Does Fine-Tuning LLMs on New Knowledge Encourage Hallucinations?
Tags: machinelearning, ai, beginners, datascience
Published: 2024-05-13 17:04:32

*This is a Plain English Papers summary of a research paper called [Does Fine-Tuning LLMs on New Knowledge Encourage Hallucinations?](https://aimodels.fyi/papers/arxiv/does-fine-tuning-llms-new-knowledge-encourage). If you like these kinds of analysis, you should subscribe to the [AImodels.fyi newsletter](https://aimodels.substack.com) or follow me on [Twitter](https://twitter.com/mikeyoung44).*

## Overview

- Large language models can struggle with hallucinating factually incorrect responses when exposed to new information during fine-tuning
- Researchers designed a controlled experiment to study the impact of new knowledge on a model's ability to utilize its pre-existing knowledge
- The study found that large language models have difficulty acquiring new factual knowledge through fine-tuning, but as new information is learned, it can linearly increase the model's tendency to hallucinate

## Plain English Explanation

Large language models, like GPT-3 or BERT, are trained on vast amounts of online text data to become highly capable at tasks like answering questions or generating human-like text. However, when these models are further trained, or "fine-tuned," on specific tasks using supervised learning, they may encounter new factual information that was not part of their original training. 

[Researchers are concerned](https://aimodels.fyi/papers/arxiv/large-language-models-hallucination-regard-to-known) that this exposure to new knowledge could cause the model to start "hallucinating" - generating factually incorrect responses that are not grounded in its pre-existing knowledge. The idea is that the model is being trained to produce specific facts, even if those facts don't match what the model already "knows."

To better understand this issue, the researchers in this study designed a controlled experiment focused on [closed-book question answering](https://aimodels.fyi/papers/arxiv/towards-holistic-evaluation-llms-factual-knowledge-recall). They varied the proportion of fine-tuning examples that introduced new knowledge the model didn't have before.

The key findings are:
- Large language models struggle to acquire new factual knowledge through fine-tuning. Examples with new information are learned much slower than those consistent with the model's existing knowledge.
- However, as the model does eventually learn the new information, it starts to [increase the model's tendency to hallucinate](https://aimodels.fyi/papers/arxiv/injecting-new-knowledge-into-large-language-models) - generating incorrect responses.

Overall, the results suggest that while fine-tuning can help language models use their existing knowledge more efficiently, [introducing significant new factual information is risky](https://aimodels.fyi/papers/arxiv/dont-believe-everything-you-read-enhancing-summarization) and may lead to unreliable or inaccurate outputs. The researchers argue that the bulk of a language model's factual knowledge should come from its initial pre-training, not from fine-tuning.

## Technical Explanation

The researchers designed a controlled experiment to study the impact of exposing large language models to new factual information during fine-tuning. They focused on the closed-book question answering task, where models must answer questions without access to external information sources.

The experimental setup involved fine-tuning a pre-trained language model on a question answering dataset, but with a twist. The researchers varied the proportion of examples in the fine-tuning dataset that contained new knowledge - facts the model did not have in its original pre-training. 

By systematically changing the ratio of "new knowledge" to "known knowledge" examples, the researchers could observe how this affected the model's ability to learn and utilize its pre-existing factual information. The [FLAME framework](https://aimodels.fyi/papers/arxiv/flame-factuality-aware-alignment-large-language-models) was used to measure the model's tendencies to hallucinate or stick to its original knowledge.

The key findings were:
1. Large language models struggle to acquire new factual knowledge through fine-tuning. Examples containing new information were learned significantly slower than those consistent with the model's pre-existing knowledge.
2. However, as the new knowledge examples were eventually learned, they linearly increased the model's tendency to hallucinate - generating factually incorrect responses.

These results suggest that the bulk of a language model's factual knowledge should come from its initial pre-training, rather than relying on fine-tuning to inject significant new information. The researchers argue this is because fine-tuning primarily teaches the model to use its existing knowledge more efficiently, rather than fundamentally expanding its knowledge base.

## Critical Analysis

The researchers provide a nuanced and well-designed study that sheds light on an important issue in large language model development. By carefully controlling the exposure to new information during fine-tuning, they were able to isolate and quantify the effects on the model's behavior.

One key strength of the study is the use of the FLAME framework to measure hallucination tendencies. This provides a robust and principled way to assess the model's factual grounding, beyond just looking at raw task performance.

However, the study is limited to the closed-book question answering task. It would be interesting to see if similar dynamics play out in other fine-tuning scenarios, such as [open-ended text generation](https://aimodels.fyi/papers/arxiv/dont-believe-everything-you-read-enhancing-summarization) or multi-task learning. The researchers acknowledge this as an area for future work.

Additionally, the study focuses on the high-level behaviors of the models, but does not delve into the underlying mechanisms that lead to hallucination. Further research could explore the model internals and architectural choices that contribute to this phenomenon.

Overall, this paper provides valuable insights into the challenges of expanding the knowledge of large language models through fine-tuning. The findings underscore the importance of robust pre-training as the foundation for factual knowledge, rather than relying on fine-tuning alone to build reliable and trustworthy AI systems.

## Conclusion

This study highlights the risks of exposing large language models to significant new factual information during fine-tuning. While fine-tuning can help models use their existing knowledge more efficiently, the researchers found that it struggles to truly expand the model's knowledge base.

Crucially, as new information is gradually learned through fine-tuning, it can actually increase the model's tendency to hallucinate - generating factually incorrect responses that are not grounded in its pre-existing knowledge. This suggests that the bulk of a language model's factual knowledge should come from its initial pre-training, rather than fine-tuning.

The findings of this paper have important implications for the development of reliable and trustworthy AI systems. They underscore the need for robust pre-training strategies and careful fine-tuning procedures to ensure language models can utilize their knowledge accurately and avoid hallucinating. As the field of large language models continues to evolve, studies like this will be crucial for guiding best practices and addressing the fundamental challenges in this area.

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