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Laura Renninger, Saeideh Ghahghaei; Crowding of parafoveal targets without focal attention. Journal of Vision 2012;12(9):325. doi: https://doi.org/10.1167/12.9.325.
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MOTIVATION When moving our eyes in the real world, the relative arrangement of objects with respect to the fovea is always changing. A target that was crowded radially could be crowded tangentially after a saccade. In this work, we examine to what degree crowding occurs in the parafovea when attention is divided between two potential target locations within a given hemifield, and whether it retains radial-tangential asymmetries. METHODS Target was an oriented gabor located in one of two locations that were positioned in the upper, lower, left or right hemifield with respect to fixation. Both target-present and target-absent locations were flanked with plaids, oriented radially or tangentially in the crowded conditions. No flankers were present in the baseline condition. Similar to previous studies (Petrov & Meleshkevich, JOV 2011), spatial frequency, target-distractor spacing and gabor size were simultaneously manipulated with an adaptive staircase to determine Gabor period threholds (Kontsevich & Tyler, Vision Research 1999). Subjects responded whether the target was tilted left or right, regardless of location. We tested eccentricities of 2.12 – 3.54deg which correspond to distances at which a 3-5 degree saccade would rotate distractors 90degrees about a target (i.e. from the radial to tangential position). RESULTS Crowding factors ranged from 0 to 1.2 for radial configurations and 0 to 0.6 for tangential configurations. Although idiosyncratic across the visual field and observers (see Petrov & Meleshkevich, Vision Research, 2011), on average the crowding asymmetry held for our 3 participants and was most pronounced in the lower and left hemifields. CONCLUSION In conditions of non-focal attention across a hemifield, crowding exists in the parafovea and on average, exhibits radial-tangential asymmetry similar to that for more eccentric targets. Naturally occurring saccades tend to be about 4 degrees in amplitude and we speculate that they may serve to "de-crowd" parafoveal stimuli.
Meeting abstract presented at VSS 2012
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