Objective evaluation of auditory evoked EEG responses

Abstract

THE averaging of often very small responses is widely used in physiology, psychology and clinical medicine to evaluate stimulus threshold levels. It is sometimes difficult to recognise responses in the average waveform because of residual activity, so a means of improving sensitivity and objectively recognising positive responses would be useful. We have previously found¹ that the averaged responses (ERA) evoked in the electroencephalogram (EEG) of a subject by auditory stimuli were produced by imposing a phase constraint on the different Fourier harmonics of the spontaneous EEG, without necessarily influencing their amplitudes.