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Neural Engineering

Neural Engineering - Poster Session A

Poster J18 - Age-Related Changes in Neural Representations of Binaural Temporal Fine-Structure Cues

Thursday, October 24, 2024
10:00 AM - 11:00 AM EST
Location: Exhibit Hall E, F & G

Introduction:  Aging is associated with hearing deficits that often do not manifest as changes in overt hearing thresholds. Rather, middle-aged and older listeners experience difficulties listening in noisy environments or segregating information from multiple speakers. One reason for these deficits may be the progressive loss of afferent synapses in the cochlea with age, which remains “hidden” to current clinical tests. This cochlear deafferentation may affect the accurate, binaural representation of temporal fine structure (TFS) cues in speech, which are critical for speaker localization and identification, especially in these noisy listening conditions. Here, we use an objective measure of binaural processing in young and middle-aged listeners with normal hearing thresholds to ascertain the changes in binaural TFS representations with age and their effects on speech in noise intelligibility.

Materials and

Methods:  54 subjects were recruited and provided informed consent to be tested for this study. Of these subjects, 27 were young adults (YA) aged 18-25 and 27 were middle-aged (MA) adults 40-60 years. All subjects had normal audiograms with thresholds ≤ 25 dB HL for octave spaced frequencies from 250Hz - 8kHz.
Objective measures of binaural TFS processing were recorded using the recently described inter-aural phase difference following response (IPDFRs). IPDFRs are phase-locked EEG-based neural ensemble responses that ‘follow’ periodic shifts in interaural phase. IPDFR’s were collected to a 520 Hz tone carrier with phase modulated at 6.8 Hz and amplitude modulated at 40.8 Hz. Phase was shifted at 0◦, 22.5◦, 45◦, and 90◦ across each ear in opposing directions, and presented at a sound level of 85 dB SPL. Controls were performed with phase shifts of 90◦ in both ears at the same polarity, thus having a phase shift but no phase difference that would result in a binaural cue. Recordings lasted ~3 hours and they were done on a 64 channel EEG system (BioSemi). IPDFRs were analyzed using established python-based EEG pipelines to extract the phase-locking amplitudes at 6.8Hz which represents the binaural phase shifts, and 40.8Hz, which is the phase-invariant envelope following response.

Results, Conclusions, and Discussions: RESULTS
Robust IPDFRs were obtained from both young and middle-aged listeners. IPDFRs decreased in amplitude with the degree of binaural separation, hence suggesting that they are a sensitive metric of binaural TFS coding. IPDFR amplitudes were significantly lower in middle-aged adults, when compared to young adults. There was no change in amplitudes of the phase-invariant EFRs at 40.8Hz, further confirming that the IPDFRs were selectively sensitive for binaural TFS coding, while the EFRs represented overall neural phase-locking abilities. EFR amplitudes were also significantly decreased in middle-aged adults compared to the young. IPDFR amplitudes that were normalized to individual EFR amplitudes showed minimal differences with age.
(ITD) (Figure 1).

CONCLUSION
Our data suggest that middle-aged listeners experience significantly reduced binaural TFS coding, and that these binaural coding deficits may be driven by overall decreases in neural phase locking with age.

DISCUSSION
Spatial hearing is critical for understanding speech in noisy conditions. The IPDFR provides an objective neurophysiological measure of binaural processing, especially of rapidly varying TFS cues. In our study, we find that middle-aged adults experience a significant decline in binaural TFS coding despite having clinically normal audiograms. These declines in TFS coding may be driven by overall decreases in neural phase-locking. The mechanisms underlying these phase-locking deficits are a subject of s future study and may include progressive cochlear deafferentation with age. These results identify the IPDFR as a promising diagnostic biomarker of binaural hearing in the clinic, that are sensitive to age-related changes in TFS coding.

Acknowledgements (Optional):