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1. Comparing human and machine's use of coarticulatory vowel nasalization for linguistic classification

   https://doi.org/10.1121/10.0027932  

   Zellou, Georgia; Kim, Lila; Gendrot, Cédric (July 2024, The Journal of the Acoustical Society of America)

   Anticipatory coarticulation is a highly informative cue to upcoming linguistic information: listeners can identify that the word is ben and not bed by hearing the vowel alone. The present study compares the relative performances of human listeners and a self-supervised pre-trained speech model (wav2vec 2.0) in the use of nasal coarticulation to classify vowels. Stimuli consisted of nasalized (from CVN words) and non-nasalized (from CVCs) American English vowels produced by 60 humans and generated in 36 TTS voices. wav2vec 2.0 performance is similar to human listener performance, in aggregate. Broken down by vowel type: both wav2vec 2.0 and listeners perform higher for non-nasalized vowels produced naturally by humans. However, wav2vec 2.0 shows higher correct classification performance for nasalized vowels, than for non-nasalized vowels, for TTS voices. Speaker-level patterns reveal that listeners' use of coarticulation is highly variable across talkers. wav2vec 2.0 also shows cross-talker variability in performance. Analyses also reveal differences in the use of multiple acoustic cues in nasalized vowel classifications across listeners and the wav2vec 2.0. Findings have implications for understanding how coarticulatory variation is used in speech perception. Results also can provide insight into how neural systems learn to attend to the unique acoustic features of coarticulation. 

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2. Variation in the production of nasal coarticulation by speaker age and speech style

   https://doi.org/10.1121/10.0036227  

   Zellou, Georgia; Cohn, Michelle (March 2025, JASA Express Letters)

   This study investigates apparent-time variation in the production of anticipatory nasal coarticulation in California English. Productions of consonant-vowel-nasal words in clear vs casual speech by 58 speakers aged 18–58 (grouped into three generations) were analyzed for degree of coarticulatory vowel nasality. Results reveal an interaction between age and style: the two younger speaker groups produce greater coarticulation (measured as A1-P0) in clear speech, whereas older speakers produce less variable coarticulation across styles. Yet, duration lengthening in clear speech is stable across ages. Thus, age- and style-conditioned changes in produced coarticulation interact as part of change in coarticulation grammars over time. 

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3. Perceptual Cue Weighting Is Influenced by the Listener's Gender and Subjective Evaluations of the Speaker: The Case of English Stop Voicing

   https://doi.org/10.3389/fpsyg.2022.840291  

   Yu, Alan C. (April 2022, Frontiers in Psychology)

   Speech categories are defined by multiple acoustic dimensions and their boundaries are generally fuzzy and ambiguous in part because listeners often give differential weighting to these cue dimensions during phonetic categorization. This study explored how a listener's perception of a speaker's socio-indexical and personality characteristics influences the listener's perceptual cue weighting. In a matched-guise study, three groups of listeners classified a series of gender-neutral /b/-/p/ continua that vary in VOT and F0 at the onset of the following vowel. Listeners were assigned to one of three prompt conditions (i.e., a visually male talker, a visually female talker, or audio-only) and rated the talker in terms of vocal (and facial, in the visual prompt conditions) gender prototypicality, attractiveness, friendliness, confidence, trustworthiness, and gayness. Male listeners and listeners who saw a male face showed less reliance on VOT compared to listeners in the other conditions. Listeners' visual evaluation of the talker also affected their weighting of VOT and onset F0 cues, although the effects of facial impressions differ depending on the gender of the listener. The results demonstrate that individual differences in perceptual cue weighting are modulated by the listener's gender and his/her subjective evaluation of the talker. These findings lend support for exemplar-based models of speech perception and production where socio-indexical features are encoded as a part of the episodic traces in the listeners' mental lexicon. This study also shed light on the relationship between individual variation in cue weighting and community-level sound change by demonstrating that VOT and onset F0 co-variation in North American English has acquired a certain degree of socio-indexical significance. 

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4. Limits of short-term perceptual training for enhancing Seoul-Korean listeners’ use of English lexical stress in spoken word recognition

   https://doi.org/10.1121/10.0026882  

   Tremblay, Annie C; Kim, Hyoju; Kim, Sahyang; Cho, Taehong (March 2024, The Journal of the Acoustical Society of America)

   This study investigates whether short-term perceptual training can enhance Seoul-Korean listeners’ use of English lexical stress in spoken word recognition. Unlike English, Seoul Korean does not have lexical stress (or lexical pitch accents/tones). Seoul-Korean speakers at a high-intermediate English proficiency completed a visual-world eye-tracking experiment adapted from Connell et al. (2018) (pre-/post-test). The experiment tested whether pitch in the target stimulus (accented versus unaccented first syllable) and vowel quality in the lexical competitor (reduced versus full first vowel) modulated fixations to the target word (e.g., PARrot; ARson) over the competitor word (e.g., paRADE or PARish; arCHIVE or ARcade). In the training (eight 30-min sessions over eight days), participants heard English lexical-stress minimal pairs uttered by four talkers (high variability) or one talker (low variability), categorized them as noun (first-syllable stress) or verb (second-syllable stress), and received accuracy feedback. The results showed that neither training increased target-over-competitor fixation proportions. Crucially, the same training had been found to improve Seoul- Korean listeners’ recall of English words differing in lexical stress (Tremblay et al., 2022) and their weighting of acoustic cues to English lexical stress (Tremblay et al., 2023). These results suggest that short-term perceptual training has a limited effect on target-over-competitor word activation. 

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5. Selective tuning of nasal coarticulation and hyperarticulation across slow-clear, casual, and fast-clear speech styles

   https://doi.org/10.1121/10.0023841  

   Cohn, Michelle; Zellou, Georgia (December 2023, JASA Express Letters)

   This study investigates how California English speakers adjust nasal coarticulation and hyperarticulation on vowels across three speech styles: speaking slowly and clearly (imagining a hard-of-hearing addressee), casually (imagining a friend/family member addressee), and speaking quickly and clearly (imagining being an auctioneer). Results show covariation in speaking rate and vowel hyperarticulation across the styles. Additionally, results reveal that speakers produce more extensive anticipatory nasal coarticulation in the slow-clear speech style, in addition to a slower speech rate. These findings are interpreted in terms of accounts of coarticulation in which speakers selectively tune their production of nasal coarticulation based on the speaking style. 

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