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- Hacker News
- A TLDR, since most comments here seem to misunderstand the result.
The idea is: a model may only have 100M neurons or whatever. But there are infinite concepts in the world. Therefore, models have to "stuff" multiple concepts per neuron.
How do you do that? Theres two ways:
1. Each neuron handles similar concepts. One neuron for dogs, a separate neuron one for cars, etc.
2. Each neuron handles a bundle of unrelated concepts. One neuron handles dogs and cars. Another neuron handles cats and numbers. And so on.
Historically, people thought #2 was correct because many neurons were found that seemingly represented multiple concepts. #2 had a cool name (polysemanticity) and was promoted in OpenAI/Anthropic blogs so it had a lot of traction.
However, this blog says #2 is wrong. Actually, the dog/car neuron is just a "V shape neuron". So #2 was just methodological error, and #1 was right all along. This is all the blog is saying.
by x312 - This is a very nice discussion, but it bothers me that what is clearly a plain error in their ZoomIn paper is being treated a bit cavalierly. (The error was claiming a neuron was a "dog and car" neuron, when in fact it was a V neuron. ZoomIn wasn't the first to make the error, but it definitely promoted it.)
This type of error may have mislead researchers for years; it was actually harmful. In my field, a correction, or perhaps retraction (depending on the centrality of the claim), would be standard for something of this magnitude.
I suppose there are different standards in different scholarly communities. And maybe it truly was impossible to know at the time that the dog/car relation was actually a V shape, but my recollection is that this type of feature was well known at the time and so the error could have (should have?) been caught a decade ago.
So: massive new discovery, or a spin on a correction that's lead scholarly research astray for almost a decade?
by _alternator_ - To cut through some of all this text - here's a link he calls "the first non-trivial neural network I feel I mostly understand:
https://already-clean.goodfire.com/microscope/medium.html?la...
by ks2048 - The tone reminds me a little of the enthusiasm from the Anthropic mechinterp team around the time of the first large-scale SAE results. A kind of hypomanic energy around the idea that we've discovered the key paradigm necessary to understand models, and all that's left is to scale it up.by aesthesia
- So we have here a massive evidentiary brief, the point of which is to argue that it is easier than we thought to, like, "sequence the AI genome" (in my estimation). We revisit famously-messy neurons, examine various tool failures, check places where messy things still hide, and catalog how "polysemanticity" is represented variously in the network.
Once sequenced, the thinking goes, we'll be able to do things like: explain and anticipate failures; predict what happens when you modulate the pathway an input takes on its way to becoming output; reconstruct algorithms the models have learned.
I'm not 100% sure this will work out like the mechinterp people think. If the neural representations and pathways are "clean" (organized into a a meaningful-to-humans hierarchy), it seems at least very plausible that the behaviors that AI xrisk people are worried about will mostly boil down to straightforward synthesis (i.e., mostly-linear-interpolation) of mostly-well-cataloged knowledge. And if that is true, then it does not seem hopeful that there would be a way to prevent the output they are worried about, other than just removing a bunch of the knowledge. So maybe there is no alignment solution at all.
by antics - I'm confused - it seems to be saying that, instead of thinking about neurons as packing together a lot of "concepts" together into one, the issue is that your view of what a "concept" is, was already prejudiced, and the neuron itself had a small clean role? Like, you can either think about this as the "Cat & Car" neuron or you can think about it as the "V shaped neuron" - one seems simpler.
But isn't the point that the neural nets learn some insanely abstract ideas anyways? So whether the complexity is "ahh we think this neuron does 100 seemingly unrelated things but we don't understand it" or "this actually is some kind of latent shared feature, but we don't know what the concept represents because the composition of the entire circuit is an arcane algorithm", we're kind of stuck, no?
This seems like a classic model-description issue more than anything.
by sigbottle - The claims seem to be an overreach of what is actually proven. We've known about progressive feature complexity and the impacts of early training structures on later training for a really long time (since CNN's, The Lottery Ticket Hypothesis, etc...) and neither of those phenomenon are mutually exclusive with parameter overloading. The Multimodal Gap work (https://arxiv.org/abs/2203.02053) seems to imply networks have a tendency towards condensed representations that are clearly not semantic and a bunch of other considerations are already on the table for discussion. I don't think these have all been considered sufficiently to start claiming we are around the corner from mechanistic interpretation.by bluejay2387
- Nick is a force of nature. Highly recommend following him on X if you don't already.
His launch post gives good context not found in the blog:
> interpretability might be the most important scientific problem in the world right now, as I don't think we can solve alignment if we don't know what we're building. I think I have good news about it. I co-authored early work in mechanistic interpretability at OpenAI and came away pessimistic, because neural networks appeared to fold into arbitrary tangled knots. years later, I started openai's first large-scale automated interpretability project, finding about 2% of neurons legible with the primitive tools we had
> with modern agentic tools and a much closer look, the picture looks totally different. the vast majority in models up to trillions of parameters are legible, and their circuits beautiful. many famous examples of tangled neurons turned out to be misunderstood. The roadblocks I expected mostly aren't there. I now think ambitious interpretability will be solved by the time we need it most, and possibly quite soon, as automated scientists keep improving. it may be a bitter lesson for interpretability: the simple thing, at absurd scale, works
by sebmellen