Wired wrote a good article about Karl Friston, the neuroscientist whose works I've puzzled over here before. Raviv writes:

Friston's free energy principle says that all life…is driven by the same universal imperative…to act in ways that reduce the gulf between your expectations and your sensory inputs. Or, in Fristonian terms, it is to minimize free energy.

Put this way, it's clearly just perceptual control theory. Powers describes the same insight like this:

[Action] is the difference between some condition of the situation as the subject sees it, and what we might call a reference condition, as he understands it.

I'd previously noticed that these theories had some weird similarities. But I want to go further and say they're fundamentally the same paradigm. I don't want to deny that the two theories have developed differently, and I especially don't want to deny that free energy/predictive coding has done great work building in a lot of Bayesian math that perceptual control theory can't match. But the foundations are the same.

Why is this of more than historical interest? Because some people (often including me) find free energy/predictive coding very difficult to understand, but find perceptual control theory intuitive. If these are basically the same, then someone who wants to understand free energy can learn perceptual control theory and then a glossary of which concepts match to each other, and save themselves the grief of trying to learn free energy/predictive coding just by reading Friston directly.