The effects of alcohol on the acoustic Reflex Relaxation Index

Normal-hearing young adults (6 M, 5 F) ingested 1.5 ml alcohol per Kg body weight over 90 min (blood alcohol level then being 0.104 +/- 0.016%), then tested for contralateral acoustic reflex (AR) threshold using an otoadmittance meter, and given the acoustic Reflex Relaxation Index (RRI) test of Norris, Stelmachowicz and Taylor. Each stimulus for the RRI was a 4-sec train of pulses at a level 10 db above AR threshold at .5, 1, or 2 kc/s, with equivalent on-time of 166.7 msec and off-time of 200 msec. AR responses were displayed on an X-Y recorder. RRI was taken as the percentage of total relation of the AR during off-times. The AR relaxed relatively more during off-times, and the RRI consequently significantly increased, in the alcohol vs the control condition, mean differences in RRI score in percent being 5.0, 12,9, and 21.3% for .5, 1, and 2 kc/s, respectively. Group mean RRI at all 3 frequencies under alcohol was close to the cut-off score suggested as "normal" by the test originators, but in 6 of the 11 Ss RRI interpretation by that criterion changed from "normal" to "not normal" under alcohol at one or more frequencies. There are unresolved differences in the effect of specific temporal stimulus patterning on RRI. Caution is recommended in interpreting RRI in the clinic as suggestive of sensorineural hearing impairment if S is at the time under the influence of a CNS depressant.