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Masters Thesis (M2) in Cognitive Science EHESS–ENS–Paris 5

The Effect of Bilingualism on Cognition: Evidence from Early and Late Bilinguals

by Chavie Fiszer

Conducted under the guidance and supervision of Christophe Pallier1

September 2008 1

CNRS

The Effect of Bilingualism on Cognition: Evidence from Early and Late Bilinguals Chavie Fiszer Abstract Previous research demonstrates that bilinguals have an advatange over monolinguals in several extra-linguistic domains. Using the Simon Task, which putatively measures inhibitory control, Bialystok, Craik, Klein, and Viswanathan (2004) illustrate that early bilinguals are faster and show less of a Simon effect than monolinguals, a disparity that becomes more pronounced in late adulthood. The posited mechanisms responsible for this advantage is enhanced inhibitory control and selective attention, due to life long daily use of two languages. However, there is some contention regarding both which cognitive functions are implicated in the Simon task and whether inhibitory control is the major mechanism underlying bilingual language processing. Previous studies have focused on highly proficient early bilinguals who may mobilize subtly different processes compared to other bilingual groups. The present study attempts to elucidate the mechanisms responsible for this bilingual cognitive advantage by comparing early and late bilinguals on both the Simon task and the Garner task, which measures selective attention, without requiring the inhibition of a response. In addition, results on the Simon task are reinterpreted to uncover an event file effect, a measure of cognitive flexibility (Hommel, 2004). Our question is: Can a second language learned in adulthood bestow the same cognitive advantage as one learned early in life? We predicted that bilinguals would demonstrate less of a Simon effect and of a Garner effect than monolinguals, with differential results for the two bilingual groups. We also expected that bilinguals would show less of an event file effect than monolinguals. We found main effects for age and congruency on the Simon task, an event file effect across all groups which interacted with age, and no Garner interference for any groups. Limitations of the present study are addressed. Further directions to reveal the dynamics of the bilingual mind are suggested.

Keywords: bilingualism, language processing, inhibition, selective attention, age of acquisition, critical period, aging, cognitive decline, executive functions, Simon effect, Garner interference, event file, feature binding, creativity

Contents

I

Introduction

1

1

Who is a bilingual? . . . . . . . . . . . . . . . . . . . . . . . .

2

1.1 AoA, proficiency, and exposure . . . . . . . . . . . . . . . . .

3

1.1.1 Critical Period Hypothesis . . . . . . . . . . . . . . . .

3

1.1.2 Competition and Interference . . . . . . . . . . . . . .

5

1.1.3 Proficiency above all? . . . . . . . . . . . . . . . . . .

6

1.1.4 Confounding factors . . . . . . . . . . . . . . . . . . .

7

1.2 Summary: bilinguals . . . . . . . . . . . . . . . . . . . . . . .

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2

9

Bilingual Language Processing . . . . . . . . . . . . . . . . . .

2.1 Selection & Control . . . . . . . . . . . . . . . . . . . . . . . . 10 2.1.1 Language selective models . . . . . . . . . . . . . . . . 10 2.1.2 Language non-selective models . . . . . . . . . . . . . 11 2.1.3 Inhibition or Activation? . . . . . . . . . . . . . . . . . 13 2.2 Summary: Bilingual Language Control . . . . . . . . . . . . . 14 3

Executive Functions & Bilingualism . . . . . . . . . . . . . . . 15

3.1 Across the life span . . . . . . . . . . . . . . . . . . . . . . . . 16 3.1.1 An inverted U . . . . . . . . . . . . . . . . . . . . . . . 16 3.1.2 Aging Adults . . . . . . . . . . . . . . . . . . . . . . . 17 3.2 Use It or Lose It . . . . . . . . . . . . . . . . . . . . . . . . . . 19 3.2.1 Physical Exercise . . . . . . . . . . . . . . . . . . . . . 19 3.2.2 Mental Exercise . . . . . . . . . . . . . . . . . . . . . . 19 3.3 Bilingualism as a lifestyle factor . . . . . . . . . . . . . . . . . 20 3.3.1 Bialystok’s children . . . . . . . . . . . . . . . . . . . . 21 3.3.2 Inhibitory Control . . . . . . . . . . . . . . . . . . . . 22 3.3.3 Feature Binding . . . . . . . . . . . . . . . . . . . . . . 23 3.3.4 Attentional Control . . . . . . . . . . . . . . . . . . . . 27 3.4 Summary: Executive Functions . . . . . . . . . . . . . . . . . 28 4

II

General Summary: The Present Study . . . . . . . . . . . . . 30

Method

31

4

III

Results

34

IV

Discussion

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4.1 Limitations . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 4.2 Future directions . . . . . . . . . . . . . . . . . . . . . . . . . 42

V

VI

VII

References

Acknowlegements

Appendix

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57

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Part I. Introduction Numerous experiments demonstrate that early bilinguals have an advantage over monolinguals in several extra-linguistic domains. In particular, bilingual children and young adults score higher on measures of creativity (Jacobs & Pierce, 1966; Kessler & Quinn, 1987), divergent thinking and imagination (Ricciardelli, 1992), problem solving (Seceda, 1991), and cognitive control (Costa, Hernández, & Sebastián-Gallés, 2007; Bialystok & Martin, 2005; Bialystok & Craik et al., 2005, 2004; Bialystok 1999). Bialystok, Craik, Klein, and Viswanathan (2004) found that bilinguals are faster than monolinguals on the Simon task, and exhibit less of a Simon effect, evidence of enhanced inhibitory control. Furthermore, the disparity between these groups increased with age. Impaired inhibition has been specifically cited as being responsible for age related deficits in mental activity (Hasher, Lustig, & Zacks, 2006; Bedard, Nichols, Barbosa, et al., 2002; Craik & Bialystok, 2005). Life long bilingualism appears to afford protection from age related cognitive decline (Bialystok Craik, & Freedman, 2007). Why might bilinguals have these advantages? Researchers agree that the lexical representations of a bilinguals’ two languages are activated simultaneously when using any one of them (Goldfarb & Tzegelov, 2008; Colomé, 2001; Dijkstra, Grainger, & van Heuven 1999; Costa, Miozzo, & Carmazza, 1999). If both lexicons are active, how does a bilingual overcome interference from the non-target language? One model of bilingual language selection claims that bilinguals achieve fluency in any one language by suppressing the non-relevant language using the executive functions of attention and inhibition. Enhanced inhibitory control due to life long daily use of two languages is believed responsible for the bilingual advantage such as is demonstrated on Simon task (Bialystok & Craik et al., 2004, 2005). However, it is not certain that active suppression of one language is required for bilingual speech production. There is substantial evidence for alternate models of language selection (Finkbeiner, Gollan, & Caramazza, 2006; Costa, La Heij &, Navarrete, 2006; Costa, Miozzo, & Caramazza,

1 Who is a bilingual?

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1999). Furthermore, research illustrates that inhibition may be dissociated into different types of inhibitory processes, which do not follow the same linear decline in aging compared to other cognitive functions (Borella, Carretti, & De Beni, 2008; Bedard et al., 2002; Cepeda, Kramer, & Gonzales de Sather, 2001). It is unclear which aspects of inhibitory control the Simon task actually measures or whether or not other mechanisms interact with an individual’s performance (Hommel, Proctor, & Vu, 2004; Ivanoff, Klein, & Lupiáˇ nez, 2002; McKee, Christie, & Klein, 2007). It is also crucial to note that bilinguals are a much more varied group than monolinguals. They may differ in respect to age of acquisition, proficiency, the context within which they have learned or use their languages, and cultural identity (Grosjean, 1998, 1989; Bialystok, 2007b). Individuals who learn a second language late in life rarely achieve native-like fluency compared to those who learn their languages in childhood, but evidence from behavioral and brain imaging studies are equivocal as to whether there is any difference between bilinguals once they are matched for proficiency. In the Bialystok & Craik et al., (2004) study bilinguals were categorized as having learned a second language before the age of six. The next question must be: Can a second language learned in adulthood bestow the same cognitive advantage as one learned early in life? To answer this question we must address three issues: (1) how do we define who is a bilingual, (2) what cognitive functions are implicated in the major hypotheses of bilingual processing, and (3) how do executive functions change across the life cycle and how are they impacted by life style factors such as bilingualism.

1

Who is a bilingual? There are many ways to become a bilingual (Michael & Gollan, 2005).

Some individuals are raised in a bilingual household, others speak one language in the home and another in school. One may immigrate to a predominately monolingual country and be required to learn a new language and a new culture, another may grow up in a bilingual society and identify with one culture. Languages may be used exclusively in either an informal or an official context, and one may be considered socially inferior (Bialystok,


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2007b). An individual may be verbally proficient in two languages, but illiterate in one of them. Over a life time, the balance of dominance between languages may shift from one to the other (Meisel, 2007; Hernandez & Kohnert, 1999). Grosjean (1989) maintains that a speaker need not be perfectly balanced in her two languages to be classified as bilingual, only that she use more than one language on a regular basis. Despite the breadth of variables inherent in a linguistic history, research has focused on three aspects of bilingualism: age of acquisition (AoA), proficiency, and amount of language use. In order to classify a bilingual we will therefore assess these three major variables, keeping in mind that these interact with each other and may be influenced by other factors as well.

1.1

AoA, proficiency, and exposure

1.1.1

Critical Period Hypothesis

Meisel (2007) remarks that the ease with which children can learn multiple languages with mere exposure supports the idea that we are programmed for multilingualism. This appears to be the case when languages are learned simultaneously in early childhood as two L1s (DeHouwer, 2005). However, given the rarity that an individual can be taken as a native speaker in more than one language, we must allow that there are some limitations to the linguistic system. One view is that there is a critical period within which a second language must be acquired in order to attain native-like performance. A critical period entails a firm window when acquisition is optimal, a rise to a plateau, followed by a steep drop where acquisition is no longer possible. Classic examples are binocular deprivation and song learning in birds (Hernandez & Li, 2007; Katz & Crowly, 2002). The limit for second language acquisition has been fixed at various points between the ages of two and fifteen (DeKeyser & Larson-Hall, 2005; Hakuta, Bialystok, & Wiley, 2003; Flege, 1999; Bialystok & Miller, 1999). But the opposite argument can be made as well: given that there are some examples, though few, of individuals who have attained native-like performance of a language learned well into adulthood, we cannot accept


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the strong version of the Critical Period hypothesis (CPH). There may well be a critical period for L1, but it is unlikely that this is true in the same way for L2 (Birdsong, 2005; Hakuta, Bialystok & Wiley, 2003). Instead of a sharp fall, ease of learning and expertise in final attainment of L2 declines very gradually across the life span with no end point (DeKeyser & LarsonHall, 2005; Hakuta et al., 2003; MacWhinney, 2005; Flege, 1999). Some studies show that adults initially learn a second language faster and then slow down with large variances in final attainment, while children start slowly, then learn quickly and achieve better results (Dekeyser & LarsonHall, 2005). Training programs have illustrated there is still substantial plasticity for the acquisition of language in adulthood, as measured by neural sensitivity and behavioral performance (Zang & Wang 2007; Osterhout et al., 2008). The limited final results seen in most adults may come from different sources. Maturational factors not specifically related to language acquisition that lead to a general decrease in the ability to learn, interference from previously acquired language patterns, and social and cultural factors may all play a role. Hernandez and Li (2007) tackle the first point by comparing second language acquisition (SLA) to skills in the domains of music and sports. They show that AoA effects are pervasive, primarily in the sensori-motor domain, which may be why certain aspects of SLA are more affected than others. For example, the window for attaining pure pitch in music appears to close at age seven (Hernandez & Li, 2007). Similarly, a decline in some elements of learning may leave its mark as a foreign accent in those who learn a language later in life, in spite of years of practice and high proficiency. Indeed, syntax, morphology, and especially phonology are harder to perfect than lexical and semantic processing (Taube-Schiff & Segalowitz, 2005). Late learners show increased neural activity in areas of motor planning and articulatory effort when processing grammatical violations even when matched for proficiency with early bilinguals (Weber-Fox & Neville, 1996 in Hernandez & Li, 2007). In addition, late learners typically have trouble with irregular items, showing more diffused neural activity compared to early bilinguals. There is less difference in semantic processing which is shared between lan-


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guages and therefore less affected by AoA (Hernandez & Li, 2007; Francis, 2005). This is in accord with Ullman’s declarative/procedural model of language acquisition. Ullman (2001) distinguishes between a memorized lexicon and a computational grammar. The former is a matter of declarative memory, the latter of implicitly learned rules. This distinction is tied to the accepted division between two memory systems: declarative and procedural. Ullman claims that late L2 learners no longer have access to the procedural system and its dedicated neural circuits which underlie native and early language acquisition, and turn to declarative memory to represent their L2–a less efficient strategy for language processing. 1.1.2

Competition and Interference

Recent behavioral and neuroimagery studies contradict Ullman’s view that L1 and L2 are subserved by distinct systems. Once high proficiency is reached, bilinguals use identical areas for both their languages (Abutalebi, 2008; Abutalebi & Green, 2007) . Abutalebi (2008) observes that the question is not so much whether L1 and L2 share cortical representations but that acquiring a new language changes the entire language network. This conforms with the competition model of SLA: adapting to a new language creates challenges that has little to do with a critical period but everything to do with learning a new language (MacWhinney, 2005; Abutalebi & Green, 2007). Cues carried over from one’s native language makes learning a new one difficult when there is a mismatch. This interference may occur across phonological, lexical, and syntactical domains. The acoustic characteristics of the native language are continually self-reinforced leading to perceptual interference with a second language (Zang & Wang, 2007). Even early highly proficient bilinguals demonstrate dominance of one of their languages on a measure of vowel categorization, a surprising example of non-plasticity in one aspect of language processing (Sebastián-Gallés & Bosch, 2005; Pallier, Bosch, & Sebastián-Gallés, 1997). Immigrant children who continue to speak their native language in the home may speak their L2 with an accent even having arrived in their new country as early as the age of four


6

(Flege, 1999). In contrast, adopted children who have been completely cut off from their native language and culture were able to attain native-like performance in their new language even when exposure to L2 began as late as age eight (Pallier, Dehaene et al., 2003). Birdsong and Mollis (2000) conclude that it is degree of language use and the specific L1-L2 pairing that is responsible for the final level of attainment. Likewise, a second language also impacts upon the first. Flege (2005) brings evidence of how phonetic categories converge after years of bilingual speech in French-English and English-French late bilinguals. After many years of using their second language, immigrants who maintain an accent in their L2 often gain an accent in their native language as well (Flege, 1999). Interference is not restricted to phonotactics. Proverbio, Adornia, and Zani (2007) demonstrate that with each additional language acquired, access to each will be slowed, including the native language, implying a limited capacity to the linguistic system. However, interference appears to play less of a role when the languages are learned in childhood. In a highly proficient group of multilingual simultaneous interpreters, early multilinguals were faster in a naming paradigm than the late multilinguals. 1.1.3

Proficiency above all?

Despite the observed differences, Abutalebi and Green (2007) review numerous brain imaging studies and conclude that once bilinguals are matched for proficiency, there is little difference between groups: bilinguals use the same areas for the same tasks in both languages independent of AoA. However, few of the studies cited compare groups of early and late bilinguals matched for proficiency within the same experimental design. Those that do, find that there are subtle differences that may be attributable to AoA. Late proficient speakers demonstrate more extensive superior temporal gyrus (STG) activity for their native language than for their L2. Finer tools may better illuminate the differences in the future. Presently, the most substantial differences between speakers remain proficiency related. Increased activity in the prefrontal cortex (PFC) is seen mostly in L2 low proficiency


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learners, an indication of the increased need for cognitive control. Chee, Soon, Lee, and Pallier (2004) demonstrate that unequal bilinguals showed greater anterior cingulate cortex (ACC) activation while proficent participants showed more efficient phonolongical processing even though behavioral results were comparable in both groups. In other words, the more skilled the speaker, the more automatic the processing, and the less effortful it appears. This is mirrored by changes in the brain as proficiency increases, such as the convergence of L1 and L2 and reduced recruitment of the PFC and the ACC. Segalowitz (2007; Segalowitz & Frenkile-Fishman, 2005) concentrates on within language performance and concurs: with increased mastery there is a qualitative jump where access fluidity is no longer a simple increase in speed, but a transition into more efficient, automatic processing. Similarly, there may be a threshold of knowledge that makes it possible for the Universal Grammar (UG) switch to initialize the parameters of the new language (Klein, 1995). Furthermore, a threshold of proficiency must be breached in order to reap the cognitive benefits of bilingualism. Ricciardelli (1992) found that higher creativity was only observed in children who were truly proficient in both their languages. The question is, once high proficiency is reached, is native-like performance in all aspects of language required to enjoy the cognitive benefits of bilingualism? In other words: Can this jump take place even with late learners? 1.1.4

Confounding factors

Although the CPH is untenable in it’s strictest sense, sufficient observational, behavioral, and imaging studies attest to a real if subtle difference between highly proficient early and late learners. Different cognitive strategies may underlie L2 processing for different kinds of bilinguals at different moments in life and different degrees of exposure (MacWhinney, 2005; DeKeyser & Larson-Hall, 2005). These may be due to more efficient cortical development when languages are learned early in life, but it does not rule out the possibility that a cognitive advantage can be reaped by late learners


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as well, though this may be due to different mechanisms. A major problem in categorizing bilinguals is that AoA and proficiency factors overlap (Proverbio et al., 2007). In a recent publication Bialystok, Craik, & Ruocco (2008) showed a graded effect linking degree of bilingual experience and better performance on a visual classification task. But in this study the balanced bilingual group had also learned their second language at an earlier age than the moderately bilingual group. Proficiency is driven by practice, or daily use, and the latter group used their L2 only rarely. AoA, proficiency, and exposure were therefore confounded. Ideally participants should be matched for proficiency and use, and differ only in regards to AoA. However, it must be conceded that both in early and late bilinguals, one language may be dominant. Cultural identity and emotional salience of each spoken language should also be assessed in order to ascertain any impact of these variables. Pallier et al. (2003) noted that the adopted group showed greater inhibition to Korean, their original native language, than the native French group, indicating that emotional factors may play an important role in language processing. Another possible confound when studying bilinguals is socioeconomic status. Morton and Harper (2007) raised this issue in an attempt to replicate Bialystok’s work but did not reach conclusive results.

1.2

Summary: bilinguals We have reviewed three factors which interact in a bilingual speaker.

Level of proficiency depends on exposure and practice, while AoA may assure higher attainment of proficiency and more efficient processing. Therefore it is crucial to examine different kinds of bilinguals with different linguistic histories, alternately focusing on each of these variables in order to discover the reason for the bilingual advantage seen in so many studies. One approach is comparing bilinguals of varying levels of proficiency to examine the changes that occur as skill increases. However, for a cognitive advantage to spill over into general non-linguistic domains, bilingual performance requires at least moderate proficiency and years of exposure, keeping in mind

2 Bilingual Language Processing

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that expertise attained at different ages may call upon different mechanisms. The best course then would be to examine bilinguals with comparable levels of proficiency and exposure, with AoA the differentiating variable. Taking into account the various views regarding AoA constraints, in the present study early bilinguals will be classified as having been exposed to a second language before the age of ten, and late bilinguals as those who were exposed to L2 after the age of fifteen. Cultural identity issues and SES must also be examined as possible confounding variables. In order to understand how and which cognitive functions are impacted by a bilingual life style, we will now examine the major hypotheses of bilingual language processing.

2

Bilingual Language Processing There are several levels of processing where a bilingual’s languages may

interact. Researchers agree that a speaker’s multiple languages draw meaning from shared semantic representations (Francis, 2005; Proverbio et al., 2007), but differ as to whether a bilingual’s two lexicons compete for selection. The Revised Hierarchical Model (Kroll & Stewart, 1994) postulates that in early L2 acquisition, a learner’s L1 mediates between the new words and their meanings, but once proficiency improves L2 draws directly from the semantic pool and access will be faster. Various paradigms have been used to show that both languages of a bilingual speaker are active when using one. Colomé (2001) showed that highly fluent Catalan-Spanish bilinguals took longer to reject a phoneme as Catalan in a Spanish word than in a control word, meaning that both languages were activated. Dijkstra, Grainger, and van Houven (1999) found facillitory effects for words that shared orthographic and semantic similarity between languages, and reduced latencies when there was phonological overlap. Using picture-naming tasks, Costa and his team (Costa and Santesteban, 2004; Costa, Miozza and Caramazza, 1999) demonstrate facilitation and disruption effects between languages. These behavioral results are bolstered by brain imaging studies which demonstrate not only shared semantic networks, but shared cortical activation for L1 and L2 (Abutalebi, 2008 for a review). The question


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then is how one language is selected over another, and how this selection is maintained. There are number of models of bilingual language processing which can be classified as either language selective or language non-selective. A different manner of language selectivity can be assumed for either comprehension, production or both. Beyond this division, models may present divergent mechanisms of language control, such as contextual cues or active inhibition of the non-target language.

2.1

Selection & Control

2.1.1

Language selective models

Language selective models hypothesize that language mode is included with the preverbal message so that the non-target language, although active, does not compete for selection (Finkbeiner, Gollan, & Caramazza, 2006; Costa, La Heij, & Navarrete, 2006; Costa, Miozzo, & Caramazza, 1999). For example, the intention to say something in French already precludes any competition from English, just as for a monolingual, the choice of a colloquial register eliminates competition from the language’s formal vocabulary. The words chosen will match meaning and style. (La Heij, 2005; Costa, Albareda, & Santesteban, 2008; Finkbeiner, Gollan, & Caramazza, 2006). Costa and his team maintain that a bilingual’s two lexicons are integrated but do not compete for selection. Most of their evidence is gleaned from a picture-naming paradigm using pairs of pictures with super-imposed words written in either of two languages. Identical elements taken from both languages are presented to bilinguals and naming latencies are measured. The important condition is when the name on the picture is in the non-target language. If languages compete, participants should be slower in naming the item because they must decide between their two languages. If latencies are faster than the control condition, it means that both the word and the picture activate the target word and no others are competing for selection. Bilinguals have consistently been found faster. This cross-language identity facilitation effect is taken as evidence that the selection mechanism considers only the lexical nodes of the target language (Costa, Miozzo, &


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Caramazza, 1999; Costa, Santesteban, & Ivanova, 2006). Hermans (2004) questions whether this paradigm is sensitive enough to support this hypothesis, but recently new evidence has been gathered with a Stroop paradigm (Costa, Albareda, & Santesteban, 2008). Outside the laboratory, the context in which a word is presented or in which production is intended or required is believed sufficient to restrict access to that language by increasing activation to the relevant one (Finkbeiner et al., 2006). Knowing this text is in English allows the Dutch/English bilingual to read without becoming confused by cross-linguistic homonyms. Schwartz and Kroll (2006) demonstrate that even less proficient bilinguals can use context to impede cross-linguistic interference, much as monolinguals use sentence context to interpret ambiguous words.

2.1.2

Language non-selective models

Most language non-selective views maintain that the non-relevant language must be actively suppressed in order to speak in the target language (Green, 1998; Meuter & Allport, 1999; Kroll, Bob, Misra, & Guo, 2008; Levy, McVeigh, Martful, & Anderson, 2007). Taking the work of Schwartz and Kroll (2006) further, Van Hell and de Groot (2008) show that only high restraint sentence contexts eliminates competition from the non-target language in a visual word, suggesting that a more active type of control must be enlisted in bilingual language processing at least when meaning is ambiguous. Green’s Inhibitory Control (IC) model proposes that lemmas are tagged for language specific information in the same way they are tagged for syntactic properties. Language task schemas inhibit or activate the relevant tags. This suppression is effectuated by the Supervisory Attentional System (SAS), or general executive functions. Implicit in this model is the belief that inhibition effects the whole of the non-target language (Green, 1998). In a seminal study, Meuter and Allport (1999) demonstrated that participants are fastest naming digits in their L1, but are slower when switching from L2 back to L1 as compared to a switch from L1 to L2. This is a direct prediction


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of Green’s IC model and has been replicated several times (Costa, Santesteban, & Ivanova, 2006; Costa & Santesteban, 2004). Switching back to the dominant L1 is more demanding because one’s native language requires greater inhibition so that it does not interfere with the weaker L2. It follows that the switching cost will be greatest for less balanced bilinguals. Levy et al. (2007) found evidence of native language attrition already present in early stages of SLA. Not all language non-selective models maintain that top-down inhibition is necessary for fluent bilingual performance. Dijkstra and Van Heuven’s Bilingual Interactive Activation (BIA)+ model assumes that a bilingual lexicons compete with each other very much like within-language words may compete. This model differs from language selective models such as presented by Costa who believes the two languages do not compete for selection at all. In the BIA+ model lexicons do compete and facilitation and interference does occur, but activation of nodes is directly affected by surrounding context, proficiency, subjective frequency of words, and the task at hand. This model resorts to limited active control from a top-down mechanism (Dijkstra, 2005) Proverbio’s research on multilingual interpreters supports this view of an initial parallel activation of words in all known languages followed by a search in the specific lexicons with limited top-down inhibition of the non target language (Proverbio et al., 2007). But Abutalebi (2008; Abutalebi & Green, 2007) interprets recent neuroimagery studies as evidence that inhibition is at the heart of bilingual performance. Notably, regions known to be implicated in task switching and control are activated specifically when a bilingual must decide between words that mean the same in different languages, but not when a monolingual chooses between synonyms. Because the entire language network changes when a new language is acquired, he believes inhibition is the primary mechanism by which the brain deals with the competition and interference inherent in a bilingual system.


2.1.3

13

Inhibition or Activation?

A recent study using a Stroop paradigm casts doubt on the very possibility of inhibiting any one language. Generally the bilingual Stroop task finds a stronger effect within language than between language, suggesting that the non-target language is suppressed. Goldfarb and Tzegelov (2008) suggest that the reason for this is actually because there is response set competition for the color words. Using color-associated words instead, they found that the Stroop effect was the same in the within language condition as in the between language condition. This means that words in the non target language cannot be suppressed. The IC model is more directly called into question by Costa (Costa, Albareda, Santesteban, 2008; Costa, La Heif, & Navarrete 2006; Costa, Santestban 2004; Costa, Caramazza 1999). The major evidence for inhibition is the asymmetrical switching cost between the weaker and the dominant language demonstrated by Meuter and Allport (1999) which changes as a function of proficiency. Costa (Costa & Santesteban, 2004; Costa, Santesteban, & Ivanova, 2006) replicated this study, finding the expected asymmetrical switching cost for unbalanced bilinguals. Second, they tested highly proficient bilinguals and found symmetrical switching costs between their two languages. They admit that the participants may be using an equal level of inhibition for both. They then tested these bilinguals with their L1 and a much weaker L3 and here as well, there was no evidence of the asymmetrical pattern–no evidence that their stronger language was being inhibited. This essentially contradicts the IC model. As a compromise, Costa et al. (2004, 2006) suggest that highly proficient bilinguals and L2 learners employ different mechanisms of language control. When one language is dominant speakers may resort to inhibitory control to achieve fluency, but in highly skilled bilinguals the language centers may be more efficiently restructured and they turn to better attentional control rather than inhibition. Segalowitz (2007; Segalowitz & Frenkiel-Fishman, 2005) observes that highly proficient speakers are not just quantitatively faster, they are qualitatively different than less skilled bilingual speakers. The ease with


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which highly proficient bilinguals can switch from one language to another may attest to a more automatic implicit functioning (Kroll et al., 2008) Segalowitz sees language as an “attention directing system” (Segalowitz & Frenkiel-Fishman, 2005, p. 645). Without saying so he may be supporting a language specific hypothesis of bilingual processing. Proficiency, context, and intention must all influence which language a bilingual will produce. Similarly, different aspects of language processing may require different levels of control. Chritoffles (2005) suggests that comprehension and production work along different channels. Reading and comprehension are more automatic (Kroll et al., 2008; Proverbio et al., 2007), relying on bottom-up systems, while production demands top-down processing. For example, suppression of any one of a bilingual’s languages is not possible in simultaneous translation. Instead, translators may constrain production to one language while leaving comprehension mutually activated (Christoffels & de Groot, 2005). Abutalebi (2008) points to multiple levels of control reflected in the activation of the PFC, the ACC, subcortical and parietal regions where each may represent different language tasks and kinds of control. It is also possible that expertise may not be the same at all ages. Aging itself or factors that correlate with age such as interference between the native language and one learned later in life, or social and psychological variables may all influence the cognitive strategies at work. The end result may be that early and late bilinguals who have comparable levels of proficiency may recruit different mechanisms of control. Segalowitz et al. (2005) claims that fluency within language performance is a matter of attentional control that becomes automatized. Can this be said about between language processing as well?

2.2

Summary: Bilingual Language Control Although the behavioral data is equivocal, neuroimagery evidence sug-

gests that some form of control is at the crux of successful bilingual performance. But the precise nature of this control is as yet unclear. Different

3 Executive Functions & Bilingualism

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strategies may be employed not only by different speakers, but by the same speaker in different contexts. For those who support the language IC model, the reason for a bilingual cognitive advantage is evident: bilinguals achieve fluency in any one language by inhibiting the non-relevant language. Enhanced inhibitory control due to life long daily use of two languages is responsible for the bilingual advantage such as is demonstrated on Simon task. The language selective model calls upon some kind of cognitive control as well, although it is not believed that this mechanism is active suppression of the non-relevant language. Instead, bilinguals may have an enhanced ability to activate and maintain goal representations. Alternatively, the mechanism recruited may depend on an individuals linguistic history. Late bilinguals may resort primarily to inhibitory control to suppress their dominant native language in order to maintain fluency in their weaker L2. Early bilinguals, may not require the same kind of control because their languages may not interact in the same way. Therefore, probing how specific cognitive mechanisms are affected by a bilingual lifestyle in both early and late learners may help determine which model of bilingual language processing prevails. We next examine general executive functions and their developmental course to ascertain how and which of these control functions are modulated by bilingual performance.

3

Executive Functions & Bilingualism Executive functions is the set of abilities that allows an individual to

select an action that is appropriate to a specific situation, inhibit inappropriate behavior and focus or maintain attention in spite of distractions. Although its components are not yet fully understood, executive function, also referred to as fluid intelligence, is assumed to include basic components like attention, inhibition, monitoring, switching, processing speed, response speed and working memory (Salthouse, 2005). These may vary between individuals, brain areas, and across the life span, and may be further subdivided. For example, goal switching demands conflict resolution, task deletion, and task reconfiguration (Monsel, 2003). Hasher, Lustig, and Zacks (2006) give primary importance to inhibition as the crucial factor in opti-


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mal mental function: control rather than capacity. Generally, these executive functions improve in childhood, remain at a high level across adulthood and decline in old age. But not all these functions follow the same trajectory and some show greater variance in the population than others (Cepeda, Kramer, & Gonzales de Sather, 2001; Borella, Carretti, & De Beni, 2008). The question is, how much can life style factors such as bilingualism effect these mechanisms?

3.1

Across the life span

3.1.1

An inverted U

The brain is a network of excitory and inhibitory neural connections. As a child grows into adolescence, she gains greater control over behavior, shifting from stimulus driven or exogenous behavior to endogenous or top-down control (Cepeda et al., 2001). Although different components change at different rates, globally an inverted U best describes the developmental course of executive functions (Zelazo, Craik, & Booth, 2004; Bedard, Nichols, & Barbosa et al., 2002; Cepeda et al., 2001). Bedard et al. (2002) examined inhibition in participants aged six to eighty-two with a stop/go paradigm and noted an inverted U shape in developmental change. Inhibitory control is the first to emerge, last to mature, remains stable over midlife, and the first to decline. Cepeda et al. (2001) demonstrated independence between different facets of cognitive processes, such as perceptual speed, working memory, and task switching. Furthermore, the amount of activation for efficient processing depends on which neural pathway, which kind of information, and which task. Differences in mental function across all ages is linked to differences in frontal lobe architecture and several subcortical structures (Crone, Donohue, & Honomichl et al., 2006; Smith & Geva et al., 2001; Colcombe & Kramer et al., 2005). Tasks requiring inhibitory control activate these areas differentially and to various degrees, suggesting the subtly different components that make up the executive processes (Hasher et al., 2006; Crone et al., 2006).


3.1.2

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Aging Adults

Aging brings about a general slowdown in processing speed, inhibitory control, interference control, and task coordination, but this decline does not follow the same rate for all components of executive function (Cepeda et al., 2001; Bedard et al., 2002; Borella et al., 2008). In the older group, inhibitory control followed a steeper decline than global processing speed. Furthermore, there was much more variation in the aging population in all aspects of executive functions that at any other period across the life span (Bedard et al., 2002). Borella et al. (2008) confirms these results. Speed and working memory was tightly correlated with age across different tasks. However, inhibition did not strongly correlate with the decline in working memory. Clearly not all facets of inhibitory control are affected by age in the same way. Hasher et al. (2006) suggest three aspects of inhibitory control: access, deletion, restraint. These allow an individual to attend only to what is relevant to the exclusion of all else, to remove information no longer relevant due to changing goals, and to withhold a strong habitual response. Bowles and Salthouse (2003) examine the age-related effects of one component of inhibition, proactive interference, also sometimes referred to as latent inhibition (Carson, Peterson, & Higgins, 2003) and is what Hasher et al. (2006) refer to as the deletion component of inhibition. Proactive interference occurs when information from a previous task interferes with new information. Bowles and Salthouse found that a decrease in older adults ability to inhibit irrelevant information was related to a decline in working memory span. This is similar to results by Ryan, Leung, Turk-Browne, and Hasher (2007) who found both inhibitory and binding deficits in older adults. The former means that too much information is encoded–a deficit in filtering. The latter denotes a deficit in binding–too little information is encoded to create relationships between objects in order that they may be remembered. Bireta, Surprenant, and Neath (2008) focused on the binding effect and confirmed that older participants can remember units but not the association between units. This suggest that older adults have trouble merging features into one


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representation, which may be the reason for their memory deficits. Aging impacts bilingual performance as it does other skills. Spanish/English bilingual older adults have more trouble switching between languages in response to an auditory cue as compared to young adults (Hernandez & Kohnert, 1999). This is consistent with impaired executive processing related to age. Increased proactive interference from previous tasks makes it more difficult for aging adults to disengage from previously activated task commands. These behavioral results mirror changes in brain function and architecture. Older adults show deterioration in the frontal lobes, reduced gray matter volume and white matter integrity (Colcombe et al., 2005). They show greater cortical activity for cognitive tasks such as the flanker paradigm than younger participants. Whether additional recruitment in a demanding task is a sign of more efficient processing depends on the nature of the task. In a verbal task, contralateral activation was linked to faster RT. In contrast, in a group of poor performing older adults, the additional activation in this area was not linked to improved performance in the case of inhibition. This suggests that activation of additional cortical regions are compensatory only when they can compliment the necessary processing patterns because they already subserve similar tasks (Colcombe et al., 2005). This conforms with the general dictum “less activation reflects more efficient processing” and is true for all ages (Zang & Wang, 2007). Poor functioning younger adults show similar brain patterns to older adults, specifically increased activation of the PFC for a difficult dual-task (Smith et al., 2000). The young participants who performed well on the task did not show activation of prefrontal regions while both older and poor performing younger participants recruited the PFC. Results confirm that the difficult element of the task was switching between the two components–operation span and equation verification–rather than each task alone. Globally these results sustain the hypothesis that aging is a decline in control mechanisms rather than declarative memory.


3.2

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Use It or Lose It The early developmental course is highly similar for all individuals; what

can explain the large variance in executive functions observed in aging adults? Some changes unfold according to genetic programing, others are experience dependent (Zang & Wang, 2007; Sur & Rubenstein, 2005). Life style factors such as physical and mental exercise can lead to lasting changes in brain connectivity and morphology. If so, it follows that speaking two languages on a regular basis should have a lasting effect on brain function. 3.2.1

Physical Exercise

Kramer and Erickson (2007) reviews numerous studies and concludes that exercise boosts cognitive functions, delaying or reducing cognitive decline. Animal studies support this claim: exercise enhances rodents ability to learn new tasks both in normal and aging animals, including those engineered for Alzheimer’s disease. Exercise increases the production of brainderived neurotrophic factor molecules (BDNF), insulin-like growth factors (IGF-1), induces the growth of new capillaries in the hippocampus and cerebellum bringing nourishment to brain cells (Dishman, Berthoud, & Booth, 2006; Kramer & Erickson, 2007). Specifically, exercise keeps the frontal cortex from decreasing in size and so has a general positive effect on executive functions. Cardiovascular health also reduces the risk of stroke. 3.2.2

Mental Exercise

Increased mental exercise has been shown to change brain morphology directly. London taxi drivers, who must learn a great deal of spatial information in order to navigate through this complex city, showed increased gray matter volume in the hippocampus relative to controls (Maguire, Gadian, Johnsrude et al., 2000). Building on her group’s earlier study, Maguire (Maguire, Woollett, & Spiers, 2006) compared London taxi drivers to London bus drivers. Both groups are under similar stress and navigate though the same city, but taxi drivers must constantly update and manipulate their spatial knowledge while bus drivers follow the same route. Only the taxi drivers showed greater gray volume in the mid-posterior hippocampi.


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However, in his review of the literature, Salthouse (2006) failed to find a significant positive effect of increased mental stimulation on brain function in aged adults. Scarmeas, Albert, Manly, and Stern (2006) demonstrate some delay in the onset of dementia for those with high cognitive reserve but with a subsequent increased rate of decline. These studies operationalize both mental stimulation and high cognitive reserve ambiguously. Mental stimulation includes an indiscriminately broad range of activities (e.g., gardening, shopping, reading, learning a new language) while high cognitive reserve is defined as higher education. Bialystok, Craik, et al. (2004) point out that research on cognitive aging has not taken into account the linguistic characteristics of subjects as a possible confounding variable. The studies reviewed by Salthouse (2006) deal with activities performed sporadically and Scarmeas et al. (2006) concentrates on past achievements. On the contrary, bilingualism is a constant state of mental exercise.

3.3

Bilingualism as a lifestyle factor

Aging bilinguals seem to have some protection for cognitive decline. A study reviewing the age at which cognitive complaints were first noted show that bilinguals turn for help over five years later than monolinguals (Bialystok, 2007a). Other experimental paradigms continue to demonstrate enhanced bilingual cognitive function in late adulthood (Bialystok, Craik, & Ruocco, 2008; Bialystok, Craik, & Ryan, 2006). Even at the earliest stages of L2 learning, changes brain activity can be measured (Osterhout et al., 2008). Here, as in Maguire’s London taxi drivers, participants were adults. It is therefore clear that bilingual experience reorganizes implicated cortical areas over years of performance, even when L2 is acquired in adulthood. But the original studies of bilingualism looked at children. The concern was that learning two languages in childhood may be a handicap (Ricciardelli, 1992). Quite the opposite was found to be true.


3.3.1

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Bialystok’s children

Bialystok’s basic hypothesis is that bilingual children develop crystallized intelligence and representational knowledge at the same rate as their monolingual cohorts but demonstrate precocious development of control processes, or fluid intelligence. Her work is in part inspired by Zelazo’s formulation of the Cognitive Complexity and Control (CCC) Theory, which assumes that the ability to manipulate rule representations is at the heart of cognitive development (Zelzo, Craik, & Booth, 2004; Bialystok, 1999). This invokes the development of inhibitory control. Zelzo’s team developed the dimensional card sort task which requires children to sort cards according to one set of rules. For example, they may be asked to sort cards according to color and ignore the shape. Until the age of 4 or 5 children have trouble adapting when sorting rules change. Their ability to inhibit a response that has become automatic but is no longer relevant has not yet matured and they continue to use the first rule. Bialystok (1999) compared the performance of bilingual and monolingual children and found that the bilingual group were more precocious in solving this task. A later study identified this advantage as the ability to ignore information that was previously but is no longer salient rather than response inhibition (Bialystok & Martin, 2004). Another study demonstrated that bilingual children succeed in reverse interpretation performance of ambiguous figures at an earlier age in comparison to their monolingual cohorts (Bialystok & Shapero, 2005). Intelligence comprises both knowledge and fluid intelligence which are interrelated and aging primarily reduces the control aspects (Craik & Bialystok, 2005). Bilinguals are not inherently more intelligent than monolinguals. On verbal tasks in any one of their languages, they usually have longer naming latencies than monolinguals, more tip of tongue experiences (TOT) and show no difference in working memory span (Michael & Gollan, 2005). The advantage demonstrated by bilinguals on cognitive tasks must then be the result of enhanced control processes and not a matter of capacity. The question remains which aspects of control are recruited for bilingual performance and to what degree.


3.3.2

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Inhibitory Control

Inhibitory control appears to have more variance in aging adults than any other aspect of mental function and at any other time across the life span (Cepeda et al., 2001, Bedard et al., 2002; Borella et al., 2008; Hasher et al., 2006). It is therefore tenable to assume that this cognitive function is more sensitive to experience than others. Bialystok, Craik, Klein, and Viswanathan (2004) illustrate that this cognitive advantage becomes more pronounced in late adulthood using the Simon task, a measure of inhibitory control and selective attention. Simon developed this task to investigate the effect of conflicting cues on information processing (Simon & Berbaum, 1990). The task requires participants to press a specific key for a specific color regardless where the colored target appears on the screen. When the target appears at the same location as the corresponding key the trial is ’congruent’; when the target appears on the opposite location of the corresponding key the trail is ’incongruent’. Individuals are faster at congruent trials and have slower reaction times on incongruent trails where they must inhibit the impulse to press the key which corresponds to the spatial dimension. The Simon effect occurs when the automatic spatial stimulus-response (S-R) correspondence must be inhibited by the task relevant non-spatial attribute, the color. The idea is that there are two routes for the stimulus to be processed. One is automatic–the spatial coding–and the other is under intentional control–carrying out the task instructions. The Simon effect is the difference in reaction time (RT) between the incongruent and congruent trails. An enhanced ability to inhibit the proponent spatial response will return less of a difference between the two measures. Ven der Lubbe and Verleger (2002) demonstrate that global speed decreases and the size of the Simon effect increases with age. Bialystok and Craik et al. (2004) compared the performance of different language groups and found that bilinguals are faster both on the congruent and incongruent conditions, and show less of a Simon effect than monolinguals. Similar results were established by Costa, Hernández, and Sebastián-Gallés (2007) with a flanker task called The Attention Network Test (ANT) (Fan, McClandliss et al., 2002, 2005).


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In this task participants must decide whether a central arrow points to the right or the left. This arrow is shown sandwhiched between flanker arrows which may point to the same or to a different direction. Here too, participants were early balanced bilinguals and monolinguals. The bilinguals were faster overall, suffered less interference from incongruent flankers, and less switching costs from incongruent to congruent trials. These results conform with Green’s IC model, suggesting that inhibition is the control mechanism underlying bilingual language processing, and promotes a language non-selective model over a language selective model. However, we have seen that Hasher et al. (2006) suggest three aspects of inhibitory control: access, deletion, restraint. It is the last one that is usually referred to as inhibition, but any of these sub-processes may be implicated in bilingual performance, and all three are confounded in the Simon task. Bialystok herself was not satisfied that inhibition was the only mechanism being measured in this task. Response inhibition, resistance to irrelevant stimuli, task switching, selective attention, working memory may all be implicated. (Bialystok, Craik et al., 2004; Bialystok, Craik, & Ryan, 2006). Furthermore, behavioral paradigms are not always sufficiently sensitive to grasp the underlying mechanisms at work. MEG recordings reveal more efficient processing in bilinguals on the Simon task even when behavioral measures between different groups converge (Bialystok, Craik, & Grady, et al., 2005). It is most likely that several cognitive processes interact in the performance of this task. It is crucial to examine these different mechanisms if we are to understand the dynamics of the bilingual mind. 3.3.3

Feature Binding

But what if the Simon task does not measure active inhibition at all? What if the Simon effect can be eliminated by an alternate analysis of the RTs? Research in visual perception suggests that planning an action requires the integration of relevant features, the binding of spatial, stimulus identity, and response dimensions into one representation. Hommel (2004) calls these fleeting representations ’event files’. When a stimulus is repeated, the event


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file need only be updated. But when presented with a stimulus where only one feature of the previously integrated event file is changed, performance is impaired because the old information must be deconstructed and bound into a new event file. Performance is faster when completely new features are presented because there is no need to update or change the preceding event file. This approach can be used for analyzing the RTs on the Simon task. Instead of contrasting congruent and incongruent trails, Hommel, Proctor, and Vu (2004) compared each trial to the previous trial. The features of each trial are integrated into a specific representation–color: red, position: left, response: right. Trials that completely match or completely mismatch the preceding one are faster than when there is a partial match. A complete match or complete mismatch does not disturb the representation, but a partial mismatch requires that the representation be deconstructed and reconfigured, which takes time. This explains why in many cases the non corresponding response is favored–that is, participants are sometimes faster in the incongruent rather than the congruent conditions. Yet we cannot deny the difference Bialystok found between monolinguals and bilinguals with the classic analysis of the Simon task. Can we link some aspect of inhibition to Hommel’s findings? In reinterpreting the results as a function of repetition and alternation, what kind of difference can we expect to find comparing these groups? A closer look at different types of inhibition will help us answer this question. Colzato et al. (2008) distinguish between active and reactive inhibition, both of which are engaged in the Simon task. Both of these appears to suppress task-irrelevant information, but the first resorts to active suppression, while the second is a side effect of attentional processes allocated to a desired goal. Their aim was to clarify which kind of inhibitory control is enhanced by a bilingual lifestyle. They found that bilinguals show increased inhibition of return (IOR) and more pronounced attentional blink. Stronger IOR means that bilinguals require more time to recuperate from inhibiting a previously cued location, suggesting that at least one type of inhibitory control is functioning above baseline in bilingual speakers. To elucidate which kind of inhibition is as work, Colzato and her team turn


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to a paradigm where active inhibition would play no role. They surmised that if bilinguals produce greater reactive inhibition, they should demonstrate worse performance on an attentional blink task. When two targets are presented between 100–500ms apart, people have trouble identifying T2 if they have identified T1. Prevailing approaches explain that the attentional mechanisms allotted to T1 are no longer free to handle additional stimuli. However, most people can identify both targets when they are presented in sequence, and it is rather the presence of distractors between the two that is responsible for the blink. Individuals who show greater attention related brain activity for T1 are more likely to miss T2. This means that greater attentional blink reflects the efficiency of noise suppression. If bilinguals have developed enhanced reactive inhibition (rather than active inhibition) they will exhibit a greater attentional blink. Their prediction was confirmed. Taken together, increased IOR and attentional blink suggests that bilinguals do not necessarily use suppression in controlling their languages but rather they have a greater capacity to maintain a goal directed behavior against the encroachment of another. What looks like inhibition of the non-target language may actually be stronger activation of the relevant representation. This conforms with the language selective hypothesis where increased activation rather than active suppression is seen as the core of bilingual language control. This also implies that the bilingual advantage on the Simon task is not due to inhibition but to their enhanced ability to build up and maintain goal representations. The event file effect observed by Hommel et al. (2004) when reinterpreting Simon RTs is a measure of just this capacity. Were we to compare different language groups, bilinguals should show shorter latencies than monolinguals on this measure. In other words, bilinguals should show greater flexibility in manipulating event files. We may now examine more clearly some of the dynamics of the bilingual mind. Binding ability is the capacity to create and reconfigure associations. Reduced ability to form associations is assumed to be at the root of the memory deficits of older adults (Bireta et al., 2007). Bilinguals show more IOR and less proactive interference (Colzato et al., 2006); aging adults show less IOR (McAullife, Chasteen, & Pratt, 2006) and more proactive interference


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(Bowles et al., 2003). We can now explain some aspects of a bilingual’s reduced cognitive decline in old age. But these results seem incompatible with the higher creativity observed in bilingual children. Creativity entails reduced latent inhibition, which means keeping some awareness of irrelevant information (Carson et al., 2003). Hasher et al. (2006) note that the deletion component of their model of inhibition can lead to a conceptual IOR. Deletion may suppress the no longer relevant word or representation to such a degree that its availability falls below baseline. Optimal updating of event files appears to require efficiency in the deletion of previous information. If so, bilinguals who have more IOR, should have more latent inhibition. Such a narrow focus does not foster creativity. How can we resolve this contradiction? Let us take a closer look at event file management. In general, children and aging adults show more partial mismatch costs than young adults in updating event files, which may reflect frontal lobe functioning (Hommel, Kray, & Lindenberger, 2006 in Colazto et al., 2006). This is not surprising, since we have seen that elderly adults have trouble with feature binding (Bireta et al., 2008; Ryan et al., 2007). Colzato et al. (2006) predicted that people who score higher on fluid intelligence (FI) will be less impaired by mismatches when updating an event file than others. This is exactly what he found. More flexibility in handing event files correlates with fluid intelligence (FI). Speed is one crucial aspect of facility in feature ’unbinding’. But even on trials where the high FI participants were as slow as those with lower FI, they still exhibited less of a cost on partial mismatches. The frontal lobes update relevant but not irrelevant information, removing the accent on the inhibition of previous information on to the ease with which new representations can be made. This is similar to Colzato’s study of bilingual performance on the attentional blink task. Bilinguals are more flexible in allotting attention to goal relevant information, activating the relevant language code rather than inhibiting the other (Colzato et al., 2008). Carson et al. (2003) illustrate that original thinking entails fluid associations, but only in high functioning individuals. Higher functioning individuals make do with the same limited brain areas as everyone else; it is precisely their


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control functions that are more efficient (Hasher et al., 2006). Bilingual speakers are constantly manipulating the richness of their linguistic endowment. They may be seen as a high functioning group by default. This approach can also explain why bilinguals are faster not only at the incongruent condition of both the Simon and the ANT task, but also on the congruent condition. Inhibition can only explain performance on the incongruent condition. The explanation for faster RTs on the congruent condition may lie with feature binding. I propose that bilinguals are more flexible in creating and reconfiguring event files and that this improves performance in all conditions. Inhibition is but a side-effect of the efficient allocation of attention. This cognitive flexibility explains not only the bilingual advantage on the Simon task and the ANT task, but also their higher scores in creativity and divergent thinking, which is contradicted by the assumption that bilinguals employ inhibition. This also means that the very test brought to sustain the IC Model may in fact be used to support the alternate hypothesis of bilingual cognitive control.

3.3.4

Attentional Control

Another step in pinpointing which is the common mechanism that is recruited in bilingual language selection, protects bilinguals from age related cognitive decline, and enhances their performance on cognitive tasks such as the Simon and ANT is to turn to another task which clearly measures one aspect of executive function. The Garner task specifically tests for attentional control rather than the ability to inhibit a response. In this task, participants must assess stimuli according to one dimension while ignoring the other. Some perceptual dimensions are separable while others are integral and cannot be processed separately. There is no difficulty in classifying a shape as a circle while ignoring size. But people have difficulty ignoring brightness while classifying color or separately processing length and width (Garner, 1978; Hollands, 2003; Patching & Quinlan, 2002; Ganel & Goodale, 2003). Reaction time slows in the orthogonal condition where the irrelevant dimension changes compared to the control condition where


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it remains constant. The difference in RT between the orthogonal and the control condition is the Garner interference (Garner, 1978). Results on the Garner task can be used to bolster the results of a sequential analysis of the Simon task by employing a color classification task with the same two colors used in the Simon task for the Garner control conditions, and alternating with different hues for the orthogonal condition. The Garner experimental condition will measure attentional control rather than inhibition of a response. Optimal performance on this task requires the ability to focus on one dimension excluding another. This mirrors the language selective model where a speaker focuses on one language rather than another without active suppression. In a very recent study Bialystok and her team rethink their original stance on inhibition as the key mechanism involved in bilingualism. MartinRhee and Bialystok (2008) examine different types of inhibitory control in bilingual and monolingual children to tease apart the mechanisms that underlie bilingual superior performance on the Simon task. They note that bilingual children are not better at inhibiting a habitual response, such as is required on a Stroop task, but only on tasks that require monitoring of different cues and directing attention to the appropriate response. In other words, the bilingual advantage already evident in bilingual children seems to imply that bilingual language control is a matter of activating the relevant language rather than inhibiting the non-target language. Only a comparison between early and late bilinguals will reveal whether both groups use the same language control mechanism.

3.4

Summary: Executive Functions

Claiming that inhibition is the basis for bilingual processing and the reason for the cognitive advantage seen in bilingual children and adults does not do justice to the complexity of the bilingual mind. There may be a tension between one kind of inhibitory control and another, where one is enhanced, another decreased, or an interaction between several mechanisms. Implementing both the Simon and Garner tasks can help disentangle which of


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these processes are responsible for the different advantages seen in bilinguals across the life span. The Simon task can be used to measure both inhibitory control following the standard analysis contrasting RTs on the incongruent and congruent conditions, and also for an event file effect with a sequential analysis. The later investigation will produce a measure of cognitive flexibility, the capacity to create and reconfigure representations. Both these abilities, inhibitory control and feature binding, are known to decline with age. These two abilities are also related to the two major hypotheses of bilingual language control. The IC model supposes that one language is inhibited in order to achieve fluency in the second. The language specific selection model believes that bilinguals allot more activation to nodes of the intended language and inhibition is but a side effect. Feature binding is precisely a matter of affording attention to a relevant representation. In contrast only one of these functions is related to creativity and divergent thinking. Creativity requires that irrelevant information remain accessible. High functioning creative individuals show less latent inhibition. In other words, if bilinguals do not inhibit their non-relevant language, but rather increase activation of the target language, they are functioning in a mode exemplary of high creativity. Irrelevant information is there, adding a shadow of richness to thought processes, with attention finely tuned to the goal at hand. Optimal performance on the Garner task entails the ability to pay attention to a relevant feature without being distracted by another without recourse to inhibition. If bilinguals reconfigure representations faster than monolinguals it means they can selectively attend to relevant information with greater flexibility. Bilinguals should be faster than monolinguals on this task. If proficiency alone can restructure brain processes for greater efficiency, both early and late groups will perform similarly. If on the other hand, different cognitive strategies are employed by early and late learners, differential results will allow us to glimpse their nature. The comparison of performance on the Simon task and the Garner task will produce a showcase of converging evidence that will allow us to identify the processes that underlie the dynamics of the bilingual mind.

4 General Summary: The Present Study

4

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General Summary: The Present Study

This present study implemented two tasks to examine the cognitive functions implicated and impacted by a bilingual life style, comparing the performance of early and late bilinguals. The Simon task was administered in order to replicate Bialystok, Craik, Klein, and Viswanathan (2004). This task putatively measures inhibition, the ability to suppress a proponent response, but the performance of this task calls upon several mechanisms: the ability to ignore irrelevant information, response suppression, and rule use. Researchers disagree whether inhibition is at the heart of bilingual language processing, although some type of control must be enlisted in bilingual performance. It is also possible that different kinds of bilinguals make use of different, and more or less efficient, mechanisms. Therefore, the Garner task was used to test for one aspect of control: the ability to focus on one dimension without being distracted by irrelevant information. Furthermore, results on the Simon task were reanalyzed to look for an event file effect, a measure of cognitive flexibility. This trait should be enhanced by years of using two languages on a regular basis. Participants belonged to one of three groups: early bilinguals, late bilinguals and monolinguals. Taking into account various views regarding second language acquisition, early bilinguals are categorized as having attained proficiency in a second language before the age of 10, and late bilinguals as having been exposed to their L2 after the age of 15. In accord with research which points to practice and proficiency as crucial factors in language processing, all participants were more than moderately proficient in L2 and used both their languages on a regular basis for over ten years. Possible confounding variables to be assessed are SES, physical exercise, and cultural identity. Our question is: Can a language learned in adulthood have the same effect as one learned early in life? This project will show whether there is a difference between early and late bilinguals on cognitive control tasks which measure selective attention, inhibitory control, and feature binding. First, we predicted that both early and late bilinguals will be faster and show less of a Simon Effect than monolinguals in the Simon task, and that

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the disparity will be larger between the older groups. If inhibitory control is differentially recruited by early and late bilinguals, late learners will outperform those who have acquired their L2 in childhood, due to late bilinguals activity inhibiting their native language. Second, we expect these groups to perform differently on the Garner task, as the ability to selectively attend to relevant information may specifically underlie language selection in early bilinguals. Third, a reanalysis of results on the Simon task for an event file effect will show that bilinguals outperform monolinguals in the ability to construct and reconstruct representations, with early bilinguals leading on this task.

Part II. Method Participants This study included forty-seven adults between the ages of 30 and 84 (M=51 years; 28 women, 19 men), divided into two age groups. The younger adult group ranged between the ages of 30 and 54; the older group ranged between 55 and 84. Participants were further categorized by language group: early bilinguals (n=16), late bilinguals (n=16), and monolinguals (n=15). Bilingual participants were speakers of a combination of any two of the following languages: French, English, Hebrew, Spanish, Yiddish, Arabic, and Russian. All were more than moderately to highly proficient in their second language and used their second language at least 20% of the time on a daily basis. The early bilinguals were raised in a bilingual environment either within the home or with one language spoken at home and another outside the home. They were exposed to their second language before the age of 10. They continued to use two languages daily throughout their lives at least ten-percent of each day. More than half of these participants were also moderately fluent in a third language. The late bilinguals also used both their languages on a daily basis for several years, but had

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learned their second language no earlier than the age of 15. The monolinguals had some exposure to other languages but where not functionally fluent in any other than their native tongue. All participants were tested by the same protocols and by the same experimenter, although testing was carried out in three different countries: France, the U.S., and Israel. Education, Socio-economic status (SES), cultural diversity, physical activity, and computer use were evaluated. Demographic factors education, SES, and exercise were not well balanced across groups, making analysis in relation to task performance problematic. Tasks and Procedures Language History Questionnaire and Education, Profession, and Physical Activity History. The questionnaires were filled out by the experimenter while interviewing each participant on their language use across their life span. Proficiency and fluency was self-graded by each participant, and percentage of usage in various situational and social contexts was noted in order to assess to what degree each language known to the participant was actually used on a daily basis. In addition, each participant was interviewed regarding years of education, work history, socio-economic status, cultural identity, and physical activity. The participants were assured that the experiment did not test intelligence or memory, so as not to create anxiety for the older adults (Ryan et al., 2007). Participants were interviewed after they had completed the experimental tasks. Garner and Simon Tasks. The experimental tasks were presented on a Dell D400 laptop with a 12” screen. The task was written and the results were collected running a Python program on the Windows XP OS. Responses were made pressing the left or right buttons of a Logitech precision game pad. Each task began with a training session: 16 trials for the Garner task, 24 trials for the Simon task. Each trial started with a white fixation cross in the center of a black background which remained visible for 500ms after which a colored square appeared until a response was carried out. For both tasks, the instructions were the same. Participants were told to keep their eyes at the center of the screen and press the left button whenever they saw

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a blue square and the right button when they saw a red square. They were instructed to respond as fast and as accurately as possible and to continue the task without stopping even if they made an error. Timing began with the appearance of the stimulus and ended when a button was pressed. The screen remained blank for 300ms before the onset of the next stimulus. The Garner task was implemented first in three blocks with two minutes of repose between each block. The dimensions were color and brightness using two hues of red and two hues of blue, rendering two conditions were brightness was held constant (const1=light blue and light red; const2=dark blue and dark red) and one experimental condition where brightness varied orthogonally with color (var=2 light and 2 dark hues mixed). Participants were asked to focus on the color and ignore changes in brightness. The blocks were presented in random order to eliminate practice effects. Each block consisted of 64 trials, half of which were blue, and half of which were red in random order, all of which appeared at the center of the screen. The Simon task was presented twice with two minutes of repose between each block. Each block consisted of 80 trials, half of which were blue and half of which were red. The colors appeared half the time on the right side of the screen and the other half to the left side of the screen. The colors and their spatial dimension were presented in a random order.

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Part III. Results Of the fifty-one people tested, four data sets had to be eliminated due to faulty recording of data. Trials with response times shorter than 200ms and longer than 1000ms were excluded from analysis as were the first two trials of each block. The Garner Task The error rates and median reaction times (RT) were computed for each subject for the “constant” and “variable” conditions and are presented in Figure 1 and 2. They were submitted to analyses of variances with Condition as a within subject variable and Language group (early bilingual, late bilinguals, monolingual) and Age group (young, old) as between subject variables. No effect was significant in the analysis of reaction times. In the error rates (ER) analysis, there was a significant interaction between Age and Language group, F(2, 41)= 3.69, p = .03, as well as an effect of Age, F(1, 41)= 10.41, p = .002 . A Tukey HSD posthoc test shows that this si mostly due to significantly higher error rates for the group of old late bilinguals. The Garner interference assessed by the effect of Condition was not significant (8ms on RTs and 2.8% ERs).

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F IGURE 1: G ARNER TASK E RROR R ATES

AS A

F UNCTION

OF

A GE

F IGURE 2: G ARNER R EACTION T IMES

AND

L ANGUAGE G ROUP

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The Simon Task Mean reaction times and error rates for the congruent and incongruent trials as a function of age and language group are presented in Figure 2 and 3. Error rates were generally low, with more errors commited on the incongruent trials (3.1%) than on congruent trials (2%). This was significant, F(1,41) = 4.14, p = .05. A three-way ANOVA for language group, age group, and congruency revealed two significant main effects. Younger adults were faster than older adults across all language groups, F(1, 41)= 6.94, p = .01. Average RT was faster on congruent trials than on incongruent trials F(1, 41) = 42.11, p < .000. There were no significant interactions between language group and age to congruency. The monolinguals in this study were faster than either of the bilingual groups, but this was not statistically significant. F IGURE 2: S IMON TASK M EAN RT S

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TABLE 1: S IMON TASK M EAN RT S ( WITH

STANDARD DEVIATIONS )

F IGURE 3: S IMON TASK M EAN ER S

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The Simon Effect was calculated for each subject as a function of age group and language group and is reported in Table 2 and represented in Figure 4. Although results are not statistically significant, a trend can be seen where older monolinguals present a larger Simon effect than either of the bilingual groups, despite their globally faster RTs. There was no correlation between age and the Simon effect. TABLE 2: S IMON E FFECT M EANS ( AND

F IGURE 4:

STANDARD DEVIATIONS )

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The Event File effect was calculated by comparing RTs to the immediately previous trial on levels of response dimensions (color, position, response key). Trials where the previous trial was the same on all response dimensions was noted as 0, trials that differed on one dimension was noted as 1, and so on. Mean RTs are reported in Figure 5. As can be seen, participants were faster when a trial was either similar or completely different from the previous trial and slowest when a trial differed on only one response dimension. A three-way ANOVA revealed that this was highly significant F(3, 105) = 50.67, p < .000. There was no interaction with language group or age.

F IGURE 5: M EAN RT S

FOR

E VENT F ILE E FFECT

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Part IV. Discussion The goal of this study was to demonstrate whether a language learned late in life can have the same beneficial cognitive effect as one learned in childhood. Concurrently, we hoped to elucidate the executive functions recruited in the performance of the Simon task which reflect those enhanced by bilingual performance. First, we predicted that both early and late bilinguals will be faster and show less of a Simon effect than monolinguals in the Simon task, and that the disparity will be larger between the older groups. This was not borne out. We found main effects for congruency and age with no relationship to language group. All participants were significantly faster on the congruent condition and RTs were slower for all older adults. An analysis of error rates for the Simon task showed significantly more errors were commited on the incongruent trials (3.1%) than on congruent trials (2%), meaning the incongruent trials required more control to override the preponent spatial response. The Simon effect tended to be smaller for older bilinguals compared to older monolinguals but standard deviations were extremely large and this did not reach significance. We also hypothesized that if inhibitory control is differentially recruited by early and late bilinguals, late learners will outperform those who have acquired their L2 in childhood. Although the Simon effect tended to be smaller for late bilinguals, this was not significant. Second, we expected these groups to perform differently on the Garner task, as the ability to ignore irrelevant information may specifically underlie language selection in early bilinguals, but no Garner interference was revealed for any group. Third, we planned to reinterpret the results on the Simon task in order to uncover an event file effect in order to show that bilinguals outperform monolinguals in the ability to construct and reconstruct representations. An event file effect was detected and this was significant for all participants, thus replicating Hommel et al. (2004). However there was no interaction with language group or age. In contrast to Bialystok’s results, the bilingual population tested here was slower than the monolingual group, although this did not reach significance. It is provocative that nonetheless, a trend was observed for less of

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a Simon effect in older bilinguals in spite of their overall slower RTs. This may suggest that the large variances in individual speed due to chance factors in such a small population are canceling out the bilingual advantage demonstrated in Bialystok’s groups. This same variation may be responsible for hiding a language linked event file effect.

4.1

Limitations The weak point of the present research was the type of participants that

were available for testing. To reveal an effect, this research requires access to a very large number of bilinguals that can be matched according to the variables being examined. This was not the case for the present project. Participants were all word of mouth volunteers and few fit precisely into the intended categories. Unlike the pool of subjects from which Bialystok and Costa chose their subjects, the bilinguals in this work were highly heterogeneous on key factors. For those classified as bilinguals, amount of daily bilingual use or exposure varied between 10% and 50%. Many spoke three or more languages at different levels of proficiency. In three cases, individuals were proficient in two languages but literate in only one of these. Some participants who were bilingual from early childhood had switched one of their languages for another during their lifetime. Others were highly proficient in two or more languages, but had been functionally monolingual for the past several years. Some read regularly in two languages but only spoke one. Categorizing these subjects as bilingual or monolingual was arduous. In addition, we had hoped to generate comparable groups on cultural identity issues to see whether bilingual immigrants who feel close to two different cultures are comparable to bilinguals who have one cultural identity, but there was too much overlap across all groups to make this comparison. In other words, the participants in the present study were a highly varied group with high degree of overlap on several confounding variables which explains the difficulty in revealing significance. Aside from this, the Garner task was not fine enough to test for attentional control. The task as it was designed for the present project was too easy and results exhibited a ceiling effect. It is possible that the hues and

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colors were not different enough to require any additional attentional effort. For a future project, this task can be redesigned using another modality such as auditory stimuli (Patching & Quinlan, 2002).

4.2

Future directions The last two decades have seen a significant increase in the number of

studies devoted to both bilingual language and extra-linguistic processing, with a surge in the last ten years (Bialystok, 2007b). The next step is to examine different bilingual groups to elucidate how different linguistic histories affect both the domains of language and general cognitive functions. This study hoped to reveal how some of these factors modulate cognitive functions. Future studies should clarify the effect of proficiency compared to exposure in regards to bilingual advantage, and how the similarity or difference between a bilingual’s languages modulates cognitive processing. Another factor that requires assessment is amount of language switching. A comparison between bilinguals who alternate often between their langauges throughout the day and those who remain in one mode for longer periods may demonstrate differential effects on cognition. Based on Carson’s and Colzato’s work, it would be intriguing to examine the dymanics of cognitive function in high functioning elderly adults (Carson et al., 2003; Colzato et al., 2006, 2008). We have seen that a major difference between older and younger adults is the ability to restrict attention to goal relevant information rather than the capacity to activate relevant concepts. In a study by May, Zacks, Hasher, and Multhaupall (1999) participants generated alternate meanings to garden sentences, but the younger adults were able to discard the incorrect interpretation more readily. However, it should be noted that this deficit can lead to better performance in some situations. Kim, Hasher, and Zacks (2007) show that older adults can access the non-filtered information for a subsequent task–they showed priming from distraction. This parallels the ability of the creative individual to manipulate information discarded by others who have a more narrow focus. A question arises: Is poor attentional control in higher functioning elderly adults the fountainhead of wisdom? If so, what is the dynamic that turns

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a deficit into an general advantage? We have seen that Ryan et al. (2007) found both inhibitory and binding deficits in older participants. Perhaps a high functioning group would show only the inhibitory but not the binding deficit. With a similar twist, the advantages bilinguals enjoy come at a cost. For the most part, any evidence of impairment comes from the linguistic domain itself. Bilinguals are slower than monolinguals at picture naming in both their languages, they have smaller reactive vocabularies, and experience more instances of TOT (Michael & Gollan, 2005). This seems to be a small price to pay for enhanced general cognitive functions and the ability to express oneself proficiently in two or more languages. A provocative question is: are bilinguals disadvantaged in any extra-lingual domain? Are there any side effects to either enhanced inhibitory control or improved event file management that can be a handicap in certain tasks besides increased attentional blink? Another important domain for investigation issues from studies demonstrating higher creativity in bilingual children. Do adult bilinguals show a similar tendency? I suggest comparing adult bilinguals and monolinguals on three measures: fluid intelligence using the Raven’s Standard Progressive Matrice test, a latent inhibition task such as employed by Carson et al. (2003), and an assessment of actual creative achievement. Lastly, comparing a bilingual society to emigrant populations speaking two languages in a monolingual society would help us gain an understanding of the effects of cultural identity and diversity. Creativity may be in part a result of cultural richness and not exclusively due to the use of two languages. A linguistic history is a life history. Eludicating the dynamics behind the bilingual cognitive advantage is a vital challenge.

Words (excluding references and appendix): 12,700

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Part VI. Acknowlegements I would like to thank Professor Christophe Pallier for his guidance and support in the conception and completion of this project. I am especially greatful for his expertise with Python programming, and his assistance with statistical analysis using R. I would also like to thank the entire Cogmaster staff for their excellence, and for creating this outstanding program. Many thanks to Professor Rebbekah Rast whose passion for psycholinguistcs directly led to the conception of this project. Special thanks to Julie Leitz who allotted me access to a complete database of scientific journals, which made my research an addictive pleasure. I also want to express my great appreciation to all those participants who agreed to be a part of this project, who shared their time and life histories with me so generously. I cannot end without thanking my husband and children, whose faith and love have kept me focused and energized throughout all my years of academic work. I owe every project’s completion to their patient proof reading skills. A special nod to my daughter Elisheva who helped me brush up on my statistics en douceur, over our morning coffee.

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Part VII. Appendix Language History Questionnaire and Education, Profession, and Physical Activity History.