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Biomedical subjects

J D Hood

Publications and source records attributed to J D Hood.

At least 37 records · Page 2Linked to original sources
PubMed1985

Cervical nystagmus due to loss of cerebellar inhibition on the cervico-ocular reflex: a case report.

Studies of the cervico-ocular reflex and the vestibulo-ocular reflex have been carried out separately and in combination on a patient with gait ataxia due to a cerebellar tumour. With the head fixed in space, body rotation to the right (left neck torsion) induced marked nystagmus to the left in darkness. Vestibulo-ocular responses to sinusoidal rotation were symmetrical while the neck was immobilised and asymmetric when it moved freely. It is suggested that the cervical nystagmus seen in this case was the result of removal of cerebellar inhibition upon the cervico-ocular reflex and that abnormal interaction of cervical and vestibular inputs could have played a role in the patient's unsteadiness.

Adenocarcinoma↗
PubMed1984

Influence of peripheral vision upon vestibulo-ocular reflex suppression.

The effect of peripheral vision upon the suppression of caloric induced nystagmus has been studied in normal subjects and patients with Parkinson's disease and cerebellar lesions. In normal subjects, caloric responses in the presence of optic fixation upon a target light viewed in darkness are further suppressed by a factor of two when background illumination is introduced. In both patient groups background illumination had significantly less effect. Additionally, optokinetic and pursuit test have revealed specific abnormalities consistent with the notion of a peripheral retinal feed-back mechanism deranged by disease. These in turn appear to have particular relevance to certain visuo-vestibular disturbances characteristic of patients in both groups.

Adolescent↗
PubMed1984

Neuro-otological manifestations of migraine.

Vestibulocochlear derangements have been studied in three groups of patients: 200 unselected patients with migraine (Series I), 80 migrainous patients referred because of their symptoms for full neuro-otological examination (Series II), and 116 patients with tension headache who served as controls (Series III). Significant differences were established between tension headache and migraine in respect of incidence and severity of symptoms and their time of onset in relation to the headache. In migraine, vestibulocochlear disturbances can occur as an aura, accompanying the headache or during headache-free periods, the highest incidence occurring during the headache. In Series I, 59 per cent reported vestibular and/or cochlear symptoms and these were of disabling severity in 5 per cent. Significantly, 50 per cent had a history of motion sickness and 81 per cent experienced phonophobia during the headache, the probable mechanism of which is discussed. Persisting vestibulocochlear derangements were found in 77.5 per cent of Series II, largely vestibular and of both central and peripheral origin. Involvement of the vertebrobasilar vascular system appears to be the most likely explanation. Possible links between Ménière's disease, benign paroxysmal vertigo and migraine are discussed.

Adolescent↗
PubMed1984

Speech discrimination in bilateral and unilateral hearing loss due to Ménière's disease.

A comparison of the speech audiograms of patients with bilateral and unilateral hearing loss due to Menière's disease has shown that when matched in respect of pure-tone hearing levels, speech discrimination at the better ear of the former is appreciably better than that at the impaired ear of the latter. In addition, while roll-over is a characteristic feature of the unilateral group it is conspicuously absent in the bilateral group. More surprisingly, in the bilateral group, despite relatively small differences in the pure-tone hearing levels at the two ears, speech discrimination at the better ear is strikingly superior to that at the poorer ear. It is concluded that patients with bilateral hearing loss selectively make use of the better ear to the neglect of the poorer ear. This could have important implications in the prescription of binaural hearing aids.

Audiometry, Pure-Tone↗
PubMed1984

Tonal adaptation.

The loudness of a continuous pure tone does not appear to change with time unless an interrupted tone is introduced at intervals during the course of the test; in consequence it is held that it is the interrupted tone which induces the loudness loss. This, however, cannot be called on to account for the marked change in quality or 'timbre' of a sustained pure tone which occurs over a period of time and which has the attributes of 'tonal adaptation', matching the time course of loudness adaptation revealed by dichotic loudness balance and other procedures. It is argued that the latter have to do with the measurement of sensation while judgement of the loudness of a continuous tone in isolation involves higher-order perceptual processes.

Acoustic Stimulation↗
PubMed1982

Loudness adaptation: real or illusory.

There is general agreement that, except at low sensation levels, the loudness of a continuous pure tone does not appear to change with time. By contrast, using a simultaneous dichotic loudness balancing procedure (SDLB) a substantial fall in loudness can be revealed. As a result it has been held that the latter does not represent a loudness loss in real terms but is a manifestation of some form of central binaural interaction possibly involving localization mechanisms. In two studies reported here, one involving a loudness scaling procedure using as a standard a reference tone of 65 dB (HL) and the other a loudness doubling procedure, a loudness loss has been clearly demonstrated following sustained stimulation with a continuous 60-dB (HL), 1000-Hz tone applied monaurally. The progression of the loudness loss with time follows a similar course to that found with the SDLB procedure. In consequence it is concluded that both represent a loudness loss in real terms and that inability to detect a change in loudness over time of a continuous tone results from the absence of any reference standard by which it can be judged.

Acoustic Stimulation↗
PubMed1980

Audiological considerations in Ménière's disease.

The audiological findings in Ménière's disease are reviewed particularly in respect of loudness recruitment and speech discrimination loss. Although recruitment is pathognomonic of all cochlear lesions, certain distinguishing features are apparent in Ménière's disease which differ from those in other non-metabolic disorders of the cochlea. With mild degrees of hearing loss, recruitment appears to aid speech discrimination supporting the suggestion that it represents the ears adjustment to failing hearing. With more profound degrees of hearing loss, there is a linear inverse relationship between maximum discrimination score and hearing level. Actual hearing aid gains preferred by patients correlate well with those predicted from a consideration of recruitment curves.

Hearing↗
PubMed1980

Influence of the speaker and other factors affecting speech intelligibility.

20 phonetically balanced word lists comprising 25 words in each and recorded on tape by a professional announcer have been tested on 45 subjects. Analysis of the results has enabled each of the 500 words to be assigned a grade of difficulty within the range 1-35. 25 'difficult' and 25 'easy' words re-recorded from the original tapes to form two new lists have been shown to retain their same grade of difficulty. With the same lists recorded by two additional speakers, however, word order difficulty was dramatically altered. Consideration has been given to various factors likely to affect word intelligibility including phonetic construction, word familiarity and word environment. None appeared to exert any marked influence. It is concluded that the characteristics of any recorded word articulation material are determined predominantly by the speaker and the recording technique adopted and are largely independent of other factors. Given sufficient experimental data upon recorded material, words can be selected out of context and re-recorded to provide test lists with virtually any desired characteristics.

Audiometry, Speech↗
PubMed1979

Vestibular suppression in peripheral and central vestibular disorders.

Caloric tests have been carried out both in the presence of optic fixation and in total darkness upon normal subjects, patients with peripheral vestibular disorders and patients with central vestibular lesions. Nystagmic responses were recorded electronystagmographically and measurements made of latency and duration of response, maximum slow component velocity and beat frequency. The relative enhancement of the response in darkness is expressed as a fixation index: maximum slow component velocity in darkness maximum slow component velocity with fixation. Compared to the normal group the peripheral group were found to have abnormally high fixation indices, the central group abnormally low. A hypothesis has been developed of the nervous mechanisms underlying the suppressive effects of optic fixation in both peripheral and central lesions which accords well with the available clinical, anatomical and physiological data. The clinical implications of the findings are discussed both in respect of their localizing value and relevance to current innovations in the design of caloric tests.

Brain Neoplasms↗
PubMed1979

Four further antibiotics related to olivanic acid produced by Streptomyces olivaceus: fermentation, isolation, characterisation and biosynthetic studies.

Four beta-lactam antibiotics with beta-lactamase inhibitory activity MM 22380, MM 22381, MM 22382 and MM 22383 containing the carbapenem nucleus have been isolated from a culture of Streptomyces olivaceus ATCC 31365. Fermentation conditions for their production and methods for their isolation are described. Evidence for a biosynthetic link between these compounds and the previously described olivanic acid derivatives MM 4550, MM 13902 and MM 17880 is presented.

Anti-Bacterial Agents↗
PubMed1979

Olivanic acids, a family of beta-lactam antibiotics with beta-lactamase inhibitory properties produced by Streptomyces species. II. Isolation and characterisation of the olivanic acids MM 4550, MM 13902 and MM 17880 from Streptomyces olivaceus.

The olivanic acids MM 4550, MM 13902 and MM 17880 are members of a new family of beta-lactam antibiotics. An isolation and purification process utilising ion-par extraction and ion-exchange chromatography is described and the metabolites are characterised by physico-chemical and biological properties.

Anti-Bacterial Agents↗
PubMed1977

Improving the reliability of speech audiometry.

A necessary feature of good recorded speech material is that each list should be identical in respect of graded order of difficulty. Extensive validatory tests have been carried out upon 20 M.R.C. word lists re-recorded by a professional announcer. It can be shown that by various manipulative procedures appreciable improvements may be obtained in the confidence limits of the material. In addition studies have been carried out upon the relationship between Speech Detection Threshold (S.D.T.) Speech Reception Threshold (S.R.T.) and Hearing level (H.L.) in normal hearing subjects. The surprising finding is that both S.D.T. and S.R.T. appear to be relatively independent of H.L. An analysis has been made of the words comprising the material in respect of their ease of recognition and is presented as an appendix.

Audiometry↗