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Sneha Suresh, Chia-Chien Wu, Daniela Gresch, Jeremy M. Wolfe; Multiple Functional Visual Fields (FVFs) surround the same fixation point during visual search. Journal of Vision 2020;20(11):716. doi: https://doi.org/10.1167/jov.20.11.716.
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When observers search for targets, they do not fixate every spot in the image. It follows that there must be a region that is processed around each fixation. This is referred to as the “Functional Visual Field” (FVF). Traditionally, the FVF has been treated as one entity. We argue that there are three FVFs at play in a search task, answering three different questions: What can be resolved if attention is directed toward it? What will be covertly attended during this fixation? Where will I explore with my next fixation? Experiment 1: Observers searched for a single target letter T among distractor Ls while the eyes were tracked. Once the target letter was clicked, a new target would appear at a random location. All letters rotated randomly to mask transients. When the next saccade landed on a target, that target must have fallen within the FVF(attend) for the previous fixation. Preceding saccades were exploring saccades, seeking to get a target inside FVF(attend). On average, these FVF(explore) saccades were significantly longer than the final FVF(attend) saccade (paired t-test, p<0.001). In Experiment 2, Ts and Ls were intermixed with smaller consonants and vowels. Observers searched for Ts, Vowels, or both in separate blocks. Again, FVF(explore) saccades were significantly longer than the final FVF(attend) saccade. Additionally, explore saccades were longer on T blocks than on Vowel blocks (p=0.006). Attend saccades were longer for Ts and Vowels, but not significantly. Our results show that task difficulty affects the size of FVF(explore) and probably of FVF(attend). FVF(resolve) is limited by acuity and crowding and depends on the stimulus. FVF(attend) and FVF(explore) are further controlled by other factors. For example, if the T was red, you could saccade to red items (FVF(explore)) that were too far away to resolve or attend.
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