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1. Modeling adaptation to a novel accent

   Hitczenko, Kasia; Feldman, Naomi H. (August 2016, Proceedings of the Annual Conference of the Cognitive Science Society)

   Listeners quickly adapt to novel accents. There are three main hypotheses for how they do so. Some suggest that listeners expand their phonetic categories, allowing more variability in how a sound is pronounced. Others argue that listeners shift their categories instead, only accepting deviations consistent with the accent. A third hypothesis is that listeners both shift and expand their categories. Most work has supported the category expansion hypotheses, with the key exception of Maye et al. (2008) who argued for a shifting strategy. Here, we apply the ideal adaptor model from Kleinschmidt & Jaeger (2015) to reexamine what conclusions can be drawn from their data. We compare adaptation models in which categories are shifted, expanded, or both shifted and expanded. We show that models involving expansion can explain the data as well as, if not better than, the shift model, in contrast to what has been previously concluded from these data. 

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2. Revisiting the left ear advantage for phonetic cues to talker identification

   https://doi.org/10.1121/10.0015093  

   Drown, Lee; Philip, Betsy; Francis, Alexander L.; Theodore, Rachel M. (November 2022, The Journal of the Acoustical Society of America)

   Previous research suggests that learning to use a phonetic property [e.g., voice-onset-time, (VOT)] for talker identity supports a left ear processing advantage. Specifically, listeners trained to identify two “talkers” who only differed in characteristic VOTs showed faster talker identification for stimuli presented to the left ear compared to that presented to the right ear, which is interpreted as evidence of hemispheric lateralization consistent with task demands. Experiment 1 ( n =  97) aimed to replicate this finding and identify predictors of performance; experiment 2 ( n =  79) aimed to replicate this finding under conditions that better facilitate observation of laterality effects. Listeners completed a talker identification task during pretest, training, and posttest phases. Inhibition, category identification, and auditory acuity were also assessed in experiment 1. Listeners learned to use VOT for talker identity, which was positively associated with auditory acuity. Talker identification was not influenced by ear of presentation, and Bayes factors indicated strong support for the null. These results suggest that talker-specific phonetic variation is not sufficient to induce a left ear advantage for talker identification; together with the extant literature, this instead suggests that hemispheric lateralization for talker-specific phonetic variation requires phonetic variation to be conditioned on talker differences in source characteristics. 

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3. Disentangling the Role of Biphone Probability From Neighborhood Density in the Perception of Nonwords

   https://doi.org/10.1177/00238309231164982  

   Steffman, Jeremy; Sundara, Megha (May 2023, Language and Speech)

   In six experiments we explored how biphone probability and lexical neighborhood density influence listeners’ categorization of vowels embedded in nonword sequences. We found independent effects of each. Listeners shifted categorization of a phonetic continuum to create a higher probability sequence, even when neighborhood density was controlled. Similarly, listeners shifted categorization to create a nonword from a denser neighborhood, even when biphone probability was controlled. Next, using a visual world eye-tracking task, we determined that biphone probability information is used rapidly by listeners in perception. In contrast, task complexity and irrelevant variability in the stimuli interfere with neighborhood density effects. These results support a model in which both biphone probability and neighborhood density independently affect word recognition, but only biphone probability effects are observed early in processing. 

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4. Individual differences in the perception of phonetic category structure predict speech-in-noise performance

   https://doi.org/10.1121/10.0028583  

   Myers, Emily; Phillips, Matthew; Skoe, Erika (September 2024, The Journal of the Acoustical Society of America)

   Speech sounds exist in a complex acoustic–phonetic space, and listeners vary in the extent to which they are sensitive to variability within the speech sound category (“gradience”) and the degree to which they show stable, consistent responses to phonetic stimuli. Here, we investigate the hypothesis that individual differences in the perception of the sound categories of one's language may aid speech-in-noise performance across the adult lifespan. Declines in speech-in-noise performance are well documented in healthy aging, and are, unsurprisingly, associated with differences in hearing ability. Nonetheless, hearing status and age are incomplete predictors of speech-in-noise performance, and long-standing research suggests that this ability draws on more complex cognitive and perceptual factors. In this study, a group of adults ranging in age from 18 to 67 years performed online assessments designed to measure phonetic category sensitivity, questionnaires querying recent noise exposure history and demographic factors, and crucially, a test of speech-in-noise perception. Results show that individual differences in the perception of two consonant contrasts significantly predict speech-in-noise performance, even after accounting for age and recent noise exposure history. This finding supports the hypothesis that individual differences in sensitivity to phonetic categories mediates speech perception in challenging listening situations. 

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5. How to use context to disambiguate overlapping categories: The test case of Japanese vowel length

   Hitczenko, Kasia; Mazuka, Reiko; Elsner, Micha; Feldman, Naomi H. (July 2018, Proceedings of the Annual Conference of the Cognitive Science Society)

   Infants learn the sound categories of their language and adults successfully process the sounds they hear, even though sound categories often overlap in their acoustics. Most researchers agree that listeners use context to disambiguate overlapping categories. However, they differ in their ideas about how context is used. One idea is that listeners normalize out the systematic effects of context from the acoustics of a sound. Another idea is that contextual information may itself be an informative cue to category membership, due to patterns in the types of contexts that particular sounds occur in. We directly contrast these two ways of using context by applying each one to the test case of Japanese vowel length. We find that normalizing out contextual variability from the acoustics does not improve categorization, but using context in a top-down fashion does so substantially. This reveals a limitation of normalization in phonetic acquisition and processing and suggests that approaches that make use of top-down contextual information are promising to pursue. 

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