Speed overestimation in intentional reaction.

When an object (A) moves up to and makes contact with another object (B), which then moves off, its motion appears passive if A is faster (launching) and active if A is slower (triggering). We showed (Parovel and Casco, 2006 Vision Research 46 4134 ^ 4142) an overestimation of B speed, proportional to A speed in launching and constant in triggering. We asked whether this speed overestimation applies not only to mechanical causality but also to intentional reaction, in which B motion is faster, starts before the arrival of A, and is perceived to intentionally escape from A. In both intentional reaction and triggering, conditions where B is perceived as self-propelled, we found overestimation (25% vs 20% respectively) independent of A speed. These results suggest that both mechanical causality and social causality phenomena are related to precise rules applied by the visual system at a low level of motion integration.