Explicit and implicit measures of body ownership and agency: affected by the same manipulations and yet independent.

Abstract

People are assumed to represent themselves in terms of body ownership and agency. Studies using the rubber- or virtual-hand illusion have assessed ownership and agency by means of explicit ownership and agency ratings and implicit measures, like proprioceptive drift in the case of ownership. These measures often show similar effects but also some discrepancies, suggesting that they rely on data sources that overlap, but not completely. To systematically assess commonalities and discrepancies, we adopted an immersed virtual hand illusion (VHI) design, in which three independent factors were manipulated: the synchrony between the movement of real and virtual effector, the type of effector, which was a virtual hand or triangle, and the spatial congruency between the real and virtual effector. Commonalities and discrepancies in the effects of these factors were assessed by crossing explicit and implicit measures for ownership and agency. While standard ratings were used as explicit measures, implicit ownership was assessed by means of proprioceptive drift and implicit agency by means of intentional binding. Results showed similar effect patterns for the two agency measures, which, however, were not correlated, different effect patterns for the two ownership measures, and a strong correlation between the two explicit measures. Taken altogether, our findings suggest that explicit and implicit measures of ownership and agency partly rely on shared informational sources, but seem to differ with respect to other sources that are integrated or with respect to the processed dimension (shape vs. time). The findings also suggest that some findings obtained with RHI designs might reflect more the unnatural situation that that design puts individuals into rather than generalizable mechanisms of computing perceived ownership and agency.