J Assoc Res Otolaryngol
August 2024
Across the wide range of land vertebrate species, spontaneous otoacoustic emissions (SOAE) are common, but not always found. The reasons for the differences between species of the various groups in their emission patterns are often not well understood, particularly within mammals. This review examines the question as to what determines in mammals whether SOAE are emitted or not, and suggests that the coupling between hair-cell regions diminishes when the space constant of frequency distribution becomes larger.
View Article and Find Full Text PDFAfrican mole-rats display highly derived hearing that is characterized by low sensitivity and a narrow auditory range restricted to low frequencies < 10 kHz. Recently, it has been suggested that two species of these rodents do not exhibit distortion product otoacoustic emissions (DPOAE), which was interpreted as evidence for a lack of cochlear amplification. If true, this would make them unique among mammals.
View Article and Find Full Text PDFOtoacoustic emissions (OAE) that were sound-induced, current-induced, or spontaneous have been measured in non-mammalian land vertebrates, including in amphibians, reptiles, and birds. There are no forms of emissions known from mammals that have not also been observed in non-mammals. In each group and species, the emission frequencies clearly lie in the range known to be processed by the hair cells of the respective hearing organs.
View Article and Find Full Text PDFThe erroneous idea that mammalian three-ossicle middle ears are superior to single-ossicle ones has influenced thinking about prostheses. Evolutionary facts and measurements indicate that single-ossicle ears are equivalent and more flexible, supporting - in spite of new technological reconstruction techniques - their continued use as prostheses.
View Article and Find Full Text PDFAs they are generally small and only hear low frequencies, lizards have few cues for localizing sound. However, their ears show extreme directionality (up to 30 dB direction-dependent difference in eardrum vibrations) created by strong acoustical coupling of the eardrums, with almost perfect internal transmission from the contralateral ear over a broad frequency range. The activity of auditory nerve fibers reflects the eardrum directionality, so all auditory neurons are directional by default.
View Article and Find Full Text PDFLizard auditory papillae have proven to be an attractive object for modelling the production of spontaneous otoacoustic emissions (SOAE). Here we use an established model (Vilfan and Duke, 2008) and extend it by exploring the effect of varying the number of oscillating elements, the strength of the parameters that describe the coupling between oscillators, the strength of the oscillators, and additive noise. The most remarkable result is that the actual number of oscillating elements hardly influences the spectral pattern, explaining why spectra from very different papillar dimensions are similar.
View Article and Find Full Text PDFSpontaneous otoacoustic emissions (SOAEs) have been observed in a variety of different vertebrates, including humans and barn owls (Tyto alba). The underlying mechanisms producing the SOAEs and the meaning of their characteristics regarding the frequency selectivity of an individual and species are, however, still under debate. In the present study, we measured SOAE spectra in lightly anesthetized barn owls and suppressed their amplitudes by presenting pure tones at different frequencies and sound levels.
View Article and Find Full Text PDFThis review summarizes paleontological data as well as studies on the morphology, function, and molecular evolution of the cochlea of living mammals (monotremes, marsupials, and placentals). The most parsimonious scenario is an early evolution of the characteristic organ of Corti, with inner and outer hair cells and nascent electromotility. Most remaining unique features, such as loss of the lagenar macula, coiling of the cochlea, and bony laminae supporting the basilar membrane, arose later, after the separation of the monotreme lineage, but before marsupial and placental mammals diverged.
View Article and Find Full Text PDFJ Comp Physiol A Neuroethol Sens Neural Behav Physiol
October 2018
In the 1940s, Georg von Békésy discovered that in the inner ear of cadavers of various vertebrates, structures responded to sound with a displacement wave that travels in a basal-to-apical direction. This historical review examines this concept and sketches its rôle and significance in the development of the research field of cochlear mechanics. It also illustrates that this concept and that of tonotopicity necessarily correlate, in that travelling waves are consequences of the existence of an ordered, longitudinal array of receptor cells tuned to systematically changing frequencies along the auditory organ.
View Article and Find Full Text PDFSOAE from the last major lizard family not yet systematically investigated, the teiids, were collected from the genera Callopistes, Tupinambis and Cnemidophorus. Although their papillae show characteristics of the family Teiidae, the papillae differ both in their size and in the arrangement of uni- and bi-directional hair-cell areas. Among these three genera, Callopistes showed few (2 or 3) SOAE peaks, whereas the other two genera showed more (up to 6 per ear).
View Article and Find Full Text PDFThe hearing organs of amniote vertebrates show large differences in their size and structure between the species' groups. In spite of this, their performance in terms of hearing sensitivity and the frequency selectivity of auditory-nerve units shows unexpectedly small differences. The only substantial difference is that therian, defined as live-bearing, mammalian groups are able to hear ultrasonic frequencies (above 15-20 kHz), whereas in contrast monotreme (egg laying) mammals and all non-mammalian amniotes cannot.
View Article and Find Full Text PDFJ Assoc Res Otolaryngol
February 2017
Comparative auditory studies make it possible both to understand the origins of modern ears and the factors underlying the similarities and differences in their performance. After all lineages of land vertebrates had independently evolved tympanic middle ears in the early Mesozoic era, the subsequent tens of millions of years led to the hearing organ of lizards, birds, and mammals becoming larger and their upper frequency limits higher. In extant species, lizard papillae remained relatively small (<2 mm), but avian papillae attained a maximum length of 11 mm, with the highest frequencies in both groups near 12 kHz.
View Article and Find Full Text PDFFrequency selectivity is a key functional property of the inner ear and since hearing research began, the frequency resolution of the human ear has been a central question. In contrast to animal studies, which permit invasive recording of neural activity, human studies must rely on indirect methods to determine hearing selectivity. Psychophysical studies, which used masking of a tone by other sounds, indicate a modest frequency selectivity in humans.
View Article and Find Full Text PDFJ Comp Physiol A Neuroethol Sens Neural Behav Physiol
October 2015
Experienced homing pigeons with extirpated cochleae and lagenae were released from six sites in upstate New York and western Pennsylvania on 17 days between 1973 and 1975 by William T. Keeton and his co-workers at Cornell University. The previously unpublished data indicate that departure directions of the operated birds were significantly different from those of sham-operated control birds (314 total), indicating that aural cues play an important part in the pigeon's navigational system.
View Article and Find Full Text PDFOtoacoustic emissions (OAEs) are faint sounds generated by healthy inner ears that provide a window into the study of auditory mechanics. All vertebrate classes exhibit OAEs to varying degrees, yet the biophysical origins are still not well understood. Here, we analyzed both spontaneous (SOAE) and stimulus-frequency (SFOAE) otoacoustic emissions from a bird (barn owl, Tyto alba) and a lizard (green anole, Anolis carolinensis).
View Article and Find Full Text PDFThe classical mammalian auditory periphery, i.e., the type of middle ear and coiled cochlea seen in modern therian mammals, did not arise as one unit and did not arise in all mammals.
View Article and Find Full Text PDFJ Assoc Res Otolaryngol
June 2013
Small changes of air pressure outside the eardrum of five lizard species led to changes in frequency, level, and peak width of spontaneous otoacoustic emissions (SOAE). In contrast to humans, these changes generally occurred at very small pressures (<20 mbar). As in humans, SOAE amplitudes were generally reduced.
View Article and Find Full Text PDFSpontaneous otoacoustic emissions (SOAEs) and stimulus frequency otoacoustic emissions (SFOAEs) have been described from lizard ears. Although there are several models for these systems, none has modeled the characteristics of both of these types of otoacoustic emissions based upon their being derived from hair cells as active oscillators. Data from the ears of two lizard species, one lacking a tectorial membrane and one with a chain of tectorial sallets, as described by Bergevin et al.
View Article and Find Full Text PDFEvolution of the cochlea and high-frequency hearing (>20 kHz; ultrasonic to humans) in mammals has been a subject of research for many years. Recent advances in paleontological techniques, especially the use of micro-CT scans, now provide important new insights that are here reviewed. True mammals arose more than 200 million years (Ma) ago.
View Article and Find Full Text PDFGeorg von Békésy was one of the first comparative auditory researchers. He not only studied basilar membrane (BM) movements in a range of mammals of widely different sizes, he also worked on the chicken basilar papilla and the frog middle ear. We show that, in mammals, at least, his data do not differ from those that could be collected using modern techniques but with the same, very loud sounds.
View Article and Find Full Text PDFAnn Otol Rhinol Laryngol
October 2010
We describe exceptional high-frequency hearing and vocalizations in a genus of pygopod lizards (Delma) that is endemic to Australia. Pygopods are a legless subfamily of geckos and share their highly specialized hearing organ. Hearing and vocalizations of amniote vertebrates were previously thought to differ clearly in their frequency ranges according to their systematic grouping.
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