INCREASING POSTURAL DEMANDS MAY AFFECT THE MAGNITUDE OF MANUAL ASYMMETRIES

Hypotheses generated by the postural origins theory (MacNeilage, 1991) about the right-hand performance advantage were examined in two exper iments manipulating postural demands. It was predicted that right-hand performance would be adversely affected when postural demands were in creased. The first experiment compared performance on the Annett pegbo ard (Annett, 1967) while participants were seated or standing. Here, i t was found that right-hand performance slowed more than performance f or the left hand in the standing condition, suggesting that the increa sed demands placed on posture control during the standing condition di d interfere with right-hand performance. Experiment two attempted to d issociate the effects of posture from those due to visual angle and ha nd/wrist. Participants per formed in the seared and standing condition s of experiment one, as well as in a second standing condition in whic h the pegboard was elevated to the same relative height as in the seat ed condition. Analyses revealed that relative to the Seated condition right-hand performance again slowed more than the left hand performanc e in the Standing-Low condition, but right-hand performance returned t o that in the Seated condition in the Standing-High condition. These r esults will be discussed in light of MacNeilage's (1991) postural orig ins theory.