How the tracking of habitual rate influences speech perception

Abstract

Listeners are known to track statistical regularities in speech. Yet, which temporal cues are encoded is unclear. This study tested effects of talker-specific habitual speech rate and talker-independent average speech rate (heard over a longer period of time) on the perception of the temporal Dutch vowel contrast /ɑ/-/a:/. First, Experiment 1 replicated that slow local (surrounding) speech contexts induce fewer long /a:/ responses than faster contexts. Experiment 2 tested effects of long-term habitual speech rate. A high-rate group listened to ambiguous vowels embedded in "neutral" speech from Talker A, intermixed with fast speech from Talker B. A low-rate group listened to the same neutral speech from Talker A, and/but to Talker B speaking at a slow rate. Between-groups comparison of the neutral trials showed that the high-rate group demonstrated a lower proportion of /a:/ responses, indicating that Talker A's habitual speech rate sounded slower when B was faster. In Experiment 3, both talkers produced speech at both rates, removing the different habitual speech rates of Talkers A and B, while maintaining the average rates differing between groups. In Experiment 3, no global rate effect was observed. Taken together, the present experiments show that a talker's habitual rate is encoded relative to the habitual rate of another talker, carrying implications for episodic and constraint-based models of speech perception.