Abstract
Scholl, Pylyshyn & Feldman (2001) has discussed “objecthood” in the context of a multiple object tracking (MOT) task. In their experiment, the target and distractor were merged by line segment or by drawing the convex hull of the two items (target merging technique). It was demonstrated that the participant's capacity to track multiple items destructed when items were merged, compared to the separate condition when items were not merged. This indicates that the target merging technique created difficulty in attending to each target item. One of the reasons for this might be because the merged items were treated as a single object. Another possibility, however, is that the merged items formed non-rigid and unnatural object, and this could have created the difficulty in attending to “part” of the object. In this study, a three-dimensional display was used to test this possibility, and to examine the effect of depth on merged MOT. Participants viewed a split display through a haploscope and perceived three-dimensional or two-dimensional stimuli. Merged and separate items were presented either two or three dimensionally. The three-dimensional rigidity was also controlled. As for the results, the tracking accuracy was higher in the 3-D condition than in the 2-D condition. This result is consistent with Viswanathan and Mingolla (in press). The rigidity of the items improved the participant's performance, and was an effective cue on 3-D MOT. However, both the 3-D and 2-D merged item conditions showed significantly lower accuracy than the separate item condition. It was concluded that this difficulty stems from the fact that the three-dimensionally merged items were treated as a single object. Supported by JSPS grant 12551001 & 13224021