Observations on the acoustic reflex threshold in institutionalized retarded adults taking mellaril and/or thorazine

The present study was designed to investigate whether mellaril and thorazine, when used alone and in combination with other medications by mentally retarded clients, either abolish acoustic reflexes or compromise estimates of hearing sensitivity based on acoustic reflex measures. Acoustic reflex thresholds were determined in 35 normal-hearing institutionalized mentally retarded subjects who were regular users of the medications under investigation. Five sensitivity prediction methods based on acoustic reflex thresholds were applied to the data. The results of the study showed that acoustic reflexes were present in most subjects. However, the accuracy of all the acoustic reflex-based sensitivity prediction methods was quite poor with greatly exaggerated predictions of hearing loss. The methods based solely on noise reflex thresholds provided better accuracy than those based on noise-tone differences. In general, the accuracy of the prediction methods decreased as the number of medications used by the subjects increased. It is argued that the results provide evidence for reticular activating system mediation of acoustic reflex activity.