Natural-amplitude saccades uncrowd targets in the parafovea L Walker, S Ghahghaei |
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Smith-Kettlewell Eye Research Institute, CA, United States
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| Crowding is typically studied during fixation with covert attention to the target, and demonstrates a radial-tangential anisotropy (Toet & Levi, 1992, Vision Research 32, 1349-1357). During natural vision, eye movements necessarily alter the relative relationship of flankers to targets. Interestingly, flankers will rotate from the radial to tangential configuration in the parafovea for 4deg saccades – coincident with the peak of the natural saccade amplitude distribution. Here we examine whether saccades indeed impact crowding of unattended parafoveal targets. In a primary task, participants made three, timed saccades between four fixation targets. During the second and third fixations, an oriented gabor target appeared off the path in the upper or lower parafovea, flanked by plaid crowders. In a secondary task, participants were asked to report the orientation of this target. Spatial frequency and flanker-target distance was manipulated to measure crowding strength. Trials with inaccurate/untimely saccades were discarded. As attention was not directed toward the target, we find an overall increase in crowding. When the relative position of flankers was manipulated to preserve radial/tangential configurations despite eye movements, the hallmark anisotropy was preserved. When eye movements served to rotate the flankers, the two fixations were cumulative and crowding factors fell between the radial and tangential bounds. |
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