The effects of contralateral noise on the masked compound action potential (CAP) were examined in human subjects. Small but significant enhancements of masked CAP amplitude (anti-masking effects) were observed in some patients with facial palsy, as well as in some subjects with healthy ears when noise was added to the contralateral ear. There were no significant differences in fractional changes of CAP by the addition of contralateral noise between subjects with healthy ears and patients with facial palsy in which acoustic reflexes of middle ear muscles (MEMs) had disappeared or were impaired. It is suggested that the anti-masking effects seen in the present study were possibly caused via the olivocochlear (OC) efferent system.
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