How to Reduce Manual Response Interference in the Multiple Task Environment

Three groups of women performed two independent tasks at the same time. Both required a manual response. All groups performed the same response with the right-hand; with the left-hand the response was either, depending on the group, identical to the right hand (depressing a button), similar (pushing a lever) or different (rotating a knob). The amount of interference between the two tasks was found to depend on the similarity of the movements required by the two hands to execute their appropriate responses. This effect was present whether the execution of the secondary response coincided with the primary response, preceded it or followed it. Thus a response can be inhibited by the fact that a similar response has just been made, or by the knowledge that a similar response will have to be made in the near future. It appears that performance in multitask environments where the operator is under speed stress will be impaired if operators are required to make similar responses on independent tasks.