Predictive extrapolation of observed body movements is tuned by knowledge of the body biomechanics.

After a moving object has disappeared, observers typically mislocate its final position to where that object would have been if it had briefly continued to move. Previous studies have shown that this "forward displacement" (FD) is significantly smaller when observers see an upper-limb movement directed away from the body that would have been biomechanically impossible to continue along the same trajectory after it has disappeared than when the movement is directed toward the body and would have been easy to continue. This finding has been argued to reflect an implicit influence of observers' biomechanical knowledge on FD. However, this effect could also result from a "landmark attraction", which has been shown to reduce the size of displacement when an object moves away, rather than toward, from a landmark. To discriminate these possibilities, we measured the FD elicited by arm movements directed away or toward the body, which would have been biomechanically impossible or easy to continue after the stimuli disappeared, and by highly similar movements of geometrical shapes. In 2 experiments, we found a significantly larger effect of movement direction for the human stimuli. Thus, knowledge of the body biomechanics influences FD for body movements. (PsycInfo Database Record (c) 2023 APA, all rights reserved).