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Brian P. Keane, Zenon W. Pylyshyn; Tracking behind occluders is not based on predicting likely reappearance locations. Journal of Vision 2004;4(8):362. doi: 10.1167/4.8.362.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose. In Multiple Object Tracking (MOT), observers follow a specified subset of identical visual objects that move independently about a display. Using a variant of MOT in which all objects instantaneously disappeared and reappeared during tracking, it was found (a) subjects track better when objects reappeared at the locus of disappearance than when they reappeared in their extrapolated trajectory, and (b) tracking deteriorated as a function of the distance that objects displaced from that locus, provided that they did not displace in their recently traveled trajectories (Keane&Pylyshyn, 2003). However, reappearance-locations might be predicted only if local occlusion/disocclusion cues enhance the appearance that movement continues while objects are invisible. The present study examines whether our previous findings can be replicated when objects move behind and emerge from (virtual) occluding edges. Method. The standard MOT task was modified so that part way through each trial, all objects on the screen disappear as though going behind occluding edges. Either 450ms or 650ms later, objects gradually reappear from disoccluding edges either (a) as if they had stopped moving during total occlusion (“minimal-move” condition) or (b) as if they had moved during total occlusion (“predicted-move” condition). Results. Previous results using instantaneously disappearing/reappearing objects were replicated. Subjects tracked better in the minimal-move than the predicted-move condition for both disappearance durations. In the predicted-move condition subjects tracked better in the 450ms duration. There was no significant difference between performance at the different durations for the minimal-move condition. Conclusion: Observers do not appear to track objects predictively under any conditions examined so far; they appear to keep track of where objects disappear but cannot extrapolate to where objects are likely to reappear.
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