Martin L. Lenhardt

Shallow-water propagation of the toadfish mating call

A mismatch between sound production and hearing in the oyster toadfish, Opsanus tau L., suggests the hypothesis that toadfish communicate over short distances. Low frequency acoustic signals (tones, noise and toadfish courtship calls) broadcast in 1 m deep water, attenuated rapidly, thereby restricting communication within a range of only several meters. Ambient noise does not appear to exert a strong selection pressure on the frequency spectrum of the boatwhistle or on the distance over which it is audible.

Acoustic coupler for skin contact hearing enhancement devices

There is provided hearing device improvements using modulation techniques adapted to the characteristics of auditory and vestibular hearing. One embodiment provides for extending hearing to the infrasonic range by extracting sounds from the high ambient noise in this range and applying them to a carrier in the ultrasonic quiet zone. Further extension of hearing into the ultrasonic range is provided by a modulation scheme which uses a fluid conduction coupler to match impedance for a vibration transducer applied to the skin. A variation on this embodiment integrates this ultrasonic hearing extension with normal acoustic headphones. Another embodiment compensates for high frequency hearing loss by a modulation scheme which uses middle ear resonance as an amplifier. A further embodiment combines ultrasonic transposition with wireless modulation to obtain secure communication.

Sea turtle auditory behavior

Little is known of sea turtles’ auditory behavior. Startles (neck contractions) were observed in 25 loggerheads (Caretta caretta) to tones from 35 to 1000 Hz, when the turtles were near the bottom of holding tanks at a depth of 1 meter. A composite audiogram revealed lowest thresholds in the 400–500 Hz range (106 dB SPL re 1 μm). Thresholds at 735 and 1000 Hz were 117 and 156 dB, respectively. Thresholds in the 100–200 Hz range were ∼124 dB, with lower frequencies being 10–12 dB higher. Tank diving behavior was elicited with 30 Hz at 164 dB. ABR thresholds to vibration clicks with peak energy at 500 Hz were 113 dB. Seismic air guns (Bolt 600) were employed in a large net enclosure. Turtles increased swimming speed for exposures in the 151–161 dB levels. Avoidance ∼175 dB was common in initial trials, before habituation. ABRs pre‐ and post‐air gun exposures revealed TTS of more than 15 dB in one animal with recovery in 2 weeks. Air guns in depths >10 m may result in more energy in the low frequencies with ...

Saccular hearing; turtle model for a human prosthesis

The saccule is a hearing organ is some vertebrates thought to be responsive to substrate vibration (bone conduction) or low‐frequency aerial sound. There was likely some overlap in these functions in the course of evolution after the sensory area to become the cochlea migrated from the saccule. That overlap is preserved in extant turtles by columella (stapes) saccular coupling via fibroelastic strands; thus both organs can respond to air conduction and bone conduction stimulation. Evoked potential data, however, reflect differential AC/BC drive to the inner ear. The columellas inertia provides the force to displace the saccular wall with the tympanum providing damping. Intense AC stimulation likely stimulates the human saccule. A proprietary stapedial saccular strut is described that serves as a surgically implanted coupling device for humans, allowing more efficient use of AC saccular hearing in clinical deafness. The human saccular resonance is about 350 Hz, which should allow for sufficient speech codi...

Vibrotactile suppression of tinnitus

At the Society’s 142nd meeting, the efficacy of high frequency bone conducted stimulation in suppressing tinnitus was presented. The hypothesized mechanism was the reprogramming of frequency tuning of auditory neurons in the central nervous system, secondarily to peripheral hearing loss. This mechanism is unlikely in cases of tinnitus in the presence of normal audiometric sensitivity. There is the possibility that hearing loss above 10 kHz can play a role in tinnitus, an association not thoroughly explored. Somatomotor stimulation influencing the quality of tinnitus has been reported, as have interconnections of the auditory and somatosensory systems. There would appear to be an evolutionary advantage of linking the sensorimotor organization of the external ear and the auditory function of the brainstem in sound localization. Thus, stimulation of the pinna and post auricular area may be a means of suppressing tinnitus. To that end a thin aluminum ceramic bimorph was constructed to fit on the inner surface...

Evolution of Ultrasonic and Supersonic Hearing in Man

The average mammalian upper frequency limit of hearing is approximately 55 kHz. Within a species, the upper limit is inversely related to the distance between the ears, as Masterton et al. (JASA 45:966, 1969) have shown that all mammalian species tested to date, with the singular exception of man, fit this relation in a well-correlated fashion. For the relation to also hold in man, a 30 to 40 kHz upper frequency limit should exist, as opposed to the limit normally measured at approximately an octave lower. Mammals with very high-frequency hearing appear to have modifications of the basilar membrane, which likely account for the observed high-frequency hearing ability. In contrast, man has a relatively broad, radially undifferentiated basilar membrane, consistent with the measured lower-frequency sensitivity. In both our laboratory and others (Corso, JASA 35:1738, 1963), the upper limit of perception of auditory-like stimuli is found to be in the range of 60 kHz to 90 kHz, provided that it is delivered via bone conduction.

Vacuum ear plug.

A passive inexpensive hearing protection device (HPD) will be described that provides hearing protection, which is simple to use and comfortable over hours of use. Protection from impact sounds will be provided by creating a negative pressure between the plug tip and the eardrum (−100‐mm H2O or −1 kPa). The negative pressure will be created by squeezing the peripheral plug end, evacuating a fixed amount of air from the canal. The aperture diameter is 0.010 in. In effect the pump plug will have a similar acoustical action on the eardrum as a normal stapedius muscle contraction, but without its limitations (too slow and fatigue). An external flexible bladder forms the end which is held in the fingers to be inserted into the ear canal. The vacuum mechanism consists of bulb on a polypropylene frame embedded in a closed cell urethane flanged housing. With a negative pressure of −2 kPa the transmission loss is 20–25 dB. It is estimated that a negative pressure of −1 kPa would result in a transmission loss of about 15 dB. The vacuum effect is maximal in the low frequencies which will also attenuate body conducted sounds by reducing ossicular inertial.A passive inexpensive hearing protection device (HPD) will be described that provides hearing protection, which is simple to use and comfortable over hours of use. Protection from impact sounds will be provided by creating a negative pressure between the plug tip and the eardrum (−100‐mm H2O or −1 kPa). The negative pressure will be created by squeezing the peripheral plug end, evacuating a fixed amount of air from the canal. The aperture diameter is 0.010 in. In effect the pump plug will have a similar acoustical action on the eardrum as a normal stapedius muscle contraction, but without its limitations (too slow and fatigue). An external flexible bladder forms the end which is held in the fingers to be inserted into the ear canal. The vacuum mechanism consists of bulb on a polypropylene frame embedded in a closed cell urethane flanged housing. With a negative pressure of −2 kPa the transmission loss is 20–25 dB. It is estimated that a negative pressure of −1 kPa would result in a transmission loss of ab...

Applying the Occupational Safety and Health Administration (OSHA) ultrasonic noise ceiling values.

The Occupational Safety and Health Administration (OSHA) voted in 2003 to accept the American Conference of Governmental Industrial Hygienists (ACGIH) increased threshold level values (TLVs) for airborne ultrasound from the more stringent levels set previously as a result of ultrasonic sickness studies reported in the 1960s. The impedance mismatch between the air and the body, which prevents most ultrasonic energy absorption, was the rationale. The TLVs were increased by 30 dB, unless solid or liquid coupling is possible, allowing the unintended transfer of acoustic energy into the worker. The TLVs were set based on two lines of evidence: (1) detectability of directly coupled ultrasound and damage reported from ultrasonic exposure. The risk of ultrasonic exposure underwater is also addressed in direct coupling to an ultrasonic source. The measurements needed are airborne sound pressure level up to 100 kHz, waterborne sound pressure up to 100 kHz, and high frequency vibration. Only a 2–5 dB threshold shift...

Tinnitus neural map; A positron emission tomography study

The neural map of tinnitus involves more than the classical auditory pathways and the limbic system. PET findings in six patients, with severe problem tinnitus, revealed the involvement of the cerebellum, insula and frontal cortices when these patients were imaged before and after high frequency bone conduction therapy. The frontal cortex and cerebellum demonstrated the highest ratios of metabolic change but changes were also noted in the thalamus and the medial temporal lobe system. The PET data supports the view that the frequency specific map of auditory cortex is dynamic and can change with high frequency therapy, presumably due to neural reorganization. The PET data further reflect alterations in multiple areas of brain in all patients to tinnitus and/or high frequency therapy. Encouraging was the observation that patients with the most dramatic change in their global pre/post PETs were also the ones who exhibited the greatest behavioral improvement in regards to tinnitus relief measured by informal ...

Airborne ultrasound enters the ear through the eyes

Musical spectrum above 20 000 Hz has been demonstrated to influence human judgments and physiology. Moreover airborne ultrasonic noise has been implicated in hearing loss, tinnitus, and other subjective effects such as headaches and fullness in the ear. Contact ultrasound, i.e., with a transducer affixed to the skin of the head/neck, is audible; assumed by bone conduction. However, lightly touching the soft tissues of the head, avoiding bone, can also produce audibility. When contact ultrasound is applied to the head, energy from 25 to ∼60 kHz can be recorded from the closed eyelid, with care to avoid sensor contact with the orbit. If the same frequency band of noise is passed through a transducer in from of the eye, with just air coupling, the same response is again recordable on the head. An acrylic barrier between the eye and the transducer eliminates the response. Once airborne ultrasound exceeds the impedance mismatch of the eye it readily propagates through the soft tissues of the eye and brain v...