August 2009
Volume 9, Issue 8
Free
Vision Sciences Society Annual Meeting Abstract  |   August 2009
Weber's law in action
Author Affiliations
  • Tzvi Ganel
    Department of Psychology, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel
  • Eran Chajut
    Department of Education and Psychology, The Open University of Israel, Raanana 43107, Israel
  • Daniel Algom
    Department of Psychology, Tel-Aviv University, Tel-Aviv 69978, Israel
Journal of Vision August 2009, Vol.9, 1165. doi:10.1167/9.8.1165
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      Tzvi Ganel, Eran Chajut, Daniel Algom; Weber's law in action. Journal of Vision 2009;9(8):1165. doi: 10.1167/9.8.1165.

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Abstract

According to Weber's law, a fundamental principle of perception, sensitivity to changes in magnitude along a given physical dimension decreases when stimulus magnitude increases. In other words, the increment needed in order to detect a change - the Just Noticeable Difference (JND) - is smaller for weak stimuli compared to stronger stimuli. Although Weber's law governs human perception for visual dimensions, including visual length, there have been no attempts to test its validity for visually-guided action rather than for perception. Based on the notion that visually-guided action and perception are mediated by distinct neuroanatomical systems, we hypothesized that Weber's law does not necessarily hold for visually-guided action. In order to test this idea, we asked observers to either grasp or make perceptual estimations of length for objects varying in length. These measurements served to assess resolution with these two functions of vision. We found that the JND increased with object size for perceptual estimations in accordance with Weber's law. For grasping, however, the JND remained invariant across different sizes of objects, violating Weber's law. In a series of follow-up experiments, we tested the presence of Weber's law in online grasping as compared with that in memory-based grasping as well as under open-loop conditions in which vision was occluded during the grasping movement. Collectively, our findings reinforce the presence of a basic dissociation between the way object size is computed for perception and for action.

Ganel, T. Chajut, E. Algom, D. (2009). Weber's law in action [Abstract]. Journal of Vision, 9(8):1165, 1165a, http://journalofvision.org/9/8/1165/, doi:10.1167/9.8.1165. [CrossRef]
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