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Aaron Fath, Geoffrey Bingham; One thing at a time: Sequential coordination in visual guidance of locomotion-to-reach. Journal of Vision 2012;12(9):194. doi: https://doi.org/10.1167/12.9.194.
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The information and means of control that allow humans to locomote (Fajen & Warren, 2004) or reach (Anderson & Bingham, 2010) is well-studied, but less is known about the coordination of these actions when locomoting-to-reach. Anderson & Bingham (2010) proposed a new informational variable, hand-centric relative disparity tau, based on the evolution of relative binocular disparities of the hand and target over time. They also proposed a new control strategy, proportional rate control, that maintains informational variables in constant proportion with their own rates of change. In Anderson & Bingham (2011), participants locomoted to targets with outstretched hands and were found to use proportional rate control with head-centric tau to guide movement. Once hand-centric tau specified a time-to-contact less than that of the head-centric tau, participants applied proportional rate control to this now more conservative variable. In the current study, ten participants locomoted to a point-light target to place a point-light on their thumb beside the target. Participants performed 30 trials in each of two conditions: locomoting with an outstretched hand and initiating a reach to the target while locomoting. Results of the former condition replicated Anderson & Bingham (2011). In the latter condition, we hypothesized that head-centric tau would be used to initiate a "ballistic" reach, at the end of which head and arm/hand would form a rigid body, control then being switched from head-centric to hand-centric tau to bring the hand to the target using proportional rate control. Reach initiation was best predicted by head-centric tau, with an overall mean value of 0.92, and individual subjects were reliable, exhibiting an average standard deviation of 0.13. Overall, reaches had a mean duration of 530ms and terminated with 678ms actual time-to-contact. Upon termination, the hand was guided to the target using proportional rate control of disparity tau, as shown by regression analysis and model fits.
Meeting abstract presented at VSS 2012
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