Dividing Attention Between the Hands and the Head: Performance Trade-Offs Between Rapid Finger Tapping and Verbal Memory

We tested a multiple resources approach to time-sharing performance which assumes that each cerebral hemisphere controls its own set of processing resources that it cannot share with the other hemisphere. Right-handed men performed a verbal memory task while concurrently tapping the index finger of either hand as rapidly as possible. Task priority was manipulated with a payoff scheme. Subjects remembered more on the verbal task when concurrently tapping with their left hands than when tapping with their right hands, and their memory performance was much better when the memory task was emphasized than when the tapping task was emphasized, regardless of hand. For the tapping task, decrements from baseline tapping rates and trade-offs between tasks were equal for both hands when subjects were reading the to-be-remembered words aloud. In contrast, during the retention interval, decrements were larger for the right hand than the left, and there were no task trade-offs. The data were interpreted to mean that on right-hand trials, both tasks required exclusively left-hemisphere resources, whereas on left-hand trials, righthemisphere resources were required to execute the tapping movements per se, but left-hemisphere resources were necessary to coordinate those movements with the movements required for overt speech. The data suggest that cognitive and motor resources may be independent types and thus underscore the importance of manipulating task priority to obtain an accurate picture of a task's resource requirements.