Biology subjects

Maddox, R. K.

Publications and source records attributed to Maddox, R. K..

At least 19 recordsLinked to original sources

bioRxiv2026

Refractoriness-Based Masking Yields Threshold-Specific Human Auditory Nerve Responses

Distinct auditory nerve (AN) fiber populations with varying thresholds and vulnerabilities to synaptopathy are observable in animal models, but standard non-invasive human measures lack the resolution to differentiate these groups of fibers. This fundamental limitation hinders the translation of findings in animals to human auditory pathologies. To overcome this, we developed a novel refractoriness-masking paradigm to non-invasively isolate threshold-specific AN fiber responses in humans. By presenting rapid click trains with cumulatively rising levels (45 to 105 dB peSPL) at a 250-microsecond inter-click interval, we sequentially masked lower-threshold fibers. Using a tympanic membrane electrode, we recorded compound action potentials (CAPs) in adults with normal hearing and isolated threshold-specific responses via waveform subtraction. Our results demonstrated that the isolated CAPs exhibited decreased latencies with increasing levels and a non-linear amplitude growth, plateauing at 90 dB peSPL before sharply increasing at 105 dB peSPL. This pattern reflects the sequential recruitment of AN fiber that were not effectively recruited by the preceding clicks. Validate conditions, in which the final two clicks had equal levels, produced substantially smaller CAPs, consistent with response suppression by refractoriness. Overall, this paradigm establishes a human measurement approach for characterizing level-threshold-dependent AN responses, providing a potential way to better investigate different AN pathologies, such as cochlear synaptopathy or auditory neuropathy.

neuroscience↗

bioRxiv2025

Attention to Psuedo-Tone Melodies Enhances Cortical but Not Brainstem Responses in Humans

Auditory selective attention, the ability to focus on specific sounds while ignoring competitors, enables communication in complex soundscapes. Though attention clearly modulates cortical responses to sound, whether and where this modulation occurs in subcortical structures remains disputed. Here, we use electroencephalography to record cortical and subcortical (auditory brainstem responses, ABRs) activity during a selective attention task. Human participants attend to a 3-note melody in one pitch range presented to one ear while ignoring a competing, interleaved melody in a different pitch range played to the other ear (Laffere et al., 2020, 2021). The melodies consist of pitch-evoking pseudo-tones formed by convolving a periodic impulse train with a brief tone pip. These stimuli allow us to measure both ABRs (elicited by each individual tone pip within a pseudo-note) and cortical responses (elicited by the onsets of pseudo-notes) simultaneously. We observed robust ABRs, but no evidence of modulation by attention. Conversely, cortical responses, measured by event related potentials (ERPs), demonstrated attentional modulation of the P1-N1 peak. We conclude that attentional modulation within the brainstem is not measurable in the well-defined peaks of the ABR, which themselves reflect processing up to the input stage to the inferior colliculus.

neuroscience↗

bioRxiv2025

Bone conducted responses using the parallel auditory brainstem response (pABR) paradigm

ObjectivesAuditory brainstem responses (ABRs) are used to diagnose hearing loss across multiple frequencies in infants and others who cannot participate in behavioral testing. The parallel ABR (pABR) paradigm measures response waveforms to all frequencies from 500- 8000 Hz in both ears all at once, rather than serially in one ear at a time. Work so far has been with air conducted stimuli through insert earphones, but bone conducted stimuli are also an essential part of diagnosing the type of hearing loss by determining the relative contributions of conductive and sensorineural hearing loss. This study aimed to confirm the feasibility of bone conduction pABR. DesignWe recruited a cohort of young adults with normal hearing. An intensity series of two-channel ABRs were measured to pABR stimuli played through ER-2 insert earphones as well as with a B-71 bone vibrator with contralateral masking. Behavioral thresholds were also measured to compare dB nHL correction factors. To keep sessions under 3.5 hours only one ear was tested with bone conduction. The ear with bone conduction and the order of transducers was counterbalanced across participants. Waveform morphologies for each transducer were compared by their wave V latencies and amplitudes and residual noise. ResultsFor the same dB nHL levels, responses to both transducers aligned well and wave V amplitudes and latencies were similar. While stimulus artifacts can be an issue with bone conduction, the steps taken to mitigate it in air conduction pABR were also effective for bone conduction: clear bone conducted responses were measured and residual noise was similar for both transducers. Bone conducted responses to 8 kHz were weak, which was not surprising given the physics of bone conduction and the output capabilities of the bone vibrator. As expected, behavioral thresholds were higher for pABR than pure tone stimuli, and by the same offset for both transducers. The dB nHL values differed due to the difference in reference equivalent threshold levels for inserts and the bone vibrator. ConclusionsAir and bone conduction provided similar waveforms, indicating that bone conduction pABR is feasible. Together with establishing dB nHL values, this work represents an important step towards translating the pABR for diagnosing all types of hearing loss.

neuroscience↗

bioRxiv2024

The effect of speech masking on the human subcortical response to continuous speech

Auditory masking--the interference of the encoding and processing of an acoustic stimulus imposed by one or more competing stimuli--is nearly omnipresent in daily life, and presents a critical barrier to many listeners, including people with hearing loss, users of hearing aids and cochlear implants, and people with auditory processing disorders. The perceptual aspects of masking have been actively studied for several decades, and particular emphasis has been placed on masking of speech by other speech sounds. The neural effects of such masking, especially at the subcortical level, have been much less studied, in large part due to the technical limitations of making such measurements. Recent work has allowed estimation of the auditory brainstem response (ABR), whose characteristic waves are linked to specific subcortical areas, to naturalistic speech. In this study, we used those techniques to measure the encoding of speech stimuli that were masked by one or more simultaneous other speech stimuli. We presented listeners with simultaneous speech from one, two, three, or five simultaneous talkers, corresponding to a range of signal-to-noise ratios (SNR; Clean, 0, -3, and -6 dB), and derived the ABR to each talker in the mixture. Each talker in a mixture was treated in turn as a target sound masked by other talkers, making the response quicker to acquire. We found consistently across listeners that ABR wave V amplitudes decreased and latencies increased as the number of competing talkers increased. Significance statementTrying to listen to someone speak in a noisy setting is a common challenge for most people, due to auditory masking. Masking has been studied extensively at the behavioral level, and more recently in the cortex using EEG and other neurophysiological methods. Much less is known, however, about how masking affects speech encoding in the subcortical auditory system. Here we presented listeners with mixtures of simultaneous speech streams ranging from one to five talkers. We used recently developed tools for measuring subcortical speech encoding to determine how the encoding of each speech stream was impacted by the masker speech. We show that the subcortical response to masked speech becomes smaller and increasingly delayed as the masking becomes more severe.

neuroscience↗

bioRxiv2024

Chimeric music reveals an interaction of pitch and time in electrophysiological signatures of music encoding

Pitch and time are the essential dimensions defining musical melody. Recent electrophysiological studies have explored the neural encoding of musical pitch and time by leveraging probabilistic models of their sequences, but few have studied how the features might interact. This study examines these interactions by introducing "chimeric music," which pairs two distinct melodies, and exchanges their pitch contours and note onset-times to create two new melodies, thereby distorting musical pattern while maintaining the marginal statistics of the original pieces pitch and temporal sequences. Through this manipulation, we aimed to dissect the music processing and the interaction between pitch and time. Employing the temporal response function (TRF) framework, we analyzed the neural encoding of melodic expectation and musical downbeats in participants with varying levels of musical training. Our findings revealed differences in the encoding of melodic expectation between original and chimeric stimuli in both dimensions, with a significant impact of musical experience. This suggests that the structural violation due to decoupling the pitch and temporal structure affect expectation processing. In our analysis of downbeat encoding, we found an enhanced neural response when participants heard a note that aligned with the downbeat during music listening. In chimeric music, responses to downbeats were larger when the note was also a downbeat in the original music that provided the pitch sequence, indicating an effect of pitch structure on beat perception. This study advances our understanding of the neural underpinnings of music, emphasizing the significance of pitch-time interaction in the neural encoding of music. Significance StatementListening to music is a complex and multidimensional auditory experience. Recent studies have investigated the neural encoding of pitch and timing sequences in musical structure, but they have been studied independently. This study addresses the gap in understanding of how the interaction between pitch and time affects their encoding. By introducing "chimeric music," which decouples these dimensions in melodies, we investigate how this interaction influences the neural activities using EEG. Leveraging and the temporal response function (TRF) framework, we found that structural violations in pitch-time interactions impact musical expectation processing and beat perception. These results advance our knowledge of how the brain processes complex auditory stimuli like music, underscoring the critical role of pitch and time interactions in music perception.

neuroscience↗

bioRxiv2024

Musical training does not enhance neural sound encoding at early stages of the auditory system: A large-scale multisite investigation

Musical training has been associated with enhanced neural processing of sounds, as measured via the frequency following response (FFR), implying the potential for human subcortical neural plasticity. We conducted a large-scale multi-site preregistered study (n > 260) to replicate and extend the findings underpinning this important relationship. We failed to replicate any of the major findings published previously in smaller studies. Musical training was related neither to enhanced spectral encoding strength of a speech stimulus (/da/) in babble nor to a stronger neural-stimulus correlation. Similarly, the strength of neural tracking of a speech sound with a time-varying pitch was not related to either years of musical training or age of onset of musical training. Our findings provide no evidence for plasticity of early auditory responses based on musical training and exposure.

neuroscience↗

bioRxiv2024

Fundamental frequency predominantly drives talker differences in auditory brainstem responses to continuous speech

Deriving human neural responses to natural speech is now possible, but the responses to male- and female-uttered speech have been shown to differ. These talker differences may complicate interpretations or restrict experimental designs geared toward more realistic communication scenarios. This study found that when a male and female talker had the same fundamental frequency, auditory brainstem responses (ABRs) were very similar. Those responses became smaller and later with increasing fundamental frequency, as did click ABRs with increasing stimulus rates. Modeled responses suggested that the speech and click ABR differences were reasonably predicted by peripheral and brainstem processing of stimulus acoustics.

neuroscience↗

bioRxiv2024

Comparing Methods for Deriving the Auditory Brainstem Response to Continuous Speech in Human Listeners

Several tools have recently been developed to derive the Auditory Brainstem Response (ABR) from continuous natural speech, facilitating investigation into subcortical encoding of speech. These tools rely on deconvolution, which models the subcortical auditory pathway as a linear system, where a nonlinearly processed stimulus is taken as the input (i.e., regressor), the electroencephalogram (EEG) data as the output, and the ABR as the impulse response deconvolved from the recorded EEG and the regressor. In this study, we analyzed EEG recordings from subjects listening to both unaltered natural speech and synthesized "peaky speech." We compared the derived ABRs using three regressors: the half-wave rectified stimulus (HWR) from Maddox and Lee (2018), the glottal pulse train (GP) from Polonenko and Maddox (2021), and the auditory nerve modeled response (ANM) from Shan et al. (2024). Our evaluation focused on the fidelity, efficiency, and practicality of each method in different scenarios. The results indicate that the ANM regressor for both peaky and unaltered speech and the GP regressor for peaky speech provided the best performance, whereas the HWR regressor demonstrated relatively poorer performance. The findings in this study will guide future research in selecting the most appropriate paradigm for ABR derivation from continuous, naturalistic speech.

neuroscience↗

bioRxiv2024

Enhanced Place Specificity of the Parallel Auditory Brainstem Response: An Electrophysiology Study

PurposeThis study investigates the effect of parallel stimulus presentation on the place specificity of the auditory brainstem response (ABR) in human listeners. Frequency-specific stimuli do not guarantee a response from the place on the cochlea corresponding only to that characteristic frequency - especially for brief and high-level stimuli. Adding masking noise yields responses that are more place specific, and a prior modeling study has suggested similar effects when multiple frequency-specific stimuli are presented in parallel. We tested this hypothesis experimentally here, comparing the place specificity of responses to serial and parallel stimuli at two stimulus frequencies and three stimulus rates. MethodsParallel ABR (pABR) stimuli were presented alongside high-pass filtered noise with a varied cutoff frequency. Serial presentation was also tested by isolating and presenting single-frequency stimulus trains from the pABR ensemble. Latencies of the ABRs were examined to assess place specificity of responses. Response bands were derived by subtracting responses from different high pass noise conditions. The response amplitude from each derived response band was then used to determine how much individual frequency regions of the auditory system were contributing to the overall response. ResultsWe found that parallel presentation improves place specificity of ABRs for the lower stimulus frequency and at higher stimulus rates. At a higher stimulus frequency, serial and parallel presentation were equally place specific. ConclusionParallel presentation can provide more place specific responses than serial for lower stimulus frequencies. The improvement increases with higher stimulus rates and is in addition to the pABRs primary benefit of faster test times.

neuroscience↗

bioRxiv2023

Multisensory perceptual learning in virtual reality may facilitate transfer to untrained locations but is impacted by training procedures.

Visual training improves performance in visually-intact and visually-impaired participants, making it useful as a rehabilitation tool. An interesting question in rehabilitation is whether invocation of multisensory integration could increase training efficacy. To investigate, participants completed a 10-day training experiment wherein they repeatedly performed a 4-way global motion direction discrimination task. On each trial, participants were presented with a 5{degrees} diameter visual global motion stimulus placed in a gaze-contingent manner at 10{degrees} azimuth/elevation. The visual-only group was presented the unimodal visual stimulus. However, for the auditory/visual (AV) group, the visual stimulus was paired with a pulsed white-noise auditory cue moving along in a direction consistent with the horizontal component of the visual motion stimulus. Direction range thresholds (DRT) were computed daily. The motion direction discrimination learning transferred fully in both groups, regardless of the presence of a feature-based attention cue. However, the figure-ground segregation learning only fully transferred to untrained locations with the addition of the feature-based attention cue. These results speak to the multiple levels of processing on which perceptual learning can operate. PACS0000, 1111 2000 MSC0000, 1111

neuroscience↗

bioRxiv2022

Music and Speech Elicit Similar Subcortical Responses in Human Listeners

Music and speech are two sounds that are unique to human beings and encountered in daily life. Both are transformed by the auditory pathway from an initial acoustical encoding to higher level cognition. Most studies of speech and music processing are focused on the cortex, and the subcortical response to natural, polyphonic music is essentially unstudied. This study was aimed to compare the subcortical encoding of music and speech using the auditory brainstem response (ABR). While several methods have recently been developed to derive the ABR to continuous speech, they are either not applicable to music or give poor results. In this study, we explored deriving the ABR through deconvolution using three regressors: 1) the half-wave rectified stimulus waveform, 2) the modeled inner hair cell potential, and 3) the auditory nerve model firing rate (ANM), where the latter two were generated from a computational auditory periphery model. We found the ANM regressor yields robust and interpretable ABR waveforms to diverse genres of music and multiple types of speech. We then used the ANM-derived ABRs to compare the subcortical responses to music and speech and found that they are highly similar in morphology. We further investigated cortical responses using the same deconvolution method, and found the responses there were also quite similar, which was unexpected based on previous studies. We conclude that when using our proposed deconvolution regressor that accounts for acoustical differences nonlinear effects on peripheral encoding, the derived brainstem and cortical responses to music and speech are highly correlated.

neuroscience↗

bioRxiv2022

Task-uninformative visual stimuli improve auditory spatial discrimination: an elusive effect with an ambiguous contribution of relative reliability

The brain combines information from multiple sensory modalities to interpret the environment. These processes, collectively known as multisensory integration, have been modeled as Bayesian causal inference, which proposes that perception involves the combination of information from different sensory modalities based on their reliability and their likelihood of stemming from the same causes in the outside world. Bayesian causal inference has explained a variety of multisensory effects in simple tasks but is largely untested in complex sensory scenes where multisensory integration can provide the most benefit. Recently, we presented data challenging the ideal Bayesian model from a new auditory spatial discrimination task in which spatially aligned visual stimuli improve performance despite providing no information about the correct response. Here, we tested the hypothesis that, despite deviating from the ideal observer, the influence of task-uninformative stimuli was still dependent on the reliabilities of auditory and visual cues. We reasoned shorter stimulus durations should lead to less reliable auditory spatial encoding, and hence stronger effects of more reliable visual cues, which are easily localized even at short durations. While our results replicated the effect from our previous study across a wide range of stimulus durations, we did not find a significant increase in effect size with shorter stimuli, leaving our principal question not fully answered.

neuroscience↗

bioRxiv2022

Humans rely more on talker identity than temporal coherence in an audiovisual selective attention task using speech-like stimuli

Audiovisual integration of speech can benefit the listener by not only improving comprehension of what a talker is saying but also helping a listener pick a particular talkers voice out of a mix of sounds. Binding, an early integration of auditory and visual streams that helps an observer allocate attention to a combined audiovisual object, is likely involved in audiovisual speech processing. Although temporal coherence of stimulus features across sensory modalities has been implicated as an important cue for non-speech stimuli (Maddox et al., 2015), the specific cues that drive binding in speech are not fully understood due to the challenges of studying binding in natural stimuli. Here we used speech-like artificial stimuli that allowed us to isolate three potential contributors to binding: temporal coherence (are the face and the voice changing synchronously?), articulatory correspondence (do visual faces represent the correct phones?), and talker congruence (do the face and voice come from the same person?). In a trio of experiments, we examined the relative contributions of each of these cues. Normal hearing listeners performed a dual detection task in which they were instructed to respond to events in a target auditory stream and a visual stream while ignoring events in a distractor auditory stream. We found that viewing the face of a talker who matched the attended voice (i.e., talker congruence) offered a performance benefit. Importantly, we found no effect of temporal coherence on performance in this task, a result that prompts an important recontextualization of previous findings.

neuroscience↗

bioRxiv2022

Speech-In-Noise Comprehension is Improved When Viewing a Deep-Neural-Network-Generated Talking Face

Listening in a noisy environment is challenging, but many previous studies have demonstrated that comprehension of speech can be substantially improved by looking at the talkers face. We recently developed a deep neural network (DNN) based system that generates movies of a talking face from speech audio and a single face image. In this study, we aimed to quantify the benefits that such a system can bring to speech comprehension, especially in noise. The target speech audio was masked with signal to noise ratios of -9, -6, -3, and 0 dB and was presented to subjects in three audio-visual (AV) stimulus conditions: 1) synthesized AV: audio with the synthesized talking face movie; 2) natural AV: audio with the original movie from the corpus; and 3) audio-only: audio with a static image of the talker. Subjects were asked to type the sentences they heard in each trial and keyword recognition was quantified for each condition. Overall, performance in the synthesized AV condition fell approximately halfway between the other two conditions, showing a marked improvement over the audio-only control but still falling short of the natural AV condition. Every subject showed some benefit from the synthetic AV stimulus. The results of this study support the idea that a DNN-based model that generates a talking face from speech audio can meaningfully enhance comprehension in noisy environments, and has the potential to be used as a "visual hearing aid."

neuroscience↗

bioRxiv2022

Inferring sources of suboptimality in perceptual decision making using a causal inference task

Perceptual decision-making has been extensively modeled using the ideal observer framework. However, a range of deviations from optimality demand an extension of this framework to characterize the different sources of suboptimality. Prior work has mostly formalized these sources by adding biases and variability in the context of specific process models but are hard to generalize to more complex tasks. Here, we formalize suboptimalities as part of the brains probabilistic model of the task. Data from a traditional binary discrimination task cannot separate between different kinds of biases, or between sensory noise and approximate computations. We showed that this was possible using a recently developed causal inference task in which observers discriminated auditory cues in the presence of choice-uninformative visual cues. An extension of the task with different stimulus durations provided evidence for an increase in the precision of the computations with stimulus duration, separate from a decrease in observation noise.

animal behavior and cognition↗

bioRxiv2021

Optimizing parameters for using the parallel auditory brainstem response (pABR) to quickly estimate hearing thresholds

ObjectivesTimely assessments are critical to providing early intervention and better hearing and spoken language outcomes for children with hearing loss. To facilitate faster diagnostic hearing assessments in infants, the authors developed the parallel auditory brainstem response (pABR), which presents randomly timed trains of tone pips at five frequencies to each ear simultaneously. The pABR yields high-quality waveforms that are similar to the standard, single-frequency serial ABR but in a fraction of the recording time. While well-documented for standard ABRs, it is yet unknown how presentation rate and level interact to affect responses collected in parallel. Furthermore, the stimuli are yet to be calibrated to perceptual thresholds. Therefore, this study aimed to determine the optimal range of parameters for the pABR and to establish the normative stimulus level correction values for the ABR stimuli. DesignTwo experiments were completed, each with a group of 20 adults (18 - 35 years old) with normal hearing thresholds ([≤] 20 dB HL) from 250 to 8000 Hz. First, pABR electroencephalographic (EEG) responses were recorded for six stimulation rates and two intensities. The changes in component wave V amplitude and latency were analyzed, as well as the time required for all responses to reach a criterion signal-to-noise ratio of 0 dB. Second, behavioral thresholds were measured for pure tones and for the pABR stimuli at each rate to determine the correction factors that relate the stimulus level in dB peSPL to perceptual thresholds in dB nHL. ResultsThe pABR showed some adaptation with increased stimulation rate. A wide range of rates yielded robust responses in under 15 minutes, but 40 Hz was the optimal singular presentation rate. Extending the analysis window to include later components of the response offered further time-saving advantages for the temporally broader responses to low frequency tone pips. The perceptual thresholds to pABR stimuli changed subtly with rate, giving a relatively similar set of correction factors to convert the level of the pABR stimuli from dB peSPL to dB nHL. ConclusionsThe optimal stimulation rate for the pABR is 40 Hz, but using multiple rates may prove useful. Perceptual thresholds that subtly change across rate allow for a testing paradigm that easily transitions between rates, which may be useful for quickly estimating thresholds for different configurations of hearing loss. These optimized parameters facilitate expediency and effectiveness of the pABR to estimate hearing thresholds in a clinical setting. HighlightsO_LIThe pABR yields robust responses across stimulus rates and intensities. C_LIO_LIThe optimal rate is 40 Hz, but using multiple rates may prove useful. C_LIO_LIThe pABR shows some adaptation with increased stimulation rate. C_LIO_LIExtended analysis windows improve response detection for low stimulus frequencies. C_LIO_LIBehavioral thresholds subtly change across pABR rate, giving similar dB nHL values. C_LI

neuroscience↗

bioRxiv2021

Spatial alignment between faces and voices improves selective attention to audio-visual speech

The ability to see a talkers face has long been known to improve speech intelligibility in noise. This perceptual benefit depends on approximate temporal alignment between the auditory and visual speech components. However, the practical role that cross-modal spatial alignment plays in integrating audio-visual (AV) speech remains unresolved, particularly when competing talkers are present. In a series of online experiments, we investigated the importance of spatial alignment between corresponding faces and voices using a paradigm that featured both acoustic masking (speech-shaped noise) and attentional demands from a competing talker. Participants selectively attended a Target Talkers speech, then identified a word spoken by the Target Talker. In Exp. 1, we found improved task performance when the talkers faces were visible, but only when corresponding faces and voices were presented in the same hemifield (spatially aligned). In Exp. 2, we tested for possible influences of eye position on this result. In auditory-only conditions, directing gaze toward the distractor voice reduced performance as predicted, but this effect could not fully explain the cost of AV spatial misalignment. Finally, in Exp. 3 and 4, we show that the effect of AV spatial alignment changes with noise level, but this was limited by a floor effect: due to the use of closed-set stimuli, participants were able to perform the task relatively well using lipreading alone. However, comparison between the results of Exp. 1 and Exp. 3 suggests that the cost of AV misalignment is larger at high noise levels. Overall, these results indicate that spatial alignment between corresponding faces and voices is important for AV speech integration in attentionally demanding communication settings.

neuroscience↗

bioRxiv2020

Exposing distinct subcortical components of the auditory brainstem response evoked by continuous naturalistic speech

Speech processing is built upon encoding by the auditory nerve and brainstem, yet we know very little about how these processes unfold in specific subcortical structures. These structures are deep and respond quickly, making them difficult to study during ongoing speech. Recent techniques begin to address this problem, but yield temporally broad responses with consequently ambiguous neural origins. Here we describe a method that pairs re-synthesized "peaky" speech with deconvolution analysis of EEG recordings. We show that in adults with normal hearing, the method quickly yields robust responses whose component waves reflect activity from distinct subcortical structures spanning auditory nerve to rostral brainstem. We further demonstrate the versatility of peaky speech by simultaneously measuring bilateral and ear-specific responses across different frequency bands, and discuss important practical considerations such as talker choice. The peaky speech method holds promise as a tool for investigating speech encoding and processing, and for clinical applications.

neuroscience↗