ACOUSTIC GAMMA ENTRAINMENT IN NORMAL-HEARING AND HEARING-IMPAIRED ADULTS

Acoustic Gamma stimulation can modulate cortical activity, yet it remains unclear how individuals with hearing impairment engage such entrainment compared with normal-hearing adults. We examined cortical synchronization during naturalistic speech listening in normal-hearing (n=17) and elderly adults with mild to moderately severe hearing loss (n=19). Across all conditions, the speech stimulus was a video podcast featuring two speakers. The concurrently presented cafeteria background noise varied systematically in modulation depth and modulated frequency range. To compare speech-in-noise with isolated stimulation, noise stimuli were also presented without speech. High-frequency audiometry revealed elevated thresholds above 8 kHz in both groups, indicating that high-frequency sensitivity may impact responsiveness to acoustic stimulation. Sounds were delivered without amplification for normal-hearing adults, while hearing-impaired participants received individualized compensation. Thirty-two-channel EEG auditory steady-state responses (ASSRs) quantified entrainment strength as SNR at 40 Hz. Repeated-measures ANOVA revealed a main effect of stimulation mode (speech-in-noise vs. noise-only), indicating reduced entrainment when continuous speech was present. Modulation conditions also significantly affected entrainment effectiveness. Hearing status alone did not yield a main effect, but its interactions with stimulation mode and modulation conditions indicated that hearing-impaired and normal-hearing adults differed in how strongly these stimulation parameters shaped entrainment. Overall, conditions with stronger modulation patterns tended to elicit stronger entrainment in hearing-impaired than in normal-hearing adults, potentially reflecting differences in effective audibility.