Arguing about embodiment with Ken Aizawa over the last few days has opened up a lot of topics that I hope to cover over the next little while. But it also primed me to notice this article at Scientific American by Patrick Haggard and Matthew Longo, summarising a recent paper adding to the growing literature on the neuroscience of tool use. I like this work, and it got me thinking how this relates to the embodied cognition literature; Ken, I'd be interested to hear your thoughts on this on.
I actually really do like this work, although as you may have guessed, not for exactly the reasons everyone else likes it. The basic result is this: if you pick up an object (say a pair of tongs, or a stick), then the cortical representation of your arm very very quickly reorganises itself to include the tool; as far as the brain is concerned, your arm is now longer than it 'actually' is.
This is (of course) grounded in perception. Dynamic touch is the name given to the way in which we can non-visually perceive characteristics such as the length of an object. Get a ruler, close your eyes, hold it at one end in your hand and wobble it round a bit. You'll quite quickly get a fairly good sense of where the tip of the ruler is, and if I asked you to reach using it you'd be ok at landing that tip somewhere without vision. Now hold the ruler in the middle and twiddle it; same basic thing. You aren't perceiving length, per se; the evidence suggests you are perceiving information about the distribution of mass in the object by the act of rotating it, which reveals the inertia (resistance to rotation) of the object. Mathematically, this is an inertia tensor.
The suggestion is that this is how you maintain 'knowledge' of where your limbs are in space. The cortical representation that everyone is excited about is being actively maintained by perception of the inertia tensor resulting from how your limbs are moving around; this is how it can change so fast, because it isn't a static thing, it simply reflects the brain maintaining perceptual contact with your arms.
Yes, the cortex does indeed seem to have some real estate that knows things about the arm; isn't this a representation and if so, is this blog now over? Well, no, I don't think so: the reason I like this tool research is that it shows that the cortex involved isn't anything like what cognitive people talk about when they talk about representations. It's fluid, in constant flux, resonating with the world and changes in it; this sounds a lot more Gibsonian than most neuroscience, and this is why I like it. We ecological types get a bad rap for dissing the brain - this is mostly just because we think there's work to do before getting to excited about fMRI. This work shows, I think, the kind of behaviour ecological types should be looking for in the brain, which, let's face it, is clearly involved in perception, action and cognition.
I wonder how people like Ken, who don't think cognition is ever really embodied, think about these cases - what the brain knows about the arm has changed in a manner driven by perception, and future behaviour with the arm is affected accordingly. An object from the world has literally crossed the boundary from the external world into the seat of bounded cognition - what does this imply? I think it implies the boundary is actually a pretty low fence; but I would be interested to hear from Ken on this when he has time :)
Carlson et al (2010) Rapid assimilation of external objects into the body schema. Psychological Science, 21(7), 1000-1005.
Turvey, MT (1996). Dynamic touch. American Psychologist, 51(11), 1134-1152.