Envelope frequency following responses are stronger for high-pass than low-pass filtered vowels

To assess hearing in response to speech, the envelope frequency following response (FFR) can be observed at the fundamental frequency of a vowel stimulus and its harmonics. FFRs are complex non-linear phenomena, which require better understanding for allowing robust inferences on the assessment of hearing and hearing aid fitting.

To evaluate the effect of stimulus bandwidth on FFR detection rates using filtered vowel stimuli with equal sound levels.

FFRs were collected whilst presenting repeated vowels (in consonant-vowel-consonant format) filtered into different bandwidths. Eighty stimuli per word were presented at 70 dB SPL LAeq through insert earphones with an inter-stimulus interval of 1 s. Responses were detected using frequency-domain Hotelling's T2 (HT2) tests for individual multiples of the fundamental frequency (F0) and for combinations of F0 multiples.

A total of 11 native English-speaking subjects with normal hearing thresholds.

Average detection rates are highest (69%) with stimuli high-pass filtered >1000 Hz, and significantly lower for low-pass filtered stimuli (40%).

High-pass filtered vowels therefore appear to elicit stronger FFRs than low-pass filtered vowels at the same dB SPL LAeq. For testing hearing using band-limited speech, filtering effects (due to hearing loss, hearing aid setting or stimulus choice) on responses must be considered.