phonetic learning in child learners. Discussion This paper adds to the handful of studies demonstrating that, like adults, child learners can improve their discrimination of a phonetic contrast via computerized training. There was no evidence of a benefit of training with multiple talkers, either for discrimination or word learning. The results also do not support the findings of greater plasticity in child learners found in a previous paper (Giannakopoulou, Uther & Ylinen, 2013a). We discuss these results in terms of various differences between training and test tasks used in the current work compared with previous literature.

The emergence, progress, and impact of sound change in progress in Seoul Korean: Implications for mechanisms of tonogenesis

Abstract This study examines the origin, progression, and impact of a sound change in Seoul Korean where the primary cue to a stop contrast in phrase-initial position is shifting from VOT to f0. Because it shares similarities with the initial phase of tonogenesis, investigating this “quasi-tonogenetic” sound change provides insight into the nature of the emergence of contrastive f0 in “tonogenetic” sound changes more generally. Using a dataset from a large apparent-time corpus of Seoul Korean, we built mixed-effects regression models of VOT and f0 to examine the time-course of change, focusing on word frequency and vowel height effects. We found that both VOT contrast reduction and f0 contrast enhancement are more advanced in high-frequency words and in stops before non-high vowels, indicating that the change is spreading across words and phonetic contexts in parallel. Furthermore, speakers suppress non-contrastive variation in f0 as f0 emerges as a primary cue. Our findings suggest that one impetus for tonogenetic change is production bias coupled with an adaptive link between the cues. We further discuss the role of Korean intonational phonology on f0 which may help explain why the phonetic precondition leads to change in Seoul Korean but not in other languages.

The time course of auditory and language-specific mechanisms in compensation for sibilant assimilation.

Models of spoken-word recognition differ on whether compensation for assimilation is language-specific or depends on general auditory processing. English and French participants were taught words that began or ended with the sibilants /s/ and /∫/. Both languages exhibit some assimilation in sibilant sequences (e.g., /s/ becomes like [∫] in dress shop and classe chargée), but they differ in the strength and predominance of anticipatory versus carryover assimilation. After training, participants were presented with novel words embedded in sentences, some of which contained an assimilatory context either preceding or following. A continuum of target sounds ranging from [s] to [∫] was spliced into the novel words, representing a range of possible assimilation strengths. Listeners’ perceptions were examined using a visual-world eyetracking paradigm in which the listener clicked on pictures matching the novel words. We found two distinct language-general context effects: a contrastive effect when the assimilating context preceded the target, and flattening of the sibilant categorization function (increased ambiguity) when the assimilating context followed. Furthermore, we found that English but not French listeners were able to resolve the ambiguity created by the following assimilatory context, consistent with their greater experience with assimilation in this context. The combination of these mechanisms allows listeners to deal flexibly with variability in speech forms.

Gradient sensitivity to acoustic detail and temporal integration of phonetic cues

Speech contains systematic covariation at the subphonemic level that could be used to integrate information over time (McMurray et al., 2003; Gow, 2001). Previous research has established sensitivity to this variation: activation for lexical competitors is sensitive to within‐category variation in voice‐onset‐time (McMurray et al., 2002). This study extends this investigation to other subphonemic speech cues by examining formant transitions (r/l and d/g), formant slope (b/w) and VOT (b/p) in an eye‐tracking paradigm similar to McMurray et al. (2002). Vowel length was also varied to examine temporal organization (e.g., VOT precedes the vowel). Subjects heard a token from each continua and selected the target from a screen containing pictures of the target, competitor and unrelated items. Fixations to the competitor increased with distance from the boundary along each of the speech continua. Unlike prior work, there was also an effect on fixations to the target. There was no effect of vowel length on the d/...

Automatic forced alignment on child speech: Directions for improvement

Phonetic analysis is labor intensive, limiting the amount of data that can be considered. Recently, automated techniques (e.g., forced alignment based on Automatic Speech Recognition - ASR) have emerged allowing for much larger-scale analyses. For adult speech, forced alignment can be accurate even when the phonetic transcription is automatically generated, allowing for large-scale phonetic studies. However, such analyses remain difficult for childrens speech, where ASR methods perform more poorly. The present study used a trainable forced aligner that performs well on adult speech to examine the effect of four factors on alignment accuracy of child speech: (1) Corpus - elicited speech (multiple children) versus spontaneous speech (single child); (2) Pronunciation dictionary - standard adult versus customized; (3) Training data - adult lab speech, corpus-specific child speech, all child speech, or a combination of child and adult speech; (4) Segment type - voiceless stops, voiceless sibilants, and vowels...

A longitudinal study of individual differences in the acquisition of new vowel contrasts

Abstract This study explores how individuals’ second language cue weighting strategies change over time and across different contrasts. The study investigates the developmental changes in perceptual cue weighting of two English vowel contrasts (/i/-/ɪ/ and /ɛ/-/ae/) by adult and child Korean learners of English during their first year of immersion in Canada. Longitudinal results revealed that adult learners had an initial advantage in L2 perceptual acquisition over children at least for the /i/-/ɪ/ contrast, but after one year some children showed greater improvements especially on the more difficult /ɛ/-/ae/ contrast. Both groups of Korean learners showed different acquisition patterns between the two vowel contrasts: they used both spectral and duration cues to distinguish /i/-/ɪ/ but generally only duration to distinguish /ɛ/-/ae/. By examining cue weights over time, this study partially confirmed the hypothesized developmental stages for the acquisition of L2 vowels first proposed by Escudero (2000) for Spanish learners of English. However, some unpredicted patterns were also identified. Most importantly, the longitudinal results suggest that individual differences in cue weighting are not merely random variability in the learner’s response patterns, but are systematically associated with the developmental trajectories of individual learners and those trajectories vary according to vowel contrast.

Individual differences in second language speech perception across tasks and contrasts: The case of English vowel contrasts by Korean learners

Abstract: The present study examines whether individual differences in second language (L2) learners’ perceptual cue weighting strategies reflect systematic abilities. We tested whether cue weights indicate proficiency in perception using a naturalistic discrimination task as well as whether cue weights are related across contrasts for individual learners. Twenty-four native Korean learners of English completed a two-alternative forced choice identification task on /ɪ/-/i/ and /ɛ/-/æ/ contrasts varying orthogonally in formant frequency and duration to determine their perceptual cue weights. They also completed a two-talker AX discrimination task on natural productions of the same vowels. In the cue-weighting task, we found that individual L2 learners varied greatly in the extent to which they relied on particular phonetic cues. However, individual learners’ perceptual weighting strategies were consistent across contrasts. We also found that more native-like performance on this task – reliance on spectral differences over duration – was related to better recognition of naturally produced vowels in the discrimination task. Therefore, the present study confirms earlier reports that learners vary in the extent to which they rely on particular phonetic cues. Additionally, our results demonstrate that these individual differences reflect systematic cue use across contrasts as well as the ability to discriminate naturally produced stimuli.

Compensatory Strategies in the Developmental Patterns of English /s/: Gender and Vowel Context Effects

Purpose The developmental trajectory of English /s/ was investigated to determine the extent to which childrens speech productions are acoustically fine-grained. Given the hypothesis that young children have adultlike phonetic knowledge of /s/, the following were examined: (a) whether this knowledge manifests itself in acoustic spectra that match the gender-specific patterns of adults, (b) whether vowel context affects the spectra of /s/ in adults and children similarly, and (c) whether children adopt compensatory production strategies to match adult acoustic targets. Method Several acoustic variables were measured from word-initial /s/ (and /t/) and the following vowel in the productions of children aged 2 to 5 years and adult controls using 2 sets of corpora from the Paidologos database. Results Gender-specific patterns in the spectral distribution of /s/ were found. Acoustically, more canonical /s/ was produced before vowels with higher F1 (i.e., lower vowels) in children, a context where lingual articulation is challenging. Measures of breathiness and vowel intrinsic F0 provide evidence that children use a compensatory aerodynamic mechanism to achieve their acoustic targets in articulatorily challenging contexts. Conclusion Together, these results provide evidence that childrens phonetic knowledge is acoustically detailed and gender specified and that speech production goals are acoustically oriented at early stages of speech development.