Explicit spatial compatibility is not critical to the object handle effect

In object perception studies, a response advantage arises when the handle of an object is congruent with the responding hand. This handle effect is thought to reflect increased motor activation of the hand most suited to grasp the object, consistent with affordance theories of object representation. An alternative explanation has been proposed, however, which suggests that the handle effect is related to a simple spatial compatibility effect (the Simon effect). In 3 experiments, we determined whether the handle effect would emerge in the absence of explicit spatial compatibility between handle and response. Stimulus and response location was varied vertically and participants made horizontally orthogonal, bimanual responses to objects' kitchen/garage category, color (as in a traditional Simon effect) or upright/inverted orientation. Categorization and inversion tasks, which relied on object knowledge, elicited a handle effect and a vertical Simon effect regarding stimulus and response locations. When participants judged object color, as per standard Simon effect paradigms, the handle effect disappeared but the Simon effect strengthened. These data demonstrate a dissociation between affordance and spatial compatibility effects and prove that affordance plays an important role in the handle effect. Models that incorporate both affordance and spatial compatibility mechanisms are discussed.