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Michael Landy, Todd Hudson; Multiple coordinate frames for reaches revealed through adaptation. Journal of Vision 2012;12(9):607. doi: 10.1167/12.9.607.
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© ARVO (1962-2015); The Authors (2016-present)
In what coordinate system are visually guided reaches encoded? We introduce a novel, sensitive method for measuring the adaptive response to reach feedback perturbation, and provide evidence that both polar and Cartesian coordinate systems are used, because adaptive responses can be made to both polar and Cartesian perturbations. Methods: Subjects made center-out reaches on a tabletop with fixed starting point and target distance, with target direction random over trials. Starting point, target, and reach endpoint feedback were shown on a frontoparallel display. During the reach, only the target was shown. After reach completion, fingertip location was shown shifted spatially. The amount of shift was a sinewave over trials. For Cartesian perturbation, on trial t, xdisplay = xfinger + A sin(2πfxt) and similarly for y perturbed with frequency fy. For polar perturbation, gain of displayed relative to actual reach extent was perturbed around 1.0 with a sinewave of frequency fγ and reach direction was perturbed at frequency fθ. For Cartesian, fx=5 and fy=7 cycle/session; A = 6 mm. For polar, the same frequencies were used, and amplitudes were set to achieve similar maximum perturbations. Bayesian methods were used to detect sinusoidal corrections in response to perturbation and to estimate parameters. Results: Under Cartesian perturbation, subjects corrected for both x and y perturbations; under polar perturbation, independent correction of gain and direction was found. In addition, correction was found for reaches to targets at which feedback was never given. Thus, observers could adapt using either coordinate system, as appropriate. The sinewave-perturbation technique provides a far more sensitive technique for measuring adaptation than the typical step-function technique, allowing the use of perturbations so small that subjects are not consciously aware of them.
Meeting abstract presented at VSS 2012
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