Human heading judgments and object-based motion information

In four experiments, we explored observers' ability to make heading judgmen ts from simulated linear and circular translations through sparse forests a nd with pursuit fixation on one tree. We assessed observers' performance an d information use in both regression and factorial designs. In all experime nts we found that observers used three sources of object-based information to make their judgments-the displacement direction of the nearest object se en (a heuristic), inward displacement towards the fovea (an invariant) and outward deceleration (a second invariant). We found no support for the idea that observers use motion information pooled over regions of the visual fi eld. (C) 1999 Elsevier Science Ltd. All rights reserved.