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Arash Fazl, Ennio Mingolla; Consistency of eye movements during multiple object tracking. Journal of Vision 2007;7(9):902. doi: 10.1167/7.9.902.
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© ARVO (1962-2015); The Authors (2016-present)
While tracking multiple objects, observers often move their eyes. This experiment studies the consistency of eye movements (EM) while subjects performed a classic MOT task, both when the targets were featurally different from the distractors and when they were not. Observers tracked red target balls among blue distractor balls during an initial “marked” interval of each trial, after which all target balls turned blue. Observers had to track the target balls during this final “unmarked” interval as well and report the original targets. The number of targets varied randomly between three and five in different trials and they moved among a maximum of seven distractors. In order to compare EM consistency between marked and unmarked intervals, we designed pairs of trials to have the same target and distractor trajectories for some of their duration. In the “salient” trials, this “common” trajectory occurred during the marked interval when all targets were red, whereas in its “non-salient” pair it happened in the unmarked interval when both sets of targets and distractors were blue. Different pairs of trials were randomly interleaved in each block. Eye movements were recorded at 500 Hz with an EyeLink II eye-tracker. Subject could track all targets in most of the trials which had three or four targets. For both trial types, each subject tracked the targets through a series of saccades, smooth pursuits and fixations. Each subject showed a unique EM signature. Within subject comparisons showed that EMs were highly consistent during the common trajectories across pairs of trials. Lasting deviations of EM trajectories on non-salient trials from trajectories on corresponding salient trials were associated with the subject's losing track of one or more targets. This finding can be a useful tool for studying attention mechanisms in MOT tasks.
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