Dynamic visual acuity

The effects of loratadine 10, 20, and 40 mg on tests of visnomotor coordination, dynamic visnal acnity, shortterm memory, digit symbol snbstitntion, and snbjective assessments of mood have been stndied (68). Triprohdine was used as an active control and impaired performance on all the tasks presented. Loratadine 40 mg caused a significant impairment of the Digit Symbol Substitution Test and the Dynamic Visual Acuity Test, but the 10 and 20 mg doses were without effect. Loratadine did not affect objective sleepiness, as measured by Multiple Sleep Latency Test (69). In other studies of loratadine in the normal 10 mg dose the sedation rate was no different from placebo (SEDA-12, 143) (SEDA-14, 136). 

In a comparison of the adverse effects of 30, 60, and 90 mg codeine the most freqnent adverse effects, headache, drowsiness, nausea, thirst, and a feehng of strangeness, occurred after 60 and 90 mg doses only. Visuomotor co-ordination was altered with 60 and 90 mg and dynamic visual acuity with 90 mg only (15). 

Bradley CM, Nicholson AN. Effects of a mu-opioid receptor agonist (codeine phosphate) on visuo-motor coordination and dynamic visual acuity in man. Br J Chn Pharmacol 1986 22(5) 507-12. 

There are many ways to measure vision. Visual acuity is the most common one. Other familiar ones include color vision, and visual field. Less common measures that may be more closely associated with the visual needs in driving include dynamic visual acuity, visual acuity in reduced illumination and under the presence of glare, contrast sensitivity, stereopsis (the ability to see depth of field with the aid of two eyes), and motion detection (the ability to distinguish very slow movement from lack of movement). The relevance of all of these functions for driving has been evaluated, and each of these functions and the evidence for their relevance is discussed below. 

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).

Vision, as described so far, appears to be a very passive system, in the sense that stimuli impinge on our eyes, and we respond to the excitation that they evoke in the retina. Dynamic visual acuity involved some active involvement but only as far as tracking a moving target. 

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).

Dynamic visual acuity (ability to observe the direction and speed of a moving object correctly). Decline in dynamic visual acuity Difficulty in determining rate of approach and time to collision of moving objects Charman (1997) Sekuler et al. (1982) Shinar and Schieber (1991) Wist etal. (2000) Wood (2002)... 

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... 

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. 

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

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