Judging and actualizing intrapersonal and interpersonal affordances.

The current study investigated the perception of intrapersonal, interpersonal, and tool-based grasping possibilities. In Experiment 1, participants judged whether they would grasp planks of wood-presented in ascending, descending, and random orders of length-using one hand (1H), two hands (2H), or with a tool that extended their reach (TH). In Experiment 2, participants physically grasped the planks using 1H, 2H, or TH. In Experiments 3 and 4, the choice of TH was replaced with a choice of grasping the planks with another person (2P). The results showed that presentation order influenced the participants' behavior differently in the judgment and action experiments. The same behavioral patterns, however, were observed when participants switched between 1H and 2H, 2H and TH, and 2H and 2P grasping. The point at which participants judged they would switch between the different modes of grasping, as well as the point at which participants physically switched between the grasping modes, occurred at similar action-scaled ratios. The equivalence of perceiving intrapersonal and interpersonal affordances is discussed.