Laser Glare in the Cockpit: Psychophysical Estimates versus Model Predictions of Veiling Luminance Distribution.

Two methods for estimating the visual effects of light scattered from a laser glare source were compared: (1) a veiling luminance (VL) model that convolves a radiometric scan of the corneal light distribution with a point-spread function to calculate the retinal distribution and (2) psychophysically determined equivalent background luminance (EBL). For six subjects, detection thresholds for a 12-arc-min-diameter test spot were measured at 24 points in the glare field (4 quadrants x 6 eccentricities between 0.25 and 8 deg). Measured Weber fractions were used to calculate EBL's for each test point. Output of the VL model matched the EBL data well, but underestimated the EBL at the smallest (0.25-deg) eccentricity and overestimated it at eccentricities from 1 to 4 deg. This model can be a useful predictor of visual decrements in a variety of glare situations.

Effects of a laser-induced temporary scotoma on target acquisition performance.

Lasers commonly used in industry and the military are increasingly being recognized as possible hazards to vision and visually guided tasks. This study examined the effects of laser-induced visual loss on target acquisition performance. An argon laser was used to produce a temporary central scotoma. Observers searched for variable-contrast aircraft that were embedded in backgrounds of differing complexity. The laser exposures increased acquisition times 2 to 12 times over baseline levels, indicating that the degree of visual deficit was task dependent. Acquisition time increased as background complexity increased and target contrast decreased. However, target motion facilitated acquisition performance and mitigated the laser effect. Although contrast had a systematic effect on acquisition performance, it was clear that factors other than contrast contributed to target visibility. Other factors that may have affected visibility included distractors and masking effects introduced by the structured backgrounds.

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.

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.

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.

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.

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.