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Hilda M. Fehd, Adriane E. Seiffert; Eye movements during multiple object tracking. Journal of Vision 2007;7(9):999. doi: 10.1167/7.9.999.
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Previous work has established that people are capable of successfully tracking multiple moving items simultaneously. While eye movements are not necessary during this tracking, people often move their eyes as the targets move. The goal of this experiment was to investigate where observers tend to look while keeping track of multiple objects. Observers viewed a display containing 8 red dots that moved randomly within a square box on a black background. Either 1 or 3 of the dots were cued as targets, leaving the rest of the dots to serve as distractors. Eye movements were recorded using an ASL 120 Hz video-based eye-tracking system. Results indicate that during 1-target trials observers' eyes were closest to the target dot significantly more of the time (96.6%) than any of the distractor dots (0.3%). This difference was also evident during 3-target trials. However, on 3-target trials, the eyes were closest to the center of the triangle formed by the three target dots for significantly more of the time (65.7%) than they were closest to any of the target dots (8.5%). This result indicates that observers tend to look toward the center of multiple targets, a finding that may reflect a strategy of attempting to minimize the eccentricity of all the targets simultaneously. Another alternative is that observers are perceptually grouping the targets to form a virtual object (Yantis, 1992, Cognitive Psychology, 24:295–340) and that they fixate at the center of this virtual object, as they do with real objects (Vishwanath & Kowler, 2003, Vision Research, 43:1637–1653). In addition, this result implies that people use a mental representation of an object's location during tracking without that object receiving direct foveation.
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