Steady‐state evoked potentials in sleeping humans to continuous modulated tones

Abstract

At a previous meeting of the society, Rickards and Clark [J. Acoust. Soc. Am. Suppl. 1 72, S54(1982)] showed that steady‐state evoked potentials could be recorded from alert humans in response to amplitude‐modulated tones over a wide range of modulation frequencies. A subsequent paper has shown that, while there is an amplitude response maximum for alert subjects at a modulation rate of approximately 40 Hz and this frequency is thus appropriate for optimum threshold detection, different circumstances apply for sleeping subjects. Sleeping subjects differ from alert subjects in both amplitude response and background EEG noise, as functions of modulation frequency. A detection efficiency function reveals that during sleep the optimum modulation frequency, dependent on stimulus carrier frequency, lies well above 40 Hz. For lower carrier frequencies a peak occurs at about 90 Hz, while at higher frequencies the optimum modulation frequency is as high as 150 Hz. These higher modulation rates allow more efficient detection than does 40 Hz. Stimuli with high modulation rates have been used successfully with sleeping subjects including neonates.