Break the curse 36 years ago! Meta launches reverse training method to eliminate the 'reversal curse' of large models

The "reversal curse" of the large language model has been solved!

This curse was first discovered in September last year, which immediately caused exclamations from LeCun, Karpathy, Marcus and other big guys.

Because the large model with unique scenery and arrogance actually has an "Achilles heel": one in "A is B" The language model trained on the above model cannot correctly answer "whether B is A".

For example, the following example: LLM knows clearly that "Tom Cruise's mother is Mary Lee Pfeiffer", but cannot answer "Mary Lee Pfeiffer's child is Tom" "Cruise".

#——This was the most advanced GPT-4 at the time. As a result, even children could have normal logical thinking, but LLM could not do it.

Based on massive data, I have memorized knowledge that surpasses almost all human beings, yet behaves so dullly. I have obtained the fire of wisdom, but am forever imprisoned in this curse. .

Paper address: https://arxiv.org/pdf/2309.12288v1.pdf

As soon as this happened, the entire network was in an uproar.

On the one hand, netizens said that the big model is really stupid, really. Knowing only "A is B" but not knowing "B is A", I finally retained my dignity as a human being.

On the other hand, researchers have also begun to study this and are working hard to solve this major challenge.

Recently, researchers from Meta FAIR launched a reverse training method to solve the "reversal curse" of LLM in one fell swoop.

Paper address: https://arxiv.org/pdf/2403.13799.pdf

Research We first observed that LLMs train in an autoregressive manner from left to right—which may be responsible for the reversal curse.

So, if you train LLM (reverse training) in the right-to-left direction, it is possible for the model to see the facts in the reverse direction.

Reverse text can be treated as a second language, leveraging multiple different sources through multitasking or cross-language pre-training.

The researchers considered 4 types of reversal: token reversal, word reversal, entity-preserving reversal and random segment reversal.

Token and word reversal, by splitting a sequence into tokens or words respectively, and reversing their order to form a new sequence.

Entity-preserving reverse finds entity names in a sequence and preserves left-to-right word order within them while doing word reversal.

Random segment inversion splits the tokenized sequence into blocks of random length and then preserves the left-to-right order within each block.

The researchers tested the effectiveness of these inversion types at parameter scales of 1.4B and 7B and showed that entity-preserving and randomized piecewise reverse training can mitigate the inverse curse. , or even eliminate it entirely in some cases.

In addition, the researchers also found that reversing before training improved the performance of the model compared to standard left-to-right training - so reverse training can as a general training method.

Reverse training method

Reverse training includes obtaining a training data set with N samples and constructing a reverse sample set REVERSE (x ).

The function REVERSE is responsible for reversing the given string. The specific method is as follows:

Word reverse: each example is first split for words, then reverse the strings at the word level, concatenating them with spaces.

Entity Preserving Inversion: Run an entity detector on a given training sample, splitting non-entities into words as well. Then the non-entity words are reversed, while the words representing entities retain their original word order.

Random segment inversion: Instead of using an entity detector, we try to use uniform sampling to randomly divide the sequence into segments with a size between 1 and k tokens, and then After reversing the segments but maintaining the word order within each segment, the segments are connected using the special token [REV].

#The above table gives examples of different types of reversal on a given string.

At this time, the language model is still trained from left to right. In the case of word reversal, it is equivalent to predicting sentences from right to left.

Reverse training involves training on standard and reverse examples, so the number of training tokens is doubled, while both forward and reverse training samples are mixed together.

Inverse transformation can be seen as a second language that the model must learn. Please note that during the inversion process, the relationship between facts remains unchanged, and the model can learn from the grammar. to determine whether it is in forward or reverse language prediction mode.

Another perspective of reverse training can be explained by information theory: the goal of language modeling is to learn the probability distribution of natural language

Reverse Task training and testing

Entity pair mapping

First create a simple symbol-based data set to study the inversion curse in a controlled environment.

Randomly pair entities a and b in a one-to-one manner. The training data contains all (a→b) mapping pairs, but only half of the (b→a) mapping pairs, and the other Half is used as test data.

The model must infer the rule a→b ⇔ b→a from the training data and then generalize it to the pairs in the test data.

The above table shows the test accuracy (%) of the symbolic reversal task. Despite the simplicity of the task, standard language model training fails completely, suggesting that scaling alone is unlikely to solve it.

In contrast, reverse training can almost solve the problem of two word entities, but its performance drops rapidly as the entities get longer.

Word reversal works fine for shorter entities, but for entities with more words, entity-preserving inversion is necessary. Random segment reversal performs well when the maximum segment length k is at least as long as the entity.

Restore the name

##The above table shows For the inversion task of determining a person's full name, when only the date of birth is given to determine a person's full name, the accuracy of the inversion task is still close to zero - this is because in the entity detection method used in this article, the date Treated as three entities, so their order is not preserved in the inversion.

If the inversion task is reduced to just determining a person's last name, word-level inversion is sufficient.

Another phenomenon that may come as a surprise is that the entity retention method can determine the person's full name, but not the person's last name.

This is a known phenomenon: language models may be completely unable to retrieve late tokens of knowledge fragments (such as last names).

Real World Facts

Here the author trained a Llama-2 with 1.4 billion parameters Model, train a baseline model of 2 trillion tokens in the left-to-right direction.

In contrast, inverse training uses only 1 trillion tokens, but uses the same subset of data to train in both directions, left-to-right and right-to-left. ——The total number of tokens in the two directions is 2 trillion, ensuring fairness and justice in terms of computing resources.

To test reversal of real-world facts, the researchers used a celebrity task that included questions such as "Who is a celebrity's mother?" along with more challenging Reverse questions, such as "Who are the children of a certain celebrity's parents?"

The results are shown in the table above. The researchers sampled the models multiple times for each question and considered it a success if any of them contained the correct answer.

Generally speaking, since the model is small in terms of number of parameters, has limited pre-training, and lacks fine-tuning, the accuracy is usually relatively low. However, reverse training performed even better.

Prophecy 36 years ago

In 1988, Fodor and Pylyshyn published an article about the thinking system in the journal "Cognition" Sexual articles.

If you really understand this world, then you should be able to understand the relationship between a relative to b, and also understand the relative relationship between b relationship to a.

Even non-verbal cognitive creatures should be able to do this.

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