Additionally, the effects of changes in plasticity changes also extend beyond linguistic abilities (see Hernandez & Li, 2007 for a review of the extant literature).Īn extension of sensorimotor model, the emergentist theory ( MacWhinney, 2004), describes the process by which a competitive interplay takes place between an individual’s L1 and L2. This loss of plasticity results in the employment of different neurocognitive mechanisms for learning language, with greater reliance on executive and metalinguistic mechanisms for later language learning. Also contributing to the effects of sensorimotor learning within the first several years after birth is the rapid development and eventual loss of plasticity of frontal - basal ganglia circuits. More specifically, sensorimotor theorists postulate that linguistic information that is learned earlier in life is dependent upon sensorimotor analysis and the recruitment of phono-articulatory brain regions ( Hernandez & Li, 2007), while later learned information preferentially recruits areas of the brain involved in semantic and executive cognitive processing ( Hernandez, Hoffman & Kotz, 2007). Proponents of the S/E model posit that information acquired in the first few years of life is obtained through both sensory and motor means. These three models emphasize different brain activity patterns that help to distinguish early from late language learning.
Finally, a third is the declarative/procedural hypothesis, initially a model of memory ( Cohen & Squire, 1980), that was subsequently adapted to describe the way in which bilingualism modulates neural activity ( Ullman, 2001a, 2001b). A second model that has been proposed is the cognitive control model put forth by Abutalebi, Green, and colleagues ( Abutalebi, 2008, Abutalebi & Green, 2007 2008). The S/E model is a neo-Piagetian framework that incorporates theoretical and neurocognitive mechanisms in the development of language learning. One understudied framework of L2 AoA is the sensorimotor/emergentist (S/E) model ( Hernandez, Li & MacWhinney, 2005 MacWhinney, 2004). Several models have been proposed as a framework for understanding the ways that L2 AoA modulates brain activity in the L2. In order to address these lingering questions about the way in which a bilingual’s L2 (AoA) modulates brain activity, we compared early and late Spanish-English bilinguals, who were matched on various L2 proficiency measures, on a past-tense generation task. A second issue facing this literature base is that many prior investigations of bilingualism have conflated L2 age of acquisition (AoA) and proficiency, factors that are known to be dissociable. Several models have been developed in an attempt to explain the functional neural differences that have been observed in bilinguals, but no consensus has been reached. First, there is an ongoing debate about the exact nature of the underlying mechanisms that are responsible for such changes. However, there are still several issues facing this relatively nascent area of study.
It is becoming clear that the age of second language (L2) learning alters neural activity during linguistic processing. These data are consistent with the S/E model of bilingual language learning, and serve as an extension of cognitive control theories. In contrast, later L2 learners recruit executive control mechanisms to generate the past tense. The data support the notion that early L2 learners devote neural resources to motor control during lexical retrieval. In contrast, later learners, to a greater degree, engaged regions involved in executive cognitive control and lexical access. Early bilinguals preferentially recruited left hemisphere sensorimotor regions involved in motoric control and articulation. To investigate the S/E model using fMRI, neural correlates of L2 age of acquisition were examined by employing a past-tense generation task on 22 L2 proficient bilinguals. At its most basic sense, the sensorimotor/emergentist (S/E) model suggests that early second language (L2) learning is preferentially reliant upon sensory and motor processes, while later L2 learning is accomplished by greater reliance on executive abilities.
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