Spatial Assimilation Effects in Sequential Movements: Effects of Parameter Value Switching and Practice Organization

David E. Sherwood

Department of Integrative Physiology
University of Colorado, Boulder

Journal of Motor Behavior, 2008, Vol. 40, No. 3, 232–245

ABSTRACT. 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° and 60° 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°–20° and 60°–60°) and different-distances (20°–60°
and 60°–20°) 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.