What kind of system of ‘coding’ of semantic information does the brain use?

January 21, 2002 by Daniel Dennett

The 5th Annual Edge Question reflects the spirit of the Edge motto: “To arrive at the edge of the world’s knowledge, seek out the most complex and sophisticated minds, put them in a room together, and have them ask each other the questions they are asking themselves.” Daniel Dennett asks: how does the brain code semantic information?

Originally published January 2002 at Edge. Published on KurzweilAI.net January 21, 2002. Read Ray Kurzweil’s Edge question here.

My question now is actually a version of the question I was asking myself in the first year, and I must confess that I’ve had very little time to address it properly in the intervening years, since I’ve been preoccupied with other, more tractable issues. I’ve been mulling it over in the back of my mind, though, and I do hope to return to it in earnest in 2002.

What kind of system of “coding” of semantic information does the brain use? We have many tantalizing clues but no established model that comes close to exhibiting the molar behavior that is apparently being seen in the brain. In particular, we see plenty of evidence of a degree of semantic localization — neural assemblies over here are involved in cognition about faces and neural assemblies over there are involved in cognition about tools or artifacts, etc — and yet we also have evidence (unless we are misinterpreting it) that shows the importance of “spreading activation,” in which neighboring regions are somehow enlisted to assist with currently active cognitive projects. But how could a region that specializes in, say, faces contribute at all to a task involving, say, food, or transportation or . . . . ? Do neurons have two (or more) modes of operation — specialized, “home territory” mode, in which their topic plays a key role, and generalized, “helping hand” mode, in which they work on other regions’ topics?

Alternatively, is the semantic specialization we have observed an illusion — are these regions only circumstantially implicated in these characteristic topics because of some as-yet-unanalyzed generalized but idiosyncratic competence that happens to be invoked usually when those topics are at issue? (The mathematician’s phone rings whenever the topic is budgets, but he knows nothing about money; he’s just good at arithmetic.) Or, to consider another alternative, is “spreading activation” mainly just noisy leakage, playing no contributing role in the transformation of content? Or is it just “political” support, contributing no content but helping to keep competing projects suppressed for awhile? And finally, the properly philosophical question: what’s wrong with these questions and what would better questions be?

Copyright © 2002 by Edge Foundation, Inc.