Contralateral noise has possible asymmetric frequency-sensitive effect on the 2F1-F2 otoacoustic emission in humans

Contralateral acoustic stimulation has been shown to produce a suppressive effect on the 2F1-F2 distortion-product otoacoustic emission (DPOAE). According to reports by other studies, there is a frequency-specific suppressive region between 1 and 2 kHz when the contralateral broadband or narrowband noise stimulation contains energy close to or near the F2 frequencies in that region. In general the broader the bandwidth of the noise stimulation, the greater is the suppressive effect. A frequency-sensitive region between 1 and 2 kHz has also been suggested as narrowband noises with center frequencies remote from the F2 frequency seems to produce suppression in the same defined region. In order to test this hypothesis, narrowband noises wide enough to elicit suppression with center frequencies unmatched to the F2 frequencies were employed in the present study. For the right ear, a strong frequency-sensitive suppressive region was noted for the F2 frequency at 2 kHz, but not at 1 and 4 kHz. The left ear had some suppression at 1 kHz, but this effect was not as robust as seen in the right ear. The apparent suppressive differences between ears suggest a possible MOC reflex asymmetry that has not previously been described for DPOAEs. These results suggest that physiological differences between ears and possibly handedness must be taken into account when examining contralateral suppression to narrowband noises. Furthermore, the frequency contributions of the contralateral stimulus may have a greater complex interaction with the cochlear physiology than previously considered.