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Mehmet Agaoglu, Susana Chung; The effect of stimulus contrast on pre-saccadic orientation discrimination. Journal of Vision 2016;16(12):1040. doi: 10.1167/16.12.1040.
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© 2017 Association for Research in Vision and Ophthalmology.
Objects that are briefly flashed around the time of saccades are grossly mislocalized. Zhang et al. (2008) demonstrated that these perceptual distortions strongly depend on stimulus contrast such that low-contrast targets are mislocalized more than high-contrast ones. Tong et al. (2012) showed that perceptual grouping by contrast and spatial distortions induced by saccades significantly interact. The purpose of this study was to determine whether similar interactions hold for a discrimination task. Seven observers reported the direction of tilt (clockwise vs. counterclockwise) of a target Gabor patch (2 cpd) presented at 15 deg eccentricity. In two-thirds of the trials, four vertically-oriented Gabors (2 cpd) surrounded the target Gabor. In randomly interleaved blocks, observers performed the task either during steady fixation, or following a saccadic eye movement toward the center of the target Gabor. In the saccade blocks, stimulus timings were adjusted for each observer so that the Gabor stimuli were presented before saccades in the majority of trials. Contrast of the target and flanking Gabors were independent of one another and were either 100% (high-contrast) or 25% (low-contrast) with equal probability. As expected, discrimination performance was worse in the presence of flanking Gabors, for both the fixation and saccade conditions—the crowding effect. In saccade conditions without flankers, significant reductions in discrimination performance as a function of target-to-saccade-onset were observed for low-contrast target Gabors. In the presence of flankers, saccades modulated performance similarly only for low-contrast, but not for high-contrast flankers. Moreover, we did not find any statistical difference between performances in the fixation and saccade conditions. Likewise, the magnitude of crowding was not influenced by saccades, which contradicts a recent report that saccade targets are released from crowding (Harrison et al., 2013). Taken together, our results suggest that pre-saccadic orientation judgments are similarly affected by contrast as perisaccadic spatial localization.
Meeting abstract presented at VSS 2016
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