Internal maps of the hand are mislocated in space and affected by posture and vision.
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1
Neuroscience Research Australia, Australia
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2
University of New South Wales, Australia
Aims: The brain’s internal maps of the hand are distorted (e.g. 1). The hand is perceived to be shorter and wider than it actually is. However, only measures of hand width and length have been reported, the perceived position of the hand and digits relative to actual position is unknown. This study measured the brain’s internal map of the position of the hand and its digits and the effect of hand posture and vision on these maps.
Methods: Ten naïve healthy human subjects sat with their left hand resting on a table. A second table was placed over the hand removing it from view. The task was to point to the tip of each finger and each metacarpophalangeal (MCP) joint of the left hand. Each landmark was pointed to 5 times in random order. I compared perceived landmark position to actual position using a 2x2x5 factorial design. Factors were vision (eyes open or closed), posture (left palm up or palm down) and digit.
Results: On average subjects perceived their fingers to be 19.4 [22.3,16.5] mm (mean [95% confidence interval]) shorter and their left hand to be 15.3 [6.29, 24.3] mm wider than reality. Subjects perceived their hand to be displaced proximally (MCP joints: 27.2 [33.2,21.2] mm, finger tips: 46.6 [52.2,40.9] mm). When the hand was palm down subjects perceived it to be displaced by 16.7 [12.1, 21.3] mm toward the ulna. There was minimal displacement with the palm up. With closed eyes the perceived proximal shift of the MCP joints reduced by ~12 mm (F(1,9)=12.36, p=0.0006) and the perceived location of the hand shifted towards the midline of the body by ~30 mm (MCP joints: F(1,9) = 63.06, p<0.0001, finger tips: F(1,9)=40.45, p<0.0001).
Conclusions: The internal map of the hand is not only distorted in shape, but is mislocated in space. Removing vision reduces the proximal mislocation and increases the medio-lateral mislocation showing that even uninformative vision influences the perceived location of the hand. Perception of the palmar surface of the hand shows a distorted shape similar to the hand dorsum, but is more spatially accurate. Importantly, this work shows that multiple dissociated elements of proprioception can be measured in one simple task.
References
1. Longo MR, Haggard P. An implicit body representation underlying human position sense. Proc Natl Acad Sci USA (2010) 107(26):11727-32. doi: 10.1073/pnas.1003483107
Keywords:
Hand,
Proprioception,
body representation,
body map,
body image schema
Conference:
Australasian Society for Psychophysiology, Inc, Coffs Harbour, Australia, 26 Nov - 28 Nov, 2014.
Presentation Type:
Poster
Topic:
Psychophysiology
Citation:
Walsh
LD
(2014). Internal maps of the hand are mislocated in space and affected by posture and vision..
Conference Abstract:
Australasian Society for Psychophysiology, Inc.
doi: 10.3389/conf.fnhum.2014.216.00026
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Received:
13 Oct 2014;
Published Online:
02 Dec 2014.
*
Correspondence:
Dr. Lee D Walsh, Neuroscience Research Australia, Sydney, Australia, l.walsh@neura.edu.au