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Sinéad Sheehan, Geoffrey P. Bingham, Mark Mon-Williams; Task space calibration in Cartesian coordinates. Journal of Vision 2008;8(6):481. doi: https://doi.org/10.1167/8.6.481.
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Introduction: Numerous studies have shown that visual space: (i) can be adapted following sensorimotor distortion; and (ii) is represented in cyclopean spherical coordinates (e.g. Vetter, Goodbody & Wolpert, 1999). We calibrated participants in a two-dimensional task workspace and tested for error patterns in Cartesian and cyclopean spherical (i.e. polar) coordinates. Methods: Using methods similar to Mon-Williams and Bingham (2007), we calibrated a) target distance or b) direction in a prehension task and tested generalization across the workspace (participant n=20). The apparatus preserved visual information about the object's location using mirrors but allowed haptic feedback about the object's location to be manipulated. The haptic feedback was changed, one dimension at a time, within a polar coordinate arrangement where the starting location of the pinched thumb and index finger, directly below the eyes, was the origin. In condition one, participants were recalibrated in distance at one location and tested at other angular directions. In condition two, participants were recalibrated in angular direction at one location and tested at other distances. We calculated the difference between pre and post calibration reach errors as a measure of the calibrations' generalization. Results: The error patterns in both the “calibrate distance” and “calibrate direction” generalized across reach space and together, were best described by shifts in a Cartesian (x,y) coordinate system. Conclusions: The results suggest that the task did not calibrate performance within a spherical (visual) coordinate system; rather, the adaptation was within a map of the workspace, i.e. an environmental frame of reference. This interpretation is consistent with the task demands, in which the visual input remained constant and the haptic information changed. Participants adapted their performance, rather than the visual information that performance was based on, to maintain accurate prehension. Calibration is therefore a task specific and functional process.
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