Contrast enhancement in frequency spectra of cochlear microphonic responses to complex stimuli

Cochlear microphonic responses were measured in pigeons and guinea pigs during stimulation with complex sounds. The acoustical stimuli had many component frequency spectra with a more or less undulating envelope. Enhancement of the peak-and-valley structure of the envelope occurred at high stimuli levels, especially if all frequency components in the stimulus had equal (cosine) phase. The observed effects could very well be modelled with a simple passive electronic network, as well as with an analytical expression that describes saturation of the cochlear microphonic at high stimulus levels.