Visual capture influences body-based indications of visual extent

Visual information regarding limb location can override proprioceptive information when there is conflict between the two—a phenomenon referred to as visual capture. In three experiments, we employed the “mirror illusion,” in which the perceived location of one's hand is influenced by the visual information specified by the mirror reflection of the other hand, to test whether visual capture influences body-based indications of the extent of objects. Participants viewed their visible hand and its reflection in a mirror after the unseen hand was positioned at one of four locations on a tabletop. The unseen hand's location appeared to be the same distance from the mirror as the visible hand's location. After viewing the visible hand and its reflection while simultaneously performing simple finger movements with both hands, participants viewed a block and had to move their unseen hand to a position that would allow them to grasp the block between their two hands. Movements of the unseen hand relative to the visible hand were biased by the visual information, reflecting errors in moved hand position given visual-proprioceptive conflict. In Experiment 1, visual capture influenced the indications of object extent for objects within reach and aligned with the viewer's midline. Experiments 2 and 3 extended these findings to indications of extent for objects outside the viewer's reach (Experiment 2) and misaligned with the viewer's midline (Experiment 3). These results suggest that visual body information has a generalizable effect on actions used to indicate space perception that extends beyond egocentric spatial localization tasks.