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Unsupervised sentiment neuron (openai.com)
603 points by gdb on April 6, 2017 | hide | past | favorite | 126 comments

Why are people being so critical about this work? Sure, the blog post provides a simplified picture about what the system is actually capable of, but it's still helpful for a non-ML audience to get a better understanding of the high-level motivation behind the work. The OpenAI folks are trying to educate the broader public as well, not just ML/AI researchers.

Imagine if this discovery were made by some undergraduate student who had little experience in the traditions of how ML benchmark experiments are done, or was just starting out her ML career. Would we be just as critical?

As a researcher, I like seeing shorter communications like these, as it illuminates the thinking process of the researcher. Read ML papers for the ideas, not the results :)

I personally don't mind blog posts that have a bit of hyped-up publicity. It's thanks to groups like DeepMind and OpenAI that have captured public imagination on the subject and accelerated such interest in prospective students in studying ML + AI + robotics. If the hype is indeed unjustified, then it'll become irrelevant in the long-term. One caveat is that researchers should be very careful to not mislead reporters who are looking for the next "killer robots" story. But that doesn't really apply here.

I personally think they did great. They targeted the blog post at a more general audience so most people can follow and get an overhead view of the idea, and then put two giant buttons for "View code" and "Read paper" right at the top of the blog post for those who want more technical writing and working code.

Agreeed. As a non-ML developer, I think this is the paragraph that sells the work, even if it may be an oversimplification:

We were very surprised that our model learned an interpretable feature, and that simply predicting the next character in Amazon reviews resulted in discovering the concept of sentiment. We believe the phenomenon is not specific to our model, but is instead a general property of certain large neural networks that are trained to predict the next step or dimension in their inputs

I think it says something very interesting about human language and information processing in general.

Is it wrong to be critical of research? Back in my previous life of doing basic research I scrutinized papers left and right.

http://karpathy.github.io/2015/05/21/rnn-effectiveness/ towards the end has similar methodology and is 1.5 years old.

Hype is an interesting thing especially when it comes from laymen.

As someone familiar with the field, you likely know this already, but the similarities between the Karpathy post from 2015 and this work from OpenAI is likely because Karpathy is a founder and lead researcher at OpenAI.

Ya but he's surprisingly absent from being a paper author.

If they're getting better results than the previous state of the art, I think the most important point of this research is its critique of previous papers! The previous state of the art research needs to consider such old, basic techniques to improve their own results.

> Hype is an interesting thing especially when it comes from laymen.

Agreed, as can attributing value to said hype.

An argument can generally be made for many things for why they "can be useful, in X situation" (like 'a layperson understand ML'), doesn't mean it has value in every context.

(Or even that it's a particularly good example for its contrived purpose - just that it could/might suffice if nothing better exists.)

From my little experience with the AI community, I think people in it love to obfuscate things. Any attempt to make a topic approachable, even if some of the details are lost, get smacked around. I face this every day in my Masters. If you don't already come with a knowledge of AI + Stats, you're on your own. The community, including the teachers, don't want to teach the mundane.

Techy people, by and large, don't understand marketing. We think that technology should sell itself, and anyone who needs convincing of the superiority of some solution is just dumber than they are. Combined with the elitism complex we see all over academia and the genuine complexity of AI research as it stands today... recipe for sociopathic disaster.

What does "knowledge of AI" mean to you?

I'm in the GA Tech program. Chose AI since I've never touched it. Every course has been terrible in this track. The lectures are awful. The readings take hours upon hours. The TAs pathologically refuse to answer guestions without channeling Confucius. Then I found old GA Tech videos and MIT open courseware. It's starting to make sense. I say all of this because intro to ai is highly rated. It can only get such a rating if it's coming from people that already know the material.

Are you in the OMSCS or on-campus program? I'm currently enrolled in CS 6601 (Artificial Intelligence) via OMSCS, and while it's extremely difficult material that requires a lot of personal investment to master, I've found both TAs and other students to be as helpful as one could reasonably expect.

OMSCS. The TAs refuse to answer questions because it could help cheating. They won't review homework because it could help cheating. They've created an environment so full of fear that it's impossible to learn from mistakes. I'm surprised the slack channel is allowed.

I've never had a direct question to a TA go unanswered (and I've asked my fair share of questions). They're not going to just give you the solution to the homework, though. I guess it depends on what kind of questions you're asking?

> next "killer robots" story ... doesn't really apply here.

Are you sure about that? We're talking about a model/robot which understand sentiments, and can generate fake reviews to boost fake products. I can easily see this being picked up by the AI hype journalists. In fact, this model could even be used for nefarious purposes.

AI hype journalists will find something to write about, regardless of the industry making their research accessible to the wider public.

Markov-chain generators have been around for a while, and have been used to throw off spam detectors. This should not stop research, but instead grow more research into adversarial usage of machine learning models.

> I can easily see this being picked up by the AI hype journalists.

Surely you mean AI journalist bots that can generate articles about how AI review bots generate fake reviews?

>Why are people being so critical about this work?

Some people can't stand to miss an opportunity to remind everyone about how smart they are.

However... one criticism I have of the article is that their first graph doesn't start the y-axis at zero, giving a false impression of how much their method improves on others.

I don't know, but this seems a bit hyped in places.

They start with:

> Our L1-regularized model matches multichannel CNN performance with only 11 labeled examples, and state-of-the-art CT-LSTM Ensembles with 232 examples.

Hmm, that sounds pretty impressive. But then later you read:

> We first trained a multiplicative LSTM with 4,096 units on a corpus of 82 million Amazon reviews to predict the next character in a chunk of text. Training took one month across four NVIDIA Pascal GPUs

Wait, what? How did "232 examples" transform into "82 million"??

OK, I get it: they pretrained the network on the 82M reviews, and then trained the last layer to do the sentiment analysis. But you can't honestly claim that you did great with just 232 examples!

This actually demonstrates something very interesting, I think: you can take an ML model trained with the "low-level prerequisite knowledge" of a subject, and then very quickly and easily teach it a high-level concept that relies on that knowledge.

Which, now that I think about it, makes the human brain and its amazing adaptive general-game-playing abilities a bit less mysterious. Since we humans all have these huge corpuses of sense-data we've been receiving reinforcement signals about since birth, we've likely built up all sorts of low-level models which we just use to predict the world for reflex responses a little bit better and faster (speech models so we can respond to what people are saying even as they're still saying it, visual models so we can throw spears where lions are going to be instead of where they are, etc.) But those low-level predictive models make it nearly effortless to build higher-level models.

I wonder if we'd take a giant leap forward in AI if we just managed to scan+emulate a regular animal brain (say, of a rat), and then built the AI as a neocortex-equivalent for that brain. It would have instant access to thousands or millions of pre-trained low-level predictive models, which it could easily discover as having outputs correlated to success and thus "attach to" during its own training.

What you describe is exactly what practitioners in the field have been doing for years. I think that's why the parent is a bit puzzled at the publication, as it's difficult to understand what's novel.

Yes, I agree with you but with a caveat. Semi-supervised learning is well known but has, I'll argue, recently fallen out of fashion in favor of throwing gallons more of labeled data at a really big neural net, crossing your fingers and hoping for the best. Usually, the neural net is either a really big conv-net with a novel architecture or a biLSTM with some elaboration on attention (which is actually closer to memory/state).

Most of the time, in neural net land, what people are doing with the fine tuning part is taking a model trained on looaads of supervised data, chopping off the head and using those features to train on smaller data. This OpenAI method is different in that it used patterns it learned on its own, instead of the recently more common technique of features extracted from a heavily label trained model to reduce the supervised learning burden in a nearby domain.

Arguably yes, this is an ancient technique but it has mostly been forgotten when it became clear that many problems are surmountable with a large enough helping of GPUs and a small moon's worth of data. OpenAI's is a good idea because it makes you say 'yeah that's obvious, pretrain a simple char rnn on loads of free text and oh wait, why has no one tried this before!?'

What is interesting here is that such a straight forward method compares so well to glittering methods that laboriously advanced the state of the art. What I also found surprising was that there was a 'neuron' that was tracking something very close to sentiment. Why?

A bit of thinking and I came to a simple idea. One way of looking at the LSTM in the practical setting (as opposed to a theoretically Turing Equivalent thing) is as a really big finite state rube goldberg machine. In learning to predict the next character, it makes sense that one set or part of a set of states it can enter/track is extremely correlated with what we humans call sentiment in review text.

In summary, the trained model can be thought of as a computable theory of amazon reviews that also works really well on IMDB reviews (and probably short but probably not sarcastic text reviews in general).

thanks for clarifying this- it isn't transfer learning at all, more like the techniques like, digging through LSTMs post hoc to find the neuron responsible for opening and closing quotation marks (insert karpathy youtube vid here), except for a more "high level" feature - in this case, sentiment.

Indeed, although I'm not as familiar with transfers this far (that is, fine-tuning models is really common with image recognition tasks, but often you take a model trained to recognize objects in images, and train it to recognize different objects in images, but you're still recognizing objects in images).

This feels a bit different, in that yesterday I would have had no strong intuition that "a char-rnn can detect text sentiment better than sota". Looking now, I can rationalize that idea. I get why it might make sense, but it was non-obvious. Do you disagree with any of that? (and if you do, I'd love to see this distance of transfer in literature, its always cool to read up on these things)

Practitioners have been doing this for vision, and transfer learning is not very popular in language. This work is the first that I have heard of that uses transfer learning for language.

What you are proposing with the rat brain simulation/scan seems pretty close to what the Blue Brain Project folks are doing: http://bluebrain.epfl.ch/page-56882-en.html

Would that be why people raised in dysfunctional or abusive families have very deep rooted issues? Everything learned later in life seems more fluid, but some of those problematic attitudes or personality traits are extremely hard to change. Seems consistent with those parts being build in lower layers with a decades long training experience. And yet at a higher level things can be learned and changed fairly easily.

This is essentially linear algebra, not behavioural psychology. I believe that one shouldn't draw such broad conclusions from a 1% improvement on some evaluation dataset.

I'm glad we're not tolerating attempts at pretending deep learning has anything to do with brains.

I was talking about the ability to use thin layers over top of broad learning. If neural networks are a realistic analogy at all, I think it fits. The roots of all this ML stuff is not straight from linear algebra even though much of the math is.

You're playing it extremely fast and loose with concepts like "low-level prerequisite knowledge" and how exactly does something "rel[y] on that knowledge", though. These aren't physical quantities like temperature where we -- as a species -- have the massive amount of low-level prerequisite knowledge that allows us to make rapid high level judgments that rely on that knowledge. The previous sentence is an example of how easy this reasoning is to abuse.

Could be possible. For example, when a child is deprived of any human and humane contact, they end up with a very very impoverished linguistic system as well as delayed development of all cognitive abilities. Could be because the lack the unsupervised training phase.

I think it's a fair claim. Labelled data is very hard to come by compared to unlabelled data. Being able to get a highly accurate model with only a small amount of labelled data is a very sought after and practical property.

The technique of training a model on a lot of data for a long time and then leveraging its sophisticated representation only learning the last layer(s) on small datasets to create accurate models is common practice.

Beating the state-of-the-art with one-shot learning is not common. Transfer learning for NLP is also quite unchartered.

Also the technique is quite novel: This is not pre-trained nets on labeled data, it is an unsupervised generative model.

Future research directions are exciting: Unsupervised prediction of the next frame in a video, and then being able to one-shot learn a wide range of visual tasks.

You might be interested in minute 50 onward [0], or this recent paper from Facebook [1].

[0] https://www.youtube.com/watch?v=-yX1SYeDHbg&list=PLE6Wd9FR--...

[1] https://arxiv.org/abs/1703.07684

Cool. I knew of previous work [1], but not the recent paper you posted. Thanks.

[1] https://arxiv.org/abs/1412.6056 "Predicting Deeper into the Future of Semantic Segmentation"

It's a good idea, but it doesn't seem very common so far.

This is what my NLP company (Luminoso) does -- we train a domain-general model of word meanings on a lot of data, then do the last step on the probably-small amount of specific data you actually have.

Even customers who are knowledgeable about machine learning usually haven't heard of the idea before. They've been assuming that the only way to do NLP is to get millions of labeled examples. Or to get a thousand labeled examples and put them into the kind of off-the-shelf algorithm that needs millions of labeled examples, which of course goes poorly.

My ML background is primarily undergraduate work, and even then it was extremely common.

It's not as easy as what you just described, especially on sequential data. Sure, people already use embeddings built by different models for different tasks (think word2vec, last layer from inception, etc.) but this rarely performs as well as what this article shows.

Thanks for the feedback — added context to that sentence to make it more clear!

The main interesting thing is that none of the Amazon data was labeled, while the 232 labeled examples were.

Very interesting, this reminds me of the 2012 paper by Andrew Ng: Building High-level Features Using Large Scale Unsupervised Learning

To further clarify: does unlabeled mean "we didn't use sentiment data" or "we were only trying to predict the next character given the prior characters", since the amazon data does come with associated 1-5 star ratings, were those used or not?

We did not use the star ratings.

Have you looked at cross referencing against the star ratings? Would be interesting to see how predictive this was of those ratings... or even if another variable in the system could predict that?

That's what I thought, and that makes this all the more interesting!

isn't it impressive? They trained a network to predict the next character and when the finished they trained the last layer to predict sentiment with only few examples. The network was able to learn sentiment somehow in the first training phase without telling it!

For me this open my mind to new opportunities when training deep learning. For example I can do the same for images: train a network to recognize objects and later use the same network to predict sentiment or prettiness for example. And the best thing is that I don't need a lot of labeled examples for the second phase of training!

Immediate thought - the network didn't learn sentiment in the training phase, it just clustered the data. The last phase was so quick to train because it was labeling already-clustered data, so a few data points in each cluster was enough to make it 'obvious'.

Actually it was only an output neuron, and for me it is the same if you call it cluster or not. It just learnt sentiment without any hint. Now I wonder if they can train it again and get the same sentiment neuron, that would mean something. Like sentiment is necessary to predict the next character? (word?)

It's essentially the nlp equivalent transfer learning from the computer vision side.

No this is quite a bit different. In transfer learning in computer vision, people are using a network trained on another, typically large dataset, and using the learned features on a different data set.

This LSTM simply learned to predict the data. It didn't learn some other supervised task.

This would be more similar to autoencoder pretraining, but even that is not quite the same.

Is this correct? My sense from the article is that they did all the training on unsupervised, and then checked one of the recurrent lines for a correlation to sentiment, not adding a layer and doing more training.

They can - because the examples weren't labelled. In principle, you could use the model to train a whole lot of other things (what age group does a product appeal to? Is this product targeted at men/women?) with just a few hundred examples.

With 82 million examples it learned how to spell each word and which word follows which in a sentence.

With the 232 examples it learned What bad sentiment sentences look like and which words occur in them.

If you are interested in looking at the model in more detail, we (@harvardnlp) have uploaded the model features to LSTMVis [1]. We ran their code on amazon reviews and are showing a subset of the learned features. Haven't had a chance to look further yet, but it is interesting to play with.

[1] http://lstm.seas.harvard.edu/client/pattern_finder.html?data...

The synthetic text they generated was surprisingly realistic, despite being generic.

If I were perusing a dozen reviews I probably wouldn't have spotted the AI-generated ones in the crowd.

the negative reviews are funny :D and this one sounds almost like its conscious:

"I couldn’t figure out how to stop this drivel. At worst, it was going absolutely nowhere, no matter what I did.Needles to say, I skim-read the entire book. Don’t waste your time."

is there a sarcasm neuron in there too?

That's a good observation. The code and trained model for this paper is on Github. It could be used to make a fake review generator. Dangerous.

We are getting better and better with automatic text generation. I wonder who will be the copyright owner of an AI-generated text, comments, songs, etc.?

A weird thought: at some point AI short stories may be far more profound than our own.

at the moment, AI short stories are derivative, so it's unlikely. They may well be better than the average, if trained on highly regarded works, but they're not completely novel.

At the moment RNN's can't remember context, so they can make stuff that looks correct, but only on the surface.

I think that'll change, eventually...

We need some kind of hierarchical approach, and/or memory.

As they say: “When you take stuff from one writer it’s plagiarism, but when you take from many writers it’s called research.”

But given the whole corpus of all human-written texts, couldn't they be as creative as us?

It depends on your philosophy on what defines creativity, and whether all creativity is derivative of observing others.

I don't have one, and I guess that's still somehow unsolved problem. But there are some works on creativity and AI. This is definitely an interesting space to observe.

Seriously. How long before we have these reviews all over Amazon?


So char-by-char models is the next Word2Vec then. Pretty impressive results.

It would be interesting to see how it performed for other NLP tasks. I'd be pretty interested to see how many neurons it uses to attempt something like stance detection.

Data-parallelism was used across 4 Pascal Titan X gpus to speed up training and increase effective memory size. Training took approximately one month.

Everytime I look at something like this I find a line like that and go: "ok that's ncie.. I'll wait for the trained model".

Yeah, part of what let word2vec make such a splash that it became the one word embedding model everyone has heard of, is that the word2vec team released their model.

This is a really cool example OpenAI has, but I don't know why I should ultimately care about their character model more than anyone else's if all we've got is their description of how cool it is.

I hope OpenAI defies their reputation for closedness and releases the model.

Yep weights will be up soon!

EDIT: in fact, weights were up at launch: https://github.com/openai/generating-reviews-discovering-sen...

Sorry for my pessimistic outlook, then! Thanks.

I don't know why I should ultimately care about their character model more than anyone else's if all we've got is their description of how cool it is.

Well an unsupervised technique that learns this much meaning from text is amazing! I meant it when I said this might supplement word2vec, and that would make it one of the most important breakthroughs in years.

The comments critical of OpenAI don't make a lot of sense. They have always been very good at releasing stuff, and my comment about waiting for a trained model should be read as jealousy over not being able to train it myself..

> OpenAI defies their reputation for closedness

Does not compute.

The 90's definition of Open? ;)

Although in this case, they did post the weights quickly.

It's very difficult to understand what the contributions are here. From what I've read so far this feels more of a proposal for future research or a press release than advancing the state of the art.

* Using large models trained on lots of data to provide the foundation for sample efficient smaller models is common.

* Transfer learning, fine tuning, character RNNs is common.

Were there any insights learned that give a deeper understanding of these phenomena?

Not knowing too much about the sentiment space, it's hard to tell how significant the resulting model is.

* advancing the state of the art

It says right at the top: "we get 91.8% accuracy versus the previous best of 90.2%" on a standard sentiment corpus. In addition, their method needs less training data than previous approaches.

* Were there any insights learned that give a deeper understanding of these phenomena?

The main appeal lies in the fact that a model trained on a (1) different and (2) very general task basically "in passing" also learned to predict sentiment (i.e., a specialized task that more or less arose from the domain the general model was trained on), and pretty much through a single neuron (out of the 4096 used). The authors speculate that this might be a general effect that could also be transferred to other prediction tasks.

If the main contribution here is the quality of the model and its interesting and powerful representation of text, I hope OpenAI does something distruptively different and releases the weights and trained model.

The accidental sentiment neuron is a function of the model, distribution of the input dataset, and the optimizer finding nice saddle points. Insight into these foundational components would make these results amazing. It sounded like training on other datasets doesn't have the same sentiment properties, which provides a lever to explore these concepts more.

At the moment it feels like the Google cat neuron. It attracted a lot of intrigue but the individual contribution from that in terms of research was more on the infrastructure side, and few people seem to refer back to that publication at this point.

That said OpenAIs mission in itself doesn't necessarily require novel research. For example, the gym is fostering a competitive atmosphere for the community to work on RL which hopefully leads to more progress in the field.

Training a model for a month is difficult and if it has captured interesting phenomena it seems in the interest of the community to release the weights and model. It would be hard for the community to reproduce this without a month of compute and 83M Amazon reviews.

Hi there, the weights and model are here: https://github.com/openai/generating-reviews-discovering-sen...

This is awesome, thanks! My apologies I must have missed it somewhere.

Also, first they write:

> We were very surprised that our model learned an interpretable feature, and that simply predicting the next character in Amazon reviews resulted in discovering the concept of sentiment.

And then they write:

> We believe the phenomenon is not specific to our model, but is instead a general property of certain large neural networks that are trained to predict the next step or dimension in their inputs.

So they can't explain why a phenomenon is occurring, but they think that it generalizes to other contexts.

I find it all very unconvincing. Is this kind of writing common in the deep learning literature?

Mind you, this is not a scientific publication but a blog post that has intentionally tried to adapt the tone to that medium, presumably to appeal to a wider audience.

(Apologies for the slightly incoherent post below)

I've been noticing a lot of work that digs into ML model internals (as they've done here to find the sentiment neuron) to understand why they work or use them to do something. Let me recall interesting instances of this:

1. Sander Dieleman's blog post about using CNNs at Spotify to do content-based recommendations for music. He didn't write about the system performance but collected playlists that maximally activated each of the CNN filters (early layer filters picked up on primitive audio features, later ones picked up on more abstract features). The filters were essentially learning the musical elements specific to various subgenres.

2. The ELI5 - Explain Like I'm Five - Python Library. It explains the outputs of many linear classifiers. I've used it to explain why a text classifier was given a certain prediction: it highlights features to show how much or little they contribute to the prediction (dark red for negative contribution, dark green for positive contribution).

3. FairML: Auditing black-box models. Inspecting the model to find which features are important. With privacy and security concerns too!

Since deep learning/machine learning is very empirical at this stage, I think improvements in instrumentation can lead to ML/DL being adopted for more kinds of problems. For example: chemical/biological data. I'd be highly curious to what new ways of inspecting such kinds of data would be insightful (we can play audio input that maximally active filters for a music-related network, we can visualize what filters are learning in an object detection network, etc.)

"The selected model reaches 1.12 bits per byte." (https://arxiv.org/pdf/1704.01444.pdf)

For context, Claude Shannon found that humans could model English text with an entropy of 0.6 to 1.3 bits per character (http://languagelog.ldc.upenn.edu/myl/Shannon1950.pdf)

I would imagine stuff like sarcasm is still out of reach though. It seems hard for humans to understand it in text based communication. Also using anything out of the standard sentimental model might throw it off. "This product is as good as <product x> (where product x has been known to perform bad." I am just trying to think of scenarios where a sentimental model would fail.

Sentimental neuron sounds fascinating too. I didn't realize individual neurons could be talked about or understood outside of the concept of the NN. I am thinking in terms of "black box" its often referenced to in some articles.

Since one of the research goal for openai is to train language model on jokes[0], I wonder how this neuron would perform with a joke corpus.


[0] https://openai.com/requests-for-research/#funnybot

>>>Sentimental neuron sounds fascinating too. I didn't realize individual neurons could be talked about or understood outside of the concept of the NN. I am thinking in terms of "black box" its often referenced to in some articles.

Yes, I agree. I recall seeing such individual neuron analysis before in Karpathy's "The Unreasonable Effectiveness of Recurrent Neural Networks". He takes a char-rnn that was training to predict the next character for source code and finds neurons that have learned to do paranthesis/bracket opening/closing.

I'm trying to understand this statement:

"The sentiment neuron within our model can classify reviews as negative or positive, even though the model is trained only to predict the next character in the text."

If you look closely at the colorized paragraph in their paper/website, you can see that the major sentiment jumps (e.g. from green to light-green and from light-orangish to red) occur with period characters. Perhaps the insight is that periods delineate the boundary of sentiment. For example:

I like this movie. I liked this movie, but not that much. I initially hated the movie, but ended up loving it.

The period tells the model that the thought has ended.

My question for the team: How well does the model perform if you remove periods?

Why would that matter? Human understanding of sentiment would also go down if you removed vital information such as punctuation.

My point would be to see how much the model is relying on punctuation. It could provide insight as to why character-based models outperform word-based models for sentiment analysis.

Note that sentiment tends to also jump at the ends of grammatical phrases. For example, "Seriously, the screenplay AND the directing were horrendous" [sudden drop in sentiment without punctuation] "and clearly done by people who could not fathom what was good about the novel."

This seems to have to do with a pretty deep understanding of grammar; the model waits until it the low-level neurons have something to pass up (decoding of a complete unit of meaning) before using that to update its sentiment neuron.

A lot of next-character or next-word prediction ends up working like this - internally, the model keeps some state and makes big changes to its understanding at points that have to do with the structure of the stream.

Can someone explain what is "unsupervised" about this? I'm guessing this is what confuses me most.

I think this work is interesting, although when you think about it, it's kind of normal that the model converges to a point where there is a neuron that indicates whether the review is positive or negative. There are probably a lot of other traits that can be found in the "features" layer as well.

There are probably neurons that can predict the geographical location of the author, based on the words they use.

There are probably neurons that can predict that the author favors short sentences over long explanations.

But what makes this "unsupervised"?

It's not labelled data. They didn't tell the model what score is associated with each review. And it learned to predict it anyway. But all it was trained to do was predict the next character.

I wouldn't expect that the neurons are orthogonal on a set of features which we find interesting (sentiment, geographical location). They could be bound up in some other basis of features that we do not find interesting. Other people do not expect this because there are papers about how to incentivize neurons to correspond to interesting features.

>> Other people do not expect this because there are papers about how to incentivize neurons to correspond to interesting features.

Could you clarify that statement? Are you saying that it was unusual for this group to find such a neuron? Also, I did not know that there are papers on how to incentivize neurons to correspond to interesting features. Could you please give me some references on those?

The paper I was thinking of is called: "InfoGAN: Interpretable Representation Learning by Information Maximizing Generative Adversarial Nets"[0]. I do not have experience training and investigating neural nets, but from what I read in that paper, there's no reason to presume you'll find neurons that represent a feature you're interested in. In the paper they alter the reward function to get neurons that correspond to the features they are interested in.

[0] https://arxiv.org/pdf/1606.03657v1.pdf

I agree the title is confusing. As far as I understand everything is unsupervised except for the sentiment neuron. The paper itself is actually a better read.

Yes, it's coincidental rather than unsupervised... The fact that to have a good "next character" prediction, you need to know about the "mindset" of the author makes sense. Especially in the context of product reviews.

Had they created a next-move predictor for chess, they wouldn't have been surprised to find a neuron representing the aggressiveness of the player.

It's a good result on its own but the word "unsupervised" is a bit annoying.

They are using the term unsupervised properly, but do I like your characterization of callling it "coincidental". That is basically the essence of unsupervised learning. We have a system doing something (typically some form of optimization), and "coincidentally" it learns something useful that we did not explicitly tell it.

Machine Learning has become more and more like archaeology after people start saying "empirically" more and only provide a single or limited datasets.

I think it's fair to criticize this blog post for being unclear on what exactly is novel here; pre-training is a straighforward and old idea, but the blog post does not even mention this. Having accessible write ups for AI work is great, but surely it should not be confusing to domain experts or be written in such a way as to exacerbate the rampant oversimplification or misreporting in popular press about AI. Still, it is a cool mostly-experimental/empirical result, and it's good that these blog posts exist these days.

For what it's worth, the paper predictably does a better job of covering the previous work and stating what their motivation was: "The experimental and evaluation protocols may be underestimating the quality of unsupervised representation learning for sentences and documents due to certain seemingly insignificant design decisions. Hill et al. (2016) also raises concern about current evaluation tasks in their recent work which provides a thorough survey of architectures and objectives for learning unsupervised sentence representations - including the above mentioned skip-thoughts. In this work, we test whether this is the case. We focus in on the task of sentiment analysis and attempt to learn an unsupervised representation that accurately contains this concept. Mikolov et al. (2013) showed that word-level recurrent language modelling supports the learning of useful word vectors and we are interested in pushing this line of work. As an approach, we consider the popular research benchmark of byte (character) level language modelling due to its further simplicity and generality. We are also interested in evaluating this approach as it is not immediately clear whether such a low-level training objective supports the learning of high-level representations." So, they question some built in assumptions from the past by training on lower-level data (characters), with a bigger dataset and more varied evaluation.

The interesting result they highlight is that a single model unit is able to perform so well with their representation: "It is an open question why our model recovers the concept of sentiment in such a precise, disentangled, interpretable, and manipulable way. It is possible that sentiment as a conditioning feature has strong predictive capability for language modelling. This is likely since sentiment is such an important component of a review" , which I tend to agree with... train a on a whole lot of reviews, it's only natural to train a regressor for review sentiment.

I think one of the most amazing parts of this is how accessible the hardware is right now. You can get world-class AI results with the cost of less than most used cars. In addition, with so many resources freely available through open-source, the ability to get started is very accessible.

> The model struggles the more the input text diverges from review data

This is where I fear the results will fail to scale. The ability to represent 'sentiment' as one neuron, and its ground truth as uni-dimensional seems most true to corpuses of online reviews where the entire point is to communicate whether you're happy with the thing that came out of the box. Most other forms of writing communicate sentiment in a more multi-dimensional way, and the subject of sentiment is more varied than a single item shipped in a box.

In otherwords, the unreasonable simplicity of modelling a complex feature like sentiment with this method, is something of an artifact of this dataset.

The neural network is savage enough to learn "I would have given it zero stars, but that was not an option." Are we humans that predictable?

The training data consisted of 82 million reviews, so I'm sure that phrase (or slight variants) occurred hundreds of thousands of times.

Could be checked by counting n-grams to see just how much it differs from other reviews.

This article is not accessible. It puts all textual examples into images and ever has some absolutely unnecessary animation. Please fix it.

Thanks for pointing this out! We've moved the textual examples into html, added alt text for images, and will be reviewing feature posts for accessibility

This is a great name for a band :-). That said, I found the paper really interesting. I tend to think about LSTM systems as series expansions and using that as an analogy don't find it unusual that you can figure out the dominant (or first) coefficient of the expansion and that it has a really strong impact on the output.

What they have done is semi-supervised learning (Char-RNN) + supervised training of sentiment. Another way to do is semi-supervised learning (Word2Vec) + supervised training of sentiment. If first approach works better, does it imply that character level learning is more performant than word level learning?

As far as I understand, it means that there must be a relation between a character's sentiment and what the next character can (/should) be for neural network to use this as a feature, am I right?

Does this mean we have unconsciously developed a language that exposes such relations?

They muse about the reason behind the sentiment neuron in the paper.

"It is an open question why our model recovers the concept of sentiment in such a precise, disentangled, interpretable, and manipulable way. It is possible that sentiment as a conditioning feature has strong predictive capability for language modelling. This is likely since sentiment is such an important component of a review."

They go on to frame that as an important consideration for further work like this:

"Our work highlights the sensitivity of learned representations to the data distribution they are trained on. The results make clear that it is unrealistic to expect a model trained on a corpus of books, where the two most common genres are Romance and Fantasy, to learn an encoding which preserves the exact sentiment of a review."

I'm wondering if a "funniness" neuron could be discovered in a model trained on millions of jokes of various funniness, or what sorts of undiscovered meaning there is in other neurons in this model.

Impressive the abstraction NNs can achieve from just character prediction. Do the other systems they compare to also use 81M Amazon reviews for training? Seems disingenuous to claim "state-of-the-art" and "less data" if they haven't.

just wondering, how many AI programs (models with complete source code) OpenAI has released?

Lot of stuff here: https://github.com/openai

Train on character-by-character basis, this is really incredible, quite opposite to human's intuition about language, but it seems a brilliant idea, and OpenAI tried it out, great!

why did they do this character by character? Would word by word make sense? Other than punctuation I'm not seeing why specific characters are meaningful units.

Word by word would require adding prior knowledge of words into the system, and they're trying to "start from scratch" as much as possible.

Why is the linear combination used to train the sentiment classifier? Why does its result get taken into account?

Is this linear combination between 2 different strings?

What's the easiest way to make a text heatmap like the ones in their blog?

Very interesting. I wonder if they tried to predict part-of-speech tags.

That would probably work. Karpathy's character based RNN could detect semantic meaning in text and code. http://karpathy.github.io/2015/05/21/rnn-effectiveness/

This has amazing potential for use in sock puppet accounts.

moved that needle I guess

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