Effects of Frequency on the Directional Auditory Sensitivity of Northern Saw-Whet Owls (Aegolius acadicus)

Many animals use sound as a medium for detecting or locating potential prey items or predation threats. Northern saw-whet owls (<i>Aegolius acadicus</i>) are particularly interesting in this regard, as they primarily rely on sound for hunting in darkness, but are also subject to predation pressure from larger raptors. We hypothesized that these opposing tasks should favor sensitivity to low-frequency sounds arriving from many locations (potential predators) and high-frequency sounds below the animal (ground-dwelling prey items). Furthermore, based on the morphology of the saw-whet owl skull and the head-related transfer functions of related species, we expected that the magnitude of changes in sensitivity across spatial locations would be greater for higher frequencies than low frequencies (i.e., more “directional” at high frequencies). We used auditory-evoked potentials to investigate the frequency-specific directional sensitivity of Northern saw-whet owls to acoustic signals. We found some support for our hypothesis, with smaller-magnitude changes in sensitivity across spatial locations at lower frequencies and larger-magnitude changes at higher frequencies. In general, owls were most sensitive to sounds originating in front of and above their heads, but at 8 kHz there was also an area of high sensitivity below the animals. Our results suggest that the directional hearing of saw-whet owls should allow for both predator and prey detection.

Can I trust my ears in VR? Head-related transfer functions and valuation methods with descriptive attributes in virtual reality

In this article, we present the current state of the art in binaural audio with the focus on head-related transfer functions (HRTFs) and valuation methods of virtual acoustics with descriptive attributes. This combination provides a methodology, which delivers the basis for research studies in virtual reality (VR) on individual and non-individual head-related transfer functions. Based on the largely explored localization perception of static audio signals, this review offers an overview of the directional hearing during head and sound source movement and multimodality in audiovisual virtual environments. Perceptual quality characteristics provide evaluation methods from which future HRTF VR experiments and virtual environments studies on binaural acoustics could benefit.

Bone conduction pathways confer directional cues to salamanders

Sound and vibration are generated by mechanical disturbances within the environment, and the ability to detect and localize these acoustic cues is generally important for survival, as suggested by the early emergence of inherently directional otolithic ears in vertebrate evolutionary history. However, fossil evidence indicates that the water-adapted ear of early terrestrial tetrapods lacked specialized peripheral structures to transduce sound pressure (e.g., tympana). Early terrestrial hearing therefore should have required nontympanic (or extratympanic) mechanisms for sound detection and localization. Here we used atympanate salamanders to investigate the efficacy of extratympanic pathways to support directional hearing in air. We assessed peripheral encoding of directional acoustic information using directionally-masked auditory brainstem response recordings. We used laser Doppler vibrometry to measure the velocity of sound pressure-induced head vibrations as a key extratympanic mechanism for aerial sound reception in atympanate species. We found that sound generates head vibrations that vary with the angle of the incident sound. This extratympanic pathway for hearing supports a figure-eight pattern of directional auditory sensitivity to airborne sound in the absence of a pressure-transducing tympanic ear.

The ultrasound guide: katydid ear pinnae code for bat call detection

Early predator detection is a key component of the predator-prey arms race, and has driven the evolution of multiple animal hearing systems. Katydids (Insecta) have a sophisticated ear consisting of paired tympana on each foreleg that receive sound externally and internally, creating a pressure-time difference receiver system capable of sensitive and accurate directional hearing, despite the small size of katydids. Some katydid species have pinnae of unknown function, which form cavities around the outer tympanal surfaces and have been hypothesised to influence the external sound paths. Combining experimental biophysics and numerical modelling on 3D ear geometries, we investigated pinna function in the katydid Copiphora gorgonensis. Pinnae induced large sound-pressure gains that enhanced sound detection at high ultrasonic frequencies (>60 kHz), matching the echolocation range of their nocturnal insectivorous bat predators. Comparing pinna resonances of sympatric katydid species supported these findings, and suggests that pinnae may have evolved for enhanced predator detection.

Cues for Directional Hearing in the Fly Ormia ochracea

Insects are often small relative to the wavelengths of sounds they need to localize, which presents a fundamental biophysical problem. Understanding novel solutions to this limitation can provide insights for biomimetic technologies. Such an approach has been successful using the fly Ormia ochracea (Diptera: Tachinidae) as a model. O. ochracea is a parasitoid species whose larvae develop as internal parasites within crickets (Gryllidae). In nature, female flies find singing male crickets by phonotaxis, despite severe constraints on directional hearing due to their small size. A physical coupling between the two tympanal membranes allows the flies to obtain information about sound source direction with high accuracy because it generates interaural time-differences (ITD) and interaural level differences (ILD) in tympanal vibrations that are exaggerated relative to the small arrival-time difference at the two ears, that is the only cue available in the sound stimulus. In this study, I demonstrate that pure time-differences in the neural responses to sound stimuli are sufficient for auditory directionality in O. ochracea.

Bonebridge – an active direct bone conduction hearing device in rehabilitation of single sided deafness Czech version

Overview Introduction: Bonebridge is a direct bone conduction hearing implantable system. The aim of the work is to present pilot results of rehabilitation of single sided deafness using this system. Material and methods: Analysis of three patients with single-sideded deafness, who underwent BB implantation in 2018 at the Department of Otorhinolaryngology and Head and Neck Surgery of St. Anna Hospital in Brno. Evaluation parameters: Bern Benefi t in Single-Sided Deafness Questionnaire, experimental examination of directional hearing and hearing in noise test. Results: Questionnaire: Within the visual analog scale in the range of –5 to +5 points, the average rating was + 2.4 points, so listening was rated as easier with Bonebridge than without hearing aids. The ability to locate the sound source was evaluated by 4 and 0–1 points in one and two respondents, respectively. Examination of spatial hearing: without hearing aid, the ability to locate the sound source was signifi cantly impaired in all the examined. With Bonebridge, with a tolerated deviation of 45°, the success rate of sound source localization was 75–100% in the range of 0–360° in the horizontal plane. Hearing in noise test: the greatest improvement in intelligibility (by 30–100%) was achieved with Bonebridge at SNR –5 dB. Conclusion: Bonebridge is not able to restore binaural hearing in patients with single sided deafness, it is a pseudo-binaural correction. Like other implantable bone conduction systems, Bonebridge is benefi tial for patients with single sided deafness in a variety of listening situations. Using experimental audiological tests, the contribution of Bonebridge to understanding sentences in acoustic noise and improving the ability to locate the sound source was found. However, validation of the results would require a larger number of probands. Keywords: single-sided deafness – BAHD – Bonebridge – bone conduction hearing implant – hearing in noise – directional hearing test

Evaluation of hearing preservation in adults with a slim perimodiolar electrode

Purpose Numerous endeavors have been undertaken to preserve hearing in cochlear implant (CI) patients. Particularly, optimization of electrode array design aims at preservation of residual hearing (RH). This study examines whether a slim perimodiolar (PM) electrode array could bear the capability to preserve hearing. Methods A total of 47 patients underwent cochlear implantation receiving the PM electrode. (i) Patients with pure tone audiogram (PTA) thresholds better than 85 dB and/or hearing loss for Freiburg speech test numbers less than 60 dB and more than 50% maximum monosyllabic understanding were assigned to the RH group (n = 17), while all others belonged to the noRH group (n = 30). (ii) Another group implanted with a slim straight, lateral wall (LW) electrode was recruited for comparison. Results We compared 17 RH–30 noRH patients all receiving the PM electrode. RH in PM recipients decreased faster than in LW recipients. No significant differences were observed between both (RH v/s noRH) groups in NRT thresholds, Freiburg speech test and A§E® phonemes. Analogous satisfaction levels were indicated through the questionnaires in terms of sound quality, hearing in silence, noise and directional hearing in both groups. Conclusions The results suggest that hearing preservation is influenced not only by electrode shape but various factors. This study opens an avenue for further investigations to elucidate and enumerate the causes for progressive hearing loss.

A narrow ear canal reduces sound velocity to create additional acoustic inputs in a microscale insect ear

Located in the forelegs, katydid ears are unique among arthropods in having outer, middle, and inner components, analogous to the mammalian ear. Unlike mammals, sound is received externally via two tympanic membranes in each ear and internally via a narrow ear canal (EC) derived from the respiratory tracheal system. Inside the EC, sound travels slower than in free air, causing temporal and pressure differences between external and internal inputs. The delay was suspected to arise as a consequence of the narrowing EC geometry. If true, a reduction in sound velocity should persist independently of the gas composition in the EC (e.g., air, CO2). Integrating laser Doppler vibrometry, microcomputed tomography, and numerical analysis on precise three-dimensional geometries of each experimental animal EC, we demonstrate that the narrowing radius of the EC is the main factor reducing sound velocity. Both experimental and numerical data also show that sound velocity is reduced further when excess CO2 fills the EC. Likewise, the EC bifurcates at the tympanal level (one branch for each tympanic membrane), creating two additional narrow internal sound paths and imposing different sound velocities for each tympanic membrane. Therefore, external and internal inputs total to four sound paths for each ear (only one for the human ear). Research paths and implication of findings in avian directional hearing are discussed.

Lung-to-ear sound transmission does not improve directional hearing in green treefrogs (Hyla cinerea)

ABSTRACTAmphibians are unique among extant vertebrates in having middle ear cavities that are internally coupled to each other and to the lungs. In frogs, the lung-to-ear sound transmission pathway can influence the tympanum's inherent directionality, but what role such effects might play in directional hearing remains unclear. In this study of the American green treefrog (Hyla cinerea), we tested the hypothesis that the lung-to-ear sound transmission pathway functions to improve directional hearing, particularly in the context of intraspecific sexual communication. Using laser vibrometry, we measured the tympanum's vibration amplitude in females in response to a frequency modulated sweep presented from 12 sound incidence angles in azimuth. Tympanum directionality was determined across three states of lung inflation (inflated, deflated, reinflated) both for a single tympanum in the form of the vibration amplitude difference (VAD) and for binaural comparisons in the form of the interaural vibration amplitude difference (IVAD). The state of lung inflation had negligible effects (typically less than 0.5 dB) on both VADs and IVADs at frequencies emphasized in the advertisement calls produced by conspecific males (834 and 2730 Hz). Directionality at the peak resonance frequency of the lungs (1558 Hz) was improved by ∼3 dB for a single tympanum when the lungs were inflated versus deflated, but IVADs were not impacted by the state of lung inflation. Based on these results, we reject the hypothesis that the lung-to-ear sound transmission pathway functions to improve directional hearing in frogs.