  Biomedical question-answering (QA) has gained increased attention for its
capability to provide users with high-quality information from a vast
scientific literature. Although an increasing number of biomedical QA datasets
has been recently made available, those resources are still rather limited and
expensive to produce. Transfer learning via pre-trained language models (LMs)
has been shown as a promising approach to leverage existing general-purpose
knowledge. However, finetuning these large models can be costly and time
consuming, often yielding limited benefits when adapting to specific themes of
specialised domains, such as the COVID-19 literature. To bootstrap further
their domain adaptation, we propose a simple yet unexplored approach, which we
call biomedical entity-aware masking (BEM). We encourage masked language models
to learn entity-centric knowledge based on the pivotal entities characterizing
the domain at hand, and employ those entities to drive the LM fine-tuning. The
resulting strategy is a downstream process applicable to a wide variety of
masked LMs, not requiring additional memory or components in the neural
architectures. Experimental results show performance on par with
state-of-the-art models on several biomedical QA datasets.
