Thinks are looking up: The extrafoveal preview effect is the largest at the upper vertical meridian, where peripheral sensitivity is worst

Despite its degraded resolution, the pre-saccadic preview of a peripheral target enhances the speed and accuracy of its post-saccadic processing (the extrafoveal preview effect). However, acuity and contrast sensitivity vary in human peripheral vision, even for iso-eccentric locations, raising the question whether these performance field asymmetries influence the preview effect. To investigate this question, we first measured performance field asymmetries during fixation. Observers indicated the orientation (relative to vertical) of one of four peripheral Gabors presented briefly at the cardinal locations (8° eccentricity, 4cpd). Gabor contrast was titrated with adaptive staircases. Consistent with previous studies, contrast sensitivity was higher at the horizontal than vertical meridian, and at the lower than upper vertical meridian. The same observers then performed a saccade-version of the same task: They previewed four tilted Gabors while fixating at the center, then received a central cue indicating to which of the Gabors to immediately saccade. During the saccade, the target Gabor orientation either remained (valid preview) or was flipped to the opposite direction (invalid preview), with equal probability. After saccade landing, observers discriminated the orientation of this second, now foveated Gabor, which disappeared shortly after saccade offset. We found a robust preview effect for all saccade directions, i.e., higher post-saccadic contrast sensitivity after valid than invalid previews. Surprisingly, the magnitude of the preview effect was inversely related to the performance field asymmetries: Largest at the upper vertical meridian, followed by the lower vertical, then horizontal meridian. This finding suggests that the visual system actively compensates for asymmetries in peripheral vision when integrating information across saccades. These results reveal a new perceptual consequence of performance field asymmetries during active vision, and demonstrate the necessity to study trans-saccadic perceptual modulations as a function of saccade direction.