The coordination of two-effector actions: spoon-feeding and intermanual prehension

The aim of this study was to assess whether kinematic characteristics of unimanual (one-effector) prehension movements can also be found in tasks where the transport and grasp components are distributed across separate effectors. Expt 1 compared prehension with spoon-feeding and showed that a number of kinematic landmarks, such as time to peak aperture, were similar. An unexpected difference between the tasks was that the onsets of the transport and grasp components in the two-effector task were not always synchronized. To control for a number of differences between the tasks used in Expt 1, such as the role of haptic and visual information, Expt 2 compared unimanual with intermanual prehension, which involved passing an object from one hand to the other. The results were consistent with those found in Expt 1. In particular, time to peak aperture was similar over the different tasks, despite a lack of consistent coupling between the components at movement onset. We conclude that the one- and two-effector tasks pose largely the same task constraints and are coordinated in a similar way. Intermanual prehension tasks thus provide a useful experimental tool for manipulations that are difficult or impossible to perform with unimanual reaching and grasping.