Distinguishing a central selection bias from a central fixation bias: The role of retinal eccentricity in visual selection.

Earlier work has shown that the eyes preferably select stimuli that are presented close to central fixation over stimuli presented further away, suggesting the existence of a central selection bias. However, so far studies have confounded retinal eccentricity with distance from the center of a display, and the observed effects may thus have been driven by what is known as the central fixation bias, which is the preference for items near the center of a display rather than the center of the retina. This study aimed to dissociate the central selection bias from the central fixation bias, and to uncover its time course. In two experiments, participants were instructed to make a single eye movement to one of two simultaneously presented singletons. The singletons were always presented at the same distance from the center of the display (thus controlling for the central fixation bias) but their eccentricity relative to the initial fixation point was varied (thus allowing for a central selection bias to operate). When the two singletons were displayed at different eccentricities, participants preferred selecting the nearest item. This central selection bias occurred rapidly and transiently, peaking around 230 ms and lasting until approximately 320 ms after display onset. Together, these results suggest that retinal eccentricity is a major factor when multiple objects compete for selection.