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Vilelmini Kalampratsidou, Elizabeth Torres; Invariant and variable relations emerge with degrees of difficulty within habitual and surprise touch-pointing motions. Journal of Vision 2014;14(10):418. https://doi.org/10.1167/14.10.418.
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© ARVO (1962-2015); The Authors (2016-present)
Movements are inherently variable. The patterns of variability as we perform motions repetitively can inform us of control strategies within the nervous system. Often we study the endpoint variability in reaching actions but less explored are the patterns of variability as the action unfolds. In this work we study the patterns of variability as the person habituates to the drawing of geometric figures with vertices prompted ahead, as the hand habituates to the touches of points that appear in succession. As the motions become highly predictive of the next vertex location and the subjects naturally gain speed, we throw in a surprise point at an unexpected location. Under these circumstances we study the interactions between various kinematic parameters at the level of the end effector and also within a subset of the joint angles of the arm (7 degrees of freedom). We ask if any relationships self-emerge during these interactions between habitual and surprised motions for spatio-temporal kinematics parameters. We used 5 levels of difficulty including two points (forming a line), three points (a triangle), four points (a square), six points (hexagon) and 11 points with increasing number of surprise points randomly thrown in the sequence. We tested already 5 participants (ongoing experiments) and found across all cases, independently of the number of vertices or surprise points, a linear relationship between the distance from point to point (in pixels) and the speed of the motion (pixels/ms). Yet across subjects the relationship between the time (ms) from point to point and the speed of the motion was non linear and well characterized by a power law with different exponents for different levels of difficulty. We discuss our results in the context of Fitt's Law and report on new findings concerning the joint angles' patterns of variability.
Meeting abstract presented at VSS 2014
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