Multiple auditory steady-state responses (MASTER): stimulus and recording parameters.

Steady-state responses evoked by simultaneously presented amplitude-modulated tones were measured by examining the spectral components in the recording that corresponded to the different modulation frequencies. When using modulation frequencies between 70 and 110 Hz and an intensity of 60 dB SPL, there were significant interactions between two stimuli when the carrier frequencies were closer than one half of an octave apart, with attenuation of the response to the lower carrier frequency. However, there were no significant decreases in response amplitude with four simultaneous stimuli provided the carrier frequencies differed 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 response when the stimuli were presented at the same sound pressure level. At modulation frequencies between 30 and 50 Hz, there were greater interactions between stimuli than at faster modulation frequencies. These results support the following recommendations for using multiple stimuli in evoked potential audiometry: (1) The multiple stimulus technique works well for steady state responses at frequencies between 70 and 110 Hz. (2) Up to four stimuli can be simultaneously presented to an ear without significant loss in amplitude of the response, provided the carrier frequencies are separated by an octave and the intensities are 60 dB SPL or less. (3) Bandpass noise might serve as a better carrier signal than pure tones.