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Biomedical subjects

M L Lenhardt

Publications and source records attributed to M L Lenhardt.

At least 19 recordsLinked to original sources
PubMed1991

Human ultrasonic speech perception.

Bone-conducted ultrasonic hearing has been found capable of supporting frequency discrimination and speech detection in normal, older hearing-impaired, and profoundly deaf human subjects. When speech signals were modulated into the ultrasonic range, listening to words resulted in the clear perception of the speech stimuli and not a sense of high-frequency vibration. These data suggest that ultrasonic bone conduction hearing has potential as an alternative communication channel in the rehabilitation of hearing disorders.

Adult↗
PubMed1988

Human skull vibratory patterns in audiometric and supersonic ranges.

The attenuation of bone-conducted stimuli across the human skull was determined in audiometric, ultrasonic, and supersonic frequency ranges (250 to 64,000 Hz). An increase in attenuation with an increase in frequency, as well as significant resonance effects, was observed. For the audiometric frequency range, bone conduction stimulation of one side of the head results in almost equal stimulation of the other side. In the ultrasonic and supersonic ranges, the contralateral side is progressively isolated.

Audiometry↗
PubMed1986

High frequency hearing in jaundiced rats.

All 8 pups in a homozygous-by-heterozygous rat mating were studied using brainstem auditory-evoked responses to clicks and to tone pips at 10, 15, 20, and 25 kc/s. Rats expressing the jaundice trait (N:4) had normal BSAER for click thresholds and latencies of Waves I-IV; however, to tone pips stimulating predominantly the more basal portions of the cochlea. Although thresholds were unaffected, there were mild prolongations of latencies of Waves II-IV representing central conduction time; the prolongation in one jaundiced rat reached significance re controls. Furthermore, amplitude of Waves II-IV to the louder tone pips were about 20% lower for the jaundiced rats. Jaundiced rats may be adequate models for central conduction delay found in human neonatal hyperbilirubinemia when species differences are controlled.

Acoustic Stimulation↗
PubMed1985

Effects of spectrum, background noise, and stimulation rate on the auditory startle reflex in hyperbilirubinemic rats.

The sensory element of the acoustic startle reflex was studied in neonatal rats. Stimulus frequency, background noise, and stimulus presentation rate all affected the reflex. The performance of jaundiced rats with central auditory pathology is initially poorer than that of nonjaundiced rats but rapidly improves to the level of the controls, suggesting that the jaundiced rats may be a model for central auditory disturbances in humans. Startle reflex measurements give no indication that jaundiced rats surviving the testing period had neural hearing loss.

Acoustic Stimulation↗
PubMed1985

Marine turtle middle-ear anatomy.

The middle-ear structures from 5 Atlantic Loggerhead (Caretta caretta) and 1 Atlantic Ridley (Lepidochelys kempi) marine turtles from dead specimens found stranded in the lower Chesapeake Bay were dissected and examined superficially and by light microscopy. The marine turtle middle ear is poorly adapted as an aerial receptor in mammalian and reptilian terms. However, it appears well designed as a peripheral component of a bone conduction system. The thick tympanum, while disadvantageous as an aerial receptor, likely enhances low-frequency bone conduction hearing. The columella directly couples the cochlea and saccule so that its movement would stimulate each end organ. Turtle hearing is probably an integration of both outputs.

Animals↗
PubMed1985

Preyer reflex in jaundiced rats: central auditory effects.

Normal control rats (N:45) and 27 genetically hyperbilirubinemic rats from an NIH colony were tested for the Preyer reflex (Pr) threshold using pure tones. About half of all animals (N:39) were tested at 4, 6, and 8 kc/s only, while 39 were also tested at 10, 15, 20, 25, and 30 kc/s. Data were not included from 3 jaundiced rats who died during the study, which began when Ss were 3 wks old. Some jaundiced rats differed from control rats in their elevated Pr thresholds for mid-frequency tones (approximately 10 kc/s) (group mean threshold difference of 6.4 db (p less than .05). Since jaundiced rats have been shown to have extensive damage in the first brain-stem synapse, neural dysfunction can be inferred. The Pr of jaundiced rats did not differ from normals at frequencies below 10 kc/s. Normal low-frequency sensitivity in jaundiced rats likely represents a tonotopic vulnerability gradient in the central auditory pathway.

Animals↗
PubMed1983

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.

Animal Communication↗
PubMed1983

Marine turtle reception of bone-conducted sound.

An individual each of the marine turtles, Caretta caretta and Lepidochelys kempi, were stimulated with audiofrequencies delivered directly to the skull. Startle responses were observed to underwater stimuli of .25 and .5 kc/s. Neural responses to underwater bone-conducted (bc) sound were recorded in another aquatic form, the snapping turtle, Chelydridae serpentina. The morphology of the neural response suggested the involvement of the auditory system in bc responsivity. Bc hearing appears to be a reception mechanism for marine turtles with the skull and shell acting as receiving surfaces. Turtles are capable of receiving the low-frequency spectrum of the natal beach, which may serve as one of the cues in nesting returns.

Animals↗
PubMed1983

Turtle shells as an auditory receptor.

Evoked responses were obtained from the brainstem of seven box turtles (T. carolina) using air conducted stimuli and also vibratory stimuli applied directly to the carapace. Both stimuli elicited similar neural electrical responses that differed chiefly in sensitivity. The vibratory responses were lower in threshold and higher in amplitude than responses to air conducted clicks. Further, simultaneous masking of vibratory clicks by air conducted noise had negligible effects, whereas vibratory masking completely suppressed the responses to airborne sound, suggesting that the turtle ear is differentially sensitive to sound and vibration. Spinal blocking of somatic pathways had negligible effects on the vibratory-evoked responses, suggesting that the latter originate in the auditory system and are stimulated by bone conduction.

Animals↗
PubMed1983

Effects of neonatal hyperbilirubinemia on Token Test performance of six-year-old children.

Token Test (TT) performance was investigated of 100 6-yr-old children who had had hyperbilirubinemia as infants. Half these Ss had been given phototherapy for that condition, half had not. Group data revealed that both subgroups performed significantly below the normed average on those sections of the TT that place the heaviest load on short-term auditory verbal memory. Ss who had not been given phototherapy outperformed those who had been given the light treatment. The TT even in abbreviated form (only 15 commands) was a useful tool in identifying short-term memory difficulties in this population. Poor short-term memory performance may predispose these children to difficulties in listening comprehension later in life.

Child↗
PubMed1982

Effects of hyperbilirubinemia on the hearing and vocal development in Gunn rats.

Jaundiced rats do not differ from normal rats in the development of frequency-specific startle responses to sound in spite of the auditory brainstem damage in the affected rats. Jaundiced rats do show a vocal motor abnormality. Behavioral auditory results support the concept of neural involvement in early vocal development; however, the site of involvement in hearing development is still ambiguous.

Animals↗
PubMed1982

Bone conduction hearing in turtles.

Audiofrequencies were delivered to specimens of 3 turtle families by ac and bc in an attempt to elicit a behavioral response. Aerial signals with intensities up to 100 db SPL failed to elicit any consistent response. The same signals delivered directly to the carapace resulted in brisk head withdrawals. There was little energy loss measured along the shell suggesting it may serve in a minor role as an acoustic receptor. Turtles could use bc hearing in short distance detection even when withdrawn into the shell. Although the ear is likely mediating the head reflex, somatic mechanoreceptors cannot be completely excluded.

Acoustic Stimulation↗
PubMed1981

Childhood central auditory processing disorder with brainstem evoked response verification.

A case of a central auditory processing disorder was caused by a unilateral low brainstem dysfunction. The diagnostic profile includes normal pure-tone hearing, normal tympanograms, absent stapedial reflexes, poor unilateral speech discrimination, and absent brainstem evoked response recordings on the affected side. History suggests this is a result of an early trauma that resulted in aberrant verbal learning. Specific diagnosis was delayed until a stapedius muscle abnormality suggested central testing.

Acoustic Impedance Tests↗
PubMed1981

Evidence for auditory localization ability in the turtle.

Evidence is presented that the semiaquatic turtle Chrysemys scripta and the terrestrial turtle Terrapene carolina major can detect the direction of a tone within their sensitive area of hearing. It is further suggested that not only can these species respond behaviorally to sound without extensive manipulation but can use limited hearing in a problem-solving situation of maze learning. Adult emydid turtles (5 C. scripta, 3 T. carolina) learned a Y-maze with a 500-c/s signal to an invisible open goal box to avoid bright light. All animals performed above chance levels, but it required over 240 trials on the average to reach 60%-correct performance. Computations suggest that binaural cues used by mammals would not be adequately encoded by the primitive auditory systems of the species studied. It is further suggested that these turtles use bone conduction by coupling their ears to the substrate to hear vibrations in the immediate area. This would appear to be a carryover from the ancient reptile stem stock. The poor middle-ear impedance system relegates air-borne sound processing to be a somewhat insensitive limited low-pass system, depending heavily on monaural cues derived from head scanning. vocal output in these species appears to be spectrally imbalanced with their auditory sensitivity. The role of species-specific vocal signalling is unclear from the present data.

Animals↗