The effects of both natural and sedated sleep on the auditory steady state evoked potential (SSEP) were evaluated in nine normal-hearing subjects. Both absolute amplitude and phase variability measures were obtained by Fourier analysis of successive samples of the averaged SSEP waveform. Amplitude decreased significantly in the sleeping state but phase variability was not substantially altered. Because it does not seem to be affected by sleep, phase variability of the SSEP is suggested as a potentially useful technique for predicting threshold sensitivity.
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