Non-native Speech Sound Learning Research Articles

Corrigendum to “Orthographic influence in the distributional learning of nonnative speech sounds”

Corrigendum to “Orthographic influence in the distributional learning of nonnative speech sounds”

No clear benefit of transcutaneous auricular vagus nerve stimulation for non-native speech sound learning

IntroductionLearning 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.MethodsWe studied adults' ability to perceive and produce unfamiliar speech sounds as well as any potential change in language learning motivation from pre- 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 discussionWe 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.

Orthographic influence in the distributional learning of non-native speech sounds

This study investigated the role of orthographic information in the acquisition of non-native speech sounds by monolingual English listeners. Two potentially important orthographic variables were explored: Orthographic compatibility (whether the orthographic information supports or contradicts the distributional information) and orthographic familiarity (whether the native and target languages share the same orthography). Ten groups of learners were trained on either a unimodal or bimodal distribution of two length continua. Out of the 10 groups, eight groups were also exposed to orthographic cues that varied in their compatibility with the distributional information (compatible vs. incompatible) and familiarity with the orthography of learners’ native language (Roman vs. Arabic). Following training, all participants performed an AX discrimination task to test their discrimination of the length contrast. The results revealed that, in general, the availability of either familiar or unfamiliar orthographic input which signaled the existence of a single length category significantly lowered learners’ discrimination of the length contrast regardless of the auditory distribution. Further, the exposure to orthographic input that supported a two-category length distinction enhanced the discrimination of the length contrast irrespective of the distribution. However, the most significant improvement occurred when both distributional information and familiar orthographic input were compatible. Overall, these findings indicate that orthographic input, regardless of its level of compatibility or familiarity, may influence the acquisition of non-native speech sounds.

Phonetic learning and vocabulary knowledge in adolescents

Individuals who perform well on tasks that measure their abilities to learn non-native speech sounds tend to also perform well on language measures such as vocabulary tests. This relationship is not well understood but may be driven by increased literacy skills among individuals with stronger phonetic learning skills. However, relatively few studies have examined the changes in performance that occur during adolescence, a time in which critical vocabulary knowledge is amassed. This is an especially interesting developmental period because studies comparing adults and children show that adults often outperform children on measures of non-native speech sound learning. In the present study, we examine the changes in non-native speech sound learning abilities that occur during adolescence. Our preliminary data confirm previous findings which show that non-native learning performance tends to increase with age. We also explore vocabulary development as a correlate of this effect. Our preliminary data suggest that the correlation between non-native phonetic learning and vocabulary grows stronger with age during adolescence. These findings support the hypothesis that phonetic learning abilities continue to develop during adolescence and that this development is relevant to language outcomes in the adolescent population.

Non-native speech sound learning as a window to individual differences in the neural encoding of speech

Non-native speech sound learning in adulthood is a skill marked by enormous individual differences, especially when compared to acquisition of speech sounds in childhood. This has led to the proposal that adult speech sound acquisition might be achieved through different mechanisms (or relying on fundamentally altered neural circuitry) compared to sound learning in infancy and childhood. One possibility we explore in a recent line of work is that individual differences in non-native speech learning are attributable to differences in the structure of brain areas responsible for processing speech, especially the transverse temporal gyrus. Of interest, the morphology of these same regions also predicts individual differences in native language speech perception, suggesting that sound acquisition (whether in childhood or adulthood) is limited by (likely innate) differences in neural architecture supporting sound processing. However, evidence that the best non-native perceivers are also the most finely-tuned native-sound perceivers is limited. Taken together, these results suggest that differences in brain structure are a soft constraint on the precision of acoustic-phonetic encoding, but that native language speech category structure is not the explanation for the difficulty of non-native sound learning.

Arousal States as a Key Source of Variability in Speech Perception and Learning

The human brain exhibits the remarkable ability to categorize speech sounds into distinct, meaningful percepts, even in challenging tasks like learning non-native speech categories in adulthood and hearing speech in noisy listening conditions. In these scenarios, there is substantial variability in perception and behavior, both across individual listeners and individual trials. While there has been extensive work characterizing stimulus-related and contextual factors that contribute to variability, recent advances in neuroscience are beginning to shed light on another potential source of variability that has not been explored in speech processing. Specifically, there are task-independent, moment-to-moment variations in neural activity in broadly-distributed cortical and subcortical networks that affect how a stimulus is perceived on a trial-by-trial basis. In this review, we discuss factors that affect speech sound learning and moment-to-moment variability in perception, particularly arousal states—neurotransmitter-dependent modulations of cortical activity. We propose that a more complete model of speech perception and learning should incorporate subcortically-mediated arousal states that alter behavior in ways that are distinct from, yet complementary to, top-down cognitive modulations. Finally, we discuss a novel neuromodulation technique, transcutaneous auricular vagus nerve stimulation (taVNS), which is particularly well-suited to investigating causal relationships between arousal mechanisms and performance in a variety of perceptual tasks. Together, these approaches provide novel testable hypotheses for explaining variability in classically challenging tasks, including non-native speech sound learning.

Structural variation in the temporal lobe predicts learning and retention of non-native speech sounds

ABSTRACT Studies of non-native speech sound learning report considerable individual variability in learning new sounds and retaining them in memory. The current study tested whether individual variation in brain structure (measured using MRI) accounts for differences in learning or retention of non-native speech sounds. Fifty-seven participants were tested on identification and discrimination of difficult non-native speech sounds in the evening before training, after training, and tested again the next morning. Surface area and volume of the left superior temporal gyrus positively predicted discrimination learning, whereas surface area of the left transverse temporal gyrus negatively predicted overnight improvement of identification. Hippocampal volume as well as gyrification of bilateral transverse temporal gyri positively predicted overnight improvement of discrimination. Findings suggest that individual differences in non-native speech sound learning can be traced to differences in brain structure supporting perception, while differences in retention are linked to the structure of hippocampal regions important for memory consolidation.

Examining group differences in between-participant variability in non-native speech sound learning

Many studies on non-native speech sound learning report a large amount of between-participant variability. This variability allows us to ask interesting questions about non-native speech sound learning, such as whether certain training paradigms give rise to more or less between-participant variability. This study presents a reanalysis of Fuhrmeister and Myers (Attention, Perception, and Psychophysics, 82(4), 2049-2065, 2020) and tests whether different types of phonetic training lead to group differences in between-participant variability. The original study trained participants on a non-native speech sound contrast in two different phonological (vowel) contexts and tested for differences in means between a group that received blocked training (one vowel context at a time) and interleaved training (vowel contexts were randomized). No statistically significant differences in means were found between the two groups in the original study on a discrimination test (a same-different judgment). However, the current reanalysis tested group differences in between-participant variability and found greater variability in the blocked training group immediately after training because this group had a larger proportion of participants with higher-than-average scores. After a period of offline consolidation, this group difference in variability decreased substantially. This suggests that the type and difficulty of phonetic training (blocked vs. interleaved) may initially give rise to differences in between-participant variability, but offline consolidation may attenuate that variability and have an equalizing effect across participants. This reanalysis supports the view that examining between-participant variability in addition to means when analyzing data can give us a more complete picture of the effects being tested.

Adults Show Initial Advantages Over Children in Learning Difficult Nonnative Speech Sounds.

Purpose Children and early adolescents seem to have an advantage over adults in acquiring nonnative speech sounds, supported by evidence showing that earlier age of acquisition strongly predicts second language attainment. Although many factors influence children's ultimate success in language learning, it is unknown whether children rely on different, perhaps more efficient learning mechanisms than adults. Method The current study compared children (aged 10-16 years) and adults in their learning of a nonnative Hindi contrast. We tested the hypothesis that younger participants would show superior baseline discriminability or learning of the contrast, better memory for new sounds after a delay, or improved generalization to a new talker's voice. Measures of phonological and auditory skills were collected to determine whether individual variability in these skills predicts nonnative speech sound learning and whether these potential relationships differ between adults and children. Results Adults showed superior pretraining sensitivity to the contrast compared to children, and these pretraining discrimination scores predicted learning and retention. Even though adults seemed to have an initial advantage in learning, children improved after a period of off-line consolidation on the trained identification task and began to catch up to adults after an overnight delay. Additionally, perceptual skills that predicted speech sound learning differed between adults and children, suggesting they rely on different learning mechanisms. Conclusions These findings challenge the view that children are simply better speech sound learners than adults and suggest that their advantages may be due to different learning mechanisms or better retention of nonnative contrasts over the broader language learning trajectory. Supplemental Material https://doi.org/10.23641/asha.12735914.

Perception of native language speech sounds does not predict non-native speech sound learning

Individual differences are often observed in laboratory studies of non-native speech sound learning. One possible explanation for this variability is that better detection of fine-grained contrasts within native language categories might facilitate non-native learning. For instance, Diaz et al. (2008) found larger MMN responses to both native and non-native speech contrasts in good compared to poor perceivers of a non-native contrast, suggesting a general speech-related skill. The current study explores whether the ability to discriminate subtle differences in native language speech sounds correlates with non-native speech sound learning. To test this, we trained participants on a non-native, Hindi dental/retroflex contrast and assessed their categorization and discrimination of a native /da/-/ta/ continuum. Additionally, participants completed a visual Flanker task in order to control for general motivation in the experimental setting. Neither native language measures nor the Flanker task predicted non-n...

Non-native Speech Learning in Older Adults.

Though there is an extensive literature investigating the ability of younger adults to learn non-native phonology, including investigations into individual differences in younger adults’ lexical tone learning, very little is known about older adults’ ability to learn non-native phonology, including lexical tone. There are several reasons to suspect that older adults would use different learning mechanisms when learning lexical tone than younger adults, including poorer perception of dynamic pitch, greater reliance on working memory capacity in second language learning, and poorer category learning in older adulthood. The present study examined the relationships among older adults’ baseline sensitivity for pitch patterns, working memory capacity, and declarative memory capacity with their ability to learn to associate tone with lexical meaning. In older adults, baseline pitch pattern sensitivity was not associated with generalization performance. Rather, older adults’ learning performance was best predicted by declarative memory capacity. These data suggest that training paradigms will need to be modified to optimize older adults’ non-native speech sound learning success.

Neural changes accompanying overnight nonnative phonetic learning

Sleep is important in the consolidation of learning, including the perceptual learning of non-native speech sounds. Previous work investigating the role of post-training sleep on nonnative phonetic learning has demonstrated that sleep significantly improves identification for a trained talker in the absence of further training. In addition, sleep appears to facilitate generalization of learning to non-native tokens produced by an untrained talker. We investigated the neural correlates of these behavioral observations using fMRI. Participants were trained in the Hindi dental-retroflex contrast in the evening on Day 1. Immediately following training, participants performed the category identification task in the scanner, and then again 12 hours later. Sleep duration was monitored via wrist Actigraphs. On Day 1, significant differences in activation for the Trained vs. Untrained Talker were identified in the supramaginal gyrus and adjacent parietal areas, whereas on Day 2, activation for both talkers was observed to move into the temporal lobes bilaterally. After sleep, and in the absence of further training, decreases in activation were observed in right superior temporal gyrus, right precentral gyrus, and left prefrontal cortex. Based on these findings, we argue that newly acquired nonnative sounds are processed in classic (i.e., more native-like) speech regions following sleep.

Consolidation during sleep stabilizes non-native speech sound learning

Learning to perceive non-native speech sound categories is a challenge for many adult listeners. Even after successful learning, individuals vary in the degree to which they can successfully retain and consolidate learned perceptual categories in memory. In this talk, I describe a recent line of work from our lab showing that sleep plays a greater role in perceptual learning of non-native speech sounds than previously supposed. Specifically, we find that consolidation processes during overnight sleep protect learned phonetic information from interference from similar sounds from one's native language. I will discuss the potential sources of native language interference by reviewing a series of studies that test the low-level acoustic and abstract phonological contributions to interference. Finally, overnight gains in performance can be specifically linked to the duration and quality of sleep, suggesting a key role for sleep, per se, in the retention of non-native speech categories over multiple sessions. Taken together, this line of research suggests that individual variability in non-native speech sound learning may in part be linked to individual differences in sleep behavior and differences in the degree of pre-sleep exposure to competing native-language phonetic contrasts.

Visual and auditory native language interference in perceptual learning of non-native speech sounds

Learning speech sounds in a second language is challenging for adults, especially when non-native phonemes are perceptually similar to those in the native language. Results from Earle and Myers (2015) suggest that auditory exposure to native language tokens that are perceptually similar to a learned non-native phonetic contrast attenuate sleep-mediated gains in perceptual learning. The present study seeks to determine whether activating abstract phonetic category representations through visual input will produce a similar interference effect on a learned non-native phonetic contrast. To test this, we trained participants to identify the Hindi dental and retroflex contrast and reassessed their performance following a period of sleep. Immediately after training, participants were exposed to interference tokens through a pseudohomophone judgment task, in which they were asked to decide if a string of letters spelled out a real word when read aloud (e.g., “drane” = drain). One group read words with /d/-initia...

Sleep and native language interference affect non-native speech sound learning.

Adults learning a new language are faced with a significant challenge: non-native speech sounds that are perceptually similar to sounds in one's native language can be very difficult to acquire. Sleep and native language interference, 2 factors that may help to explain this difficulty in acquisition, are addressed in 3 studies. Results of Experiment 1 showed that participants trained on a non-native contrast at night improved in discrimination 24 hr after training, while those trained in the morning showed no such improvement. Experiments 2 and 3 addressed the possibility that incidental exposure to perceptually similar native language speech sounds during the day interfered with maintenance in the morning group. Taken together, results show that the ultimate success of non-native speech sound learning depends not only on the similarity of learned sounds to the native language repertoire, but also to interference from native language sounds before sleep.

Visual Feedback of Tongue Movement for Novel Speech Sound Learning.

Pronunciation training studies have yielded important information concerning the processing of audiovisual (AV) information. Second language (L2) learners show increased reliance on bottom-up, multimodal input for speech perception (compared to monolingual individuals). However, little is known about the role of viewing one's own speech articulation processes during speech training. The current study investigated whether real-time, visual feedback for tongue movement can improve a speaker's learning of non-native speech sounds. An interactive 3D tongue visualization system based on electromagnetic articulography (EMA) was used in a speech training experiment. Native speakers of American English produced a novel speech sound (/ɖ/; a voiced, coronal, palatal stop) before, during, and after trials in which they viewed their own speech movements using the 3D model. Talkers' productions were evaluated using kinematic (tongue-tip spatial positioning) and acoustic (burst spectra) measures. The results indicated a rapid gain in accuracy associated with visual feedback training. The findings are discussed with respect to neural models for multimodal speech processing.

Emergence of category-level sensitivities in non-native speech sound learning.

Over the course of development, speech sounds that are contrastive in one's native language tend to become perceived categorically: that is, listeners are unaware of variation within phonetic categories while showing excellent sensitivity to speech sounds that span linguistically meaningful phonetic category boundaries. The end stage of this developmental process is that the perceptual systems that handle acoustic-phonetic information show special tuning to native language contrasts, and as such, category-level information appears to be present at even fairly low levels of the neural processing stream. Research on adults acquiring non-native speech categories offers an avenue for investigating the interplay of category-level information and perceptual sensitivities to these sounds as speech categories emerge. In particular, one can observe the neural changes that unfold as listeners learn not only to perceive acoustic distinctions that mark non-native speech sound contrasts, but also to map these distinctions onto category-level representations. An emergent literature on the neural basis of novel and non-native speech sound learning offers new insight into this question. In this review, I will examine this literature in order to answer two key questions. First, where in the neural pathway does sensitivity to category-level phonetic information first emerge over the trajectory of speech sound learning? Second, how do frontal and temporal brain areas work in concert over the course of non-native speech sound learning? Finally, in the context of this literature I will describe a model of speech sound learning in which rapidly-adapting access to categorical information in the frontal lobes modulates the sensitivity of stable, slowly-adapting responses in the temporal lobes.

Brain structural correlates of individual differences at low-to high-levels of the language processing hierarchy: A review of new approaches to imaging research

In the domain of language and audition, studies have shown large individual differences, within the normal range (i.e. in healthy, non-expert individuals), in performance on tasks involving speech sound processing, vocabulary knowledge, and reading, these in both monolingual and bilingual participants and in native and non-native language contexts. These individual differences have often been related to individual differences in brain structure. Evidence for structural differences is especially striking since brain structure can be assumed to be more stable, or less malleable, than brain function. Brain function, on the other hand, can be expected to change, or be plastic, after only very short periods of training/learning. The present paper provides a review of studies that have investigated the brain structural correlates of normative individual differences in aspects of language-related performance, these spanning a hierarchy in terms of the underlying complexity of processing and brain networks involved. Specifically, the review is structured so as to describe work examining the following domains, which involve progressively increasing levels of complexity in terms of the posited perceptual/cognitive sub-functions involved: 1) lower-level acoustic processing; 2) phonetic processing, including non-native speech sound learning, learning to use pitch information linguistically, non-native speech sound articulation, and phonetic expertise; 3) working memory for verbal and for pitch information; 4) semantics, in the context of lexical knowledge and of semantic memory; 5) reading; 6) syntax, both natural and artificial; 7) bilingualism; and finally 8) executive control of language in the contexts of fluency and of speech-in-noise processing. Results are discussed and synthesized in the context of lower to higher-level brain regions thought to be functionally involved in these respective domains, which are very often, if not always, the very ones that structurally partly predict domain-specific performance.

Perceptual learning of non-native speech contrast and functioning of the olivocochlear bundle

The purpose of this study was to investigate the relationship between perceptual learning of non-native speech sounds and strength of feedback in the medial olivocochlear bundle (MOCB). Discrimination abilities of non-native speech sounds (Malayalam) from its native counterparts (Hindi) were monitored during 12 days of training. Contralateral inhibition of otoacoustic emissions were measured on the first and twelfth day of training. Results suggested that training significantly improved reaction time and accuracy of identification of non-native speech sounds. There was a significant positive correlation between the slope (linear) of identification scores and change in distortion product otoacoustic emission inhibition at 3000 Hz. Findings suggest that during perceptual learning feedback from the MOCB may fine tune the brain stem and/or cochlea. However, such a change, isolated to a narrow frequency region, represents a limited effect and needs further exploration to confirm and/or extend any generalization of findings.SumarioEl propósito de este estudio fue investigar la relación entre el aprendizaje perceptual de sonidos no nativos del lenguaje y la fuerza de la retroalimentación en el fascículo olivo-coclear medial (MOCD). Se monitoreó la capacidad de discriminación de sonidos no nativos del lenguaje (Mayayalam) con sus contrapartes nativas (Hindi) durante un entrenamiento de 12 días. Se midió la inhibición contralateral de las emisiones otoacústicas en el primero y el último día del entrenamiento. Los resultados sugieren que el entrenamiento mejoró significativamente el tiempo de reacción y la exactitud de identificación de los sonidos no nativos del lenguaje. Existió una correlación significativamente positiva entre la pendiente (lineal) de los puntajes de identificación y el cambio en la inhibición de las emisiones otoacústicas por productos de distorsión en 3000 Hz. Los hallazgos sugieren que durante el aprendizaje perceptual, la retroalimentación del MOCB puede afinar las funciones del tallo cerebral y/o la cóclea. Sin embargo, tal cambio, limitado a una región estrecha de frecuencia, representa un efecto limitado y requiere de una exploración ulterior para confirmar y/o extender cualquier generalización sobre los hallazgos.

Perceptual learning of non-native speech sounds: The importance of features from an attention to dimensions perspective.

Research on the acquisition of non-native speech sounds is frequently conducted within the framework of theories that were originally developed to account for aspects of cross-language speech perception (e.g., PAM, NLM, and the SLM). Such theories typically focus on the influence of native phonetic categories on the perception of non-native speech, and second language learning researchers may tend to adopt this category-focused view although these theories make few strong predictions about learning. Interestingly, despite their focus on the role of categories, all of these theories incorporate the same assumption: That learning (of both first- and second-language contrasts) progresses by reweighting of phonetic features. This talk presents an overview of results from a series of studies that support this core assumption, suggesting that features, not categories, should play the central role in structuring our understanding of phonetic learning, especially with respect to such short-term adult learning as may be obtained in the laboratory or classroom. Taking such a perspective facilitates connections between theories of linguistic and non-linguistic perceptual learning, reduces dependence on category-based models of speech perception and production, and may provide a more principled basis for making predictions about what non-native contrasts should be easy or difficult to learn.