Coherent reflection without traveling waves: On the origin of long-latency otoacoustic emissions in lizards

Abstract

Lizard ears produce otoacoustic emissions with characteristics often strikingly reminiscent of those measured in mammals. The similarity of their emissions is surprising, given that lizards and mammals manifest major differences in aspects of inner ear morphology and function believed to be relevant to emission generation. For example, lizards such as the gecko evidently lack traveling waves along their basilar membrane. Despite the absence of traveling waves, the phase-gradient delays of gecko stimulus-frequency otoacoustic emissions ͑SFOAEs͒ are comparable to those measured in many mammals. This paper describes a model of emission generation inspired by the gecko inner ear. The model consists of an array of coupled harmonic oscillators whose effective damping manifests a small degree of irregularity. Model delays increase with the assumed sharpness of tuning, reflecting the build-up time associated with mechanical resonance. When tuning bandwidths are chosen to match those of gecko auditory-nerve fibers, the model reproduces the major features of gecko SFOAEs, including their spectral structure and the magnitude and frequency dependence of their phase-gradient delays. The same model with appropriately modified parameters reproduces the features of SFOAEs in alligator lizards. Analysis of the model demonstrates that the basic mechanisms operating in the model are similar to those of the coherent-reflection model developed to describe mammalian emissions. These results support the notion that SFOAE delays provide a noninvasive measure of the sharpness of cochlear tuning.

Using Stimulus Frequency Emissions to Characterize Cochlear Function in Mice

“…Preliminary data are provided for wildtype and prestin V499G/Y501H KI mice (referred to here simply as 499) expressing a mutant prestin and showing reduced sensitivity [8]. The SFOAE data from 499 KI mice show loss of sensitivity and no frequency selectivity consistent with previous reports using [2,7], this approach allows us to study the BM-OHC-TM system in young mutant mice and their controls.…”

Comparison of Otoacoustic Emissions Within Gecko Subfamilies: Morphological Implications for Auditory Function in Lizards

“…Thirdly, the extension towards higher frequencies appears consistent with a comparison of tympanic membrane velocity response curves in phylogentically matched gecko pairs (Werner et al 2002). Fourthly, SOAEs and low-level SFOAEs rapidly fall off towards the noise floor above the highest ANF characteristic frequencies in Gekko (Manley et al 1996;Bergevin and Shera 2010). Fifthly, SOAE suppression characteristics and SFOAE delays have been shown to correlate well to ANF tuning (Köppl and Manley 1994;Manley et al 1996;Bergevin and Shera 2010).…”

“…Fourthly, SOAEs and low-level SFOAEs rapidly fall off towards the noise floor above the highest ANF characteristic frequencies in Gekko (Manley et al 1996;Bergevin and Shera 2010). Fifthly, SOAE suppression characteristics and SFOAE delays have been shown to correlate well to ANF tuning (Köppl and Manley 1994;Manley et al 1996;Bergevin and Shera 2010). Lastly, ABR audiograms for Anolis carolinensis extend out to higher frequencies relative to Gekko (Brittain-Powell et al 2010), consistent with OAE magnitudes (Manley and Gallo 1997;Bergevin et al 2010b).…”

“…Additionally, a recent report indicated that the gecko family Pygopodidae has exceptional high-frequency sensitivity (Manley and Kraus 2010), apparently correlated to the frequency content of their vocalizations (Weber and Werner 1977). Lastly, theoretical models for OAE generation in gecko have been described (Bergevin and Shera 2010;Gelfand et al 2010). Taken together, geckos thus make an ideal group for a systematic study of how morphological features relate to OAE generation.…”

The Effects of Air Pressure on Spontaneous Otoacoustic Emissions of Lizards

“…On the other hand, Bergevin and Shera (2010) showed that a mechanical model of the lizard inner ear, which does not exhibit travelling waves, can model stimulus frequency otoacoustic emissions (SFOAE) in lizards. A further analysis of the model showed that it operates similar to a coherent reflection model of the cochlea.…”