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Four tasks were tested in single and pairwise combined performances to investigate their mutual interference. The results demonstrate that functionally dissimilar tasks, in terms of the activities required in processing and responding, can be performed together with much less decrement than functionally identical tasks. The short-term memory function, furthermore, is extremely disruptive when required in one or both of two simultaneously performed discrete, reaction-time tasks.
Robert A. North (Sat,) studied this question.