  While many contemporary large language models (LLMs) can process lengthy
input, they still struggle to fully utilize information within the long
context, known as the lost-in-the-middle challenge. We hypothesize that it
stems from insufficient explicit supervision during the long-context training,
which fails to emphasize that any position in a long context can hold crucial
information. Based on this intuition, our study presents information-intensive
(IN2) training, a purely data-driven solution to overcome lost-in-the-middle.
Specifically, IN2 training leverages a synthesized long-context question-answer
dataset, where the answer requires (1) fine-grained information awareness on a
short segment (~128 tokens) within a synthesized long context (4K-32K tokens),
and (2) the integration and reasoning of information from two or more short
segments. Through applying this information-intensive training on Mistral-7B,
we present FILM-7B (FILl-in-the-Middle). To thoroughly assess the ability of
FILM-7B for utilizing long contexts, we design three probing tasks that
encompass various context styles (document, code, and structured-data context)
and information retrieval patterns (forward, backward, and bi-directional
retrieval). The probing results demonstrate that FILM-7B can robustly retrieve
information from different positions in its 32K context window. Beyond these
probing tasks, FILM-7B significantly improves the performance on real-world
long-context tasks (e.g., 23.5->26.9 F1 score on NarrativeQA), while
maintaining a comparable performance on short-context tasks (e.g., 59.3->59.2
accuracy on MMLU). Github Link: https://github.com/microsoft/FILM.
