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Mutsumi Suganuma, Kazuhiko Yokosawa; Items in MOT are easily lost when they chase each other. Journal of Vision 2003;3(9):584. doi: 10.1167/3.9.584.
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© ARVO (1962-2015); The Authors (2016-present)
Based on a multiple object tracking (MOT) paradigm, Scholl, Pylyshyn, & Feldman (2001) reported that when the pairs of items were “merged”, participants ability to track them were significantly disrupted. This disruption also occurred when the items were merged for a short time (Scholl & Feldman, 2002), or in a three-dimensional display (Suganuma & Yokosawa, 2002). Scholl et al. (2001) argued that in an item merging display, visual objecthood was mediated by the whole (i.e. two items plus a merging line), but not by each item. However, in previous studies concerning this item-merging effect, the items were always visually connected with the merging line. Therefore, both factors of visual connectedness and of perceptual grouping are confound. Our aim was to isolate both factors on MOT display. To solve this problem, we tested an item-merging display without merging lines. In our experiments, four target and four distractor items were presented. During the movement sequence for 14 seconds, the target and the distractor items were made in a pair, and the target ‘chased’ the distractor (or vice versa). Participants' performance for the chasing condition was significantly lower than that for the control condition (ordinary MOT), and was worse when the items made a chasing movement in a close distance to each other. Thus, we have observed a similar result to the item merging effect even without visually presented merging lines. These results indicate that the visual objecthood which each item possessed was disrupted by perceptual grouping (caused by the factor of uniform destiny or proximity). This shows that both perceptual grouping and visual connectedness affects MOT. However, the error rate of chasing condition was higher than that of the line or rubber band conditions of Scholl et al. (2001). This indicates that visual connectedness plays an important role than perceptual grouping (or than Gestalt laws) on the item merging effect.
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