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Gavin Buckingham, Gordon Binsted, David P. Carey; Bimanual coupling in left and right space: which hand is yoked to which?. Journal of Vision 2008;8(6):60. doi: 10.1167/8.6.60.
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Several studies have demonstrated that, when reaching toward targets at the same time, functional asymmetries in both reaction time and movement duration are substantially reduced (i.e. Kelso et al., 1983). To investigate which hand is coupled to which (i.e. which hand is ‘in charge’) we combined the well known performance deficits seen when a hand reaches into contralateral space (i.e. Carey et al., 1998), in a bimanual context. Right handed participants performed 1 and 2 handed reaches to the left or right sides of space, meaning in the bimanual conditions, a contralateral reach was yoked to an ipsilateral reach. It was predicted that the yoking between a contralateral reaching left hand would be to able to utilise some of the ipsilateral reaching right hand's properties to improve performance relative to an equivalent unimanual movement. Results suggest however that the ‘bimanual cost’ of reaching with 2 hand proved too strong, and a pattern of right hand ipsilateral ‘compromises’, to maintain coupling was seen. Therefore, in a second experiment participants performed reaches of differing amplitudes, such that a contralateral reach could be combined with a shorter ipsilateral reach - the combination most likely to show an improvement on a unimanual equivalent. When the ‘bimanual cost’ was accounted for, the left hand was improved at input level (i.e. reaction time), and the right hand was improved at output level (i.e. movement duration) relative to equivalent ipsilateral reaches. The results are discussed in relation to strategic attentional biases to overcome the increased difficulties posed to the central nervous system by reaching with 2 hands concurrently.
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