Exploring individual differences in native phonetic perception and their link to nonnative phonetic perception.

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. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

Contribution of acoustic cues to prominence ratings for four Mandarin vowels.

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.

The effects of high versus low talker variability and individual aptitude on phonetic training of Mandarin lexical tones.

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.

Different Responses to Altered Auditory Feedback in Younger and Older Adults Reflect Differences in Lexical Bias.

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.

Differences in cue weights for speech perception are correlated for individuals within and across contrasts.

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.

Examining Factors Influencing the Viability of Automatic Acoustic Analysis of Child Speech.

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.

The Role of Lexical Status and Individual Differences for Perceptual Learning in Younger and Older Adults.

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.

Individual Talker and Token Covariation in the Production of Multiple Cues to Stop Voicing.

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.

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.

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 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.

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.

Cue integration in categorical tasks: insights from audio-visual speech perception.

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.

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.

Perception of speech reflects optimal use of probabilistic speech cues.

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.