Scaling Parameter Effects in Contrastive Pre-training and Alignment Fine-tuning for Zero-Shot Dense Encoder Retrieval

Abstract

Abstract: Dense retrievers utilize pre-trained backbone language models (e.g., BERT, LLaMA) that are fine-tuned via contrastive learning to perform the task of encoding text into sense representations that can be then compared via a shallow similarity operation, e.g. inner product. Recent research has questioned the role of fine-tuning vs. that of pre-training within dense retrievers, specifically arguing that retrieval knowledge is primarily gained during pre-training, meaning knowledge not acquired during pre-training cannot be sub-sequentially acquired via fine-tuning. We revisit this idea here as th

Research Question

What is the comparative impact of scaling model parameters during contrastive pre-training versus alignment fine-tuning on the zero-shot retrieval performance of dense encoders across heterogeneous domains like PubMedQA and ScienceQA?

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