The impact of a central or peripheral visual field loss on the vision strategy used to guide walking was determined by measuring walking paths of visually impaired participants. An immersive virtual environment was used to dissociate the expected paths of the optic-flow and egocentric-direction strategies by offsetting the walker's point of view from the actual direction of walking. Environments consisted of a goal within a forest, the goal alone, or the forest alone following a brief presentation of the goal. The first two environments allowed an evaluation of the visual information used in a goal-directed task whereas the third environment investigated the information used in a memory-guided task. Participants had either a central (CFL) or peripheral visual field loss (PFL) or were fully sighted (FS). Results showed that, for the goal-directed task, the CFL group was less influenced by optic flow than was an age-matched FS group. Optic flow decreased heading error by only 1.3 degrees (16%) in the CFL group compared to 3.6 degrees (42%) in the FS group. The PFL group showed an optic-flow influence (2.4 degrees or 26%) comparable to an older, age-matched FS group (2.9 degrees or 31%). For the memory-guided task, all but the PFL group had heading errors comparable to those obtained in the goal-alone scene, demonstrating the ability to use an egocentric-direction strategy with a stored representation of either the goal's position or an offset relative to a landmark instead of a visible goal. The paths of the PFL group veered significantly from the predicted paths of both the optic-flow and egocentric-direction strategies. The findings of this study suggest that central vision is important for using optic flow to guide walking, whereas peripheral vision is important for establishing and/or updating an accurate representation of spatial structure for navigation.
Robots for surgery and rehabilitation have emerged and are gaining popularity among patients and medical doctors with their obvious benefits, such as overcoming obstacles from human users’ physical restraints, reducing physicians’ workload, and enhancing the efficacy of medical treatment. The development of medical robots meets two challenges related to their special application environments, including sterilization hazards and size/weight limitation. Medical robots (e.g., surgical robots) usually need to have close contact with human skin or organs, which need to be sterilized. However, chemical or heat sterilization on the robots poses an inevitable risk of damage on the motors, sensors, and other electronic components. The size of the surgical robot needs to be compact to gain access to surgical sites. The rehabilitation robots that patients wear have to limit their size and weight. Wire-driven actuation is a potential solution to solve these issues by avoiding the use of bulky mechanical gears and links and locating the electronic components far away from the sterilization environment. This paper presents the development of a novel wire-driven universal joint for medical robot design. With its special structure, this robotic joint has self-decoupled kinematics which can simplify its control system and increase motion accuracy. Benchtop experiments are conducted to verify the functionality of this joint and the effectiveness of its self-decoupled kinematics.
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