The vestigial pinna-orienting system in humans briefly suppresses superior auricular muscle activity during reflexive orienting toward auditory stimuli.

The vestigial pinna-orienting system in humans is capable of increasing the activity of several auricular muscles in response to lateralized transient auditory stimuli. For example, transient increases in electromyographic activity in the posterior auricular muscle (PAM) to an attention-capturing stimulus have been documented. For the current study, surface electromyograms (EMGs) were recorded from the PAMs and superior auricular muscles (SAMs) of 10 normal-hearing participants. During the experiments, lateralized transient auditory stimuli, such as a crying baby, a shattering vase, or the participant's first names, were presented. These transient stimuli were either presented in silence or when participants actively listened to a podcast. Although ipsilateral PAM activity increased in response to transient stimuli, the SAM displayed the opposite behavior, i.e., a brief, ipsilateral suppression of activity. This suppression of ipsilateral SAM activity was more frequent on the right (75%) than left side (35%), whereas an ipsilateral PAM increase was roughly equal in prevalence on the two sides (left: 90%, right: 95%). During the active listening task, SAM suppression on the right ear was significantly larger in response to ipsilateral stimuli, compared with contralateral ones (P = 0.002), whereas PAM activity increased significantly (P = 0.002). Overall, this study provides evidence of a systematic transient suppression of the SAM during exogenous attention. This could suggest a more complex system than previously assumed, as the presence of synchronized excitatory and inhibitory components in different auricular muscles points toward a coordinated attempt at reflexively orienting the pinna toward a sound.NEW & NOTEWORTHY This study provides evidence that two auricular muscles in humans, the posterior and superior auricular muscles (PAM, SAM), react fundamentally different to lateralized transient auditory stimuli, especially during active listening. Although the PAM reacts with a transient increase in ipsilateral activity, ongoing ipsilateral SAM activity is briefly suppressed at the same time. This indicates the presence of a more complex and nuanced pinna-orienting system, with synchronized excitatory and inhibitory components in humans, than previously suspected.

Effect of sound-induced vibrations of the pinna on head-related transfer functions: Experimental and numerical investigations.

Numerical simulations of head-related transfer functions (HRTFs) conventionally assume a rigid boundary condition for the pinna. The human pinna, however, is an elastic deformable body that can vibrate due to incident acoustic waves. This work investigates how sound-induced vibrations of the pinna can affect simulated HRTF magnitudes. The work will motivate the research question by measuring the sound-induced vibrational patterns of an artificial pinna with a high-speed holographic interferometric system. Then, finite element simulations are used to determine HRTFs for a tabletop model of the B&K 5128 head and torso simulator for a number of directions. Two scenarios are explored: one where the pinna is modeled as perfectly rigid, and another where the pinna is modeled as linear elastic with material properties close to that of auricular cartilage. The findings suggest that pinna vibrations have negligible effects on HRTF magnitudes up to 5 kHz. The same conclusion, albeit with less certainty, is drawn for higher frequencies. Finally, the importance of the elastic domain's material properties is emphasized and possible implications for validation studies on dummy heads 1as well as the limitations of the present work are discussed in detail.

Variability in the rigid pinna motions of hipposiderid bats and their impact on sensory information encoding.

Many bat species, e.g., in the rhinolophid and hipposiderid families, have dynamic biosonar systems with highly mobile pinnae. Pinna motion patterns have been shown to fall into two distinct categories: rigid rotations and non-rigid motions (i.e., deformations). In the present work, two questions regarding the rigid rotations have been investigated: (i) what is the nature of the variability (e.g., discrete subgroups or continuous variation) within the rigid motions, (ii) what is its acoustic impact? To investigate the first question, rigid pinna motions in Pratt's leaf-nosed bats (Hipposideros pratti) have been tracked with stereo vision and a dense set of landmark points on the pinna surface. Axis-angle representations of the recorded rigid motions have shown a continuous variation in the rotation axes that covered a range of almost 180° in azimuth and elevation. To investigate the second question, the observed range of rigid pinna motions has been reproduced with a biomimetic pinna. Normalized mutual information between acoustic inputs associated with every pair of the rigid pinna motions showed that even small changes in the rotation axis resulted in more than 50% new sensory information encoding capacity (i.e., normalized mutual information less than 50%). This demonstrates a potential sensory benefit to the observed variability in the rigid pinna rotations.

The blastema and epimorphic regeneration in mammals.

Studying regeneration in animals where and when it occurs is inherently interesting and a challenging research topic within developmental biology. Historically, vertebrate regeneration has been investigated in animals that display enhanced regenerative abilities and we have learned much from studying organ regeneration in amphibians and fish. From an applied perspective, while regeneration biologists will undoubtedly continue to study poikilothermic animals (i.e., amphibians and fish), studies focused on homeotherms (i.e., mammals and birds) are also necessary to advance regeneration biology. Emerging mammalian models of epimorphic regeneration are poised to help link regenerative biology and regenerative medicine. The regenerating rodent digit tip, which parallels human fingertip regeneration, and the regeneration of large circular defects through the ear pinna in spiny mice and rabbits, provide tractable, experimental systems where complex tissue structures are regrown through blastema formation and morphogenesis. Using these models as examples, we detail similarities and differences between the mammalian blastema and its classical counterpart to arrive at a broad working definition of a vertebrate regeneration blastema. This comparison leads us to conclude that regenerative failure is not related to the availability of regeneration-competent progenitor cells, but is most likely a function of the cellular response to the microenvironment that forms following traumatic injury. Recent studies demonstrating that targeted modification of this microenvironment can restrict or enhance regenerative capabilities in mammals helps provide a roadmap for eventually pushing the limits of human regeneration.

Thermal effects of mobile phones on human auricle region.

Mobile phones have become an indispensable utility to modern society, with international use increasing dramatically each year. The GSM signal operates at 900 MHz, 1800 MHz and 2250 MHz, may potentially cause harm to human tissue. Yet there is no in silico model to aid design these devices to protect from causing potential thermal effect. Here we present a model of sources of heating in a mobile phone device with experimental verification during the phone call. We have developed this mobile phone thermal model using first principles on COMSOL® Multiphysics modelling platform to simulate heating effect in human auricle region due to mobile phone use. In particular, our model considered both radiative and non-radiative heating from components such as the lithium ion battery, CPU circuitry and the antenna. The model showed the distribution and effect of the heating effect due to mobile phone use and considered impact of battery discharge rate, battery capacity, battery cathode material, biological tissue distance, antenna radio-wave frequency and intensity. Furthermore, the lithium ion battery heating was validated during experiments using temperature sensors with an excellent agreement between simulated and experimental data (<1% variation). Mobile phone heating during a typical call has also been simulated and compared with experimental infrared thermographic imaging. Importantly, we found that 1800 MHz frequency of data transmission showed the highest temperature increase in the fat/water phantom used in this simulation. We also successfully compared heating distribution in human auricle region during mobile phone use with clinical thermographic images with reasonable qualitative and quantitative agreements. In summary, our model provides a foundation to conceive thermal and other physical effects caused by mobile phone use and allow for the understanding of potential negative health effects thus supporting and promoting personalized and preventive medicine using thermography.

Externalization of remote microphone signals using a structural binaural model of the head and pinna.

In a remote microphone (RM) system, a talker speaks into a microphone and the signal is transmitted to the hearing aids worn by the hearing-impaired listener. A difficulty with remote microphones, however, is that the signal received at the hearing aid bypasses the head and pinna, so the acoustic cues needed to externalize the sound source are missing. The objective of this paper is to process the RM signal to improve externalization when listening through earphones. The processing is based on a structural binaural model, which uses a cascade of processing modules to simulate the interaural level difference, interaural time difference, pinna reflections, ear-canal resonance, and early room reflections. The externalization results for the structural binaural model are compared to a left-right signal blend, the listener's own anechoic head-related impulse response (HRIR), and the listener's own HRIR with room reverberation. The azimuth is varied from straight ahead to 90° to one side. The results show that the structural binaural model is as effective as the listener's own HRIR plus reverberation in producing an externalized acoustic image, and that there is no significant difference in externalization between hearing-impaired and normal-hearing listeners.

[Impact of microphone position on sound localization in cochlear implant users]. / Einfluss der Mikrofonposition auf die akustische Lokalisation bei Cochlea-Implantat-Nutzern.

OBJECTIVE: The delivery of directional cues of a hearing device microphone are highly dependent on the position of the microphones. The aim of this work was the evaluation of different microphone positions with regard to the transmission of interaural time and level differences as well as the spectral characteristics and its impact on the localization abilities. METHODS: Head-related transfer functions of 30 subjects were measured with three different omnidirectional microphones at different positions: in the pinna (ITP), behind the ear (BTE), at the entrance of the ear canal (EEC). Sound localization abilities of 12 bilateral CI users was assessed for the microphone positions ITP and BTE. RESULTS: Only the microphone positions in the ear (ITP, EEC) could sample the spectral cues of the pinna. However, the positioning of the microphone inside of the pinna did not significantly improve sound localization abilities compared to BTE microphones. For sound incidence from rear significantly less front-back confusions were achieved with the microphone inside of the pinna. CONCLUSION: The microphone position in the pinna showed only a slight improvement in sound localization compared with BTE microphones in CI users. A precondition for better sound localization abilities is the improvement of the delivery of temporal and spectral fine structure cues in CI systems.

Horseshoe bats and Old World leaf-nosed bats have two discrete types of pinna motions.

Horseshoe bats (Rhinolophidae) and the related Old World leaf-nosed bats (Hipposideridae) both show conspicuous pinna motions as part of their biosonar behaviors. In the current work, the kinematics of these motions in one species from each family (Rhinolophus ferrumequinum and Hipposideros armiger) has been analyzed quantitatively using three-dimensional tracking of landmarks placed on the pinna. The pinna motions that were observed in both species fell into two categories: In "rigid rotations" motions the geometry of the pinna was preserved and only its orientation in space was altered. In "open-close motions" the geometry of the pinna was changed which was evident in a change of the distances between the landmark points. A linear discriminant analysis showed that motions from both categories could be separated without any overlap in the analyzed data set. Hence, bats from both species have two separate types of pinna motions with apparently no transitions between them. The deformations associated with open-close pinna motions in Hipposideros armiger were found to be substantially larger compared to the wavelength associated with the largest pulse energy than in Rhinolophus ferrumequinum (137% vs 99%). The role of the two different motions in the biosonar behaviors of the animals remains to be determined.

Minimum Audible Angles Measured with Simulated Normally-Sized and Oversized Pinnas for Normal-Hearing and Hearing-Impaired Test Subjects.

The human pinna introduces spatial acoustic cues in terms of direction-dependent spectral patterns that shape the incoming sound. These cues are specifically useful for localization in the vertical dimension. Pinna cues exist at frequencies above approximately 5 kHz, a frequency range where people with hearing loss typically have their highest hearing thresholds. Since increased thresholds often are accompanied by reduced frequency resolution, there are good reasons to believe that many people with hearing loss are unable to discriminate these subtle spectral pinna--cue details, even if the relevant frequency region is amplified by hearing aids.One potential solution to this problem is to provide hearing-aid users with artificially enhanced pinna cues-as if they were listening through oversized pinnas. In the present study, it was tested whether test subjects were better at discriminating spectral patterns similar to enlarged-pinna cues. The enlarged-pinna patterns were created by transposing (T) generic normal-sized pinna cues (N) one octave down, or by using the approach (W) suggested by Naylor and Weinrich (System and method for generating auditory spatial cues, United States Patent, 2011). The experiment was cast as a determination of simulated minimum audible angle (MAA) in the median saggital plane. 13 test subjects with sloping hearing loss and 11 normal-hearing test subjects participated. The normal-hearing test subjects showed similar discrimination performance with the T, W, and N-type simulated pinna cues, as expected. However, the results for the hearing-impaired test subjects showed only marginally lower MAAs with the W and T-cues compared to the N-cues, while the overall discrimination thresholds were much higher for the hearing-impaired compared to the normal-hearing test subjects.

Vertical normal modes of human ears: Individual variation and frequency estimation from pinna anthropometry.

Beyond the first peak of head-related transfer functions or pinna-related transfer functions (PRTFs) human pinnae are known to have two normal modes with "vertical" resonance patterns, involving two or three pressure anti-nodes in cavum, cymba, and fossa. However, little is known about individual variations in these modes, and there is no established model for estimating their center-frequencies from anthropometry. Here, with geometries of 38 pinnae measured, PRTFs were calculated and vertical modes visualized by numerical simulation. Most pinnae were found to have both Cavum-Fossa and Cavum-Cymba modes, with opposite-phase anti-nodes in cavum and either fossa or cymba, respectively. Nevertheless in both modes, fossa involvement varied substantially across pinnae, dependent on scaphoid fossa depth and cymba shallowness. Linear regression models were evaluated in mode frequency estimation, with 3322 measures derived from 31 pinna landmarks. The Cavum-Fossa normal mode frequency was best estimated [correlation coefficient r = 0.89, mean absolute error (MAE) = 257 Hz or 4.4%] by the distance from canal entrance to helix rim, and cymba horizontal depth. The Cavum-Cymba normal mode frequency was best estimated (r = 0.92, MAE = 247 Hz or 3.2%) by the sagittal-plane distance from concha floor to cymba anterior wall, and cavum horizontal depth.

Influence of voxelization on finite difference time domain simulations of head-related transfer functions.

The scattering around the human pinna that is captured by the Head-Related Transfer Functions (HRTFs) is a complex problem that creates uncertainties in both acoustical measurements and simulations. Within the simulation framework of Finite Difference Time Domain (FDTD) with axis-aligned staircase boundaries resulting from a voxelization process, the voxelization-based uncertainty propagating in the HRTF-captured sound field is quantified for one solid and two surface voxelization algorithms. Simulated results utilizing a laser-scanned mesh of Knowles Electronics Manikin for Acoustic Research (KEMAR) show that in the context of complex geometries with local topology comparable to grid spacing such as the human pinna, the voxelization-related uncertainties in simulations emerge at lower frequencies than the generally used accuracy bandwidths. Numerical simulations show that the voxelization process induces both random error and algorithm-dependent bias in the simulated HRTF spectral features. Frequencies fr below which the random error is bounded by various dB thresholds are estimated and predicted. Particular shortcomings of the used voxelization algorithms are identified and the influence of the surface impedance on the induced errors is studied. Simulations are also validated against measurements.

Modeling human echolocation of near-range targets with an audible sonar.

Blind humans echolocate nearby targets by emitting palatal clicks and perceiving echoes that the auditory system is not able to resolve temporally. The mechanism for perceiving near-range echoes is not known. This paper models the direct mouth-to-ear signal (MES) and the echo to show that the echo enhances the high-frequency components in the composite MES/echo signal with features that allow echolocation. The mouth emission beam narrows with increasing frequency and exhibits frequency-dependent transmission notches in the backward direction toward the ears as predicted by the piston-in-sphere model. The ears positioned behind the mouth detect a MES that contains predominantly the low frequencies contained in the emission. Hence the high-frequency components in the emission that are perceived by the ears are enhanced by the echoes. A pulse/echo audible sonar verifies this model by echolocating targets from 5 cm range, where the MES and echo overlap significantly, to 55 cm. The model predicts that unambiguous ranging occurs over a limited range and that there is an optimal range that produces the highest range resolution.

Influence of stimulation position on the sensitivity for bone conduction hearing aids without skin penetration.

OBJECTIVE: This study explores the influence of stimulation position on bone conduction (BC) hearing sensitivity with a BC transducer attached using a headband. DESIGN: (1) The cochlear promontory motion was measured in cadaver heads using laser Doppler vibrometry while seven different positions around the pinna were stimulated using a bone anchored hearing aid transducer attached using a headband. (2) The BC hearing thresholds were measured in human subjects, with the bone vibrator Radioear B71 attached to the same seven stimulation positions. STUDY SAMPLE: Three cadaver heads and twenty participants. RESULTS: Stimulation on a position superior-anterior to the pinna generated the largest promontory motion and the lowest BC thresholds. Stimulations on the positions superior to the pinna, the mastoid, and posterior-inferior to the pinna showed similar magnitudes of promontory motion and similar levels of BC thresholds. CONCLUSION: Stimulations on the regions superior to the pinna, the mastoid, and posterior-inferior to the pinna provide stable BC transmission, and are insensitive to small changes of the stimulation position. Therefore it is reliable to use the mastoid to determine BC thresholds in clinical audiometry. However, stimulation on a position superior-anterior to the pinna provides more efficient BC transmission than stimulation on the mastoid.

Dynamic sound localization in cats.

Sound localization in cats and humans relies on head-centered acoustic cues. Studies have shown that humans are able to localize sounds during rapid head movements that are directed toward the target or other objects of interest. We studied whether cats are able to utilize similar dynamic acoustic cues to localize acoustic targets delivered during rapid eye-head gaze shifts. We trained cats with visual-auditory two-step tasks in which we presented a brief sound burst during saccadic eye-head gaze shifts toward a prior visual target. No consistent or significant differences in accuracy or precision were found between this dynamic task (2-step saccade) and the comparable static task (single saccade when the head is stable) in either horizontal or vertical direction. Cats appear to be able to process dynamic auditory cues and execute complex motor adjustments to accurately localize auditory targets during rapid eye-head gaze shifts.

An investigation of matching symmetry in the human pinnae with possible implications for 3D ear recognition and sound localization.

The human external ears, or pinnae, have an intriguing shape and, like most parts of the human external body, bilateral symmetry is observed between left and right. It is a well-known part of our auditory sensory system and mediates the spatial localization of incoming sounds in 3D from monaural cues due to its shape-specific filtering as well as binaural cues due to the paired bilateral locations of the left and right ears. Another less broadly appreciated aspect of the human pinna shape is its uniqueness from one individual to another, which is on the level of what is seen in fingerprints and facial features. This makes pinnae very useful in human identification, which is of great interest in biometrics and forensics. Anatomically, the type of symmetry observed is known as matching symmetry, with structures present as separate mirror copies on both sides of the body, and in this work we report the first such investigation of the human pinna in 3D. Within the framework of geometric morphometrics, we started by partitioning ear shape, represented in a spatially dense way, into patterns of symmetry and asymmetry, following a two-factor anova design. Matching symmetry was measured in all substructures of the pinna anatomy. However, substructures that 'stick out' such as the helix, tragus, and lobule also contained a fair degree of asymmetry. In contrast, substructures such as the conchae, antitragus, and antihelix expressed relatively stronger degrees of symmetric variation in relation to their levels of asymmetry. Insights gained from this study were injected into an accompanying identification setup exploiting matching symmetry where improved performance is demonstrated. Finally, possible implications of the results in the context of ear recognition as well as sound localization are discussed.

Dynamometric Analysis of Normative Auricular Stiffness and Comparison With Operated Prominent Ears.

AIM: Stiffness of the auricular cartilage is the main determining factor for the choice of operative technique of the prominent ear deformity. The aim of this study is to evaluate the stiffness of normal appearing ears objectively and quantitatively, compare the results with the operated prominent ear patients, and present prospective short-term dynamometric evaluation of the operated prominent ear patients. PATIENTS AND METHODS: A total of 190 volunteers without ear deformities were recruited and 9 age groups were formed: group (5-9), group (10-14), group (15-19), group (20-24), group (25-29), group (30-34), group (35-39), group (40-49), and group (50+). Total 28 ears (14 patients) with otoplasty were included in the study as group (operated 5-9) and group (operated 10-14). In addition, 3 patients with prominent ear deformity were prospectively followed for dynamometric changes that occur with otoplasty operation. The auriculocephalic angle (ACA) was measured once and auricle to scalp distance was measured at 4 different standardized levels. Ear stiffness was measured on each ear individually at 4 different points over the antihelix using digital computer-aided dynamometry. Each ear was compared in terms of ACA, distance, and dynamometric values. FINDINGS: Dynamometric values tend to increase with age, which increase and peak around 35 years of age and declines after 40 years of age. Measurements of the first 2 age groups were statistically different compared with the other groups. Postoperative dynamometric measurements (DNM) of group (operated 5-9) were similar with normative values of group (5-9) and postoperative satisfaction visual analogue scale (VAS) score was 92.8%. Postoperative DNM of group (operated 10-14) were higher compared with normative values of group (10-14) for each different measuring level and the postoperative satisfaction VAS score was 75.3. A total of 3 patients with prominent ears had lower dynamometric values preoperatively; these values approached closer to normative values of their age group postoperatively. CONCLUSIONS: Results show that auricular cartilage stiffens and malleability decreases with increased age. This stiffness peaks in the 35-39 age group and declines after 40 years of age. Dynamometric values increase, at all levels, suggesting increased cartilage stiffness is related to age. In the scope of these results, cartilage sparing techniques are more suitable for 5 to 14 years of age and cartilage-cutting techniques are more suitable for older patients.

Hearing in alpacas (Vicugna pacos): audiogram, localization acuity, and use of binaural locus cues.

Behavioral audiograms and sound localization abilities were determined for three alpacas (Vicugna pacos). Their hearing at a level of 60 dB sound pressure level (SPL) (re 20 µPa) extended from 40 Hz to 32.8 kHz, a range of 9.7 octaves. They were most sensitive at 8 kHz, with an average threshold of -0.5 dB SPL. The minimum audible angle around the midline for 100-ms broadband noise was 23°, indicating relatively poor localization acuity and potentially supporting the finding that animals with broad areas of best vision have poorer sound localization acuity. The alpacas were able to localize low-frequency pure tones, indicating that they can use the binaural phase cue, but they were unable to localize pure tones above the frequency of phase ambiguity, thus indicating complete inability to use the binaural intensity-difference cue. In contrast, the alpacas relied on their high-frequency hearing for pinna cues; they could discriminate front-back sound sources using 3-kHz high-pass noise, but not 3-kHz low-pass noise. These results are compared to those of other hoofed mammals and to mammals more generally.

External auricle temperature enhances ear-based wearable accuracy during physiological strain monitoring in the heat.

Body core temperature (Tc) monitoring is crucial for minimizing heat injury risk. However, validated strategies are invasive and expensive. Although promising, aural canal temperature (Tac) is susceptible to environmental influences. This study investigated whether incorporation of external auricle temperature (Tea) into an ear-based Tc algorithm enhances its accuracy during multiple heat stress conditions. Twenty males (mean ± SD; age = 25 ± 3 years, BMI = 21.7 ± 1.8, body fat = 12 ± 3%, maximal aerobic capacity (VO2max) = 64 ± 7 ml/kg/min) donned an ear-based wearable and performed a passive heating (PAH), running (RUN) and brisk walking trial (WALK). PAH comprised of immersion in hot water (42.0 ± 0.3 °C). RUN (70 ± 3%VO2max) and WALK (50 ± 10%VO2max) were conducted in an environmental chamber (Tdb = 30.0 ± 0.2 °C, RH = 71 ± 2%). Several Tc models, developed using Tac, Tea and heart rate, were validated against gastrointestinal temperature. Inclusion of Tea as a model input improved the accuracy of the ear-based Tc algorithm. Our best performing model (Trf3) displayed good group prediction errors (mean bias error = - 0.02 ± 0.26 °C) but exhibited individual prediction errors (percentage target attainment ± 0.40 °C = 88%) that marginally exceeded our validity criterion. Therefore, Trf3 demonstrates potential utility for group-based Tc monitoring, with additional refinement needed to extend its applicability to personalized heat strain monitoring.

Characterization of the time-variant behavior of a biomimetic beamforming baffle.

Horseshoe bats can actively change the shapes of their noseleaves and outer ears on time scales that are comparable to the duration of the biosonar pulses and echoes. When the shape deformations and the emission or reception of the ultrasonic signals overlap in time, the result is a time-variant diffraction process. Such a dynamic process provides additional flexibility that could potentially be used to enhance the encoding of sensory information. However, such a function remains hypothetical at present. To investigate the time-variant properties of deforming baffles such as the outer ears of horseshoe bats, the acoustic behavior of a biomimetic microphone baffle modeled on these biological structures has been investigated. The methods employed to characterize this device included representations in the time-delay domain as well as in the time-frequency domain. It was found that characterization methods which do not employ Fourier transforms revealed even more substantial time-variant effects than were apparent from time-frequency domain characterizations such as beampatterns obtained for different times in the deformation cycle. Furthermore, conspicuous correlates of asymmetries in the time-variant physical shapes were found in some characterizations that could be used to link dynamic baffle geometry with acoustic behavior.

Mechanism for generating peaks and notches of head-related transfer functions in the median plane.

It has been suggested that the first spectral peak and the first two spectral notches of head-related transfer functions (HRTFs) are cues for sound localization in the median plane. Therefore, to examine the mechanism for generating spectral peaks and notches, HRTFs were calculated from four head shapes using the finite-difference time-domain method. The comparison between HRTFs calculated from the whole head and the pinna-related transfer functions calculated from the segmented pinna indicated that the pinna determines the basic peak-notch pattern of the HRTFs. An analysis of the distribution patterns of pressure nodes and anti-nodes on the pinna computed in the steady state for sinusoidal excitations confirmed that the first three peaks correspond to the first three normal modes of the pinna. The analysis also revealed that at the first spectral notch frequencies, one or two anti-nodes appeared in the cymba and the triangular fossa, and a node developed in the concha. Furthermore, according to changes in the instantaneous pressure distribution patterns on the pinna, three types of mechanisms were hypothesized for inducing the node in the concha depending on the source elevation angle.