Overlearning of non-native speech sounds does not result in superior consolidation after a period of sleep.

Recent studies suggest that sleep-mediated consolidation processes help adults learn non-native speech sounds. However, overnight improvement was not seen when participants learned in the morning, perhaps resulting from native-language interference. The current study trained participants to perceive the Hindi dental/retroflex contrast in the morning and tested whether increased training can lead to overnight improvement. Results showed overnight effects regardless of training amount. In contrast to previous studies, participants in this study heard sounds in limited contexts (i.e., one talker and one vowel context), corroborating other findings, suggesting that overnight improvement is seen in non-native phonetic learning when variability is limited.

Non-native phonetic learning is destabilized by exposure to phonological variability before and after training.

Phonological variability is a key factor in many phonetic training studies, but it is unclear whether variability is universally helpful for learners. The current study explored variability and sleep consolidation in non-native phonetic learning. Two groups of participants were trained on a non-native contrast in one vowel context (/u/) and differed in whether they were also tested on an untrained context (/i/). Participants exposed to two vowels during the test were less accurate in perception of trained speech sounds and showed no overnight improvement. These findings suggest that introducing variability even in test phases may destabilize learning and prevent consolidation-based performance improvements.

Are Faster Participants Always Faster? Assessing Reliability of Participants' Mean Response Speed in Picture Naming.

Studies of language production often make use of picture naming tasks to investigate the cognitive processes involved in speaking, and many of these studies report a wide range of individual variability in how long speakers need to prepare the name of a picture. It has been assumed that this variability can be linked to inter-individual differences in cognitive skills or abilities (e.g., attention or working memory); therefore, several studies have tried to explain variability in language production tasks by correlating production measures with scores on cognitive tests. This approach, however, relies on the assumption that participants are reliable over time in their picture naming speed (i.e., that faster speakers are consistently fast). The current study explicitly tested this assumption by asking participants to complete a simple picture naming task twice with one to two weeks in between sessions. In one experiment, we show that picture naming speed has excellent within-task reliability and good test-retest reliability, at least when participants perform the same task in both sessions. In a second experiment with slight task variations across sessions (a speeded and non-speeded picture naming task), we replicated the high split-half reliability and found moderate consistency over tasks. These findings are as predicted under the assumption that the speed of initiating responses for speech production is an intrinsic property or capacity of an individual. We additionally discuss the consequences of these results for the statistical power of correlational designs.

Relationships between native and non-native speech perception.

Individuals differ in their ability to perceive and learn unfamiliar speech sounds, but we lack a comprehensive theoretical account that predicts individual differences in this skill. Predominant theories largely attribute difficulties of non-native speech perception to the relationships between non-native speech sounds/contrasts and native-language categories. The goal of the current study was to test whether the predictions made by these theories can be extended to predict individual differences in naive perception of non-native speech sounds or learning of these sounds. Specifically, we hypothesized that the internal structure of native-language speech categories is the cause of difficulty in perception of unfamiliar sounds such that learners who show more graded (i.e., less categorical) perception of sounds in their native language would have an advantage for perceiving non-native speech sounds because they would be less likely to assimilate unfamiliar speech tokens to their native-language categories. We tested this prediction in two experiments in which listeners categorized speech continua in their native language and performed tasks of discrimination or identification of difficult non-native speech sound contrasts. Overall, results did not support the hypothesis that individual differences in categorical perception of native-language speech sounds is responsible for variability in sensitivity to non-native speech sounds. However, participants who responded more consistently on a speech categorization task showed more accurate perception of non-native speech sounds. This suggests that individual differences in non-native speech perception are more related to the stability of phonetic processing abilities than to individual differences in phonetic category structure. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Distributional properties of semantic interference in picture naming: Bayesian meta-analyses.

Studies of word production often make use of picture-naming tasks, including the picture-word-interference task. In this task, participants name pictures with superimposed distractor words. They typically need more time to name pictures when the distractor word is semantically related to the picture than when it is unrelated (the semantic interference effect). The present study examines the distributional properties of this effect in a series of Bayesian meta-analyses. Meta-analytic estimates of the semantic interference effect first show that the effect is present throughout the reaction time distribution and that it increases throughout the distribution. Second, we find a correlation between a participant's mean semantic interference effect and the change in the effect in the tail of the reaction time distribution, which has been argued to reflect the involvement of selective inhibition in the naming task. Finally, we show with simulated data that this correlation emerges even when no inhibition is used to generate the data, which suggests that inhibition is not needed to explain this relationship.

Reliability and validity for perceptual flexibility in speech.

The study of perceptual flexibility in speech depends on a variety of tasks that feature a large degree of variability between participants. Of critical interest is whether measures are consistent within an individual or across stimulus contexts. This is particularly key for individual difference designs that aredeployed to examine the neural basis or clinical consequences of perceptual flexibility. In the present set of experiments, we assess the split-half reliability and construct validity of five measures of perceptual flexibility: three of learning in a native language context (e.g., understanding someone with a foreign accent) and two of learning in a non-native context (e.g., learning to categorize non-native speech sounds). We find that most of these tasks show an appreciable level of split-half reliability, although construct validity was sometimes weak. This provides good evidence for reliability for these tasks, while highlighting possible upper limits on expected effect sizes involving each measure.

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.

Structural neural correlates of individual differences in categorical perception.

Listeners perceive speech sounds categorically. While group-level differences in categorical perception have been observed in children or individuals with reading disorders, recent findings suggest that typical adults vary in how categorically they perceive sounds. The current study investigated neural sources of individual variability in categorical perception of speech. Fifty-seven participants rated phonetic tokens on a visual analogue scale; categoricity and response consistency were measured and related to measures of brain structure from MRI. Increased surface area of the right middle frontal gyrus predicted more categorical perception of a fricative continuum. This finding supports the idea that frontal regions are sensitive to phonetic category-level information and extends it to make behavioral predictions at the individual level. Additionally, more gyrification in bilateral transverse temporal gyri predicted less consistent responses on the task, perhaps reflecting subtle variation in language ability across the population.

Correction to: Desirable and undesirable difficulties: Influences of variability, training schedule, and aptitude on nonnative phonetic learning.

Due to a production error, some IPA symbols were not included. The original article has been corrected.

Desirable and undesirable difficulties: Influences of variability, training schedule, and aptitude on nonnative phonetic learning.

Adult listeners often struggle to learn to distinguish speech sounds not present in their native language. High-variability training sets (i.e., stimuli produced by multiple talkers or stimuli that occur in diverse phonological contexts) often result in better retention of the learned information, as well as increased generalization to new instances. However, high-variability training is also more challenging, and not every listener can take advantage of this kind of training. An open question is how variability should be introduced to the learner in order to capitalize on the benefits of such training without derailing the training process. The current study manipulated phonological variability as native English speakers learned a difficult nonnative (Hindi) contrast by presenting the nonnative contrast in the context of two different vowels (/i/ and /u/). In a between-subjects design, variability was manipulated during training and during test. Participants were trained in the evening hours and returned the next morning for reassessment to test for retention of the speech sounds. We found that blocked training was superior to interleaved training for both learning and retention, but for learners in the interleaved training group, higher pretraining aptitude predicted better identification performance. Further, pretraining discrimination aptitude positively predicted changes in phonetic discrimination after a period of off-line consolidation, regardless of the training manipulation. These findings add to a growing literature suggesting that variability may come at a cost in phonetic learning and that aptitude can affect both learning and retention of nonnative speech sounds.

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.

Brain-behavior relationships in incidental learning of non-native phonetic categories.

Research has implicated the left inferior frontal gyrus (LIFG) in mapping acoustic-phonetic input to sound category representations, both in native speech perception and non-native phonetic category learning. At issue is whether this sensitivity reflects access to phonetic category information per se or to explicit category labels, the latter often being required by experimental procedures. The current study employed an incidental learning paradigm designed to increase sensitivity to a difficult non-native phonetic contrast without inducing explicit awareness of the categorical nature of the stimuli. Functional MRI scans revealed frontal sensitivity to phonetic category structure both before and after learning. Additionally, individuals who succeeded most on the learning task showed the largest increases in frontal recruitment after learning. Overall, results suggest that processing novel phonetic category information entails a reliance on frontal brain regions, even in the absence of explicit category labels.