Sound Change Proceeds Incrementally Within Adult Lifespans: Real-time Evidence From /s/-retraction in Australian English

Knowledge of the mechanisms of phonetically motivated sound changes is incomplete and based primarily on apparent—rather than real-time—evidence. How exactly does an innovative variant become the new norm within individual and population-level grammars? Here, eighteen L1 English speakers were recorded in 2014 and again in 2022. Acoustic analysis of sibilants in /str/ shows (i) coarticulatory /s/-retraction for all speakers in 2014 and (ii) a group-level increase in the degree of /s/-retraction in 2022. Perception data show that increased /s/-retraction was audible to listeners. Increased /s/-retraction also matched the outcome of simulated interaction between the speaker participants in an agent-based model. However, the effects of sound change are not predictable within idiolects: some speakers’ production targets shifted incrementally in the opposite direction of the group-level trend.