Coherence between one random and one periodic signal-application to the EEG during sensory stimulation

Coherence between a pulse train representing periodic stimuli and the EEG has been used in the objective detection of steady-state evoked potentials, based on its sampling distribution under the null hypothesis of no responses. In order to use this coherence as a measure of the strength of responses, its sample distribution must be established under the alternative hypothesis. In this paper, the statistics of coherence estimates between one random and one periodic signal is investigated, with the aim of obtaining its confidence limits and the probability of detecting a response, if such is present. The results are then verified in Monte Carlo simulations and applied to the EEG of 14 subjects.