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Carly J. Leonard, Zenon W. Pylyshyn, Elias H. Cohen, John L. Dennis; The effect of a secondary monitoring task on Multiple Object Tracking. Journal of Vision 2002;2(7):240. doi: 10.1167/2.7.240.
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© ARVO (1962-2015); The Authors (2016-present)
Previous research has shown that observers are able to track at least four moving targets among identical distractors. According to Pylyshyn's account, tracking uses a preattentive mechanism called a Visual Index (or FINST). Several people have challenged the assumption that MOT is preattentive. Treisman (1993) showed that a simultaneous task of monitoring color changes at the screen border results in poorer performance on both tasks. We hypothesize that a task that involves indexing an additional visual object (e.g., the border) may interfere with tracking, but that a task that involves an already-indexed object might not. Subjects performed a MOT task with 4 targets as well as a simultaneous task involving monitoring the occurrence of a specific color change at one of four locations: on a target, non-target, border, and fixation. Both tracking and monitoring performance were recorded. The results showed that tracking was not significantly affected by the monitoring task regardless of its location (although the trend was in the expected direction, with the best performance occurring when the monitored change was on the target and the worst when on the border). There were, however, significant differences in reaction times to the secondary monitoring task, as well as differences in the frequency with which the monitored events was missed. The longest RT occurred when the change was at fixation and the shortest when it was on the border. Perhaps even more surprising was the consistent finding that the frequency with which the monitored event was missed was very much higher when it occurred on a target. An attempt is made to reconcile these findings with the general assumption that MOT requires attention. Among the relevant factors that are considered is the difficulty of the tracking task and the possible role of inattentional blindness and nontarget inhibition.
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