Spatial assimilation effects in sequential movements: effects of parameter value switching and practice organization.

In Experiment 1, the author extended earlier work by investigating spatial assimilations in sequential aiming movements when participants were able to preplan only the 1st movement of a 2-movement sequence. Right-handed participants (N = 20) aged 18-22 years tried unimanual rapid lever reversals of 20 degrees and 60 degrees with an intermovement interval of 2.5 s. Following the 1st movement, participants made a same-distance movement, different-distance movement, or no movement in a randomly determined order. Participants overshot the short-distance target and undershot the long-distance target for both movements in the sequence, but the errors were greater when the 2nd movement differed from the 1st one. In Experiment 2, right-handed participants (N = 20) demonstrated greater assimilation effects after random practice than after blocked practice of both same-distances (20 degrees -20 degrees and 60 degrees -60 degrees ) and different-distances (20 degrees -60 degrees and 60 degrees -20 degrees ) sequences, although spatial errors were greater in different-distances conditions than in same-distances conditions. Overall, the experiments showed that parameter-value switching and practice organization are 2 major sources of spatial inaccuracy in sequential aiming movements.