Abstract
Subjects performed two rapidly successive tasks. They first pressed a key to stop a digital counter at one of three stopping times. The key-press was followed after a variable interval by the presentation of one of three lights, which required a choice response. 20 students and 20 flight cadets participated in the main experiment. Both responses showed impairment in the dual-task condition. The delay of the choice response was affected by the stopping time and by the interval between the key-press and the second stimulus. Complete refractoriness for a period of 200 msec. was observed only for the shortest stopping-time. In the other conditions, the delay of the second response decreased gradually with decreasing response-stimulus interval. The results do not support single-channel theory and are better explained by a capacity-sharing model on the assumption that preparation for a choice-response requires effort.
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