INTERLIMB AMPLITUDE DIFFERENCES, SPATIAL ASSIMILATIONS, AND THE TEMPORAL STRUCTURE OF RAPID BIMANUAL MOVEMENTS

When subjects make rapid bimanual aiming movements over different dist ances, spatial assimilations are shown; the shorter distance limb over shoots when paired with a longer distance limb. According to Marteniuk and MacKenzie's (1980) model of two-hand control, the magnitude of th e spatial assimilations are directly related to the interlimb differen ce in end location, with larger differences resulting in larger assimi lation effects. In order to test this prediction of the model, twelve right-handed female subjects (aged 18-23) combined 30-degrees, 40-degr ees, 50-degrees, and 60-degrees lever reversal movements in the left h and with a standard 60-degrees reversal movement in the right hand. Th e left limb overshot by 4.8-degrees (16%) and the right limb undershot by 2.6-degrees (4.3%) in the 30-degrees-60-degrees dual condition rel ative to single movements. No other spatial assimilations were found, suggesting that spatial assimilations were limited to bimanual conditi ons where interlimb differences in end location were greater than 20-d egrees. Relative timing was maintained across limbs and conditions, su ggesting the same temporal structure was utilized in both single and b imanual movements.