Chaeeun Lim¹ (), Dhanraj Vishwanath², Fulvio Domini¹; ¹Brown University, ²University of St Andrews

Imagine two different visuomotor tasks directed at a cup in front of you: either reaching to touch the front or back of the cup separately or grasping it from front-to-back. Intuitively, the first task could be solved with egocentric information (an estimate of distance), while the second task would additionally require exocentric information (an estimate of depth). Indeed, a previous study suggested that reaching to points on two separated rods involved only egocentric information such as vergence angle and accommodation, whereas grasping both rods involved exocentric information specified by cues such as relative disparity. Here, we asked whether this dissociation persists when the observer is asked to either reach to or grasp the front and back of the same object (a binocularly viewed virtual paraboloid). To manipulate exocentric information independently from egocentric information, we added a texture gradient to disparity information that, according to previous studies examining cue combination, should result in a greater perceived exocentric depth. Contrary to the idea that reaching relies solely on egocentric cues, our findings reveal that reaching distance to points on the same object is influenced by both egocentric and exocentric information, mirroring the pattern observed in grasping tasks. Strikingly, participants consistently overestimated the depth interval between the front and back of the object in both reaching and grasping. This overestimation intensified with an additional texture cue, particularly at greater viewing distances, aligning with predictions of a summative model of cue integration (Intrinsic Constraint model). Paradoxically, when subjects reached at the same point in space, its position was underestimated when it represented the object’s front and overestimated when it represented the back. The present findings suggest that the visual system does not exclusively rely on egocentric information to estimate reaching distance for points on the same extended object, but it also incorporates exocentric information.

Acknowledgements: This material is based upon work supported by the National Science Foundation under Grant No.2120610.