1. Those maps you mention aren’t static (or maps, per se, but that’s another story). They’re flexible and their current layout simply reflects what you’ve been up to recently; so when you pick up a tool that object gets incorporated almost immediately. So our cortical ‘sense of self’ is just ‘what we typically look like’ – it’s use-dependant, like the shape of muscles. The only reason the brain thinks we typically have two arms is that we do typically have two arms: change that, and the brain changes with it.

2. This is related to the process of calibration: the various perceptual systems continuously calibrate and recalibrate each other to preserve accuracy. Left to its own devices, any perceptual system drifts and gets noisy. This process is ongoing and, with some limits, you can recalibrate the system quite extensively. That’s the point of the timing relationship between the visual and tactile information – these are informing each other, but only if they are in a suitable temporal range.

The net result is that the only reason the brain thinks we have two hands is that a) we do but critically b) all our perceptual systems continuously inform the brain of this fact, actively maintaining that cortical organisation. Change (b) and cortex quickly (with some limits) reorganises.

Anyway…I like all this recent work from these guys, I think it’s interesting, but I just get a bit grouchy about it being couched in terms of illusions. More interesting things are going on – what we ‘know’ about ourselves is actively maintained by the perceptual systems, and this isn’t even a little bit static.