Pliers, not fingers: tool-action effect in a motor intention paradigm.

Tool-use representations have been suggested to be supported by the representation of hand actions and/or by the representation of tool actions. A major issue is to know which one of these two representations is preferentially activated when people intend to use a tool. To address this issue, we developed a paradigm in which, in 20% of trials, participants had to press a button and actually use pliers to move an object in response to a predefined target symbol. Importantly, two masks hiding the symbols performed "opening" or "closing" actions before symbols appeared. In Experiment 1, participants used normal pliers: Hand's opening actions induced pliers' opening actions and vice versa for hands' closing actions. Results indicated a compatibility effect between masks' actions and pliers' actions. Participants were faster to press the button in response to the target symbol when opening and closing actions of the masks were congruent with the corresponding actions of the hand. In Experiment 2 participants used inverse pliers: Hand's opening actions involved pliers' closing actions and vice versa. In this situation, results showed that the congruency of masks' actions occurred with pliers' actions and not hand's actions. Altogether, these findings demonstrate that intention of use is preferentially based on the representation of tool actions, and have important implications for the domain of neuropsychology of tool use and the theories of goal-directed behavior.