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We investigated how the control of a compliant object is realized by the redundancy of wrist anatomy. Subjects had to balance a one degree-of-freedom inverted pendulum using elastic linkages controlled by wrist flexion/extension (FE) and forearm pronation/supination (PS). Haptic feedback of the interaction forces between the pendulum and the wrist was provided by a robotic interface. By tuning the mechanical properties of the virtual pendulum and the stiffness of the elastic linkages it was possible to study various dynamical regimes of the simulated object. Twenty subjects (divided in two groups) were tested in four days performing the same task but with different presentation order. The stabilization strategy adopted by the subjects was characterized by primarily using the PS DoF when the pendulum was linked to stiff springs and characterized by a relatively fast dynamic response; in contrast, the stabilization task was shared by both DoFs in case of lower spring stiffness and slower dynamics of the virtual object. This video shows a haptic device in use.

The full article can be found here: http://doi.ieeecomputersociety.org/10.1109/TOH.2012.35

Tactile motion guidance systems aim to direct the user's movement toward a target pose or trajectory by delivering tactile cues through lightweight wearable actuators. This study evaluates 10 forms of tactile feedback for guidance of wrist rotation to understand the traits that influence the effectiveness of such systems. We present five wearable actuators capable of tapping, dragging across, squeezing, twisting, or vibrating against the user's wrist; each actuator can be controlled via steady or pulsing drive algorithms. Ten subjects used each form of feedback to perform three unsighted movement tasks: directional response, position targeting, and trajectory following. The results show that directional responses are fastest when direction is conveyed through the location of the tactile stimulus or steady lateral skin stretch. Feedback that clearly conveys movement direction enables subjects to reach target positions most quickly, though tactile magnitude cues (steady intensity and especially pulsing frequency) can also be used when direction is difficult to discern. Subjects closely tracked arbitrary trajectories only when both movement direction and cue magnitude were subjectively rated as very easy to discern. The best overall performance was achieved by the actuator that repeatedly taps on the subject's wrist on the side toward which they should turn. In the paper, they describe the supplemental material as "Fig. 2 shows isometric drawings of the four custom actuators, and this paper's supplemental video, which can be found on the Computer Society Digital Library at http://doi.ieeecomputersociety.org/10.1109/ToH.2012.33, shows all of the actuators in use. This video shows four novel tactile actuators in use.

The full article can be found here: http://doi.ieeecomputersociety.org/10.1109/ToH.2012.33