Extending Subcortical EEG Responses to Continuous Speech to the Sound-Field

Abstract

The auditory brainstem response (ABR) is a valuable clinical tool for objective hearing assessment, which is conventionally detected by averaging neural responses to thousands of short stimuli. Progressing beyond these unnatural stimuli, brainstem responses to continuous speech presented via earphones have been recently detected using linear temporal response functions (TRFs). Here, we extend earlier studies by measuring subcortical responses to continuous speech presented in the sound-field, and assess the amount of data needed to estimate brainstem TRFs. Electroencephalography (EEG) was recorded from 24 normal hearing participants while they listened to clicks and stories presented via earphones and loudspeakers. Subcortical TRFs were computed after accounting for non-linear processing in the auditory periphery by either stimulus rectification or an auditory nerve model. Our results demonstrated that subcortical responses to continuous speech could be reliably measured in the sound-field. TRFs estimated using auditory nerve models outperformed simple rectification, and 16 minutes of data was sufficient for the TRFs of all participants to show clear wave V peaks for both earphones and sound-field stimuli. Subcortical TRFs to continuous speech were highly consistent in both earphone and sound-field conditions, and with click ABRs. However, sound-field TRFs required slightly more data (16 minutes) to achieve clear wave V peaks compared to earphone TRFs (12 minutes), possibly due to effects of room acoustics. By investigating subcortical responses to sound-field speech stimuli, this study lays the groundwork for bringing objective hearing assessment closer to real-life conditions, which may lead to improved hearing evaluations and smart hearing technologies.

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

“…Another possible reason for the differences may be the underlying ISI distributions used to create the clicks. In this study, a pseudorandom Poisson process was used to create randomized click trains as in prior work (Bachmann et al, 2024;Maddox and Lee, 2018). Although the mean rates matched mean f0s, the exponential ISI distribution characteristic of a Poisson process (Figure 2) differed from the speech ISI distributions and may account for some of the ABR differences between the two types of stimuli.…”

“…Click stimuli were also created as before (Bachmann et al, 2024;Maddox and Lee, 2018) but with stimulus rates corresponding to the shifted speech f0s (123, 150, 183 stim / s). A total of 150 unique 1 s epochs were created with a pseudorandom Poisson process controlling the timing of the click trains.…”

“…Click ABRs, however, are usually evoked with lower stimulation rates than the typical speech f0s (>60 Hz), confounding the comparison. The lower rates are necessary for periodic stimulation due to the response window, but are also generally done for randomized stimuli (Bachmann et al, 2024;e.g., Maddox and Lee, 2018;Maddox, 2019, 2022), except for specific studies with high-rate clicks (e.g., Valderrama et al, 2012). In this study, matching the mean click rate to the mean speech f0s brought the click and speech ABRs into a similar amplitude range, suggesting that stimulation rate may partially account for the previously described click-speech ABR differences.…”

L-type calcium channel blockade with verapamil prevents noise induced neuronal dys-synchrony

“…Auditory function can be assessed throughout the auditory pathway by analyzing individual peaks present in the ABR wave form (Bachmann et al, 2024;Chang et al, 2022;Jiang et al, 2021;Wood et al, 2019). For example, peripheral auditory function corresponds to the first peak (Wave I) of the ABR, present at about 2 msec from the onset of the stimulus (Chang et al, 2022;Wood et al, 2019).…”

“…Central auditory function has been correlated with peaks II-V of the ABR wave form. Specifically, the neuronal synchronous activity in the inferior colliculus can be assessed by analyzing peak V (Wave V) at approximately 6 msec from the onset of the stimulus (Bachmann et al, 2024;Chang et al, 2022;Jiang et al, 2021;Wood et al, 2019). Similar to the peripheral effects of noise over exposure, a loss of neuronal synchrony was observed centrally, as indicated by decreases in ABR Wave V amplitude at both 12 and 20 kHz.…”