Envelope-following response and modulation transfer function in the dolphin's auditory system

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.

Section: Discussionsupporting

confidence: 81%

Section: Auditory Steady-state Responses (Assrs) To Modulated Tonesmentioning

confidence: 99%

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

Schrode

Bee

2015

“…The MRTFs measured in pygmy killer whales were similar in shape to those MRTFs observed in other odontocetes such as the bottlenose dolphin (Dolphin et al, 1995;Supin and Popov, 1995), beluga whale (Dolphin et al, 1995;Klishin et al, 2000), killer whale (Szymanski et al, 1998), beaked whale (Cook et al, 2006), Risso's dolphin (Grampus griseus) (Mooney et al, 2006) and white-beaked dolphin (Lagenorhynchus albirostris) (Mooney et al, 2009). In the pygmy killer whales MML0802 and MML0803, the MRTF showed maximum peaks at modulation frequencies of 500 and 1000Hz ( Fig.3; supplementary material Fig.S3).…”

Section: Modulation Rate Transfer Functionmentioning

confidence: 71%

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

Montie

Manire

Mann

2011

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

“…A 16 ms portion of the response was fast-Fourier transformed (FFT; 256 points) and viewed in the frequency spectrum. The magnitude of the EFR was reflected by a peak in the FFT at the 1 kHz modulation rate (Supin and Popov, 1995). Sound levels were then decreased in steps of 5-10 dB until responses (EFRs and FFT peaks) were no longer visually detectable for two to three trials.…”

Section: Calibrations and Data Analysismentioning

confidence: 99%

Hearing pathways in the Yangtze finless porpoise,Neophocaena asiaeorientalis asiaeorientalis

Mooney

Ketten

et al. 2013

How an animal receives sound may influence its use of sound. While 'jaw hearing' is well supported for odontocetes, work examining how sound is received across the head has been limited to a few representative species. The substantial variation in jaw and head morphology among odontocetes suggests variation in sound reception. Here, we address how a divergent subspecies, the Yangtze finless porpoise (Neophocaena asiaeorientalis asiaeorientalis) hears low-, mid-and high-frequency tones, as well as broadband clicks, comparing sounds presented at different locations across the head. Hearing was measured using auditory evoked potentials (AEPs). Click and tone stimuli (8, 54 and 120 kHz) were presented at nine locations on the head and body using a suctioncup transducer. Threshold differences were compared between frequencies and locations, and referenced to the underlying anatomy using computed tomography (CT) imaging of deceased animals of the same subspecies. The best hearing locations with minimum thresholds were found adjacent to a mandibular fat pad and overlaying the auditory bulla. Mean thresholds were not substantially different at locations from the rostrum tip to the ear (11.6 dB). This contrasts with tests with bottlenose dolphins and beluga whales, in which 30-40 dB threshold differences were found across the animals' heads. Response latencies increased with decreasing response amplitudes, which suggests that latency and sensitivity are interrelated when considering sound reception across the odontocete head. The results suggest that there are differences among odontocetes in the anatomy related to receiving sound, and porpoises may have relatively less acoustic 'shadowing'.