We like to talk to one another and are skilled at doing so. Conversational turns between proficient speakers, for instance, couple closely in time within the multimodal context of everyday conversation. Such synchrony strongly suggests that proficient speakers are able to manage the twin demands of understanding the current utterance and planning the next to allow fluent interaction. What of the late learner of a second language (L2)? This chapter discusses the interactional challenge they face. It focuses on the processes of language control required for learning and using an L2. Bottom-up processes of language control, for example, allow learners to produce new constructions and offer plans for speech production. Top-down processes of language control, by contrast, bind new constructions and vocabulary into the language network and are required to control interference from the speaker's first language. Age affects the regions of the brain involved in representing the vocabulary and constructions of an L2 and the regions involved in controlling their use. Individual differences in these regions will therefore influence trajectories to interactional proficiency. But their capacity is open to change. Exercise, among other factors, can enhance the capacity of these regions. Thus, fitness may affect the trajectory to interactional proficiency. Even more optimistically, learning and using an L2 may itself lead to positive adaptive changes. Tailoring learning to identified individual differences offers the best prospect for the enjoyable learning of an L2 in the third age.

Introduction

Language use is a form of communicative action with conversation as the primary and multimodal site for such action. A noticeable feature of conversations between proficient speakers of a language is that the interval between successive turns can be quite short with a modal delay between them of 200 ms – a figure that appears to be relatively constant across different languages (Levinson, 2016). One implication is that listeners may understand utterances and plan their responses during the turn of the current speaker.