The ground side of an object: perceived as shapeless yet processed for semantics.

Traditional theories of perception posit that only objects access semantics; abutting, patently shapeless grounds do not. Surprisingly, this assumption has been untested until now. In two experiments, participants classified silhouettes as depicting meaningful real-world or meaningless novel objects while event-related potentials (ERPs) were recorded. The borders of half of the novel objects suggested portions of meaningful objects on the ground side. Participants were unaware of these meaningful objects because grounds are perceived as shapeless. In Experiment 1, in which silhouettes were presented twice, N400 ERP repetition effects indicated that semantics were accessed for novel silhouettes that suggested meaningful objects in the ground and for silhouettes that depicted real-world objects, but not for novel silhouettes that did not suggest meaningful objects in the ground. In Experiment 2, repetition was manipulated via matching prime words. This experiment replicated the effect observed in Experiment 1. These experiments provide the first neurophysiological evidence that semantic access can occur for the apparently shapeless ground side of a border.