Seminars in Hearing Research at Purdue (SHRP)

Date: Thursday, October 20, 2022

Time: 10:30 – 11:20 am

Location: LYLE 1150

Title: Rapid Assessment of Temporal Processing from the Peripheral and Central Auditory Pathway using Dynamic Amplitude Modulated Stimuli

Speaker: Ed Bartlett, Professor in Biological Sciences and Biomedical Engineering 

Abstract: Background: Envelope or amplitude modulation (AM) cues in a signal are critically important for the perception of complex signals, e.g., speech. Neural coding of AM can be noninvasively probed using the envelope following response (EFR), which receives contributions from both cortical (slower fluctuations, <40 Hz) and subcortical (faster fluctuations, >100 Hz) generators. As subcortical versus cortical signatures of AM representations vary across hearing loss etiologies, the EFR has great diagnostic potential. AM representations are routinely evaluated by the temporal modulation transfer function (tMTF), which is the strength of the EFR as a function of AM frequency. Currently, tMTF is measured serially for discrete sinusoidally amplitude modulated (sAM) tones. This process is time-consuming and inefficient, impeding clinical translation. Here we present a dynamically varying AM tone (dAM) used to measure a tMTF. I will analyze the tMTF obtained with and without hearing pathologies (aging, inflammation).  Methods: EEG responses were obtained using sub-dermal needle electrodes in rodent models.  In rodents, carrier frequencies and amplitude modulation rates varied based on species-specific differences. Tones with dynamically varying AM, the frequency of which increased exponentially from 9 Hz to 1.5 kHz over one second, and identical carrier frequencies were also used to elicit EFRs and the tMTFs were compared. Fast Fourier transforms were used to calculate discrete EFR amplitudes. A spectrally specific frequency-demodulation-based analysis was used to calculate EFR amplitudes from dAM stimuli.  Results: Robust tMTFs were obtained for discrete sAM stimuli from all species tested. Preliminary results show strong tracking of dAM envelopes in rodents, which can be used to estimate the tMTF at a fine frequency resolution. These tMTFs are comparable to those obtained using discrete sAM tones. In humans, preliminary results suggest that tracking of dAM envelopes was comparable to sAM stimuli, but only at lower modulation frequencies. Ongoing analysis is aimed at refining the dAM stimuli (trajectories, timescales) to optimize AM tracking while simultaneously reducing recording times in humans.   Conclusions: These results suggest that dynamically varying AM tones can be used to efficiently estimate the tMTF. However, further optimization is needed to obtain robust tMTF estimates in humans at higher AM frequencies. When combined with spectrally specific analysis, the dAM tone can be used to substantially speed up the tMTF measuring time, paving the way for potential clinical translation.

Zoom Info: https://purdue-edu.zoom.us/j/4326340458

Meeting ID: 432 634 0458

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