Projecting the self outside the body: Body representations underlying proprioceptive imagery

Recent research has shown that proprioception relies on distorted representations of body size and shape. By asking participants to localise multiple landmarks on their occluded hand, perceptual maps of hand size and shape can be constructed and compared to actual hand structure. These maps are different from the actual size and shape of the occluded hand, revealing underestimation of finger length and overestimation of hand width. Here we tested whether the same distorted body model underlies proprioceptive imagery (i.e. imagining the hand at a specific location, and in a different posture than it actually is). In Experiment 1, participants placed their left hand under an occluding board (real condition) or imagined their left hand under the board (imagined condition). Highly similar distortions were found in both conditions. Furthermore, results across the two conditions were strongly correlated. In Experiment 2, participants completed the real condition and two imagined conditions. In the imagined-fist condition, participants held their left hand in a fist, in their lap, while in the imagined-flat condition, participants held their left hand flat, with palm down, in their lap. In both imagined conditions, participants were asked to imagine their left hand lying flat, with palm down, under the occluding board. A similar pattern of distortions was found in all three conditions. These results suggest that both proprioception and proprioceptive imagery reply on a common stored model of the body's metric properties.