Modulation rate transfer functions to low-frequency carriers in three species of cetaceans

SUMMARYIn June 2008, two pygmy killer whales (Feresa attenuata) were stranded alive near Boca Grande, FL, USA, and were taken into rehabilitation. We used this opportunity to learn about the peripheral anatomy of the auditory system and hearing sensitivity of these rare toothed whales. Three-dimensional (3-D) reconstructions of head structures from X-ray computed tomography (CT) images revealed mandibles that were hollow, lacked a bony lamina medial to the pan bone and contained mandibular fat bodies that extended caudally and abutted the tympanoperiotic complex. Using auditory evoked potential (AEP) procedures, the modulation rate transfer function was determined. Maximum evoked potential responses occurred at modulation frequencies of 500 and 1000Hz. The AEP-derived audiograms were U-shaped. The lowest hearing thresholds occurred between 20 and 60kHz, with the best hearing sensitivity at 40kHz. The auditory brainstem response (ABR) was composed of seven waves and resembled the ABR of the bottlenose and common dolphins. By changing electrode locations, creating 3-D reconstructions of the brain from CT images and measuring the amplitude of the ABR waves, we provided evidence that the neuroanatomical sources of ABR waves I, IV and VI were the auditory nerve, inferior colliculus and the medial geniculate body, respectively. The combination of AEP testing and CT imaging provided a new synthesis of methods for studying the auditory system of cetaceans. Supplementary material available online at

Section: Modulation Rate Transfer Functionsupporting

confidence: 72%

Live CT imaging of sound reception anatomy and hearing measurements in the pygmy killer whale, Feresa attenuata

Montie

Manire

Mann

2011

“…The carrier frequencies were modulated at a rate of 1000·Hz, with a modulation depth of 100%. This modulation rate was chosen based on ideal measurement modulation rates for similar odontocetes (Dolphin et al, 1995). A 30·ms break of no sound was alternated between the 20·ms stimulus presentations.…”

Section: Sounds Presented To the Animalmentioning

confidence: 99%

Hearing measurements from a stranded infant Risso's dolphin, Grampus griseus

Nachtigall

Yuen

Mooney

et al. 2005

SUMMARY An infant Risso's dolphin (Grampus griseus) was rescued from the beach in Southern Portugal, and an audiogram was measured using auditory evoked potentials (AEP) and envelope following response (EFR) techniques for frequencies from 4 to 150 kHz. The stimuli used were custom sinusoidally amplitude-modulated (SAM) tone-bursts, and the AEP responses were collected,averaged and analyzed to quantify the animal's physiological response and,thereby, hearing thresholds. The infant animal showed a wide range of best sensitivity, with the lowest threshold of 49.5 dB re. 1 μPa at 90 kHz. The audiogram showed a typical mammalian ∪-shape with a gradual, low-frequency slope of 16.4 dB octave-1 and a sharp high-frequency increase of 95 dB octave-1. When compared with an audiogram of an older Risso's dolphin obtained using behavioral methods, the threshold values at upper frequencies were much lower for this infant animal, and this infant heard higher frequencies. These results redefine the hearing capabilities of Risso's dolphins by demonstrating very high-frequency sensitivity.

“…Our results, therefore, support the hypothesis that the well-known adaptations of the frog peripheral auditory system for processing natural sounds in the spectral domain may also extend to processing in the temporal domain. It is potentially surprising that species-specific adaptations in temporal processing might arise in the periphery, because the peripheral auditory system is generally considered to function as a low-pass envelope filter (Carney, 1993;Dau et al, 1996;Dolphin et al, 1995;Frisina, 2001). However, adaptations of the peripheral auditory system for particular modulation rates have been identified in at least one previous study.…”

Section: Discussionmentioning

confidence: 99%

“…2). MRTFs typically have an overall low-pass shape consistent with phaselocking in the auditory nerve (Dolphin and Mountain, 1992;Dolphin et al, 1994Dolphin et al, , 1995Finneran et al, 2007;Gall et al, 2012). In the present study, we recorded ASSRs in response to tones of three different carrier frequencies modulated at AM rates between 12.5 Hz and 800 Hz (in one-octave steps).…”

Section: Introductionmentioning

confidence: 91%

Evolutionary adaptations for the temporal processing of natural sounds by the anuran peripheral auditory system

Schrode

Bee

2015

Sensory systems function most efficiently when processing natural stimuli, such as vocalizations, and it is thought that this reflects evolutionary adaptation. Among the best-described examples of evolutionary adaptation in the auditory system are the frequent matches between spectral tuning in both the peripheral and central auditory systems of anurans (frogs and toads) and the frequency spectra of conspecific calls. Tuning to the temporal properties of conspecific calls is less well established, and in anurans has so far been documented only in the central auditory system. Using auditoryevoked potentials, we asked whether there are species-specific or sex-specific adaptations of the auditory systems of gray treefrogs (Hyla chrysoscelis) and green treefrogs (H. cinerea) to the temporal modulations present in conspecific calls. Modulation rate transfer functions (MRTFs) constructed from auditory steady-state responses revealed that each species was more sensitive than the other to the modulation rates typical of conspecific advertisement calls. In addition, auditory brainstem responses (ABRs) to paired clicks indicated relatively better temporal resolution in green treefrogs, which could represent an adaptation to the faster modulation rates present in the calls of this species. MRTFs and recovery of ABRs to paired clicks were generally similar between the sexes, and we found no evidence that males were more sensitive than females to the temporal modulation patterns characteristic of the aggressive calls used in male-male competition. Together, our results suggest that efficient processing of the temporal properties of behaviorally relevant sounds begins at potentially very early stages of the anuran auditory system that include the periphery.