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bioRxiv · 10.1101/2023.05.18.541028

The Extrafoveal Preview Effect is More Pronounced Where Perception is Poor

Liu, X.·Melcher, D.·Carrasco, M.·Hanning, N. M.
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Abstract

The pre-saccadic preview of a peripheral target enhances the efficiency of its post-saccadic processing, termed the extrafoveal preview effect. Peripheral visual performance -and thus the quality of the preview- varies around the visual field, even at iso-eccentric locations: it is better along the horizontal than vertical meridian and along the lower than upper vertical meridian. To investigate whether these polar angle asymmetries influence the preview effect, we asked human participants (to preview four tilted gratings at the cardinals, until a central cue indicated to which one to saccade. During the saccade, the target orientation either remained or slightly changed (valid/invalid preview). After saccade landing, participants discriminated the orientation of the (briefly presented) second grating. Stimulus contrast was titrated with adaptive staircases to assess visual performance. Expectedly, valid previews increased participants post-saccadic contrast sensitivity. This preview benefit, however, was inversely related to polar angle perceptual asymmetries; largest at the upper, and smallest at the horizontal meridian. This finding reveals that the visual system compensates for peripheral asymmetries when integrating information across saccades, by selectively assigning higher weights to the less-well perceived preview information. Our study supports the recent line of evidence showing that perceptual dynamics around saccades vary with eye movement direction. Significance StatementWe constantly make saccadic eye movements to bring relevant visual information into the fovea, which has the highest acuity. Before each saccade, we use "previewed" peripheral information to support our post-saccadic vision. Our sensitivity varies around the visual field -at the same eccentricity it is best along the horizontal meridian and worst at the upper vertical meridian. An optimal visual system should rely more on previewed information with higher precision. Our study reveals the opposite: peripheral preview shapes subsequent post-saccadic foveal processing more at locations where peripheral vision is worse. This finding implies that the human visual system compensates for sensitivity differences around the visual field when integrating information across eye movements.

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Liu, X., Melcher, D., Carrasco, M., Hanning, N. M.. 2023-05-18. The Extrafoveal Preview Effect is More Pronounced Where Perception is Poor. https://doi.org/10.1101/2023.05.18.541028

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