Envelope-following response amplitude and cochlear traveling wave delay

Potential clinical roles of the envelope following response (EFR), such as diagnostic testing and amplification verification, are promising. Despite its potential, variability in response amplitude due to various stimulus characteristics is not yet fully understood. The purpose of this study was to evaluate the effects of cochlear traveling wave delay on EFR amplitude. EFRs were recorded on young, normal hearing individuals using amplitude-modulated tones to represent first (F1) and second formants (F2) of vowel stimuli. EFR stimuli were created with a fixed fundamental frequency and a fixed formant carrier frequency. Stimulus conditions employed a dynamic frequency approach by sweeping the second formant over a range of frequencies to result in different F0-related phase delays. Instantaneous amplitudes were assessed as the difference in response between F1-only and F1F2 conditions. Systematic increases and decreases in amplitude were expected to correspond with calculated differences in phase delay. However, the expected trends were not observed and very minimal differences between these conditions were shown overall. These EFR amplitude findings to various vowel-simulated stimuli were not consistent with previous research from Wall (2018). Variability in noise estimates and differences between target and actual phase delay values may have contributed to these trends. A clear understanding of cochlear delay and its potential effects on amplitude variability of the EFR must be obtained before vowel-elicited EFRs can be implemented as an effective clinical tool