Abstract
Humans are able to perceive unique types of biological motion presented as point light displays (PLDs). Thirty years ago, Runeson and Fryholm (1983) studied observers' perceptions of weights lifted by actors who moved deceptively to feign the object's mass. They identified that, in spite of the lifter's acting, the PLDs provided enough information about the kinematics necessary to lift the object for the observer to form an accurate perception. However, research also shows that PLDs contain information about human expectation and emotion (e.g., Dittrich et al., 1996). This study improves on Runeson and Fryholm's paradigm by having observers judge the weights lifted by a participant who is under the influence of the size weight illusion. The lifter performed lifts of boxes that varied in size (small, medium, large) and weight (25 lbs, 50 lbs, 75 lbs). Moreover, the participants viewed these lifts across 4 different PLD conditions: box-at-rest, moving box, lifter only, box-and-lifter; and 1 full video condition. The results indicate that participants display the least absolute error when judging the full video condition. Furthermore, in the absence of either box or lifter PLD information, the participants' are not able to significantly differentiate the various box weights. These findings suggest that accurate PLD perceptions depend on information about both the actor and the objects. These results are relevant to processes of observational learning and indicate that PLDs may be insufficient for tasks requiring complex kinematic extraction.
