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Daniel Linares, Alex White, Alex Holcombe; Object localization at speeds below and above the attentive tracking limit. Journal of Vision 2008;8(6):502. doi: 10.1167/8.6.502.
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© ARVO (1962-2015); The Authors (2016-present)
Attending to a moving object helps to keep track of it among other objects. We wondered what the consequences for object localization would be if attentive tracking were prevented by using objects traveling too fast to be tracked. We measured performance in a position judgment and a sensorimotor synchronization task for a range of speeds above and below the limit of attentive tracking. To measure the tracking limit, a luminance-defined blob among identical distractors orbiting the fixation point was cued at the beginning of an interval of orbiting and subjects attempted to identify it at the end. A low speed limit of 1.5 rps was found, replicating Verstraten, Cavanagh and Labianca (2000). To test position judgments, one to four blobs orbited fixation. The task was to report a blob's position at the unpredictable time of a cue such as a change in fixation color. Finally, in the sensorimotor synchronization task, the same subjects were asked to press a button at the moment the blob became aligned with a stationary landmark. Responses in the sensorimotor synchronization task were much more precise, indicating that the position judgment task underestimates our abilities. For both tasks however, precision was constant in temporal units regardless of blob speed — the standard deviation of responses corresponded to ∼100 ms of the blob's trajectory for the position judgment task, and ∼50 ms for the sensorimotor synchronization task. The absence of a drop in precision at high speeds indicates that neither task relies on attentive tracking. This was especially surprising for the synchronization task, as estimating time-of-alignment might benefit from the progressive updating of position and velocity earlier in the trajectory. Moreover, there was no relationship between speed and the bias in position judgments (a.k.a. the flash-lag effect), further dissociating attentive tracking and object localization.
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