Biology subjects

Bidelman, G.

Publications and source records attributed to Bidelman, G..

At least 19 recordsLinked to original sources

bioRxiv2026

Older adults show overexaggerated and larger noise-related degradation in their neural tracking of speech

BackgroundSpeech-in-noise (SIN) perception is a difficult everyday listening task that becomes more difficult with age. Neural tracking of target speech is associated with successful speech perception in clean and noise-degraded listening environments. How aging impacts neural tracking of speech and relates to behavioral decrements in older adults SIN perception remains unclear. To address these questions, we measured neural speech tracking during a continuous SIN perception task in younger and older adults via multichannel EEG. MethodParticipants (n=83) monitored a continuous stream of syllables (~4.5 Hz) presented in quiet and noise conditions during EEG recordings. We assessed neural phase-locking value (PLV) to the acoustic speech envelope to investigate interactions between aging, hearing loss, and stimulus noise on neural synchronization to speech. ResultsCompared to younger adults, older adults demonstrated less behavioral sensitivity to noise effects than young adults and had higher overall PLV to target speech. Older adults also showed greater noise-related degradations in neural speech processing relative to younger listeners. Age remained a strong predictor of behavioral responses to speech even after controlling for hearing loss. Covarying for hearing loss removed most age-related effects on neural PLV. ConclusionOlder adults demonstrate overexaggerated neural tracking to ongoing speech presented in quiet and greater noise-related reductions in neurobehavioral speech processing than young adults. Our results support the decline-compensation hypothesis, corroborate unusually large speech envelope encoding in older listeners, and suggest more robust neural synchronization to the speech signal is not always perceptually advantageous.

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bioRxiv2026

Testing differential effects of periodicity and predictability in auditory rhythmic cueing of concurrent speech

Entrainment and predictive coding aid speech perception in both quiet and noisy environments. Isochronous, periodic auditory rhythmic cues facilitate entrainment and temporal expectations which can benefit encoding and perception of target speech. However, most studies using isochronous cues confound periodicity with predictability. To this end, we characterized how systematic changes in the acoustic dimensions of stimulus rate, target phase, periodicity, and predictably of an entraining sound precursor impact the subsequent identification of concurrent speech targets. Target concurrent vowel pairs were preceded by rhythmic woodblock cues which were either periodic-predictable (PP, isochronous rhythm), aperiodic-predictable (AP, accelerating rhythm), or aperiodic-unpredictable (AU, random rhythm). The number of pulses per rhythm was roved to further manipulate predictability. Stimuli also varied in presentation rate (2.5, 4.5, 6.5 Hz) and target speech phase (in-phase, 0{degrees}; out-of-phase, 90{degrees}, 180{degrees}) relative to the preceding entraining rhythm. We also measured participants musical pulse continuation and standardized speech-in-noise perception abilities. We did not observe any effects of stimulus rhythm, rate, or target phase on target speech identification accuracy. However, reaction times were slowest at the nominal speech rate (4.5 Hz) and were most disrupted by out-of-phase presentations following the PP rhythm. Double-vowel task performance was associated with stronger musical pulse continuation abilities, but not speech-in-noise perception. Our results support the notion that entraining rhythmic cues rely on top-down processing but are relatively muted when stimulus predictability is unknown. Additionally, we find that individual differences in musical pulse perception may underlie the benefits of rhythmic cueing on subsequent speech perception.

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bioRxiv2026

Neural microstates underlying categorical speech perception using Bayesian nonparametrics

Categorical perception (CP) reflects the human auditory systems ability to map continuous acoustic signals onto discrete categories. Understanding the relationship between neural dynamics and perceptual decisions is central to speech-language processing. Here, we implemented a data-driven approach using Bayesian nonparametrics and machine learning to characterize the relationship between auditory cortical responses and speech categorization behaviors. By applying a hierarchical Dirichlet process hidden Markov Model (HDP-HMM) to source-reconstructed event-related potential (ERP) data, we identified temporally distinct neural microstates that capture the evolving stages of speech categorization without imposing predefined temporal windows. Machine learning classifiers, including extreme gradient boosting (XGBoost), support vector machines, and random forests, were applied to decode prototypical (Tk1/5) versus ambiguous (Tk3) speech sound tokens from the microstate data. Using whole-brain activity, the XGBoost classifier achieved the highest decoding accuracy of 94.1% with an area under the curve (AUC) 94.1% within a specific encoding microstate occurring approximately 200-250 ms after stimulus onset. A reduced set of 15 informative brain regions identified via Shapley additive explanations (SHAP) yielded comparable classification performance (90.3% accuracy; AUC 90.0%), with many regions localized to frontal, temporal, and parietal regions in the left hemisphere. Furthermore, neural activity within these regions robustly predicted listeners behavioral identification slopes (R2 = 0.92, p < 0.00001), linking microstate-specific cortical dynamics to individual differences in perceptual gradiency of speech perception. These findings demonstrate that speech categorization emerges within temporally discrete neural microstates during early sensory-perceptual encoding and is supported by a selective, distributed cortical network with clear behavioral relevance.

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bioRxiv2026

Auditory brainstem-cortical anatomy constrains the magnitude of frequency-following responses (FFRs) and event-related potentials (ERPs) coding speech-in-noise

Speech-evoked brain potentials provide a window into the neural encoding of speech, experience-dependent plasticity, and deficits in central auditory processing from communication disorders. Stronger and faster frequency-following responses (FFRs) and cortical event-related potentials (ERPs) have been interpreted as reflecting more robust and efficient auditory-sensory processing across brainstem and cortical levels. Importantly, these neural signatures relate to real-world listening skills like speech-in-noise (SIN) perception. Yet, how these speech-evoked FFRs/ERPs relate to underlying auditory anatomical structures is unknown. Using a multimodal imaging approach, we recorded FFRs and ERPs to clean and noise-degraded speech sounds to assess the strength of listeners neural encoding of speech at brainstem (FFR) and cortical (ERP) levels. MRI volumetrics of midbrain and transverse temporal gyrus (Heschls gyrus) quantified morphological variation in subcortical and cortical anatomy that underly these EEG potentials. The QuickSIN assessed behavioral SIN abilities. Results showed that larger and thicker right (but not left) Heschls gyrus was related to listeners SIN abilities as well as the size of their cortical ERPs. Structural and functional measures interacted at a subcortical level. For listeners with smaller midbrain volumes, larger speech FFRs were associated with better QuickSIN scores; whereas in individuals with larger midbrain volumes, larger FFRs were related to poorer QuickSIN. Our findings reveal common functional signatures of speech processing (FFRs, ERPs) are constrained by the anatomy of their underlying generators and suggest a complex interplay between auditory brain structure and function in accounting for perceptual SIN capacity.

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bioRxiv2026

Elliptical speech reveals the use of broad phonetic categories aids noise-degraded speech perception

We investigated links between perceptual gradiency in phonetic categorization and speech-in-noise (SIN) perception in listeners with varying music backgrounds. Categorization was measured for vowels and stops using phoneme labeling tasks. Speech discrimination and transcription were assessed using "elliptical speech" sentences [Miller and Nicely (1955). JASA, 27, 338-352] which use featural substitutions that renders them meaningless in clean conditions but surprisingly improves their recognition under noise. We hypothesized listeners who use broader perceptual equivalency classes at the phoneme and/or sentence level would show better SIN. Perception of elliptical speech was indeed resilient to noise but this elliptical benefit varied with music background; nonmusicians showed larger susceptibility and noise-related benefit from ellipses than musicians. Phoneme categorization and elliptical sentence perception were also associated with QuickSIN performance but in opposite ways depending on musicianship. Broader phonetic category usage was related to better SIN in nonmusicians but poorer SIN in musicians. Findings suggest listeners can use broader/narrower perceptual equivalency classes and top-down inference to cope with noise degradation but this depends on auditory demographics. Musically naive listeners can use broader phonetic categories to aid SIN perception while expert listeners can use narrower categories in otherwise similar speech contexts. PACS numbers43.66, 43.71

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bioRxiv2024

Musicianship modulates cortical (but not brainstem) effects of attention on processing musical triads

BackgroundMany studies have demonstrated benefits of long-term music training (i.e., musicianship) on the neural processing of sound, including simple tones and speech. However, the effects of musicianship on the encoding of simultaneously presented pitches, in the form of complex musical chords, is less well-established. Presumably, musicians stronger familiarity and active experience with tonal music might enhance harmonic pitch representations, perhaps in an attention-dependent manner. Additionally, attention might influence chordal encoding differently across the auditory system. To this end, we explored the effects of long-term music training and attention on processing of musical chords at brainstem and cortical levels. MethodYoung adult participants were separated into musician and nonmusician groups based on extent of formal music training. While recording EEG, listeners heard isolated musical triads that differed only in the chordal third: major, minor, and detuned (4% sharper third from major). Participants were asked to correctly identify chords via key press during active stimulus blocks and watched a silent movie during passive blocks. We logged behavioral identification accuracy and reaction times and calculated information transfer based on the behavioral chord confusion patterns. EEG data were analyzed separately to distinguish between cortical (event-related potential, ERP) and subcortical (frequency-following response, FFR) evoked responses. ResultsWe found musicians were (expectedly) more accurate, though not faster, than nonmusicians in chordal identification. For subcortical FFRs, responses showed stimulus chord effects but no group differences. However, for cortical ERPs, whereas musicians displayed P2 ([~]150 ms) responses that were invariant to attention, nonmusicians displayed earlier and reduced P2 during passive listening. Listeners degree of behavioral information transfer (i.e., success in distinguishing chords) was also better in musicians and correlated with their neural differentiation of chords, assessed via pairwise differences in the ERPs. ConclusionsOur data suggest long-term music training strengthens even the passive cortical processing of musical sounds, supporting more automated brain processing of musical chords with less reliance on attention. Our results also suggest the degree to which listeners can behaviorally distinguish chordal triads is directly related to their neural specificity to musical sounds primarily at cortical rather than subcortical levels.

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bioRxiv2024

Auditory-motor entrainment and listening experience shape the perceptual learning of concurrent speech

BackgroundPlasticity from auditory experience shapes the brains encoding and perception of sound. Though prior research demonstrates that neural entrainment (i.e., brain-to-acoustic synchronization) aids speech perception, how long- and short-term plasticity influence entrainment to concurrent speech has not been investigated. Here, we explored neural entrainment mechanisms and the interplay between short- and long-term neuroplasticity for rapid auditory perceptual learning of concurrent speech sounds in young, normal-hearing musicians and nonmusicians. MethodParticipants learned to identify double-vowel mixtures during [~]45 min training sessions with concurrent high-density EEG recordings. We examined the degree to which brain responses entrained to the speech-stimulus train ([~]9 Hz) to investigate whether entrainment to speech prior to behavioral decision predicted task performance. Source and directed functional connectivity analyses of the EEG probed whether behavior was driven by group differences auditory-motor coupling. ResultsBoth musicians and nonmusicians showed rapid perceptual learning in accuracy with training. Interestingly, listeners neural entrainment strength prior to target speech mixtures predicted behavioral identification performance; stronger neural synchronization was observed preceding incorrect compared to correct trial responses. We also found stark hemispheric biases in auditory-motor coupling during speech entrainment, with greater auditory-motor connectivity in the right compared to left hemisphere for musicians (R>L) but not in nonmusicians (R=L). ConclusionsOur findings confirm stronger neuroacoustic synchronization and auditory-motor coupling during speech processing in musicians. Stronger neural entrainment to rapid stimulus trains preceding incorrect behavioral responses supports the notion that alpha-band ([~]10 Hz) arousal/suppression in brain activity is an important modulator of trial-by-trial success in perceptual processing.

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bioRxiv2024

Hearing in categories aids speech streaming at the "cocktail party"

Our perceptual system bins elements of the speech signal into categories to make speech perception manageable. Here, we aimed to test whether hearing speech in categories (as opposed to a continuous/gradient fashion) affords yet another benefit to speech recognition: parsing noisy speech at the "cocktail party." We measured speech recognition in a simulated 3D cocktail party environment. We manipulated task difficulty by varying the number of additional maskers presented at other spatial locations in the horizontal soundfield (1-4 talkers) and via forward vs. time-reversed maskers, promoting more and less informational masking (IM), respectively. In separate tasks, we measured isolated phoneme categorization using two-alternative forced choice (2AFC) and visual analog scaling (VAS) tasks designed to promote more/less categorical hearing and thus test putative links between categorization and real-world speech-in-noise skills. We first show that listeners can only monitor up to [~]3 talkers despite up to 5 in the soundscape and streaming is not related to extended high-frequency hearing thresholds (though QuickSIN scores are). We then confirm speech streaming accuracy and speed decline with additional competing talkers and amidst forward compared to reverse maskers with added IM. Dividing listeners into "discrete" vs. "continuous" categorizers based on their VAS labeling (i.e., whether responses were binary or continuous judgments), we then show the degree of IM experienced at the cocktail party is predicted by their degree of categoricity in phoneme labeling; more discrete listeners are less susceptible to IM than their gradient responding peers. Our results establish a link between speech categorization skills and cocktail party processing, with a categorical (rather than gradient) listening strategy benefiting degraded speech perception. These findings imply figure-ground deficits common in many disorders might arise through a surprisingly simple mechanism: a failure to properly bin sounds into categories.

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bioRxiv2023

Cross-linguistic and acoustic-driven effects on multiscale neural synchrony to stress rhythms

We investigated how neural oscillations code the hierarchical nature of stress rhythms in speech and how stress processing varies with language experience. By measuring phase synchrony of multilevel EEG-acoustic tracking and intra-brain cross-frequency coupling, we show the encoding of stress involves different neural signatures (delta rhythms = stress foot rate; theta rhythms = syllable rate), is stronger for amplitude vs. duration stress cues, and induces nested delta-theta coherence mirroring the stress-syllable hierarchy in speech. Only native English, but not Mandarin, speakers exhibited enhanced neural entrainment at central stress (2 Hz) and syllable (4 Hz) rates intrinsic to natural English. English individuals with superior cortical-stress tracking capabilities also displayed stronger neural hierarchical coherence, highlighting a nuanced interplay between internal nesting of brain rhythms and external entrainment rooted in language-specific speech rhythms. Our cross-language findings reveal brain-speech synchronization is not purely a "bottom-up" but benefits from "top-down" processing from listeners language-specific experience. HighlightsO_LINeural oscillations at delta and theta bands synchronize with stress and syllable rhythms. C_LIO_LIHierarchical delta-theta phase coupling mirrors speech rhythm hierarchy. C_LIO_LILanguage experience shapes multiscale brain-to-speech entrainment. C_LIO_LIOptimized brain-to-speech synchronization occurs at natural stress (2 Hz) and syllable (4 Hz) rates. C_LIO_LIAmplitude cues dominate the neural oscillatory encoding of stress rhythm. C_LI

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bioRxiv2023

Myogenic artifacts masquerade as neuroplasticity in the auditory frequency-following response (FFR)

The frequency-following response (FFR) is an evoked potential that provides a neural index of complex sound encoding in the brain. FFRs have been widely used to characterize speech and music processing, experience-dependent neuroplasticity (e.g., learning, musicianship), and biomarkers for hearing and language-based disorders that distort receptive communication abilities. It is widely assumed FFRs stem from a mixture of phase-locked neurogenic activity from brainstem and cortical structures along the hearing neuraxis. Here, we challenge this prevailing view by demonstrating upwards of [~]50% of the FFR can originate from a non-neural source: contamination from the postauricular muscle (PAM) vestigial startle reflex. We measured PAM, transient auditory brainstem responses (ABRs), and sustained frequency-following response (FFR) potentials reflecting myogenic (PAM) and neurogenic (ABR/FFR) responses in young, normal-hearing listeners with varying degrees of musical training. We first establish PAM artifact is present in all ears, varies with electrode proximity to the muscle, and can be experimentally manipulated by directing listeners eye gaze toward the ear of sound stimulation. We then show this muscular noise easily confounds auditory FFRs, spuriously amplifying responses by 3-4x fold with tandem PAM contraction and even explaining putative FFR enhancements observed in highly skilled musicians. Our findings expose a new and unrecognized myogenic source to the FFR that drives its large inter-subject variability and cast doubt on whether changes in the response typically attributed to neuroplasticity/pathology are solely of brain origin.

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bioRxiv2023

Short- and long-term experience-dependent neuroplasticity interact during the perceptual learning of concurrent speech

Plasticity from auditory experiences shapes brain encoding and perception of sound. However, whether such long-term plasticity alters the trajectory of short-term plasticity during speech processing has yet to be investigated. Here, we explored the neural mechanisms and interplay between short- and long-term neuroplasticity for rapid auditory perceptual learning of concurrent speech sounds in young, normal-hearing musicians and nonmusicians. Participants learned to identify double-vowel mixtures during [~]45 minute training sessions recorded simultaneously with high-density EEG. We analyzed frequency-following responses (FFRs) and event-related potentials (ERPs) to investigate neural correlates of learning at subcortical and cortical levels, respectively. While both groups showed rapid perceptual learning, musicians showed faster behavioral decisions than nonmusicians overall. Learning-related changes were not apparent in brainstem FFRs. However, plasticity was highly evident in cortex, where ERPs revealed unique hemispheric asymmetries between groups suggestive of different neural strategies (musicians: right hemisphere bias; nonmusicians: left hemisphere). Source reconstruction and the early (150-200 ms) time course of these effects localized learning-induced cortical plasticity to auditory-sensory brain areas. Our findings confirm domain-general benefits for musicianship but reveal successful speech sound learning is driven by a critical interplay between long- and short-term mechanisms of auditory plasticity that first emerge at a cortical level.

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bioRxiv2022

Unraveling Spatial-Spectral Dynamics of Speech Categorization Speed using Convolutional Neural Network

1The process of categorizing sounds into distinct phonetic categories is known as categorical perception (CP). Response times (RTs) provide a measure of perceptual difficulty during labeling decisions (i.e., categorization). The RT is quasi-stochastic in nature due to individuality and variations in perceptual tasks. To identify the source of RT variation in CP, we have built models to decode the brain regions and frequency bands driving fast, medium and slow response decision speeds. In particular, we implemented parameter optimized convolutional neural network (CNN) to classify listeners behavioral RTs from their neural EEG data. We adopted visual interpretation of model response using Guided-GradCAM to identify spatial-spectral correlates of RT. Our framework includes (but is not limited to): (i) a data augmentation technique designed to reduce noise and control the overall variance of EEG dataset; (ii) bandpower topomaps to learn the spatial-spectral representation using CNN; (iii) large-scale Bayesian hyper-parameter optimization to find best performing CNN model; (iv) ANOVA and post-hoc analysis on Guided-GradCAM activation values to measure the effect of neural regions and frequency bands on behavioral responses. Using this framework, we observe that - {beta} (10-20 Hz) activity over left frontal, right prefrontal/frontal, and right cerebellar regions are correlated with RT variation. Our results indicate that attention, template matching, temporal prediction of acoustics, motor control and decision uncertainty are the most probable factors in RT variation.

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bioRxiv2022

Cochlear summating potentials to paired-clicks predict speech-in-noise perception and hearing acuity

Objective assays of human cochlear synaptopathy (CS) have been challenging to develop. Its suspected if relative summating potential (SP) changes are different in CS listeners. In this proof-of-concept study, young, normal-hearing adults were recruited and assigned to a low/high-risk group for having CS based on their audiograms at 9-16 kHz. SPs to paired-clicks with varying inter-click intervals isolated non-refractory receptor components of cochlear activity. Abrupt increases in SPs to paired- vs. single-clicks were observed in high-risk listeners. Critically, overexaggerated SPs predicted speech-in-noise and subjective hearing abilities, suggesting relative SP changes to rapid clicks might help identify putative synaptopathic listeners.

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bioRxiv2022

Perceptual warping exposes categorical representations for speech in human brainstem responses

The brain transforms continuous acoustic events into discrete category representations to downsample the speech signal for our perceptual-cognitive systems. Such phonetic categories are highly malleable and heir percepts can change depending on surrounding stimulus context. Previous work suggests these acoustic-phonetic mapping and perceptual warping of speech emerge in the brain no earlier than auditory cortex. Here, we examined whether these auditory-category phenomena inherent to speech perception occur even earlier in the human brain, at the level of auditory brainstem. We recorded speech-evoked frequency following responses (FFRs) during a task designed to induce more/less warping of listeners perceptual categories depending on stimulus presentation order of a speech continuum (random, forward, backward directions). We used a novel clustered stimulus paradigm to rapidly record the high trial counts needed for FFRs concurrent with active behavioral tasks. We found serial stimulus order caused perceptual shifts (hysteresis) near listeners category boundary confirming identical speech tokens are perceived differentially depending on stimulus context. Critically, we further show neural FFRs during active (but not passive) listening are enhanced for prototypical vs. category-ambiguous tokens and are biased in the direction of listeners phonetic label even for acoustically-identical speech stimuli. Our data expose FFRs carry category-level information and suggest top-down processing actively shapes the neural encoding and categorization of speech at subcortical levels. These findings suggest the acoustic-phonetic mapping and perceptual warping in speech perception occur surprisingly early along the auditory neuroaxis, which might aid understanding by reducing ambiguity inherent to the speech signal.

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bioRxiv2022

Age-related hearing loss alters real-time dynamics of auditory cortical-brainstem coding during speech perception

Real-time modulation of brainstem frequency-following responses (FFRs) by online changes in cortical arousal state via the corticofugal (top-down) pathway has been demonstrated previously in young adults and is more prominent in the presence of background noise. FFRs during high cortical arousal states also have a stronger relationship with speech perception. Aging is associated with increased auditory brain responses, which might reflect degraded inhibitory processing within the peripheral and ascending pathways, or changes in attentional control regulation via descending auditory pathways. Here, we tested the hypothesis that online corticofugal interplay is impacted by age-related hearing loss. We measured EEG in older adults with normal-hearing (NH) and mild to moderate hearing-loss (HL) while they performed speech identification tasks in different noise backgrounds. We measured power to index online cortical arousal states during task engagement. Subsequently, we split brainstem speech-FFRs, on a trial-by-trial basis, according to fluctuations in concomitant cortical power into low or high FFRs to index cortical-brainstem modulation. We found cortical power was smaller in the HL than NH group. In NH listeners, -FFRs modulation for clear speech (i.e., without noise) also resembled that previously observed in younger adults for speech in noise. Cortical-brainstem modulation was further diminished in HL older adults in the clear condition and by noise in NH older adults. Machine learning classification showed low FFR frequency spectra yielded higher accuracy for classifying listeners perceptual performance in both NH and HL participants. Moreover, low FFRs decreased with increased hearing thresholds at 0.5-2 kHz for clear speech but noise generally reduced low FFRs in the HL group. Collectively, our study reveals cortical arousal state actively shapes brainstem speech representations and provides a potential new mechanism for older listeners difficulties perceiving speech in cocktail party-like listening situations in the form of a miss-coordination between cortical and subcortical levels of auditory processing.

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bioRxiv2021

Nonlinear dynamics in auditory cortical activity reveal the neural basis of perceptual warping in speech categorization

Surrounding context influences speech listening, resulting in dynamic shifts to category percepts. To examine its neural basis, event-related potentials (ERPs) were recorded during vowel identification with continua presented in random, forward, and backward orders to induce perceptual nonlinearities. Behaviorally, sequential order shifted listeners categorical boundary vs. random delivery revealing perceptual warping (biasing) of the heard phonetic category dependent on recent stimulus history. ERPs revealed later ([~]300 ms) activity localized to superior temporal and middle/inferior frontal gyri that predicted listeners hysteresis magnitudes. Findings demonstrate that top-down, stimulus history effects on speech categorization are governed by interactions between frontotemporal brain regions.

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bioRxiv2021

Functional plasticity coupled with structural predispositions in auditory cortex shape successful music category learning

Categorizing sounds into meaningful groups helps listeners more efficiently process the auditory scene and is a foundational skill for speech perception and language development. Yet, how auditory categories develop in the brain through learning, particularly for nonspeech sounds, is not well understood. Here, we asked musically naive listeners to complete a brief ([~]20 min) training session where they learned to identify sounds from a nonspeech continuum (minor-major 3rd musical intervals). We used multichannel EEG to track behaviorally relevant neuroplastic changes in the auditory event-related potentials (ERPs) pre- to post-training. To rule out mere exposure-induced changes, neural effects were evaluated against a control group of 14 nonmusicians who did not undergo training. We also compared individual categorization performance with structural volumetrics of bilateral primary auditory cortex (PAC) from MRI to evaluate neuroanatomical substrates of learning. Behavioral performance revealed steeper (i.e., more categorical) identification functions in the posttest that correlated with better training accuracy. At the neural level, improvement in learners behavioral identification was characterized by smaller P2 amplitudes at posttest, particularly over right hemisphere. Critically, learning-related changes in the ERPs were not observed in control listeners, ruling out mere exposure effects. Learners also showed smaller and thinner PAC bilaterally, indicating superior categorization was associated with structural differences in primary auditory brain regions. Collectively, our data suggest successful auditory categorical learning of nonspeech sounds is characterized by short-term functional changes (i.e., greater post-training efficiency) in sensory coding processes superimposed on preexisting structural differences in bilateral auditory cortex.

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bioRxiv2020

Speech categorization is better described by induced rather than evoked neural activity

Categorical perception (CP) describes how the human brain categorizes speech despite inherent acoustic variability. We examined neural correlates of CP in both evoked and induced EEG activity to evaluate which mode best describes the process of speech categorization. Using source reconstructed EEG, we used band-specific evoked and induced neural activity to build parameter optimized support vector machine (SVMs) model to assess how well listeners speech categorization could be decoded via whole-brain and hemisphere-specific responses. We found whole-brain evoked {beta}-band activity decoded prototypical from ambiguous speech sounds with ~70% accuracy. However, induced {gamma}-band oscillations showed better decoding of speech categories with ~95% accuracy compared to evoked {beta}-band activity (~70% accuracy). Induced high frequency ({gamma}-band) oscillations dominated CP decoding in the left hemisphere, whereas lower frequency ({theta}-band) dominated decoding in the right hemisphere. Moreover, feature selection identified 14 brain regions carrying induced activity and 22 regions of evoked activity that were most salient in describing category-level speech representations. Among the areas and neural regimes explored, we found that induced {gamma}-band modulations were most strongly associated with listeners behavioral CP. Our data suggest that the category-level organization of speech is dominated by relatively high frequency induced brain rhythms.

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