Understanding language processing in variable populations on their own terms: Towards a functionalist psycholinguistics of individual differences, development, and disorders.

Classic psycholinguistics seeks universal language mechanisms for all people, emphasing the "modal" listener: hearing, neurotypical, monolingual, young adults. Applied psycholinguistics then characterizes differences in terms of their deviation from modal. This mirrors naturalist philosophies of health which presume a normal function, with illness as a deviation. In contrast, normative positions argue that illness is partially culturally derived. It occurs when a person cannot meet socio-culturally defined goals, separating differences in biology (disease) from socio-cultural function (illness). We synthesize this with mechanistic functionalist views in which language emerges from diverse lower level mechanisms with no one-to-one mapping to function (termed the functional mechanistic normative approach). This challenges primarily psychometric approaches-which are culturally defined-suggesting a process-based approach may yield more insight. We illustrate this with work on word recognition across multiple domains: cochlear implant users, children, language disorders, L2 learners, and aging. This work investigates each group's solutions to the problem of word recognition as interesting in its own right. Variation in process is value-neutral, and psychometric measures complement this, reflecting fit with cultural expectations (disease vs. illness). By examining variation in processing across people with a variety of skills and goals, we arrive at deeper insight into fundamental principles.