Impedance audiometry in the squirrel monkey. Sensorineural losses.

Acoustic reflex thresholds for pure tones and broad-band noise were measured before and after treatment of nine squirrel monkeys. Experimental sensorineural hearing loss was created in six monkeys by ototoxic drug administration (gentamicin) and in three monkeys by exposure to intense sound. Extent of cochlear damage was assessed histopathologically, in the case of permanent loss induced by the ototoxic agent, and inferred from exposure history, in the case of the reversible loss induced by exposure to intense sound. Posttreatment changes in relationships among acoustic reflex thresholds (noise-tone difference [NTD]) reflected approximate degree of cochlear damage. Serial measurement of changes in the NTD in acoustic reflex thresholds appears to be a worthwhile and useful technique for monitoring sensorineural levels in the squirrel monkey.