Back to the Future: The Role of Past and Future Context Predictability in Incremental Language Production

Abstract

Contextual predictability shapes how we choose and encode words in production. The effects of a word’s predictability given preceding or past context are generally well-understood in both production and comprehension, but studies of naturalistic production have also revealed a poorly understood yet robust backward predictability effect of a word given only its future context, which may be linked to future planning. Across two studies of naturalistic speech, we revisit backward predictability using improved operationalizations, introducing Conditional Pointwise Mutual Information (conditional PMI), a conceptually motivated information-theoretic measure that quantifies the information shared between a word and future sequence under the constraints imposed by the past context. Study 1 shows that this measure reproduces predictability effects of future context on phonetic reduction while remaining non-redundant with backward predictability. Study 2 moves from reduction to word choice, examining substitution errors within a novel generative framework that models lexical contextual influences to predict the identity of the word that surfaces as an error. Within this framework, we find that past-conditioned predictability increases likelihood of erroneous selection, whereas future-conditioned predictability reduces it. In predicting error identity, conditional PMI emerges as the strongest contextual predictor, subsuming backward predictability. Together, these findings illuminate how past and future context shape word choice and encoding, linking contextual predictability to mechanisms of incremental planning in sentence production.