Hand dominance, attention, and the choice between responses

Thirty pairs of matched right- and left-handed subjects carried out a serial C.RT task involving reaches between 2.4 cm square contact grids set at 2.4 cm intervals in a horizontal line. In one condition they responded with the right hand alone, in a second with the left and in a third they had to choose between hands on each trial responding to left side grids with the left hand and to right side grids with the right.

All subjects took longer to respond when they had to choose between hands than when they used either hand alone. In the one-hand conditions neither group showed any effect of hand dominance. When choices had to be made between hands both groups responded faster with their dominant than with their nondominant hands.

Analysis of the results was undertaken in terms of two hypothetical systems of instructions which might control machines designed to carry out similar tasks. It is concluded that in some tasks hand dominance can be described in terms of an attentional bias towards the field of operation of one effector rather than another. In the present task the effects of such possible attentional biases were shown not to interact with other effects, such as the facilitation of successive responses by repeated use of the same limb. These latter effects seem to depend on processes underlying execution of responses rather than choices between responding limbs.