Illusory ownership of a virtual child body causes overestimation of object sizes and implicit attitude changes.

An illusory sensation of ownership over a surrogate limb or whole body can be induced through specific forms of multisensory stimulation, such as synchronous visuotactile tapping on the hidden real and visible rubber hand in the rubber hand illusion. Such methods have been used to induce ownership over a manikin and a virtual body that substitute the real body, as seen from first-person perspective, through a head-mounted display. However, the perceptual and behavioral consequences of such transformed body ownership have hardly been explored. In Exp. 1, immersive virtual reality was used to embody 30 adults as a 4-y-old child (condition C), and as an adult body scaled to the same height as the child (condition A), experienced from the first-person perspective, and with virtual and real body movements synchronized. The result was a strong body-ownership illusion equally for C and A. Moreover there was an overestimation of the sizes of objects compared with a nonembodied baseline, which was significantly greater for C compared with A. An implicit association test showed that C resulted in significantly faster reaction times for the classification of self with child-like compared with adult-like attributes. Exp. 2 with an additional 16 participants extinguished the ownership illusion by using visuomotor asynchrony, with all else equal. The size-estimation and implicit association test differences between C and A were also extinguished. We conclude that there are perceptual and probably behavioral correlates of body-ownership illusions that occur as a function of the type of body in which embodiment occurs.

The role of haptic feedback for the integration of intentions in shared task execution.

Recent developments strive for realizing robotic systems that not only interact, but closely collaborate with humans in performing everyday manipulation tasks. Successful collaboration requires the integration of the individual partner's intentions into a shared action plan, which may involve continuous negotiation of intentions. We focus on collaboration in a kinesthetic task, i.e., joint object manipulation. Here, ways must be found to integrate individual motion and force inputs from the members of the human-robot team, in order to achieve the joint task goal. Before guidelines on how robots should act in this process can be formulated, clarification on whether humans use the haptic channel for communicating their intentions is needed. This paper investigates this question in an experimental setup involving two collaborating humans. We consider physical effort as well as performance as indicators of successful intention integration. Our results strongly suggest that intention integration is enhanced via the haptic channel, i.e., that haptic communication takes place, especially in the case of shared decision situations. This provides a motivation for future investigations to model the process of intention integration itself in order to realize successful haptic human-robot collaboration.