Multiple auditory steady-state responses to bone-conduction stimuli in adults with normal hearing

ASSR thresholds to bone-conduction stimuli were determined in 10 adults with normal hearing using mastoid placement of the bone oscillator. ASSRs to 0-50 dB HL bone-conduction stimuli and to 30-60 dB HL air-conduction stimuli were compared. The effect of alternating stimulus polarity on air- and bone-conduction ASSRs was also investigated. Stimuli were bone- and air-conduction amplitude-modulated tones (500-4000 Hz carrier frequencies, modulated at 77-101 Hz). ASSRs were recorded using the Rotman MASTER research system. Mean (1SD) bone-conduction ASSR thresholds were 22(11), 26(13), 18(8), and 18(11) dB HL for 500, 1000, 2000, and 4000 Hz, respectively. Except for a steeper slope at 500 Hz, ASSR intensity-amplitude functions for binaural bone- and air-conduction stimuli showed the same slopes; intensity-phase-delay functions were steeper at 1000 Hz for ASSRs to bone-conduction stimuli. ASSR amplitudes and phases did not differ for single- versus alternated-stimulus polarities for both bone- and air-conduction stimuli. The steeper amplitude slope for ASSRs to 500 Hz stimuli may reflect a nonauditory contribution to the ASSR.