Abstract
Alvarez & Cavanagh (VSS 2004) showed that attentive tasks presented to left and right cerebral hemispheres appear to be carried out independently, so observers perform a pair of tasks presented to different hemispheres much better than when they are presented to the same hemisphere. We further explore this important finding by using a pair of multiple object tracking (MOT) tasks involving tracking 2 targets out of 4 identical objects, which were presented in two separate quadrants of a display. We tested whether stressing one of the two tasks by increasing its speed results in poorer performance on that task and/or the paired task when the two tasks are presented in the same hemisphere compared with when they are presented in different hemispheres. The assumption that resources for the speeded-up task could be borrowed from the paired same-hemisphere task but not from the paired different-hemisphere task leads to several predictions. An increase in difficulty of one task should result in greater performance decrement in the second task in the same-hemisphere condition compared with the different-hemisphere condition. Moreover, since resources cannot be borrowed from the second task in the dual-hemisphere condition the decrement in performance on the speeded-up task itself should be greater in the dual-hemisphere condition than in the same-hemisphere condition. We used several baseline measures to assess the degree of interaction between tasks in the dual-hemisphere presentations compared with matched single-hemisphere presentations and confirmed all the above predictions, as well as the original A & C findings, thus adding strang support to the conclusion that one hemisphere is unable to draw upon attentional resources from the other hemisphere to help with an increasingly difficult task.
This research was supported by NIH research grant R01 MH60924 to ZWP.