Path completion after haptic exploration without vision: implications for haptic spatial representations

Subjects haptically explored two legs of a triangular path and responded by returning to the origin. Seven conditions were tested, varying in (1) whether the path was imaginally displaced between the initial exploration and the response; (2) the nature of the displacement, if present--rotation or translation; (3) variability in the origin location across trials; and (4) instructions to complete a triangle versus remembering the origin location. Mean distance and angle responses were modeled by the encoding-error model (Fujita, Klatzky, Loomis, & Golledge, 1993), which attributes errors to misencoding of the path legs and angle. The model failed to predict the finding of systematic errors in response distance but not response angle, a dissociation that held when the path was undisplaced or imaginally translated. Rotation before responding produced errors more consistent with the model. The data suggest use of a body-centered representation to complete undisplaced or imaginally translated paths, but adoption of an object-centered representation after imagined rotation, as is more consistent with pathway completion using whole-body locomotion.