Simultaneous acquisition of 40- and 80-Hz auditory steady-state responses for a direct comparison of response amplitude, residual noise and signal-to-noise ratio.

PURPOSE

The purpose of this study was to establish a paradigm that allows for the simultaneous recording of auditory steady-state responses (ASSRs) to two largely different modulation rates.

METHODS

In 21 normal-hearing adults, ASSRs for 40- and 80-Hz modulation rates were recorded in (1) a classical monotic single-stimulus condition, (2) a monotic simultaneous condition, where 40 Hz was paired with a 1-kHz carrier and 80 Hz with a 2-kHz carrier, and (3) a dichotic simultaneous condition with the same modulation rate/carrier pairing. Response amplitudes, residual noises, and signal-to-noise ratios were compared across conditions.

RESULTS

Whereas the multiple-stimulus paradigms reduced the 40-Hz ASSR amplitude compared to the single condition, there was hardly any change for the 80-Hz ASSR. In all conditions, the 40-Hz ASSR was considerably larger than the 80-Hz ASSR. The residual noise was only 1.4 times larger for 40 Hz than for the 80 Hz.

CONCLUSION

The proposed procedure using multiple stimuli with largely different modulation rates can be used to study differences in their responses and residual noise under identical states of vigilance. The amplitude reduction caused by the interaction between multiple stimuli has to be taken into account when interpreting the results.