Quantifying hand preference using a behavioural continuum.

Bishop, Ross, Daniels, and Bright (1996) proposed a novel approach to quantifying hand preference (QHP) using a single behavioural measure. The extent to which individuals used their dominant hand to reach across the midline to pick up cards discriminated subgroups of right-handers, similarly categorised by their scores on the Edinburgh Handedness Inventory. This study aimed to investigate whether (1) the QHP approach was able to differentiate subgroups within the left-handed as well as right-handed populations, (2) left-handers behave like mirror-image right-handers, and (3) if interacting with the environment in extrapersonal space is influenced by the level of fine motor skill demanded by the task. Results support the use of the QHP to discriminate subgroups of both left- and right-handers, particularly when the task demands very fine motor skill or very little. Left-handers behaved as mirror-images of the right-handers except when performing the unskilled motor task in which they showed greater readiness to use the nonpreferred hand. These results suggest that interaction with the environment in extrapersonal space may be a key factor contributing to manual dominance and that the lateralisation of fine motor skill interacts with this attentional bias.