Sarah Lassise¹, Marina Pace², Benjamin van Buren³; ¹The New School, ²The New School, ³The New School

Imagine you are in a crowd trying to detect the movements of an assassin. Which entities would your visual system most readily interpret as chasing you? Intuitively, you might be biased to see chasing among figural regions—objects—rather than ground regions (spaces between and within objects and surfaces). However an alternative possibility is that you readily see chasing in any bounded visual region that moves appropriately, independently of whether you perceive it as figure or ground. Subjects wore 3D anaglyph glasses and played a ‘keepaway’ game, using the mouse to move a small disc around a rectangle presented in front of a textured background. The rectangle was populated by moving Objects (circular cutouts of background texture presented in front of the rectangle) and Holes (circular apertures which revealed parts of the background as they moved). On each trial, the subject tried to detect and evade one of the shapes, which chased their cursor with one of four degrees of chasing subtlety—with heading updates 0° toward their cursor, or drawn from a +/- 60/120/180° range centered on their cursor. Chasing detection and evasion were greater for Objects than Holes across subtlety levels, but for both types of entities, the rate of detecting and evading the shape as a function of chasing subtlety followed a strikingly-similar U-shaped curve: Subjects easily detected and evaded obvious 0° chasing shapes, fell prey to 60/120° shapes approaching obliquely like assassins, and easily evaded ‘incompetent’ 180° shapes chasing too indirectly to approach. These results show that chasing detection favors figural objects, but that holes can still be perceived as chasing to some extent. The similar effects of chasing subtlety for Objects and Holes are consistent with a chasing detector that operates over the movements of bounded regions, which is only partially sensitive to figure–ground distinctions.