PubMed Health⌕ Search

Biomedical subjects

M L Lenhardt

Publications and source records attributed to M L Lenhardt.

13 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↗
PubMed1979

Pneumatic whistle for animal hearing tests.

A hand activated pneumatic whistle produced a stable acoustic burst. The whistle was adjustable and the frequency could be selected over a range of 6-14 kilohertz. The whistle was useful in screening hearing in animals.

Animals↗