Low level acoustic reflex thresholds

The acoustic reflex threshold (ART) can be detected at lower than normal sound pressure levels by means of facilitation. This procedure entails simultaneous presentation of a high frequency tone at a level just below the ART and a threshold seeking stimulus. The threshold seeking stimulus is presented in decrements until no further reflex activity can be observed. Difference values between normal and reduced ARTs were obtained from 18 normal hearing and 18 sensorineural hearing-impaired ears. Each subject was exposed to twelve conditions: threshold seeking signals of pure tones or octave bands of noise were presented in conjunction with a 4000 Hz facilitating tone in either the same ear (monotic mode) or in opposite ears (dichotic mode). Threshold shifts were significantly greater for the normal hearing subjects than for the hearing-impaired subjects. In the hearing-impaired ears, the facilitated ART produced a lesser degree of threshold reduction or no apparent threshold shift. For the normal hearing ears, the monotic mode of signal presentation produced greater threshold shifts than the dichotic mode.