Presaccadic attention sharpens visual acuity around the visual field

[Background] Visual perception is limited by spatial resolution, which declines with eccentricity and differs for polar angle locations around the visual field–it is better along the horizontal than vertical meridian and along the lower- than upper- vertical meridian. To compensate for poor peripheral resolution, we make saccadic eye movements to bring peripheral objects into high-acuity foveal vision. Already before saccade onset, visual attention shifts to the saccade target location and prioritizes visual processing. However, it is unknown whether this presaccadic shift of attention sharpens spatial resolution. [Goal] We investigated whether presaccadic attention enhances peripheral spatial resolution and whether this effect interacts with polar angle asymmetries–is the benefit the same or differential across locations, thereby compensating for the asymmetries. [Methods] We measured acuity thresholds at 7.5° eccentricity at the four polar angle meridians while participants either maintained fixation, or prepared saccades toward (valid) or away (invalid) from the test stimulus presented shortly before saccade onset. The spatial frequency of the test grating was varied using adaptive staircases in an orientation discrimination task. [Results] (I) We confirmed polar angle asymmetries in acuity during fixation. (II) Saccade preparation toward the test (valid) benefitted performance by decreasing acuity thresholds, and saccade preparation away from the test (invalid) impaired performance by increasing acuity thresholds, compared to fixation. (III) The extent of these acuity effects was similar for all four locations. [Conclusion] Our results reveal that presaccadic attention sharpens acuity, which can facilitate a smooth transition from peripheral to foveal representation. This robust effect of presaccadic attention does not change polar angle differences in acuity, thereby not compensating for the asymmetries. We are currently investigating presaccadic modulations of the contrast sensitivity function around the visual field to assess how saccade preparation, acuity, contrast sensitivity and polar angle asymmetries interact.