Tool Use in Left-Brain-Damaged Patients: Difficulties in Reasoning but Not in Estimating the Physical Properties of Objects.

Objective: The purpose of this study was to deepen our understanding of the cognitive bases of human tool use based on the technical reasoning hypothesis (i.e., the reasoning-based approach). This approach assumes that tool use is supported by the ability to reason about an object's physical properties (e.g., length, weight, strength, etc.) to perform mechanical actions (e.g., lever). In this framework, an important issue is to understand whether left-brain-damaged (LBD) individuals with tool-use deficits are still able to estimate the physical object's properties necessary to use the tool. Method: Eleven LBD patients and 12 control participants performed 3 original experimental tasks: Use-Length (visual evaluation of the length of a stick to bring down a target), Visual-Length (to visually compare objects of different lengths) and Addition-Length (to visually compare added lengths). Participants were also tested on conventional tasks: Familiar Tool Use and Mechanical Problem-Solving (novel tools). Results: LBD patients had more difficulties than controls on both conventional tasks. No significant differences were observed for the 3 experimental tasks. Conclusion: These results extend the reasoning-based approach, stressing that it might not be the representation of length that is impaired in LBD patients, but rather the ability to generate mechanical actions based on physical object properties. General Scientific Summary Tool-use deficits can decrease the autonomy of patients and their quality of life. For example, if patients show difficulties in determining the sharpness of a knife, they may endanger themselves. This study provides insights into the understanding of the cognitive origins of tool-use deficits.