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R Sekuler

Publications and source records attributed to R Sekuler.

At least 19 recordsLinked to original sources
PubMed1992

Temporal and spatial integration in dynamic random-dot stimuli.

Random-dot cinematograms comprising many different, spatially intermingled local motion vectors can produce a percept of global coherent motion in a single direction. Thresholds for discriminating the direction of global motion were measured under various conditions. Discrimination thresholds increased with the width of the distribution of directions in the cinematogram. Thresholds decreased as the duration of area of the cinematogram increased. Temporal integration for global direction discrimination extends over about 465 msec (9.3 frames) while the spatial integration limit is at least as large as 63 deg2 (circular aperture diameter = 9 deg). The large spatial integration area is consistent with the physiology of higher visual areas such as MT and MST.

Discrimination, Psychological↗
PubMed1992

Vision, aging, and driving: the problems of older drivers.

Although there are well-recognized declines in visual functioning with age, their contribution to the problems of older persons on tasks in the natural environment, including driving, are largely unknown. Adults ranging in age from 22-92 years were surveyed in regard to their visual difficulties when driving and performing everyday tasks. The visual problems of drivers increased with age along five different visual dimensions: unexpected vehicles, vehicle speed, dim displays, windshield problems, and sign reading. Several of the age-related visual problems that were reported appear to be related to the types of automobile accidents more common among older drivers. The study also replicated the findings from an earlier investigation of non-driving tasks that showed visual declines with age on five dimensions: visual processing speed, light sensitivity, dynamic vision, near vision and visual search. These findings indicate promising areas of research regarding the effects of visual aging on tasks in the natural environment.

Adult↗
PubMed1991

Using metamers to explore motion perception.

We examined conditions under which two quite different types of random-dot cinematograms were perceptually matched. In one stimulus type, directions of motion were defined by a uniform distribution; in the other, directions were drawn from a discrete set of just a few, widely separated directions. Cinematograms whose range of uniformly distributed directions lay between 180 and 270 deg could be matched by cinematograms containing just 6-10 discrete directions. The number of discrete directions required for a match was a nonmonotonic function of the range of directions present in the other cinematogram. The results are consistent with a line-element model in which the outputs of 12 direction-selective mechanisms, each with a half-amplitude half-bandwidth of 30 deg, are combined nonlinearly to produce the percept of motion.

Humans↗
PubMed1990

Assimilation and contrast in motion perception: explorations in cooperativity.

Motions within one region of the field influence motion seen elsewhere. To explore this phenomenon we used cinematograms comprised of alternating strips within which dots (i) tended to move in one direction, or (ii) moved in random directions (dynamic noise). When alternating strips were narrow, motion in one direction induced a similar direction of illusory motion in the adjoining dynamic noise (assimilation); when alternating strips were wide, motion tended to induce an illusory opposed motion in the dynamic noise (contrast). Since this illusory motion exhibits hysteresis, it probably results from spatially distributed, cooperative processes. The shift from assimilation to contrast, as the cinematogram's strips increase in size, suggests that facilitatory and inhibitory influences of the network extend over different distances.

Contrast Sensitivity↗
PubMed1990

How the visual system detects changes in the direction of moving targets.

To determine how the visual system represents information about change in target direction, we studied the detection of such change under conditions of varying stimulus certainty. Target direction was either held constant over trials or was allowed to vary randomly. When target direction was constant the observer could be certain about that stimulus characteristic; randomizing the target direction rendered the observer uncertain. We measured response times (RTs) to changes in target direction following initial trajectories of varying time and distance. In different conditions, the observer was uncertain about either the direction of the initial trajectory, or the direction of change or both. With brief initial trajectories in random directions, uncertainty about initial direction elevated RTs by 50 ms or more. When the initial trajectories were at least 500 ms, this directional uncertainty ceased to affect RTs; then, only uncertainty about the direction of change affected RTs. We discuss the implications of these results for (i) schemes by which the visual system might code directional change; (ii) the visual integration time for directional information; and (iii) adaptational processes in motion perception.

Attention↗
PubMed1990

Self-reported visual problems of older drivers.

We conducted a survey in order to gain insights into the reasons older persons decide to give up driving. Our survey focused on vision. We probed the relationship between visual deficiencies and driving status by asking older people about the problems they encountered while performing routine visual tasks. The results showed that older persons who had recently given up driving reported more visual problems than did their driving counterparts. These problems related to difficulties in dynamic vision, visual processing speed, visual search, light sensitivity, and near vision. The results suggested that older persons are sensitive to their own visual deficits and that this awareness influences decisions about driving.

Activities of Daily Living↗
PubMed1989

Direction perception in complex dynamic displays: the integration of direction information.

We created random-dot cinematograms in which each dot's successive movements were independently drawn from a Gaussian distribution of directions of some characteristic bandwidth. Such a display, comprising many different, spatially intermingled local motion vectors, can produce a percept of global coherent motion in a single direction. Using pairs of cinematograms, direction discrimination of global motion was measured under various conditions of direction distribution bandwidth, exposure duration, and constancy of each dot's path. A line-element model gave an excellent account of the results: (i) over a considerable range, discrimination was unaffected by the cinematogram's direction distribution bandwidth; (ii) only for the briefest presentations did changes in duration have an effect; (iii) so long as the overall directional content of the cinematogram remained unchanged, the constancy or randomness of individual dots' paths did not affect discrimination. Finally, the line-element model continued to give a good account of the results when we made additional measurements with uniform rather than Gaussian distributions of directions.

Discrimination, Psychological↗
PubMed1988

Visual changes in daily life throughout adulthood.

A pair of surveys asked healthy adults about their everyday visual problems. Participants ranged in age from 18 to 100 and were screened for major visual impairment. Respondents rated the frequency of difficulty they had performing visual tasks such as reading, recognizing objects, picking out a face in a crowd, seeing in dimly lit environments, seeing moving objects, and so on. The surveys revealed five dimensions that declined with increasing age: visual processing speed, light sensitivity, dynamic vision, near vision, and visual search. The percentage of respondents reporting a decline in these visual dimensions increased two- to sixfold across the adult life span. Varying rates of visual decline for different tasks suggest that various aspects of vision age at different rates.

Activities of Daily Living↗
PubMed1987

Direction-specific improvement in motion discrimination.

With training, an observer's ability to discriminate similar directions of motion gradually improves. A series of studies reveals that this improvement, (1) is restricted to the trained direction and other, similar directions, (2) persists for at least several months, (4) shows appreciable, but not complete, transfer between the two eyes, and (5) is largely restricted to the stimulated region of the field. Moreover, the improvement in direction discrimination does not produce a concomitant change in detection thresholds. In all likelihood, most of the improvement in direction discrimination represents a change in visual function, rather than changes in nonsensory processes.

Discrimination, Psychological↗
PubMed1987

Ocular fixation control as a function of age and exposure duration.

In previous work we reported that fixation stability did not deteriorate in older adults over relatively long viewing durations. In the present study we reanalyzed the data to examine potential aging effects on fixational control for viewing durations typically used in psychological experimentation. Monocular eye movements were recorded in 12 older and 12 younger observers using a dual Purkinje image technique, while observers fixated a stationary target. The two-dimensional scatter of eye positions was measured during nine viewing durations ranging from 100 ms to 12.8 s. Fixational control of the two groups was comparable at all of the viewing durations. Both younger and older observers were able to maintain fixation within an area several times smaller than the size of the fovea. Implications for aging studies that use briefly presented visual stimuli are discussed.

Adult↗
PubMed1987

A "hidden" deficit in central vision in diabetic pan-retinal photocoagulation patients.

Adaptation ability in the center of vision was tested in diabetic patients treated with pan-retinal photocoagulation for diabetic retinopathy and in normal control subjects. This was accomplished with a specially designed contrast sensitivity testing regimen. Patients with retinopathy showed "hidden" deficits, losses in adaptation ability that could not be measured by standard clinical tests, such as visual acuity. This new test thus quantifies a previously unmeasured visual problem that affects the everyday visual function of these patients.

Adaptation, Ocular↗
PubMed1986

Improving visual perception in older observers.

Younger observers (M = 21 years) proved to be better than older observers (M = 68 years) at discriminating one direction of motion from another, highly similar one. Several days' practice steadily improved performance for both groups equally. Improvement was well restricted to the direction with which that observer practiced, and the full gains were retained for at least 1 month. Control measurements with various degrees of optical blur demonstrate that direction discrimination does not require a well-focussed retinal image. This rules out optical factors as the potential cause of the prepractice differences between groups.

Adult↗
PubMed1986

Visual localization: age and practice.

Older people seem to be highly susceptible to the distracting effects of irrelevant or interfering visual stimuli. We studied this susceptibility using visual displays in which observers had to localize the position of a face. When a face appeared in isolation, observers of all ages did equally well; when distracting stimuli surrounded the face, older observers alone performed poorly. Brief periods of practice produce substantial and long-lasting improvement in performance.

Adult↗
PubMed1986

Contrast sensitivity during provoked visual impairment in multiple sclerosis.

Many patients with multiple sclerosis have subjective visual complaints that are intensified by exercise (Uhthoff's symptom). We report a case demonstrating the utility of contrast sensitivity testing in such visual complaints. Contrast sensitivity was measured before and after exercise in a multiple sclerosis patient with Uhthoff's symptom and in two healthy control subjects. A short exercise period reduced the patient's contrast sensitivity for some target sizes, but had no effect on his visual acuity; a longer exercise period produced a greater, more uniform loss of contrast sensitivity and also reduced visual acuity. Contrast sensitivities and visual acuities of the control subjects were not affected by exercise.

Adult↗
PubMed1986

Visual fixation stability in older adults.

Visual fixation of a small, stationary target was measured in 12 young observers (mean age = 22 yr) and in 12 older observers (mean age = 70 yr). The two groups' fixation behavior did not differ on various dimensions of fixation stability: mean fixation area, intra-subject variability, or changes in fixation over successive test periods. Connections between these results and age-related changes in the oculomotor system are discussed.

Adult↗
PubMed1985

Role of the crystalline lens in the spatial vision loss of the elderly.

This study examined the contribution of the crystalline lens to the spatial contrast sensitivity loss experienced by many healthy older adults. Spatial contrast sensitivity was measured in three groups of adults: older adults who had undergone cataract extraction and intraocular lens (IOL) insertion; older adults who were in good ocular health (agematched to the first group); and young adults also in good ocular health. Older adults had decreased contrast sensitivity at higher spatial frequencies compared to young adults, agreeing with earlier reports. In addition, both groups of older adults had similar contrast sensitivity at higher frequencies, contrary to what would be expected if the aged, noncataractous crystalline lens significantly hampered contrast transfer in the healthy older eye. Results imply that the crystalline lens is not primarily responsible for the spatial sensitivity loss of healthy older adults. Furthermore, these data indicate that for at least some IOL patients, spatial vision can be restored to a level similar to their agemates who have no history of lens opacity or ocular disease.

Adult↗