Effort and salience jointly drive saccade selection.

Abstract

Choosing where to move the eyes ('saccade selection') is one of the most frequent human decisions and fundamentally shapes perception. Currently, saccade selection is thought to be predominantly driven by the observer's goals, selection history, and by the physical salience of stimuli. Recent work demonstrates that the inherent effort associated with planning and executing saccades ('saccade costs') also drives saccade selection: participants prefer making affordable over costly saccades. Do saccade costs still affect saccade selection when other factors such as salience attract gaze? Here, we addressed if, and how, saccade costs and salience together drive saccade selection by having participants freely choose between two potential saccade targets in different directions. Saccade targets either differed in salience or not, allowing us to disentangle the effects of saccade costs and salience. We observed that salience predicted saccade selection: participants chose salient over non-salient targets. Furthermore, saccade costs predicted saccade selection when equally salient targets were presented. When the possible targets differed in salience, the effect of saccade costs on saccade selection was reduced but not eliminated. Further analyses demonstrate that saccade costs and salience jointly drive saccade selection. Together, our results are in line with an accumulating body of work, and show that the role of effort in saccade selection is robust to salience. We conclude that effort must be considered a fundamental factor that drives where the eyes are moved.