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D Henderson

Publications and source records attributed to D Henderson.

At least 235 records · Page 13Linked to original sources
PubMed1982

Detection of sinusoidally amplitude modulated noise by the chinchilla.

Amplitude modulation thresholds for sinusoidally amplitude modulated noise were obtained from four monaural chinchillas using shock-avoidance conditioning procedures. The noise was band limited at either 10 or 20 kHz, amplitude modulated at frequencies between 2 and 4096 Hz and presented at levels between 52 and 73 dB SPL. The modulation thresholds of the chinchilla were approximately 9% (-- 2 dB) at modulation frequencies below 32 Hz. At higher modulation frequencies, thresholds increased at the rate of 1.9 dB/octave. Modulation thresholds were also measured in human listeners using the same experimental apparatus. Amplitude modulation functions for both subject groups exhibited low-pass characteristics; however, the thresholds for humans were better than those of the chinchilla at modulation frequencies below 64 Hz.

Acoustic Stimulation↗
PubMed1982

Gap detection in hearing-impaired chinchillas.

Auditory temporal resolution is known to deteriorate with sensorineural hearing loss; however, there is considerable intersubject variability in human studies. The purpose of the present study was to obtain measures of temporal resolution in the chinchilla as the degree of noise-induced hearing loss was systematically varied. Gap-detection thresholds, a measure of temporal resolution, were evaluated at four levels of noise-induced asymptotic threshold shift (ATS). Gap thresholds were normal when the pure-tone thresholds were elevated approximately 15 dB. With a hearing loss of approximately 30 dB, the gap thresholds were longer than normal if compared at the same sound pressure level, but within normal limits if compared at the same sensation level. When the hearing loss exceeded 40 dB, gap thresholds were longer than normal both in terms of sound pressure level and sensation level. These results show that there is an orderly breakdown in temporal resolution as the degree of noise-induced ATS increases. The results are related to neural data and models of temporal resolution.

Acoustic Stimulation↗
PubMed1982

Is the equal energy rule applicable to impact noise?

The equal energy hypothesis (EEH) is a theoretical framework for evaluating the acoustic trauma associated with a wide variety of noise exposures. Most of the data supporting the EEH have been large scale demographic studies. Controlled laboratory studies, especially with impulse noise, have brought into question the generality and validity of the EEH. The present study assessed the hearing loss resulting from four impact noise exposures having equal energy, but different peak levels (107, 113, 119, 125 dB SPL) and repetition rates (4/s, 1/s, 1/4s, 1/16s). Hearing loss was assessed at 0.5, 2, and 8 kHz in four groups of chinchillas using the auditory evoked response. The animals were exposed for five days and developed an asymptotic threshold shift (ATS) during the exposure. The animals, however, did not develop the same amounts of ATS for each exposure as predicted by the EEH; instead the hearing loss increased with peak level.

Animals↗
PubMed1981

Ultrastructural changes to the cochlea resulting from impulse noise.

Following impulse noise trauma to chinchillas, observation of plastic-embedded surface preparations of the organ of Corti showed no consistent relationship between cochlear hair cell loss and permanent hearing loss (Hamernik et al. 1980). In some animals there was a loss of hearing when hair cells were present. The cochleas from that experiment were examined with transmission electron microscopy to determine at the ultrastructural level if there was damage to the sensory cells that would explain the change in threshold sensitivity. Ultrastructural changes in cochlear hair cells include an increase in lysosomes, multivesicular bodies, vacuolization of subsurface cisternae, and proliferation of Hensen bodies. These changes are observed in all experimented animals. Alterations to the ultrastructure of the stereocilia vary from animal to animal and on the outer hair cells, the changes include loosening of the stereocilia membranes, loss of stiffness, fusion of the stereocilia and disintegration of the rootlets. These changes are observed only in animals that have a permanent threshold shift after noise trauma.

Animals↗
PubMed1981

Influence of vibration on asymptotic threshold shift produced by impulse noise.

Monaural chinchillas were exposed for 10 days to one of these conditions: (1) whole-body vibration (30 Hz, 1 g rms acceleration); (2) impact noise (113 dB peak SPL 1/s) or (3) a combination of whole-body vibration and impact noise. Thresholds were monitored before, during and after the exposure using the auditory-evoked response or behavioral conditioning techniques. Vibration alone had essentially no effect on threshold. Exposure to impact noise produced a stable asymptotic level of threshold shift 2-8 h after exposure onset. The asymptotic threshold shift was roughly 35 and 43 dB SPL at 0.5 and 8.0 kHz, respectively. Exposure to impact noise plus vibration produced an asymptotic threshold shift at 0.5 and 8.0 kHz that was approximately 10 dB greater than noise alone. The combination group also showed greater permanent threshold shifts and greater hair cell losses than the group exposed only to impact noise. The results imply that impact noise and whole-body vibration, at levels commonly found in industrial settings, can interact to increase the susceptibility of the chinchilla cochlea to noise-induced hearing loss.

Animals↗
PubMed1980

Stingose. A new and effective treatment for bites and stings.

Stingose, an aqueous solution of 20% aluminum sulphate and 1.1% surfactant, has been developed as a wide-acting and effective first-aid treatment designed to counteract the venoms of insects, bees, marine stingers and stinging plants. Rapid application to prevent further systemic abosorption is necessary. As virtually all characterized insect, marine, and spiked-fish venoms contain a protein component, it is proposed that the Al3+ ion in Stingose interacts with proteins and long-chain polysaccharide components to denature and inactivate the venoms. It is also proposed that an osmotic fluid movement towards the high ionic strength solution could account for part of the action of the product. In an extensive field trial which involved 1003 cases, the over-all success of first-aid treatment with Stingose in 997 cases and partial success in six cases was extremely high. Further work is to be undertaken to study the range of envenomations against which Stingose is active.

Adult↗
PubMed1980

Stingose.

Explore the source record for details and available documents.

Alum Compounds↗
PubMed1980

VIII nerve response to click stimuli in normal and pathological cochleas.

A flat 30--50 dB hearing loss was established in chinchillas following a 5 day exposure to an octave band of noise (354--708 Hz, 95 dB SPL). After exposure, single auditory nerve fiber recordings were obtained using click and tone burst stimuli. The thresholds of units from the noise-treated animals were elevated 30--70 dB and the tuning curves were abnormally broad. At the threshold for click stimulation, the fiber latencies were shorter in the noise-treated animals than those in normal animals. However, the latencies for the two groups were similar when stimulated at the same intensities. As indicated by the number of peaks in the PST histograms obtained with clicks, the units from the noise-treated animals showed considerably more damping in the neural response than those from normal units. The temporal spacing between the peaks in the histograms for units of similar CF was the same in the normal and noise-treated groups, although this cannot be taken to infer that an individual unit PST histogram would remain the same after noise exposure as before. These limited neural data therefore show changes in the same direction as those in the transient mechanical response of the basilar membrane reported by Robles et al.

Animals↗
PubMed1980

The interaction of whole body vibration and impulse noise.

Three groups of chinchillas, each consisting of five monaural animals, were exposed to one of three conditions: 1 h of sinusoidal, 30-Hz vibration at 1 g rms; 50 noise impulses at 155 dB, 1.5-m A duration, at the rate of 1/min; or a combination of the vibration and the impulse noise. Before exposure, and at various times after exposure, each animal's auditory evoked responses (AER) were measured at seven frequencies between 0.5 and 8.0 kHz. Thirty days after the exposure all animals were sacrificed for cochlear surface preparation histology. Chinchillas exposed to the vibration alone showed no significant temporary or permanent change in AER thresholds. The group exposed to impulse noise showed a maximum median TTS of from 34 dB at 0.5 kHz to 72 dB at 2 kHz and a flat PTS of 15-20 dB between 1 and 2.8 kHz. The combination group at all test times and frequencies showed a greater TTS and PTS than did the groups exposed to noise or vibration alone. The cochleograms are related in a variety of ways with hearing thresholds. The data from all three groups of experimental animals are consistent and demonstrate a potentiating effect of vibration on an impulse noise exposure.

Animals↗