Produced as part of the SPAR program (fall 2023) under the mentorship of Nina Rimsky.

Introduction

Given recent advances in the AI field, it’s highly likely LLMs will be increasingly used to make decisions that have broad societal impact — such as resume screening, college admissions, criminal justice, etc. Therefore it will become imperative to ensure these models don’t perpetuate harmful societal biases.

One way we can evaluate whether a model is likely to exhibit biased behavior is via red-teaming. Red-teaming is the process of “attacking” or challenging a system from an adversarial lens with the ultimate goal of identifying vulnerabilities. The underlying premise is that if small perturbation in the model can result in undesired behaviors, then the model is not robust.

In this research project, I evaluate the robustness of Llama-2-7b-chat along different dimensions of societal bias by using activation steering. This can be viewed as a diagnostic test: if we can “easily” elicit biased responses, then this suggests the model is likely unfit to be used for sensitive applications. Furthermore, experimenting with activation steering enables us to investigate and better understand how the model internally represents different types of societal bias, which could help to design targeted interventions (e.g. fine-tuning signals of a certain type).

Methodology & data

Activation steering (also known as representation engineering) is a method used to steer an LLMs response towards or away from a concept of interest by perturbing the model’s activations during the forward pass. I perform this perturbation by adding a steering vector to the residual stream at some layer (at every token position after an initial prompt). The steering vector is computed by taking the average difference in residual stream activations between pairs of biased (stereotype) and unbiased (anti-stereotype) prompts at that layer. By taking the difference between paired prompts, we can effectively remove contextual noise and only retain the “bias” direction. This approach to activation steering is known as Contrastive Activation Addition [1].

For the data used to generate the steering vectors, I used the StereoSet Dataset, which is a large-scale natural English dataset intended to measure stereotypical biases across various domains. In addition, I custom wrote a set of gen...

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