Representation of acoustic signals in the eighth nerve of the Tokay gecko: I. Pure tones

Sams-Dodd, Frank; Capranica, Robert R.

doi:10.1016/0378-5955(94)90083-3

Cited by 25 publications

(13 citation statements)

References 37 publications

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“…Additionally, there is little difference apparent below~1.2 kHz, except for Hemidactylus, which maintains relatively high N SFOAE values. The upward N SFOAE trends in Figure 4 indicate that the delay (in number of stimulus cycles) increases with frequency, similarly to ANF tuning estimates Sams-Dodd and Capranica 1994;Manley et al 1999).…”

Section: Resultsmentioning

confidence: 67%

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

Bergevin

2010

JARO

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Otoacoustic emissions (OAEs) are sounds emitted by the ear and provide a non-invasive probe into mechanisms underlying peripheral auditory transduction. This study focuses upon a comparison of emission properties in two phylogenetically similar pairs of gecko: Gekko gecko and Hemidactylus turcicus and Eublepharis macularius and Coleonyx variegatus. Each pair consists of two closely related species within the same subfamily, with quantitatively known morphological properties at the level of the auditory sensory organ (basilar papilla) in the inner ear. Essentially, the comparison boils down to an issue of size: how does overall body size, as well as the innerear dimensions (e.g., papilla length and number of hair cells), affect peripheral auditory function as inferred from OAEs? Estimates of frequency selectivity derived from stimulus-frequency emissions (emissions evoked by a single low-level tone) indicate that tuning is broader in the species with fewer hair cells/shorter papilla. Furthermore, emissions extend outwards to higher frequencies (for similar body temperatures) in the species with the smaller body size/narrower interaural spacing. This observation suggests the smaller species have relatively improved high-frequency sensitivity, possibly related to vocalizations and/or aiding azimuthal sound localization. For one species (Eublepharis), emissions were also examined in both juveniles and adults. Qualitatively similar emission properties in both suggests that inner-ear function is adult like soon after hatching and that external body size (e.g., middle-ear dimensions and interaural spacing) has a relatively small impact upon emission properties within a species.

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Section: Resultsmentioning

confidence: 67%

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

Bergevin

2010

JARO

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“…Symbols show individual gecko nerve data points. Triangles show data from Sams- Dodd and Capranica (1994). B-D: responses from a low best frequency auditory nerve fiber to ipsilateral stimulation, 600 Hz, 70 dB.…”

Section: Auditory Nerve Encodes the Phase Of The Auditory Stimulusmentioning

confidence: 98%

Binaural processing by the gecko auditory periphery

Christensen‐Dalsgaard

Tang

Carr

2011

Journal of Neurophysiology

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Lizards have highly directional ears, owing to strong acoustical coupling of the eardrums and almost perfect sound transmission from the contralateral ear. To investigate the neural processing of this remarkable tympanic directionality, we combined biophysical measurements of eardrum motion in the Tokay gecko with neurophysiological recordings from the auditory nerve. Laser vibrometry shows that their ear is a two-input system with approximately unity interaural transmission gain at the peak frequency (∼ 1.6 kHz). Median interaural delays are 260 μs, almost three times larger than predicted from gecko head size, suggesting interaural transmission may be boosted by resonances in the large, open mouth cavity (Vossen et al. 2010). Auditory nerve recordings are sensitive to both interaural time differences (ITD) and interaural level differences (ILD), reflecting the acoustical interactions of direct and indirect sound components at the eardrum. Best ITD and click delays match interaural transmission delays, with a range of 200-500 μs. Inserting a mold in the mouth cavity blocks ITD and ILD sensitivity. Thus the neural response accurately reflects tympanic directionality, and most neurons in the auditory pathway should be directional.

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“…Whereas the low-frequency portion of the papilla is covered by a continuous tectorial membrane, the hair cells sensitive to frequencies above ϳ1 kHz are covered by discrete sections of tectorium ͑sallets͒, which couple small groups of hair cells together into a single radial row ͑Wever, 1978͒. Although gecko ears apparently lack analogs of BM traveling waves ͑Manley et al, 1999͒, they produce robust otoacoustic emissions ͑Manley et al, 1996;Bergevin et al, 2008͒ and have auditory-nerve fiber ͑ANF͒ responses with thresholds and frequency tuning comparable to many mammals ͑Eatock et al, 1981;Sams-Dodd and Capranica, 1994;Manley et al, 1999͒. Since our purpose here is to explore the origin of longlatency OAEs in a mechanical system without basilarmembrane traveling waves, we simplify the analysis by boiling the many exquisite details of gecko functional anatomy down to a few idealized mechanical elements. Taken together, these elements provide perhaps the simplest realization of a mechanically tuned inner ear.…”

Section: A Model Inspired By the Gecko Inner Earmentioning

confidence: 99%

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

Bergevin

Shera

2010

The Journal of the Acoustical Society of America

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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.

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Representation of acoustic signals in the eighth nerve of the Tokay gecko: I. Pure tones

Cited by 25 publications

References 37 publications

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

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

Binaural processing by the gecko auditory periphery

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

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