Comparison of the identifiability of the low intensity ABR and MLR in the mentally handicapped patient.

The auditory brain stem response and the middle latency response were recorded from low intensity click stimuli in 48 patients with mental handicaps. In the 23 patients (45 ears) with normal hearing thresholds, the ABR was found to have a lower test-retest variability than the MLR. This lower variability will correspond to higher identifiability at threshold. In the 25 patients with a hearing loss, four had MLRs recorded in ears with absent ABRs. In five of these ears no auditory response would have been detected if ABRs alone were recorded. Based on the above findings, the following recommendations can be made. Recording the ABR with open filters is the desired method for threshold detection in most subjects. If no response is obtained it is desirable to record a MLR. The recording of a MLR is probably more important in laboratories recording responses with steep filter slopes, since a greater portion of the slow wave activity, P phi (V) complex, will be phase shifted into the later portion of the time base.