Bilingualism and Cognitive Reserve: A Critical Overview and a Plea for Methodological Innovations

Abstract

The decline of cognitive skills throughout healthy or pathological aging can be slowed down by experiences which foster cognitive reserve (CR). Recently, some studies on Alzheimer's disease have suggested that CR may be enhanced by life-long bilingualism. However, the evidence is inconsistent and largely based on retrospective approaches featuring several methodological weaknesses. Some studies demonstrated at least 4 years of delay in dementia symptoms, while others did not find such an effect. Moreover, various methodological aspects vary from study to study. The present paper addresses contradictory findings, identifies possible lurking variables, and outlines methodological alternatives thereof. First, we characterize possible confounding factors that may have influenced extant results. Our focus is on the criteria to establish bilingualism, differences in sample design, the instruments used to examine cognitive skills, and the role of variables known to modulate life-long cognition. Second, we propose that these limitations could be largely circumvented through experimental approaches. Proficiency in the non-native language can be successfully assessed by combining subjective and objective measures; confounding variables which have been distinctively associated with certain bilingual groups (e.g., alcoholism, sleep disorders) can be targeted through relevant instruments; and cognitive status might be better tapped via robust cognitive screenings and executive batteries. Moreover, future research should incorporate tasks yielding predictable patterns of contrastive performance between bilinguals and monolinguals. Crucially, these include instruments which reveal bilingual disadvantages in vocabulary, null effects in working memory, and advantages in inhibitory control and other executive functions. Finally, paradigms tapping proactive interference (which assess the disruptive effect of long-term memory on newly learned information) could also offer useful data, since this phenomenon seems to be better managed by bilinguals and it becomes conspicuous in early stages of dementia. Such considerations may shed light not just on the relationship between bilingualism and CR, but also on more general mechanisms of cognitive compensation.

A core avenue for transcultural research on dementia: on the cross‐linguistic generalization of language‐related effects in Alzheimer's disease and Parkinson's disease

“…So far, research on CR in bilinguals with AD has largely neglected this factor, as most samples included participants who spoke widely diverse language pairs. In the studies by Bialystok and colleagues, for instance, bilingual participants spoke any of several native languages (e.g., German, Yiddish, Polish, Farsi, and French)-for a review, see Calvo et al, (2015). In particular, some of the studies reporting null results have assessed only distant language pairs (Crane et al, 2010;Kousaie and Phillips, 2012;Zahodne et al, 2014).…”

“…On the other hand, insights from the embodied cognition framework point to deficits in syntax and action-verb processing as early (and even preclinical) markers of PD (García and Ibáñez, 2014;Garcia et al, 2016;. Both lines of research have attracted increasing attention in recent years, leading to novel theoretical Calvo et al, 2015;Cardona et al, 2013;Bak, 2013) and clinical (Bialystok et al, 2007;Alladi et al, 2015;García & Ibáñez, 2014;Melloni et al, 2015) formulations of potential relevance for public health (Bialystok et al, 2016;García et al, 2017;Bocanegra et al, 2017).…”

The Protective Effect of Cantonese/Mandarin Bilingualism on the Onset of Alzheimer Disease

“…However, inconsistent results have been reported in other studies [5-7], which demonstrated that the age of dementia diagnosis was not significantly different between bilinguals and monolinguals. The potential reasons for the contradictory findings suggested by Calvo et al [8] were methodological differences in the definition of bilingualism, the sample design, the definition of age of onset, and the consideration of other variables known to affect CR. Moreover, diverse language pairs used by the bilinguals in different studies may also contribute to the discrepancies.…”

Aphasia in Bilinguals

“…This perspective, however, remains controversial and sometimes no bilingual advantage on cognition is reported (e.g., Dick et al, 2019). Calvo, García, Manoiloff & Ibáñez (2016) in a review paper found that only that around 60-70% of published data have found a cognitive reserve effect of bilingualism on cognitive decline. Recently Lehtonen et al (2018) compared the bilinguals' and monolinguals' performance in six executive domains based on 152 studies on adults.…”