Patterns in the Cochlear Potentials of the Tokay Gecko (Gekko Gecko)

Abstract

The nature and origin of the nonlinearity in the cochlear potentials of the lizard Gekko gecko are investigated. Potentials recorded from silver ball electrodes on the round window and in the cochlea are averaged in an on-line computer and measured on a wave analyzer. The waveform of the potentials follows the frequency of the stimulating sound at low intensity and appears in general as a frequency doubling. Fourier analysis of the potentials reveals a second harmonic that is often larger than the fundamental, depending on the frequency of the stimulating sound. Action potentials, middle ear structures, and middle ear muscles contribute to the distortion only to a small degree. This distortion must thus arise in the inner ear structures. Differences between potentials from two sites of recording support this hypothesis. The findings are analyzed in comparison with mammalian cochlear potentials and discussed in relation to anatomical characteristics of the auditory structures of the Gekko gecko.