Perceptual control theory (PCT) is a psychological theory of animal and human behavior. PCT postulates that an organism’s behavior is a means of controlling its perceptions. The model is based on the principles of negative feedback [1]. It is to some extent an application of the ideas used in the engineering discipline of control theory to the modeling of the human mind and behavior.
PCT postulates that layers of control systems, which have access to a metric to optimize and some set of policies or actions, can maintain balancing-acts for difficult, high-abstraction things without developing any explicit model for how those actions relate to the metric being tracked. The brain is postulated to be one of these multi-layered PCTs.
Physical movements are a favorite case-study, since they’re relatively easy to break down into this these sorts of layered control theory sub-problems. An important subtlety is that the control systems are optimizing for the perception of a state, rather than for a concrete environmental state itself.
Actions and behaviors develop because they do something to reduce the mismatch between internal perception, and the stimulus readings received.
Controversy
It’s unclear whether PCT is a valid theory. It doesn’t significantly constrain the space of possible minds that could be built from it, and the advocates of the theory on the blog were unable to make a clear case for it. Experimental results for its quality as an algorithm seemed lackluster; see these critical comments about the paper version of this technical report, which claim that the correct results may have been achieved more through parameter-fitting than PCT.
Some anecdotally found it more useful for explaining bugs in human behavior, than for modeling what would be ideal behavior.
Under-Characterized Information Storage
This seems to be a common category of complaints about Perceptual Control Theory.
This blog post called out that PCT “has no theory of information or how that information comes to be made,” and this post grappled with a similar problem: struggling to find a place for implicit models, priors, and updates when working with a PCT framework. (This comment may have made a case for at least some embedded implicit priors.)
Notable Posts
Kennaway’s What is control theory, and his prior post Without Models
SSC book reviews of Surfing Uncertainty and Behavior: The Control of Perception
Scott Alexander theorizes that it’s analogous to Friston’s Free Energy Principle, here and here
Vaniver’s Introduction to Control Theory, and review of Behavior: The Control of Perception
His personal-blog thoughts on the topic here
Friston’s Free Energy doesn’t have its own page. But I think a lot of the PCT-relevant conversation on LW, ends up under that term. Unlike the “mostly just intro-posts” under the PCT term proper, FFE seems to have more-recent engagement, so I think FFE has more of a presence here than PCT.
In retrospect, not including those was a mistake.
Here’s a (non-exhaustive) handful of the FFE posts:
Neural Annealing: Toward a Neural Theory of Everything (crosspost)
Scott: God Help Us, Let’s Try To Understand Friston On Free Energy and Mental Mountains
Quick mention in My computational framework for the brain
In trying not to be vague, I veered towards writing too much. So if someone could take what I wrote and destroy half of it (or destroy all of it, and write a new and better thing) that would be lovely.
(In a slight inversion of PCT, I feel very sick of looking at my own writing.)
Pretty sure we had quite a bit more discussion of PCT on here in the last few years, would be great for someone to add it.
I share the impression that there’s been a bit more talk and thought on it.
But I tried out the obvious search terms on here, and for the life of me I can’t find it. (Other than a few side-mentions, which it didn’t seem worth tagging.)
Free Energy Principle gets mentioned a few more times, but I don’t know that it’s quite the same thing.