The overall goal of this study is to determine if information about the steady-state and time variant acoustic features of speech sounds are preserved in the scalp-recorded Frequency Following Response (FFR) recorded from normal-hearing human subjects. The long-term objective is to determine how this human FFR representation of speech sounds is altered in hearing-impaired individuals who experience significant reduction in their ability to discriminate speech sounds. The impetus for this study is derived from animal studies that have demonstrated that the spectrum of steady-state vowels and time-variant consonant-vowel syllables are well represented in the phase locked activity of populations of auditory-nerve fibers. These studies have also demonstrated that information concerning voice pitch is preserved in this robust phase-locked activity. The human FFT reflects synchronous, phase- locked activity in a population of auditory neurons in the rostral brainstem and thus provides a noninvasive window into the physiological mechanisms underlying the processing of speech sounds. specifically, it was reasoned that since phase-locking appears to play a dominant role in the representation of speech sounds, the human FFR (reflecting such a phase-locking in a population of neural elements) should preserve information about certain acoustic features of speech sounds. Consistent with the three specific aims of this study several experiments, using synthetic speech sounds, are proposed to address several issues related to : FFR representation of periodic steady-state and time-varying vowels in the presence of background noise; and v. FFR representation of voice pitch of both steady-state and time variant speech sounds. The experimental strategy is to simply apply several specific auditory-nerve population experiments (as outline above) to the human FFR in the effort to look for brainstem neuronal correlates of representation of speech sounds. TO date, knowledge about neural representation of speech sounds in normal-hearing and hearing-impaired human subjects will not only contribute to an understanding of brainstem mechanisms mediating representation of speech sounds but also, may have implications in terms of clinical diagnostic utility.
| Pandya, Pritesh K; Krishnan, Ananthanarayan (2004) Human frequency-following response correlates of the distortion product at 2F1-F2. J Am Acad Audiol 15:184-97 |
| Krishnan, Ananthanarayan (2002) Human frequency-following responses: representation of steady-state synthetic vowels. Hear Res 166:192-201 |
| Krishnan, A; Parkinson, J (2000) Human frequency-following response: representation of tonal sweeps. Audiol Neurootol 5:312-21 |
| Krishnan, A (1999) Human frequency-following responses to two-tone approximations of steady-state vowels. Audiol Neurootol 4:95-103 |
