Abstract
Advances in the non-invasive neuroimaging of the human brain help us explore the neural basis of individual behavioural differences. They make it possible to explore how such differences affect the ease of acquiring new skills and how skill acquisition in turn modifies the neural substrate. Such explorations carry important practical implications because they suggest that training may be more effective if such differences are taken into account. They carry important theoretical implications because they help us understand how different neural regions work together to achieve skilled performance.
Research reported in this timely Special Issue illustrates these developments in the context of bilingualism. For example, as Golestani et al. report, neuroanatomical variation affects the ease with which individuals may master non-native phonological distinctions and Ingvalson et al. report how training adapted to prior ability can optimise the learning of a novel phonological contrast. At a different level in the processing hierarchy, when native English speakers learn a tonal language, such as Chinese, their brains show structural changes in regions that link the pitch of words to their meaning. Structural changes (in grey or white matter) are consequent on functional demand.
Learning a new language challenges the substrate in a specific way: competing representations must be learned for already acquired concepts and their use imposes an additional demand on circuits involved in language control. Subcortical, as well frontal, cortical areas are implicated in learning a new language and in language use. Wattendorf et al. explore the conjecture that early bilingual experience may affect the functioning of this frontal-subcortical circuit and identify an interesting contrast between early and late trilingual speakers. Further explorations are important, because exercise of this circuit is held to underlie the reputed cognitive advantages of bilingual speakers in the control of interference and task switching. Neurocomputational accounts are needed and Stocco et al. advance one. They suppose that subcortical structures control the flow of information within the cortical network, but predict that bilinguals will show a disadvantage in some tasks because of increased cortical (top-down) control over behaviour.
The precise extent and nature of the changes induced through bilingual or multilingual experience is not known. The papers in this Special Issue provide an exciting view of the territory and, of equal importance, identify the terra incognita to challenge us all.