This Special Issue of Applied Psycholinguistics raises not only several issues about the human brain's behavior as manifest in the processing of language, but it is also intended to elicit scientific dialogue.

Normal aging is an inevitable race between increasing knowledge and decreasing cognitive capacity. Crucial to understanding and promoting successful aging is determining which of these factors dominates for particular neurocognitive functions. Here, we focus on the human capacity for language, for which healthy older adults are simultaneously advantaged and disadvantaged. In recent years, a more hopeful view of cognitive aging has emerged from work suggesting that age-related declines in executive control functions are buffered by life-long bilingualism. In this paper, we selectively review what is currently known and unknown about bilingualism, executive control, and aging. Our ultimate goal is to advance the views that these issues should be reframed as a specific instance of neuroplasticity more generally and, in particular, that researchers should embrace the individual variability among bilinguals by adopting experimental and statistical approaches that respect the complexity of the questions addressed. In what follows, we set out the theoretical assumptions and empirical support of the bilingual advantages perspective, review what we know about language, cognitive control, and aging generally, and then highlight several of the relatively few studies that have investigated bilingual language processing in older adults, either on their own or in comparison with monolingual older adults. We conclude with several recommendations for how the field ought to proceed to achieve a more multifactorial view of bilingualism that emphasizes the notion of neuroplasticity over that of simple bilingual versus monolingual group comparisons.

The impacts of bilingualism upon the human brain, specifically in terms of the neuroplastic and neurofunctional changes upon general cognitive functions and on cognitive decline, are currently attracting much attention not only from the neuroscience and psycholinguistic communities but also from the general public. Researchers are especially focused on the putative protective effects of bilingualism upon cognitive decline.

The inevitable decline of cognitive function with aging and the high incidence of clinical impairment make understanding the process of cognitive decline and the search for remediation an urgent priority. However, in spite of massive efforts in research and development, the effectiveness of pharmacological treatments for cognitive impairment remains extremely limited (Zhu et al., in press). Therefore, there is growing interest in the set of lifestyle factors that serve to maintain cognitive function even in the presence of neuropathology. These factors, called cognitive reserve (Stern, 2002), include education, occupational status, socioeconomic class, and involvement in physical, intellectual, and social activities (Bennett, Schneider, Tang, Arnold, & Wilson, 2006; Stern et al., 1994). Bilingualism appears to be another potent source of cognitive reserve (Bialystok, Craik, Green, & Gollan, 2009). For these reasons, a comprehensive review of the small but growing literature on bilingualism and cognition in aging is timely and scientifically important.

Studying bilingualism is complicated. Baum and Titone's Keynote Article concludes with a discussion of three particularly thorny issues in bilingualism research: (a) bilinguals are not a homogeneous group, (b) bilingualism is not randomly assigned, and (c) the effects of bilingualism are often more complicated than simple advantages or disadvantages/delays. On this latter point, Baum and Titone consider how binary thinking about bilingualism as good or bad can limit the kinds of research questions that we ask. Here, I expand on this issue by showing how some apparent bilingual advantages and disadvantages can be illusory. I describe two examples of reasonable, justifiable, and prudent experimental designs that initially led to misleading conclusions about the effects of bilingualism on development. While both of these examples are drawn from research with bilingual infants, they nonetheless have implications for how we interpret the results of studies of bilingualism across the life span.

Baum and Titone's Keynote Article is a welcome addition to the ongoing and flourishing study of the neurocognitive effects of bilingualism. By focusing their review on executive control in bilinguals from the perspectives of both aging and neuroplasticity in general they have broadened our thinking in useful ways. Because my own research has focused on the early stages of aging and bilingualism in preschool and school-age children, I have chosen to comment on their review with reference to these kinds of learners. I will also focus on the language acquisition part of this discussion because at the heart of the issue is how and to what extent acquisition of more than one language affects cognitive development. My comments reinforce what I believe are important observations in their review and simultaneously seek to extend their call to expand our frames of reference in research on bilinguals even further.

An important proposal in the insightful Keynote Article by Baum and Titone is that the field of bilingualism research needs to attend more closely to intersubject variability in order to understand the nature of neuroplastic changes in the brains of bilingual speakers as they age. I agree. Understanding such variability and its drivers (such as the contexts of language use that Baum and Titone nicely comment on in the Montreal milieu) will help us develop theoretical accounts of the cognitive control processes recruited in bilingual speakers and establish how adaptive changes to these processes mediate the effects of normal aging; yield protective effects against neurodegenerative disease, such as Alzheimer disease; and modulate language recovery poststroke in bilingual speakers. In this commentary I explore some aspects of this variability and commend, in line with the views expressed in the Keynote Article, the value of relating behavioral indices to whole brain structural magnetic resonance imaging for enriching our understanding of experience-dependent changes. Allied to tractography studies, such research can help us develop a rich picture of the major drivers of neuroplastic changes.

Baum and Titone address several issues related to bilingual advantages in executive control that are often overlooked in this literature but warrant further consideration and empirical investigation. We limit our comments to two issues: the problem of establishing the directional relationship between bilingualism and executive control and the problem of decomposing executive control.

In this comprehensive review by Baum and Titone, the authors promote the notion that bilingualism should be thought of as an agent of neuroplastic change over the life span. Their proposal offers a context within which to view early enrichment, one element of which is the early learning of two languages. The review points out the complexities of studying bilingualism and highlights empirical gaps in research that are critical to our understanding of how experience with language, especially exposure to two languages, might affect the neurocognitive system. The framework brings together disparate sets of studies in the literature across multiple methods, models, and disparate repertoires of descriptive terms.

In the last two decades, there has been an upsurge of research on bilingualism recognizing that bilinguals may be more representative language users than their monolingual peers (e.g., Kroll, Dussias, Bogulski, & Valdes Kroff, 2012). The excitement about bilinguals is related not only to their neglected status in the past literature but also to a set of twin discoveries that have catapulted research on bilingualism into central view in psycholinguistics, cognitive and developmental neuroscience, and gerontology. One of these discoveries is that both languages are active when bilinguals read, listen to speech, and plan speech in either of their two languages (for a review, see Kroll et al., 2012). The other discovery is that bilingualism appears to confer a set of consequences to domain general cognition and to the neural structures that support it (e.g., Bialystok, Craik, Green, & Gollan, 2009). Those consequences are observed across the lifespan and are particularly evident when cognitive resources are challenged because of the normal or pathological trajectory of aging (e.g., Gold, Kim, Johnson, Kriscio, & Smith, 2013). The focus of the new research is on how these two discoveries might be related. The parallel activity of the two languages and the interactions across them require that the bilingual develops skill in language selection to enable fluent performance. The hypothesis that has guided the recent flurry of research is that bilingual minds and brains change as a consequence of having to regulate the two languages. In their Keynote Article, Baum and Titone provide a comprehensive and current summary of the existing evidence on this hypothesis.

A wealth of research on experience-related plasticity has shown that specific experiences, such as musical training (Herholz & Zatorre, 2012) or juggling (Draganski et al., 2004), can modify brain function and structure and induce long-term changes in cognitive behavior throughout the life span. In their comprehensive Keynote Article, Baum and Titone focus on the neural and cognitive implications of lifelong experience with multiple languages. They discuss empirical studies on bilingualism, executive control, and aging to enhance our understanding of the frequently observed executive control advantages in bilinguals and how lifelong bilingualism may contribute to the development of cognitive reserve and buffer age-related declines in executive control functions. In reframing these issues in terms of neuroplasticity, Baum and Titone propose to “embrace the inherent individual variability among bilinguals in all its glory” and identify key issues related to individual variability to pave the way to new avenues of research. We fully concur with Baum and Titone's general recommendation to embrace variability among bilinguals to advance our understanding of bilingualism, aging, and neuroplasticity, but we would like to particularly highlight the importance of the earlier stages of second language (L2) learning and the emergence of executive control advantages, a topic we believe has been understudied in this domain. How much bilingual experience is needed to affect executive control?

For several years now, headlines around the world have been trumpeting the cognitive control advantages enjoyed by bilinguals. As the story goes, a lifetime of experience selecting between two competing languages leads to improvements in control that generalize beyond the domain of language. It even protects the brain from the untoward effects of aging.

The scientific process applied to any domain is a thing of power and beauty. It enables its practitioners to systematically and rigorously pursue questions of importance, in a manner that is, by necessity, adaptive and tenacious. As was his way with most matters of relevance to psychology, the words of William James (The Principles of Psychology, 1890) are illustrative here:

Un grand merci à Shari Baum and Debra Titone for their review paper, “Moving Toward a Neuroplasticity View of Bilingualism, Executive Control and Aging.” (Please note the code switch in that previous sentence is part of my effort to build my cognitive reserve.) The authors are to be congratulated for providing a timely and constructive review of the current state of our understanding of the potential impact of bilingualism on executive control processes and cognitive aging. In this short commentary, I will comment on one of their key contributions to the discussion, namely, that researchers should embrace and address the individual variability among bilinguals.