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Joe Anderson, Geoffrey Bingham; Visually guided reaching using proportional rate control of disparity tau: Data and model. Journal of Vision 2008;8(6):309. doi: 10.1167/8.6.309.
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© ARVO (1962-2015); The Authors (2016-present)
Introduction: What information is used for modulating velocity during approach in targeted reaching? We propose a novel strategy for the visual guidance of reaching based on the use of disparity tau to control approach to matched disparity. We hypothesize that the rate of change of disparity tau is kept in proportion to disparity tau. Previous research using a slider apparatus to examine this question produced mixed results (Anderson & Bingham, 2007). Here, we used normal reaches at preferred rates to test alternative disparity tau-based strategies. In simulations, we found that maintaining a constant ratio of disparity tau to its rate of change produced reach-like trajectories. We isolated the use of binocular disparity in a distance matching reach task to test this hypothesis.
Methods: Eight participants were asked to match in darkness the distance of a point-light on their finger to a target point-light by reaching at preferred rates. Participants reached under conditions of visual guidance or no visual guidance and with or without a perturbed inter-pupillary distance. The latter rendered vergence information unreliable and inaccurate, thus requiring online use of disparity matching for successful reaches. Reach trajectories were recorded using a Mini-bird motion measurement system.
Results: Results show that participants used a constant ratio strategy beginning just before the decelerative portion of the reach and ending at contact. Statistical tests showed that disparity tau-dot decreased while the disparity tau/tau-dot ratio remained constant. These results replicated those from a concurrent study of walking-to-reach (Anderson & Bingham, submitted). Finally, the detailed forms of these reach trajectories were modeled using a mass-spring model of reaching driven by proportional rate disparity tau information.
Conclusion: The first dynamical model of online guidance of reaching complete with appropriate information variables was supported.
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