Detecting Edited Knowledge in Language Models

Knowledge editing techniques (KEs) can update language models' obsolete or inaccurate knowledge learned from pre-training. However, KE also faces potential malicious applications, e.g. inserting misinformation and toxic content. Moreover, in the context of responsible AI, it is instructive for end-users to know whether a generated output is driven by edited knowledge or first-hand knowledge from pre-training. To this end, we study detecting edited knowledge in language models by introducing a novel task: given an edited model and a specific piece of knowledge the model generates, our objective is to classify the knowledge as either "non-edited" (based on the pre-training), or ``edited'' (based on subsequent editing). We initiate the task with two state-of-the-art KEs, two language models, and two datasets. We further propose a simple classifier, RepReg, a logistic regression model that takes hidden state representations as input features. Our results reveal that RepReg establishes a strong baseline, achieving a peak accuracy of 99.81%, and 97.79% in out-of-domain settings. Second, RepReg achieves near-optimal performance with a limited training set (200 training samples), and it maintains its performance even in out-of-domain settings. Last, we find it more challenging to separate edited and non-edited knowledge when they contain the same subject or object.