How do humans mediate with the external physical world? From perception to control of articulated objects

Many actions in our daily life involve operation with articulated tools. Despite the ubiquity of articulated objects in daily life, human ability in perceiving the properties and control of articulated objects has been merely studied. Articulated objects are composed of links and revolute or prismatic joints. Moving one part of the linkage results in the movement of the other ones. Reaching a position with the tip of a tool requires adapting the motor commands to the change of position of the endeffector different from the action of reaching the same position with the hand. The dynamic properties are complex and variant in the movement of articulated bodies. For instance, apparent mass, a quantity that measures the dynamic interaction of the articulated object, varies as a function of the changes in configuration. An actuated articulated system can generate a static, but position-dependent force field with constant torques about joints. There are evidences that internal models are involved in the perception and control of tools. In the present work, we aim to investigate several aspects of the perception and control of articulated objects and address two questions, The first question is how people perceive the kinematic and dynamic properties in the haptic interaction with articulated objects? And the second question is what effect has seeing the tool on the planning and execution of reaching movements with a complex tool? Does the visual representation of mechanism structures help in the reaching movement and how? To address these questions, 3D printed physical articulated objects and robotic systems have been designed and developed for the psychophysical studies. The present work involves three studies in different aspects of perception and control of articulated objects. We first did haptic size discrimination tasks using three different types of objects, namely, wooden boxes, actuated apparatus with two movable flat surfaces, and large-size pliers, in unimanual, bimanual grounded and bimanual free conditions. We found bimanual integration occurred in particular in the free manipulation of objects. The second study was on the visuo-motor reaching with complex tools. We found that seeing the mechanism of the tool, even briefly at the beginning of the trial, improved the reaching performance. The last study was about force perception, evidences showed that people could take use of the force field at the end-effector to induce the torque about the joints generated by the articulated system.