ASA 127th Meeting M.I.T. 1994 June 6-10

2aPP16. Brainstem auditory steady-state responses to multiple simultaneous stimuli.

Human Neurosci. Res. Unit, Univ. of Ottawa, 451 Smith Rd., Ottawa, ON K1H 8M5, Canada

Brainstem auditory steady-state responses can be evoked by tones that are amplitude-modulated at rates of 70--110 Hz [Cohen et al., J. Acoust. Soc. Am. 90, 2467--2479 (1991)]. Steady-state responses to several stimuli presented simultaneously can be independently assessed by Fourier analysis if each stimulus is presented at a different rate [Regan, Human Brain Electrophysiology (1989)]. Could auditory brainstem steady-state responses to tones of different frequencies be recorded simultaneously? The first experiment presented tones to the right ear using carrier frequencies of 500, 1000, 2000, and 4000 Hz and modulation rates of 81, 89, 97, and 105 Hz, respectively. The response amplitudes when the stimuli were presented simultaneously were not significantly different from when the stimuli were presented alone. The second experiment presented tones of 500 and 2000 Hz modulated at 81 and 97 Hz to the left ear and tones of 500 and 2000 Hz modulated at 89 and 105 Hz to the right ear. The amplitude of the response was slightly but significantly larger when the tones were presented to both ears simultaneously than when they were presented alone. The simultaneous stimulation technique should therefore facilitate the physiological evaluation of human auditory function.