Jones Samuel Kyle, Davies-Thompson Jodie, Tree Jeremy
Department of Psychology, Swansea University, Swansea, United Kingdom.
Front Hum Neurosci. 2021 Mar 22;15:621772. doi: 10.3389/fnhum.2021.621772. eCollection 2021.
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.
双语能力已被视为一种潜在的认知因素，与痴呆症发病延迟有关，同时也能增强健康个体的执行功能。然而，最近，在几次重复实验失败后，这一说法受到了质疑。目前尚不清楚这些相互矛盾的研究结果是反映了不同研究中对双语能力的定义方式，还是测量双语效果时的方法局限性。一个关键问题是，尽管有观点认为双语能力能对认知过程产生普遍保护作用（即认知储备假说），但报告双语差异的研究往往集中在特定领域的实验范式上。本研究采用了更广泛的方法，考虑双语能力对个体内多种认知功能的影响。我们使用了19种通常与双语效果相关的不同认知功能测量方法，为215名非临床参与者形成了一个“认知概况”。我们招募了说威尔士语的人，他们作为双语者群体具有高度同质性，以此作为隔离双语标准的方式。我们试图确定这样的分析是否会根据收集到的认知概况所驱动的新兴模式，独立地对双语/单语参与者群体进行分类，从而显现出群体差异。训练了多个预测模型，以独立识别双语者、老年人（60 - 90岁）和高学历者的认知概况。尽管成功地根据年龄和教育程度对认知概况进行了分类，但该模型区分双语和单语认知能力的成功率并不高于随机概率。使用双语能力的替代定义并仅对老年人进行重复建模，也得到了类似的结果。那么在所有情况下，使用我们的“自下而上”分析方法，没有证据表明双语能力作为一个变量会显示出不同的认知表现——因此，我们得出结论，即使在老年人群中，双语者与单语者在认知上也没有差异。我们认为，那些报告了双语优势的研究（通常招募移民群体）很可能混淆了其他可能导致所报告优势的关键变量。我们建议未来的研究改进本研究中使用的机器学习方法，以进一步探究双语能力与认知之间的复杂关系。
