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ABSTRACT: The assured clear distance ahead (ACDA) rule holds the operator of a motor vehicle responsible to avoid collision with any obstacle that might appear in the vehicle's path. Although widely considered a fundamental responsibility of safe driving, the ACDA rule is routinely violated by most drivers under nighttime conditions. This fact does not necessarily imply reckless disregard for public safety, however. Rather the troublesome discrepancy between drivers' behavior and the principles of safe driving may be understood in terms of vehicle operators' lack of awareness of selective losses of visual function that occur in low light. This theoretical perspective holds basic implications both for traffic regulations and for assessment of liability in nighttime road accidents.
Accident Analysis & Prevention 01/1998; 30(1):93-9. · 1.87 Impact Factor
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H W Leibowitz
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ABSTRACT: To illustrate the interdependence between the solution of practical problems and the search for fundamental mechanisms, their relationship within the contexts of the history of night myopia and the problem of nighttime traffic accidents is discussed. Night myopia, or nearsightedness at night, which has been a problem since the late 18th century, was shown to be the result of a recently discovered oculomotor mechanism, the intermediate resting position of accommodation. With this knowledge, the handicap of nearsightedness at night ( a major problem in nighttime viewing such as driving and military operations) is readily amenable to solution. Recent developments in our knowledge of the functional significance of the nervous system has led to an increased understanding of the cause and to amelioration of nighttime traffic accidents. These developments illustrate the symbiotic relationship between basic and applied research and the benefits to be gained by consideration of both objectives.
American Psychologist 05/1996; 51(4):366-70. · 6.87 Impact Factor
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ABSTRACT: The effects of tilted and vertical optokinetic drum stripes on self-reports of motion sickness and electrogastrograms (EGG's) were measured to investigate possible differences in the effects of stripe orientation. The EGG is a non-invasive measure of gastric myoelectric activity. The normal frequency is 3 cpm, and dysrhythmic 4-9 cpm activity, gastric tachyarrhythmia, has been found to be associated with motion sickness symptoms, particularly nausea. It is theorized that these symptoms are related to a sensory mismatch between the visual and vestibular systems elicited by the drum's rotation.
We hypothesized that tilted stripes would elicit more symptoms than vertical stripes due to an additional sensory mismatch between the visual and vestibular verticals.
We divided 45 subjects into 2 stripe orientation groups: Vertical, and Tilted 15 degrees in the direction of drum movement. After the subject sat inside the stationary drum for a 6-min baseline, the drum was rotated (10 rpm) for a maximum of 16 min, followed by a 6-min recovery period. Throughout the experiment we measured the subjects' EGG's and subjective symptoms of motion sickness (SSMS).
During rotation and recovery, gastric tachyarrhythmic activity was higher for subjects in the Tilted condition; the difference between stripe conditions was significant during rotation (p < 0.05). There were, however, no differences between SSMS scores.
Off-vertical stripes increase the dysrhythmic activity of the stomach that often precedes or accompanies nausea and other symptoms of motion sickness.
Aviation Space and Environmental Medicine 02/1996; 67(1):30-3. · 0.88 Impact Factor
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ABSTRACT: The primary objective of the three studies completed was to determine whether motion sickness susceptibility was related to different measures of visual persistence. In these studies, motion sickness susceptibility was determined by exposing the subjects to a rotating optokinetic drum while the electrogastrogram and subjective indices of motion sickness were recorded concurrently. Subjects were tested for persistence of visual cues using one or more of the following procedures: a walking task, a computer simulation task, a temporal measures of vection, and three measures of spatial abilities. In Experiment 1, 50 subjects were tested; in Experiment II, 24; and in Experiment III, 45 were studied. Mixed results were obtained in the three experiments, but in general, those subjects who showed greater persistence, reported more severe symptoms of motion sickness. In addition, those subjects who did poorly on a water level test of spatial abilities, reported greater symptoms of motion sickness. We continue to believe that perceptual/cognitive style is germane to the issue of individual differences in responding to rapidly changing visual environments.
07/1995;
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ABSTRACT: Contrast sensitivity involves distinguishing threshold luminance differences and is usually assessed using static sine-wave gratings over a range of different spatial frequencies. The purpose of this study was to determine the effects of various levels of acute alcohol intoxication on contrast sensitivity to stationary and moving sine-wave gratings. Moving gratings required the subjects to make pursuit eye movements. A secondary goal was to investigate whether any alcohol-related effects were associated with any measures of intoxication.
Male volunteers (N = 8) participated in three counterbalanced, double-blind, testing sessions (low alcohol, moderate alcohol and placebo) plus a control session with no beverage. Breath alcohol concentration and two subjective measures of intoxication were measured for each subject. Static and dynamic contrast sensitivity were determined for electronically generated sine-wave gratings that were either stationary or traveled in a circular path with a diameter of 9 cm (3.7 degrees) at 51.7 rpm, thus requiring the subject to make smooth pursuit eye movements.
The mean blood alcohol concentration measured in the moderate alcohol condition was 0.043% and in the low alcohol condition 0.011%. Moderate dose alcohol consumption significantly impaired both static and dynamic contrast with a greater effect for moving targets.
Objective and subjective measures of intoxication were unrelated to the alcohol-related losses in contrast sensitivity. Although most states currently prohibit driving with BACs of 0.08-0.10%, the present data indicate reliable visual impairment at approximately half of that level (.44%).
Journal of studies on alcohol 06/1995; 56(3):261-6.
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ABSTRACT: Although the eyes and the heart serve very different purposes, each receives autonomic innervation. Capitalizing on recent theoretical and technological innovations in the understanding and assessment of oculomotor and cardiovascular behavior, three experiments measured behavioral covariation between the oculomotor and cardiovascular systems. Measures of dark focus and dark vergence indexed oculomotor tone, and the spectral decomposition of variations in heart rate indexed cardiovascular control mechanisms. In Experiment 1, individual differences in cardiovascular parameters could predict individuals' dark vergence (R2 = .806) but not their dark focus (R2 = .404). In Experiment 2, the same parameters were measured from subjects who experience either panic attacks (n = 11) or blood phobia (n = 9). Heart rate was positively correlated with dark vergence and the two subject groups were separable based on both oculomotor and cardiovascular variables. Using a within-subjects approach, Experiment 3 found that both dark vergence and dark focus tended to be nearer during sympathetic dominance of the heart than during parasympathetic dominance, within-subjects variations in cardiovascular parameters could predict dark focus, and between-subjects variations in interbeat intervals could predict dark vergence. Shared patterns of autonomic activation may be responsible for this eye-heart link.
Integrative Physiological and Behavioral Science 04/1995; 30(1):46-67. · 2.43 Impact Factor
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ABSTRACT: Contrast sensitivity was measured for 12 healthy young males while sober, after ingestion of an alcohol placebo, and after ingestion of alcohol (95% grain alcohol; mean estimated blood alcohol level = .088%). Observations were made for both stationary gratings and gratings that traveled through a circular path and required pursuit eye movements. The significant alcohol-related reduction in contrast sensitivity was 2.6 times greater for moving (.29-log-unit reduction) than for stationary gratings (.11-log-unit reduction). The loss in contrast sensitivity for the moving gratings of high spatial frequency (12 cpd) was particularly severe (.37 log unit). Estimated blood alcohol level was correlated with the loss in contrast sensitivity for moving gratings (r = .61), but not with the loss for stationary gratings. Estimated blood alcohol level was strongly correlated with the difference between the loss in contrast sensitivity to moving and stationary gratings (r = .75). These results are consistent with reports that alcohol consumption degrades the ability to make pursuit eye movements. Subjects' perceived intoxication level was not a reliable predictor of any index of visual performance.
Perception & Psychophysics 10/1994; 56(3):261-7. · 1.37 Impact Factor
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ABSTRACT: An earlier study from our laboratory provided initial support for the hypothesis that information facilitating visual guidance persists in the absence of retinal stimulation. The present study supports and extends this hypothesis with three experiments in which visually occluded subjects positioned a point of light at the location of a previously viewed target and also walked in the direction of a previously viewed path. In both tasks, performance was possible following occlusion, and in all cases, performance slowly and significantly decreased with longer durations of occlusion. This decay in performance was gradual and had a "half-life" of greater than 15 sec. Absolute performance was correlated across tasks. The effect of occlusion on absolute error in the localization performance was relatively stable within individuals over a 3-week period. The biological utility of guidance information persistence is discussed along with implications for space constancy, illusions of motion, and problems of disorientation.
Perception & Psychophysics 11/1993; 54(4):431-8. · 1.37 Impact Factor
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ABSTRACT: Examples of the inaccessibility of mental processes by means of verbal recall are described with particular reference to the accuracy of quantitative estimates of size, distance, and duration. Evidence is presented in support of the hypothesis that nonverbal retrieval techniques are more accurate than quantitative verbal estimates. Implications for the judicial process are considered.
Perception 02/1993; 22(9):1051-60. · 1.31 Impact Factor
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ABSTRACT: This study was designed to establish reference data for the effects of head position and visual conditions on the standing posture of healthy women ages 55 to 70. Center of pressure (CoP) data were analyzed using ANOVA models. Total CoP displacement was 45% greater (significant, p less than .05) when the subjects stood with their heads back and their eyes closed, as compared to standing looking straight ahead. Visual surrounds consisting of vertical visual cues resulted in less postural sway (PS) than surrounds made of horizontal visual cues (significant, p less than .05 for anteroposterior CoP range). Experimentally reduced visual acuity resulted in greater PS, while changes in ambient lighting and spatial frequency of visual cues affected PS minimally. These results suggest that a reduction in the height of shelving, and the provision of high-contrast visual cues and vertical geometric patterns are potential intervention strategies to optimize vestibular sensory input and visual orientational cues for the maintenance of stability during stance.
Journal of Gerontology 10/1992; 47(5):M151-8.
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ABSTRACT: Contrast thresholds for sinusoidal gratings of 1.5-18 cpd were measured in young (M = 24 years) and older adults (M = 69 years). Thresholds were determined for stationary gratings, and for gratings that traveled along a circular path at 5, 10, and 15 deg/sec. For static gratings, age differences in thresholds were greater for intermediate and higher spatial frequencies. Grating motion increased thresholds for all observers, but older adults exhibited threshold increases at lower target velocities than the young. Age differences in velocity effects were generally greater at intermediate and higher spatial frequencies. Results are discussed in relation to age changes in temporal resolution and smooth pursuit gain.
Journal of Gerontology 06/1992; 47(3):P172-5.
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ABSTRACT: Despite the documented health hazards associated with stair descent, the mechanisms of falling on stairs remain relatively unexamined. The objectives of this study were to define kinematic variables that could be used to describe foot-stair spatial relationships during the mid-stair phase of stair descent, and to investigate the effects of various visual and environmental conditions on those variables in a group of 36 healthy women between the ages of 55 and 70. Foot clearance and foot placement were measured through high-speed film analysis. Clearance between the foot and the stair during swing phase was small under all visual conditions. Degraded visual acuity had a significant effect on cadence, foot placement, and foot clearance, but visual surround conditions did not. The kinematic variables used in this experiment may be helpful in future studies to assess the results of interventions aimed at reducing the frequency of falls on stairs.
Journal of Gerontology 12/1991; 46(6):M188-95.
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ABSTRACT: Ambient illumination during civil twilight, which occurs approximately a half hour before sunrise and after sunset, has traditionally been characterized as posing no restriction on normal visual activities. However, consideration of the selective degradation of visual-recognition functions and the concurrent sparing of visual-guidance functions at the prevailing (relevant) luminance levels suggests that this characterization of civil twilight is no longer appropriate, particularly in light of the visual demands of industrialized society. Rather, special notice should be taken of the implications of selective degradation of visual recognition during civil twilight for traffic safety and other visually demanding hazardous tasks.
Applied Optics 08/1991; 30(24):3501-3. · 1.41 Impact Factor
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ABSTRACT: When luminance is lowered, both vergence and accommodation tend to shift toward different and individually characteristic resting postures, commonly referred to as dark-vergence and dark-focus. In order to determine the luminance level at which these two mechanisms correspond to a target distance, subjects viewed a light spot 0.4 mm in diameter, corresponding to 1.4 to 2.7 min arc, located at the individually determined dark-focus position. As the luminance of a binocularly viewed spot increased, accommodation did not change significantly from the target distance. However, fusional vergence gradually shifted from the dark-vergence to the target position. The critical luminance level at which the 2 responses were coupled for the 12 observers ranged from 0.01 to 0.45 cd/m2, with distinct individual differences. In a second experiment, the target was positioned at distances different from the dark-focus and luminance was set at 0.5 and 1.0 log unit higher than the subject's critical luminance level. At lower luminance levels, mononuclear focus tended to remain at the individual dark-focus, whereas the binocular focus tended to correspond to the target distance. These differences can be attributed to vergence accommodation. Previous studies on night myopia reported that a negative correction based on one-half of the individual dark focus was superior to a full dark-focus correction. The present results suggest that this difference is due to vergence accommodation and that the optimum correction for night myopia depends, in part, on the critical luminance level for activation of fusional vergence.
Optometry and Vision Science 04/1991; 68(3):220-5. · 2.11 Impact Factor
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ABSTRACT: Automobile accidents among older adults may be related to difficulties in judging the speed of other vehicles. To examine this possibility, 3 groups of observers in the young adult, middle-aged, and older adult age ranges were asked to estimate the velocity of an isolated automobile traveling at 15-50 mph (24-80 kph). Across all age groups, perceived and actual velocity were related by a power function with an exponent of 1.36. Age was significantly and positively correlated with intercepts, but negatively correlated with exponents; that is, older observers showed less sensitivity to changes in actual velocity. Results bear on the issues of ontogenetic changes in accident involvement and sensitivity to motion.
Psychology and Aging 04/1991; 6(1):60-6. · 2.73 Impact Factor
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ABSTRACT: Approximately 60% of healthy human subjects experience motion sickness when exposed to a rotating optokinetic drum. The purpose of the present study was to determine the effects of certain visual factors on susceptibility to motion sickness. Vection data (illusory self-motion), horizontal eye movement recordings, subjective motion sickness report, and a measure of gastric myoelectric activity (electrogastrogram, EGG) were obtained from 45 subjects, who were randomly divided into the following three groups: a control group that observed the entire visual field with no fixation, a group that fixated on a central target, and a third group that had a visual field restricted to 15 degrees. The experimental session was divided into the following three 12-min periods: baseline, drum rotation, and recovery. The results showed that fixation greatly reduced nystagmus and slightly reduced vection. The restricted visual field slightly reduced nystagmus and greatly reduced vection. Both of these manipulations significantly reduced symptoms of motion sickness and tachyarrhythmia, the abnormal gastric myoelectric activity that usually accompanies nausea.
Aviation Space and Environmental Medicine 09/1990; 61(8):712-5. · 0.88 Impact Factor
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ABSTRACT: Two experiments examined the link between vergence effort and subjective reports of visual fatigue following prolonged near work. In Experiment 1, dark vergence and reports of visual fatigue symptoms associated with computer use were measured in 104 persons. Dark vergence was significantly correlated with four of six symptoms of visual fatigue. In Experiment 2, 16 subjects who exhibited clear "Heuer effects" (systematic gaze-related changes in dark vergence) read from a video display terminal (VDT) at a distance of 20 cm for 60 min under two gaze elevation conditions: 20 deg above and 20 deg below a baseline gaze elevation. This manipulation was designed to vary the amount of vergence effort required to fixate the VDT. Results indicate a positive relation between vergence effort and visual fatigue both within and between subjects, and that prolonged near work leads to decreased vergence accuracy at far distances. Implications for VDT workstation design are discussed.
Human Factors The Journal of the Human Factors and Ergonomics Society 07/1990; 32(3):341-57. · 1.19 Impact Factor
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ABSTRACT: The contrast sensitivity function (CSF), although containing more information than traditional measures of acuity, has found difficulty gaining clinical acceptance. The hesitancy of clinicians to adopt the CSF stems, in part, from the fact that it is not as readily interpreted as is acuity. In order to facilitate such interpretation, five indices of spatial vision which are derivable from the CSF were examined in a sample of 287 persons aged 5 to 85 years. All indices were found to be both age-sensitive and strongly related to each other, but bandwidth of the CSF was chosen as a practical index for clinical settings. In a second study, acuity and CSF bandwidth were measured under 0 to +/- 1 D optical blur. It was found that the correction providing best acuity also maximized CSF bandwidth, and that bandwidth was more sensitive to optical blur than was acuity. Results support the assertion that CSF bandwidth is a readily interpreted index of spatial vision that can be measured efficiently within the context of clinical refraction.
Optometry and Vision Science 05/1990; 67(4):260-7. · 2.11 Impact Factor
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ABSTRACT: Refractive error was measured at 0 degrees to 40 degrees temporal to fixation in 10 young adults (M age = 26 years) and 10 older adults (M age = 63 years). Older adults exhibited a greater amount of sphere (i.e., overall) error, but no more so in the periphery than in the fovea. Although age differences were small, younger adults were found to exhibit more peripheral astigmatism than the older adults. Discrepancies between obtained results and those of Millodot (1985) may be attributed to the relationship between peripheral astigmatism and presenting refractive status. Alternatively, a two-mechanism model of age-related change in lens curvature is capable of accounting for across-study outcome differences. Recommendations are made concerning optimal viewing conditions for the study of age differences in visual perceptual processes.
Psychology and Aging 10/1989; 4(3):372-5. · 2.73 Impact Factor
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Human Factors The Journal of the Human Factors and Ergonomics Society 01/1989; 30(6):677-87. · 1.19 Impact Factor
