Rachel M. Theodore

Individual talker differences in voice-onset-time: contextual influences.

Previous research indicates that talkers differ in phonetically relevant properties of speech, including voice-onset-time (VOT) in word-initial stop consonants; some talkers have characteristically shorter VOTs than others. Previous research also indicates that VOT is robustly affected by contextual influences, including speaking rate and place of articulation. This paper examines whether these contextual influences on VOT are themselves talker-specific. Many tokens of alveolar ti (experiment 1) or labial pi and velar ki (experiment 2) were elicited from talkers across a range of rates. VOT and vowel duration (a metric of rate) were measured for each token. Hierarchical linear modeling analyses showed that (1) VOT increased as rate decreased for all talkers, but the magnitude of the increase varied significantly across talkers; thus the effect of rate on VOT was talker-specific; (2) the talker-specific effect of rate was stable across a change in place of articulation; and (3) for all talkers VOTs were shorter for labial than velar stops, and there was no significant variability in the magnitude of this displacement across talkers; thus the effect of place on VOT was not talker-specific. The implications of these findings for how listeners might accommodate talker differences in VOT during speech perception are discussed.

Language exposure facilitates talker learning prior to language comprehension, even in adults

Adults show a native language advantage for talker identification, which has been interpreted as evidence that phonological knowledge mediates talker learning. However, infants also show a native language benefit for talker discrimination, suggesting that sensitivity to linguistic structure due to systematic language exposure promotes talker learning, even in the absence of functional phonological knowledge or language comprehension. We tested this hypothesis by comparing two groups of English-monolingual adults on their ability to learn English and French voices. One group resided in Montréal with regular exposure to spoken French; the other resided in Storrs, Connecticut and did not have French exposure. Montréal residents showed faster learning and better retention for the French voices compared to their Storrs-residing peers. These findings demonstrate that systematic exposure to a foreign language bolsters talker learning in that language, expanding the gradient effect of language experience on talker learning to perceptual learning that precedes sentence comprehension.

Attention modulates specificity effects in spoken word recognition: Challenges to the time-course hypothesis

Findings in the domain of spoken word recognition have indicated that lexical representations contain both abstract and episodic information. It has been proposed that processing time determines when each source of information is recruited, with increased processing time being required to access lower-frequency episodic instantiations. The time-course hypothesis of specificity effects has thus identified a strong role for retrieval mechanisms mediating the use of abstract versus episodic information. Here we conducted three recognition memory experiments to examine whether the findings previously attributed to retrieval mechanisms might instead reflect attention during encoding. The results from Experiment 1 showed that talker-specificity effects emerged when subjects attended to the individual speakers, but not when they attended to lexical characteristics, during encoding, even though processing times at retrieval were equivalent. The results from Experiment 2 showed that talker-specificity effects emerged when listeners attended to talker gender but not when they attended to syntactic characteristics, even though the processing times at retrieval were significantly longer in the latter condition. The results from Experiment 3 showed no talker-specificity effects when all listeners attended to lexical characteristics, even when processing at retrieval was slowed by the addition of background noise. Collectively, these results suggest that when processing time during retrieval is decoupled from encoding factors, it fails to predict the emergence of talker-specificity effects. Rather, attention during encoding appears to be the putative variable.

Attention modulates the time-course of talker-specificity effects in lexical retrieval

Listeners retain in memory phonetic characteristics associated with individual talkers. It has been proposed that talker-specificity effects, while robust, emerge late in processing, reflecting increased time to activate lower-frequency instantiations for individual talkers. Here we test the hypothesis that attention to talker characteristics modulates the time-course of talker-specificity effects. Two groups of listeners participated in encoding and recognition phases. During encoding, all listeners heard words produced by two talkers, but only half of them were required to identify talker gender. During recognition, all listeners heard a series of words and indicated whether each word had been presented during encoding. Critically, some of the words were previously presented in the same voice and some in a different voice. Results showed no difference in mean hit rate or reaction time between the two groups, indicating that the encoding manipulation did not globally affect recognition memory or response...

Examination of the Locus of Positional Effects on Children's Production of Plural -"s": Considerations from Local and Global Speech Planning.

PURPOSE Prosodic and articulatory factors influence childrens production of inflectional morphemes. For example, plural -s is produced more reliably in utterance-final compared to utterance-medial position (i.e., the positional effect), which has been attributed to the increased planning time in utterance-final position. In previous investigations of plural -s, utterance-medial plurals were followed by a stop consonant (e.g., dogsbark), inducing high articulatory complexity. We examined whether the positional effect would be observed if the utterance-medial context were simplified to a following vowel. METHOD An elicited imitation task was used to collect productions of plural nouns from 2-year-old children. Nouns were elicited utterance-medially and utterance-finally, with the medial plural followed by either a stressed or an unstressed vowel. Acoustic analysis was used to identify evidence of morpheme production. RESULTS The positional effect was absent when the morpheme was followed by a vowel (e.g., dogseat). However, it returned when the vowel-initial word contained 2 syllables (e.g., dogsarrive), suggesting that the increased processing load in the latter condition negated the facilitative effect of the easy articulatory context. CONCLUSIONS Childrens productions of grammatical morphemes reflect a rich interaction between emerging levels of linguistic competence, raising considerations for diagnosis and rehabilitation of language disorders.

Perceptual prothesis in native Spanish speakers

Previous research suggests a perceptual bias exists for native phonotactics [D. Massaro and M. Cohen, Percept. Psychophys. 34, 338–348 (1983)] such that listeners report nonexistent segments when listening to stimuli that violate native phonotactics [E. Dupoux, K. Kakehi, Y. Hirose, C. Pallier, and J. Mehler, J. Exp. Psychol.: Human Percept. Perform. 25, 1568–1578 (1999)]. This study investigated how native‐language experience affects second language processing, focusing on how native Spanish speakers perceive the English clusters /st/, /sp/, and /sk/, which represent phonotactically illegal forms in Spanish. To preserve native phonotactics, Spanish speakers often produce prothetic vowels before English words beginning with /s/ clusters. Is the influence of native phonotactics also present in the perception of illegal clusters? A stimuli continuum ranging from no vowel (e.g., ‘‘sku’’) to a full vowel (e.g., ‘‘esku’’) before the cluster was used. Four final vowel contexts were used for each cluster, result...

More than a boundary shift: Perceptual adaptation to foreign-accented speech reshapes the internal structure of phonetic categories.

The literature on perceptual learning for speech shows that listeners use lexical information to disambiguate phonetically ambiguous speech sounds and that they maintain this new mapping for later recognition of ambiguous sounds for a given talker. Evidence for this kind of perceptual reorganization has focused on phonetic category boundary shifts. Here, we asked whether listeners adjust both category boundaries and internal category structure in rapid adaptation to foreign accents. We investigated the perceptual learning of Mandarin-accented productions of word-final voiced stops in English. After exposure to a Mandarin speaker’s productions, native-English listeners’ adaptation to the talker was tested in 3 ways: a cross-modal priming task to assess spoken word recognition (Experiment 1), a category identification task to assess shifts in the phonetic boundary (Experiment 2), and a goodness rating task to assess internal category structure (Experiment 3). Following exposure, both category boundary and internal category structure were adjusted; moreover, these prelexical changes facilitated subsequent word recognition. Together, the results demonstrate that listeners’ sensitivity to acoustic–phonetic detail in the accented input promoted a dynamic, comprehensive reorganization of their perceptual response as a consequence of exposure to the accented input. We suggest that an examination of internal category structure is important for a complete account of the mechanisms of perceptual learning.

Reading ability reflects individual differences in auditory brainstem function, even into adulthood

HIGHLIGHTSBrainstem representation of sound relates to reading ability into adulthood.Brainstem‐reading relationships are evident for speech and non‐speech stimuli.Lower adult literacy level is associated with earlier auditory brainstem responses. ABSTRACT Research with developmental populations suggests that the maturational state of auditory brainstem encoding is linked to reading ability. Specifically, children with poor reading skills resemble biologically younger children with respect to their auditory brainstem responses (ABRs) to speech stimulation. Because ABR development continues into adolescence, it is possible that the link between ABRs and reading ability changes or resolves as the brainstem matures. To examine these possibilities, ABRs were recorded at varying presentation rates in adults with diverse, yet unimpaired reading levels. We found that reading ability in adulthood related to ABR Wave V latency, with more juvenile response morphology linked to less proficient reading ability, as has been observed for children. These data add to the evidence indicating that auditory brainstem responses serve as an index of the sound‐based skills that underlie reading, even into adulthood.

Voice-sensitive brain networks encode talker-specific phonetic detail

HighlightsSpeech carries information about the talker as well as the linguistic message.This study tested neural sensitivity to phonetic information associated with talkers.Right hemisphere areas were identified that respond to the “typicality” of phonetic information for a given talker. ABSTRACT The speech stream simultaneously carries information about talker identity and linguistic content, and the same acoustic property (e.g., voice‐onset‐time, or VOT) may be used for both purposes. Separable neural networks for processing talker identity and phonetic content have been identified, but it is unclear how a singular acoustic property is parsed by the neural system for talker identification versus phonetic processing. In the current study, listeners were exposed to two talkers with characteristically different VOTs. Subsequently, brain activation was measured using fMRI as listeners performed a phonetic categorization task on these stimuli. Right temporoparietal regions previously implicated in talker identification showed sensitivity to the match between VOT variant and talker, whereas left posterior temporal regions showed sensitivity to the typicality of phonetic exemplars, regardless of talker typicality. Taken together, these results suggest that neural systems for voice recognition capture talker‐specific phonetic variation.

Lexically guided perceptual tuning of internal phonetic category structure

Listeners use lexical information to retune the mapping between the acoustic signal and speech sound representations, resulting in changes to phonetic category boundaries. Other research shows that phonetic categories have a rich internal structure; within-category variation is represented in a graded fashion. The current work examined whether lexically informed perceptual learning promotes a comprehensive reorganization of internal category structure. The results showed a reorganization of internal structure for one but not both of the examined categories, which may reflect an attenuation of learning for distributions with extensive category overlap. This finding points towards potential input-driven constraints on lexically guided phonetic retuning.