In martial arts classes, students are often taught to treat weapons as extensions of their own body. But this is more than just a metaphor. It turns out that when we use tools – not just swords and spears, but toothbrushes and rakes as well – our brain treats them as temporary body parts.
According to some psychologists, our brains rely on a mental representation of our bodies called the “body schema”, which allows us to coordinate our various parts and to interact with the world around us. Now, Lucilla Cardinali from INSERM, France has found that we incorporate tools into this mental plan after using them for just a few minutes. It’s confirmation of an idea that has been kicking around for almost a century.
She recruited 14 volunteers and asked them to grab a block in the middle of a table, that was always the same distance away. Then, they had to repeat the same actions with a grabber – a long, mechanical lever tipped with a two-fingered “hand” – and then a third time, with their own hand again.
Small LEDs on the volunteers’ hands allowed Cardinali to track their movements and calculate the speed and acceleration of their arms. She found that they reached for the block differently after they had been accustomed to the grabber, taking longer to accelerate their hands more slowly and to seize the block (although once they actually touched the blocks, they grasped them in just the same way as before). The delays even affected the speed at which they pointed at the block, a behaviour that wasn’t “trained” by the grabber.