Expecting to lift a box together makes the load look lighter

The action abilities of an individual observer modulate his or her perception of spatial properties of the environment and of objects. The present study investigated how joint action abilities shape perception. Four experiments examined how the intention to lift an object with another individual affects perceived weight. In Experiments 1, 2a, and 2b, participants judged the perceived weight of boxes while expecting to lift them either alone or with a co-actor. In Experiment 3, the co-actor was healthy or injured. Participants intending to lift a box with a co-actor perceived the box as lighter than participants intending to lift the same box alone, provided that the co-actor appeared healthy and therefore capable of helping. These findings suggest that anticipated effort modulates the perception of object properties in the context of joint action. We discuss implications for the role of action prediction and action simulation processes in social interaction

Imitation of coordinated actions: How do children perceive relations between different parts?

Young children not only need to learn how to perform isolated actions, but also temporally and spatially coordinated actions such as using a knife and fork. Routes to learning such coordinated actions include imitation and participation in joint action. However, little is known about the mechanisms guiding transmission of coordinated actions through observation and joint action performance. This paper reports an experiment comparing children's tendency to imitate multiple, coordinated actions following demonstration by a single model acting bimanually (Bimanual Observation condition), two models performing the same actions jointly with one performing each hand action (Joint Observation condition) and a condition in which the child actively takes part in the joint action demonstration by performing one part in coordination with a partner (Joint Action condition). When children were subsequently left alone to perform the task independently, they were more likely to imitate both coordinated actions in the two observation conditions than in the Joint Action condition, with no difference between performance in Bimanual and Joint Observation conditions. It is argued that this is due to children being more able to form a global representation of both actions and the relations between the two when observing from a distance than when actively involved in the task

Differing Dynamics of Intrapersonal and Interpersonal Coordination: Two-finger and Four-Finger Tapping Experiments

Finger-tapping experiments were conducted to examine whether the dynamics of intrapersonal and interpersonal coordination systems can be described equally by the Haken-Kelso-Bunz model, which describes inter-limb coordination dynamics. This article reports the results of finger-tapping experiments conducted in both systems. Two within-subject factors were investigated: the phase mode and the number of fingers. In the intrapersonal experiment (Experiment 1), the participants were asked to tap, paced by a gradually hastening auditory metronome, looking at their fingers moving, using the index finger in the two finger condition, or the index and middle finger in the four-finger condition. In the interpersonal experiment (Experiment 2), pairs of participants performed the task while each participant used the outside hand, tapping with the index finger in the two finger condition, or the index and middle finger in the four-finger condition. Some results did not agree with the HKB model predictions. First, from Experiment 1, no significant difference was observed in the movement stability between the in-phase and anti-phase modes in the two finger condition. Second, from Experiment 2, no significant difference was found in the movement stability between the in-phase and anti-phase mode in the four-finger condition. From these findings, different coordination dynamics were inferred between intrapersonal and interpersonal coordination systems against prediction from the previous studies. Results were discussed according to differences between intrapersonal and interpersonal coordination systems in the availability of perceptual information and the complexity in the interaction between limbs derived from a nested structure