Adaptation of the acoustically emitted 2f1−f2 combination tone

Abstract

Recent studies suggest that the 2f1−f2 ear‐canal distortion product is produced by nonlinearities in the motion of the cochlear partition. Given its cochlear origin, we attempted to use the acoustically emitted combination tone (ACT) to indirectly examine changes in cochlear mechanics that may be associated with long‐term adaptation (i.e., adaptation lasting several seconds) of eighth‐nerve responses. We examined the effects of 1‐min tonal exposures the amplitude of the 2f1−f2 ACT in the ear canals of cats. These effects were compared with post‐exposure changes in the whole‐nerve action potential (AP) responses to tone bursts that resulted from similar exposures. Both the distortion product and N1 amplitudes were reduced for several seconds following exposure. The reduction in ACT amplitude suggests that 1‐min exposures can alter cochlear mechanics. The fact that the same exposure tones cause reductions in N1 amplitude further suggests that neurally measured long‐term adaptation is linked to changes in th...