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Dongjun He, Fang Fang; Perceptual learning reduces crowding effect and the size of population receptive field in V2. Journal of Vision 2015;15(12):107. doi: 10.1167/15.12.107.
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© 2017 Association for Research in Vision and Ophthalmology.
Crowding is the identification difficulty for a target in the presence of nearby flankers. Previous studies have shown that perceptual learning could reduce crowding effect. However, the underlying neural mechanisms of the perceptual improvement are still largely unknown. It has been hypothesized that the reduction of crowding effect might be due to the shrinkage of neurons’ receptive field by training. Here, we used the fMRI-based population receptive field (pRF) technique to examine this issue. Subjects were trained with an orientation discrimination task for five days. In the task, a target grating (radius: 1.25°; contrast: 1.0; spatial frequency: 2 cycles/°) was centered at 6.25° eccentricity with two adjacent flankers positioned radially. The target and flankers rotated round the fixation point and were displaced 20° every 2 seconds. Subjects needed to detect a near-threshold orientation change in the 2 second intervals. Before and after training, subjects viewed the same stimuli and performed the same task as those during training. Meanwhile, we acquired BOLD signals for estimating the pRF of the voxels in visual cortex. We found that, after training, subjects’ orientation discrimination threshold reduced by 66% and the pRF size in V2 decreased significantly. These results support the above mentioned hypothesis. We speculate that the pRF size reduction might serve to prevent the interference from flankers and thus weaken the crowding effect.
Meeting abstract presented at VSS 2015
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