The effect of prolonged driving on the vigilance of Army truck drivers was srudied in cooperation with the American Association of State Highway Officials. A decrement in performance was predicted on the basis of long shifts, a highly repetitive cask, reported physical fatigue, and vehicle noise and vibration.Ss were 42 enlisted Army truck drivers (Men = 23 yr.). Ss drove large, heavily loaded commercial trucks repeatedly around experimental highway driving loops in 9-hr. shifts. One shifc consisted of 7 hr. of actual driving time sequenced in 6 driving periods of 90, 90, 90, 60, 45, and 30 min. Four 15-min. rest pauses and one 40-min. meal break were interspersed among driving periods. Ss monitored a visual discrimination task continuously during driving. Visual display units of 15 lights arranged in a circular fashion were mounted on truck dashboards. Signals appearing in 6 "critical" (red) panels were responded to by means of a foot pedal. Signals appearing in the 9 "noncritical" (white) panels were to be ignored. Critical signals were programmed at the rate of 30 per hour; inter-signal intervals ranging from 5 to 390 sec. occurred in random order. Non-critical signals appeared at the rate of 90 per hour. Signals were oP 1-sec. duration.The absolute level of vigilance was high. Critical signal detections aver---aged 83% for all driving periods combined. False detections averaged only 4% for all driving periods.There was no between-period performance decrement ( F = 1.21; df = 5/200; P > .25). N o measure of within-period decrement was possible. The absolute detection levels indicated, however, that any decrement that may have occurred within periods was relatively small.Individual differences in critical detection scores were wide (Range = 21 to 100%) and highly reliable (odd versus even driving periods, roc = .93; df = 40; P < .01). The range of individual scores became greater as the vigil progressed, resulting in a significant increase in inter-subject variance from --Driving period 1 to 6 ( t = 3.17; df = 41; P < .01).In view of past research, one possible explanation for the present lack of decrement is the relative complexity of the task. Performance decrements have been found repeatedly for simple (single signal source) vigilance tasks (Baker, 1959), but the evidence for decrement in complex (multiple signal source) vigilance tasks is scant (Frankmann & Adams, 1962 ). Also, the experimental task may have served as a stimulant co rather than a measure of vigilance performance.REFERENCES BAKER, C. H. Towards a theory of vigilance.
A visual coincidence timing task was used to compare the level of performance (constant error) and the intra-individual variability of 100 normal and 100 educable mentally retarded children. The mean performance of the intellectually normal children on this task was significantly superior to that of the retarded children, and the intra-individual variability of the latter was significantly greater than that of the former. The hypothesis that high intra-individual variability and depressed level of performance are closely associated was not supported.
This study assessed the stability of identification of severe underachieving readers as a function of the tests used in the process of identification. The recognition of "stability of identification" over a number of tests would provide evidence to support the notion of severe underachieving readers being a "naturally occurring" group rather than being an artefact of the tests chosen to so identify. Three hundred boys and 278 girls, between the ages of 9 and 11 years, were given tests of non-verbal intelligence and reading. The regression approach, with chronological age and non-verbal intelligence as the predictor variables, was used to calculate 16 residual distributions. Multiple comparisons of the lowest 50 places over each paired combination of the 16 residual distributions offered qualified support for the notion that severe underachieving readers are indeed a "naturally occurring" group, rather than being test specific.
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