Statistical properties of spontaneous otoacoustic emissions in one bird and three lizard species

Spontaneous otoacoustic emissions were recorded in the barn owl Tyto alba guttata (five ears), and in three lizard species (Callopistes maculatus, one ear; Varanus exanthematicus, seven ears; Gerrhonotus leiocephalus, one ear). The barn owl ears emitted one or two emission frequencies; the lizard ears had one, two, or three emissions. For each peak in the emission spectrum, an amplitude distribution was obtained. By comparing the spectrum and the histogram, it is concluded that the emission signals obeyed partly sinusoidal and partly noise statistics. The latter is presumably caused by random amplitude fluctuations of the emissions. Four out of 7 owl emissions and 7 out of 16 lizard emissions were dominated by sinusoidal statistics. For these emissions, the relative rms amplitude fluctuation ranged from 0.13 to 0.41 for the barn owl, and from 0.04 to 0.29 for the lizards. These emissions must have been generated by an active oscillator in the ear. In one barn owl ear, mutual suppression of two neighboring emissions was observed. This caused one of the two emissions to deviate substantially from sinusoidal statistics. The 11 remaining emissions were dominated by noise statistics, presumably due to large amplitude fluctuations. For these emissions, our data are not conclusive on whether an active oscillator is involved in the emission generation.