Advance information modulates the global effect even without instruction on where to look

Abstract

When observers are asked to make an eye movement to a visual target in the presence of a near distractor, their eyes tend to land on a position in between the target and the distractor, an effect known as the global effect. While it was initially believed that the global effect is a mandatory eye movement strategy, recent studies have shown that explicit instructions to make an eye movement to a certain part of the scene can overrule the effect. We here investigate whether such top-down influences are also found when people are not actively involved in an explicit eye movement task, but instead, make eye movements in the service of another task. Participants were presented with arrays of yellow and green discs, each containing a letter, and were asked to identify a target letter. Because the discs were presented away from fixation, participants made an eye movement to the array of discs on most of the trials. An analysis of the landing sites of these eye movements revealed that, even without an explicit instruction, observers take the advance information about the colour of the disc containing the target into account before moving their eyes. Moreover, when asking participants to maintain fixation for intervals of different durations, it was found that the implicit top-down influences operated on a very similar time-scale as previously observed for explicit eye movement instructions.