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Annie Tran, Mandy Skoranski, Sarah Wells, James Hoffman; Spacing and set size effects in MOT may reflect different underlying mechanisms.. Journal of Vision 2012;12(9):555. doi: 10.1167/12.9.555.
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The multiple object tracking task (MOT), introduced by Pylyshyn and Storm (1988), requires observers to track a small number of moving objects embedded in identical moving distractors. Increasing the number of objects to be tracked (set size), as well as their proximity to distractors, reduces tracking accuracy during MOT. The effects of these two variables may reflect a common underlying mechanism in which increases in set size or proximity of targets and distractors requires increases in attention to maintain accurate tracking performance (Alvarez and Franconeri, 2007). Event-related brain potentials (ERPs) provide a useful window on the putative role of attention in MOT. For example, Drew and Vogel (2008) found that MOT elicited a sustained negativity over posterior electrode sites that increased in amplitude with increases in set size, up to the maximum number of objects each observer could track. According to a single mechanism account, one might expect that decreasing spacing between objects would have similar effects on the CDA since reduced spacing, like set size, would require increased allocation of attention to maintain performance. We examined this by varying both set size and minimum inter-object spacing in an MOT task. We found that increasing set size from 1 to 2 objects increased CDA amplitude over contralateral posterior sites, replicating the results of Drew and Vogel (2008). However, decreasing spacing reduced CDA amplitude over both hemispheres. A follow-up experiment using confidence judgments replicated these results and ruled out increased guessing as a cause of these effects. These results suggest that spacing and set size effects on MOT accuracy may reflect different underlying mechanisms.
Meeting abstract presented at VSS 2012
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