Presaccadic attention enhances and reshapes the Contrast Sensitivity Function around the visual field

Abstract

Contrast sensitivity, which constrains our vision, decreases from fovea to periphery, from the horizontal to the vertical meridian, and from the lower vertical to the upper vertical meridian. The Contrast Sensitivity Function (CSF) depicts how contrast sensitivity varies with spatial frequency (SF). To overcome these visual constraints, we constantly make saccadic eye movements to foveate on relevant objects in the scene. Already before saccade onset, presaccadic attention shifts to the saccade target and enhances perception. However, it is unknown whether and how it modulates the interplay between contrast sensitivity and SF, and if this effect varies around polar angle locations. Contrast sensitivity enhancement may result from a horizontal or vertical shift of the CSF, increase in bandwidth, or any combination. Here, we investigated these possibilities by extracting key attributes of the CSF using Hierarchical Bayesian Modeling, which enables precise estimation of the CSF parameters by decomposing the variability of the dataset into multiple levels. The results reveal that presaccadic attention (1) enhances contrast sensitivity across SF, (2) increases the most preferred and the highest discernable SF, and (3) narrows the bandwidth. Therefore, presaccadic attention bridges the gap between presaccadic and post-saccadic input by increasing visibility at the saccade target. Counterintuitively, the presaccadic enhancement in contrast sensitivity was more pronounced where perception is better -along the horizontal than the vertical meridian- exacerbating polar angle asymmetries. Our results call for an investigation of the differential neural modulations underlying presaccadic perceptual changes for different saccade directions. Significance statementThe contrast sensitivity function (CSF) describes how our ability to perceive contrast depends on spatial frequency. Contrast sensitivity is highest at the fovea and decreases in the periphery, especially at vertical locations. We thus make saccadic eye movements to view objects in detail. Already before moving our eyes, presaccadic attention enhances perception at the target location. But how does it influence the interplay between spatial frequency and contrast sensitivity, and does its effect vary around the visual field? Using Hierarchical Bayesian Modeling, we show that presaccadic attention enhances and reshapes the CSF to prepare the periphery for upcoming fixation. Counterintuitively, it does so more at horizontal locations where vision is stronger, suggesting smoother perception across horizontal than vertical eye movements.