Depth Affects Where We Look

Abstract

Understanding how we spontaneously scan the visual world through eye movements is crucial for characterizing both the strategies and inputs of vision. Despite the importance of the third or depth dimension for perception and action, little is known about how the specifically three-dimensional aspects of scenes affect looking behavior. Here we show that three-dimensional surface orientation has a surprisingly large effect on spontaneous exploration, and we demonstrate that a simple rule predicts eye movements given surface orientation in three dimensions: saccades tend to follow surface depth gradients. The rule proves to be quite robust: it generalizes across depth cues, holds in the presence or absence of a task, and applies to more complex three-dimensional objects. These results not only lead to a more accurate understanding of visuo-motor strategies, but also suggest a possible new oculomotor technique for studying three-dimensional vision from a variety of depth cues in subjects--such as animals or human infants--that cannot explicitly report their perceptions.

Depth cue combination in spontaneous eye movements

“…Our results for saccades extend those recently published by Wexler and Ouarti (2008), who showed that spontaneous saccade directions follow the tilt axis of an inclined plane, for a variety of depth cues that were presented singly (other recent work that reports compatible results is Jansen, Onat, & König, 2009). The fact that spontaneous saccade directions are aligned with the surface depth gradient of a purely disparity-defined plane as shown by Wexler and Ouarti (2008) excludes the possibility that the luminance gradient, always correlated with the perspective tilt axis, guided saccade directions in that and the current study.…”

“…The fact that spontaneous saccade directions are aligned with the surface depth gradient of a purely disparity-defined plane as shown by Wexler and Ouarti (2008) excludes the possibility that the luminance gradient, always correlated with the perspective tilt axis, guided saccade directions in that and the current study. Earlier, Vishwanath and Kowler (2004) reported that saccade landing positions were related to the 3D geometric cues of the saccade targets revealing that depth cues are important in driving saccades, whereas luminance has been shown to have at the most a moderate effect on saccade landing positions (Melcher & Kowler, 1999;Spering, Montagnini, & Gegenfurtner, 2008).…”

“…The fact that experienced observers made stereotypical saccades, when instructed to fixate, probably means that this instruction was interpreted as an additional task. All inexperienced observers, both in the current study and in that of Wexler and Ouarti (2008), showed a robust correlation between their spontaneous eye movements and the 3D structure of the stimulus.…”

“…Recently, it has been reported that depth is an important variable in driving eye movements: the directions of spontaneous saccades tend to follow depth gradients, or, equivalently, surface tilts (L. Jansen, S. Onat, & P. König, 2009;M. Wexler & N. Ouarti, 2008).…”

“…Recently, another link has been found between 3D perception and eye movements: spontaneous saccade directions have been shown to be highly aligned with the direction of the depth gradient, or tilt, of planes inclined in depth (Wexler & Ouarti, 2008). 1 This effect was shown to hold for different depth cues (disparity, perspective, texture gradients, presented without cue conflict) and to generalize to objects composed of multiple planes.…”