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Mark Mon-Williams, Rachel Coats, Geoff P. Bingham; Reaching with feeling. Journal of Vision 2004;4(8):411. doi: 10.1167/4.8.411.
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Skilled movement requires the coordination of perception variables and action variables in respect to their absolute scale and number. The issue of how these variables are transformed in order to close the loop between perception and action is fundamental to our understanding of skilled behaviour. We manipulated the physical properties (location and size) of a visually constant object in order to explore the role of somatosensory feedback information in the calibration of visual information for action. All participants (n=60) were asked to reach-and-grasp a 6cm wide virtual object placed 20cm from the starting position before and after exposure to distorted somatosensory feedback to discover whether the system adapted to the distortion. In Expt 1, group 1 (distance change only, n=10) reached to a 4cm block that was moved gradually either out or in by 1cm until it changed by 10cm (no size change). Group 2 (size change only, n=10) reached to a block at 25cm after which the object size was increased or decreased by 0.5cm until it changed by 4cm. Expt 2 used four groups (n=40). In all cases, the object changed in distance by 1cm until it had moved (inwards or outwards) by 10cm and in size by 0.5cm until it had grown (or shrunk) by 4cm. Group A reached for a 4cm object at 15cm which moved outwards and increased in size. Group B reached for an 8cm object at 25cm which moved inwards and decreased in size. Group C reached for a 4cm object at 25cm which moved in and increased in size. Group D reached for a 8cm object at 15cm which moved out and decreased in size. The data showed that distorted somatosensory feedback causes a recalibration of action as indexed by changes in reach distance and grasp aperture. Groups A and B (expt 2) showed increased effects from expt 1 whereas group C and D showed decreased effects. Our data provide a novel insight into the indivisible relationship between somatosensory, visual and motor variables.
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