Spontaneous otoacoustic emissions in two gecko species, Gekko gecko and Eublepharis macularius

Spontaneous otoacoustic emissions (SPOAE) of the gecko species Gekko gecko and Eublepharis macularius appear as broad spectral peaks (bandwidth 44 to 170 Hz) between 1 and 4.5 kHz that have peak levels of -7 to 10 dB SPL. Most ears showed SPOAE at many frequencies. In some ears, the peaks were superimposed on a broad baseline emission. The instantaneous frequency of any emission varied rapidly within its bandwidth limits and frequencies in the center of the band occurred most commonly, but not with higher levels than frequencies on the periphery of the band. SPOAE were temperature dependent, rising in frequency with an increase in temperature and falling with a decrease in temperature (rate of change from 54 to 107 Hz/degrees C), with no systematic changes in peak level except that at the temperature extremes, the SPOAE disappeared into the noise. External tones suppressed SPOAE peak level in a frequency-dependent way. Isosuppression tuning curves were V-shaped. In restricted frequency ranges, facilitation also occurred. External tones also caused shifts in the frequency of SPOAE; frequency "pushing" was more common than "pulling." The maximal frequency shift observed was 313 Hz. In general, the SPOAE characteristics strongly resemble those already reported in the bobtail lizard Tiliqua rugosa.