COPING WITH SYSTEMATIC BIAS DURING BILATERAL MOVEMENT

The present studies examined the nature of kinematic interlimb interfe rence during bilateral elbow movements of 1:1, 2:1 and 3:1 frequency r atios and the manner in which subjects cope with coordination bias. An alysis of movement trajectories in the first experiment indicated prog ressively greater angular velocity assimilation across 2:1 and 3:1 con ditions. The desired temporal relationship was maintained by slowing o r pausing the low-frequency movement al peak extension while the high- frequency arm produced intervening cycles. An increase in amplitude wa s also evident for concurrent, homologous cycles. Movement smoothness was emphasized and additional practice was provided in a second experi ment. This resulted ill dissociated peak angular velocity between limb s and eliminated hesitations and amplitude effects, Bias was still evi dent, however, as an intermittent. approach toward a 1:1 ratio within each cycle. This systematic tendency was somewhat greater al the lower of two absolute frequency combinations but was not influenced by the role of each arm in producing the higher or lower frequency movement. The findings from the first experiment suggest that subjects initially accommodate interlimb kinematic assimilation, while producing the int ended timing ratio, by Intermittently slowing or pausing the lower-fre quency movement. This attenuates the need for bilaterally-disparate mo vement parameters and provides additional time for organizing residual kinematic differences, perhaps reducing ''transient coupling.'' Evide nce from the second experiment indicates that subtle relative motion p references are still evident following sufficient practice to perform the movements smoothly. The within-cycle locations of the points of gr eatest interlimb bias for the 2:1 rhythms were positively displaced fr om those previously observed for 1:1 oscillations. The persistent coor dination tendencies noted ill both experiments perhaps reflect an assi milation/compensation cycle and constitute one potential source of the systematic error that often emerges during the acquisition of complex skills.