Tracking multiple identical moving objects: Analysis of recent findings

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Abstract
We have been using a Multiple Object Tracking (MOT) paradigm (Pylyshyn & Storm, 1988) to explore people's ability to track a number (usually 4 or 5) of designated visual targets when these are intermixed among a number of nontargets, all of which are identical and move independently in unpredictable ways. This paper will summarize some recent unanticipated results, several of which are being reported at this conference. Here I will discuss one such result in greater detail: the finding that observers can track the set of targets accurately while losing track of which one is which (in terms of some unique identifier assigned to them at the start of a trial). In other words target ID performance drops more rapidly with time than tracking performance. This result is puzzling because correct tracking logically requires that observers keep track of each individual item and trace it back in time to a particular item that was made briefly distinct at the start of the trial (in other words, a “correspondence problem” must be continuously solved for each target). Recent studies have suggested that the more rapid drop in ID performance relative to tracking performance may arise because observers more easily confuse targets they are tracking with other targets that they are also tracking than with nontargets that they are systematically ignoring. We found that targets that come close to other targets during a trial frequently switch identities, whereas targets that come close to nontargets are more readily kept distinct. Possible reasons for this are explored, including the proposal that nontargets are inhibited during tracking. Data are presented showing that under certain conditions nontargets may indeed be inhibited. The implications of such an inhibitory mechanism will be discussed. The various phenomena associated with MOT will be illustrated with animated demonstrations.

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