Brain treats tools as temporary body parts

By Ed Yong | June 22, 2009 12:00 pm

Blogging on Peer-Reviewed ResearchIn 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.

To Cardinali, these results suggested that after using the grabber, the volunteers’ had included it into their mental representation of their own arms. Because of that, they felt that their arms were longer than they actually were and reached for the block more slowly.

Before accepting that interpretation, Cardinali had to rule out the possibility that they were simply a bit more tired in the second session. To do that, she repeated the experiment with another group of volunteers who used a grabber while their wrist were weighed down with 300g weights. Despite the extra load, this group of volunteers showed the same changes as the previous lot who used the lighter tool – clearly, their delay wasn’t affected by the weight of the device, but the fact that it was used in the first place.

But the clearest evidence for Cardinali’s theory came from a final experiment, where she touched the volunteers on their wrist, elbow or middle finger and asked them to use their opposite index finger to point directly above the point of contact. This simple request showed that after using the grabber, the volunteers overestimated the length of their arm. Their pointing fingers indicated a larger distance between their fingertip and elbow, or between their wrist and elbow, than they did before they had used the tool.

These studies show that our brains are quick to update our body schemas when tools fall into our hands, and that the revised representations last for at least 10-15 minutes. This ability to quickly treat tools as our own body parts probably underlies our vaunted aptitude with tools.

Reference: To be published in Current Biology

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Comments (18)

  1. When I ride my bicycle, it actually feels like an extension of my body; it’s like the pedals and cranks are part of my feet and my actual height is really my height on the bike. It sounds kind of eerie when I describe it, but it actually feels quite natural.

  2. That German Guy

    1:
    Yep, it’s sort of a zen-ish kind of thing ;) I get the same way with my bike, but also with workshop: Before I got good with the lathe, my thought process was “turn wheel A .5 revolutions clockwise, turn wheel B 2 revolutions counterclockwise”, now it is “move tool to XYZ”. After four years, the lathe was so much a part of my body that I kept screwing up and digging the tool into the part way too deep when it broke and I got a very similar but yet different one, which had a slightly different gear ration on the Y axis.

  3. Martin

    This happens to me when I’ve been riding a horse as well. The horse’s body quickly starts to feel like an extension of my own, and my height in the saddle feels like my real height. It feels strange to come down and realize that I’m not 8 feet tall and I can only move about miles per hour.

  4. DC Elzinga

    This happens with cars, too. I have read that this is one possible motivator for road rage. We expand our sense of self to encompass the car and its actions.

  5. Lobster

    If my car is an extension of myself, my proprioception is a bit off. I seem to think it’s a lot wider than it really is.

  6. Micropipettes and bass guitar for me, then.

  7. Laen

    ..Or maybe the brain treats the body like a tool?
    What if we move the boundary from “body/not body” to “brain/not brain”. Then the body is just a tool that we (our brain) has to figure out how to use, and other tools aren’t much different.

  8. Medievalist Jon

    Well, this is just very interesting. Maybe this is a bad comparison, but I wonder if reading a novel creates a kind of mental extension, as if that imaginary world were part of perception.

  9. megan

    I have always felt this when I learned to drive large trucks and buses. Once I got my bearings and coordination it’s like my body or sense of boundaries can make me ‘feel’ a close parked car when backing or turning and when too close or out of control it’s like the ‘part of my body’ tingles waiting for contact or the accident.

  10. Peter Anderson

    It would be interesting to compare electronic/digital tools with mechanical ones. I expect that there would be a significant difference in the degree to which the two types of tools are assimilated into the body image, especially over long periods of time. Digital tools are comprised of black boxes (chips and algorithms) housed in plastic that resist assimilation because they are inscrutable to the senses. Mechanical tools would invite assimilation to greater or lesser degree depending on the aptness of their design and the tangibility of their components.

  11. Tenebras

    I don’t know about that, Peter. Purely anecdotal, of course, but when I’m gaming on my laptop, the keys and mouse feel just as natural to me as a bike does when you’re riding it. And my Wacom tablet feels just as natural as a regular pencil. *shrug* In fact, on the rare occasion nowadays when I actually do draw with a real pencil on paper, it feels very alien for a few moments until I get used it.
    Although, I think that probably someone who used a tool very often would more quickly assimilate it into their body schema than a tool they weren’t used to, digital or otherwise.

  12. JAHarberger

    It seems there must be three (or more) types of tool and that only some of them are really to be viewed as bodily extensions. This is because of the nature in which they are used. One type of tool, like a pencil or knife, is used in a similar fashion to the way we use our bodies. They are also used to manipulate a third object, and in this sense they are part of us. The second type would be a vehicle, where, because we are attached to it, and move with it, it becomes part of us. The third type would be like a keyboard, which is really the object being manipulated, and our fingers are the tool, in which case our minds would not attempt to identify it as a bodily extension.

  13. Tenebras

    What about a mouse? Since you have to actually hold it, instead of just pressing buttons?

  14. Beth

    I can totally believe this. It’s very common with assistive devices. I sometimes use a walker or a wheelchair (and have used them much more often in the past). If I’m using one and someone kicks a wheel, my thoughts are “don’t kick me”. Of course, assistive devices become much more personal than other tools. If someone needs an assistive device, it tends to be “them” whether or not they’re using it at the moment.
    The training bit, how people grabbed the block differently with their hands after having to get it with the tool… My walking was/is impaired by a neurological disorder. Some people in the field (neurologists? physical therapists? I don’t know, I saw it on a video) encourage the use of walkers, especially four-wheeled walkers, even if a patient can walk but with a limp. The idea is that, with a walker, a more normal gait would become natural, that the walker could help to retrain the brain concerning how to walk. That exploits this feature, I guess (though with longer training and hopefully lasting difference). Seems to have helped me. :)

  15. Cari

    Was it incorporated into the data that there was little to no experience using the tool in question? When one is inexperienced with using a tool, it’s inherent that there will be deceleration in order to understand and manipulate the tool in a correct fashion. With experience, the user can then use the tool in a quicker, more exacting way, and this may skew the results (ie. professional fencers, etc.).

  16. xMANTAx

    As an 18-year martial artist, I totally agree with the article’s premise. I’m primarily a swordsman, but have used many different weapon types over the years. I’m glad someone has given some validity to what I’ve thought for years. I used to think that I was getting more and more precise in my movements, when actually my brain was just further assimilating the weapons into natural body parts. Switching from one weapon to another of a slightly different weight, length, or shape mid-practice can throw me off quite a bit for the first few moments. With unfamiliar weapons, I think about hitting something with them, with a sword, I just think about hitting something.

  17. We experimented with bidirectional remote mechanical touch devices (for sending physical feelings) while communicating via mobile phones and later while videoconferencing. When the artifical touch is inputed/recieved via simple devices, while paired with conversation, such as, “I miss you”. The
    AT (Artifical Touch of, for instance, sighly squeezing the partner’s hand) feels personal and real. The partners feel as if they are in actual contact. Regarding the other theme, our bodies are wonderfull two-sided robotic devices for our two-sided brains. http://www.RealTimeTouch.com

  18. LL

    Laen – “What if we move the boundary from “body/not body” to “brain/not brain”.”
    In this context that makes sense to me, and it fits with the way we often describe ‘our bodies’ rather than ‘us’. But then I would think of feeling my brain inside my head.. rather than feeling my body outside my brain..
    JAHarberger: “…The third type would be like a keyboard, which is really the object being manipulated, and our fingers are the tool, in which case our minds would not attempt to identify it as a bodily extension.”
    I would agree- I have never felt the sensation that my piano is part of my body, but I have with a paint brush. My friend who is a violinist feels her bow to be part of her body and maybe this is because it is held rather than pressed, and used to manipulate a third object as you say.

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