Search PubMed⌕ Search

Biomedical subjects

R Sekuler

Publications and source records attributed to R Sekuler.

At least 55 records · Page 3Linked to original sources
PubMed1983

Contrast sensitivity of hemodialysis patients.

The contrast sensitivity of patients undergoing hemodialysis therapy for chronic renal failure was measured and compared to that of a control group. Both contrast sensitivity and visual acuity of the patients were reduced. Ocular and fundoscopic exams revealed differences between the patients and controls, but these differences could not fully account for the visual deficits. The visual deficits could be expected to cause reduced visibility under everyday conditions for the patients.

Adult↗
PubMed1982

A specific and enduring improvement in visual motion discrimination.

Training improves the ability of human observers to discriminate between two similar directions of motion. This gradual improvement is specific to the direction on which an observer is trained, and it endures for several months. Improvement does not affect motion perception generally, nor does it depend on recognition of details of the movement.

Discrimination, Psychological↗
PubMed1982

Motion processing in peripheral vision: reaction time and perceived velocity.

Reaction times to motion onset were measured as a function of eccentricity of presentation. These were compared with measurements of perceived speed at various eccentricities. For slowly moving targets, both dependent measures changed substantially with eccentricity: RT increased and perceived speed declined. For more rapidly moving targets, both dependent measures were unchanged by eccentricity. These results may be related to the difference between retinotopic distribution of neural mechanisms responsive to low rates of temporal modulation and the retinotopic distribution of neural mechanisms responsive to higher rates of temporal modulation.

Humans↗
PubMed1982

Thresholds for seeing visual phantoms and moving gratings.

Moving visual phantoms look like real gratings and generate movement aftereffects as do real gratings. Three experiments have been carried out to test whether phantoms resemble real gratings in other ways. Changes in the spatiotemporal frequency of an inducing grating effect the minimum contrast at which it will induce phantoms, but only insofar as the changes affect the visibility of the inducing gratings. Changes in the areal extent of the inducing grating and in the extent of the gap across which phantoms must be induced alter the visibility of the phantoms but, again, only to the extent that the changes affect the visibility of the inducing gratings themselves. Phantoms induced by high-contrast gratings may be cancelled by gratings of near-threshold contrast when the latter are presented 180 degrees out of phase with the inducing gratings. It is concluded that the appearance of phantoms is governed solely by the detectability of their inducing gratings, but that the effects of phantoms on pattern-sensitive channels are not the same as are the effects of real gratings. The pattern characteristics of phantoms thus do not represent a spread of energy from inducing to phantom regions of visual space or their neural representations.

Figural Aftereffect↗
PubMed1982

Assessing spatial vision of older people.

The contrast sensitivity function provides a more comprehensive and sensitive measure of spatial vision than does visual acuity. A large-sample study of contrast sensitivity during the adult years revealed that observers over age 60 have a substantial loss of sensitivity to intermediate and high frequencies. All observers wore their best possible optical correction for the test distance and were free from significant ocular pathology. We further report that older observers have difficulty perceiving faces under low contrast conditions, which is predictable from the characteristics of their contrast sensitivity functions.

Adult↗
PubMed1982

Aging and visual function of military pilots: a review.

This report reviews what is known about the effects of age on visual function and discusses the implications of age-related changes in vision for the flying performance of military pilots. Most visual functions decline to some degree with age, and the rate of decline has been roughly characterized in the general population. There is, however, virtually no data on military pilots, and extrapolation from the general population requires caution. Individual variation in the effects of age is great, and military pilots are a select group presumably in better general health than the general population. Several visual functions that decline with age seem particularly relevant to pilot performance: contrast sensitivity, dynamic acuity, recovery from glare, function under low illumination, and information processing. Vision examinations currently given to military and commercial pilots do not measure these visual functions. The feasibility of supplementing existing vision examinations with measurements of these functions should be explored; such an assessment should consider both research issues and policy implications. Research is needed on several major problems in this area. It is not possible at present to characterize well the effect of changes in visual function on the performance of complex tasks, such as flying. This report suggests several specific measures that might help characterize the effects of changes in visual function on pilot performance. Data on changes in visual functions with age should be collected from military pilots, preferably with multivariate, longitudinally designed studies. Research is suggested to assess the extent to which experienced pilots may compensate for declining visual functions and to determine how such compensation is achieved. The report suggests studies on the interaction of age with other factors, such as cardiovascular changes, that may affect performance, especially under stress.

Adaptation, Physiological↗
PubMed1981

Adaptive processing of visual motion.

Three studies relating perception of motion to stimulus uncertainty are reported. Generally, detectability declines when the observer is uncertain about the direction in which a target will move, but the visibility loss associated with direction uncertainty can be attenuated if the observer has adequate practice. This attenuation seems to depend upon the observer's ability to switch among directionally selective visual mechanisms in an adaptive fashion. The implications of these findings for models of motion detection are discussed.

Adaptation, Ocular↗
PubMed1981

Aging and low-contrast vision: face perception.

Previous work showed that despite good visual acuity, many healthy older people require more contrast to see gratings of low and intermediate spatial frequencies than do younger observers. Here we report that a daily perceptual activity, which relies on lower spatial frequency information, is also adversely affected: as compared to young individuals, many older individuals require more contrast to detect a face and to discriminate between two faces. Ocular pathology, optical changes within the eyeball, and variation in criterion are ruled out as explanations for the age-related elevation in threshold.

Adult↗
PubMed1980

Human aging and spatial vision.

The ability to see spatial structures of a wide range of sizes was measured for two groups of observers (mean ages, 18 and 73 years). All observers had good visual acuity. Although older and younger observers did not differ in ability to see targets with fine structure (high spatial frequencies), older observers were only one-third as sensitive to targets with coarse structure (low spatial frequencies) as were younger observers or to changes in criterion. Older observers were also less able than younger observers to see moving targets. The reduced sensitivity of the older observers may adversely affect routine perceptual activities, such as face recognition and visually guided postural behavior, that depend upon low spatial frequencies.

Adult↗
PubMed1980

Human vision favors centrifugal motion.

Reaction times to motion onset were measured for targets in the peripheral field. Horizontal motion away from fixation evoked faster reactions than did motion toward fixation. The difference between motion toward fixation and motion away from fixation (i) increases with stimulus eccentricity, (ii) is not found when motion is along a vertical axis, and (iii) fails to affect contrast thresholds. The anisotropy between centrifugal and centripetal motion is correlated with differences in the apparent speed of targets moving in the two directions.

Female↗
PubMed1980

Spatial vision and aging. I: Contrast sensitivity.

Contrast sensitivity functions (CSFs) were measured for two groups of healthy observers, a younger group with mean age 18.5 years and an older group with mean age 73 years. Although the two groups had virtually identical sensitivities to high spatial frequencies (gratings with narrow bars), the younger observers were three times more sensitive at low and intermediate spatial frequencies (gratings with wider bars) than were the older observers. Groups did not differ in relative sensitivity to gratings flickered at two rates, .33 and 6 Hz. The reduced sensitivity of older observers to low spatial frequencies cannot be explained in terms of optical factors or as the result of ocular pathology; it probably reflects a loss in that visual sub-system responsible for detecting low spatial frequency, temporally transient targets.

Adolescent↗