Figure 1.

Experimental setup of the perceptual crossing paradigm. (A) The physical setup. The two participants can only engage with each other via a haptic human-computer interface that reduces their scope for bodily interaction to a minimum of horizontal left to right movement and tactile sensation. Each player’s interface consists of two parts: (1) a trackball that controls the displacement of their “avatar” in an invisible 1D virtual environment; and (2) a hand-held haptic feedback device that vibrates at a constant frequency for as long as the avatar overlaps another virtual object and remains off otherwise. (B) The virtual setup. Players are embodied as minimal avatars on an invisible line that wraps around after 600 units of space. Each avatar consists of a binary contact sensor and a body object. Unbeknownst to the players a “shadow” object is attached to each avatar body at a fixed distance of 150 units. There are also two static objects, one for each player. All objects are four units long and can therefore only be distinguished interactively in terms of their different affordances for engagement.