An evaluation measure (EM) guides a learner's choice of grammar when more than one is compatible with available input. EM must be universal, so children receiving comparable input acquire comparable grammars. It must favor the choices children actually make. The theoretical shift from rule-based grammars to principles-and-parameter-based grammars…

Recent research has shown that speakers are sensitive to non-contrastive phonetic detail present in nonnative speech (e.g. Escudero et al. 2012; Wilson et al. 2014). Difficulties in interpreting and implementing unfamiliar phonetic variation can lead nonnative speakers to modify second language forms by vowel epenthesis and other changes. These…