Addressing themes from the Douglas Fir Group's (2016) transdisciplinary framework, this paper bridges boundaries between cognitive and social disciplines by showing how social contextual factors can affect the psycholinguistic development of complexity, accuracy, and fluency (CAF) in learner language. Sociolinguistic and sociocultural frameworks are blended with use of a multidimensional psycholinguistic frame, CAF, to analyze speech samples produced by 10 adult learners of English across different developmental levels as they all produced narratives containing constructed dialogue. Learners enacted imagined 'voices' that were significantly more accurate and fluent compared to their narrative baseline voices. Our findings suggest that emerging L2 proficiency consists of many distinct voices that can significantly differ in accuracy of grammatical forms and fluency; related studies show they also differ in suprasegmentals, nonverbals, discourse style, and expressed social stance. Learners' ability to produce such voices in constructed dialogue supports a view of their proficiency as heteroglossic, complex, dynamic, and holistic, and of language play as facilitative of SLA. Theoretical and practical implications for L2 learning, instruction, and assessment are considered.