Abstract
Previous research has revealed the uniqueness-facilitation effect in the multiple object tracking (MOT) task: simple distinct identities and surface features of moving targets could facilitate attentional tracking. By adapting compound stimuli, the present study investigated whether the global or local properties played the main role in the uniqueness-facilitation effect in the MOT task. The uniqueness of local properties, of global properties or of both local and global properties were considered. Observers’ tracking performance in alternative conditions were compared with that in the homogeneous condition wherein all stimuli have identical local and global properties. Results from two experiments suggest that the global properties played the key role in facilitating tracking. The distinctiveness of local properties can also facilitate tracking with global properties being homogeneous. However, when the stimuli’s global properties are distinct from each other—whether the local properties being unique or not—observers’ tracking performance can achieve the same level as that in the unitary-uniqueness condition wherein the moving objects were distinct unitary letters. These results revealed a global superiority effect in the MOT task. Finally, the facilitation effects of the global and local properties might depend on the stimulus sparsity. When the compound stimuli had fewer local elements, the uniqueness facilitation effect on tracking decreased.
Highlights
Previous studies have shown that Human’s visual system can simultaneously keep track of several discrete moving objects (Pylyshyn and Storm, 1988; Scholl and Pylyshyn, 1999; Scholl et al, 2001; vanMarle and Scholl, 2003; Horowitz et al, 2007)
A repeated measures analysis of variance (ANOVA) indicated a significant main effect [F(4,64) = 37.070, p < 0.001, η2p = 0.699, Power (1– β) > 99%]
Post hoc tests with Bonferroni correction revealed that the tracking accuracy of observers in the local-uniqueness condition was significantly higher than the accuracy in the homogeneous condition [local-uniqueness vs. homogeneous: t(16) = 3.415, p = 0.035 (Bonferroni adjusted p-value, the same below), Cohen’s d = 0.53], providing evidence that the distinctiveness of the objects’ local properties could facilitate observers’ tracking when their global properties were identical
Summary
Previous studies have shown that Human’s visual system can simultaneously keep track of several discrete moving objects (Pylyshyn and Storm, 1988; Scholl and Pylyshyn, 1999; Scholl et al, 2001; vanMarle and Scholl, 2003; Horowitz et al, 2007) They provided evidence that in the multiple object tracking (MOT) task, observers can localize a number of independently and unpredictably moving identical targets in a field of identical distractors. Makovski and Jiang (2009a,b) showed that observers’ tracking performance was enhanced when the objects were of unique colors or 1-digit numbers, relative to that when the objects consisted of the same features or when the targets’ features paired with the distractors They revealed the cause to be the visual working memory mechanism operating parallel to the attentive tracking. One possible explanation is that the processing of complex identities consumed extra resources and had a small capacity in visual working memory (Liu et al, 2012)
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