Handbook of Psychology, Volume 4: Experimental Psychology

Motor Coordination 341

Figure 12.16 (a) Mean amplitudes of short and long reversal movements as a function of the cuing interval in a timed-response experiment, shown separately
for the left and right hand and the target amplitude of the other hand. (b) Correlations between amplitudes of bimanual reversal movements for the four different
amplitude combinations (after Heuer, Spijkers, Kleinsorge, van der Loo, & Steglich, 1998).

amplitudes and then to produce amplitudes according to the
cues as far as this was possible.
The continuous lines in Figure 12.16a show how, with in-
creasing preparation time, short and long movements reach
their final amplitudes, beginning at an intermediate default
amplitude. Broken lines show the temporal evolution of
the short and long movement amplitudes when the target am-
plitude for the other hand was different, long and short, re-
spectively. With long cuing intervals the already described
asymmetric amplitude assimilation was found in that the am-
plitude of the short movement was enhanced by the concur-
rent requirement to produce a long-amplitude movement

with the other hand, whereas the long-amplitude movement

was not affected by the concurrent short-amplitude move-

ment of the other hand. However, at short intervals there was

also a transient reduction of the long amplitude, although the

amplitude difference of the two hands was actually smaller

than at long cuing intervals. In Figure 12.16b the correlations

between the amplitudes of the two hands are shown: They

stay at a high level for same-amplitude movements as the

cuing interval increases, but they are rapidly reduced for dif-

ferent-amplitude movements. These basic findings have been

replicated for different amplitude differences of the two

hands (Heuer, Kleinsorge, Spijkers, & Steglich, 2001) and