Suppression of mutually incompatible proprioceptive and visual action effects in tool use.

Movements of a tool typically diverge from the movements of the hand manipulating that tool, such as when operating a pivotal lever where tool and hand move in opposite directions. Previous studies suggest that humans are often unaware of the position or movements of their effective body part (mostly the hand) in such situations. It has been suggested that this might be due to a "haptic neglect" of bodily sensations to decrease the interference of representations of body and tool movements. However, in principle this interference could also be decreased by neglecting sensations regarding the tool and focusing instead on body movements. While in most tool use situations the tool-related action effects are task-relevant and thus suppression of body-related rather than tool-related sensations is more beneficial for successful goal achievement, we manipulated this task-relevance in a controlled experiment. The results showed that visual, tool-related effect representations can be suppressed just as proprioceptive, body-related ones in situations where effect representations interfere, given that task-relevance of body-related effects is increased relative to tool-related ones.