The author hints at this but it seems like one issues is that while JEPA is good at distinguishing between unpredictable noise and predictable features, the model has no way of assigning importance to different predictable features.

So for a system where it’s very difficult to exactly reach the desired end state, the model needs to choose between (for example):

- reaching a relatively achievable scene where 95% of the features in the latent are correct, which includes stuff like visible enemies, Mario’s position on the screen etc

- reaching a far more difficult to access scene where there’s a bunch of differences in the actual level visuals, but theres a match on the latent for the tiny set of pixels in HUD that indicate you’ve hit the victory condition

We obviously know that it’s not good enough to reach an early scene that looks similar to the victory condition but isn’t. The model doesn’t.

In a sense, this is what the linear probe helps with - it allows us to re-weight the latent and say “actually, while the latent encodes many things about the world, the thing we really care about is the X position.”

I’d be curious what happened if rather than planning actions on cross entropy of a final scene, the model just tried to find the actions that maximize the predicted X value of the probe.