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Gavin Ng, Alejandro Lleras, Simona Buetti; The width of the functional viewing field is sensitive to distractor-target similarity even in efficient singleton search. Journal of Vision 2017;17(10):220. doi: https://doi.org/10.1167/17.10.220.
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© ARVO (1962-2015); The Authors (2016-present)
Contrary to most models of visual search, recent work from our lab showed that variability in efficient search is meaningful and systematic. Reaction times (RTs), which reflect stage one processing times, increase logarithmically with set size, indicating an exhaustive processing of the scene, even in the presence of an easily visible singleton target. This increase is modulated by distractor-target similarity. The functional viewing field (FVF) - the region surrounding fixation from which useful information can be extracted - has been shown to be smaller in inefficient compared to efficient search tasks. Here we show that the size of the FVF, like RTs, is variable even in efficient search tasks. We monitored eye movements as observers discriminated the direction of a singleton target. In higher distractor-target similarity displays, observers' initial saccades landed further away from the target than in low distractor-targetsimilarity displays, even though search was efficient with both types of distractors. Furthermore, observers executed more fixations, indicating that the FVF was smaller in higher distractor-target displays. Interestingly, regardless of distractor-target similarity, observers fixated closer to the target when there were more items in the display. This presumably results from observers switching to a smaller FVF in order to determine the identity of the target once it is located. Additionally, we found that initial saccade latencies (ISLs) were not affected by total set size, suggesting that initial processing of the display is not exhaustive but restricted to the FVF. However, the first eye movement was sensitive to distractor type: ISLs were significantly longer for higher distractor-target similarity displays and most of the initial saccades were directed towards the target. Our results show that the size of the FVF is modulated by distractor-target similarity even in efficient visual search, and that this affects the initial processing time of the search display.
Meeting abstract presented at VSS 2017
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