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David Fencsik, Leigha Wendel, Jeremy Wolfe, Todd Horowitz; Faster is more efficient in visual search for motion. Journal of Vision 2011;11(11):1302. doi: https://doi.org/10.1167/11.11.1302.
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© ARVO (1962-2015); The Authors (2016-present)
How does the visual system use speed to guide visual search? According to the absolute speed hypothesis, the fastest moving object in the environment will be the most salient and will be found most efficiently. This hypothesis is supported by search asymmetry studies showing that moving targets are found more efficiently among stationary distractors than vice versa (e.g., Verghese & Pelli, 1992) and that fast targets are found more efficiently among slow distractors than vice versa (Ivry & Cohen, 1992). However, Rosenholtz (1999, 2001) argued that the multidirectional motion of the stimuli in these studies confounded the experimental design by enhancing the salience of faster-moving stimuli. She proposed an alternative relative speed hypothesis in which an object's salience depends on the difference between its speed and the speeds of other objects in the environment, regardless of which is moving faster.
In order to differentiate between these two hypotheses, we designed visual search stimuli that avoid the confound identified by Rosenholtz. In each experiment, 12 participants viewed a display of windowed square-wave gratings. While the windows were always stationary, the gratings could drift. All of the gratings in a given display drifted in the same direction. In Experiment 1, the search target moved while the distractors were stationary, or the target was stationary while the distractors moved. In Experiment 2, the search target moved either more slowly or more quickly than the distractors. In both experiments, the fastest-moving object in the environment was the easiest to detect; search slopes were near 0 ms/item. Slower-moving targets were harder to detect; search slopes were over 50 ms/item. These results support the absolute speed hypothesis over the relative speed hypothesis. The visual system appears to be biased towards the fastest moving object in the environment at the expense of slower-moving ones.
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