On the Persistence of Tool-Based Compatibility Effects

Using tools, such as simple levers, makes specific demands on the motor system. Two related performance decrements have been reported: The costs that arise when required tool movements and movements of the operating hand are spatially incompatible (hand-tool compatibility), and the costs that arise when relevant stimuli and tool movements are spatially incompatible (stimulus-tool compatibility). We performed two experiments to test the boundary conditions of both effects. Experiment 1 revealed a strong hand-tool compatibility effect despite visual occlusion of the hand and instructions to ignore hand movements. Experiment 2 revealed influences of stimulus-tool compatibility despite instructions to ignore the tool and to pay attention to the operating hand alone. These results suggest that lever movements of the type studied here become automatically represented and constrain motor performance.