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Xiaoli Zhang, Christopher M Jones, Julie D Golomb; Decoding 3D spatial location across saccades in human visual cortex. Journal of Vision 2020;20(11):546. doi: https://doi.org/10.1167/jov.20.11.546.
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Visual signals are initially processed as two-dimensional images on our retina. To perceive a 3D world, depth information can be reconstructed from the binocular disparity between the 2D retinal images from both eyes. However, in daily life, we make frequent eye movements and consequently the 2D retinal inputs constantly change. How is depth position represented in the brain across saccades compared to during sustained fixations? In an fMRI scanner, while wearing red-green anaglyph glasses to facilitate 3D perception, participants passively viewed a random dot patch that stimulated one of four 3D locations in each 16-second block. Each location was defined by its 2D position (above or below screen center; vertical information), and its depth position (in front of or behind central screen plane). Participants fixated on a fixation dot located at the vertical center and the screen depth plane, but offset horizontally either to the left or right of the screen center. In half of the blocks, the fixation dot remained in the same location throughout the block (no-saccade blocks). In the other blocks, the fixation dot repeatedly alternated between the left and right sides to trigger saccades (saccade blocks). With multivariate pattern analysis, we could decode depth information in no-saccade blocks in intermediate/later visual areas, consistent with previous studies. Importantly, in saccade blocks, despite the retinal changes in horizontal position induced by the saccades, we could decode depth information to a similar extent as in no-saccade blocks. In contrast, little vertical or depth information could be decoded across no-saccade blocks with different eye positions in any visual areas, indicating eye-position-dependency during stable fixation. In conclusion, representations of spatial locations (2D and depth) may become more tolerant of eye positions during “dynamic” saccades, perhaps due to active remapping during saccades which may encourage more stable representations of the world.
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