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Tzvi Ganel, Gal Namdar; Weber's law in bimanual grasping and perceptual estimations. Journal of Vision 2016;16(12):452. doi: 10.1167/16.12.452.
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© 2017 Association for Research in Vision and Ophthalmology.
According to Weber's law, a fundamental principle of visual perception, the visual resolution for object size decreases in a linear fashion with an increase in size. Previous studies from our lab and from other labs have shown, however, that unlike perceptual estimations, that adhere to Weber's law, the resolution of grasping movements during single-handed grasping is not affected by the object's size and therefore does not adhere to Weber's law. Therefore, it has been argued that the control of action is not affected by the same psychophysical laws that affect perception. The purpose of the current study was to extend this proposal by looking at actions beyond single hand grasping, which also allows looking at a considerably wider range of stimulus size beyond that used in previous studies. To this purpose, we asked participants to grasp or to estimate the size of large objects using both their hands. The Just Noticeable Differences (JNDs) during movement trajectories served as a measure for the visual resolution to size. The results showed that similarly to unimanual grasps, bimanual grasps did not adhere to Weber's law. In contrast, JNDs for perceptual estimations of the same objects increased in a linear fashion with object size, in agreement with Weber's law. These findings indicate that unlike perception, the visual resolution of visuomotor control is absolute and does not depend on object size.
Meeting abstract presented at VSS 2016
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