Abstract
Bilingualism has been identified as a potential cognitive factor linked to delayed onset of dementia as well as boosting executive functions in healthy individuals. However, more recently, this claim has been called into question following several failed replications. It remains unclear whether these contradictory findings reflect how bilingualism is defined between studies, or methodological limitations when measuring the bilingual effect. One key issue is that despite the claims that bilingualism yields general protection to cognitive processes (i.e., the cognitive reserve hypothesis), studies reporting putative bilingual differences are often focused on domain specific experimental paradigms. This study chose a broader approach, by considering the consequences of bilingualism on a wide range of cognitive functions within individuals. We utilised 19 measures of different cognitive functions commonly associated with bilingual effects, to form a “cognitive profile” for 215 non-clinical participants. We recruited Welsh speakers, who as a group of bilinguals were highly homogeneous, as means of isolating the bilingualism criterion. We sought to determine if such analyses would independently classify bilingual/monolingual participant groups based on emergent patterns driven by collected cognitive profiles, such that population differences would emerge. Multiple predictive models were trained to independently recognise the cognitive profiles of bilinguals, older adults (60-90 years of age) and higher education attainment. Despite managing to successfully classify cognitive profiles based on age and education, the model failed to differentiate between bilingual and monolingual cognitive ability at a rate greater than that of chance. Repeated modelling using alternative definitions of bilingualism, and just the older adults, yielded similar results. In all cases then, using our “bottom–up” analytical approach, there was no evidence that bilingualism as a variable indicated differential cognitive performance – as a consequence, we conclude that bilinguals are not cognitively different from their monolingual counterparts, even in older demographics. We suggest that studies that have reported a bilingual advantage (typically recruiting immigrant populations) could well have confounded other key variables that may be driving reported advantages. We recommend that future research refine the machine learning methods used in this study to further investigate the complex relationship between bilingualism and cognition.
Highlights
Dementia is characterised by a continuous and largely irreversible decline in cognitive processing
Patients are diagnosed through showing deficits in cognitive domains such as memory, attention, problem solving, recognition, and language processing (World Health Organization, 2012)
While controversial bilingualism has been argued to be one such activity that contributes to increased cognitive reserve as well as enhancing cognition among non-clinical individuals (Grant et al, 2014)
Summary
Dementia is characterised by a continuous and largely irreversible decline in cognitive processing. While controversial (see Zahodne et al, 2014) bilingualism has been argued to be one such activity that contributes to increased cognitive reserve as well as enhancing cognition among non-clinical individuals (Grant et al, 2014). This bilingual advantage has been demonstrated over multiple cognitive domains and across several age groups with the greatest differences among children and older adults (Bialystok, 2017). Proponents of the bilingual effects on cognition argue that the failed replications to not take into account the complex nature of bilingualism and use narrow domain specific tasks that are not sensitive enough, on their own, to detect the more salient domain general effect of bilingualism on cognition (Bialystok, 2016)
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