May 2008
Volume 8, Issue 6
Free
Vision Sciences Society Annual Meeting Abstract  |   May 2008
Visible surface area and prehension movement patterns
Author Affiliations
  • Jennifer Charles
    School of Psychology, University of Aberdeen, Scotland, UK
  • Sam Kent
    School of Psychology, University of Aberdeen, Scotland, UK
  • Erik Jansson
    School of Psychology, University of Aberdeen, Scotland, UK
  • Mark Mon-Williams
    School of Psychology, University of Aberdeen, Scotland, UK
Journal of Vision May 2008, Vol.8, 304. doi:10.1167/8.6.304
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      Jennifer Charles, Sam Kent, Erik Jansson, Mark Mon-Williams; Visible surface area and prehension movement patterns. Journal of Vision 2008;8(6):304. doi: 10.1167/8.6.304.

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Abstract

Visual information about an object's distance and size determines the reach-to-grasp movement pattern. If vision specifies that object A has a smaller grasp surface area than object B, then slower movements will be programmed to A. Smaller grasp surfaces afford slower movements because more on-line visual feedback corrections are required. But what happens if the thumb and index finger have different sized grasp surface areas? In experiment 1, participants (n=8) reached-to-grasp one of nine objects directly in front of their hand in the sagittal plane at one of three distances (10, 30, 50cm). Each object consisted of a block with a dowel attached so that the ends extended to either side. The objects were the same width (5cm) but made with three different dowel diameters (3, 2, 1cm). The dowel was either the same width on both sides, or one of the six possible asymmetric configurations (10 trials per condition, total=270). Duration was affected by the surface size (duration decreased linearly as size increased) but only as a function of the thumb's surface: the finger's surface had no effect. The position of the object provided a clear line-of-sight of the thumb's surface (but not the finger's). Thus, these results can be explained by: (i) the thumb and index finger's ‘opposition vector’ being controlled as a single coordinative structure; (ii) the opposition vector being maneuvered with respect to the visible (fixated) object surface. Experiment 2 directly tested this by manipulating the vertical height of conical frusta so that: (a) the upper surface was visible but not the lower surface; (b) the lower surface was visible but not the upper; (c) the upper and lower surfaces were equally visible. Our findings show the importance of considering the visible surface area as a critical task constraint when attempting to understand prehension movement patterns.

Charles, J. Kent, S. Jansson, E. Mon-Williams, M. (2008). Visible surface area and prehension movement patterns [Abstract]. Journal of Vision, 8(6):304, 304a, http://journalofvision.org/8/6/304/, doi:10.1167/8.6.304. [CrossRef]
Footnotes
 We'd like to thank Action Medical Research for supporting this research.
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