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David C. Knill; Differences in cue weighting for action and perception. Journal of Vision 2004;4(8):834. doi: 10.1167/4.8.834.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: (1) To determine the relative contributions of binocular and monocular slant cues to the control of reaching movements. (2) To compare cue weights for motor control with cue weights for perceptual judgments. Methods: Motor task: Subjects viewed a textured disk in a 3D virtual environment with full binocular vision. They moved a cylinder from a starting platform and placed it flush onto the target surface. An optical tracking system was used to measure the position and orientation of the cylinder in real-time. On each trial, a real target surface, invisible to subjects, was positioned and oriented in alignment with the virtual target surface by a robot arm. On half of the trials, the binocular cues (disparity) and monocular cues (outline shape and texture) suggested slightly different slants. We correlated the orientation trajectories of cylinders on the cue-conflict trials with the slants suggested by each set of cues. Perceptual tasks: Using the same stimuli, subjects indicated the perceived slants of stimuli either by setting a 3D line probe to be perpendicular to the displayed surface (visual matching) or manually rotating a cylinder to a position that “felt” like it was flush on the surface (haptic matching). Results: Subjects' orienting movements depended most strongly on binocular cues at low target slants and for irregular figures. Monocular cues contribute much more for large target slants and for circular figures. Similar results were found for the perceptual tasks, but overall, subjects gave significantly more weight to monocular cues for the perceptual tasks than for the motor tasks (@ 30% more). Conclusions: Overall, the visuomotor system appears to rely more heavily on binocular cues than does the perceptual system. Based on these results and others, we argue that the differences may reflect properties of the on-line control phase of movements rather than the planning phase.
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