Acuity static

Figure 32-11 Visual field results obtained with static threshold testing in a 71-year-old woman with acute class 6 Graves ophthalmopathy. (A) Central and paracentral defects in left visual field are associated with 20/60 (6/18) visual acuity...

By their very nature, tasks which enable one to measure spatiotemporal accuracy are complex or higher-level sensory-motor tasks. These place demands on a large number of lower-level PRs such as visual acuity, dynamic visual perception, range of movement, strength, simple reaction times, acceler-ation/deacceleration, static steadiness, dynamic steadiness, prediction, memory, open-loop movements, concentration span, attention switching, that is, central executive function or supervisory attentional system (multitask abilities), utilization of preview, and learning. 

The implication of the third conclusion is that a small deterioration in static acuity for a young driver may not have very severe implications for his or her dynamic acuity. But the same small deterioration in static acuity for an older driver - one that would still qualify that driver to drive - may be associated with a severe deterioration in dynamic visual acuity, and one that is arguably much more relevant to driving. Similar very large age-related deteriorations in dynamic acuity relative to static acuity were obtained in a later study on 890 Indiana drivers (Shinar, 1977). 

All that remains now is to actually demonstrate that dynamic visual acuity is relevant to driving safety and crash involvement or at least more relevant than static visual acuity. This in fact was demonstrated by Burg (1968) and Shinar (1977) on California and Indiana drivers, respectively. With the very large number of drivers involved in both studies, even a small effect of little practical significance can be statistically significant. And in fact the correlations between dynamic visual acuity and crashes - while they were statistically significant and higher than the correlations between static visual acuity and crashes - were still quite low on the order of r = 0.1 in both studies. 

Figure 4-4. Dynamic visual acuity as a function of age and angular speed of the moving target, relative to static visual acuity (from Burg, 1966, with permission from the American Psychological Association).

The elusiveness of such relationships and explanations for our inability to find them was offered in a review of the state of the art in this area by Westlake (2000). It is difficult to establish the relation between visual impairment and crash rates because visually impaired drivers tend to restrict their driving habits and change their behaviour to compensate for their visual loss. Crashes are fortunately rare events with multiple causes, and the effects of a driver s visual impairment are dwarfed by other factors such as the annual mileage driven, the driver s age, inattention, intoxication, and speeding. Furthermore, it is unsurprising that it is difficult to predict crash rates from measures of static visual acuity and the peripheral visual... 

Burg, A. (1966). Visual acuity as measured by dynamic and static tests a comparative evaluation. J. Appl. Psychol. 50(6), 460-466. 

Figure 7-12. Age related deterioration (a) in static acuity under optimal (photopic), low illumination (Mesopic), and glare conditions, and (b) in dynamic visual acuity, ability to detect motion across the visual field (Central Angular Motion - CAM), and forward motion (Central Movement in Depth - CMD) (from Shinar and Schieber, 1991, data from Shinar, 1977).

Clayton (1976) reviewed 35 studies that examined the effects of different depressants (barbiturates, non-barbiturates, tranquilizers, and antidepressants) on various skills. After grouping the effects into sensory/perceptual, cognitive, and motor fimctions, it appeared that most drugs did not produce significant impairments on most of the tasks. However, some effects were discemable. Of the sensory/perceptual fimctions, critical flicker fusion and dynamic visual acuity were impaired by several of the drugs whereas static acuity, depth... 

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