Imagined and actual motor performance were compared to determine what facto
r(s) drive limb selection for programming movements in contralateral hemisp
ace. Forty right-handed blindfolded subjects were asked to 'reach' via audi
tory stimulus for a small object placed at multiple locations in hemispace.
Two conditions were included: arms uncrossed and arms crossed. With the un
crossed condition, responses were similar. with arms crossed, subjects had
the choice of keeping the limbs, crossed, reacting to proximity, or uncross
ing the arms to reach ipsilaterally. In this condition subjects 'imagined'
that they would maintain the crossed position and reach with the hand close
st to the stimulus in both right and left hemispace. However, during 'actua
l' reaching, responses differed. For left held stimuli, participants kept t
he arms crossed, but in response to right-field stimuli, subjects preferred
to uncross the limbs in order to reach with the dominant hand. These findi
ngs suggest that while motor dominance is the primary factor in limb choice
fur action in ipsilateral hemispace, it appears that object proximity driv
es limb selection for reaching in contralateral hemispace. (C) 2001 Academi
c Press.