Abstract
Recently we reported an attempt to measure the attentional demand of the Multiple Object Tracking (MOT) task, which many people have claimed requires considerable attentional resources. The experiment we reported appeared to support this contention since tracking performance was worse when carried out simultaneously with a color-change monitoring task. However the monitoring task we used required an immediate response, so it is possible that this decrement in tracking was not due to the attentional requirement of visual monitoring, but to the requirement of responding while tracking. Method: In the present studies we compared performance on MOT while monitoring for a brief change in the color of targets, nontargets or an area-matched fixation point. We also measured baseline tracking performance without monitoring, or on trials when a monitored event failed to occur. We examined dual task performance under both an immediate-response (forced choice) condition and a delayed response condition, in which the observer had to indicate whether a color change had taken place only after completing the tracking trial. Results: We found that tracking performance was worse when monitoring than in the baseline control, but only when the response was made immediately, during tracking. When the response to the monitoring task was made at the end of each trial no decrement in tracking performance was observed and all monitored locations led to the same tracking performance. This finding is compatible with other findings (e.g., Alvarez, Horowitz & Wolfe, 2000) showing that observers can track without decrement while engaged in a secondary task such as search. It is also compatible with the view (Pylyshyn, 2001) that tracking involves a preconceptual mechanism. These findings suggest that apparent attentional tasks such as MOT may not draw on the same resource as other apparent attentional tasks such as monitoring or search.