Unpacking the Influence of Retrieval Augmented Generation (RAG) on Language Models: A Mechanistic Analysis

  • Researchers explore how Retrieval Augmented Generation (RAG) affects language models (LMs), focusing on reasoning and factual accuracy.
  • Study examines if LMs rely more on RAG-provided external context than their internal parametric memory for factual queries.
  • Techniques like Causal Mediation Analysis and Attention Contributions are used to analyze LLaMa-2 and Phi-2 models.
  • Findings indicate LMs show reduced reliance on internal memory in the presence of RAG context.
  • Attention Contributions reveal models prioritize external context over internal knowledge for factual predictions.

Main AI News:

Researchers from Microsoft, the University of Massachusetts Amherst, and the University of Maryland, College Park, delve into the impact of Retrieval Augmented Generation (RAG) on language models (LMs), specifically examining how it influences reasoning and factual accuracy. Their study investigates whether LMs increasingly rely on external RAG context rather than their parametric memory when generating responses to factual queries.

Traditionally, efforts to enhance LM accuracy involve refining internal model parameters or integrating external retrieval systems to bolster contextual understanding during inference. Techniques such as ROME and MEMIT focus on adjusting internal parameters to update the model’s knowledge base. Yet, the balance between utilizing internal (parametric) knowledge and external (non-parametric) RAG context remains understudied within RAG implementations.

To address this gap, the researchers propose a mechanistic analysis of RAG pipelines to ascertain the extent to which LMs depend on external context vis-à-vis their internal memory when answering factual queries. Their investigation employs advanced LMs—LLaMa-2 and Phi-2—and applies methodologies like Causal Mediation Analysis, Attention Contributions, and Attention Knockouts.

Key techniques utilized by the researchers include:

  1. Causal tracing: Identifying critical hidden states in the model pivotal for factual predictions. Through comparative analyses between corrupted, clean, and restoration runs, the study measures the Indirect Effect (IE) to gauge the significance of specific hidden states.
  2. Attention contributions: Evaluating attention weights between the subject token and the output’s last token. This analysis determines the extent to which each token receives attention, elucidating whether the model predominantly relies on RAG-provided external context or internal knowledge.
  3. Attention knockouts: Manipulating attention weights to block information flow between tokens, thereby observing the impact on prediction quality. This technique identifies essential connections crucial for accurate predictions.

The findings highlight that under RAG context, both LLaMa-2 and Phi-2 models exhibit reduced dependence on internal parametric memory. Specifically, subject token Indirect Effects diminish significantly with RAG context, indicating heightened reliance on external contextual cues. Moreover, the last token residual stream derives enriched information primarily from attribute tokens in the context rather than subject tokens in the query. Attention Contributions and Knockouts further underscore that models prioritize external context over internal memory for factual predictions, although the precise mechanisms driving this preference remain complex and warrant further investigation.


Understanding how Retrieval Augmented Generation affects language models’ reliance on external context versus internal memory is pivotal for businesses leveraging AI-driven insights. As LMs increasingly prioritize external context for factual accuracy, organizations should consider integrating robust external data sources to enhance AI performance in decision-making processes and information retrieval tasks. This strategic approach ensures alignment with evolving AI capabilities, optimizing operational efficiency and maintaining competitive advantage in dynamic market landscapes.