Stop before you saccade:: Looking into an artificial peripheral scotoma

Abstract

We investigate whether adults with healthy vision can move their eyes toward an informative target area that is initially hidden by a gaze-contingent scotoma in the periphery, when they are under time pressure. In the experimental task, participants have to perform an object-comparison task, requiring a same-different judgment about two silhouettes. One silhouette is visible, while the other is hidden under the scotoma. Despite time pressure and the presence of the visible silhouette, most participants are able to move their eyes toward the informative region to reveal the hidden silhouette. Saccades to the hidden stimulus occur when the visible stimulus is presented directly opposite in either fixed or variable locations, and when the visible stimulus is presented at an adjacent location. Older participants are also able to perform this task. First saccades in the direction of the hidden stimulus have longer latencies compared to saccades towards the visible one. This suggests the use of a deliberate, non-reflexive saccade strategy ('stop before you saccade'). A subset of participants occasionally makes curved saccades that are first aimed towards the visible stimulus and then towards the hidden one. We discuss the implications of our findings for patients who have a biological scotoma, for example in macular degeneration.