Is mere exposure enough? the effects of bilingual environments on infant cognitive development

Bilinguals purportedly outperform monolinguals in nonverbal tasks of cognitive control (the ‘bilingual advantage’). The most common explanation is that managing two languages during language production constantly draws upon, and thus strengthens, domain general inhibitory mechanisms (Green, 1998). However, this theory cannot explain why a bilingual advantage has been found in preverbal infants (Kovacs & Mehler, 2009). An alternative explanation is needed. We propose that exposure to more varied, less predictable (language) environments drive infants to sample more by placing less weight on consolidating familiar information in order to orient sooner to (and explore) new stimuli. To confirm the bilingual advantage in infants and test our proposal, we administered four gaze-contingent eye-tracking tasks to 7- to 9-month-old infants who were being raised in either monolingual (n = 51) or bilingual (n = 51) homes. We could not replicate the finding by Kovacs and Mehler that bilingual but not monolingual infants inhibit learned behaviour (experiment 1). However, we found that infants exposed to bilingual environments do indeed explore more than those exposed to monolingual environments, by potentially disengaging attention faster from one stimulus in order to shift attention to another (experiment 3) and by switching attention more frequently between stimuli (experiment 4). These data suggest that experience-driven adaptations may indeed result in infants exposed to bilingual environments switching attention more frequently than infants exposed to a monolingual environment.有研究表明，双语者在认知控制的非言语任务中表现优于单语者，即「双语优势效应（bilingual advantage）」。目前最主流的解释为：语言产出过程中对两种语言的管理会持续调用并强化领域一般性抑制机制（domain general inhibitory mechanisms，Green, 1998）。然而，该理论无法解释为何在前言语婴儿中也能观测到双语优势效应（Kovacs & Mehler, 2009），因此需要提出替代性解释。本研究认为，接触更多元化、可预测性更低的（语言）环境会促使婴儿增加采样行为：通过减少对巩固熟悉信息的权重，从而更快地定向并探索新刺激。为验证婴儿群体中的双语优势效应并检验本研究提出的假说，我们对7至9月龄的婴儿开展了四项注视依存型眼动追踪（gaze-contingent eye-tracking）任务，这些婴儿分别成长于单语家庭（n=51）与双语家庭（n=51）。我们未能重复Kovacs与Mehler的实验发现：双语婴儿而非单语婴儿会抑制习得行为（实验1）。但我们发现，成长于双语家庭的婴儿确实比单语家庭婴儿的探索行为更多，具体表现为能更快地将注意力从某一刺激上脱离并转移至另一刺激（实验3），以及在不同刺激间更频繁地切换注意力（实验4）。上述数据表明，由经验驱动的适应性调整，确实会使成长于双语环境的婴儿比单语环境婴儿更频繁地切换注意力。