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Biomedical subjects

A R Thornton

Publications and source records attributed to A R Thornton.

At least 19 recordsLinked to original sources
PubMed1991

A non-invasive, objective test of endolymphatic hydrops.

Our previous work has shown that auditory brainstem responses (ABRs) can be used to measure the basilar membrane travelling wave velocity (TWV). Based upon the hypothesis that increased pressure in the scala media will increase the stiffness of the basilar membrane and, hence, increase the speed of the travelling wave. ABRs have been used to provide a means of objectively testing for endolymphatic hydrops. Ten normally hearing subjects and 20 Meniere's patients were tested. The data for the Meniere's group show that the TWV was within normal limits at all frequencies tested, except 5.7 kHz. At this frequency, the TWV greatly exceeded that of the normal group. A short duration (15-30 min) clinical test has been developed which involves the recording of two masked brainstem responses and the measurement of the difference in wave V latencies. Clinical verification that the technique is valid was obtained by monitoring patients undergoing glycerol dehydration. The additional hardware to enable this test to be carried out with a standard evoked response system has been constructed and three, parallel, clinical trials are in hand. Currently, this technique is being applied to longitudinal studies of Meniere's patients and to evaluating the action and efficacy of various drugs. A double-blind trial using a placebo and two different drugs is underway and preliminary results are presented here.

Adolescent↗
PubMed1991

Apparent travelling wave velocity changes in cases of endolymphatic hydrops.

This study attempted to develop a test which would be specific for endolymphatic hydrops. It is based upon the hypothesis that increased pressure in the scala media will alter the stiffness of the basilar membrane and hence increase the speed of the travelling wave. Auditory brainstem-derived responses were used to measure the basilar membrane travelling wave velocity in normals and to take the equivalent measures in Meniere's patients. Ten normally hearing subjects and 20 Meniere's patients were tested. The data for the Meniere's group showed that the travelling wave velocities were within normal limits at all frequencies tested, except 5.7 kHz where the travelling wave velocity greatly exceeded that of the normal group. A theoretical possibility that these findings may be the result of damaged and broadened VIIIth nerve tuning curves is discussed but travelling wave measures and psychophysical tuning curve measurements on the Meniere's group, normals and noise-induced hearing loss (NIHL) cases showed that this was not a significant factor. The data indicate that this technique can detect endolymphatic hydrops and a short duration clinical procedure has been devised.

Adolescent↗
PubMed1991

Isochronic mapping: a preliminary report of a new technique.

A new technique which we have named 'isochronic mapping' is described. The conventional technique of plotting isopotential maps shows little or no contrast for far-field potentials such as the auditory brainstem response (ABR). However, by modifications to the mapping software, the latency values of a peak can be plotted and lines of equal time or isochronic maps can be produced. Data from a normal subject has been obtained for both the compound and derived ABRs and are described in detail. The data are clear but the time delays between earliest and latest projections of a peak are hard to interpret. For monaural click stimulation, wave JV of the ABR projects first to the contralateral side of the head then moves towards the stimulated ear arriving some 0.3 ms later. Possible interpretations of this finding are discussed but further experimentation is needed to develop our understanding of these data.

Acoustic Stimulation↗
PubMed1978

Speech-discrimination scores modeled as a binomial variable.

Many studies have reported variability data for tests of speech discrimination, and the disparate results of these studies have not been given a simple explanation. Arguments over the relative merits of 25- vs 50-word tests have ignored the basic mathematical properties inherent in the use of percentage scores. The present study models performance on clinical tests of speech discrimination as a binomial variable. A binomial model was developed, and some of its characteristics were tested against data from 4120 scores obtained on the CID Auditory Test W-22. A table for determining significant deviations between scores was generated and compared to observed differences in half-list scores for the W-22 tests. Good agreement was found between predicted and observed values. Implications of the binomial characteristics of speech-discrimination scores are discussed.

Humans↗
PubMed1978

The validity of the derived cochlear nerve and brainstem evoked responses of the human auditory system.

It was considered that for a number of reasons, the derived response concept might not necessarily be valid when applied to the cochlear nerve and brainstem evoked responses (CBER). A statistical comparison of response measures of amplitude and latency was made between derived and non-derived responses, each representing response contributions initiated by the same locations along the cochlear partition. Relatively few statistical differences were detected. Therefore the technique of waveform summation and the production of derived response waveforms from complex responses, recorded under appropriate masking conditions, was considered to be a valid operation.

Brain Stem↗
PubMed1978

Frequency specific components of the cochlear nerve and brainstem evoked responses of the human auditory system.

A technique of high-pass (HP) masking was used to obtain masked cochlear nerve and brainstem evoked responses (CBER) of the human auditory system. The masking noise was extended progressively into the lower frequency regions of the cochlea for consecutively recorded responses, and the effect upon the response waveform was observed. Masked response waveforms were then subtracted to produce derived CBER waveforms representing activity initiated at specific frequency locations along the cochlear partition. Derived response components from various frequency bands were characterized and related to changes in the complex CBER during the process of frequency selective high-pass masking.

Adult↗
PubMed1978

Cochlear travelling wave velocities calculated from the derived components of the cochlear nerve and brainstem evoked responses of the human auditory system.

From the latency difference between corresponding components of the different derived cochlear nerve and brainstem evoked responses (CBER) and the cochlear location difference between the appropriate derived band centre frequencies (CF), estimates of the travelling wave velocity at various locations along the cochlear partition were calculated. Calculated velocities compared favourably with velocity data obtained using widely contrasting techniques. Derived CBER waveforms were therefore considered to truly represent neural activity initiated by activity at specific frequency regions along the cochlear partition.

Audiometry, Evoked Response↗
PubMed1978

Derived cochlear nerve and brainstem evoked responses of the human auditory system. The effect of masking in the derived band.

Derived cochlear nerve and brainstem evoked responses (CBER) were obtained for various frequency bands and were masked using special maskers. These maskers were designed to match exactly the intensity/frequency profile characteristics of the bands from which derived CBERs were obtained. Derived responses were markedly affected whenever the masker frequency limits coincided with the corresponding derived band. Other derived responses from adjacent bands were not affected. Since adjacent derived bands overlap, these overlapping regions were not considered to be represented in the derived responses. Therefore the actual frequency regions which the derived responses represented were considered to be smaller than the derived bands calculated from the physical parameters of the high-pass masking noises.

Brain Stem↗
PubMed1978

The technical aspects of cochlear implantation.

The historical development of attempts to provide some hearing ability, in totally deaf patients, by electrical stimulation of the cochlear nerve is reviewed to the point at which single channel intracochlear electrodes were tried in patients. The results obtained with this type of prosthesis are described and discussed in terms of the possible physiological mechanisms involved. Results obtained from promontory stimulation are also presented as a means of patient selection and are compared with the results from intracochlear electrodes. Based on these findings, the approaches for the development of multichannel intracochlear electrodes and for a single channel electrode with speech processing are described. The problems involved with materials, coding, electrode isolation and transmission are considered and the current results in these areas are detailed. Such results imply that the long-term prospects of developing a prosthesis that could provide adequate speech intelligibility are good.

Animals↗
PubMed1977

Effects of stimulus frequency and intensity on the middle componenets of the averaged auditory eletroencephalic response.

Middle components (latency 8-50 msec) of the averaged auditory electroencephalic response (AAER), evoked by brief duration tone bursts, were recorded from 11 normal-hearing subjects. Latency and amplitude measurements were made on five peaks (Na, Pa, Nb, Pb, and Nc) of the AAER waveforms recorded for 27 experimental conditions: three conditions of stimulus frequency (250, 1000, and 4000 Hz) at each of nine conditions of signal intensity (a no-stimulus control and 10, 20, 30, 40, 50, 60, 70, and 80 dB fe: group thresholds). Latency for each peak decreased with increased stimulus frequency, and it tended to decrease slightly with increases in stimulus intensity. Amplitude input-output characteristics varied with stimulus frequency and response peak. In general, the most linear input-output characteristics occurred for the early peaks and high stimulus frequencies. Characteristics for later peaks and lower frequencies tended to asymptote at moderate stimulus intensities. Between-subject variability was not much greater than within-subject variability for the single event auditory evoked potential (AEP). The variance of the AEP, however, was nearly as great (as much as two-thirds) as the variance of the background EEG, despite the large difference between AEP and background EEG amplitude.

Acoustic Stimulation↗
PubMed1976

Subjective and electrophysiologic tests in brain-stem lesions.

A battery of subjective and electrophysiologic auditory and vestibular tests were administered to 22 patients with neurologically confirmed brain-stem lesions to investigate the interrelationships between the test results. Acoustic-reflex and simultaneous midplane binaural loudness-balance abnormalities were related to N2 and N3 abnormalities on the brain-stem evoked-response measures. Unilateral abnormalities in low-redundancy speech tests, prolonged auditory reaction times, and reduced loudness growth on the alternate binaural loudness-balance test were related to ipsilateral N4 abnormalities or contralateral N5 abnormalities on the brain-stem evoked-response measures.

Acoustic Stimulation↗
PubMed1976

Time-intensity trade for speech: a temporal speech-Stenger effect.

Time-intensity trade for selected spondaically stressed words was investigated using a centering method for interaural time delays of 0.00, 1.00, 2.00, 2.25, 2.50, and 2.75 msec at five levels of presentation: 0-, 25-, 40-, 55-, AND 70-DB HL (ANSI, 1969). Lateralization effects increased with level of presentation, with a maximum lateralization effect of between 22 and 30 dB occuring with an interaural time delay of 2.25 msec. Multiple images were perceived by all subjects with an interaural time delay of 2.75 msec and by some subjects with an interaural time delay of 2.50 msec at high levels of presentation. No "ear effect" was observed for any of the listeners. A potential clinical application is discussed for this temporal speech-Stenger effect.

Adult↗
PubMed1976

Neurological applications of surface-recorded electrocochleography.

A new outpatient technique, involving the recording of auditory-evoked responses from scalp electrodes, is described. Responses are obtained from the cochlea, cochlear nerve, and auditory brain stem nuclei. The effects of various disorders on these responses are illustrated and the procedure is assessed as a diagnostic technique.

Auditory Perception↗
PubMed1975

Distortion of averaged post-auricular muscle responses due to system bandwidth limits.

Substantially different waveform details have been reported in various studies of the post-auricular muscle (PAM) response. By examining the high frequency limits of the pass-bands used to record the response it would appear that the system bandwidth limits have affected the waveform. Recordings were made using a very wide bandwidth, and were used to obtain power spectra of these PAM responses. These determined the minimum bandwidth requirements to avoid distortion of the waveform. It seems clear that a substantial proportion of the differences reported have been due to the use of a recording bandwidth which has distorted the response.

Acoustic Stimulation↗
PubMed1975

The adaptation of cochlear and brainstem auditory evoked potentials in humans.

The adaptation of the responses from the cochlear nerve and the auditory brainstem nuclei was studied using a burst of four clicks as the stimulus. Nine experimental conditions were obtained from three stimulus levels (60, 70 and 80 dB SL) and from three intervals between click in the burst (15, 24 and 32.5 msec). Six subjects were each tested three times for each of the experimental conditions and the techniques used and results obtained are summarized. Various models of the adaptation of the brainstem responses are proposed which predict different results. The results for the adaptation of the N1 response are basically in agreement with previous work, and the more central brainstem responses showed less adaptation than the peripheral responses. These findings may be explained by postulating different adaptation mechanisms for the peripheral and central responses. The 60dB stimulus level condition gave rise to more adaptation than the 80dB level, and this is in agreement with studies of low and high threshold reception systems reported elsewhere.

Adaptation, Physiological↗
PubMedDate not supplied

Electrophysiological studies of the auditory system.

Electrophysiological measures of cochlear function can be obtained using the techniques of transtympanic electrode and surface electrocochleography. These provide measures of the basic parameters of the cochlear microphonic, cochlear nerve and auditory brainstem nuclei action potentials, which enable the functional mechanisms of the cochlea and auditory pathway to be defined for normally hearing subjects and, by comparison, give diagnostic information about the pathologies involved in auditory disorders. Data are presented on the values and variability of the responses obtained from normally hearing subjects. The comparative values of each technique in estimating auditory threshold, cochlear function and in evaluating neurological conditions are discussed using data from clinical patients.

Acoustic Stimulation↗