Seminars in Hearing Research at Purdue
Talks in 2021-2022
LYLE 1150 [hybrid via Zoom: Thursdays 1030-1120am]
August 26, 2021
Discussion led by Michael Heinz, Hari Bharadwaj, and Andrew Sivaprakasam (SLHS/BME)
Audiology Research Diagnostic Core (ARDC): Updates and discussion on data sharing
Our inaugural "seminar" for this season will be an update and discussion on the PIIN Grand Challenges project towards establishing infrastructure for precision auditory neuroscience at Purdue.
September 2, 2021
Agudemu Borjigin, PhD candidate, Weldon School of Biomedical Engineering
Deep Neural Networks for Speech Enhancement in Cochlear ImplantsDespite excellent performance in quiet, cochlear implants (CIs) usually fail to restore normal levels of intelligibility in noisy environments. Current state-of-the-art signal processing strategies in CIs provide limited benefits in terms of noise reduction or masking release. Recent developments in the field of machine learning have produced deep neural network (DNN) models with impressive performance in both speech enhancement and separation tasks. With sponsorship from hearing implant manufacturer— MED-EL, this work was an exploratory attempt to evaluate the use of DNN models as front-end pre-processors for enhancing CI users’ speech understanding in noisy environments. This talk will focus on model architectures, dataset, workflow (tools and resources), objective evaluation results, and pilot data collected from CI subjects.
September 9, 2021
Jonatan Märcher-Rørsted, PhD candidate, Technical University of Denmark (DTU)
Age-related reduction in frequency-following responses as a potential marker of cochlear neural degeneration
Previous studies have reported an age-related reduction in frequency-following responses (FFRs) in listeners with clinically normal audiometric thresholds. This has been argued to reflect an age-dependent decline in neural synchrony in the central auditory system. However, age-dependent degeneration of auditory nerve (AN) fibers may have little effect on audiometric sensitivity and may yet affect the suprathreshold coding of temporal information. This peripheral loss of temporal information may not be recovered centrally and may thus also contribute to reduced phase-locking accuracy in the auditory midbrain. Here, we investigated whether age-related reductions in the FFR could, at least in part, reflect age-dependent peripheral neural degeneration.
We combined human electrophysiology and auditory nerve (AN) modelling to investigate whether age-related changes in the FFR would be consistent with peripheral neural degeneration. A reduction in the FFR response in the older listeners was found across stimulation frequencies for both sweep and static pure-tone stimulation. Older listeners also showed significantly shallower MEMR growth level functions compared to the younger listeners, which could indicate a loss of low spontaneous rate fibers in the AN. Despite having clinically normal audiometric thresholds, the older listeners had significantly reduced sensitivity at frequencies above 8 kHz compared to the young group. The computational simulations suggested that such experimental results can be accounted for by neural degeneration already at the stage of the AN whereas a loss of sensitivity due to OHC dysfunction at higher frequencies could not explain the observed reduced FFR in the older listeners. These results are consistent with a peripheral source of the FFR reductions observed in older normal-hearing listeners, and indicate that FFRs at lower carrier frequencies may potentially be a sensitive marker of peripheral neural degeneration.
September 16, 2021
William Salloom, PhD candidate, PULSe program (Strickland lab)
The effect of broadband elicitor duration on transient-evoked otoacoustic emissions and a behavioral measure of gain reduction
Humans are able to encode sound over a wide range of intensities despite the fact that neurons in the auditory periphery have much smaller dynamic ranges. There is a feedback system that originates at the level of the brainstem that may help solve the dynamic range problem. This system is the medial olivocochlear reflex (MOCR), which is a bilateral sound-activated system which decreases amplification of sound by the outer hair cells in the cochlea. Much of the previous research on the MOCR in animals and humans has been physiologically based, and has used long broadband noise elicitors. However, the effect of the duration of broadband noise elicitors on similar behavioral tasks is unknown. Additionally, MOCR effects measured using otoacoustic emissions (OAEs), have not consistently shown a positive correlation with behavioral gain reduction tasks. This may be due to different methodologies being utilized for the OAE and behavioral tasks, and/or due to the analysis techniques not being optimized to observe a relationship. In the current study, we explored the effects of ipsilateral broadband noise elicitor duration both physiologically and behaviorally in the same subjects. Both measures used similar stimuli in a forward-masking paradigm. We tested two research questions: 1) Are the time constants of the physiological and behavioral measures similar to one another (thus reflecting the same mechanism) 2) Can the changes in physiological responses by the elicitor predict the changes in behavioral responses in the same subjects, as a function of elicitor duration. By keeping our stimuli and subjects consistent throughout the study, as well as using various methods analyze our OAE data, we have optimized the conditions to determine the relationship between physiological and behavioral measures of gain reduction. The findings for both of these questions will be discussed. Understanding these effects is not only of fundamental importance to how the auditory system adapts to sound over time, but is also of practical importance in laboratory settings that use broadband noise to elicit the MOCR.
September 23, 2021
Ravinderjit Singh, PhD candidate, BME/MSTP (Bharadwaj lab)
A system-identification approach to characterize cortical temporal coding
Many studies have investigated how subcortical temporal processing, measured via brainstem evoked potentials (e.g., ABRs and FFRs) may be influenced by aging, hearing loss, musicianship, and other auditory processing disorders. However, human studies of cortical temporal processing are often restricted to the 40 Hz steady-state response. One possible reason for the limited investigation is the lack of a fast and easy method to characterize temporal processing noninvasively in humans over a range of modulation frequencies. Without a broadband characterization of cortical temporal processing, it is difficult to disentangle the different components that may contribute to the overall EEG response, and discover their respective functional correlates. Here, we use a system-identification approach where white noise, modulated using a modified maximum length sequence (m-seq), is presented to quickly obtain a stereotypical and repeatable auditory cortical “impulse” response (ACR) capturing broadband cortical modulation coding (up to 75 Hz) with EEG. Using principal component analysis (PCA) across different EEG sensors, we found that the overall response is composed of five components that can be distinguished by virtue of latency, and/or scalp topography. Furthermore, the components spanned different frequency ranges within the overall temporal modulation transfer function (tMTF), and differed in their sensitivities to manipulations of attention and/or task demands. Interestingly, we also find that the ACR shows nonlinear behavior, in that the relative magnitudes of the constituent components are different when measured using broadband modulations versus a series of sinusoidal modulations.
September 30, 2021
Jeffrey Lucas, Professor, Department of Biological Sciences
Resources that are relevant in the entire hierarchy of life? Information is one…
Biology is a hierarchical phenomenon. The investigation of biological systems is also, necessarily, hierarchical. Unfortunately, there is relatively little crosstalk across disciplines that address biological phenomena at different scales. For example, structural biologists don’t often talk to community ecologists. NSF funded a series of country-wide workshops that focused on this issue with the hope of finding possible research protocols that bridge disciplines. Our group in these workshops focused on the possibility that scale-independent resources might help scale-dependent scientific inquiry. I’ll talk about the 4 “resources” we identified: energy, conductance, storage, and information, with an emphasis on the idea that information is truly a resource that is critical to all biological systems irrespective of scale. I offer 3 (+1) examples of how information organizes systems from tiny to massive. You’ll also see where niche construction fits into the big, and sometimes into the smaller, picture.