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Biomedical subjects

A R Thornton

Publications and source records attributed to A R Thornton.

At least 73 records · Page 4Linked to original sources
PubMed1984

The effects of stimulus rise-time and polarity on the auditory brainstem responses.

Auditory brainstem responses were recorded in response to condensation and rarefaction clicks of variable rise-time. The changes in latency and amplitude of response components, as a function of rise-time, were not consistent with the hypothesis that the evoked potential is generated only by the rarefaction stimulus phase. An alternative model is proposed whereby the click evoked potential is composed of two distinct components. The major component in the response is insensitive to stimulus polarity. In addition a small, but significant, polarity sensitive potential is present which inverts when the stimulus polarity is inverted. It is suggested that the inversion of this latter component gives rise to the latency and amplitude changes observed when the polarity of the stimulus is inverted.

Adult↗
PubMed1983

Construction of a simple auditory stimulus polarity indicator.

A device is described which gives a fast, reliable indication of the onset polarity of transient auditory stimuli. The instrument can be inexpensively constructed and is easily calibrated. It greatly simplifies the task of polarity calibration both in new equipment and in existing equipment after modifications have been made. This device will be of use to research laboratories and clinical departments who are currently recording auditory evoked potentials.

Brain Stem↗
PubMed1983

The effects of contralateral masking upon brainstem electric responses.

Brainstem electric responses (BSER) were recorded simultaneously to give records which were ipsilateral and contralateral to the test ear. Eight normally hearing subjects were presented with a fixed stimulus level in one ear and various levels of masking in the other ear. Responses to binaural stimulation were also recorded. It appears from the analysis of results that, for normal subjects, contralateral masking has no statistically significant effect upon the BSER. For the responses obtained from the stimulated side the analyses of variance showed a significant subject effect but no significant masking level effect from 0 to 80 dB Sensation Level of masking. For the responses obtained from the masked side the same conclusions seem to apply. As contralateral masking has no adverse effect upon the BSER in normal subjects and has had considerable use on clinical patients, with no significant problem, the normal audiometric use of masking is recommended for BSER recording.

Adult↗
PubMed1980

Predicting speech discrimination from the audiometric thresholds.

To develop a method for predicting a speech discrimination score (SDS) from audiometric thresholds (SRT and pure-tones) three prediction systems were investigated: a stepwise multiple regression procedure, smear-and-sweep analysis and a clinical classification of the audiometric configuration. Test results of 529 ears with sensorineural hearing loss were taken from copies of audiograms obtained as part of a normal audiology clinic caseload. The three prediction systems had similar predictive ability and yielded slightly higher correlations with the SDS than those in previously reported studies. Squared correlations in this study ranged from 0.58 to 0.60. Smear-and-sweep analysis yielded the best results; however, its complexity makes clinical application difficult at this time. The stepwise multiple regression models or the clinical classification system provided more clinically useful methods for predicting the SDS. An over-riding influence of increasing variability in the SDS with increased hearing loss was observed and significantly limited the accuracy of prediction for the moderate-to-severe hearing loss groups. Small changes in the slope of the audiometric configuration were noted to affect the SDS only when the degree of hearing loss was slight.

Audiometry↗
PubMed1980

Low-frequency hearing loss: perception of filtered speech, psychophysical tuning curves, and masking.

Four subjects with low-frequency hearing loss were evaluated to determine whether their responses to low-frequency stimulation might be the result of stimulation of nerve fibers with higher characteristic frequencies. Two masking paradigms were employed to indirectly investigate the contribution of high-frequency nerve fibers to the detection of low-frequency stimuli: (1) masking of a low-level, fixed-frequency probe by a variable-frequency pure-tone masker (psychophysical tuning curve) and (2) masking of pure tones by a high-level, fixed-frequency pure-tone masker. Low-frequency remote masking by tones and displacements in the tips of tuning curves to higher frequencies were interpreted as evidence that low-frequency signals near threshold were being detected by high-frequency fibers in three of the subjects. Three subjects were also tested with high-pass, low-pass, and unfiltered speech both in quiet and in the presence of a high-pass noise masker. Results were interpreted as showing a relatively small contribution of high-frequency fibers to the perception of low-frequency speech.

Adolescent↗
PubMed1980

Evoked potentials and contingent negative variation during treatment of multiple sclerosis with spinal cord stimulation.

Cervical somatosensory evoked potentials, brainstem evoked potentials, visual evoked potentials, and the cerebral contingent negative variation were recorded in patients with definite multiple sclerosis before, during, and after spinal cord stimulation. Improvements were seen in the cervical somatosensory and brainstem evoked potentials but neither the visual evoked potential nor the contingent negative variation changed in association with spinal cord stimulation. The results indicate that spinal cord stimulation acts at spinal and brainstem levels and that the clinical improvements seen in patients are caused by an action at these levels rather than by any cerebral arousal or motivational effect. The evoked potentials were not useful in predicting which patients were likely to respond to stimulation.

Brain Stem↗
PubMed1980

A brief communication on bone conduction artefacts.

The various factors which may be involved in the incorrect measurement of bone-conduction threshold are outlined. One of these factors, airborne radiation from the vibrator, has been investigated for three Radioear vibrators, the B70A, B71 and B72. The results indicate that false bone-conduction threshold values could arise, due to the airborne radiation component, mainly with the B72 vibrator.

Audiometry↗
PubMed1980

Electrophysiological responses and stimulus parameters associated with spinal cord stimulation.

Cervical somatosensory-evoked potentials and brainstem-click-evoked potentials were recorded from 10 patients with multiple sclerosis before and after a trial of spinal cord stimulation. An improvement in amplitude of the cervical somatosensory-evoked potential was seen in 7 out of 8 patients, while 3 out of 10 showed a decrease in latency of the brainstem-evoked potential. Stimulus currents were measured during spinal cord stimulation, and those patients requiring high currents to evoke a sensation did not derive clinical benefit from spinal cord stimulation.

Brain Stem↗
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↗