ResponsesThe Multiple Auditory steady-state response (MASTER) technique enables multiple tones to be tested at the same time. The figure shows four stimuli that will be presented to the left ear and four stimuli presented to the right ear. The carrier frequencies are 500 Hz, 1000 Hz, 2000 Hz, and 4000 Hz and the modulation frequencies for the left ear (77, 85, 93, 101) must be different than those for the right (79, 87, 95, 103).
|Carrier (Hz)||Modulation (Hz)|
|The four separate stimuli are combined in the time domain and are presented to the participant as complex tonal stimuli.|
Because the cochlea is tonotopically organized the 4 tones are each sensed by the respective tonal area on the basilar membrane.
The hair cells in each tonal area fire with the maximum of the AM envelope for each tonal frequency, and therefore the evoked steady-state responses are produced at the frequency of modulation of each carrier frequency. The signals are compared to background EEG activity (grey in figure) using the F-ratio statistic, and if the signal to noise ratio is large enough a response is considered significant (i.e., the participant heard the tone).