Do exploratory arm movements contribute to maximum reach distance judgements?

Exploratory movements provide information about agents' action capabilities in a given environment. However, little is known about the specifics of these exploratory movements, such as which movements are necessary to perceive a given action capability. This experiment tested whether arm movements contributed to judgements of maximum reach distance. Participants made judgements about their maximum reach distance by walking to the point farthest from an object from which they still perceived the object to be reachable. Over the course of two sets of nine judgements, participants' arms either swung naturally by their sides (Unrestricted Condition) or were held together behind their backs (Restricted Condition). Arm movement restriction increased maximum reach distance judgement error when compared with unrestricted judgements. In addition, judgement error improved over trials only when exploratory arm movements were unrestricted, and the improvements did not carry over to subsequent judgements made when exploratory arm movements were restricted. Arm movement restriction did not increase the variability of judgement error when compared with unrestricted judgements. The results indicate that exploration is necessary to generate affordance information, show that restricted exploration degrades affordance perception, and suggest that maximum reach distance exists at the global array level. In addition, they have practical implications for operational situations in which actors' arm movements are restricted, such as when military personnel wear body armour.