Stanislaw, H., California State University, Stanislaus, USA
Over the past 50 years, the field of human factors has moved away from attempts to "fit the man to the machine" and its concomitant emphasis on the study of individual differences. The focus now is on "fitting the machine to the man," and determining how tasks should be designed to ensure optimal performance. One application of this approach is in situations requiring the concurrent performance of two tasks. Interference in dual- task situations is predicted to be minimized by ensuring that stimuli for the two tasks are presented to separate sensory modalities and are processed using different cognitive codes. This presentation describes an extensive series of experiments designed to test contemporary models of dual-task performance. Participants performed simultaneous auditory and visual tasks that varied in difficulty, and in the cognitive codes they involved. Task priority was also manipulated. The tasks interfered with each other to a significant degree, and were affected as predicted by the difficulty and priority manipulations. However, the cognitive codes did not interfere with each other in the predicted manner. Furthermore, the effects of gender were sizeable: In many instances, male dual-task performance was better than female single-task performance. These findings suggest that current theories of dual-task performance must be revised, and that renewed emphasis should be placed upon the study of individual differences.