Methodological Issues in Research on Bilingualism, Cognitive Aging, and Cognitive Reserve

Laura Zahodne and Jennifer Manly

Studies of the relationship between bilingualism and dementia have yielded discrepant results.

This talk will explore four methodological issues that may help to explain these discrepancies,

clarify our understanding of the relationship between bilingualism and cognitive function in

older adults, and guide future research studies of bilingualism and cognitive reserve. First,

designs to distinguish causation from association in studies of bilingualism and dementia risk

will be discussed. Second, the critical step of distinguishing cognitive level from cognitive

change, and interpreting cross-sectional versus longitudinal or incidence studies, will be

discussed. Many variables, such as general intellectual ability, socioeconomic status and life

experiences, are difficult to disentangle from bilingualism and could also influence cognitive

aging trajectories and risk for dementia. These confounds are more problematic in studies

based in memory disorders clinics than in community-based studies of older adults. Therefore,

the third methodological issue discussed will be how results change when we are better able to

isolate and quantify the independent effect of bilingualism on executive function, cognitive

decline or dementia incidence. Historical changes in immigration policies and conditions in the

native country may be powerful tools to understand the conditions and experiences that travel

along with bilingualism and how they relate to cognitive aging. Fourth, the potential

advantages of assessing bilingualism skills on a continuum for studies of cognitive reserve and

cognitive aging trajectories will be discussed.