Evidence for a critical period in second language acquisition is used as one of the major supports for the theory of Universal Grammar. However, emergentist theory offers a alternative to critical period theory by emphasizing the competitive interplay between multiple languages during childhood and by focusing on the dual action of competition and entrenchment. The emergentist account avoids the need to invoke a critical period by emphasizing the motto formulated by Elizabeth Bates that 'modules are made, not born'.

A detailed account of these relations can be constructed within the framework of the Unified Competition Model. As in the classic (1989) version of the Competition Model, competition is at the core of a set of non-modular interacting forces. However, in the Unified Model the various inputs to competition are described in terms of these six additional subcomponents: arenas, cues, fluency, storage, codes, and resonance. Learning is viewed as a resonant process that relies on storage, chunking, and support to acquire new mappings.

This talk examines a variety of data from transcript analyses, role assignment experiments in 15 languages, ERP studies of Spanish L2 learners, and new online studies of in vivo second language learning in French and Chinese L2. These data underscore the need for an increasingly precise combined psychological and linguistic analysis of the various forces leading to levels of generalization in L1 learning, transfer effects in L2 learning, and recovery from various forms of interlanguage competition.