Cool paper. I think the semantic similarity result is particularly interesting.
As I understand it you've got a circuit that wants to calculate something like Sim(A,B), where A and B might have many "senses" aka: features but the Sim might not be a linear function of each of thes Sims across all senses/features.
So for example, there are senses in which "Berkeley" and "California" are geographically related, and there might be a few other senses in which they are semantically related but probably none that really matter for copy suppression. For this reason wouldn't expect the tokens of each of to have cosine similarity that is predictive of the copy suppression score. This would only happen for really "mono-semantic tokens" that have only one sense (maybe you could test that).
Moreover, there are also tokens which you might want to ignore when doing copy suppression (speculatively). Eg: very common words or punctuations (the/and/etc).
I'd be interested if you have use something like SAE's to decompose the tokens into the underlying feature/s present at different intensities in each of these tokens (or the activations prior to the key/query projections). Follow up experiments could attempt to determine whether copy suppression could be better understood when the semantic subspaces are known. Some things that might be cool here:
- Show that some features are mapped to the null space of keys/queries in copy suppression heads indicating semantic senses / features that are ignored by copy suppression. Maybe multiple anti-induction heads compose (within or between layers) so that if one maps a feature to the null space, another doesn't (or some linear combination) or via a more complicated function of sets of features being used to inform suppression.
- Similarly, show that the OV circuit is suppressing the same features/features you think are being used to determine semantic similarity. If there's some asymmetry here, that could be interesting as it would correspond to "I calculate A and B as similar by their similarity in the *california axis* but I suppress predictions of any token that has the feature for anywhere on the West Coast*).
I'm particularly excited about this because it might represent a really good way to show how knowing features informs the quality of mechanistic explanations.
Cool work! I'd be excited to see whether latents found via this method are higher quality linear classifiers when they appear to track concepts (eg: first letters) and also if they enable us to train better classifiers over model internals than other SAE architectures or linear probes (https://transformer-circuits.pub/2024/features-as-classifiers/index.html).
Cool work!
Have you tried to generate autointerp of the SAE features? I'd be quite excited about a loop that does the following:
I suspect this is nicer than language modelling in that you can programmatically generate your data labels from explanations rather than relying on LMs. Of course you could just a priori decide what probes to train but the loop between autointerp and next probe seems cool to me. I predict that current SAE training methods will result in long description lengths or low recall and the tradeoff will be poor.
Great work! I think this a good outcome for a week at the end of ARENA (Getting some results, publishing them, connecting with existing literature) and would be excited to see more done here. Specifically, even without using an SAE, you could search for max activating examples for each steering vectors you found if you use it as an encoder vector (just take dot product with activations).
In terms of more serious followup, I'd like to much better understand what vectors are being found (eg by comparing to SAEs or searching in the SAE basis with a sparsity penalty), how much we could get out of seriously scaling this up and whether we can find useful applications (eg: is this a faster / cheaper way to elicit model capabilities such as in the context of sandbagging).
I think that's exactly what we did? Though to be fair we de-emphasized this version of the narrative in the paper: We asked whether Gemma-2-2b could spell / do the first letter identification task. We then asked which latents causally mediated spelling performance, comparing SAE latents to probes. We found that we couldn't find a set of 26 SAE latents that causally mediated spelling because the relationship between the latents and the character information, "exogenous factors", if I understand your meaning, wasn't as clear as it should have been. As I emphasized in a different comment, this work is not about mechanistic anomalies or how the model spells, it's about measurement error in the SAE method.
This thread reminds me that comparing feature absorption in SAEs with tied encoder / decoder weights and in end-to-end SAEs seems like valuable follow up.
Thanks Egg! Really good question. Short answer: Look at MetaSAE's for inspiration.
Long answer:
There are a few reasons to believe that feature absorption won't just be a thing for graphemic information:
If a feature is active for one prompt but not another, the feature should capture something about the difference between those prompts, in an interpretable way. Empirically, however, we often find this not to be the case – often a feature fires for one prompt but not another, even when our interpretation of the feature would suggest it should apply equally well to both prompts.
In terms of what I really want to see people look at: What wasn't clear from Meta-SAEs (which I think is clearer here) is that absorption is important for interpretable causal mediation. That is, for the spelling task, absorbing features look like a kind of mechanistic anomaly (but is actually an artefact of the method) where the spelling information is absorbed. But if we found absorption in a case where we didn't know the model knew a property of some concept (or we didn't know it was a property), but saw it in the meta-SAE, that would be very cool. Imagine seeing attribution to a latent tracking something about a person, but then the meta-latents tell you that the model was actually leveraging some very specific fact about that person. This might really important for understanding things like sycophancy...
Great work! Using spelling is very clear example of how information gets absorbed in the SAE latent, and indeed in Meta-SAEs we found many spelling/sound related meta-latents.
Thanks! We were sad not to have time to try out Meta-SAEs but want to in the future.
I have been thinking a bit on how to solve this problem and one experiment that I would like to try is to train an SAE and a meta-SAE concurrently, but in an adversarial manner (kind of like a GAN), such that the SAE is incentivized to learn latent directions that are not easily decomposable by the meta-SAE.
Potentially, this would remove the "Starts-with-L"-component from the "lion"-token direction and activate the "Starts-with-L" latent instead. Although this would come at the cost of worse sparsity/reconstruction.
I think this is the wrong way to go to be honest. I see it as doubling down on sparsity and a single decomposition, both of which I think may just not reflect the underlying data generating process. Heavily inspired by some of John Wentworth's ideas here.
Rather than doubling down on a single single-layered decomposition for all activations, why not go with a multi-layered decomposition (ie: some combination of SAE and metaSAE, preferably as unsupervised as possible). Or alternatively, maybe the decomposition that is most useful in each case changes and what we really need is lots of different (somewhat) interpretable decompositions and an ability to quickly work out which is useful in context.
It seems that PIBBSS might be pivoting away from higher variance blue sky research to focus on more mainstream AI interpretability. While this might create more opportunities for funding, I think this would be a mistake. The AI safety ecosystem needs a home for “weird ideas” and PIBBSS seems the most reputable, competent, EA-aligned place for this! I encourage PIBBSS to “embrace the weird,” albeit while maintaining high academic standards for basic research, modelled off the best basic science institutions.
I was a recent PIBBSS mentor, and am a mech interp person who is likely to be considered mainstream by many people and for this reason I wanted to push back on this concern.
A few thoughts:
Some final notes:
I'll share this in the PIBBSS slack to see if other's want to comment :)
Thanks for posting this! I've had a lot of conversations with people lately about OthelloGPT and I think it's been useful for creating consensus about what we expect sparse autoencoders to recover in language models.
Maybe I missed it but:
I think a number of people expected SAEs trained on OthelloGPT to recover directions which aligned with the mine/their probe directions, though my personal opinion was that besides "this square is a legal move", it isn't clear that we should expect features to act as classifiers over the board state in the same way that probes do.
This reflects several intuitions:
Some other feedback:
Oh, and maybe you saw this already but an academic group put out this related work: https://arxiv.org/abs/2402.12201 I don't think they quantify the proportion of probe directions they recover, but they do indicate recovery of all types of features that been previously probed for. Likely worth a read if you haven't seen it.