The Divergent Lexicon: Lexical Overlap Decreases With Age in a Large Corpus of Conversational Speech

Changes in language processing and production accompanying aging have most commonly been interpreted as evidence for age-related cognitive decline. A recent proposal (Ramscar et al., 2014) challenges that interpretation, asserting instead that such changes emerge as a consequence of—and in order to support—processes of lifelong learning like continued vocabulary growth. Under this account, the mechanisms of language processing and production do not deteriorate with age, but rather the computational complexity of the underlying information processing task increases as more data is observed over the lifespan. The current study examines whether spoken language displays properties consistent with the notion of lifelong learning by examining the relationship between age, within-speaker lexical diversity, and between-speaker lexical overlap in a conversational speech corpus, Switchboard I. We find older speakers exhibit more diverse lexicons, and that they share fewer words with interlocutors than younger speakers.