Moving toward a neuroplasticity view of bilingualism, executive control, and aging

Abstract

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.

Full text

Applied Psycholinguistics 35 (2014), 857–894
doi:10.1017/S0142716414000174
KEYNOTE ARTICLE
Moving toward a neuroplasticity view
of bilingualism, executive control,
and aging
SHARI BAUM and DEBRA TITONE
McGill University
ADDRESS FOR CORRESPONDENCE
Shari Baum or Debra Titone, Centre for Research on Brain, Language & Music, McGill University,
3640 de la Montagne, Montreal, QC H3G 2A8, Canada. E-mail: shari.baum@mcgill.ca or
debra.titone@mcgill.ca
ABSTRACT
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 dom-
inates 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.
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 func-
tions. Here, we focus on the human capacity for language, for which healthy older
adults are simultaneously advantaged and disadvantaged. Older adults have greater
word knowledge than younger adults and make greater use of context when using
language than do younger adults (Wingfield & Tun, 2007). However, age-related
© Cambridge University Press 2014 0142-7164/14 $15.00

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Baum & Titone: Bilingualism, executive control, and aging
deficits in perceptual acuity (Murphy, Daneman, & Schneider, 2006; Schneider,
Daneman, & Pichora-Fuller, 2002; Schneider, Li, & Daneman, 2007; Stewart &
Wingfield, 2009; Tun, McCoy, & Wingfield, 2009; Wingfield, McCoy, Peelle,
Tun, & Cox, 2006) and executive control functions, such as working memory and
inhibitory capacity, counter these advantages (Burke, 1997; Burke & Shafto, 2004;
Darowski, Helder, Zacks, Hasher, & Hambrick, 2008; Hasher, Lustig, & Zacks,
2007; S. Martin, Brouillet, Guerdoux, & Tarrago, 2006; Salthouse & Meinz, 1995).
Thus, language processes that rely on executive control, such as the resolution of
linguistic competition during spoken and written comprehension and production,
are especially vulnerable for older adults (Abada, Baum, & Titone, 2008; Copeland
& Radvansky, 2007; Kjelgaard, Titone, & Wingfield, 1999; May, Zacks, Hasher, &
Multhaup, 1999; Meyer & Federmeier, 2010; Peelle, Troiani, Wingfield, & Gross-
man, 2010; Robert & Mathey, 2007; Titone et al., 2006; Wright & Newhoff, 2002).
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 (Bialystok & Craik, 2010; Bialystok, Craik, & Freedman,
2007; Bialystok, Craik, & Luk, 2012; Bialystok, Craik, Klein, & Viswanathan,
2004; Fernandes, Craik, Bialystok, & Kreuger, 2007). Fluent bilinguals know tens
of thousands of words in each language but make few noticeable errors when
they listen to, read, or speak in either language (Kroll, Bobb, Misra, & Guo,
2008; Kroll, Van Hell, Tokowicz, & Green, 2010). The ease with which bilinguals
perform this remarkable feat is attributed to their heightened use of executive
control in resolving cross-language conflict (Abutalebi & Green, 2007; Bialystok
et al., 2004; Bialystok & Craik, 2010; Bialystok, Craik, & Luk, 2008a; Bialystok
& Viswanathan, 2009; Carlson & Meltzoff, 2008; Festman, Rodriguez-Fornells,
& Munte, 2010; Hernandez, 2009; Hernandez & Meschyan, 2006; Luo, Luk,
& Bialystok, 2010; Perani & Abutalebi, 2005; Rodriguez-Fornells, Balaguer, &
Munte, 2006). Moreover, the repeated experience or “exercise” of using executive
control to manage cross-language activation has led many to hypothesize that
bilinguals should outperform monolinguals in cognitive control.
Consistent with this view, several studies show that bilingual older adults per-
form significantly better than monolingual older adults on a variety of executive
control tasks (Bialystok et al., 2004; Bialystok & Craik, 2010; Bialystok et al.,
2007, 2008a; Fernandes et al., 2007). It is more striking that executive control
advantages in bilingual older adults arguably forestall the onset of pathological
aging symptoms by approximately 4 years (Bialystok et al., 2007), although there
are limits on this estimate (Chertkow et al., 2010). Bilingualism in older adults
is thought to increase cognitive reserve (Bialystok et al., 2008a; Chertkow et al.,
2010; Gollan, Montoya, Cera, & Sandoval, 2008) and in so doing leaves indelible
marks on brain structure and connectivity similar to other highly specialized skills,
such as musical expertise or navigational experience (Bialystok & DePape, 2009;
Chakravarty & Vuust, 2009; Hyde et al., 2007; Mechelli, Price, Friston, & Ash-
burner, 2005; Oechslin, Imfeld, Loenneker, Meyer, & Jancke, 2010; Sluming et al.,
2002; Woollett, Spiers, & Maguire, 2009). However, the extant claims concerning
a bilingual “advantage” are not without controversy (e.g., Chertkow et al., 2010;
Gollan, Salmon, Montoya, & Galasko, 2011; Kousaie & Phillips, 2012), probably
because many of the studies to date have relied on relatively coarse comparisons

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of bilinguals and monolinguals, who are quite heterogeneous both between and
within groups.
Here, we argue that in order to make progress in understanding how bilingualism
affects executive control in older adults, or in any population, we must first reframe
the issue as a specific instance of neuroplasticity more generally. In so doing, it
will be important to redirect attention onto three crucial issues that have heretofore
been deemphasized by the tendency to perform relatively coarse group compar-
isons (e.g., bilinguals vs. monolinguals). These issues include (a) embracing the
inherent individual variability among bilinguals; (b) thinking more seriously about
how other kinds of individual differences, including preexisting neurocognitive
capacities or sociocultural factors, may affect the kinds of communicative experi-
ences that bilinguals seek out, which in turn can impact any relationship between
language and executive control; and (c) adopting statistical approaches that respect
the complexity of the question through multifactorial analyses, thus enabling us
to pose and test more sophisticated questions.
In building to these conclusions, we first selectively review what is currently
known and unknown with respect to bilingualism, executive control, and aging,
with the ultimate goal of identifying crucial lapses in current knowledge and targets
for future research. We first set out the theoretical assumptions and empirical
support of the bilingual advantages perspective, review what we know about
language, executive 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 by suggesting that the current framing of these issues in terms of
bilingual advantages may ultimately distract from the potential importance of this
body of work, which is to highlight how being bilingual can potentially act as an
agent of neuroplastic change over the life span.
THEORETICAL FOUNDATIONS OF THE BILINGUAL ADVANTAGES VIEW
Some underlying assumptions of the bilingual advantages view are that the neu-
rocognitive operations that support moment-by-moment language processing dif-
fer between bilinguals and monolinguals and that these differences accrue over the
life span to create significant neuroplastic change in the bilingual brain. Whether
such differences exist, and whether they are quantitative, qualitative, or both,
remain open questions that are part and parcel of the discussion regarding the
notion of bilingual advantages. It is thus instructive to consider the ways in which
the bilingual experience could differ from the monolingual experience and whether
such differences could potentially sculpt the neurocognitive substrate of executive
control functions generally.
Perhaps the most obvious way the bilingual experience differs from the mono-
lingual experience is in terms of the automatic and simultaneous activation of
multiple linguistic forms across virtually all levels of language. When bilinguals
bring any idea to mind and retrieve linguistic labels or grammatical frames with
which to verbalize it, or when they hear or read any linguistic stimulus presented to
them, there is always a risk of experiencing some form of linguistic or conceptual
ambiguity that must be managed. Of note, the degree of automatic cross-language

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activation depends on many factors, including the kind of language task in which
one is currently engaged, the relative degree of first language (L1) and second lan-
guage (L2) knowledge and proficiency, cross-language or within-language cues
from the present context, and the differences between the L1 and L2 in question
(Blumenfeld & Marian, 2011; Dijkstra, Miwa, Brummelhuis, Sappelli, & Baayen,
2010; Kroll, Dussias, Bogulski, & Valdes Kroff, 2012; Libben & Titone, 2009;
Marian & Spivey, 1999; Mercier, Pivneva, & Titone, 2014; Schwartz & Kroll,
2006; Titone, Libben, Mercier, Whitford, & Pivneva, 2011; Van Assche, Duyck,
& Hartsuiker, 2012; van Hell & de Groot, 2008; van Hell & Tanner, 2012). Thus,
bilinguals arguably experience greater executive control demands because of the
need to inhibit cross-language linguistic representations and to selectively attend
to target language linguistic representations. This form of executive control has
been referred to in the bilingualism literature as “local” inhibition (de Groot &
Christoffels, 2006). Numerous studies show evidence of local cross-language acti-
vation and inhibition during language production and comprehension (Blumenfeld
& Marian, 2011; Christoffels, Firk, & Schiller, 2007; Dijkstra, 2005; Green, 2011;
Guo, Liu, Misra, & Kroll, 2011; Kroll et al., 2008; Macizo, Bajo, & Martin,
2010; Martin, Macizo, & Bajo, 2010; Misra, Guo, Bobb, & Kroll, 2012; Pivneva,
Mercier, & Titone, 2014).
A second way in which the bilingual experience can differ from the monolingual
experience is in the need to manage activation of two or more language systems
in anticipation of a specific upcoming communicative demand. For example,
if bilingual individuals speak English at home and French at work, they may
use substantial executive control resources to downregulate activation of English
generally (and upregulate French) the moment they enter their French-speaking
workplace. Similarly, they may then use executive control resources to downregu-
late activation of French generally (and upregulate English) once they return home
to their English-speaking families. This form of executive control has been referred
to as “global” inhibition in the bilingualism literature (de Groot & Christoffels,
2006), and several studies show evidence of global inhibition, particularly during
language production (Abutalebi, Tettamanti, & Perani, 2009; Green, 1998; Guo
et al., 2011; Kroll et al., 2008; Meuter & Allport, 1999; Misra et al., 2012;
Pivneva, Palmer, & Titone, 2012; Von Studnitz & Green, 2002). For example, the
bilingualism literature shows costs during language production that are associated
with switching between first and second language blocks, suggesting that there is
some cognitive overhead associated with tuning into one global language system
over another (Campbell, 2005; Costa & Santesteban, 2004; Meuter & Allport,
1999; Misra et al., 2012). It is even more interesting that these global switch costs
are asymmetric in that performance is significantly more impaired when bilinguals
engage in an L1 speaking block that follows an L2 speaking block, compared to
the reverse situation, when an L2 speaking block follows an L1 speaking block
(e.g., Meuter & Allport, 1999). Such asymmetries suggest that if bilinguals first
speak in an L2-only block, they recruit executive control to globally downregulate
activation of their L1 to maintain L2 fluency. Consequently, when they switch
to an L1 speaking block, performance is lower than it would have been had the
prior L2 block not been encountered. In contrast, when bilinguals first speak in
an L1 block, there is less of a need to recruit executive control to globally inhibit

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the L2, as the L2 is less entrenched to begin with compared to the L1. Thus,
when they switch to the L2, performance is the same as it would have been had
the L1 block not come first. The existence of asymmetric switching costs of this
kind provide compelling evidence for the bilingual capacity of downregulating
an entire language as a function of task demands (for consistent evidence in a
passive listening comprehension task, see also Mercier, Pivneva, & Titone, in
press). Such asymmetries may be indicative of switching between an overlearned
and less practiced task generally, regardless of whether the task is linguistically
oriented (Kiesel et al., 2010).
Thus, the bilingual experience with language potentially differs from the mono-
lingual experience in at least two ways: the need to use executive control to manage
local cross-language activation that arises during language processing, and the
need to use executive control to manage activation of an entire language system
globally, presumably with the aim of preempting future anticipated demands of
local cross-language activation. There are other variations of this basic distinction.
For example, de Groot (2011, p. 280) provides a comprehensive overview of the
several theoretical dimensions along which bilingual language processing models
vary that are relevant to notions of bilingual language control, two of which are key
for our purposes. The first, scope, pertains to whether executive control extends to
specific representations within a particular language (i.e., single words) versus all
elements of a particular language (i.e., the entire language system). The second,
direction, pertains to whether control processes are initiated after encountering or
generating a particular linguistic item (i.e., reactively) or prior to encountering a
particular linguistic item (i.e., proactively). In our view, these two dimensions may
not be completely orthogonal. That is, executive control processes that are more
likely to target individual words might tend to occur reactively, whereas execu-
tive control processes that keep a whole language downregulated given specific
communicative demands would tend to occur proactively. However, it may be
possible to isolate all four combinations of these two dimensions within particular
experimental tasks (reviewed in de Groot, 2011).
It is interesting that the ways that bilingualism researchers have discussed
language control have analogues in the nonlinguistic executive control literature.
For example, the distinction between global and local executive control fits with
recent work in the general executive control literature (Braver, 2012). Accord-
ing to the dual mechanisms of control framework, proactive control maintains
goal-relevant information in anticipation of future demands, for example, when
bilinguals globally downregulate knowledge of one language and shift attention to
another language. In contrast, reactive control acts as a late correction mechanism
for high competition stimuli encountered in real time, for example, when bilinguals
locally downregulate semantically incompatible meanings of interlingual homo-
graphs when reading or nontarget object labels when speaking. This distinction is
somewhat different from other executive control frameworks, which distinguish
between a common executive control capacity (i.e., the unity of executive func-
tion), and distinct subsystems of switching and context updating (i.e., the diversity
of executive function; Miyake & Friedman, 2012).
Regardless of the exact executive control framework to which one subscribes,
the distinctions between proactive/global versus reactive/local control during

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bilingual language processing fit with an influential model of bilingual language
production (which could conceivably be extended to comprehension) known as
the inhibitory control (IC) model. According to the IC model, language production
is framed as a communicative action that is analogous to nonlinguistic physical
actions (Abutalebi & Green, 2008; Green, 1998), in that it can have goals that are
routine or nonroutine (Shallice & Burgess, 1996). Within this view, L1 language
production would be a routine communicative action whereas L2 language pro-
duction would be nonroutine. Moreover, language production requires inhibitory
control at two levels. At the language schema level, inhibitory control modulates
the relative activation and inhibition of L1 and L2 generally, for example, whether
one is about to communicate with a monolingual speaker of one’s L1 where the
L2 should optimally be suppressed versus engaging in simultaneous translation
where the L1 and L2 must remain simultaneously engaged. At the word selection
level, inhibitory control fine-tunes the relative activation and inhibition of specific
words within each language.
Consistent with the idea that language control and nonlinguistic executive
control engage shared neural systems, general executive control functions and
executive control functions used during bilingual language processing (language
processing generally) recruit similar brain networks. For example, Abutalebi and
Green (2007) extended the IC model to incorporate neurocognitive evidence about
bilingual language production. Here, they identified a network of cortical regions
involving the prefrontal cortex (PFC), inferior parietal, and anterior cingulate
cortex (ACC) and subcortical structures (basal ganglia, the head of the caudate
nucleus in particular) that modulate competition between L1 and L2 knowledge
activation during bilingual language production. It is interesting that the PFC
(inferior and lateral regions) and ACC are also involved in nonlinguistic general
executive control tasks in a comparable manner (e.g., Braver, 2012). Common
to both views, activation of the PFC is associated with the exertion of executive
control (both reactive and proactive, across PFC subregions according to the dual
mechanisms of control literature), whereas the ACC generates error monitoring
signals that signal the need for reactive control and may subsequently trigger the
application of proactive control to resist future errors.
Abutalebi and Green (2007) also noted the implications of this model for the
role of L2 proficiency in bilingual language control. When L2 proficiency is
low, L2 language production is more controlled and less automatic (see also
Favreau & Segalowitz, 1983; Segalowitz, 2010; Segalowitz & Hulstijn, 2005), thus
requiring inhibitory control (prefrontal function, in particular; see also Petrides,
1998). However, when L2 proficiency is high, L2 production is automatic and
less dependent on inhibitory control, although L1 production effort might instead
increase due to a collateral weakening of the links between word forms and
concepts in the L1 (Bialystok, 2001; Bialystok, Luk, Peets, & Yang, 2010; Gollan
et al., 2008; Gollan, Slattery, et al., 2011; Ivanova & Costa, 2008; Michael &
Gollan, 2005; Whitford & Titone, 2012) or to an increased likelihood of intrusions
of L2 knowledge onto L1 processing.
To summarize thus far, several important theoretical views of bilingualism
presume that cross-language activation generated during in the moment bilingual
language processing creates executive control demands that differ from those

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experienced by monolinguals, though there is ongoing debate about whether such
differences are quantitative (i.e., just more of what monolinguals normally experi-
ence), qualitative (i.e., fundamentally different from what monolinguals normally
experience), or both. However, the bilingual advantages view takes this link a step
further by stating that these in the moment bilingual experiences collectively lead
to enduring changes in the minds and brains of bilinguals over developmental
time. Thus, we now turn to some of the empirical research that addresses this idea
with respect to bilingual children and young adults.
EMPIRICAL FOUNDATIONS OF THE BILINGUAL ADVANTAGES VIEW
One of the first papers to speak to the issue of bilingual advantages was a landmark
study by Peal and Lambert (1962). Prior to this study, the scientific research
emphasized the notion that bilinguals had substantial disadvantages with respect
to monolinguals in terms of language proficiency and general intellectual function
(Peal & Lambert, 1962). The impression from this early literature was that being
bilingual was highly undesirable and to be avoided. Peal and Lambert contradicted
the negative view of bilingualism by showing that bilingual children actually
performed better than monolingual children on a battery of verbal and nonverbal
IQ tests and language proficiency and language attitude tests when methodological
confounds of prior work were controlled (e.g., socioeconomic status, quality of
schooling). This finding was among the first to highlight the notion that the
bilingual experience creates opportunities rather than liabilities for children to
engage in mental flexibility, including the ability to switch between not only
languages but also cultures. Other research followed from this work showing that
the experience of being bilingual can lead to other targeted advantages in general
cognitive capacities that are presumably required of being bilingual, including
metalinguistic awareness, linguistic rule learning, and executive control, which is
the focus of this paper (Adesope, Lavin, Thompson, & Ungerleider, 2010; Ben-
Zeev, 1977; Bialystok, 1986, 1988; Bialystok et al., 2004; Galambos & Goldin-
Meadow, 1990; Galambos & Hakuta, 1988; Salvatierra & Rosselli, 2011).
Bialystok and colleagues initiated the recent surge of interest regarding this
question by building upon the original results of Peal and Lambert in children
and extending this work to new bilingual groups, such as younger and older
adults, and pathological populations (reviewed in Bialystok et al., 2012). Bia-
lystok initially investigated one particular area of bilingual advantages that had
received a great deal of early attention: metalinguistic awareness (e.g., Bialystok,
1988). By conducting experiments that were designed to parse the exact process
by which bilingual children performed better on metalinguistic tasks, Bialystok
and colleagues concluded that it had less to do with the availability of linguis-
tic knowledge and more to do with an increased ability to selectively attend to
competing linguistic cues or constraints (Bialystok & Majumder, 1998; Martin-
Rhee & Bialystok, 2008). This realization thus pushed the locus of the bilingual
advantages effect to more domain-general aspects of cognition, such as selective
attention. In pursuing this hypothesis, Bialystok and colleagues, along with other
research groups, observed bilingual advantages in children across a variety of
tasks that arguably tap into executive control, similar in spirit to the original

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work by Peal and Lambert. As reviewed in Bialystok et al. (2012), these include
block design from the Wechsler Intelligence Scale for Children, the flanker task,
and the Simon task, as well as executive control tasks that are less lab-based
and more similar to real-world experience (e.g., Noelting’s juice task, theory of
mind tasks; Bialystok & Majumder, 1998; Costa, Hern´
andez, & Sebasti´
an-Gall´
es,
2008; Goetz, 2003; Kov´
acs, 2009; Martin-Rhee & Bialystok, 2008; Yang, Yang,
& Lust, 2011). Bialystok and colleagues replicated these findings in bilingual
younger adults and in bilingual older adults, which we discuss in more detail in
later sections (Bialystok et al., 2004, 2008; Colzato et al., 2008; Hilchey & Klein,
2011; Prior & MacWhinney, 2010; Rubio-Fernandez & Glucksberg, 2012).
However, subsequent work questioned such findings. With respect to studies
of children, at least one study failed to find significant bilingual advantages on
one measure of executive control in children: the Simon task (Morton & Harper,
2007). This led the authors to conclude that prior findings of bilingual advantages
arose because of potential confounds with bilingual status such as socioeconomic
status or immigration status, problems that were claimed to be controlled in the
study that produced null group results. However, socioeconomic status was argued
to be controlled in prior reports (Bialystok, 2009), as all the children tested were
recruited deliberately from upper middle class school districts, thus making it
likely that socioeconomic status was not a factor. Bialystok also argued that the
null effect observed by Morton and Harper may have arisen because of a lack of
power for detecting such an effect attributable to large response time variability
combined with a relatively small sample size in their study (n=17; Bialystok,
2009; see also Kroll & Bialystok, 2013). Although reports of null results can
be important empirical anchor points (i.e., to avoid “file drawer problems” in
scientific reporting), there are unfortunately many uninteresting roads that can
lead to null results, such as lack of power, differences across particular tasks or
participant samples, and choice of particular tasks. From our view, while a failure
to replicate a group effect is certainly inconsistent with a theory that predicts
a group effect, the ability to attribute the original group effect to a particular
confounding variable remains a hypothesis until such an experiment is undertaken
showing affirmatively that the effect of interest is present only under conditions
where the confound is present and absent under conditions when the confound is
not present (e.g., crossing bilingual status with socioeconomic status and showing
a bilingual advantage for one group but not the other).
With respect to studies of younger adults, similar questions have arisen in
that two notable papers have questioned different assumptions of the bilingual
advantages view. First, a comprehensive review of the literature on this topic
failed to find any bilingual advantage with respect to inhibitory control (Hilchey
& Klein, 2011), although they did note bilingual advantages in reaction times
generally among bilinguals across both conflict and nonconflict conditions of var-
ious executive control tasks. Second, a recent empirical paper also raised questions
about the validity of bilingual advantages among young adults (Paap & Greenberg,
2013). However, as Paap and Greenberg note, it is possible that their study, as well
as other bilingual advantage studies, inadvertently included unidentified sources
of variability that led to particular experimental outcomes, a situation which is
particularly problematic in the context of null group findings. For example, a

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later empirical paper coauthored by Hilchey and Klein (2011; Misra et al., 2012)
found that bilinguals were advantaged over monolinguals on a task that assessed
inhibition of return, which reflects the ability to disengage attention from a task-
irrelevant peripheral cue. Of note, they found that bilinguals who had higher L2
proficiency were even more advantaged than bilinguals with lower L2 proficiency.
This highlights two important potential sources of variability in such studies:
the kinds of tasks used and their sensitivity for assessing executive control and
the kinds of bilinguals tested and how they differ qualitatively and quantitatively
(see also Bialystok, 2006; Costa, Hern´
andez, Costa-Faidella, & Sebasti´
an-Gall´
es,
2009; Costa et al., 2008; Hern´
andez, Costa, Fuentes, Vivas, & Sebasti´
an-Gall´
es,
2010). For example, Costa and colleagues found that the bilingual advantage is
specific to executive control tasks that are maximally demanding (e.g., Costa et al.,
2009), and Kroll and Bialystok (2013) have argued that bilingual advantages might
be more about general mental flexibility than any specific cognitive component.
Thus, several sources of unidentified variability may have contributed to the
null group results reported by Paap and Greenberg (2013). For example, as they
mention themselves, the bilinguals tested in their study came from a very wide
array of language and cultural backgrounds and were immersed in an English
language university context where the bilingual experience could have been more
of the subtractive versus additive type (see Peal & Lambert, 1962, for a discussion
of how these two types of bilingualism might lead to different cognitive outcomes).
Finally, degree of bilingualism was only assessed using a single self-report measure
consisting of a 10-point scale, where people endorsed global qualitative statements
about their bilingualism that may have been difficult to distinguish and that may
have overlooked crucial aspects of the bilingual experience that are relevant for
the recruitment of executive control (e.g., daily language switching). The nature
of this single questionnaire is worth considering (i.e., Beginner, know some words
and basic grammar; advanced beginner, can converse with a native speaker only
on some topics and with quite a bit of difficulty; intermediate, can converse with
a native speaker on most everyday topics, but with some difficulty; advanced
intermediate, can converse with little difficulty with a native speaker on most
everyday topics, but with less fluency than a native speaker; near fluency, almost
as good as a typical native speaker on both everyday topics and specialized topics
I know about; fluent, as good as a typical native speaker; super fluency, better
than a typical native speaker). Although such categories are descriptively rich,
it is unclear whether they can capture nuanced differences among bilinguals in
the way that multiple languages are used while speaking, reading, listening, or
historically. For example, there is evidence suggesting that only certain classes
of bilingual behavior, such as switching, are related to individual differences in
executive control (Festman & Braun, 2012; Festman et al., 2010; Festman &
Munte, 2012; Prior & Gollan, 2011).
Thus, the field of bilingualism is likely to benefit by more thoroughly char-
acterizing these different sources of variability. However, it is possible that even
under the best of circumstances, assessing the nature of the relationship between
executive control and bilingualism using only cognitive tasks may lack the nuance
necessary to identify such a relationship definitively. One means of examining
this relationship more closely is by searching for neurofunctional overlap or

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neuroplastic changes in one domain that are associated with changes in the other.
Thus, in the next section, we consider some of the relatively small number of stud-
ies that have addressed the claims regarding a bilingual advantage using functional
and structural neuroimaging methods.
NEUROFUNCTIONAL EFFECTS OF BILINGUALISM
Before reviewing the studies on bilingualism in particular, it is important to provide
some background regarding neuroplastic changes across the life span more gener-
ally. From before birth through adolescence, there is evidence of rapid growth of
the brain in terms of synaptogenesis, neurogenesis, and neuronal migration, which
yields increases in both gray and white matter density (for reviews, see Stiles &
Jernigan, 2010; Tau & Peterson, 2010). Simultaneously and subsequently, sub-
stantial synaptic pruning occurs, which can be associated with automatization of
behavior and efficiency of function. There is also experience-dependent plasticity
that occurs throughout the life span, inducing both short- and long-term changes
in neural circuitry (e.g., Aydin et al., 2007; Luders, Toga, Lepore, & Gaser, 2009;
I. Park et al., 2009). Advanced aging is generally associated with reductions in
gray and white matter density (atrophy; e.g., Kennedy & Raz, 2009), with the
frontal lobes most susceptible to deterioration (McGinnis, Brickhouse, Pascual, &
Dickerson, 2011; Raz, 2000; Raz et al., 2005; West, 1996). The structural declines
may be associated with increases in functional activation (overactivation) in other
(linked) regions, including reduced suppression of the so-called default network
(i.e., the network activated during the resting state) during cognitively demanding
tasks (Grady, McIntosh, & Craik, 2003; Grady, Springer, Hongwanishkul, McIn-
tosh, & Winocur, 2006; Park & Bischof, 2011; Park, Carp, Hebrank, Park, & Polk,
2010; Park, Polk, Hebrank, & Jenkins, 2010), along with evidence of decreased
connectivity within the resting state network in older adults (e.g., Grady et al.,
2010; Park, Carp, et al., 2010). Nonetheless, recent investigations have shown that
despite age-related neuronal decline the aging brain is still sensitive to experience-
dependent plasticity (Bavelier, Levi, Li, Dan, & Hensch, 2010; Park & Bischof,
2011) .
Of particular relevance to the current discussion, evidence has been reported
suggestive of changes in gray matter density and volume in specific brain regions
associated with the development of certain skills, for example, musical perfor-
mance (Elbert, Pantev, Wienbruch, Rockstroh, & Taub, 1995; Herholz & Zatorre,
2012), juggling (Draganski et al., 2004), navigation (Maguire et al., 2000), and
acquisition of a second language (Berken et al., 2012; Klein et al., 2012; Mechelli
et al., 2004). Recent data have also reported improved white matter integrity in
bilingual older adults relative to monolinguals using diffusion tensor imaging
(Luk, Bialystok, Craik, & Grady, 2011; but see Mohades et al., 2012, for diffusion
tensor imaging findings in children; and Cummine & Boliek, 2013, for inconsistent
findings in young adults). The findings of these studies provide a neurostructural
basis to support the notion of a cognitive advantage associated with bilingualism.
With regard to functional neuroimaging studies of bilinguals, numerous studies
have focused on language switching, which has been shown to activate dorsolat-
eral prefrontal cortex as well as portions of the left inferior frontal gyrus, bilateral

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temporal lobes, and bilateral caudate nuclei (Abutalebi et al., 2008; Guo et al.,
2011; Hernandez, 2009; Wang, Kuhl, Chen, & Dong, 2009; see also Crinion
et al., 2006; Kim, Relkin, Lee, & Hirsch, 1997; Wang, Xue, Chen, Xue, & Dong,
2007). Most of the frontal regions activated have also been independently impli-
cated in general executive control, supporting a connection between the domains
(e.g., Abutalebi & Green, 2008; Hedden & Gabrieli, 2010; see also Bialystok
et al., 2005; Luk, Anderson, Craik, Grady & Bialystok, 2010). It is interesting
that, even at subcortical levels, there is evidence to suggest that bilingualism
yields changes in processing. In particular, bilingual individuals display a more
accurate frequency-following response in brain stem auditory evoked potentials
recording (e.g., Krizman, Marian, Shook, Skoe, & Kraus, 2012). Such effects
have been demonstrated for trained musicians as well (Kraus & Chandrasekaran,
2010), suggesting a more general benefit associated with specific types of auditory
experience.
However, despite the application of sophisticated brain imaging technology,
studies on the representation of L1 and L2 are still needed (Chee, 2006; Dehaene
et al., 1997; Kim et al., 1997; Klein, Milner, Zatorre, Meyer, & Evans, 1995; Klein
et al., 2006). Although such variables as age of L2 acquisition (e.g., Hernandez
& Li, 2007; Kim et al., 1997) and the proficiency of the participants have been
explored to some extent (Chee, Soon, Lee, & Pallier, 2004; Perani et al., 1998),
few studies have taken into consideration the processing and production charac-
teristics of individual subjects or subject groups. Moreover, although numerous
investigations have explored neurofunctional patterns in bilinguals with different
ages of acquisition (e.g., Wartenburger et al., 2003), very few have focused on
potential alterations in brain structure as a function of bilingualism (cf. Berken
et al., 2012; Klein et al., 2012; Mechelli et al., 2004).
AGING, COGNITION, AND LANGUAGE
To better understand the potential links between bilingualism and executive control
functions in older adults, it is important to consider broader issues pertaining to
aging, cognition and language generally. Over the past 30 years, a great deal of
work has investigated the cognitive and linguistic changes associated with normal
healthy aging. As already noted, it is well known that, as we age, our brains
change in terms of both structure and function (e.g., Hedden & Gabrieli, 2004).
How those brain changes map onto cognitive performance and how observable
behavioral changes map onto neural changes remain areas of intense investigation.
Several lines of evidence have demonstrated that aging is generally associated
with decreased processing speed (e.g., Salthouse, 1986, 1996), reduced sensory
acuity (Schneider et al., 2002, 2007; Schneider, Pichora-Fuller, Kowalchuk, &
Lamb, 1994; Schneider, Speranza, & Pichora-Fuller, 1998), and reductions in
working memory and other executive control functions, such as inhibition (Burke,
1997; Darowski et al., 2008; Hasher et al., 2007; Hedden & Gabrieli, 2004;
Salthouse & Meinz, 1995). It is not surprising that language processes that rely on
executive control, such as the resolution of linguistic competition during spoken
and written comprehension (and production), are especially vulnerable for older
adults (Abada et al., 2008; Copeland & Radvansky, 2007; Kjelgaard et al., 1999;

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Lee & Federmeier, 2011, 2012; May et al., 1999; Meyer & Federmeier, 2010;
Peelle et al., 2010; Robert & Mathey, 2007; Titone et al., 2006; Wright & Newhoff,
2002).
To illustrate the interplay between aging, cognition, and language, we briefly
consider several studies of spoken word recognition that have compared older and
younger adults in terms of monolingual language processing (though it is often
unknown whether prior studies in the “monolingual” literature have included
participants who also knew other languages). As is well known, most theories
of spoken word recognition posit some form of competition between potential
word candidates (Luce & Pisoni, 1998; McClelland & Elman, 1986; Vitevitch,
Luce, Pisoni, & Auer, 1999; Zhuang, Randall, Stamatakis, Marslen-Wilson, &
Tyler, 2011). For example, when people hear a target word (e.g., cap), they im-
mediately activate other words that share a spoken word onset (e.g., can,cat)or
that are phonologically similar to the target word in other ways (e.g., gap,tap;
Allopenna, Magnuson, & Tanenhaus, 1998; Connine, Blasko, & Titone, 1993;
Connine, Blasko, & Wang, 1994; Connine, Titone, & Blasko, 1991; Connine,
Titone, Deelman, & Blasko, 1997). Listeners must thus inhibit partially activated
competitors (e.g., can) while simultaneously enhancing the activation of intended
word (cap) for comprehension to be successful.
These processes appear to be less efficient in older relative to younger adults,
particularly in the context of increased task demands associated with recognition
of lower frequency words (e.g., Revill & Spieler, 2012), words from higher den-
sity lexical neighborhoods (e.g., Taler, Aaron, Steinmetz, & Pisoni, 2010), words
with reduced contextual support (e.g., Sommers & Danielson, 1999; Wingfield,
Aberdeen, & Stine, 1991), and words presented in the context of noise (e.g.,
Ben-David et al., 2011; Taler et al., 2010). Of note, while changes in peripheral
auditory sensitivity and associated speech discrimination difficulties may certainly
exacerbate such age-related impairments (Pichora-Fuller, 2003a, 2003b; Sommers
& Danielson, 1999; Tremblay, Piskosz, & Souza, 2003; Wingfield et al., 1991), im-
paired spoken word processing in older adults is observed even when participants
are carefully screened for peripheral hearing ability.
For instance, Sommers and Danielson (1999; see also Sommers, 1996) exam-
ined spoken word identification in healthy older and younger adults and whether
the availability of supportive semantic context would alleviate any age-related
impairments. They compared older and younger adults’ recognition of words with
large and small numbers of competitors (hard vs. easy, respectively, defined in
terms of neighborhood density and frequency) in isolation and in the context of
low- and high-predictable sentence contexts, at two different signal to noise ratios.
The authors found that older adults were impaired relative to younger adults in the
recognition of high-density hard words in isolation; however, they reaped greater
benefit from the addition of supportive sentential context. In a second experiment,
the investigators correlated performance on inhibitory skills (as measured by a
speeded classification task and an auditory Stroop task) with word recognition
performance in the older adults and found a significant relationship between in-
hibitory ability and hard word recognition. Based on these results, they concluded
that impaired inhibition of lexical competitors contributes to age-related word
recognition deficits (see also Taler et al., 2010).

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More recent investigations have confirmed a link between impaired inhibitory
capacity and reduced word recognition performance. For instance, Ben-David
et al. (2011) used eye-tracking (i.e., the visual world paradigm) to examine auditory
word recognition in older and younger adults. In this paradigm, people hear spoken
words while they view pictures on a computer screen that bear some relation to the
spoken words they are hearing. For example, people might hear the word beaker,
and see displays that contain a picture of a beaker (the target), unrelated control
words (table), and different kinds of competitors, such as a word-onset competitor
(beetle) or a word-rhyme competitor (speaker). Based on an analysis of which
pictures people look at as they hear the spoken word, it is possible to evaluate which
lexical candidates were partially activated in memory as the spoken word unfolded
acoustically. It is interesting that Ben-David et al. found that older adults showed
the same pattern of looks to word-onset competitor pictures, suggesting equivalent
competition for these lexical items. However, they showed greater looks to rhyme
pictures, suggesting greater competition from such candidate words (Ben-David
et al., 2011; for similar findings related to word frequency, see Revill & Spieler,
2012).
It is, of course, crucial to note that the findings reviewed above refer to group
patterns and, in many instances, studies of older adults assume that older adults
exhibit declines in cognitive functions and do not test those functions explicitly. It
is self-evident that there is a great deal of interindividual heterogeneity in patterns
of cognitive decline and resilience, as well as a lack of uniformity in age-related
changes across cognitive and linguistic domains. Many factors undoubtedly con-
tribute to this variability, including biological and environmental ones; neuroplas-
ticity and compensatory abilities also vary across individuals, contributing further
to the heterogeneity seen. For example, structural magnetic resonance imaging
analyses have shown differences across different areas of the brain in the rate
at which gray matter atrophies with increasing age (Good et al., 2001; Ohnishi,
Matsuda, Tabira, Asada, & Uno, 2001; Resnick, Pham, Kraut, Zonderman, &
Davatzikos, 2003; Sowell et al., 2003). Some functional neuroimaging investi-
gations have demonstrated more bilateral activation in older relative to younger
adults, particularly in those who perform well on the tasks under examination,
possibly indicative of compensatory reorganization of function (Cabeza, Ander-
son, Locantore, & McIntosh, 2002; Grady, Bernstein, Beig, & Siegenthaler, 2002;
Reuter-Lorenz et al., 2000; but cf. Logan, Sanders, Snyder, Morris, & Buckner,
2002) .
As an example of one cognitive or language-based factor that may influence
the variability in the effects of age-related changes, the so-called Nun Study, a
longitudinal investigation of aging and dementia, reported a strong negative re-
lationship between language complexity in autobiographical essays completed in
young adulthood (as measured by content or idea density) and the development of
dementia later in life (Riley, Snowdon, Desrosiers, & Markesbery, 2005; Snowdon,
Kemper, & Mortimer, 1996; Tyas, Snowdon, Desrosiers, Riley, & Markesbery,
2007). In a follow-up investigation, Farias and colleagues examined idea density
in a group of older individuals and found that, even when measured in an ag-
ing population, idea density continued to predict later cognitive decline (Farias
et al., 2012). These findings suggest that greater linguistic abilities in early life

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confer resilience to age-related cognitive decline. In a related investigation, Iacono
and colleagues examined the autopsied brains of four groups of subjects from
whom cognitive measures had been obtained shortly before death: a group of
asymptomatic Alzheimer disease (AD) participants, a group of patients with mild
cognitive impairment (MCI), a group of patients with AD, and a normal control
group free from cognitive impairment (Iacono et al., 2009; most of the participants
had also been in the Nun Study). The investigators reported neuronal hypertrophy
in the asymptomatic AD group compared to both the MCI and control groups.
The asymptomatic AD group (as well as the control group) also demonstrated
higher idea density scores relative to the MCI and AD groups. Taken together,
the findings support previous results indicating that stronger language skills may
confer some form of cognitive reserve and that neuronal hypertrophy may reflect
a compensatory response that helps to preclude cognitive impairment despite the
presence of AD pathology in the brain (Iacono et al., 2009; see also Rentz et al.,
2010). Extending this conclusion, one might argue that bilingualism inherently
represents a type of advanced language ability, and thus one might predict that
bilingualism, too, would confer cognitive reserve. It is also possible that there
are inherent differences in the brains of individuals who are better at language
in young adulthood and have greater neurocognitive capacities in later life, a key
point to which we return later.
BILINGUAL LANGUAGE PROCESSING IN HEALTHY OLDER ADULTS
We now turn to the relatively small number of studies that specifically investigate
bilingualism in healthy older adults. Like the studies of bilingual younger adults
reviewed above, this work tends to comprise two distinct but related types. The
first type includes studies of language processing performance in bilingual older
adults. This work typically examines bilingual older adults in relation to bilingual
younger adults and thus addresses the basic issue of whether there are general
effects of age in the ability of bilinguals to manage cross-language activation
during bilingual language processing. The second type includes studies of execu-
tive control performance in bilingual older adults. This work typically examines
bilingual older adults in relation to monolingual older adults completing a variety
of executive control tasks and thus addresses the issue of whether being bilingual
confers executive control advantages. Thus, the former assesses only language
processing, or the link between bilingual language processing and executive con-
trol functions locally, in the moment, as language processes occur. In contrast,
the latter assesses whether such local dependencies (which are often presumed in
this literature by using language history as a proxy) lead to enduring changes in
executive control generally.
With respect to lexical processing in bilinguals, investigations with young adults
have demonstrated activation of candidates from both languages simultaneously
(termed nonselective access), particularly if the target language is the listener’s L2
(e.g., Blumenfeld & Marian, 2007; Broersma & Cutler, 2011; Canseco-Gonzalez
et al., 2010; Marian & Spivey, 2003a, 2003b). The coactivation of candidates from
multiple languages increases the need for suppression of competitors (Dijkstra,
Van Jaarsveld, & Ten Brinke, 1998; Green, 1998). To date, only a limited number

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of studies have explored word recognition in older adult bilinguals. In one recent
investigation of written language processing, Kousaie and Phillips (2010) used
reaction time and electrophysiological measures (specifically the N400, which is
thought to reflect the ease of conceptual integration) to examine lexical priming
effects for interlingual homographs (words that share spelling but not meaning
across two languages; e.g., for French/English, the string coin which means corner
in French) in younger and older adult bilinguals (Kousaie & Phillips, 2010). They
used a word triplet paradigm common in research on unilingual processing of
ambiguous words (Hagoort, 1989; Milberg, Blumstein, & Dworetzky, 1987) and
hypothesized that younger adults would demonstrate priming effects irrespective
of whether the prime and target appeared in the same language (i.e., the triplets
“shoe-coin-money” and “soulier-coin-money” should both yield shorter reaction
times and reduced N400 amplitudes; Kousaie & Phillips, 2010, p. 28). In contrast,
because older adults have frequently been shown to be more sensitive to context
(e.g., Wingfield & Tun, 2007; Wingfield, Tun, McCoy, Stewart, & Cox, 2006),
older adults were predicted to only demonstrate priming in the language-consistent
conditions. Both reaction time and event-related potential results supported their
predictions, with younger adults exhibiting priming in both language-consistent
and language-inconsistent contexts (i.e., nonselective access) and older adults only
displaying priming in the language-consistent contexts, indicating their increased
reliance on contextual information to facilitate language processing (Kousaie &
Phillips, 2010).
A more recent investigation, focused on spoken language processing (Mercier,
Sudarshan, Pivneva, Baum, & Titone, 2014), made use of eye-tracking in the visual
world paradigm to examine the level of both within-language and cross-language
competition for lexical activation in older and younger French–English bilingual
adults. Participants were presented with an auditory word (in English) along with a
set of four pictures, which either included a within-language word onset competitor
or a cross-language word onset competitor, as well as two unrelated distractors.
Eye movement data revealed that older adult bilinguals exhibited greater within-
and possibly cross-language competition, particularly for participants whose pro-
ficiency in English (as an L2) was relatively low, in keeping with the IC model
(Abutalebi & Green, 2007; Green, 1998).
With respect to language production, most studies have suggested a disadvan-
tage of bilingualism, particularly in naming tasks. For example, young adult bilin-
guals name pictures more slowly than monolinguals, have lower accuracy rates
on naming tests, and produce fewer words in category fluency tasks (e.g., Gollan,
Fennema-Notestine, Montoya, & Jernigan, 2007; Gollan, Montoya, Fennema-
Notestine, & Morris, 2005; Gollan, Montoya, & Werner, 2002; Kohnert, Hernan-
dez, & Bates, 1998; Roberts, Garcia, Desrochers, & Hernandez, 2002). According
to Gollan and colleagues (2002; Gollan & Silverberg, 2001), these disadvantages
are presumably linked to lower frequencies of use of any given word due to the
use of a larger number of different words by bilinguals across two languages:
the so-called weaker links, or frequency-lag, hypothesis (Gollan et al., 2002;
Gollan & Silverberg, 2001). Moreover, it has been hypothesized that this bilingual
disadvantage in production should be reduced in older adults because they have
had more time to make frequent use of all words in both languages (e.g., Gollan

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et al., 2008). Alternatively, if the bilingual disadvantage is instead due to cross-
language competition for production, then the disadvantage should increase in
older adults who may be unable to effectively inhibit competitors and control
language activation (e.g., Hernandez & Kohnert, 1999). In one study that directly
addressed the naming disadvantage and its purported explanations in older adults,
Gollan and colleagues (2008) found support for the weaker links hypothesis by
demonstrating that, while both younger and older bilingual adults exhibited larger
effects of frequency than did monolinguals, effects of language dominance for low
frequency words (with the nondominant language yielding larger frequency effects
than the dominant language) were reduced in older adults compared to younger
adults. The authors contend that these findings support the weaker links hypothesis
because the older adults had greater opportunity to use the low frequency words
in their nondominant language over a lifetime and thus were less affected by their
(low) frequency (Gollan et al., 2008).
Turning to studies of executive functions in older adult bilinguals, by far the
most data supporting the notion of a bilingual advantage in aging has come from
investigations of specific executive functions in bilingual relative to monolingual
groups. In a series of investigations based in part on Green’s (1998) IC model of
bilingual processing, Bialystok and colleagues (e.g., Bialystok, 2006; Bialystok
et al., 2005; Bialystok et al., 2004) have examined the performance of older (and
younger) adults on tasks that tap executive control. In the majority of such stud-
ies, the investigators have compared monolingual and (relatively heterogeneous)
bilingual participants with respect to their performance on tasks incorporating
conflict conditions. As an example, in one of their earlier studies with older adults,
Bialystok and colleagues (2004) made use of the Simon task (Simon, 1969) in
which participants are required to learn an association of a colored square, for
example, with a specific key press on the left or right side of a keyboard or pad.
The color may appear on the same side as the associated key (a congruent condi-
tion) or on the opposite side (a conflict condition). Normal, monolingual young
adults demonstrate increased response times in the conflict condition due to the
cost associated with inhibiting the “misleading” cue (i.e., the Simon effect). Older
adults typically show an increased Simon effect relative to their younger peers.
Both young and older bilinguals exhibit a reduction in the magnitude of the Simon
effect compared to monolingual participants, with the reduction even greater for
the older bilingual individuals (e.g., Bialystok et al., 2004). These findings have
been interpreted to suggest that bilingualism confers resistance to age-related
cognitive decline, at least with regard to inhibition of irrelevant or misleading cues
(Bialystok et al., 2004; see also, Bialystok, 2006; Bialystok et al., 2005; but cf.
Hilchey & Klein, 2011). As already discussed, this protective advantage has been
attributed to the frequent need, on the part of bilingual speakers, to switch between
languages and thus to exercise inhibitory control (Festman et al., 2010; Prior &
Gollan, 2011).
In another investigation that reported cognitive reserve associated with bilin-
gualism, Kav´
e, Eyal, Shorek, and Cohen-Mansfield (2008) conducted a longitu-
dinal study of a large group of older individuals. Participants who were bilingual,
trilingual, or multilingual (according to self-report) were tested on two cognitive
screening measures at three points in time over the course of 12 years. The findings

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demonstrated a strong relationship of number of languages spoken with cognitive
test results across the three test intervals (Kav´
e et al., 2008), again suggesting that
proficiency in more than one language provides cognitive benefits to individuals.
Similar beneficial effects of number of languages were also found in pathological
populations to be reviewed later (i.e., Chertkow et al., 2010).
In contrast to these investigations, Kousaie and Phillips failed to find an ad-
vantage over monolingual peers in a group of older bilinguals on a Stroop in-
terference task (Kousaie & Phillips, 2012). The authors were careful to control
important variables with respect to their participants, including proficiency, age
of acquisition, and sociocultural factors such as immigrant status. Kousaie and
Phillips (2012) were fortunate to have had access to groups of highly proficient
nonimmigrant bilinguals, rare in most previous studies of older bilingual popula-
tions. Given the absence of a bilingual advantage in their experiment, the authors
raise questions concerning the degree to which sociocultural factors might have
contributed to previous demonstrations of such an advantage (Kousaie & Phillips,
2012).
The majority of investigations reviewed thus far have focused on behavioral
measures of cognitive function as a window into neuroplastic changes associated
with bilingualism; only a handful have as yet directly explored neuroanatomical
and neurofunctional patterns in older adult bilinguals. As alluded to in a previous
section, one particularly interesting investigation examined both structural (via
diffusion tensor imaging) and functional (resting-state) connectivity in older adult
bilinguals (Luk et al., 2011; but cf. Cummine & Boliek, 2013). The findings re-
vealed greater white matter integrity (as measured by fractional anisotropy) mainly
in portions of the corpus callosum and the superior longitudinal fasciculi (bilater-
ally) in older bilinguals relative to their monolingual peers. In their investigation
of patterns of resting state connectivity (often reduced in older individuals; Grady
et al., 2010; Park et al., 2010), increased anterior–posterior connectivity emerged in
the group of older bilinguals compared to monolinguals (Luk et al., 2011). These
provocative findings suggest a neuroanatomical basis for the cognitive reserve
attributed to bilingualism in the aging population.
In another recent investigation, Gold, Kim, Johnson, Kryscio, and Smith (2013)
made use of a perceptual task-switching paradigm in a functional magnetic reso-
nance imaging study of younger and older adult bilingual and monolingual par-
ticipants. They found that older and younger bilingual individuals (from a diverse
set of language and sociocultural backgrounds and primarily immigrants to the
United States) performed better than the monolinguals and that the commonly oc-
curring age-related increase in neural activation was reduced in the bilingual older
adults compared to their monolingual peers. The authors interpret these findings
as supportive of the view that bilingualism serves as a buffer against cognitive and
neural decline associated with aging (Gold et al., 2013). However, bear in mind
the caveats raised by the Kousaie and Phillips (2012) study regarding drawing
conclusions without carefully controlling for sociocultural factors. Nonetheless,
the findings of these few investigations are certainly suggestive of a neuroplastic
effect of bilingualism on age-related cognitive decline (for data on young adults,
see also Berken et al., 2012; Klein et al., 2012; Mechelli et al., 2004). As noted
earlier, we believe that these types of investigations will prove a particularly fruitful

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means of advancing our understanding of the relationship between bilingualism,
executive control, and aging.
BILINGUALISM AND PATHOLOGICAL AGING
In this section, we turn to studies of pathological aging that are relevant to the
potential links among bilingualism, executive control, and aging. The purported
increase in cognitive reserve associated with bilingualism has led investigators to
examine its potential clinical significance for the development and (degenerative)
progress of dementia. In a now landmark study, Bialystok, Craik, and Freedman
(2007) hypothesized that the increased cognitive reserve associated with bilingual-
ism has the potential to delay the onset of dementia. To test this hypothesis, they
conducted a retrospective analysis of patients who had been referred to a memory
clinic in the Toronto area for potential diagnosis of dementia. Within that pool, the
investigators identified a subset of participants who had spent the majority of their
lives (at least since early adulthood) regularly using two languages. In comparing
this subgroup with monolingual 4 years on average in the bilingual group but no
difference in the rate of decline subsequent to diagnosis (Bialystok et al., 2007).
Based on these data, the authors concluded that bilingualism helps individuals to
tolerate the disease, though it does not fundamentally alter the pathological brain
process (Bialystok et al., 2007; see also Craik, Bialystok, & Freedman, 2010).
As would be expected, given the exciting nature of such findings and their
potential clinical significance, numerous researchers are now investigating the
generality and reliability of the reported bilingualism effect. In one subsequent
study, Chertkow et al. (2010) questioned whether the bilingual advantage in the
original study arose for one of several reasons, which included the following: the
inclusion of patients with a mixed group of dementias, using a somewhat subjective
measure of age of onset, and potential sociocultural confounds of the bilingual and
monolingual groups (i.e., bilingual immigrants vs. unilingual native Canadians).
In a new investigation, they therefore compared groups of monolinguals, bilin-
guals, and multilingual speakers (each of which included a subgroup of immigrants
to Montreal) who spoke English and French. Their comparisons revealed no effect
of immigrant status on age of diagnosis of dementia; however, there was a small
but statistically significant effect of number of languages spoken on age of diag-
nosis (Chertkow et al., 2010). In comparing only the nonimmigrant subgroups of
English–French bilinguals with groups of English and French monolinguals (who
thus had had similar life experiences), the authors reported that, in contrast to
Bialystok et al.’s (2007) findings, the monolingual groups were diagnosed at later
ages than the bilingual group. Based on these and other analyses of their relatively
large sample, Chertkow et al. (2010) concluded that there was limited support
for bilingualism (i.e., knowledge of only two languages) providing a protective
advantage against the onset of dementia but suggesting that knowledge of more
than two languages (i.e., multilingualism) may confer some measure of cognitive
reserve.
In a similar vein, Gollan, Salmon, et al. (2011) found that second language
proficiency affected age of diagnosis for dementia only in individuals with lower
degrees of education; the authors interpreted their findings as indicative of the

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potential of bilingualism to increase cognitive reserve but only in individuals
who may not already have achieved their maximum potential as a result of other
factors (e.g., high levels of education; Gollan, Slattery, et al., 2011; see also
Sanders, Hall, Katz, & Lipton, 2012). However, one problem with all of these
studies, acknowledged by the authors themselves, is that they are cross-sectional
in nature, rendering conclusions of a longitudinal nature difficult. It may also be
important to examine population-level prevalence and incidence statistics, as well
as ages of onset of dementia/diagnosis in countries outside of North America
where bilingualism is the norm. Population-based studies may make it possible to
statistically control for numerous factors that have the potential to also influence
cognitive capacity, including personal and social factors (education, availability
of health services, stigma associated with diagnosis, etc.).
BRINGING IT TOGETHER
In this selective review focused on bilingualism and executive control in the
aging population, we have considered the foundations of the bilingual advantages
perspective as well as the data that have been gathered in support thereof. It is
clear from our discussion of the available behavioral data that there are numer-
ous tantalizing findings that address the relationship between bilingualism and
cognitive control; however, variability in study outcomes is also prevalent. The
functional neuroimaging data also reveal some inconsistencies and interpretive
dilemmas. While such measures of brain function may be considered somewhat
more directly representative of language and cognitive processing, they are only as
good as the tasks and participant populations included. In our view, investigations
incorporating structural neuroimaging seem to hold more hope of reflecting true
and lasting effects of bilingualism on the brain. In what follows, we turn to a
consideration of how the field may begin to come to grips with the heterogeneity
across individuals, languages, tasks and paradigms, in an effort to advance our
understanding of language and cognitive processing in bilingual older adults.
We focus on three main themes that we believe will lead to advances in our
understanding of bilingualism and aging, and neuroplasticity generally.
Theme 1: Bilinguals differ in ways that matter: let us embrace this variability.
Perhaps the single most important concern that plagues the vast majority of studies
of bilingual speakers, whether younger or older, is the limited control or the system-
atic exploration of the language-learning characteristics and language proficiency
of participants. Many of the existing studies on L2 acquisition and processing
have been confounded by the tendency to include, in a single-subject group, indi-
viduals whose language learning characteristics and histories differ significantly
(e.g., degree of fluency, early vs. late age of L2 acquisition, native language,
country of origin, ratio of L1/L2 usage in daily life, community norms with re-
spect to language switching, subtractive vs. additive bilingual situations) without
explicitly investigating the import of such variables and focusing exclusively on
group-level comparisons. Thus, participant-related heterogeneity both within and
across studies makes it extremely difficult to draw convincing conclusions, and

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even more important, it prevents us from capitalizing on systematic variability
among bilinguals that is likely related to the use of executive control during
language processing (Green, 1998, 2011; Thierry & Wu, 2010). Such differences
among bilinguals are almost completely lost for approaches that emphasize group
differences alone.
For example, Green (2011) describes an array of “behavioral ecologies” that are
possible for bilinguals, which are self-evident to anyone who is bilingual or lives
in a highly bilingual community. Given that every behavioral ecology will recruit
language and executive control in a different way, it is essential for the field to
move beyond simplistic global group comparisons (e.g., monolingual vs. bilingual)
and move toward a more nuanced understanding of how the specific ways that
bilinguals control linguistic knowledge might relate to specific executive control
processes. Consider an informal sampling of the kinds of bilingual behaviors one
can encounter in a highly bilingual city like Montreal. At one extreme, many people
are clear simultaneous bilinguals, having learned both English and French from the
moment they are born, often to parents of mixed or equally simultaneous linguistic
backgrounds. For these people, the behavioral ecology is one of high language
integration and normative mixing, where everyone in a family may speak two
(or more) languages, and what is nonnormative (and thus potentially demanding
with respect to executive control recruitment) is single language use where one
of two highly proficient languages (i.e., two pseudo-L1s, though in practice one
is usually dominant) must be unnaturally suppressed. At the other extreme, many
people are clear sequential bilinguals, having learned a single language in the
home and another in a different social context but then having to function in
an exclusive other-language or highly mixed language contexts for substantial
portions of their day (such is the case for the children of both authors). For these
people, the behavioral ecology is one of normative linguistic exclusivity usually
of the L1, and thus what is nonnormative (and thus potentially highly demanding
with respect to executive control recruitment) is the use of L2 generally and the
need to suppress accidental code mixes of one language into the other, mostly
from the L1 to L2 direction.
In addition to the possible extremes of sequential versus simultaneous bilin-
gualism, there are many points in between. They include bilinguals who are better
at speaking/listening their L2 versus reading/writing and vice versa; bilinguals
who fluently carry on conversations that are highly code-mixed within sentences,
in an intentional rather than unintentional way; those who carry on conversations
where one person speaks consistently in English while the other consistently
responds in French; and bilinguals who know more than two languages and must
integrate knowledge of the third language with knowledge of the other two. The
demands for bilinguals along this entire continuum of language use can be very
different in communities as a function of sociocultural factors, such as whether
the two known languages are equally high status or where one language is higher
status than another (as originally indicated by Peal & Lambert, 1962). The incen-
tive to appear nativelike and to maintain language exclusivity of the high-status
language might recruit executive control differently than in the case where two
languages are equally valued. Moreover, such differences in language status can
operate at a societal or individual level (i.e., whether a given child must speak one

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language at a particular school in order to be accepted by the majority of his or her
peers).
Thus, with respect to language variables alone, there are clear quantitative and
qualitative differences within the bilingual experience that can have major impli-
cations for executive control. In addition, while quantitative differences among
bilinguals (e.g., increased overall L2 exposure of global L2 proficiency) are likely
correlated with particular qualitative spheres of bilingual use (e.g., the likelihood
of participating in highly mixed bilingual interactions), these two dimensions of
bilingualism may not be completely independent. Thus, there could be two indi-
viduals who are matched on global L2 ability or exposure but differ dramatically
in how their exposure/usage is distributed over the course of a day; some may
consistently find themselves in mixed linguistic environments where all people
code-switch intentionally and fluently, whereas others may consistently find them-
selves in compartmentalized linguistic environments, where they spend part of the
day in their L1 and part of the day in their L2. Such differences have potential
implications for the kinds of language control operations bilinguals will engage in
and thus which executive control systems become “exercised” over the long term.
There are also other key sources of systematic variability that hinder coarse
group comparison approaches. As explicitly noted by virtually all players in
the literature, including Bialystok and colleagues, bilingualism is not the only
road to neuroplastic changes to executive control networks within the brain or
to increased cognitive reserve (Bialystok et al., 2012). Thus, it can easily be the
case that detecting any positive influence of bilingualism will be more difficult
in populations who already benefit from other sources of enrichment (e.g., high
socioeconomic status and all the wide-ranging advantages that come with it, along
with many other daily living advantages). Equally important is that monolinguals
differ as well, with some showing “non-native-like” language performance in their
one and only known language (Pakulak & Neville, 2010). Thus, if one must do
group comparisons, it is important to characterize monolingual variability before
understanding the effects of adding a second (or third) language. We know from
the monolingual literature that executive control is important for many aspects of
within-language ambiguity, thus an important question for future work is to disen-
tangle exactly where bilinguals differ qualitatively rather than only quantitatively
from the monolingual case.
Characterizing and accounting for participant variability becomes somewhat
more complex with respect to bilingual older adults. One must also be cautious
about numerous other participant-related factors, including sensoriperceptual de-
clines, changes in speed of processing and motor response times, psycho- and
neurotropic medication use, and more. In addition, one must also think concretely
about the ways in which bilingual older adults necessarily differ from any bilingual
younger adult control group. For example, is it enough to simply control overall L2
proficiency across an older and younger bilingual group? Maybe not. There may
be fundamental differences in the bilingual experience between older and younger
adults that pertain to how members of each group experienced their bilingualism in
a larger societal or historical context. Turning again to examples from the authors’
own geographic region (Montreal), attitudes toward bilingualism and the use of
English versus French have changed enormously over the lifetime of any bilingual

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older adult we can now recruit into the lab, ranging from almost total linguistic
balkanization, where most people spoke English and French was marginalized
(prior to the Quiet Revolution), to societal changes that led to an almost opposite
situation where French is the language of government and English is the minority
language with bilingualism on the rise (after the Quiet Revolution), to today where,
at least in Montreal, almost all people are fluent in both French and English and
bilingualism is commonplace. Thus, by definition, any older adult recruited into
our lab will have sampled every sociocultural point along this timeline, although
their formative language learning experience may be specific to a particular era,
perhaps corresponding to the time they were in school. In contrast, any younger
adult recruited into a lab will have only sampled one endpoint along this timeline,
by definition. Thus, to the extent that differences in the bilingual experience relate
to sociocultural factors, it will be impossible to perfectly match older and younger
bilinguals within certain bilingual communities.
How are we to reasonably handle all of this variability? At the very least, we must
adequately characterize it both in terms of self-report and objective measures where
possible (and to do the same for item-level variability in our stimulus materials
in equally robust and thorough ways). Then, we ought to use this information in
evaluating the outcome of our experiments (e.g., did our effect of interest vary as a
function of L2 ability or some other dimension). While many studies examine such
factors, many do not, and such information is highly valuable. As a second step, the
field at large may greatly benefit from large-scale, epidemiological approaches that
systematically identify the component ways that the bilingual experience varies
globally and then statistically reduce this undoubtedly high dimensional space to a
smaller number of core dimensions. This may require efforts that span laboratories
and geographic locations. If such cross-laboratory approaches are not feasible
in the short term, similar approaches could occur within the context of single
studies that have sufficiently large sample sizes (for the pitfalls of small sample
sizes in making bilingual vs. monolingual comparisons, see Kroll & Bialystok,
2013).
As a third step, it may be time to reconsider our traditional statistical approaches,
such as repeated measures analysis of variance, so that our research questions and
designs are not limited by our statistical tools. To this end, an increasing number
of researchers within psycholinguistics are using regression-style or other multi-
variate approaches that do not force experimenters to compress natural variability
into two or three discrete categories. Thus, many language researchers are now
turning to linear mixed effects regression modeling in studies of bilingualism
(Dijkstra et al., 2010; Gollan & Goldrick, 2012; Pivneva et al., 2012; Van Assche,
Duyck, Hartsuiker, & Diependaele, 2009; Whitford & Titone, 2012), which while
not entirely straightforward (Baayen, 2008; Barr, Levy, Scheepers, & Tily, 2013)
allows researchers to examine how both participant-level and item-level variabil-
ity simultaneously affect dependent variables of interest. Similar approaches have
also been used within the neuroimaging community as attested by advances in
statistical techniques such as partial least squares analyses (McIntosh, Bookstein,
Haxby, & Grady, 1996). We believe that such approaches, which ultimately change
the way we can think about our experimental designs, will be absolutely crucial
for characterizing how bilingualism alters the structure and function of the brain.

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They will be especially vital for understanding bilingual older adults, who vary
within and between groups in other key ways as well.
Theme 2: Do bilinguals have advantages because they had them to begin with? Let
us better distinguish cause from consequence.
One common argument regarding questions concerning the effects of bilingualism
on the brain, is that people don’t generally choose to be bilingual but rather they
are born to families whose geographic locations or personal circumstances put
them into a bilingual situation (e.g., Bialystok et al., 2012). Given this view, any
correlation one sees between being bilingual and other cognitive capacities implies
a degree of causality that may not be considered for other types of overlearned skills
(e.g., learning to play a musical instrument, training to become an elite athlete).
The vast majority of work linking bilingualism to domain-general cognition is
correlational, relying on inherent differences among bilinguals the moment they
walk through the laboratory door.
There may be truth to this assumption. Children do not actively choose or self-
select to be raised in a bilingual context. They are either born to such a context or
they find themselves in such a context due to the choices of their parents. Many
children raised in exclusively English-speaking Montreal households (including
those of the authors and many other Quebec immigrants) are required to attend
French school by law. Thus, these children have the great fortune of being im-
mersed in a bilingual social context and will undoubtedly become bilingual. If
they reap any cognitive benefits from being bilingual, it is not likely that their
brains were already constructed that way ahead of time. However, this may not be
the whole story, and assumptions regarding preexisting capacities and causality
might deserve greater empirical scrutiny. For example, although a child may
be serendipitously placed into a bilingual context and may become functionally
bilingual, it remains possible that the kind of bilingual that they become may vary
as a function of preexisting cognitive capacities, which in turn influence the social
experience they later seek. Thus, a child with an outstanding working memory
or executive control capacity may be more likely to put herself or himself into
communicative situations that involve intensive L2 exposure or language mixing
(e.g., choosing to spend equal or more amounts of time with L2-speaking peers
in the playground vs. L1-speaking peers). It is conceivable that small, local social
decisions of this sort could compound over time such that people who end up being
better bilinguals in older adulthood were actually more cognitively flexible to begin
with. Such a possibility is suggested by the Nun Study previously described (e.g.,
Snowdon et al., 1996). Here, the women who had greater cognitive resiliency in
older adulthood were exactly those women who had had greater language skills
in young adulthood.
Thus, studies that move beyond correlational approaches and that directly test
the causes and consequences of bilingual proficiency and style are essential.
These are of course difficult to do, as they would involve longitudinal studies
over large time scales, or more experimentally oriented studies of the effects of
second language training on cognition, or vice versa. Although many longitudinal
studies exist regarding bilingual acquisition (Genesee, 2009, 2010), these are

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typically time limited, spanning only a few years during childhood at most. Until
funding agencies award research grants with multidecade terms, within-participant
longitudinal studies of the kind necessary may not be feasible. However, studies
that investigate the causes and consequences of bilingualism in other experimental
ways, such as the impact of language training on cognitive control, or more
recently, the impact of executive control training on language, may be of great
use.
Some studies have shown training-related transfer from L2 learning to executive
control (Martensson et al., 2012); however, testing the question in this direction
requires intense L2 learning situations and unusually motivated, self-selected
learners who may already differ in cognitive control. Other work has looked at
the effects of formal instruction in simultaneous interpretation (Christoffels, 2006;
Christoffels & de Groot, 2004; de Groot & Christoffels, 2006; Elmer, Meyer, &
Jancke, 2010; A. Green, Nicholson, Vaid, White, & Steiner, 1990; Macizo & Bajo,
2006) and could presumably follow people throughout training to assess whether
the ability to switch between two languages while engaging in simultaneous
interpretation would enhance domain-general aspects of nonlinguistic cognitive
control. However, here again, there is a possible issue of self-selection in that
the individuals who survive intensive training in simultaneous interpretation may
have had excellent executive control to begin with. However, if bilingualism and
domain-general cognition exercise the same neurocognitive substrate, transfer
should also occur from the direction of executive control to language processing.
Consistent with this idea, recent work suggests transfer from conflict resolution
training to L1 syntactic ambiguity resolution (Hussey & Novick, 2012). We believe
that more studies of this kind, which involve true experimental manipulations,
will be crucial for working out the many issues raised by the notion of bilingual
advantages in both younger and older adults.
Theme 3: Is it really “bilingual advantages” we are after? Let us reframe the issue to
address life-long neuroplasticity.
In recent years, a great deal of ink has been spilled, and perhaps many voices may
have gone hoarse, debating the existence or nonexistence of bilingual advantages
in executive control in older adults and in bilinguals generally. As alluded to
previously in this paper and by others, this debate is situated within a particular
sociocultural and scientific context. In a sociocultural sense, in the past, and
in many different parts of the world even today, being bilingual was seen as a
cognitive liability. Such a viewpoint has serious implications for how parents
decide to raise their children and for how societies make decisions concerning
resource allocation to bilingual education (i.e., whether it should be done at all,
if so, at what age should it be introduced). Prior to about 10–15 years ago, the
scientific study of bilingualism was seen as marginal to mainstream concerns
about the psychology and cognitive neuroscience of language and as a specialty
area. In recent years, times have changed, and rightly so given the number of
people worldwide who speak more than one language, which is often claimed to
exceed the number of people worldwide who speak only one language. This shift
in both sociocultural and scientific attitudes about bilingualism has arisen from

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some of the important empirical and theoretical work beginning with Peal and
Lambert (1962) and continuing through the current research era that is intensively
focused on whether bilingualism leads to cognitive benefits generally. Thus, from
a sociocultural and scientific standpoint, the search for bilingual advantages has
done a great service to the field at large by shining a light on the remarkable
capacities of bilinguals and how these capacities relate to more general cognitive
capacities.
Of course, the issues raised here go beyond mere debate because there is actual
empirical evidence to be considered. As we have seen, the question of whether
bilinguals are advantaged compared to monolinguals is hard to answer with a
simple “yes” or “no,” given existing empirical evidence. Many studies show
bilingual advantages across the life span, particularly in children, older adults,
and during pathological aging, and the findings of many of these studies are quite
compelling. Other studies show no advantage or, at least, differences in findings.
Consequently, the clearest answer thus far involves the somewhat unsatisfying and
all too common “it depends” response, where there are many candidate differences
across studies, including the nature of the tasks; differences among bilinguals,
monolinguals, or between groups; and the like. There is also the general difficulty
associated with the interpretation of null effects: did they arise because there truly
is no difference, or was there a lack of power, or an odd sampling issue?
However, we believe that the larger problem is that if one asks a simple question
about a complex phenomenon, one is likely to get a simple (and unsatisfying)
answer. Thus, if we ask different and potentially more sophisticated questions
about bilingualism, as many people are now doing, we may come upon more
interesting and clearer answers, or at the very least fruitful directions for future
work.
For example, what follows are open questions about which we are most in-
trigued. Which aspects of using more than one language induce neuroplastic
changes in the human brain? Are there parallels in monolingual language pro-
cessing, or are there certain things that bilinguals do that have no parallel with
monolinguals? Are differences with respect to language processing among bilin-
guals and compared to monolinguals qualitative or quantitative in nature? Are
these differences and their relation to executive control static over the life span, or
do they vary in systematic ways? Are there fundamental parallels to nonlinguistic
behaviors, such as musical expertise or other complex motoric behaviors? What
can the different aspects of bilingual language function tell us about executive
control generally? Are certain bilingual behaviors, such as mixing, always more
taxing cognitively, or does it depend on the way in which a given bilingual in-
dividual acquired knowledge of his or her multiple languages or on differences
between the structures of the languages in question? How do multiple contribu-
tors to cognitive reserve, including bilingualism, accumulate within individuals?
Does being bilingual have less of an impact if someone is already engaged in
high-cognitive reserve activities? One senses that questions arising from trying
to understand failures to replicate a bilingual advantage may be potentially more
interesting than clear demonstrations of the effect itself! Thus, from the standpoint
of generating new lines of research, the bilingual advantages hypothesis has been
an unmitigated success. Let us build upon this success by moving into the next

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phase of inquiry, which is to dig deeper regarding the specific points of contact
within and across language and general executive control domains. Let us move
beyond “yes” or “no” questions.
FINAL REMARKS
At the outset of this paper, we noted that with advancing age comes a conflict
between a vast amount of knowledge and experience accumulated over many
years and the natural structural and functional brain changes that occur in later
life, tending to lead to decrements in cognitive capacities. Throughout the discus-
sion we have highlighted investigations that suggest that experience-dependent
plasticity yields both short- and long-term changes. In particular, following Bia-
lystok and others (Bialystok & Craik, 2010; Bialystok et al., 2004, 2007), lifelong
bilingualism (among other factors) may contribute to the development of cognitive
reserve and thus improve cognitive and linguistic processing efficiency in older
adults. One important question that has not been addressed in the bilingualism
literature, in contrast to other domains focused on experience-dependent plasticity
in aging (e.g., exercise, see Voss, Nagamatsu, Liu-Ambrose, & Kramer, 2011; cog-
nitive training, see Lustig, Shah, Seidler, & Reuter-Lorenz, 2009; Noack, Lovden,
Schmiedek, & Lindenberger, 2009) is how one might translate these findings to
recommendations for individuals or social policies. Should we suggest that, upon
retirement, everyone should learn a second language (much like recommending an
active and engaged lifestyle in older adulthood is now touted in the popular media)?
Is it too late at that point for neurocognitive benefits to accrue? Should we instead
recommend that multiple languages be taught from the earliest possible ages,
providing the greatest potential for neuroplastic effects? Based on the relatively
limited data collected to date, it is clearly too early to draw definitive conclusions
or recommend large-scale changes to social policy regarding the consequences of
bilingualism. Nonetheless, the increasing number of studies demonstrating both
structural and functional neural alterations associated with bilingualism hold great
promise that in the near future we may be able to identify those aspects of language
learning that are most crucial to the development of cognitive reserve and thus
have the greatest potential to influence quality of life for older adults.
In the literature on the influence of exercise on neuroplastic changes in aging,
research has suggested that not only does exercise induce the growth of nerve
cells and blood vessels, it appears to increase production of important chemicals
in the brain, including brain-derived neurotrophic factor, which may be important
in the survival and repair of neural tissue (e.g., Voss et al., 2011). Similarly, in the
domain of cognitive training, of particular interest are investigations demonstrating
transfer effects from the trained domain to other aspects of cognition (e.g., Lustig
et al., 2009; Noack et al., 2009) and associated underlying neural changes (e.g.,
Jones et al., 2006; Kelly & Garavan, 2005; Klingberg, 2010). It is important
to note that investigators in these domains are beginning to highlight the crucial
importance of examining individual differences in the effects of training in order to
truly understand the underlying mechanisms and explain why certain individuals
benefit more from specific training than do others (Garrett, MacDonald, & Craik,
2012). As research in the field of bilingualism and aging continues to grow, we

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suggest that more interdisciplinary studies are needed that can begin to tackle
the mechanisms underlying the neuroanatomical and neurophysiological changes
associated with being bilingual.
ACKNOWLEDGMENT
The order of authors is alphabetical. Both contributed equally to the paper.
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