Stronger discounting of external cause by action in human adults: evidence for an action-based hypothesis of visual...

When an actor performs an action on an external object, the actor feels that he or she is exerting a force on that object. By extension, when an observer views a collision between 2 objects, he or she is able to perceive the force that is exerted on the objects during the collision. The latter case is puzzling, as force is not a visual feature per se. In a series of 6 experiments, the present study aimed to clarify whether and how the experience of acting on an object influences causal impressions of collision. In the study, an external cause object and a participant's finger both made contact with an effect object, which subsequently started moving. Participants' ratings of causality revealed that causal impressions of the finger were stronger than those of the cause object (i.e., stronger discounting of the causality of the object by finger touch). Discounting was not due to the occasional earlier finger touches or attention distraction from the cause object. In addition, showing images of a finger touch to participants without having them undertake actual action did not result in the same discounted causality as would an actual action. These results are discussed in terms of the action-based hypothesis of collision perception, which holds that the impression of exertion of force when observing a collision event is derived from the mechanoreceptor experience of acting on an object.