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Introduction: Learning to understand and speak a new language can be challenging and discouraging for adults. One potential tool for improving learning is transcutaneous auricular vagus nerve stimulation (taVNS), which modulates perception, memory, and attention systems. It has recently been reported that taVNS can improve English speakers' ability to perceive unfamiliar Mandarin tones. The current project explored the potential benefits of taVNS for language learning beyond tone perception. Methods: We studied adults' ability to perceive and produce unfamiliar speech sounds as well as any potential change in language learningmotivation frompre- to post-training. Forty-five native English speakers were divided into three groups and were trained to perceive German sounds: one group received stimulation during easier-to-learn sounds (vowels), one group received stimulation during harder-to-learn sounds (fricatives), and a control group received no stimulation. Results and discussion: We did not find evidence that taVNS improved perception or production of the German sounds, but there was evidence that it did improve some aspects of motivation. Specifically, the group that received taVNS during easier sounds showed a significant decrease in feelings of tension/pressure about language learning, while the other groups did not. Overall, the present study does not find that taVNS holds benefits for the acquisition of new speech sounds; however, the field is nascent, and so the potential applications of taVNS for language learning remain to be clarified. [ABSTRACT FROM AUTHOR]

High vowels have higher f0 than low vowels, creating a context effect on the interpretation of f0. Since onset F0 is a cue to stop voicing, the vowel context is expected to influence voicing judgements. Listeners categorized syllables starting with high ("bee"-"pea") and low ("bye"-"pie") vowels varying orthogonally in VOT and onset F0. Listeners made use of both cues as expected. Furthermore, vowel height affected listeners' categorization. Syllables with the low vowel /a/ elicited more voiceless responses compared to syllables with the high vowel /i/. This suggests that listeners compensate for vowel intrinsic effects when making other phonemic judgements. [ABSTRACT FROM AUTHOR]

Purpose: Previous work has found that both young and older adults exhibit a lexical bias in categorizing speech stimuli. In young adults, this has been argued to be an automatic influence of the lexicon on perceptual category boundaries. Older adults exhibit more top-down biases than younger adults, including an increased lexical bias. We investigated the nature of the increased lexical bias using a sensorimotor adaptation task designed to evaluate whether automatic processes drive this bias in older adults. Method: A group of older adults (n = 27) and younger adults (n = 35) participated in an altered auditory feedback production task. Participants produced target words and nonwords under altered feedback that affected the 1st formant of the vowel. There were 2 feedback conditions that affected the lexical status of the target, such that target words were shifted to sound more like nonwords (e.g., less-liss) and target nonwords to sound more like words (e.g., "kess-kiss"). Results: A mixed-effects linear regression was used to investigate the magnitude of compensation to altered auditory feedback between age groups and lexical conditions. Over the course of the experiment, older adults compensated (by shifting their production of 1st formant) more to altered auditory feedback when producing words that were shifted toward nonwords (less-liss) than when producing nonwords that were shifted toward words (kess-kiss). This is in contrast to younger adults who compensated more to nonwords that were shifted toward words compared to words that were shifted toward nonwords. Conclusion: We found no evidence that the increased lexical bias previously observed in older adults is driven by a greater sensitivity to top-down lexical influence on perceptual category boundaries. We suggest the increased lexical bias in older adults is driven by postperceptual processes that arise as a result of age-related cognitive and sensory changes.

Purpose: Heterogeneous child speech was force-aligned to investigate whether (a) manipulating specific parameters could improve alignment accuracy and (b) forced alignment could be used to replicate published results on acoustic characteristics of /s/ production by children. Method: In Part 1, child speech from 2 corpora was force-aligned with a trainable aligner (Prosodylab-Aligner) under different conditions that systematically manipulated input training data and the type of transcription used. Alignment accuracy was determined by comparing hand and automatic alignments as to how often they overlapped (%-Match) and absolute differences in duration and boundary placements. Using mixed-effects regression, accuracy was modeled as a function of alignment conditions, as well as segment and child age. In Part 2, forced alignments derived from a subset of the alignment conditions in Part 1 were used to extract spectral center of gravity of /s/ productions from young children. These findings were compared to published results that used manual alignments of the same data. Results: Overall, the results of Part 1 demonstrated that using training data more similar to the data to be aligned as well as phonetic transcription led to improvements in alignment accuracy. Speech from older children was aligned more accurately than younger children. In Part 2, /s/ center of gravity extracted from force-aligned segments was found to diverge in the speech of male and female children, replicating the pattern found in previous work using manually aligned segments. This was true even for the least accurate forced alignment method. Conclusions: Alignment accuracy of child speech can be improved by using more specific training and transcription. However, poor alignment accuracy was not found to impede acoustic analysis of /s/ produced by even very young children. Thus, forced alignment presents a useful tool for the analysis of child speech.

Purpose: This study examined whether older adults remain perceptually flexible when presented with ambiguities in speech in the absence of lexically disambiguating information. We expected older adults to show less perceptual learning when top-down information was not available. We also investigated whether individual differences in executive function predicted perceptual learning in older and younger adults. Method: Younger (n = 31) and older adults (n = 27) completed 2 perceptual learning tasks composed of a pretest, exposure, and posttest phase. Both learning tasks exposed participants to clear and ambiguous speech tokens, but crucially, the lexically guided learning task provided disambiguating lexical information whereas the distributional learning task did not. Participants also performed several cognitive tasks to investigate individual differences in working memory, vocabulary, and attentionswitching control. Results: We found that perceptual learning is maintained in older adults, but that learning may be stronger in contexts where top-down information is available. Receptive vocabulary scores predicted learning across both age groups and in both learning tasks. Conclusions Implicit learning is maintained with age across different learning conditions but remains stronger when lexically biasing information is available. We find that receptive vocabulary is relevant for learning in both types of learning tasks, suggesting the importance of vocabulary knowledge for adapting to ambiguities in speech.

Adults differ considerably in their perception of both native and nonnative phonemes. For instance, when presented with continua of native phonemes on two-alternative forced choice (2AFC) or visual analog scaling (VAS) tasks, some people show sudden changes in responses (i.e., steep identification slopes) and others show gradual changes (i.e., shallow identification slopes). Moreover, some adults are more successful than others at learning unfamiliar phonemes. The predictors of these individual differences and the relationships between them are poorly understood. It also remains unclear to what extent different tasks (2AFC vs. VAS) may reflect distinct individual differences in perception. In two experiments, we addressed these questions by examining the relationships between individual differences in performance on native and nonnative phonetic perception tasks. We found that shallow 2AFC identification slopes were not related to shallow VAS identification slopes but were related to inconsistent VAS responses. Additionally, our results suggest that consistent native perception may play a role in promoting successful nonnative perception. These findings help characterize the nature of individual differences in phonetic perception and contribute to our understanding of how to measure such differences. This work also has implications for encouraging successful acquisition of new languages in adulthood. Public Significance Statement: Successfully perceiving speech sounds is a crucial skill for spoken communication; yet individuals show differences in how they perceive both native and nonnative speech sounds. We studied the relationships between performance on different native and nonnative speech perception tasks, finding that (a) different tasks measure different subtleties and (b) people with consistent perception of native speech sounds tend to be better at accurately perceiving nonnative sounds. These findings have implications for understanding the nature of individual differences in speech perception and for helping adults to learn new languages successfully. [ABSTRACT FROM AUTHOR]

Purpose: The developmental trajectory of English /s/ was investigated to determine the extent to which children's 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 F[subscript 1] (i.e., lower vowels) in children, a context where lingual articulation is challenging. Measures of breathiness and vowel intrinsic F[subscript 0] 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 children's phonetic knowledge is acoustically detailed and gender specified and that speech production goals are acoustically oriented at early stages of speech development.

Purpose: Previous work has found that both young and older adults exhibit a lexical bias in categorizing speech stimuli. In young adults, this has been argued to be an automatic influence of the lexicon on perceptual category boundaries. Older adults exhibit more top-down biases than younger adults, including an increased lexical bias. We investigated the nature of the increased lexical bias using a sensorimotor adaptation task designed to evaluate whether automatic processes drive this bias in older adults. Method: A group of older adults (n = 27) and younger adults (n = 35) participated in an altered auditory feedback production task. Participants produced target words and nonwords under altered feedback that affected the 1st formant of the vowel. There were 2 feedback conditions that affected the lexical status of the target, such that target words were shifted to sound more like nonwords (e.g., less-liss) and target nonwords to sound more like words (e.g., kess-kiss). Results: A mixed-effects linear regression was used to investigate the magnitude of compensation to altered auditory feedback between age groups and lexical conditions. Over the course of the experiment, older adults compensated (by shifting their production of 1st formant) more to altered auditory feedback when producing words that were shifted toward nonwords (less-liss) than when producing nonwords that were shifted toward words (kess-kiss). This is in contrast to younger adults who compensated more to nonwords that were shifted toward words compared to words that were shifted toward nonwords. Conclusion: We found no evidence that the increased lexical bias previously observed in older adults is driven by a greater sensitivity to top-down lexical influence on perceptual category boundaries. We suggest the increased lexical bias in older adults is driven by postperceptual processes that arise as a result of age-related cognitive and sensory changes., The already complex task of speech perception becomes more difficult with age, as sensory and cognitive declines cause listening performance to decrease. Older adults are susceptible to a variety of [...]

The acoustic cues for prosodic prominence have been explored extensively, but one open question is to what extent they differ by context. This study investigates the extent to which vowel type affects how acoustic cues are related to prominence ratings provided in a corpus of spoken Mandarin. In the corpus, each syllable was rated as either prominent or non-prominent. We predicted prominence ratings using Bayesian mixed-effect regression models for each of four Mandarin vowels (/a, i, ɤ, u/), using fundamental frequency (F0), intensity, duration, the first and second formants, and tone type as predictors. We compared the role of each cue within and across the four models. We found that overall duration was the best predictor of prominence ratings and that formants were the weakest, but the role of each cue differed by vowel. We did not find credible evidence that F0 was relevant for /a/, or that intensity was relevant for /i/. We also found evidence that duration was more important for /ɤ/ than for /i/. The results suggest that vowel type credibly affects prominence ratings, which may reflect differences in the coordination of acoustic cues in prominence marking. [ABSTRACT FROM AUTHOR]

Purpose: Heterogeneous child speech was force-aligned to investigate whether (a) manipulating specific parameters could improve alignment accuracy and (b) forced alignment could be used to replicate published results on acoustic characteristics of/s/ production by children.Method: In Part 1, child speech from 2 corpora was force-aligned with a trainable aligner (Prosodylab-Aligner) under different conditions that systematically manipulated input training data and the type of transcription used. Alignment accuracy was determined by comparing hand and automatic alignments as to how often they overlapped (%-Match) and absolute differences in duration and boundary placements. Using mixed-effects regression, accuracy was modeled as a function of alignment conditions, as well as segment and child age. In Part 2, forced alignments derived from a subset of the alignment conditions in Part 1 were used to extract spectral center of gravity of/s/ productions from young children. These findings were compared to published results that used manual alignments of the same data.Results: Overall, the results of Part 1 demonstrated that using training data more similar to the data to be aligned as well as phonetic transcription led to improvements in alignment accuracy. Speech from older children was aligned more accurately than younger children. In Part 2, /s/ center of gravity extracted from force-aligned segments was found to diverge in the speech of male and female children, replicating the pattern found in previous work using manually aligned segments. This was true even for the least accurate forced alignment method.Conclusions: Alignment accuracy of child speech can be improved by using more specific training and transcription. However, poor alignment accuracy was not found to impede acoustic analysis of/s/ produced by even very young children. Thus, forced alignment presents a useful tool for the analysis of child speech.Supplemental Material: https://doi.org/10.23641/asha. 7070105, Acoustic analysis of speech has traditionally required labor-intensive hand annotation of segment boundaries or acoustic events. The time-consuming nature of the process has limited the scale of these studies. There [...]

Purpose: The developmental trajectory of English /s/ was investigated to determine the extent to which children's 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 [F.sub.1] (i.e., lower vowels) in children, a context where lingual articulation is challenging. Measures of breathiness and vowel intrinsic [F.sub.0] 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 children's phonetic knowledge is acoustically detailed and gender specified and that speech production goals are acoustically oriented at early stages of speech development., Along tradition of developmental studies assume (implicitly or explicitly) that what is heard by adult transcribers accurately reflects children's production targets; in other words, what adults transcribe represents what children [...]

English-speakers' learning of a French vowel contrast (/schwa/-/slashed o/) was examined under six different stimulus conditions in which contrastive and noncontrastive stimulus dimensions were varied orthogonally to each other. The distribution of contrastive cues was varied across training conditions to create single prototype, variable far (from the category boundary), and variable close (to the boundary) conditions, each in a single talker or a multiple talker version. The control condition involved identification of gender appropriate grammatical elements. Pre- and posttraining measures of vowel perception and production were obtained from each participant. When assessing pre- to posttraining changes in the slope of the identification functions, statistically significant training effects were observed in the multiple voice far and multiple voice close conditions.

Listeners are exquisitely sensitive to fine-grained acoustic detail within phonetic categories for sounds and words. Here we show that this sensitivity is optimal given the probabilistic nature of speech cues. We manipulated the probability distribution of one probabilistic cue, voice onset time (VOT), which differentiates word initial labial stops in English (e.g., "beach" and "peach"). Participants categorized words from distributions of VOT with wide or narrow variances. Uncertainty about word identity was measured by four-alternative forced-choice judgments and by the probability of looks to pictures. Both measures closely reflected the posterior probability of the word given the likelihood distributions of VOT, suggesting that listeners are sensitive to these distributions. (Contains 1 table and 4 figures.)

Purpose: This study examined whether older adults remain perceptually flexible when presented with ambiguities in speech in the absence of lexically disambiguating information. We expected older adults to show less perceptual learning when top-down information was not available. We also investigated whether individual differences in executive function predicted perceptual learning in older and younger adults. Method: Younger (n = 31) and older adults (n = 27) completed 2 perceptual learning tasks composed of a pretest, exposure, and posttest phase. Both learning tasks exposed participants to clear and ambiguous speech tokens, but crucially, the lexically guided learning task provided disambiguating lexical information whereas the distributional learning task did not. Participants also performed several cognitive tasks to investigate individual differences in working memory, vocabulary, and attention-switching control. Results: We found that perceptual learning is maintained in older adults, but that learning may be stronger in contexts where top-down information is available. Receptive vocabulary scores predicted learning across both age groups and in both learning tasks. Conclusions: Implicit learning is maintained with age across different learning conditions but remains stronger when lexically biasing information is available. We find that receptive vocabulary is relevant for learning in both types of learning tasks, suggesting the importance of vocabulary knowledge for adapting to ambiguities in speech., Listeners regularly encounter unexpected variation in speech, to which they must adapt in order to successfully perceive the signal. Various causes for these idiosyncrasies include accent and dialect differences, speech [...]

While perceptual categories exhibit plasticity following recently heard speech, evidence of effects on production has been mixed. We tested the influences of perceptual plasticity on production with an implicit distributional learning paradigm. In Experiment 1, we exposed participants to an unlabelled bimodal distribution of voice onset time (VOT) using bilabial stop consonants, with a longer category boundary than is typical. Participants' perceptual category boundaries shifted towards longer VOT, with a congruent increase in production VOT. Experiment 2 found evidence of perceptual transfer of these shifts to a different speaker and different syllables, and different words in production. Experiment 3 showed no shifts following exposure to a VOT boundary shorter than typical. We conclude that when listeners adjust their perceptual category boundaries, these changes may affect production categories, consistent with models where speech perception and production categories are linked, but with category boundaries influencing the link between perception and production. [ABSTRACT FROM AUTHOR]

High variability (HV) training has been found to be more effective than low variability (LV) training when learning various non-native phonetic contrasts. However, little research has considered whether this applies to the learning of tone contrasts. The only two relevant studies suggested that the effect of HV training depends on the perceptual aptitude of participants (Perrachione et al., 2011; Sadakata & McQueen, 2014). The present study extends these findings by examining the interaction between individual aptitude and input variability using natural, meaningful second language input (both previous studies used pseudowords). A total of 60 English speakers took part in an eight session phonetic training paradigm. They were assigned to high/low/high-blocked variability training groups and learned real Mandarin tones and words. Individual aptitude was measured following previous work. Learning was measured using one discrimination task, one identification task and two production tasks. All tasks assessed generalization. All groups improved in both the production and perception of tones which transferred to untrained voices and items, demonstrating the effectiveness of training despite the increased complexity compared with previous research. Although the LV group exhibited an advantage with the training stimuli, there was no evidence for a benefit of high-variability in any of the tests of generalisation. Moreover, although aptitude significantly predicted performance in discrimination, identification and training tasks, no interaction between individual aptitude and variability was revealed. Additional Bayes Factor analyses indicated substantial evidence for the null for the hypotheses of a benefit of high-variability in generalisation, however the evidence regarding the interaction was ambiguous. We discuss these results in light of previous findings. [ABSTRACT FROM AUTHOR]

This study investigates the relationship between speech perception and production using explicit phonetic imitation. We used manipulated natural vowel (head-had) stimuli varying in spectral quality and duration in both perception and production tasks to explore the perception-production link in a direct and controlled way. We examined (1) whether individual listeners' perceptual cue weights are related to their patterns of phonetic imitation and (2) phonological and perceptual constraints underlying phonetic imitation. Results showed that better perceptual abilities (i.e. larger cue weights) were related to better imitation of vowel duration. Furthermore, imitation of vowel spectral quality was mediated by contrast maintenance while vowel duration was not. Overall, vowel duration was better imitated despite being the less important cue perceptually. These results suggest that speech perception and production are indeed linked at the individual level, and both linguistic and perceptual-cognitive factors play a role in this process. [ABSTRACT FROM AUTHOR]

Speech perception requires multiple acoustic cues. Cue weighting may differ across individuals but be systematic within individuals. The current study compared individuals' cue weights within and across contrasts. Forty-two listeners performed a two-alternative forced choice task for four out of five sets of minimal pairs, each varying orthogonally in two dimensions. Individuals' cue weights within a contrast were positively correlated for bet-bat, Luce-lose, and sock-shock, but not for bog-dog and dear-tear. Importantly, individuals' cue weights were also positively correlated across contrasts. This indicates that some individuals are better able to extract and use phonetic information across different dimensions. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Background/Aims: Previous research found that individual talkers have consistent differences in the production of segments impacting the perception of their speech by others. Speakers also produce multiple acoustic-phonetic cues to phonological contrasts. Less is known about how multiple cues covary within a phonetic category and across talkers. We examined differences in individual talkers across cues and whether token-by-token variability is a result of intrinsic factors or speaking style by examining within-category correlations. Methods: We examined correlations for 3 cues (voice onset time, VOT, talker-relative onset fundamental frequency, f0, and talker-relative following vowel duration) to word-initial labial stop voicing in English. Results: VOT for /b/ and /p/ productions and onset f0 for /b/ productions varied significantly by talker. Token-by-token within-category variation was largely limited to speaking rate effects. VOT and f0 were negatively correlated within category for /b/ productions after controlling for speaking rate and talker mean f0, but in the opposite direction expected for an intrinsic effect. Within-category talker means were correlated across VOT and vowel duration for /p/ productions. Some talkers produced more prototypical values than others, indicating systematic talker differences. Conclusion: Relationships between cues are mediated more by categories and talkers than by intrinsic physiological relationships. Talker differences reflect systematic speaking style differences. [ABSTRACT FROM AUTHOR]

The article discusses the correlation of vowel lengthening on the intelligibility of occluded lombard speech. Topics include Lombard speech is an instinctual adaptation for improving communication in noise; When speaking in noise, people's vocal effort is automatically adjusted in order to improve the intelligibility of their speech; and three measurements of the intelligibility of the stimuli are presented.

Purpose: The developmental trajectory of English /s/ was investigated to determine the extent to which children's 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 children's phonetic knowledge is acoustically detailed and gender specified and that speech production goals are acoustically oriented at early stages of speech development. [ABSTRACT FROM AUTHOR]

English-speakers' learning of a French vowel contrast (/ə/–/ø/) was examined under six different stimulus conditions in which contrastive and noncontrastive stimulus dimensions were varied orthogonally to each other. The distribution of contrastive cues was varied across training conditions to create single prototype, variable far (from the category boundary), and variable close (to the boundary) conditions, each in a single talker or a multiple talker version. The control condition involved identification of gender appropriate grammatical elements. Pre- and posttraining measures of vowel perception and production were obtained from each participant. When assessing pre- to posttraining changes in the slope of the identification functions, statistically significant training effects were observed in the multiple voice far and multiple voice close conditions. [ABSTRACT FROM PUBLISHER]

Previous cue integration studies have examined continuous perceptual dimensions (e.g., size) and have shown that human cue integration is well described by a normative model in which cues are weighted in proportion to their sensory reliability, as estimated from single-cue performance. However, this normative model may not be applicable to categorical perceptual dimensions (e.g., phonemes). In tasks defined over categorical perceptual dimensions, optimal cue weights should depend not only on the sensory variance affecting the perception of each cue but also on the environmental variance inherent in each task-relevant category. Here, we present a computational and experimental investigation of cue integration in a categorical audio-visual (articulatory) speech perception task. Our results show that human performance during audio-visual phonemic labeling is qualitatively consistent with the behavior of a Bayes-optimal observer. Specifically, we show that the participants in our task are sensitive, on a trial-by-trial basis, to the sensory uncertainty associated with the auditory and visual cues, during phonemic categorization. In addition, we show that while sensory uncertainty is a significant factor in determining cue weights, it is not the only one and participants' performance is consistent with an optimal model in which environmental, within category variability also plays a role in determining cue weights. Furthermore, we show that in our task, the sensory variability affecting the visual modality during cue-combination is not well estimated from single-cue performance, but can be estimated from multi-cue performance. The findings and computational principles described here represent a principled first step towards characterizing the mechanisms underlying human cue integration in categorical tasks. [ABSTRACT FROM AUTHOR]

Abstract: Listeners are exquisitely sensitive to fine-grained acoustic detail within phonetic categories for sounds and words. Here we show that this sensitivity is optimal given the probabilistic nature of speech cues. We manipulated the probability distribution of one probabilistic cue, voice onset time (VOT), which differentiates word initial labial stops in English (e.g., “beach” and “peach”). Participants categorized words from distributions of VOT with wide or narrow variances. Uncertainty about word identity was measured by four-alternative forced-choice judgments and by the probability of looks to pictures. Both measures closely reflected the posterior probability of the word given the likelihood distributions of VOT, suggesting that listeners are sensitive to these distributions. [Copyright &y& Elsevier]

• Phonetic training can enable learners to distinguish between non-native phonemes. • Seminal studies propose that high talker variability (HV) is key to generalisation. • We conducted a replication (N = 166) of seminal studies to test for such a HV benefit. • All evidence for a HV benefit was ambiguous, contradicting original findings. • Our study raises questions about the true size and robustness of the HV benefit. Acquiring non-native speech contrasts can be difficult. A seminal study by Logan, Lively and Pisoni (1991) established the effectiveness of phonetic training for improving non-native speech perception: Japanese learners of English were trained to perceive /r/-/l/ using minimal pairs over 15 training sessions. A pre/post-test design established learning and generalisation. In a follow-up study, Lively, Logan and Pisoni (1993) presented further evidence which suggested that talker variability in training stimuli was crucial in leading to greater generalisation. These findings have been very influential and "high variability phonetic training" is now a standard methodology in the field. However, while the general benefit of phonetic training is well replicated, the evidence for an advantage of high over lower variability training remains mixed. In a large-scale replication of the original studies using updated statistical analyses we test whether learners generalise more after phonetic training using multiple talkers over a single talker. We find that listeners learn in both multiple and single talker conditions. However, in training, we find no difference in how well listeners learn for high vs low variability training. When comparing generalisation to novel talkers after training in relation to pre-training accuracy, we find ambiguous evidence for a high-variability benefit over low-variability training: This means that if a high-variability benefit exists, the effect is much smaller than originally thought, such that it cannot be detected in our sample of 166 listeners. [ABSTRACT FROM AUTHOR]