It has been suggested that the integration of multiple body-related sources of information within the peri-personal space (PPS) scaffolds body ownership. However, a normative computational framework detailing the functional role of PPS is still missing. Here we cast PPS as a visuo-proprioceptive Bayesian inference problem whereby objects we see in our environment are more likely to engender sensations as they come near to the body. We propose that PPS is the reflection of such an increased a priori probability of visuo-proprioceptive coupling that surrounds the body. To test this prediction, we immersed participants in a highly realistic virtual reality (VR) simulation of their right arm and surrounding environment. We asked participants to perform target-directed reaches toward visual, proprioceptive, and visuo-proprioceptive targets while visually displaying their reaching arm (body visible condition) or not (body invisible condition). Reach end-points are analyzed in light of the coupling prior framework, where the extension of PPS is taken to be represented by the spatial dispersion of the coupling prior between visual and proprioceptive estimates of arm location. Results demonstrate that if the body is not visible, the spatial dispersion of the visuo-proprioceptive coupling relaxes, whereas the strength of coupling remains stable. By demonstrating a distance-dependent alteration in visual and proprioceptive localization attractive pull toward one another (stronger pull at small spatial discrepancies) when the body is rendered invisible – an effect that is well accounted for by the visuo-proprioceptive coupling prior – the results suggest that the visible body grounds visuo-proprioceptive coupling preferentially in the near vs. far space.

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The Active Handrest is a large workspace assistive robotic device that has been shown to significantly improve the user performance of various movement tasks. This device has the potential to assist highly accurate motions without the need for a robotically enabled or comanipulated tool while allowing the user to retain complete control over a grasped tool. This paper evaluates the Active Handrest's effect on the kinematics of user movements together with various virtual fixture control strategies to further improve the human performance while using the Active Handrest. The most effective fixture strategy for tracing straight lines is first determined. Then, this fixture strategy is directly implemented on the Active Handrest's motions. Finally, the performance of different fixture strategies is assessed through speed-accuracy tradeoff and movement kinematics. It is concluded that fixtures implemented on the Active Handrest are as effective as those implemented on a grasped tool, which enables users of the Active Handrest high accuracy with ordinary tools such as a scalpel or paint brush. The performance is further improved when fixtures are implemented on both the Active Handrest and the grasped tool.

This paper presents a tactile display device for replicating compliance sensation when interacting with deformable and nondeformable compliant objects in a virtual environment. Two small tilting plates approximately reproduce surface deformations of a compliant object. In addition to tactile information, kinesthetic information is rendered through a modified haptic paddle force feedback device. The tilting plates are moved in conjunction with the measured position of the user's finger as they pressed into the virtual surface. In a psychophysical experiment, we evaluated the effect of adding tilting motion of the device's actuated plates on the perceived compliance of a virtual surface with a kinesthetic stiffness of 60 N/mm. The experiment results indicate that tilting rates of 5, 10, and 20 deg/cm reduced the perceived stiffness of the surface by 3, 9, and 17 N/m, respectively. The advantages of the new device include its light-weight, low-cost, and simple design. These device features make it practical to integrate this compliance display with user interfaces for applications such as video games or even robotic surgery.