Perceptual learning of time-compressed speech: more than rapid adaptation

Attention capture by own name decreases with speech compression

Auditory stimuli that are relevant to a listener have the potential to capture focal attention even when unattended, the listener's own name being a particularly effective stimulus. We report two experiments to test the attention-capturing potential of the listener's own name in normal speech and time-compressed speech. In Experiment 1, 39 participants were tested with a visual word categorization task with uncompressed spoken names as background auditory distractors. Participants' word categorization performance was slower when hearing their own name rather than other names, and in a final test, they were faster at detecting their own name than other names. Experiment 2 used the same task paradigm, but the auditory distractors were time-compressed names. Three compression levels were tested with 25 participants in each condition. Participants' word categorization performance was again slower when hearing their own name than when hearing other names; the slowing was strongest with slight compression and weakest with intense compression. Personally relevant time-compressed speech has the potential to capture attention, but the degree of capture depends on the level of compression. Attention capture by time-compressed speech has practical significance and provides partial evidence for the duplex-mechanism account of auditory distraction.

Central Auditory Processing Dysfunction in Service Members and Veterans: Treatment Considerations and Strategies

PURPOSE

Military risk factors such as blast exposure, noise exposure, head trauma, and neurotoxin exposure place Service members and Veterans at risk for deficits associated with auditory processing dysfunction. However, there is no clinical guidance specific to the treatment of auditory processing deficits in this unique population. We provide an overview of available treatments and their limited supporting evidence for use in adults, emphasizing the need for multidisciplinary case management and interdisciplinary research to support evidence-based solutions.

METHOD

We explored relevant literature to inform the treatment of auditory processing dysfunction in adults, with emphasis on findings involving active or former military personnel. We were able to identify a limited number of studies, pertaining primarily to the treatment of auditory processing deficits through the use of assistive technologies and training strategies. We assessed the current state of the science for knowledge gaps that warrant additional study.

CONCLUSIONS

Auditory processing deficits often co-occur with other military injuries and may pose significant risk in military operational and occupational settings. Research is needed to advance clinical diagnostic and rehabilitative capabilities, guide treatment planning, support effective multidisciplinary management, and inform fitness-for-duty standards. We emphasize the need for an inclusive approach to the assessment and treatment of auditory processing concerns in Service members and Veterans and for evidence-based solutions to address complex military risk factors and injuries.

Perceptual Learning of Noise-Vocoded Speech Under Divided Attention

Speech perception performance for degraded speech can improve with practice or exposure. Such perceptual learning is thought to be reliant on attention and theoretical accounts like the predictive coding framework suggest a key role for attention in supporting learning. However, it is unclear whether speech perceptual learning requires undivided attention. We evaluated the role of divided attention in speech perceptual learning in two online experiments (N = 336). Experiment 1 tested the reliance of perceptual learning on undivided attention. Participants completed a speech recognition task where they repeated forty noise-vocoded sentences in a between-group design. Participants performed the speech task alone or concurrently with a domain-general visual task (dual task) at one of three difficulty levels. We observed perceptual learning under divided attention for all four groups, moderated by dual-task difficulty. Listeners in easy and intermediate visual conditions improved as much as the single-task group. Those who completed the most challenging visual task showed faster learning and achieved similar ending performance compared to the single-task group. Experiment 2 tested whether learning relies on domain-specific or domain-general processes. Participants completed a single speech task or performed this task together with a dual task aiming to recruit domain-specific (lexical or phonological), or domain-general (visual) processes. All secondary task conditions produced patterns and amount of learning comparable to the single speech task. Our results demonstrate that the impact of divided attention on perceptual learning is not strictly dependent on domain-general or domain-specific processes and speech perceptual learning persists under divided attention.

Impaired perceptual phonetic plasticity in Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative condition primarily associated with its motor consequences. Although much of the focus within the speech domain has focused on PD's consequences for production, people with PD have been shown to differ in the perception of emotional prosody, loudness, and speech rate from age-matched controls. The current study targeted the effect of PD on perceptual phonetic plasticity, defined as the ability to learn and adjust to novel phonetic input, both in second language and native language contexts. People with PD were compared to age-matched controls (and, for three of the studies, a younger control population) in tasks of explicit non-native speech learning and adaptation to variation in native speech (compressed rate, accent, and the use of timing information within a sentence to parse ambiguities). The participants with PD showed significantly worse performance on the task of compressed rate and used the duration of an ambiguous fricative to segment speech to a lesser degree than age-matched controls, indicating impaired speech perceptual abilities. Exploratory comparisons also showed people with PD who were on medication performed significantly worse than their peers off medication on those two tasks and the task of explicit non-native learning.

Rapid but specific perceptual learning partially explains individual differences in the recognition of challenging speech

Perceptual learning for speech, defined as long-lasting changes in speech recognition following exposure or practice occurs under many challenging listening conditions. However, this learning is also highly specific to the conditions in which it occurred, such that its function in adult speech recognition is not clear. We used a time-compressed speech task to assess learning following either brief exposure (rapid learning) or additional training (training-induced learning). Both types of learning were robust and long-lasting. Individual differences in rapid learning explained unique variance in recognizing natural-fast speech and speech-in-noise with no additional contribution for training-induced learning (Experiment 1). Rapid learning was stimulus specific (Experiment 2), as in previous studies on training-induced learning. We suggest that rapid learning is key for understanding the role of perceptual learning in online speech recognition whereas longer training could provide additional opportunities to consolidate and stabilize learning.

Increased reliance on top-down information to compensate for reduced bottom-up use of acoustic cues in dyslexia

Speech recognition is a complex human behavior in the course of which listeners must integrate the detailed phonetic information present in the acoustic signal with their general linguistic knowledge. It is commonly assumed that this process occurs effortlessly for most people, but it is still unclear whether this also holds true in the case of developmental dyslexia (DD), a condition characterized by perceptual deficits. In the present study, we used a dual-task setting to test the assumption that speech recognition is effortful for people with DD. In particular, we tested the Ganong effect (i.e., lexical bias on phoneme identification) while participants performed a secondary task of either low or high cognitive demand. We presumed that reduced efficiency in perceptual processing in DD would manifest in greater modulation in the performance of primary task by cognitive load. Results revealed that this was indeed the case. We found a larger Ganong effect in the DD group under high than under low cognitive load, and this modulation was larger than it was for typically developed (TD) readers. Furthermore, phoneme categorization was less precise in the DD group than in the TD group. These findings suggest that individuals with DD show increased reliance on top-down lexically mediated perception processes, possibly as a compensatory mechanism for reduced efficiency in bottom-up use of acoustic cues. This indicates an imbalance between bottom-up and top-down processes in speech recognition of individuals with DD.

Adaptive Plasticity Under Adverse Listening Conditions is Disrupted in Developmental Dyslexia

OBJECTIVE

Acoustic distortions to the speech signal impair spoken language recognition, but healthy listeners exhibit adaptive plasticity consistent with rapid adjustments in how the distorted speech input maps to speech representations, perhaps through engagement of supervised error-driven learning. This puts adaptive plasticity in speech perception in an interesting position with regard to developmental dyslexia inasmuch as dyslexia impacts speech processing and may involve dysfunction in neurobiological systems hypothesized to be involved in adaptive plasticity.

METHOD

Here, we examined typical young adult listeners (N = 17), and those with dyslexia (N = 16), as they reported the identity of native-language monosyllabic spoken words to which signal processing had been applied to create a systematic acoustic distortion. During training, all participants experienced incremental signal distortion increases to mildly distorted speech along with orthographic and auditory feedback indicating word identity following response across a brief, 250-trial training block. During pretest and posttest phases, no feedback was provided to participants.

RESULTS

Word recognition across severely distorted speech was poor at pretest and equivalent across groups. Training led to improved word recognition for the most severely distorted speech at posttest, with evidence that adaptive plasticity generalized to support recognition of new tokens not previously experienced under distortion. However, training-related recognition gains for listeners with dyslexia were significantly less robust than for control listeners.

CONCLUSIONS

Less efficient adaptive plasticity to speech distortions may impact the ability of individuals with dyslexia to deal with variability arising from sources like acoustic noise and foreign-accented speech.

Brain activity predicts future learning success in intensive second language listening training

This study explores neural mechanisms underlying how prior knowledge gained from pre-listening transcript reading helps comprehend fast-rate speech in a second language (L2) and applies to L2 learning. Top-down predictive processing by prior knowledge may play an important role in L2 speech comprehension and improving listening skill. By manipulating the pre-listening transcript effect (pre-listening transcript reading [TR] vs. no transcript reading [NTR]) and type of languages (first language (L1) vs. L2), we measured brain activity in L2 learners, who performed fast-rate listening comprehension tasks during functional magnetic resonance imaging. Thereafter, we examined whether TR_L2-specific brain activity can predict individual learning success after an intensive listening training. The left angular and superior temporal gyri were key areas responsible for integrating prior knowledge to sensory input. Activity in these areas correlated significantly with gain scores on subsequent training, indicating that brain activity related to prior knowledge-sensory input integration predicts future learning success.

Effects of auditory training on low-pass filtered speech perception and listening-related cognitive load

Studies supporting learning-induced reductions in listening-related cognitive load have lacked procedural learning controls, making it difficult to determine the extent to which effects arise from perceptual or procedural learning. Here, listeners were trained in the coordinate response measure (CRM) task under unfiltered (UT) or degraded low-pass filtered (FT) conditions. Improvements in low-pass filtered CRM performance were larger for FT. Both conditions showed training-related reductions in cognitive load as indexed by a secondary working memory task. However, only the FT condition showed a correlation between CRM improvement and secondary task performance, suggesting that effects can be driven by perceptual and procedural learning.

Effects of stimulus repetition and training schedule on the perceptual learning of time-compressed speech and its transfer

Perceptual learning can facilitate the recognition of hard-to-perceive (e.g., time-compressed or spectrally-degraded) speech. Although the learning induced by training with time-compressed speech is robust, previous findings suggest that intensive training yields learning that is partially specific to the items encountered during practice. Here, we asked whether three parameters of the training procedure - the overall number of training trials (training intensity), how these trials are distributed across sessions, and the number of semantically different items encountered during training (set size) - influence learning and transfer. Different groups of participants (69 normal-hearing young adults; nine to 11 participants/group) completed different training protocols (or served as an untrained control group) and tested on the recognition of time-compressed sentences taken from the training set (learning), new time-compressed sentences presented by the trained talker (semantic transfer), and time-compressed sentences taken from the training set but presented by a different talker (acoustic transfer). Compared to untrained listeners, all training protocols yielded both learning and transfer. More intense training resulted in greater item-specific learning and greater acoustic transfer than less intense training with the same number of training sessions. Training on a smaller set size (i.e., greater token repetition during training) also resulted in greater acoustic transfer, whereas distributing practice over a number of sessions improved semantic transfer. Together, these data suggest that whereas practice on a small set that results in stimulus repetition during training is not harmful for learning, distributed training can support transfer to new stimuli, perhaps because it provides multiple opportunities to consolidate learning.

Age, Hearing, and the Perceptual Learning of Rapid Speech

The effects of aging and age-related hearing loss on the ability to learn degraded speech are not well understood. This study was designed to compare the perceptual learning of time-compressed speech and its generalization to natural-fast speech across young adults with normal hearing, older adults with normal hearing, and older adults with age-related hearing loss. Early learning (following brief exposure to time-compressed speech) and later learning (following further training) were compared across groups. Age and age-related hearing loss were both associated with declines in early learning. Although the two groups of older adults improved during the training session, when compared to untrained control groups (matched for age and hearing), learning was weaker in older than in young adults. Especially, the transfer of learning to untrained time-compressed sentences was reduced in both groups of older adults. Transfer of learning to natural-fast speech occurred regardless of age and hearing, but it was limited to sentences encountered during training. Findings are discussed within the framework of dynamic models of speech perception and learning. Based on this framework, we tentatively suggest that age-related declines in learning may stem from age differences in the use of high- and low-level speech cues. These age differences result in weaker early learning in older adults, which may further contribute to the difficulty to perceive speech in daily conversational settings in this population.

Efficient Neural Coding in Auditory and Speech Perception

Speech has long been recognized as 'special'. Here, we suggest that one of the reasons for speech being special is that our auditory system has evolved to encode it in an efficient, optimal way. The theory of efficient neural coding argues that our perceptual systems have evolved to encode environmental stimuli in the most efficient way. Mathematically, this can be achieved if the optimally efficient codes match the statistics of the signals they represent. Experimental evidence suggests that the auditory code is optimal in this mathematical sense: statistical properties of speech closely match response properties of the cochlea, the auditory nerve, and the auditory cortex. Even more interestingly, these results may be linked to phenomena in auditory and speech perception.

Learning to decipher time-compressed speech: Robust acquisition with a slight difficulty in generalization among young adults with developmental dyslexia

Learning to decipher acoustically distorted speech serves as a test case for the study of language-related skill acquisition in persons with developmental dyslexia (DD). Deciphering this type of input is rarely learned explicitly and does not yield conscious insights. Problems in implicit and procedural skill learning have been proposed as possible causes of DD. Here we examined the learning of time-compressed (accelerated) speech and its generalization to novel materials among young adults with DD compared to typical readers (TD). All participants completed a training session that involved judging the semantic plausibility of sentences, during which the level of time-compression was changed using an adaptive (staircase) procedure according to each participant's performance. In the test, phase learning (test on same items) and generalization (test on new items and same items spoken by a new speaker) were assessed. Both groups showed robust gains after training. Moreover, after training, the initial disadvantage of the DD group was no longer significant. After training, both groups experienced relative difficulties in deciphering learned tokens spoken by a different voice, though participants with DD were less able to generalize the gains to deciphering new tokens. Thus, DD individuals benefited from repeated experience with time-compressed speech no less than typical readers, but their evolving skill was apparently more dependent on the specific characteristics of the tokens. Atypical generalization, which indicates that perceptual learning is contingent on lower-level features of the input though does not necessarily point to impaired learning potential per se, may explain some of the contradictory findings in published studies of speech perception in DD.

Effects of Time-Compressed Speech Training on Multiple Functional and Structural Neural Mechanisms Involving the Left Superior Temporal Gyrus

Time-compressed speech is an artificial form of rapidly presented speech. Training with time-compressed speech (TCSSL) in a second language leads to adaptation toward TCSSL. Here, we newly investigated the effects of 4 weeks of training with TCSSL on diverse cognitive functions and neural systems using the fractional amplitude of spontaneous low-frequency fluctuations (fALFF), resting-state functional connectivity (RSFC) with the left superior temporal gyrus (STG), fractional anisotropy (FA), and regional gray matter volume (rGMV) of young adults by magnetic resonance imaging. There were no significant differences in change of performance of measures of cognitive functions or second language skills after training with TCSSL compared with that of the active control group. However, compared with the active control group, training with TCSSL was associated with increased fALFF, RSFC, and FA and decreased rGMV involving areas in the left STG. These results lacked evidence of a far transfer effect of time-compressed speech training on a wide range of cognitive functions and second language skills in young adults. However, these results demonstrated effects of time-compressed speech training on gray and white matter structures as well as on resting-state intrinsic activity and connectivity involving the left STG, which plays a key role in listening comprehension.

Estudo do teste de fala comprimida em crianças

RESUMO Objetivo Analisar o desempenho das crianças sem alteração do processamento auditivo central no teste de fala comprimida. Método Trata-se de um estudo do tipo descritivo, observacional, transversal. Participaram do estudo 22 crianças com idade entre 7 e 11 anos, normo-ouvintes, sem transtorno do processamento auditivo central. Para descartar esse transtorno, foram aplicados o questionário Scale of Auditory Behaviors, a avaliação simplificada do processamento auditivo e o teste dicótico de dígitos na etapa de integração binaural. Nas crianças sem alteração, foi aplicado o teste de fala comprimida. Resultados Os indivíduos apresentaram melhor desempenho na lista de monossílabos do que na de dissílabos, apesar de não haver diferença significativa. Não houve influência da ordem de apresentação das listas, das variáveis gênero e orelha no desempenho do teste. Em relação à idade, apenas na lista de dissílabos houve diferença no desempenho. Conclusão Foi possível concluir que a média de acertos das crianças no Teste de Fala Comprimida foi inferior aos achados na literatura nacional em adultos. Houve diferença no desempenho do Teste de Fala Comprimida com a idade apenas na lista de dissílabos. Não houve diferença quanto à ordem de apresentação das listas de aplicação nem em relação ao tipo de estímulo.

Teste de fala comprimida em idosos

RESUMO Objetivo Avaliar o desempenho de idosos no teste de fala comprimida segundo as variáveis orelha, ordem de apresentação e idade, além de analisar a ocorrência de erros. Método O estudo é caracterizado como observacional, descritivo, quantitativo, analítico e do tipo transversal primário, o qual envolveu 22 idosos entre 60 e 80 anos de idade, portadores de audição normal ou com perda neurossensorial de grau leve. Os idosos foram submetidos à aplicação do teste de fala comprimida apenas com dissílabos e com taxa de compressão de 60%, por meio do método de compressão de tempo eletromecânico. Em cada orelha, foi aplicada uma lista de 50 dissílabos, sendo a ordem de início de teste aleatória. Resultados Quanto ao desempenho no teste, verificou-se que não houve diferença estatística entre as orelhas e os idosos apresentaram resultados aquém do encontrado na população adulta. Encontrou-se significância estatística de melhor desempenho para a segunda orelha de início de teste. A maior ocorrência de erros se deu para as palavras que iniciaram com os fonemas /p/ e /d/. A presença de encontro consonantal na palavra também aumentou a ocorrência de erros. Conclusão Os idosos apresentam pior desempenho na habilidade de fechamento auditivo, quando avaliados por meio do teste de fala comprimida, em comparação aos indivíduos adultos. Este resultado sugere que os idosos têm dificuldades para reconhecer a fala quando esta lhe é apresentada numa velocidade aumentada. Sendo assim, estratégias devem ser utilizadas para facilitar o processo comunicativo, independentemente da presença de uma perda auditiva.

The perceptual learning of time-compressed speech: A comparison of training protocols with different levels of difficulty

Speech perception can improve substantially with practice (perceptual learning) even in adults. Here we compared the effects of four training protocols that differed in whether and how task difficulty was changed during a training session, in terms of the gains attained and the ability to apply (transfer) these gains to previously un-encountered items (tokens) and to different talkers. Participants trained in judging the semantic plausibility of sentences presented as time-compressed speech and were tested on their ability to reproduce, in writing, the target sentences; trail-by-trial feedback was afforded in all training conditions. In two conditions task difficulty (low or high compression) was kept constant throughout the training session, whereas in the other two conditions task difficulty was changed in an adaptive manner (incrementally from easy to difficult, or using a staircase procedure). Compared to a control group (no training), all four protocols resulted in significant post-training improvement in the ability to reproduce the trained sentences accurately. However, training in the constant-high-compression protocol elicited the smallest gains in deciphering and reproducing trained items and in reproducing novel, untrained, items after training. Overall, these results suggest that training procedures that start off with relatively little signal distortion (“easy” items, not far removed from standard speech) may be advantageous compared to conditions wherein severe distortions are presented to participants from the very beginning of the training session.

Normal and Time-Compressed Speech

Short-term and long-term learning effects were investigated for the German Oldenburg sentence test (OLSA) using original and time-compressed fast speech in noise. Normal-hearing and hearing-impaired participants completed six lists of the OLSA in five sessions. Two groups of normal-hearing listeners (24 and 12 listeners) and two groups of hearing-impaired listeners (9 listeners each) performed the test with original or time-compressed speech. In general, original speech resulted in better speech recognition thresholds than time-compressed speech. Thresholds decreased with repetition for both speech materials. Confirming earlier results, the largest improvements were observed within the first measurements of the first session, indicating a rapid initial adaptation phase. The improvements were larger for time-compressed than for original speech. The novel results on long-term learning effects when using the OLSA indicate a longer phase of ongoing learning, especially for time-compressed speech, which seems to be limited by a floor effect. In addition, for normal-hearing participants, no complete transfer of learning benefits from time-compressed to original speech was observed. These effects should be borne in mind when inviting listeners repeatedly, for example, in research settings.

The effects of exposure and training on the perception of time-compressed speech in native versus nonnative listeners

The present study investigated the effects of language experience on the perceptual learning induced by either brief exposure to or more intensive training with time-compressed speech. Native (n = 30) and nonnative (n = 30) listeners were each divided to three groups with different experiences with time-compressed speech: A trained group who trained on the semantic verification of time-compressed sentences for three sessions, an exposure group briefly exposed to 20 time-compressed sentences, and a group of naive listeners. Recognition was assessed with three sets of time-compressed sentences intended to evaluate exposure-induced and training-induced learning as well as across-token and across-talker generalization. Learning profiles differed between native and nonnative listeners. Exposure had a weaker effect in nonnative than in native listeners. Furthermore, native and nonnative trained listeners significantly outperformed their untrained counterparts when tested with sentences taken from the training set. However, only trained native listeners outperformed naive native listeners when tested with new sentences. These findings suggest that the perceptual learning of speech is sensitive to linguistic experience. That rapid learning is weaker in nonnative listeners is consistent with their difficulties in real-life conditions. Furthermore, nonnative listeners may require longer periods of practice to achieve native-like learning outcomes.

Speech perception at positive signal-to-noise ratios using adaptive adjustment of time compression

Positive signal-to-noise ratios (SNRs) characterize listening situations most relevant for hearing-impaired listeners in daily life and should therefore be considered when evaluating hearing aid algorithms. For this, a speech-in-noise test was developed and evaluated, in which the background noise is presented at fixed positive SNRs and the speech rate (i.e., the time compression of the speech material) is adaptively adjusted. In total, 29 younger and 12 older normal-hearing, as well as 24 older hearing-impaired listeners took part in repeated measurements. Younger normal-hearing and older hearing-impaired listeners conducted one of two adaptive methods which differed in adaptive procedure and step size. Analysis of the measurements with regard to list length and estimation strategy for thresholds resulted in a practical method measuring the time compression for 50% recognition. This method uses time-compression adjustment and step sizes according to Versfeld and Dreschler [(2002). J. Acoust. Soc. Am. 111, 401-408], with sentence scoring, lists of 30 sentences, and a maximum likelihood method for threshold estimation. Evaluation of the procedure showed that older participants obtained higher test-retest reliability compared to younger participants. Depending on the group of listeners, one or two lists are required for training prior to data collection.

The effects of training length on the perceptual learning of time-compressed speech and its generalization

Brief exposure to time-compressed speech yields both learning and generalization. Whether such learning continues over the course of multi-session training and if so whether it is more or less specific than exposure-induced learning is not clear, because the outcomes of intensive practice with time-compressed speech have rarely been reported. The goal here was to determine whether prolonged training on time-compressed speech yields additional learning and generalization beyond that induced by brief exposure. Listeners practiced the semantic verification of time-compressed sentences for one or three training sessions. Identification of trained and untrained tokens was subsequently compared between listeners who trained for one or three sessions, listeners who were briefly exposed to 20 time-compressed sentences and naive listeners. Trained listeners outperformed the other groups of listeners on the trained condition, but only the group that was trained for three sessions outperformed the other groups when tested with untrained tokens. These findings suggest that although learning of distorted speech can occur rapidly, more stable learning and generalization might be achieved with longer, multi-session practice. It is suggested that the findings are consistent with the framework proposed by the Reverse Hierarchy Theory of perceptual learning.

Experience with a talker can transfer across modalities to facilitate lipreading

Rosenblum, Miller, and Sanchez (Psychological Science, 18, 392-396, 2007) found that subjects first trained to lip-read a particular talker were then better able to perceive the auditory speech of that same talker, as compared with that of a novel talker. This suggests that the talker experience a perceiver gains in one sensory modality can be transferred to another modality to make that speech easier to perceive. An experiment was conducted to examine whether this cross-sensory transfer of talker experience could occur (1) from auditory to lip-read speech, (2) with subjects not screened for adequate lipreading skill, (3) when both a familiar and an unfamiliar talker are presented during lipreading, and (4) for both old (presentation set) and new words. Subjects were first asked to identify a set of words from a talker. They were then asked to perform a lipreading task from two faces, one of which was of the same talker they heard in the first phase of the experiment. Results revealed that subjects who lip-read from the same talker they had heard performed better than those who lip-read a different talker, regardless of whether the words were old or new. These results add further evidence that learning of amodal talker information can facilitate speech perception across modalities and also suggest that this information is not restricted to previously heard words.

Speech perception under adverse conditions: insights from behavioral, computational, and neuroscience research

Adult speech perception reflects the long-term regularities of the native language, but it is also flexible such that it accommodates and adapts to adverse listening conditions and short-term deviations from native-language norms. The purpose of this article is to examine how the broader neuroscience literature can inform and advance research efforts in understanding the neural basis of flexibility and adaptive plasticity in speech perception. Specifically, we highlight the potential role of learning algorithms that rely on prediction error signals and discuss specific neural structures that are likely to contribute to such learning. To this end, we review behavioral studies, computational accounts, and neuroimaging findings related to adaptive plasticity in speech perception. Already, a few studies have alluded to a potential role of these mechanisms in adaptive plasticity in speech perception. Furthermore, we consider research topics in neuroscience that offer insight into how perception can be adaptively tuned to short-term deviations while balancing the need to maintain stability in the perception of learned long-term regularities. Consideration of the application and limitations of these algorithms in characterizing flexible speech perception under adverse conditions promises to inform theoretical models of speech.

Reversal of age-related neural timing delays with training

Neural slowing is commonly noted in older adults, with consequences for sensory, motor, and cognitive domains. One of the deleterious effects of neural slowing is impairment of temporal resolution; older adults, therefore, have reduced ability to process the rapid events that characterize speech, especially in noisy environments. Although hearing aids provide increased audibility, they cannot compensate for deficits in auditory temporal processing. Auditory training may provide a strategy to address these deficits. To that end, we evaluated the effects of auditory-based cognitive training on the temporal precision of subcortical processing of speech in noise. After training, older adults exhibited faster neural timing and experienced gains in memory, speed of processing, and speech-in-noise perception, whereas a matched control group showed no changes. Training was also associated with decreased variability of brainstem response peaks, suggesting a decrease in temporal jitter in response to a speech signal. These results demonstrate that auditory-based cognitive training can partially restore age-related deficits in temporal processing in the brain; this plasticity in turn promotes better cognitive and perceptual skills.