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L Proctor

Publications and source records attributed to L Proctor.

16 recordsLinked to original sources
PubMed1997

Representation of sound localization cues in the auditory thalamus of the barn owl.

Barn owls can localize a sound source using either the map of auditory space contained in the optic tectum or the auditory forebrain. The auditory thalamus, nucleus ovoidalis (N.Ov), is situated between these two auditory areas, and its inactivation precludes the use of the auditory forebrain for sound localization. We examined the sources of inputs to the N.Ov as well as their patterns of termination within the nucleus. We also examined the response of single neurons within the N.Ov to tonal stimuli and sound localization cues. Afferents to the N.Ov originated with a diffuse population of neurons located bilaterally within the lateral shell, core, and medial shell subdivisions of the central nucleus of the inferior colliculus. Additional afferent input originated from the ipsilateral ventral nucleus of the lateral lemniscus. No afferent input was provided to the N.Ov from the external nucleus of the inferior colliculus or the optic tectum. The N.Ov was tonotopically organized with high frequencies represented dorsally and low frequencies ventrally. Although neurons in the N.Ov responded to localization cues, there was no apparent topographic mapping of these cues within the nucleus, in contrast to the tectal pathway. However, nearly all possible types of binaural response to sound localization cues were represented. These findings suggest that in the thalamo-telencephalic auditory pathway, sound localization is subserved by a nontopographic representation of auditory space.

Acoustic Stimulation↗
PubMed1997

Benign paroxysmal positional vertigo.

Benign paroxysmal positional vertigo (BPPV) has received renewed clinical interest. At the Johns Hopkins Otological Vestibular Laboratory, 781 patients were tested on more than one occasion between September 1976 and November 1992. Of these patients, 187 (24%) were found to have positional nystagmus consistent with a diagnosis of BPPV. A retrospective analysis of these patients' records, including vestibular test and eye movement reports, audiograms, questionnaires, and hospital charts was performed. After this review, the nystagmus, initially diagnosed as due to BPPV, was believed to be a manifestation of another disease process in 36 cases. Of the remaining 151 cases, 52 (34%) presented with no significant preceding disorder and have been termed primary BPPV. In the remaining 99 patients we found coexisting or associated disorders which included Meniere's disease, head trauma, prior ear surgery, vestibular neuronitis, migraine, and others. Forty-five of these 151 patients (31%) had an associated diagnosis of Meniere's disease. To our knowledge a significant association between Meniere's disease and BPPV has not been reported. A review of the literature with discussion of BPPV and the associated disorders is offered.

Audiometry↗
PubMed1995

Stimulus-independent thought depends on central executive resources.

Stimulus-independent thoughts (SITs) are streams of thoughts and images unrelated to immediate sensory input. Four experiments examined the contribution of aspects of working memory to production of SITs. In Experiments 1 and 2, interventions that were targeted on, respectively, phonological and visuospatial components of working memory both interfered with production of SITs, but there was evidence that these tasks also made demands on central executive resources. Experiments 3 and 4 specifically examined the hypothesis that production of SITs and control of nonproceduralized tasks both depend on central executive resources, and so should show mutual interference. In Experiment 3, prior practice on pursuit rotor and memory tasks reduced the interference with SITs from concurrent task performance. In Experiment 4, randomness within a task involving random-number generation was less when SITs were being produced concurrently than it was when they were not. The results suggest that production of SITs depends on central executive resources.

Adult↗
PubMed1993

Controlling the caloric labyrinthine stimulus: restoring surface temperature.

The duration of the conventional caloric stimulus is too long and the termination of the stimulus is uncontrolled. This study explores the use of a brief terminal "washout" irrigation pulse at 37 degrees C which is intended to 1. shorten the duration of action of the caloric stimulus and 2. eliminate uncertainty over the magnitude and duration of the terminal portion of the thermal labyrinthine stimulus. Twelve normal subjects were tested with 1. conventional 30-second irrigations, 2. 30-second irrigations plus a "washout" pulse, and 3. temperature-switching caloric (TSC) irrigations plus a "washout" pulse. Clinical test scores were comparable with all three irrigation methods. The "washout" pulse produced only a slight shortening of the conventional 30-second irrigation responses.

Adult↗
PubMed1989

The influence of a relative support group on carers' emotional distress.

Research has shown that the supporters of relatives with dementia suffer high levels of stress and strain and it is the severity of stress which determines whether the dependent remains in the community or becomes institutionalized. This study evaluated the outcome of a 6-week, closed group, educational programme on reported levels of stress and strain on five supporters. Results showed an increase in the severity of problems presented by the carers whilst there was a decrease in their emotional distress. However, these results suggest that the carers in the present study were experiencing much higher levels of stress and strain than those of supporters in a larger investigation, where the eventual outcome was institutionalization of the dependents. The implications for the future of community care are discussed and a large scale survey of carers, including monitoring of eventual outcome for dependents, is recommended.

Dementia↗
PubMed1987

A study of potential vestibulotoxic effects of once daily versus thrice daily administration of tobramycin.

Tobramycin 5.1 mg/kg/day was administered for 9 days to 20 healthy human volunteers to determine the potential vestibulotoxicity of once daily versus thrice daily treatment regimens. Vestibular function was tested carefully before, during, and following drug administration, using a battery of postural and caloric tests. Although subjects receiving the once daily regimen performed better on the postural tests, we feel this does not necessarily indicate an adverse effect in either group. The caloric test was the primary measure of vestibular function in this experiment, and this test appeared to demonstrate a slight adverse effect during drug administration of equal magnitude in both treatment groups. The results of this experiment indicate that there is no significant difference in the risk of adverse vestibular effects between once daily and thrice daily tobramycin administration.

Adult↗
PubMed1986

'Demand characteristics' in body-size estimation in anorexia nervosa.

We asked 24 patients with anorexia nervosa and 30 normal controls to estimate their body-size several times, each time using different instructions. The degree of over-estimation was found to vary predictably with the wording of the instructions. Informing the subject that she had made an error without specifying the direction of the error resulted in reduced over-estimation on a subsequent trial, for both anorexics and controls. 'Internally directed' instructions were associated with a greater degree of over-estimation than 'external' instructions in both groups, but particularly in anorexic subjects. Our results indicate the necessity of controlling the 'demand characteristics' of such experiments.

Adult↗
PubMed1980

Corneoretinal potential variations: significance in electronystagmography.

Spontaneous variations in the corneoretinal potential (CRP) may introduce large errors when using electronystagmography (ENG) to measure responses during clinical caloric testing. Whether or not conventional calibration techniques are adequate to control such measurement errors has not been established. We studied CRP variations in normal subjects and patients by measuring calibration before and after a series of caloric tests. Among patients the CRP either rose or fell in a random manner; we were unable to discover independent measures that might serve to predict the magnitude or polarity of the CRP changes. Among normal subjects the CRP consistently dropped during each caloric test, probably due to longer periods of eye closure imposed in this group. Recalibration before each caloric test, using an averaging technique, would greatly reduce (but not eliminate) ENG measurement errors.

Action Potentials↗
PubMed1978

Acute vertigo.

Explore the source record for details and available documents.

Humans↗
PubMedDate not supplied

Acute vestibular paralysis in herpes zoster oticus.

A case of herpes zoster oticus is presented in which the lateral and superior semicircular canals of the labyrinth were affected unilaterally. The results of several electronystagmographic examinations are described and correlated with the patient's description of symptoms. This case study indicates that disease affecting the lateral semicircular canal is reliably detected by the conventional caloric test. However, the fact that the posterior semicircular canal remained intact could not be inferred from the results of the caloric test in this case. Also the appearance of nystagmus upon eye closure appears to have been a more sensitive index of the state of the disease process than was the caloric test.

Adult↗
PubMedDate not supplied

Reference values for serial vestibular testing.

This study defines the normal limits of day-to-day variation in vestibular function. A short-acting caloric test was used and nystagmus intensity was measured by means of an interactive computerized technique. Data were analyzed from 30 normal subjects tested on three successive days and from ten of these subjects who were also tested on 11 additional occasions. Individual caloric test scores generally remained between 55% and 170% of their initial value; narrower ranges resulted when scores were averaged together. There was very little habituation of caloric responses. The upper normal limits of test-retest variation in scores for right-left difference and directional preponderance of caloric responses were 24% and 22%, respectively.

Caloric Tests↗
PubMedDate not supplied

Stimulation of the vestibular receptor by means of step temperature changes during continuous aural irrigation.

A technique for rapid, balanced hot/cold stimulation of the vestibular receptor is presented. During continuous aural irrigation the temperature of the irrigation fluid is switched between hot and cold values at times computed according to a mathematical model of heat conduction in the labyrinth area. As a result, the induced temperature difference across the lateral semicircular canal describes an approximately sinusoidal time course, reaching peak values of equal magnitude but opposite sign. Application of the test to 32 clinical subjects demonstrated that the heat conduction model and the analysis used in timing the sequence of thermal pulses was accurate. We expect that, with further refinements, the new technique will prove superior to conventional caloric test methods in the detection and measurement of subtle as well as gross abnormalities of the vestibular system.

Adult↗
PubMedDate not supplied

Factors contributing to variability of caloric test scores.

Data were analyzed from 30 healthy male subjects, examined on three successive days with caloric, rotatory, optokinetic, gait and posture tests. Data were also analyzed from 11 additional test sessions performed on 10 of these subjects. A short-acting caloric test was used and nystagmus intensity was measured by means of an interactive computerized technique. Large inter-individual differences were noted for all test results and these differences remained consistent as tests were repeated. Factors which may contribute to inter- and intra-subject variability of caloric test scores are identified and discussed.

Body Temperature↗