Word learning in early, middle and late adulthood

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In the field of cognitive aging, it is well established that some cognitive functions remain relatively stable over the lifespan (e.g., long-term representations, automatic processes, implicit learning) while others progressively decline (e.g., executive control, memory maintenance/retrieval, and speed). Language use shows a mixed aging trajectory as well: Phonological, lexical, semantic and syntactic knowledge is relatively preserved, whereas the ease of access to that knowledge and control over its activation tend to degrade with age. How this dissociation affects the dynamics and efficiency of word learning over the lifespan is unclear.The purpose of this research programme is to investigate the age-related stability vs. decline of several key word-learning mechanisms that have been documented in the word-acquisition literature in infancy and childhood, and to establish the extent to which compensatory trade-offs (e.g., reliance on stored knowledge) can stave off the decline of learning mechanisms that involve a greater degree of executive control and explicit computation. A better understanding of how the mechanisms underpinning word learning change over the lifespan has important consequences for older adults' quality of life. Indeed, owing to today's increased life expectancy and the expectation that many of those additional years will be spent in relatively good health, opportunities for older adults to acquire new knowledge, new skills, or learn new languages have flourished.The target groups will be young adults (< 25y), middle-age adults (40y to 50y), and older adults (> 65y). The middle-age group is critical because it will enable us not only to draw a more accurate trajectory of word learning mechanisms, but also to establish whether compensation based on context and long-term representations begins to operate earlier than traditionally assumed. The learning mechanisms under study will be: (1) Adjacent dependencies: This represents a form of domain-general learning based on implicitly computing statistical regularities in the speech input. We expect this type of learning to be comparatively robust over time. (2) Non-adjacent dependencies: This will instantiate a form of word learning that relies on both association and abstraction, a more complex form of learning that could potentially engage processing resources that are in short supply in older adults. (3) Abstract patterns: These experiments will instantiate abstract pattern learning and generalisation to entirely new materials, unlike adjacent dependencies which require no generalisation to new materials and non-adjacent dependencies which require only partial generalisation to new materials. (4) Rule-based abstraction (first-order logic): This will be similar to the previous set of experiments, except that the abstract patterns defining the acceptable words of the language will be regulated by a grammar containing logical operators (equivalent to if, then, else). This is the most language-specific form of learning of the four sets. Its resilience to aging is largely unknown.The above learning mechanisms will be compared to their matched explicit-learning counterpart. As a whole, this study will highlight the dynamics and plasticity of language learning over the lifespan and, in doing so, will contribute to our theoretical understanding of language processing, language learning, and cognitive aging.