Surprise! Uniform Information Density Isn't the Whole Story: Predicting Surprisal Contours in Long-form Discourse

TL;DR

This paper challenges the Uniform Information Density hypothesis by proposing that discourse structure influences information rate, and demonstrates that hierarchical discourse predictors better predict surprisal contours in natural language.

Contribution

It introduces the Structured Context Hypothesis, linking discourse hierarchy to information rate modulation, and empirically shows hierarchical predictors outperform uniform models.

Findings

Hierarchical predictors significantly predict surprisal contours.

Deeply nested discourse structures are more predictive.

UID alone does not fully explain information rate fluctuations.

Abstract

The Uniform Information Density (UID) hypothesis posits that speakers tend to distribute information evenly across linguistic units to achieve efficient communication. Of course, information rate in texts and discourses is not perfectly uniform. While these fluctuations can be viewed as theoretically uninteresting noise on top of a uniform target, another explanation is that UID is not the only functional pressure regulating information content in a language. Speakers may also seek to maintain interest, adhere to writing conventions, and build compelling arguments. In this paper, we propose one such functional pressure; namely that speakers modulate information rate based on location within a hierarchically-structured model of discourse. We term this the Structured Context Hypothesis and test it by predicting the surprisal contours of naturally occurring discourses extracted from large language models using predictors derived from discourse structure. We find that hierarchical predictors are significant predictors of a discourse's information contour and that deeply nested hierarchical predictors are more predictive than shallow ones. This work takes an initial step beyond UID to propose testable hypotheses for why the information rate fluctuates in predictable ways