Three experiments were designed to investigate the underlying processes in bimanual control. With one hand alone, or with both simultaneously, subjects moved styli from the midline of the body to lateral targets as quickly and accurately as possible. The distance moved and the weight of the styli were varied. Results of reaction time, movement time, and kinematic trajectory analyses question the conclusions of Kelso, Southard and Goodman (1979) regarding the synchronicity of movement of the two limbs. Temporal parameters for the two limbs indicated marked departures from synchronicity, and there was evidence for a left-right asymmetry. The dependent variables of movement time and constant error indicated that there was interaction between the two limbs. The results are discussed in terms of three postulated processes underlying bimanual movement: limb selection (one or two), specification of movement locations and the specification of movement intensities.

The study was designed to determine whether the magnitude of force and the timing of force are response parameters involved in the organisation of a rapid forearm flexion to a target. The magnitude of torque and the timing of torque were manipulated independently through manipulations of the total moment of inertia and movement time, and the effect of these manipulations on premotor and motor reaction times was observed. Planned comparison analyses revealed that premotor and motor reaction times increased when a movement, which required the same magnitude of torque as in a fast movement, was performed slower. However, premotor and motor reaction times were not affected when movements were performed at the same speed, but differed with respect to the magnitude of torque required. These results indicate that a different timing requirement in the forthcoming movement is associated with a corresponding change in the amount of central processing time required. Therefore, the timing of torque appears to be a parameter of the movement that is organised in advance of movement execution. However, a change in the specification for the magnitude of torque does not affect the amount of time needed to organise the movement.

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