Biomedical subjects

J G May

Publications and source records attributed to J G May.

At least 37 records · Page 2Linked to original sources

PubMed1990

Eye movement indices of mental workload.

Four investigations were carried out to assess the feasibility of using eye movement measures as indices of mental workload. In the first experiment, saccadic extent was measured during free viewing while subjects performed low, moderate and high complexity, auditory tone counting as the workload tasks. The range of saccadic extent decreased significantly as tone counting complexity (workload) was increased. In the second experiment the range of spontaneous saccades was measured under three levels of counting complexity with a visual task that did not require fixation or tracking. The results indicated that the extent of saccadic eye movements was significantly restricted as counting complexity increased. In the third experiment, the effects of practice were examined and decreased saccadic range under high tone counting complexity was observed even when significant increases in performance occurred with practice. Finally, in experiment 4, the first experiment was repeated with additional optokinetic stimulation and the saccadic range was again observed to decrease with tone counting complexity. The results indicated that the extent of spontaneous and elicited eye movements was significantly restricted as counting complexity increased. We conclude that this measure may provide a valuable index of mental workload.

Adult↗

PubMed1990

Emotional processing and fear measurement synchrony as indicators of treatment outcome in fear of flying.

Minimal-therapist-involvement stress inoculation training was used to treat flying phobics. Relative to no-treatment controls, treatment subjects reported more fear reduction, were more likely to participate in an exposure session, and flew more during a two-month follow-up period. Subjects who exhibited synchronous changes in heart rate and report of anxiety during exposure had greater fear reduction than subjects showing less synchrony. Subjects who voluntarily took plane flights in the two months following treatment showed greater indications of emotional processing during in vivo exposure. Relative to flight avoiders, fliers had higher mean heart rate in the plane, a greater reduction in heart rate from the beginning to the end of the flight, and greater reported fear reduction from pre- to post-flight.

Adult↗

PubMed1990

Relaxation pretraining, pulse wave velocity and thermal biofeedback in the treatment of essential hypertension.

Twelve white male subjects with a physician's diagnosis of essential hypertension participated in the study over a 3- to 4-month period (23-38 sessions). Subjects were assigned to one of four sequences of training in which the order of presentation of pulse wave velocity (PWV) or thermal feedback, and presence or absence of relaxation pretraining were varied. The overall effectiveness of the treatment program was demonstrated by average blood pressure decreases of 8.8 mm Hg/4.1 mm Hg from initial session measures to follow-up one month after completion of the program. Systolic pressures were significantly lower at follow-up but not diastolic. In addition, 3 subjects had ceased taking any blood pressure medication by follow-up, and maintained normal pressure. The effectiveness of relaxation pretraining was demonstrated by the fact that relaxation pretrained subjects attained significantly greater blood pressure decreases from baseline to the last 3 sessions of training, and by the fact that relaxation pretraining appeared critical in the acquisition of PWV feedback training.

Adult↗

PubMed1990

Visual motion response properties of neurons in dorsolateral pontine nucleus of alert monkey.

1. In this study we sought to characterize the visual motion processing that exists in the dorsolateral pontine nucleus (DLPN) and make a comparison with the reported visual responses of the middle temporal (MT) and medial superior temporal (MST) areas of the monkey cerebral cortex. The DLPN is implicated as a component of the visuomotor interface involved with the regulation of smooth-pursuit eye movements, because it is a major terminus for afferents from MT and MST and also the source of efferents to cerebellar regions involved with eye-movement control. 2. Some DLPN cells were preferentially responsive to discrete (spot and bar) visual stimuli, or to large-field, random-dot pattern motion, or to both discrete and large-field visual motion. The results suggest differential input from localized regions of MT and MST. 3. The visual-motion responses of DLPN neurons were direction selective for 86% of the discrete visual responses and 95% of the large-field responses. Direction tuning bandwidths (full-width at 50% maximum response amplitude) averaged 107 degrees and 120 degrees for discrete and large-field visual motion responses, respectively. For the two visual response types, the direction index averaged 0.95 and 1.02, indicating that responses to stimuli moving in preferred directions were, on average, 20 and 50 times greater than responses to discrete or large-field stimulus movement in the opposite directions, respectively. 4. Most of the DLPN visual responses to movements of discrete visual stimuli exhibited increases in amplitude up to preferred retinal image speeds between 20 and 80 degrees/s, with an average preferred speed of 39 degrees/s. At higher speeds, the response amplitude of most units decreased, although a few units exhibited a broad saturation in response amplitude that was maintained up to at least 150 degrees/s before the response decreased. Over the range of speeds up to the preferred speeds, the sensitivity of DLPN neurons to discrete stimulus-related, retinal-image speed averaged 3.0 spikes/s per deg/s. The responses to large-field visual motion were less sensitive to retinal image speed and exhibited an average sensitivity of 1.4 spikes/s per deg/s before the visual response saturated. 5. DLPN and MT were quantitatively comparable with respect to degree of direction selectivity, retinal image speed tuning, and distribution of preferred speeds. Many DLPN receptive fields contained the fovea and were larger than those of MT and more like MST receptive fields in size.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1990

Response persistence of cat retinal ganglion cells to the temporally discrete presentation of sinewave gratings.

The neural basis of visible persistence is not well understood. In the present study the initial onset responses of cat retinal ganglion cells to the abrupt onset and offset of sinewave gratings were examined to determine if ganglion cells display a degree of response persistence that might account for the phenomenon of visible persistence. The responses of X and Y ganglion cell axons were tested using single-unit extracellular recording techniques. Both cell types displayed some degree of response persistence and over a limited range of short stimulus durations response persistence was inversely related to stimulus duration. These data suggest that neural persistence at the ganglion cell level may be the initial physiological basis for some types of visible persistence.

Animals↗

PubMed1990

Changes in ERG amplitude following laser induced damage to the primate retina.

The flash evoked ERG is used extensively as a measure of retinal function. To understand better the relationship between extent of retinal damage and the ERG we created multistage laser lesions in one eye each of three Macaca fascicularis monkeys. An argon-dye laser was used to deliver 630 nm energy to cumulative quarter sectors of the temporal hemiretina and the foveal region at two week intervals. Latencies of the a- and b-waves and amplitude from the trough of the a-wave to peak of the b-wave were measured preoperatively and one week after each new lesion. Following the last recording session the eyes were removed and prepared for histological examination. In general, but depending on stimulus condition, the maximum decrease in ERG amplitude (50-70% of normal) occurred following the third or fourth sector lesions. These lesions accounted for a loss of the outer nuclear layer in 18-25% of the entire retinal surface area extending from the edge of the fovea into the anterior equatorial region. Surprisingly, subsequent lesions of the remaining sector and fovea did not result in further reduction of ERG amplitudes. Significant increases in amplitudes were even observed for some stimulus conditions following these final lesions. Latencies of the a- and b-waves were not affected. The fact that in the present study ERG amplitudes recovered, suggest that such values may be tenuous evidence of amount of functional retina in laser-lesioned eyes.

Analysis of Variance↗

PubMed1990

Visual persistence of spatially filtered images.

Periodic stimuli such as sine-wave gratings and checkerboard patterns have been used in many studies of visual perception. It is well known that with such stimuli, visual persistence increases as spatial frequency increases and as contrast decreases. It is not clear, however, that similar relationships obtain for aperiodic stimuli such as natural images. Digitized images of objects (a face and a vase) were submitted to two-dimensional Fourier analysis. Four pairs of spatial frequency band-limited images were created for each image. Each pair consisted of a normal (NP) and a scrambled (SP) phase version, with the magnitude spectrum and space-averaged luminance the same within each pair. Filter bandwidths were one octave wide. Threshold persistence was measured for each spatially filtered image. Visual persistence for SP images increased significantly as spatial frequency increased, whereas no significant differences were found for NP images. This suggests that the temporal processing of complex, aperiodic visual images is influenced by the spatial frequency and contrast of local features within the image and cannot be predicted by space-averaged estimates of contrast and spatial frequency.

Adult↗

PubMed1990

The transfer of adaptation between actual and simulated rotary stimulation.

It is well known that continued exposure to motion environments leads to adaptation, but it is not clear whether such changes are specific to the particular type of motion experienced. The present investigation sought to evaluate the extent of transfer between real motion and visually-induced apparent motion. In addition, the direction of motion was varied and these two factors, mode of exposure and direction of rotation, were examined in a cross-adaptational design. Thirty-two subjects were pre- and posttested on measures of disorientation after active bodily rotation and visually-induced self-vection. Two groups received ten consecutive trials of active bodily rotation (clockwise or counter-clockwise) for 4 consecutive days. Two other groups received ten consecutive trials of visually-induced self-vection (clockwise or counter-clockwise) in a rotating drum for 4 consecutive days. During the exposure phase, dizziness and self-vection increased over trials for the groups exposed to the drum, while dizziness remained unchanged over trials for the groups exposed to bodily rotation. Repeated exposure to bodily rotation resulted in improved walking performance over trials and days. Subjects exposed to bodily rotation exhibited increased tolerance to visually-induced self-vection; however, exposure to visually-induced self-vection did not result in greater tolerance to bodily rotation. No support for directional specificity was evident.

Adaptation, Physiological↗

PubMed1990

Spatial localization discrepancies: a visual deficiency in poor readers.

In two studies, we compared the size of the spatial discrepancies made by young, good and poor readers when locating patterns in space. In the first study, each child was asked to point to the location of a briefly displayed pattern in a 7 x 7 matrix, and the discrepancy between the target's location and the child's response was recorded. The pattern was either a shape or a letter, and the target appeared at nine distances from the middle of the display. The discrepancies made by both groups of children increased with eccentricity, but the rate of increase was significantly greater for the poor readers. The second study required that two temporally and spatially separated target patterns be located on each trial. The discrepancies between their positions and the positions specified by the children were recorded for each target as a function of its eccentricity, and the results for both targets were similar to those obtained in the first study. That is, the discrepancies made by both groups of children increased with eccentricity, but the rate of increase was significantly greater for the poor readers. It was argued that the results of both studies are consistent with the hypothesis that poor readers are handicapped by a low-level processing or perceptual deficiency in the visual encoding system.

Achievement↗

PubMed1990

Generalization of tolerance to motion environments.

The aim of the present investigation was to determine to what extent training tolerance to one motion stimulus would generalize other motion experiences. Twenty subjects prone to motion sickness were selected and assigned to one of four groups after pretesting in a Dichgans and Brandt drum to determine their susceptibility to visually-induced apparent motion. They were also pretested with a VDT display of an expanding surface, and on a revolving/tilting chair. Subjects were assigned to one of the four groups by matching their mean tolerance to visually-induced motion. Subjects in the first group served as controls and received only cognitive counseling regarding their ability to tolerate motion environments. Subjects in the other groups received the same counseling coupled with incremental exposures to the drum, chair, or VDT, respectively. Posttests on each apparatus revealed that the treatments involving the chair and the drum provided specific increases in tolerance to the device used during treatment, and that the treatment involving the chair provided a generalized tolerance to visually-induced motion. These results support the notion that there are both specific and general components in learning to tolerate motion environments.

Adaptation, Physiological↗

PubMed1989

Striped pattern of labeling in ground squirrel superior colliculus following intraocular HRP injections.

In the 13-lined ground squirrel (Citellus tridecemlineatus), intravitreal injections of horseradish peroxidase (HRP) or wheat germ-agglutinated HRP (WGA-HRP) tracers produced a striped pattern of labeling in the contralateral superficial gray (SGS) of the superior colliculus in most, but not all, cases. The stripes extended dorsoventrally throughout the SGS in a rostral-medial to caudal-lateral orientation. In general, the striped labeling was more distinct and was observed more frequently with the HRP, rather than the WGA-HRP, tracer.

Animals↗

PubMed1989

Retinal projections in the ground squirrel (Citellus tridecemlineatus).

The retinal projections of the thirteen-lined ground squirrel were determined by tracing anterograde transport of intravitreally injected horseradish peroxidase (HRP) or wheat-germ conjugated horseradish peroxidase (WGA-HRP). Label was seen in the suprachiasmatic nucleus and adjacent anterior hypothalamic area, the accessory optic system (the medial, dorsal, and lateral terminal nuclei), the dorsal and ventral lateral geniculate nuclei, the intergeniculate leaflet, the pretectal nuclei (the anterior, posterior, and olivary pretectal nuclei and the nucleus of optic tract), and the superior colliculus. Most of these structures were labeled bilaterally, with dense contralateral label and sparse ipsilateral label, a pattern typical for animals with laterally placed eyes. However, the suprachiasmatic nucleus and the nucleus of the optic tract received input only from the contralateral eye. In contrast to previous degeneration studies, the sensitive HRP tracers (in conjunction with cytochrome-oxidase reactivity) revealed an elaborate organization within the lateral geniculate nucleus (dorsal LGN, ventral LGN, and intergeniculate leaflet) that is consistent with existing organizational schemes for other mammalian species.

Animals↗

PubMed1989

An evaluation of cognitive-behavioral therapy for training resistance to visually-induced motion sickness.

This investigation examined the techniques for reducing visually-induced motion sickness. On the basis of their responses to a motion sickness history questionnaire, 32 subjects were selected and assigned to 1 of 4 groups such that the groups were matched on the basis of their ability to tolerate visually-induced apparent motion (VM). One group received 10 sessions of desensitization training only (DT); a second group received 10 sessions of cognitive therapy only (CT); a third group received 10 sessions of combined desensitization and cognitive therapy treatment (CG); and a fourth group received no treatment (C). (There are many speculations about why and how an individual's response changes with repeated stimulation. We have arbitrarily selected the term desensitization to connote the decrease in sensitivity over time with repeated exposures). The results indicated that only the groups which received cognitive therapy (i.e., CT and CG) exhibited significant increases in tolerance to VM when pretreatment measures were compared to posttreatment measures. No significant differences in pre- vs. posttreatment measures were observed in the desensitization only or control groups (i.e., DT and C). A similar pattern of results was obtained with the symptomatology data.

Adolescent↗

PubMed1989

Reduction of visually-induced motion sickness elicited by changes in illumination wavelength.

This experiment was undertaken to assess the degree of stimulus generalization in visually-induced motion sickness. Sixteen subjects participated in six sessions in which they were exposed to a rotating field of vertical stripes for five 4-min trials. This stimulus elicited the perception of self-vection. In the first three sessions, the stripes were illuminated by one monochromatic light (red or green) and in the last three sessions, the stripes were illuminated by the other monochromatic light. Magnitude estimates of motion sickness increased significantly within sessions, but the rate at which this measure increased was significantly diminished across trials in the last three-session block. Magnitude estimates of vection increased within sessions and decreased across sessions, but did not increase with color change. These results can be explained in terms of a model of stimulus generalization and have implications for the reduction of motion sickness in applied settings.

Adolescent↗

PubMed1988

Temporal order judgements in good and poor readers.

The amount of time required to make accurate (75% correct) temporal order judgements was measured in groups of 3rd and 4th grade children who were selected on the basis of reading ability. The stimuli, two words (Box and Fox), were tachistoscopically presented to the left and right or above and below a fixation point. Subjects were asked to say which word came first under one condition, or which position contained the stimulus that occurred first under another condition. The stimulus onset asynchrony (SOA) was varied in half octave steps until threshold was determined. The results indicate that good readers required significantly longer SOAs to achieve 75% correct than adults, but significantly shorter SOAs than poor readers. There was not a significant difference in thresholds for the word and position conditions for adults or good readers, but poor readers required significantly more time to achieve criterion for the word condition. The word thresholds were highly correlated (-0.77) with reading level, but the correlation between position threshold and reading level was not significant. The implications of a temporal order deficit are discussed.

Adult↗

PubMed1988

EEG biofeedback and relaxation training in the control of epileptic seizures.

Research utilizing sensorimotor rhythm (SMR) biofeedback with epileptics suggests that it is useful in decreasing seizures. Subjects were 6 young adults with a diagnosis of epilepsy of at least two years who had been unable to control their seizures with different regimens of anticonvulsant medications. Subjects ranged from severely mentally handicapped to above average functioning. Seizure type, frequency, and duration were recorded by subjects and caretakers. Measures of operant learning were percent time in SMR. The experiment utilized a single subject multiple baseline design which consisted of 6 phases: baseline one, relaxation training; baseline two, biofeedback training one; baseline three, biofeedback treatment two and follow-up. The results of this study are in agreement with other studies using SMR biofeedback. All subjects were able to significantly increase percent time in SMR. Five out of the 6 subjects demonstrated decreases in seizure frequency during the treatment phase. Two of the 6 subjects benefited from relaxation training. Four subjects demonstrated significant negative correlations between percent SMR and seizure rats. Consistent with other studies utilizing multiple baseline designs, a majority of the subjects did not follow the design of the study.

Adult↗

PubMed1988

Clinical and serum lipid findings in a large family with autosomal dominant retinitis pigmentosa.

Retinitis pigmentosa, of unknown cause, has recently been associated with decreased amounts of the polyunsaturated fatty acid, docosahexaenoic acid, in the plasma of affected as compared with unaffected relatives. It has been suggested that this finding may serve as a marker for the disease and might indicate alterations in photoreceptor cell metabolism. The authors studied 54 members of a family with dominantly inherited retinitis pigmentosa in five generations. In addition to the typical clinical findings of retinitis pigmentosa, eight persons also had a bull's eye maculopathy, and four persons had uni- or bilateral optic nerve drusen. When the authors determined the plasma fatty acid and lipid contents, they saw the expected age-related effect on cholesterol and triglycerides, but an unexpected, significant reduction in fatty acids in the unaffected controls as compared with persons with retinitis pigmentosa. The authors' results emphasize the heterogeneity of phenotypic expression of retinitis pigmentosa within a single family.

Adolescent↗

PubMed1988

Teller acuity cards versus clinical judgment in the diagnosis of amblyopia with strabismus.

Teller acuity card testing, which is a form of the preferential-looking procedure, is a popular way of assessing visual acuity in preverbal patients. The authors suspected that the clinical judgment of a pediatric ophthalmologist is superior to the Teller acuity cards in diagnosing amblyopia when strabismus is present. Acuity card and fixation preference measurements on each eye were compared at the same clinical visit in a group of 108 strabismic patients. The authors found that the acuity cards could be used to detect amblyopia. However, the pediatric ophthalmologist was more sensitive in diagnosing amblyopia than the Teller acuity cards in the presence of strabismus.

Amblyopia↗