The Influence of Sensation Level on Speech-Evoked Envelope Following Responses

Objectives: To evaluate sensation level (SL)-dependent characteristics of envelope following responses (EFRs) elicited by band-limited speech dominant in low, mid, and high frequencies. Design: In 21 young normal hearing adults, EFRs were elicited by 8 male-spoken speech stimuli-the first formant, and second and higher formants of /u/, /a/ and /i/, and modulated fricatives, /j/ and /s/. Stimulus SL was computed from behaviorally measured thresholds. Results: At 30 dB SL, the amplitude and phase coherence of fricative-elicited EFRs were similar to 1.5 to 2 times higher than all vowel-elicited EFRs, whereas fewer and smaller differences were found among vowel-elicited EFRs. For all stimuli, EFR amplitude and phase coherence increased by roughly 50% for every 10 dB increase in SL between similar to 0 and 50 dB. Conclusions: Stimulus and frequency dependency in EFRs exist despite accounting for differences in audibility of speech sounds. The growth rate of EFR characteristics with SL is independent of stimulus and its frequency.