A comment on neural representations

I noticed by chance that my previous blog post on the metaphor of neural representations has been commented on reddit. It appeared that my argument that the representation metaphor is often misused in neuroscience was not fully understood. I will try to respond to those comments here. Here is one comment:

The brain is a representational system because it takes stimuli from the world, transduces it to a neural signal, and then acts on it.”

What is meant here is that perception is indirect in the sense that it is mediated by the activity of neurons. Certainly, this is obviously true if perception arises from the activity of the nervous system. It is also adequate to call, say, retinal activity a representation, but only in the sense that it is a representation for an external observer. For the brain, that activity is just everything it will ever “see” from the world, so it is not a representation, it is the actual input. The problem is that the case for neural representations is generally made (as in the above quote) from the point of view of the external observer, in which it is a trivial statement (outside world and neural firing are different), but then there is a semantic shift in which neural activity is assumed to form representations for the brain, which is an entirely different claim, and a much more difficult one to back up or even make sense of.

Another comment actually illustrates this point:

Suppose I'm looking at dots on a radar screen for things which are underwater. If I can never actually go underwater to compare the dots with the original stimuli, are the dots merely a "presentation" rather than a "representation? I don't think so...

Well actually: if all you ever had the chance to see in your life were those dots, then indeed they would not be representations for you, they would just be dots on the screen. They become representations once you know they can stand for submarines or whales.

There is another sense of representations that is a bit less trivial, and which was posted as a comment to my post:

Abilities like speech perception would be impossible without representation, as each instantiation of a word is unique (noisy).”

What is meant here is that representations are needed for the formation of perceptual categories. But here the term “representation” is inadequate. A sculpture of a man is not a category of man, it's just a piece of stone that looks like a man. What is meant here is rather abstraction, not representation.

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