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Biomedical subjects

J G May

Publications and source records attributed to J G May.

At least 55 records · Page 3Linked to original sources
PubMed1988

The effects of spatial frequency and temporal waveform on three measures of temporal processing.

The effects of spatial frequency and temporal transition of sine-wave grating onset and offset were assessed using measures of reaction time, visual persistence, and temporal order judgements. The stimuli were lateralized fields, separated by 1 degree of visual angle. Slow temporal transition resulted in significantly poorer performance than did abrupt onset and offset, but spatial frequency had a minimal effect. Thus, the latency, temporal resolution, and temporal ordering of events are mediated by a mechanism that is sensitive to abrupt temporal transients. The stimulus conditions employed did not result in a shift in the point of subjective simultaneity.

Attention↗
PubMed1988

Reaction time measures of backward masking.

We employed both simple and choice reaction time (RT) paradigms in which the subjects were required to respond to 3.0 cycles per degree (c/d) square-wave gratings presented to one eye, while checkerboard masks were presented at various stimulus-onset asynchronies to the other eye. No masking was evident using the simple RT paradigm, but with the choice RT task, checkerboard masks presented to the contralateral eye of three subjects resulted in substantial decreases in response speed when the test preceded the mask by stimulus-onset asynchronies of 25 to 75 ms. Masks that contained lower fundamental spatial frequencies (1.0 c/d) than the target were more effective than masks containing fundamental spatial frequencies (6.0 c/d) higher than the target, while masks that contained fundamental components identical to those in the target (3.0 c/d) produced maximum masking. The results offer support for the sustained-transient theory of visual processing and validate RT as a technique for examining spatio-temporal factors in masking.

Adult↗
PubMed1988

Smooth-pursuit eye movement deficits with chemical lesions in the dorsolateral pontine nucleus of the monkey.

1. Anatomical and single-unit recording studies suggest that the dorsolateral pontine nucleus (DLPN) in monkey is a major link in the projection of descending visual motion information to the cerebellum. Such studies coupled with cortical and cerebellar lesion results suggest a major role for this basilar pontine region in the mediation of smooth-pursuit eye movements. 2. To provide more direct evidence that this pontine region is involved in the control of smooth-pursuit eye movements, focal chemical lesions were made in DLPN in the vicinity of previously recorded visual motion and pursuit-related neurons. Eye movement responses were subsequently recorded in these lesioned animals under several behavioral paradigms. 3. A major deficit in smooth-pursuit performance was produced after unilateral DLPN lesions generated either reversibly with lidocaine or more permanently with ibotenic acid. Pursuit impairments were observed during steady-state tracking of sinusoidal target motion as well as during the initiation of pursuit tracking to sudden ramp target motion. Through the use of the latter technique, initial eye acceleration was reduced to less than one-half of normal for animals with large lesions of the dorsolateral and lateral pontine nuclei. 4. The pursuit deficit in all animals was directional in nature and was not dependent on the visual hemifield in which the motion stimulus occurred. The largest effect for horizontal tracking occurred in all animals for pursuit directed ipsilateral to the lesion. Animals also showed major deficits in one or both directions of vertical pursuit, although the primary direction of the vertical impairment was variable from animal to animal. 5. Chemical lesions in the DLPN also produced comparable deficits in the initiation of optokinetic-induced smooth eye movements in the ipsilateral direction. In contrast to this effect on the initial optokinetic response, in the one lesioned animal studied during prolonged constant velocity optokinetic drum rotation, smooth eye speed increased slowly over a 10- to 15-s period to reach a level that closely matched drum speed. These results suggest that pathways outside the DLPN can generate the steady-state optokinetic response. 6. Saccades to stationary targets were normal after DLPN lesions, but corrective saccades made to targets moving in the direction ipsilateral to the lesion were much more hypometric than similar prelesion control saccades. 7. The pursuit deficits produced by lidocaine injections recovered within 30 min. The ibotenic acid deficits were maximal approximately 1 day after the injection and recovered rapidly thereafter over a time period of 3-7 days.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1987

The effects of grating complexity on transient evoked potentials.

In the present investigation, the effects of spatial frequency (1.0, 3.0 and 9.0 c/deg), grating complexity (1 + 3 or 3 + 9), and relative phase relationships (peaks-add or peaks-subtract) on the amplitude and latency of VEP components were examined with a pattern appearance (50 msec, 1.9 Hz) technique. The effects of temporally modulating one spatial component of a complex grating while the other component was continuously viewed were also investigated. Two components of the response obtained with pattern appearance were differentially affected by these stimulus manipulations. In general, most conditions that involved spatial complexity resulted in a loss of information that could be obtained when simple sine-waves were used.

Adult↗
PubMed1987

Ganglioside administration in retinitis pigmentosa.

The retinitis pigmentosa process typically causes variably progressive visual loss due to retinal photoreceptor and pigment epithelial cell deterioration. No effective agent either to retard or stop the deterioration has been known. Because gangliosides have been shown to have a variety of trophic effects on peripheral nervous tissue, we administered a daily 40 mg intramuscular dose in a prospective, double-blind, randomized, placebo-controlled trial in 30 persons with retinitis pigmentosa with or without congenital deafness. When we compared baseline performance on the two principal study outcomes, visual field area and electroretinographic response amplitudes, there was a marginally statistically significant increase in visual field area in the ganglioside-treated group. The subgroup of subjects who had recordable electroretinograms at baseline and who received the drug showed in three of five cases an increase in amplitude to all stimuli. These results appear encouraging; however, the data must be interpreted cautiously because the numbers of individuals are very small. Further study of the possible benefits of ganglioside administration to retinitis pigmentosa patients appears warranted.

Adult↗
PubMed1987

A comparison of two methods of training resistance to visually-induced motion sickness.

This report concerns the use of two methods of training subjects to tolerate visually-induced motion sickness (VMS). Sixteen subjects were selected on the basis of their response to a motion sickness history questionnaire and assigned to one of four groups on the basis of their ability to tolerate visually-induced motion (VM). One group received 10 sessions of confidence building and desensitization training (BT); a second group received 10 sessions of EMG and temperature biofeedback (FB); a third group received 10 sessions of BT and 10 sessions of FB (BTFB); and a fourth group received no treatment (C). The results indicated that the BT and BTFB groups exhibited significant increases in tolerance to VM when pretreatment measures were compared to posttreatment measures, while no significant differences in pre-post measures were observed in the FB or C groups. A similar pattern emerged from the symptomatology data.

Behavior Therapy↗
PubMed1987

Measures of auditory evoked potentials during optokinetic stimulation.

In this investigation auditory brainstem responses (ABR) elicited by click stimuli were recorded before, during, and after optokinetic stimulation in subjects that were (N = 10) or were not (N = 10) prone to visually induced motion sickness. The latency of Wave I, and the I-III and I-V interwave intervals were measured. A significant increase in the I-III interwave interval occurred only during optokinetic stimulation. Neither the Wave I latency nor the interwave interval differed with respect to subject groups and this factor did not interact with any other variables. These results suggest that optokinetic stimulation may alter neural activity in the region of the superior olivary complex, a structure known to be important in sound-source localization.

Brain Stem↗
PubMed1986

Different patterns of corticopontine projections from separate cortical fields within the inferior parietal lobule and dorsal prelunate gyrus of the macaque.

Corticopontine projection patterns were studied after injections of an 3H-leucine and 3H-proline mixture into each of four distinct cortical fields within the inferior parietal lobule and dorsal prelunate gyrus. Different preferential patterns of pontine labeling were observed for each of the four cortical areas studied. Multiple injections across the dorsal aspect of the prelunate gyrus (area DP) yielded scattered patches of label limited to the dorsolateral pontine nuclear region. A single injection within the lateral intraparietal area (area LIP), located in the caudal portion of the lateral bank of the intraparietal sulcus resulted in a series of labeled patches across the dorsal tier of cells stretching across the dorsal portions of the dorsolateral, peduncular and dorsal pontine nuclei. Injection of the cortex on the caudal aspect of the inferior parietal convexity (area 7a) produced multiple patches of label along the lateral margin of the ventral, lateral, and dorsolateral nuclei. Injection of area 7b resulted in label along the lateral aspects of the ventral, lateral and dorsolateral nuclei, as seen with area 7a injections, as well as additional label in the ventromedial portions of the ventral, peduncular and paramedian pontine nuclei. These results provide supporting anatomic evidence for the functional subdivision of the inferior parietal lobule and dorsal aspect of the prelunate gyrus and provide new information about the organization of cortical projections to the primate pontine nuclei.

Animals↗
PubMed1985

Corticopontine projection in the macaque: the distribution of labelled cortical cells after large injections of horseradish peroxidase in the pontine nuclei.

We studied the distribution of corticopontine cells in the monkey cerebral cortex. Horseradish peroxidase (HRP) was injected into the brainstem of monkeys in an attempt to fill the pontine nuclei on one or both sides. In control animals we injected the medullary pyramids or varied the route, size, or location of pontine injections. All retrograde filled corticopontine neurons were layer V pyramidal cells. Corticopontine cells were distributed within a largely continuous area of cortex which extended from the cingulate cortex medially to the sylvian fissure laterally; from the superior temporal fissure caudally to the medial part of the frontal granular cortex rostrally. Areas 4 and 6 of Brodmann (1905) contained the highest density of filled cells. In the primary visual cortex, area 17, there were a few labelled cells restricted to the rostral portion of the upper bank of the calcarine fissure, in a region representing the lower periphery of the visual field. The results are discussed in relation to the possible functions of the corticopontine system, especially the role of the extrastriate visual areas in visually guided movement.

Animals↗
PubMed1984

Spatio-temporal processing in multiple sclerosis.

The processing of spatial and temporal detail was investigated in patients with multiple sclerosis. Normal observers and 13 patients with optic neuritis secondary to multiple sclerosis performed a battery of visual tests that included contrast sensitivity, temporal integration, evoked potentials, and visual masking. The multiple sclerosis patients exhibited losses of pattern processing, and these deficits became more noticeable when the patterns were presented briefly. Moreover, these patients exhibited diverse response patterns for the different visual tests. For some, temporal integration functions appeared severely attenuated, while evoked potential latency was within normal limits. Others displayed poor performance in the visual masking test, yet contrast sensitivity functions were comparable to those of the control group. We suggest that a battery of tests that incorporates spatial as well as temporal stimuli is necessary for the detection of visual dysfunction in multiple sclerosis.

Adult↗
PubMed1984

Spatial frequency tuning in the visual evoked potential elicited by sine-wave gratings.

This investigation examined the onset response of the transient visually evoked potential elicited by the appearance-disappearance of sine-wave gratings at various levels of spatial frequency, suprathreshold contrast, and stimulus duration. The response was most easily characterized by two negative-positive complexes that were differentially tuned to spatial frequency. The earlier complex peaked at high spatial frequencies while the later complex peaked at low spatial frequencies. For both complexes, amplitude showed only slight variations across three-octave ranges of contrast and duration. Latency was curvilinearly related to spatial frequency, decreased with increasing contrast, and showed no apparent change as a function of duration.

Adult↗
PubMed1983

Preliminary visual results of pediatric epikeratophakia.

Although cataract surgery is feasible in children with unilateral cataracts, visual rehabilitation depends on optical correction and conscientiously maintained amblyopia therapy. Epikeratophakia for the correction of aphakia was performed in 47 children (50 grafts). Postoperative keratometry readings showed an average increase of 12.68 diopters in early patients. With new tissue-handling techniques, the last eight patients showed an average increase of +16.80 D, with -0.64-D overrefraction for emmetropia. Visual results indicate that epikeratophakia is an effective primary procedure for patients with unilateral traumatic cataracts and that it is superior to leaving vision uncorrected in children who have had unilateral congenital cataracts removed and are contact-lens intolerant. Further studies with younger patients will be necessary to define its role in neonates; however, individual results demonstrate that good vision is obtainable with epikeratophakia.

Cataract Extraction↗
PubMed1983

Learned helplessness and the facilitation of biofeedback performance.

The present article reports the results of two studies, which, taken together, support the hypothesis that learned helplessness resulting in effort cessation, while detrimental to performance on cognitive tasks, is actually facilitative to performance in a biofeedback relaxation task. Data are presented indicating that false failure feedback leads to the typically reported decrement in performance on a cognitive arithmetic task, while such feedback leads to enhanced performance in biofeedback relaxation. Self-report data suggest that this occurs because when subjects encounter failure, they revise their expectancies of future success downward and consequently plan to exert less effort. Reduction of effort is proposed as the common mechanism underlying the contrast in results between the arithmetic and biofeedback tasks. Results are discussed in terms of their implications for the way in which theories of self-efficacy and learned helplessness are commonly interpreted.

Biofeedback, Psychology↗
PubMed1983

The relationship between temporal integration and persistence.

We measured the persistence for gratings of three different spatial frequencies after they had been equated for visibility by manipulating: (1) the contrast of the stimulus, (2) the duration of the stimulus, or (3) both contrast and duration. When we presented gratings of equal apparent contrast and equal duration, persistence increased with increasing spatial frequency. This effect occurred when apparent contrast was equated in terms of extended-duration or brief duration contrast sensitivity. However, when we examined persistence using gratings equated for temporal integration (i.e. equal apparent contrast but unequal durations), no differences in persistence as a function of spatial frequency were observed. Thus, the increase in persistence which is typically found with higher spatial frequencies can be accounted for by knowledge of the spatio-temporal characteristics of the visual system. Our findings are discussed in terms of the notion of different filter time-constants for different spatial channels.

Afterimage↗