Local and global affordances and manual planning.

The present study aimed to demonstrate that motor planning processes are affected by ignored affordances of a main body of an object. Participants were asked to select the hand of response according to the property of the local component (a stalk) of the object (a fruit) while they were holding a precision or a power grip devices. The size of a main body of an object was observed to prime hand selection processes asymmetrically. Right-hand responses were facilitated when the stalk was a part of a precision grip object (e.g. a strawberry) or displayed alone. In contrast, left-hand responses were facilitated when the stalk was a part of a power grip object (e.g. an apple). This data supported our previously presented view that the different hemispheres have differential roles in the early planning of manual actions. The object information that is relevant to precision grip planning appears to be processed predominantly in the left-hemisphere whereas the information that is relevant to power grip planning appears to be processed predominantly in the right-hemisphere. In Experiment 3, the irrelevant fruit body had a slight effect on motor planning even though the stalk was spatially separated from the fruit body. The priming effect was entirely eliminated when, in addition to the spatial separation, the stalk was semantically disassociated from the fruit body (Experiment 4), and when the objects used in Experiment 1 were replaced by two dimensional abstract objects (Experiment 2). Experiments 2, 3 and 4 suggested that affordances of an irrelevant main body of an object influences motor planning processes only when the local target component of the object is analysed as a meaningful part of a graspable object.