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Hal S. Greenwald, David C. Knill; Grasping for cues: Visual cue integration for object manipulation. Journal of Vision 2007;7(9):69. doi: 10.1167/7.9.69.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose. We measured the separate influences of monocular and binocular cues on planning and executing arm movements aimed at picking up an object. Method. Subjects viewed a large coin (7 cm diameter, 0.95 cm thickness) that was suspended in a virtual environment binocularly under central fixation. A robot arm positioned an unseen physical coin so that it was co-aligned with the virtual coin in the workspace. The coin's slant (orientation in depth) varied randomly across trials, and we introduced cue conflicts of 0–10° between the monocular cues (contour and texture) and binocular information (disparity) that defined the coin's orientation either at the beginning of each trial or following a mask that appeared upon movement initiation to prevent subjects from becoming aware of changes. Subjects reached for and picked up the real coin by the edges and from the side using a precision grip, and we optically tracked the positions of each subject's thumb and index finger throughout each trial. We used the vector between these fingers as an indicator of the subject's estimate of the coin's orientation. No visual feedback about the positions of the fingers was available until the fingertips made contact with the coin. Results. Subjects were very accurate about how they positioned their fingers to pick up the coin since the mean orientation of the vector between the fingers typically matched the orientation of the coin with a standard deviation of 3–4° on cue-consistent, unperturbed trials. As in a previous study involving object placement (Greenwald et al., 2005), binocular information dominated the execution phase of the movements (the normalized binocular weight was 0.6–0.7). Conclusion. The cue weights we measured during this grasping task were similar to those found for object placement, suggesting that our previous findings generalize to other visuomotor tasks.
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