Welcome to The Nonlinear Library, where we use Text-to-Speech software to convert the best writing from the Rationalist and EA communities into audio. This is: Scarce Channels and Abstraction Coupling, published by johnswentworth on February 28, 2023 on The AI Alignment Forum.

Epistemic Status: mental model and intuitive story

Scarce Channels vs Scarce Modules

Let’s distinguish between two kinds of system-regimes: “scarce channels” and “scarce modules”.

A prototypical “scarce modules” system would be one of those 19th-century families living with 12 people in a 500 square foot (46 square meter) home. When at home, everyone knows what everyone else is doing all the time; there is zero privacy. Communication channels are highly abundant - everyone has far more information than they want about what everyone else is doing. Indeed, communication channels exist by default. Conversely, though, modules are scarce - it’s hard for one or more family members to carve out a part of the space which is isolated from the rest of the family, and interacts only through some limited channels.

A prototypical “scarce channels” system, by contrast, would be a few hundred 19th-century fur trappers spread out over half of Montana. Most of the time, none of them are anywhere near each other; nobody has any idea what’s going on with anyone else. Communication channels are scarce - getting information to another person is difficult and expensive. Conversely, though, modules are highly abundant - it’s very easy for one or a few trappers to carve out a space which is isolated from the rest, and which interacts only through some limited channels (like e.g. occasionally visiting the nearest town). Indeed, modules exist by default.

I want to use this as a mental model for complex adaptive systems, like neural nets or brains.

Key hypothesis: neural nets or brains are typically initialized in a “scarce channels” regime. A randomly initialized neural net generally throws out approximately-all information by default (at initialization), as opposed to passing lots of information around to lots of parts of the net. A baby’s brain similarly throws out approximately-all information by default, as opposed to passing lots of information around to lots of parts of the brain. I’m not particularly going to defend that claim here; rather, I raise it as a plausible hypothesis for how such systems might look, and next we’ll move on to an intuitive story for how an adaptive system in the “scarce channels” regime interacts with natural abstractions in its environment.

The upshot is that, when an adaptive system is in the “scarce channels” regime, lots of optimization pressure is required to induce an information channel to form. For instance, picture such a system as a bunch of little pieces, which initially don’t talk to each other at all:

In order for an information channel to form from one end to the other, each of the individual pieces along the line-of-communication need to be individually optimized to robustly pass along the right information:

So, intuitively, the number of bits-of-optimization required to form that information channel should scale roughly with the number of pieces along the line-of-communication.

Furthermore, when information channels do form, they should be approximately as small as possible. Optimization pressure will tend to induce as little information passing as the system can get away with, while still satisfying the optimization criterion.

Abstraction Coupling

Next question: what sort of patterns-in-the-environment could induce communication channels to form?

Well, here’s a situation where communication channels probably won’t form: train a neural net in an environment where the reward/loss its output receives is independent of the input. Or, for a generative net, an environment where the tokens/pixels are all independent.

More generally, suppose our adaptive system interfaces with the environment in two different places (and possibly more, ...