Leveraging Human Demonstrations to Mitigate Reward Over-Optimization in Large Language Models
Core Concepts
Reward Calibration from Demonstration (RCfD) leverages human demonstrations and a reward model to recalibrate the reward objective, avoiding incentivizing the language model to exploit the reward model and promoting more natural and diverse language generation.
Abstract
The paper introduces Reward Calibration from Demonstration (RCfD), a novel reinforcement learning (RL) objective that leverages human demonstrations and a reward model to mitigate reward over-optimization (ROO) in large language models (LLMs).
Key highlights:
- RL has been essential for finetuning LLMs, but can lead to ROO, where the LLM exploits the reward model to generate unnatural language.
- Existing approaches address ROO by adding KL regularization, which requires computationally expensive hyperparameter tuning.
- RCfD shifts the objective from directly maximizing the reward function to minimizing the distance between the LLM's and the demonstrations' rewards. This avoids incentivizing the LLM to exploit the reward model.
- RCfD is evaluated on three language tasks, achieving comparable performance to carefully tuned baselines while mitigating ROO.
- In a multi-reward setting, RCfD automatically recalibrates the rewards based on demonstrations, outperforming methods that require extensive hyperparameter tuning.
- RCfD offers a promising approach for tackling complex language RL tasks where human demonstrations are available, providing inherent predictability and requiring minimal tuning.
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Countering Reward Over-optimization in LLM with Demonstration-Guided Reinforcement Learning
Stats
The average log-likelihood of sentences generated by the initial LLM diminishes with longer sentences, indicating exposure bias. This is not observed in the demonstrations.
Optimizing the reward function directly leads to reward over-optimization, with the LLM generating unnatural and repetitive sentences.
RCfD successfully calibrates the sequence-level log-likelihood of generations with those of demonstrations, maintaining good language quality.
Quotes
"Reward over-optimization (ROO) may englobe various language optimization artifacts such as reward hacking, language drift or overfitting."
"RCfD utilizes human demonstrations and a reward model to guide the LLM towards generating outputs that achieve similar rewards to those of the demonstrations."
"By targeting a point on the Pareto frontier through demonstrations, RCfD controls the optimization process."
Deeper Inquiries
How can RCfD be extended to handle settings where demonstrations are not available for all prompts
RCfD can be extended to handle settings where demonstrations are not available for all prompts by implementing a method to predict the reward of the demonstration. This can be achieved by training a regressor or a separate model to estimate the reward that would be assigned to a completion based on the prompt alone. By using this predicted reward as a proxy for the demonstration reward, RCfD can still align the model's behavior with the desired outcomes even in the absence of explicit demonstrations. This approach allows RCfD to generalize to prompts without specific demonstrations and adapt to a wider range of scenarios where demonstration data may be limited or unavailable.
What are the potential biases introduced by the demonstration data, and how can they be mitigated in the RCfD framework
Potential biases introduced by the demonstration data in the RCfD framework include biases inherent in the dataset used to collect the demonstrations, biases in the reward model used to evaluate the demonstrations, and biases in the language model itself. To mitigate these biases, several strategies can be employed:
Diverse Data Collection: Ensure that the demonstration dataset is diverse and representative of the target task to reduce bias.
Fair Reward Model: Train the reward model on unbiased data and regularly update it to prevent bias from affecting the evaluation of demonstrations.
Bias Correction: Implement bias correction techniques such as reweighting or resampling to account for any biases present in the demonstration data.
Regular Monitoring: Continuously monitor the performance of the RCfD framework and the model's behavior to detect and address any biases that may arise during training.
By incorporating these strategies, RCfD can mitigate biases in the demonstration data and promote fair and unbiased learning outcomes.
How can RCfD be adapted to handle dynamic or evolving reward functions in real-world applications
To handle dynamic or evolving reward functions in real-world applications, RCfD can be adapted in the following ways:
Online Learning: Implement an online learning approach where the reward function is continuously updated based on new data and feedback. RCfD can adapt to these changes by recalibrating the reward objective using the updated reward model.
Adaptive Calibration: Develop mechanisms within RCfD to dynamically adjust the calibration of the reward function based on changes in the reward model or task requirements. This adaptive calibration ensures that the model remains aligned with the evolving reward function.
Feedback Loop: Establish a feedback loop between the reward model, demonstrations, and the language model to incorporate real-time feedback and updates into the training process. This feedback loop allows RCfD to quickly adapt to changes in the reward function and maintain optimal performance in dynamic environments.
By incorporating these adaptive strategies, RCfD can effectively handle dynamic or evolving reward functions and ensure robust performance in real-world applications.