MULTIPLE AUDITORY STEADY-STATE RESPONSES (MASTER) - STIMULUS AND RECORDING PARAMETERS

Steady-state responses evoked by simultaneously presented amplitude mo dulated tones were measured by examining the spectral components in th e recording that corresponded to the different modulation frequencies. When using modulation frequencies between 70 and 110 Hz and an intens ity of 60 dB SPL, there were significant interactions between two stim uli when the carrier frequencies were closer than one half of an octav e apart, with attenuation of the response to the lower carrier frequen cy. However, there were no significant decreases in response amplitude with four simultaneous stimuli provided the carrier frequencies diffe red by one octave or more. Higher intensities (70 dB SPL) resulted in greater interactions between the stimuli than when low intensities (35 dB SPL) were used. Modulation frequencies could be as closely spaced as 1.3 Hz without affecting the responses. Using broad-band noise as a carrier instead of a pure tone resulted in a significantly larger res ponse when the stimuli were presented at the same sound pressure level . At modulation frequencies between 30 and 50 Hz, there were greater i nteractions between stimuli than at faster modulation frequencies. The se results support the following recommendations for using multiple st imuli in evoked potential audiometry: (1) The multiple stimulus techni que works well for steady state responses at frequencies between 70 an d 110 Hz. (2) Up to four stimuli can be simultaneously presented to an ear without significant loss in amplitude of the response, provided t he carrier frequencies are separated by an octave and the intensities are 60 dB SPL or less. (3) Bandpass noise might serve as a better carr ier signal than pure tones.