UBC Theses and Dissertations
Multiple brainstem auditory steady-state response interactions for different stimuli Wood, Lori Laraine
Auditory steady-state responses (ASSRs) have been shown to be accurate in predicting thresholds of individuals with hearing loss. Although new stimuli are being proposed and clinically implemented, there are no data to indicate whether response interactions would be adversely affected by their use. This study investigated the effects of three different stimuli (AM, AM/FM and AM²) at two different intensities (60 dB HL and 80 dB HL) on response amplitudes and interactions in normal-hearing adults. Stimuli were generated by the Rotman MultiMASTER research system and presented via air conduction through EAR-3A insert earphones. Carrier frequencies of 0.5, 1, 2, and 4 kHz were 80-Hz modulated in three conditions: individually (monotic single; MS), simultaneously in one ear (monotic multiple; MM), and simultaneously in both ears (dichotic multiple; DM). It was predicted that stimuli with broader spectra would result in greater amplitudes. This was demonstrated in the MS condition by the AM/FM stimulus, which evoked responses significantly larger than those to both AM and AM² stimuli at all frequencies except 0.5 kHz at 60 and 80 dB HL. In the multiple (MM and DM) conditions, response amplitudes to AM² were significantly larger than AM and AM/FM response amplitudes at both intensities. It was also predicted that more interactions would be found when using stimuli with broader spectra, even at moderate intensities. This was illustrated by the drop in amplitude by the AM/FM stimulus in the multiple conditions versus in the single condition, even at 60 dB HL. Relative efficiency values in the multiple conditions were never less than that found in the single condition at 60 dB HL; at 80 dB HL, the majority (83%) of comparisons were more efficient in the multiple conditions than the single condition. Based on these results, the optimal stimulus to use appears to be dependent on the chosen condition. In the single condition, AM/FM stimuli result in the largest response amplitudes, however, in the multiple condition, AM² stimuli provide the best combination of amplitude values and testing efficiency.
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