Normative characteristics of ipsilateral acoustic reflex adaptation.

Contralateral and ipsilateral acoustic reflex adaptation (decay) were examined using 500-, 1000-, and 2000-Hz tonal activators for stimulation periods of 30 seconds in 30 normal subjects. For these normal subjects, ipsilateral adaptation always exceeded contralateral adaptation, although differences between the two conditions were not significant. In addition, contralateral and ipsilateral acoustic reflex adaptation of four subjects with varying degrees of sensorineural hearing loss were compared to the normative data. Results for these impaired ears indicated that a longer period of activation may be necessary to distinguish between normal reflex adaptation and adaptation which may occur in cochlear pathology. Further, in three normal ears and two ears with cochlear pathology, ipsilateral adaptation equaled or exceeded 50% of the initial value within 10 seconds of activation. This finding suggests that the same criterion which is used for establishing abnormal contralateral adaptation cannot be used for abnormal ipsilateral adaptation.