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Bruno Richard, Dave Ellemberg, Aaron Johnson; Non-parametric test to describe response time and eye movement distributions in visual search. Journal of Vision 2010;10(7):1317. doi: https://doi.org/10.1167/10.7.1317.
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© ARVO (1962-2015); The Authors (2016-present)
Visual search is one of the most common paradigms used to study attention, and the three main tasks that have emerged to study visual search include feature, conjunction and spatial-configuration. It is well documented that for the spatial-configuration tasks response times are twice as long when there is no target compared to the target present condition. Further, for both target absent and present conditions, response time increase as the number of distracters increases. The objective of the present study is to investigate two gaps in this literature. Little to nothing is known about the role of eye movements in this relationship. Second, the current statistical analyses used to study these response times rest on the assumption of a normal distribution; that is not the case for the distribution of response times in this task, which are known to be skewed. The present study measured response times, the number of fixations and fixation duration in a group of 20 adults by means of a spatial-configuration visual search task consisting of Gabor. The results indicate that eye movements are dispersed for conditions, in which the target was absent, and consistent, almost pattern like, when the target was present. Response time results varied according to the fixation maps, but fixation duration measures did not. In agreement with previous reports, we found that response time was greater in the target absent condition and increased systematically as the numbers of distracters increased. The Kolmogorov-Smirnov test showed a similar pattern of results, where the differences between the two slopes increased as the number of distracters increased, but plateau after 8 distracters. The typical slope difference, at the 50% threshold, was found to be smaller than 2:1, suggesting that the difference between target present and target absent search tasks might not be as large as previously expected.
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