The effects of two drugs having opposite effects on the central nervous system were investigated using a newly developed visual vigilance task. Twenty-four male volunteers (median age = 20) performed the task on three separate occasions; after consuming placebo, caffeine (200 mg), or diphenhydramine (25 mg), in a double-blind, Latin Square design. At least 2 days intervened between drug administrations. Caffeine use was restricted for 10 h and smoking for 3 h before drug administration. When compared with placebo, caffeine significantly increased the number of correct responses and decreased response times, whereas diphenhydramine decreased the number of correct responses and increased response times. Low habitual consumers of caffeine (< 100 mg/day) and non-smokers had more correct responses than did high habitual caffeine consumers (> 100 mg/day) and smokers, but only in the placebo condition. Non-smokers had faster response times than smokers only in the placebo condition. Both caffeine and diphenhydramine altered certain aspects of mood.
The effects of heat and altitude on complex cognitive tasks involved in artillery fire direction center operations were examined. Five six-man groups received one week of intensive training on tasks involving message reception and decoding, arithmetic conversions, and reception and recording of meteorological data. Each group then performed the tasks for 7 h during each of the following daily series of conditions: control (sea level, normal temperature), altitude (4300 m, normal temperature), control (sea level, normal temperature), heat (sea level, 35°C, 88% RH). All tasks were significantly and similarly affected by altitude and by heat, although individuals differed considerably in degree and type of stress response. Errors of omission greatly exceeded errors of commission. This approach, anchored firmly in basic psychological processes and theory, is considered to be of significant potential value as a technique for analyzing stress-sensitive factors in complex cognitive performance.
This study was designed to determine the comparative accuracy with which trained and untrained observers could judge distances to a target and to assess the correspondence of those judgments with other judgments, by the same observers, from photographic slides of the same target and scene at identical viewing distances. 9 experienced and 15 untrained observers estimated distances ranging from 600 to 1550 m in 50-m increments. Photographic slides were made of the target at each distance and, 1 mo. later, observers made the same judgments from the slides. It was found that averages of the group's judgments in the field very closely approximated true target distances. However, judgments of the individual observers were so erratic and inaccurate as to render questionable the interpretation of those averages. In addition, while the averages of the group indicated that judgments from two-dimensional slides could be substituted fro three-dimensional real-world judgments, detailed analysis of the individual observers' performances dramatically contradicted this conclusion.
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