Effect of contralateral sound stimulation on the distortion product 2 f1− f2 in humans: Evidence of a frequency specificity

Abstract

The frequency characteristics of the suppression by contralateral stimulations, of the cubic 2 f 1− f 2 distortion products (DPOAEs), were studied during 63 sessions performed in 39 humans with normal hearing. Each session consisted of exposure to five successive series of randomized contralateral NBN frequencies centered between 0.25 and 8 kHz, while measuring 2 f 1− f 2 set at one of the four studied frequencies, i.e., 1, 2, 3 or 5 kHz. For each value of 2 f 1− f 2, analysis of variance and Student's t-test were used in order to indicate and, if necessary, to localize, a possible significant frequency specificity. Results showed that the suppression exerted on 2 f 1− f 2 DPOAEs by contralateral sound stimulation, is frequency specific, at least for middle frequencies of 1 and 2 kHz. The frequency specificity is specially marked when 2 f 1− f 2 = 1 kHz with contralateral NBN central frequencies around 1 kHz. When 2 f 1− f 2 = 2 kHz, central frequencies which induced a significant suppressive effect include frequencies around 2 kHz and also lower frequencies around 1 kHz. These observations support the interpretation that the suppression of the DPOAE is mediated by the medial olivo-cochlear efferent system.