Effect of Stimulus Level and Bandwidth on Speech-Evoked Envelope Following Responses in Adults With Normal Hearing

Abstract

Results suggest that the EFR paradigm is sensitive to changes in level and audible bandwidth. This may be a useful tool as an objective-aided outcome measure considering its running speech-like stimulus, representation of spectral regions important for speech understanding, level and bandwidth sensitivity, and clinically feasible test times. This paradigm requires further validation in individuals with hearing loss, with and without hearing aids.

Phase‐locked responses to the vowel envelope vary in scalp‐recorded amplitude due to across‐frequency response interactions

“…The lower amplitude in response to /ε/ was likely not due to: (a) smaller EFR contributions by individual formant bands in /ε/; EFR contributions from each formant band were larger in /ε/ than /u/, on average (Figure ), (b) overall higher (i.e., favorable) stimulus level for /u/ than /ε/ (when no SPL weighting was applied; Easwar, et al. ; Akhoun et al., ) because formant EFR contributions were dependent on the formant band frequency (Figure d) and not formant band level, and (c) between‐vowel relative differences in F1‐ and F2+‐contributed EFR amplitude; F2+ contributions were similarly larger than F1 contributions for both vowels (Figure d). Therefore, the likely factors contributing to lower average net EFR amplitudes to /ε/ at 0° F2+ envelope phase delay, similar to the original vowel, are the larger (near 180°) phase difference between formant EFR contributions together with larger individual F1 and F2+ EFR contributions compared to /u/ (Figure ).…”

“…Dual‐ f 0 vowels were created using a method similar to that described in Easwar, et al. (). In brief, the original token was lowered in f 0 using the function “Convert/Change gender” in Praat (Boersma, ), by 11.03 Hz for /ε/ (lowered average f 0 = 86.73 Hz), and by 9.20 Hz for /u/ (lowered average f 0 = 80.94 Hz).…”

“…Dual‐ f 0 vowels were expected to elicit two EFRs simultaneously; one at the lowered f 0 elicited by the F1 band, and one at the original f 0 elicited by the F2+ band (Easwar, et al. ).…”

“…Two f 0 tracks were necessary to estimate EFRs elicited by the dual‐ f 0 vowels (second of 10 stimulus variants), one corresponding to the lowered f 0 , and one corresponding to the original f 0 (similar to Easwar, et al. ). Details of FA implementation are in Choi et al.…”

“…Similar observations have been made with vowel stimuli, as a function of formant band number. Although the first formant band with predominantly resolved harmonics is higher in stimulus level than higher formant bands, the EFR amplitudes at f 0 elicited by each band are similar (Easwar, Purcell, Aiken, Parsa, & Scollie, ; Laroche et al., ). These observations together suggest that relative EFR contributions from each formant band will likely vary across vowel identities as formant bands may carry predominantly resolved harmonics or unresolved harmonics, or a combination of both.…”