Behavioral and Cortical Responses to Frequency Changes in Vowel-Like Stimuli in Listeners With Normal and Impaired Hearing

Abstract

Objectives: This study proposes a new method for detecting cortical responses to formant frequency changes using the auditory change complex (ACC). These can be used as a proxy for discrimination performance between spectral characteristics of vowels. Design: We generated two sets of vowel-like stimuli, each of which contained four sinusoids with carrier frequencies chosen to correspond to the first three formants of the vowels/u/ and/i/, respectively. During EEG recordings, the second formant ( F 2) frequency changed in different step sizes to evoke an ACC response. We collected responses for both a hearing-impaired group (10 participants) and a control group with normal hearing (9 participants) and furthermore compared these to a behavioral measure of formant frequency discrimination. Results: The size of the change in the frequency of the F 2 formant, as well as the presence of hearing impairment, significantly affected the ACC response. Larger frequency changes produced larger ACC response amplitudes, specifically for the/u/ stimuli with more lower-frequency content. Responses tended to be lower overall for the hearing-impaired participants. Moreover, the ACC magnitude was correlated with behavioral formant discrimination thresholds. Conclusions: Taken altogether, these results lend support to the use of an ACC paradigm to assess frequency discrimination abilities objectively with speech-like stimuli. This study shows reliable responses as well as correlation with behavioral discrimination, which highlight the paradigm’s potential suitability for clinical purposes.