Intermodulation distortion in the cochlea: could basal vibration be the major cause of round window CM distortion?

Acoustic and cochlear microphonic (CM) distortion products (DPs) have been measured at the meatus and round window, respectively, in the gerbil. It was hoped to deduce the relationship between round window CM distortion and vibrational energy of cochlear origin recorded as acoustic DP emissions in the meatus. Five different distortion components have been studied. For moderate intensities of stimulation, correlation between ear canal acoustic and CM distortion signals in respect of level and delay provides evidence of a common transmission path. One explanation of this is that the CM is being generated as a direct result of cochlea-generated vibration which reaches the base of the cochlea. The basalward propagation of these signals is discussed.