Reflex modulation and loudness recruitment.

Eyeblink reflexes to airpuffs to the orbit are inhibited by preliminary tones even of low intensity, and the amount of inhibition or "reflex modulation" (RM) is correlated with tone loudness. Brief pure tones were presented 100 msec prior to an airpuff to the eye and eyeblink amplitude was recorded in 7 normal-hearing adults. Tones of several levels were either in quiet or in a white noise of 73.5 dbC. As tones increased in intensity, RM increased faster to stimulation in the masked than in the unmasked ear, simulating the classical "pseudo-recruitment" in the noise-masked ear. In addition, very rapid growth of RM was found at 4 kc/s in a patient with sensorineural impairment of 70 db at that frequency as compared with the RM from a frequency with normal HTL. These data confirm the potential of RM in the objective quantification of loudness recruitment.