Introduction
With the recent growth of bilingualism research many studies have suggested that bilingualism benefits non-linguistic task performance. Specifically, bilingualism has been associated with differential performance on a variety of executive control tasks, including the Attention Network Test (ANT; Pelham & Abrams, Reference Pelham and Abrams2014; Tao, Marzecová, Taft, Asanowicz & Wodniecka, Reference Tao, Marzecová, Taft, Asanowicz and Wodniecka2011), Simon (Bialystok, Craik, Klein & Viswanathan, Reference Bialystok, Craik, Klein and Viswanathan2004; Bialystok, Craik & Luk, Reference Bialystok, Craik and Luk2008), and Stroop (Bialystok et al., Reference Bialystok, Craik and Luk2008; Coderre, Van Heuven & Conklin, Reference Coderre, van Heuven and Conklin2013) wherein bilinguals have shown smaller effects of conflict, as measured by reduced reaction time, across these tasks. These findings have recently come under scrutiny (e.g., Paap, Johnson & Sawi, Reference Paap, Johnson and Sawi2015; Duñabeitia, Hernández, Antón, Macizo, Estévez, Fuentes & Carreiras, Reference Duñabeitia, Hernández, Antón, Macizo, Estévez, Fuentes and Carreiras2014), with multiple studies failing to replicate previous results (e.g., Paap & Greenberg, Reference Paap and Greenberg2013; but see Zhou & Krott, published online November 25, 2015, on the effects of data trimming) and calls for better cognitive models of the relationship between non-linguistic function and bilingualism (Paap, Johnson & Sawi, Reference Paap, Johnson and Sawi2016). However, these calls fail to recognize the potential of bilingualism as a transdisciplinary field, where investigators from different disciplines work together to create new theories that move beyond discipline-specific approaches. It is only by continuing to investigate that we can begin to develop theories that account for the effects of bilingualism.
While the behavioral advantages associated with bilingualism were initially attributed specifically to improved inhibitory control, more recent theories have suggested that the variety of potential bilingual experiences may result in differing effects on brain and behavior (e.g., Bialystok & Barac, Reference Bialystok, Barac, Li and Grosjean2013; Green & Abutalebi, Reference Green and Abutalebi2013; see Macnamara & Conway, Reference Macnamara and Conway2014, for a longitudinal demonstration of the effects of changing bilingual demands on cognitive control and working memory). This interpretation is based partially on data showing bilinguals’ improved reaction time on tests of inhibitory control is not limited to conflict trials (e.g., Hilchey & Klein, Reference Hilchey and Klein2011; but see Hilchey, Saint-Aubin & Klein, Reference Hilchey, Saint-Aubin, Klein and Schwieter2015, for a review of recent issues replicating these findings) and data showing enhanced accuracy in other domains, such as spatial working memory (verbal working memory tasks typically elicit no effect or a bilingual disadvantage, due to lexical interference; Bialystok, Craik, Green & Gollan, Reference Bialystok, Craik, Green and Gollan2009; Luo, Craik, Moreno & Bialystok, Reference Luo, Craik, Moreno and Bialystok2013).
Executive control processes, however, do not operate in a vacuum. These processes interact with other daily cognitive tasks, such as encoding and retrieval. Consequently, researchers have begun to examine the effect of bilingualism on memory as well. One of the first studies in this area examined the performance of younger (M = 20.5 years) and older (M = 70.1 years) monolinguals and bilinguals on a free recall task. The stimuli were presented auditorily, and the investigators found that both older age and bilingualism were associated with lower recall scores (Fernandes, Craik, Bialystok & Kreuger, Reference Fernandes, Craik, Bialystok and Kreuger2007). Since then, however, studies examining bilingual memory have shown more positive effects of bilingualism (Ljungberg Hansson, Andrés, Josefsson & Nilsson, Reference Ljungberg, Hansson, Andrés, Josefsson and Nilsson2013; Schroeder & Marian, Reference Schroeder and Marian2012; Wodniecka, Craik, Luo & Bialystok, Reference Wodniecka, Craik, Luo and Bialystok2010). For example, Wodniecka and colleagues (Reference Wodniecka, Craik, Luo and Bialystok2010) found that older (M = 70.8 years, averaged across both experiments) bilinguals were advantaged at non-verbal recollection, although only at the longest lag. Schroeder and Marian (Reference Schroeder and Marian2012) found a similar bilingual advantage in older (M = 80.8 years) adults in a recall test. Additionally, they showed that recall performance was positively correlated with a reaction time advantage on the Simon task, suggesting a relationship between the advantage bilinguals experience in episodic memory and executive control. Ljungberg and colleagues (Reference Ljungberg, Hansson, Andrés, Josefsson and Nilsson2013), who examined episodic memory in 178 older (M = 49.9 years at baseline, participants were followed for 20 years) bilinguals and monolinguals, presented further supporting evidence. Their analyses found that bilinguals were significantly advantaged on the episodic recall tasks, while a similar advantage was found for letter, but not category, fluency. Letter fluency is commonly thought to require more executive control skill compared with category fluency (see Martin, Wiggs, Lalonde & Mack, Reference Martin, Wiggs, Lalonde and Mack1994), and consequently the authors interpreted these results as supporting the notion that executive control advantages are related to advantages in episodic memory.
To summarize, the majority of previous work examining the effects of bilingualism on episodic memory found positive effects in older adults that were related to executive functioning. However, many of these studies either did not test or did not find effects in younger adults. One possible reason for this is that the item memory tasks used in the aforementioned studies were not difficult enough to tap into the differences between young bilinguals and monolinguals (Costa, Hernández, Costa-Faidella & Sebastián-Gallés, Reference Costa, Hernández, Costa-Faidella and Sebastián-Gallés2009). To test this notion we sought to examine the effect of bilingualism on memory performance using a relatively difficult source memory task that would recruit executive control. In the typical source memory task, individuals are asked to retrieve not simply whether an item was presented previously, but in what context the item previously appeared (e.g., location or color of a word). Consequently, it has been argued that source memory is more difficult than item memory as it cannot rely on familiarity, but requires recollection and monitoring processes beyond that which is required for item memory (Johnson, Hashtroudi & Lindsay, Reference Johnson, Hashtroudi and Lindsay1993; Mitchell & Johnson, Reference Mitchell and Johnson2009; Schacter, Harbluk & McLachlan, Reference Schacter, Harbluk and McLachlan1984; Shimamura & Squire, Reference Shimamura and Squire1991; Spaniol & Grady, Reference Spaniol and Grady2012).
Given the previous literature on executive functioning in bilinguals, we predicted that bilinguals would be advantaged at a source memory task in comparison with monolinguals. Furthermore, given the difficulty of the task, one might expect that this advantage would present in young bilinguals, as task difficulty has been identified as one of the key factors affecting the ability to observe differences between bilinguals and monolinguals (Costa et al., Reference Costa, Hernández, Costa-Faidella and Sebastián-Gallés2009). Consequently, we hypothesized that bilinguals should show improved performance on a test of source memory and that this advantage would increase as task difficulty and hence the need for executive functioning increased. More specifically, we hypothesized that this bilingual advantage would be related to their inhibitory control and/or working memory abilities. To test this, we developed a source memory task that specifically manipulated these factors (based on a task by Yubero, Gil, Paul & Maestú, Reference Yubero, Gil, Paul and Maestú2011; see the Methods section). If the effect of bilingualism was due to one or another of these factors, then we expected to find an interaction between language group and condition of the source memory task. Alternatively, improved bilingual performance across conditions would indicate a general effect of bilingualism, which would be congruent with current findings in the neuroimaging literature that bilinguals show differential function and structure across the brain, and not only in structures associated with executive control (e.g., Grant, Dennis & Li, Reference Grant, Dennis and Li2014; Hervais-Adelman, Moser-Mercer & Golestani, Reference Hervais-Adelman, Moser-Mercer and Golestani2011; Li, Legault & Litcofsky, Reference Li, Legault and Litcofsky2014). Equal performance, or a monolingual advantage, would not be predicted by current theories of bilingual language production and cognitive control, and would instead add to the literature suggesting that the effect of bilingualism on cognitive control is limited (de Bruin, Treccani & Della Sala, Reference de Bruin, Treccani and Della Sala2015; Paap et al., Reference Paap, Johnson and Sawi2015).
Methods
Participants
English monolingual participants (19 female, 6 male) and bilingual participants (20 female, 6 male) completed the experiment. Participants were recruited from the Penn State Psychology subject pool and compensated with course credit. Participants’ ages ranged from 18 to 26. Participants were divided into language groups post hoc based on their self-ratings of their bilingual status and proficiency in their L2. Participants whose average L2 proficiency across reading, writing, listening, and speaking was at least 5 out of 7 were admitted to the bilingual group. Participants who considered themselves monolingual or rated their L2 proficiency as less than 4 out of 7 were admitted to the monolingual group. Participants whose average L2 proficiency did not fit into one of these groups were excluded from analysis (5 participants, for a final sample of 20 monolingual participants, 16 female, 4 male). Among the bilingual group, 35% of the participants reported English as their first language (L1). Other L1s included Chinese, Korean, Czech, Nepali, Thai, Polish, Malayalam, Spanish, Hebrew, and Russian. L2s included English, Spanish, French, German, Malay and Hungarian. Among the monolingual group, participants reported taking Spanish, German, French and Latin. There was no significant difference between the Peabody Picture Vocabulary Test (PPVT; Dunn & Dunn, Reference Dunn and Dunn1997) scores of the bilinguals and monolinguals, indicating high English proficiency in both groups (see Table 1). Bilinguals, however, reported both significantly higher L2 proficiency (t (44) = 9.176 equal variances not assumed, p < .001) and significantly more time spent using the L2 than monolinguals (t (44) = 5.521 equal variances not assumed, p < .001).
Table 1. Means (SD) of participants’ language background measures.
1 Scores represent accuracy on the PPVT. 2Scale ranged from 1 to 7: 1 = Not at all proficient, 7 = Native-like. *Asterisks represent a significant difference between groups.
Materials
Background tasks
In addition to our source memory task (described below), participants also completed several tasks measuring their language abilities and general cognitive functioning. English language ability was measured using the Peabody Picture Vocabulary Test, a normalized test of English vocabulary (Dunn & Dunn, Reference Dunn and Dunn1997). In this task, participants hear a word while viewing four pictures and then identify which picture represents the word. Item memory was assessed with the Logical Memory I task (Glisky, Rubin & Davidson, Reference Glisky, Rubin and Davidson2001). In this task, participants hear two stories, one of which is repeated, and then are asked to recite the story as closely as possible. Their recitation was scored for details, and scores from this test were normalized using the WMS-III scoring guide (Wechsler, Reference Wechsler1997b).
Working memory was assessed using two tasks. The letter-number sequencing (LNS) task requires participants to listen to a string of numbers and letters, repeating back each by providing the numbers followed by letters, in ascending order (Wechsler, Reference Wechsler1997a). The spatial span task requires participants to observe a spatial tapping pattern on a board with raised tiles and then replicate that pattern. Participants first complete the task with sequences of increasing length in the forward direction, and then in the backward direction (Wechsler, Reference Wechsler1997a).
Inhibitory control was assessed using the Flanker task (adapted from Emmorey, Luk, Pyers & Bialystok, Reference Emmorey, Luk, Pyers and Bialystok2008). In this task participants complete three types of blocked tasks: control blocks, Go-Nogo blocks, and conflict blocks. In control blocks, participants see one arrow and are asked to identify its direction. In Go-Nogo blocks, the arrow is flanked by either diamonds (Go trials) or Xs (Nogo trials). In conflict blocks the center arrow is flanked by five arrows, which may be in the same direction (congruent trials) or a conflicting direction (incongruent trials). In addition, participants completed a mixed block with conflict and Go-Nogo trials. This task allows for the calculation of the classic Flanker effect, by subtracting the reaction time to congruent trials (where all arrows face the same direction) from incongruent trials (where the flanking arrows face the opposite direction) in the conflict block. In addition, we are able to compute mixing costs by subtracting the RTs to Go, congruent, and incongruent trials in single blocks from the RTs to those same trial types in the mixed block.
Experimental task
Our source memory task (SMT) was adapted from Yubero and colleagues (Reference Yubero, Gil, Paul and Maestú2011) to manipulate category membership and source difficulty in order to emphasize the need for inhibitory control and working memory, respectively. Each stimulus consisted of an image of a concrete object set on a colored background. The category membership of the object and the number of background colors presented to the participant during each encoding block were factorially manipulated, so that we had four conditions: Same Category(SC)/10 Colors (10Diff), SC/2 Colors (2Diff), Different Categories (DC)/10Diff, and DC/2Diff. In the inhibitory control stress (SC) conditions, the objects shown in a block were members of the same category (e.g., cameras), as remembering many exemplars from a single category requires the participant to inhibit the categorical gist in order to encode individual details to be used at retrieval (see Levy & Anderson (Reference Levy and Anderson2002) for a review of established paradigms, such as retrieval-induced forgetting and the think/no-think paradigm, that use category membership as a manipulation of inhibition). In the DC condition, each object came from a different category (e.g., camera, fork, butterfly, etc). We paired this manipulation with a manipulation of the number of background colors presented during a block, as many current standardized measures of working memory, such as Digit Span and the Letter-Number Sequencing task (Wechsler, Reference Wechsler1997a), all increase the number of items in order to test working memory. In the high working memory stress conditions (10Diff), participants were exposed to a unique background color for each trial and in the low working memory stress conditions (2Diff), participants were exposed to only two background colors during the block.
Procedure
Participants gave their consent and completed a language history questionnaire (Li, Zhang, Tsai, & Puls, Reference Li, Legault and Litcofsky2014), the PPVT, source memory task, strategy questionnaire, Flanker task, the Letter-Number Sequencing task and two measures from the Wechsler Memory Scale-III: Logical Memory I and Spatial Span, both forwards and backwards. Participants completed the SMT as described below.
In the SMT participants completed 8 encoding blocks (2 from each condition), each followed by a recognition block. Each encoding block consisted of 10 trials and each trial was presented for 3 seconds in the center of the computer screen. Recognition blocks consisted of 12 items: 6 targets or previously seen items, 4 distractor items that consisted of a previously seen object with a different background color, and 2 completely new items (presented on a colored background that was shown in the preceding encoding block). Presentation of block order was pseudorandomly distributed such that blocks of the same condition did not occur consecutively. During encoding, participants were asked to remember the picture and the background color. During retrieval, they made old/new recognition judgments to each item/source pair, and then rated their confidence on a 1–7 Likert scale from not at all confident to highly confident. After completing the task, participants completed a strategy questionnaire that asked them to indicate if they had used any of the following strategies (or a combination thereof) while completing the SMT: passive viewing/no strategy, repetition, sentence generation, imagery, meaningful grouping, or another strategy.
Results
We used a mixed repeated measures ANOVA as implemented in SPSS 22 (IBM Corp., 2013) to analyze the data from our SMT and assess the influence of both Memory Condition and Language Background on median reaction time (RT), as well as accuracy. The RT model showed a significant main effect of Condition F(3,44) = 68.06, p < .001, as well as Language Background F(1,44) = 6.316, p = .016. The main effect of Condition was characterized by slower RTs during the conditions that stressed working memory (DC/10Diff) and inhibitory control (SC/2Diff), as well as the combined (SC/10Diff) condition. The RT results are summarized in Figure 1. Results show that the bilinguals were significantly faster than the monolinguals across all conditions.
Figure 1. Median Reaction Time on the Source Memory Task for Monolinguals and Bilinguals. Error bars represent standard error.
In contrast to these dramatic group differences in RT, the accuracy results show that despite the varying difficulty, participants in both groups maintained high accuracy across all conditions of the SMT. In the mixed repeated measures ANOVA assessing accuracy, only Condition exhibited a significant main effect (F(3, 44) = 26.24, p < .001) although the effect of Language Background exhibited a marginal effect (F(3,44) = 3.56, p = .066). The accuracy results are summarized in Figure 2.
Figure 2. Mean Accuracy on the Source Memory Task for Monolinguals and Bilinguals. Error bars represent standard error.
In addition to the analysis of the source memory data, we also examined the effect of Language Background on flanker task performance. Our a priori hypothesis was that there would be a difference in the flanker effect between the two groups, but we did not observe this (t (44) = 1.304, p = .201), and we also did not observe an effect of language background on the mixing cost data (F(2, 44) = 1.828, p = .183) which we analyzed using a 3 (Congruent, Incongruent, Go) x 2 (Monolingual, Bilingual) ANOVA. We further investigated overall task performance using a 2 (Congruent, Incongruent) x 2 (Monolingual, Bilingual) mixed repeated measures ANOVA. That analysis revealed significant main effects of both Trial Type (F(1,44) = 180.41, p < .001) and Language Background (F(1,44) = 4.63, p = .037) such that bilinguals were significantly faster than monolinguals during conflict blocks (see Table 2 for details and Figure 3 for an illustration).
Table 2. Means (SD) of memory and inhibitory control performance.
1 Scores represent an average number of strategies used, rather than accuracy or reaction time. 2The first row for the Flanker task shows the Flanker effect, whereas the second and third rows show the results on individual trial types. Smaller Flanker effects represent better performance. *Asterisks represent a significant difference between groups.
Figure 3. Mean Reaction Time on the Flanker Task for Monolinguals and Bilinguals. Error bars represent standard error.
In order to assess the extent to which our cognitive measures related to their associated conditions (e.g., the Flanker task with the SC condition) in the SMT, we correlated the scores on the relevant cognitive measure with the accuracy and RT across each of the relevant SMT conditions, using a Bonferroni correction for multiple comparisons. If we first consider our tests of working memory, the LNS and spatial span tasks, we observe that RT performance on the SC/10Diff condition (stressing working memory and inhibitory control) of our source memory task was positively correlated with RT in the LNS task (R = .411, p = .005). The results for the DC/10Diff condition (stressing only working memory) and the accuracy data were trending but did not survive correction. In addition, we did not observe any significant correlations between participants’ spatial span and their source memory performance. We also examined the relationship between our measure of inhibitory control, the Flanker task, and the relevant conditions of our task, but there were no significant relationships. Our test of item memory, the Logical Memory task, also did not correlate with source memory performance, and we observed no between groups differences for this task (t (44) = 1.573, p = .124).
Discussion
This study is the first to examine the influence of bilingualism on source memory. Specifically, our results show that bilinguals make faster source memory decisions than monolinguals, without compromising accuracy. Furthermore, this speed benefit occurs across each of the conditions of our task, suggesting that the effect of bilingualism is ubiquitous in the SMT and not limited to conditions emphasizing inhibitory control. When we consider these results in the context of our original hypotheses, our findings are congruent with a general effect of bilingualism, as opposed to an effect specifically tied to inhibitory control or working memory processes. This general effect of bilingualism is congruent with current findings in the neuroimaging literature that show, compared to monolinguals, bilinguals exhibit both widespread functional and structural differences that are not isolated to structures associated with executive control (e.g., Grant et al., Reference Grant, Dennis and Li2014; Hervais-Adelman et al., Reference Hervais-Adelman, Moser-Mercer and Golestani2011; Li et al., Reference Li, Legault and Litcofsky2014a). Furthermore, the overarching nature of the observed RT difference, especially in the absence of accuracy differences between groups, is congruent with current approaches that view bilingual experience as a source of general neuroplasticity rather than an ‘advantage’ over monolinguals (Baum & Titone, Reference Baum and Titone2014).
Our analysis of the Flanker task supports this assertion. We, like others in the field (see Hilchey & Klein, Reference Hilchey and Klein2011) did not observe a difference in the size of the Flanker effect between monolinguals and bilinguals. However, we did observe significant differences between these groups in overall speed, such that bilinguals were generally faster than monolinguals for both congruent and incongruent trials, a finding that is congruent with the bilingual executive processing advantage (BEPA) hypothesis, if not the bilingual inhibitory control advantage (BICA) hypothesis. However, given the overall lack of replication of the BEPA effect since 2011 (Hilchey et al., Reference Hilchey, Saint-Aubin, Klein and Schwieter2015), we question the value of this explanation. An alternative possibility is that the advantage we observe is due to improved processing speed, rather than executive control.
Processing speed, like executive control, improves during development and deteriorates during aging, and while its effects may overlap with those associated with inhibition and working memory, it has also been shown to be functionally distinct from those processes (Albinet, Boucard, Bouquet & Audiffren, Reference Albinet, Boucard, Bouquet and Audiffren2012; Kail & Salthouse, Reference Kail and Salthouse1994; McAuley & White, Reference McAuley and White2011). Furthermore, processing speed can also affect non-speeded processes, such as memory (e.g., McCabe, Roediger, McDaniel, Balota & Hambrick, Reference McCabe, Roediger, McDaniel, Balota and Hambrick2010; Perrotin, Isingrini, Souchay, Clarys & Taconnat, Reference Perrotin, Isingrini, Souchay, Clarys and Taconnat2006). This pattern is largely congruent with the current literature investigating the cognitive effects of bilingualism, in that results are more robust in children and older adults and have extended beyond inhibition into working and episodic memory. Surprisingly, only one published study that we are aware of (Bonifacci, Giombini, Bellochi & Contento, Reference Bonifacci, Giombini, Bellocchi and Contento2011) has specifically investigated processing speed, but even this study did not use a standardized measure of processing speed. Another, more recent, study by Blumenfeld, Schroeder, Bobb, Freeman and Marian (Reference Blumenfeld, Schroeder, Bobb, Freeman and Marian2016) administered a word recognition and Stroop task to younger and older monolinguals and bilinguals, and used the overall response times on these tasks to index processing speed. They found that some effects, such as residual target activation and competitor inhibition, showed between group differences even after controlling for processing speed, but others such as target activation were influenced by differences in processing speed between the groups. Understanding how bilingualism may affect processing speed and how those effects may relate to cognitive control represents an important area for future research. Given that measures of processing speed share some – but not all – variance with traditional inhibitory control measures, it is possible that some of the replication issues in the current bilingualism literature may be due to the focus on inhibition and executive control, rather than processing speed more generally.
Of course, there are reasons to focus on inhibition, the largest being that many models of bilingual language processing suggest that bilinguals use inhibition to control activation of the unintended language. This reasoning neglects, however, the fact that many of these very same models also involve increasing the activation of the intended language (e.g., the BIA+ and the Inhibitory Control model; Dijkstra & Van Heuven, Reference Dijkstra and van Heuven2002; Green, Reference Green1998). A focus on the language activation aspect of language selection is relevant because current models of action selection (e.g., Verbruggen, McClaren & Chambers, Reference Verbruggen, McLaren and Chambers2014) suggest that action selection and control can be modeled as a competitive process wherein one response is selected over another based on the rate at which accumulating information for each option reaches an action threshold. This idea of accumulating information in the action selection literature is analogous to the idea of activation in the language selection literature, and consequently processing speed may be a relevant factor in the success of language selection.
While our results cannot speak to this hypothesis directly, as we did not administer standard measures of processing speed, future research should investigate this possibility. Our results are a first step towards understanding the effects of bilingual experience on source memory and other complex memory tasks. While we did not see an interaction between complexity and language group in our data, we did observe that the effect of bilingualism was limited to the source memory task, and not the item memory task. This pattern of results is congruent with studies finding that processing speed is critical for estimating task complexity effects in both young and older adults (Oberauer & Kliegel, Reference Oberauer and Kliegl2001; Rodríguez-Villagra, Göthe, Oberauer & Kliegel, Reference Rodríguez-Villagra, Göthe, Oberauer and Kliegl2013).
Another avenue for future research could investigate the relationship between bilingualism, processing speed, and white matter. Previous research has shown that increased myelination, which speeds neural communication, is related to processing speed throughout the lifespan (Chevalier, Kurth, Doucette, Wiseheart, Deoni, Dean, O'Muircheartaigh, Blackwell, Munakata & LeBourgeois, Reference Chevalier, Kurth, Doucette, Wiseheart, Deoni, Dean, O'Muircheartaigh, Blackwell, Munakata and LeBourgeois2015; Ferrer, Whitaker, Steele, Green, Wendelken & Bunge, Reference Ferrer, Whitaker, Steele, Green, Wendelken and Bunge2013; Penke, Maniega, Murray, Gow, Valdes Hernandez, Clayden, Starr, Wardlaw, Bastin & Deary, Reference Penke, Maniega, Murray, Gow, Valdes Hernandez, Clayden, Starr, Wardlaw, Bastin and Deary2010; Peters, Ikuta, Derosse, John, Burdick, Gruner, Prendergast, Szeszko & Malhotra, Reference Peters, Ikuta, Derosse, John, Burdick, Gruner, Prendergast, Szeszko and Malhotra2014). In addition, previous research has observed increased white matter integrity in bilingual populations (see García-Pentón, Fernández García, Costello, Duñabeitia & Carreiras, Reference García-Pentón, Fernández García, Costello, Duñabeitia and Carreiras2015, for a review). Investigating the neural mechanism behind our results has the potential for immense practical importance, as a speed advantage in youth could translate to reduced slowing in old age, and consequently preserved cognitive functions (see Kail & Salthouse, Reference Kail and Salthouse1994, for the role of cognitive slowing in aging; Alladi, Bak, Duggirala, Surampudi, Shailaja, Shukla, Chaudhuri & Kaul, Reference Alladi, Bak, Duggirala, Surampudi, Shailaja, Shukla, Chaudhuri and Kaul2013, for preserved cognitive functions in older bilinguals). An important step to develop this line of research would be to replicate this study in older adults, as one might expect that the RT difference we observed may be enhanced in aging, where source memory shows substantial age-related decline in monolinguals (e.g., Naveh-Benjamin, Reference Naveh-Benjamin2000).
To review, this study is the first to examine the effect of bilingualism in source memory. Our results showed that young adult bilinguals are able to make source memory judgments more quickly than their monolingual peers without compromising accuracy, and this overall speed advantage was also evident in our results from the Flanker task. These results support previous research suggesting that the effects of bilingualism are both widespread and multi-faceted, and may inspire a new research direction into the relationship between bilingualism and processing speed.
