Speed of processing, anticipation, inhibition and ... - Wiley Online Library

Developmental Science 14:2 (2011), pp 256–269

DOI: 10.1111/j.1467-7687.2010.00974.x

PAPER Speed of processing, anticipation, inhibition and working memory in bilinguals Paola Bonifacci, Lucia Giombini, Ste´phanie Bellocchi and Silvana Contento Department of Psychology, University of Bologna, Italy

Abstract Literature on the so-called bilingual advantage is directed towards the investigation of whether the mastering of two languages fosters cognitive skills in the non-verbal domain. The present study aimed to evaluate whether the bilingual advantage in nonverbal skills could be best defined as domain-general or domain-specific, and, in the latter case, at identifying the basic cognitive skills involved. Bilingual and monolingual participants were divided into two different age groups (children, youths) and were tested on a battery of elementary cognitive tasks which included a choice reaction time task, a go ⁄ no-go task, two working memory tasks (numbers and symbols) and an anticipation task. Bilingual and monolingual children did not differ from each other except for the anticipation task, where bilinguals were found to be faster and more accurate than monolinguals. These findings suggest that anticipation, which has received little attention to date, is an important cognitive domain which needs to be evaluated to a greater extent both in bilingual and monolingual participants.

Introduction During the past 25 years the study of bilingualism from a cognitive point of view has attracted the attention of an increasingly large number of researchers. The early years of bilingual research were mainly focused on the linguistic aspects of a bilingual brain, that is, how the two languages are mastered together in a bilingual brain, whether bilingual speakers have two separate lexicons (Paradis, 2000) or one large ‘bilingual’ lexicon (Brysbaert, 1998), what the underlying mechanisms are that allow language lexical access and lexical selection, and so on (Bhatia & Ritchie, 1996). In the past decade an increasing number of studies has shifted to the ‘non-verbal’ skills of a bilingual brain, with a basic underlying question: to what extent does the mastering of two languages have a more general effect on basic cognitive (non-verbal) skills? In other words, is there an advantage in performing cognitive tasks for bilinguals compared to monolinguals? And, if so, which are the precise cognitive processes in which it is possible to observe the bilingual advantage? These are intriguing questions which have the potential to impact upon more general topics, such as the effect of language on cognitive development. The first contributions to literature on what is now commonly called the bilingual advantage varied across different domains, for example, creativity (Kessler & Quinn, 1987), problem solving (Bain, 1975; Kessler &

Quinn, 1980), and perceptual disembedding (Duncan & De Avila, 1979). However, a fundamental contribution to the development of research in this field has come from Green’s (1998) ‘inhibitory hypothesis’. He proposed a model based on inhibitory control in which the nonrelevant language is suppressed by the same executive functions that are used generally to control attention and inhibition. If this model is correct, then bilinguals should have extensive practice in exercising inhibitory control, an experience that they may generalize across cognitive domains (Meuter & Allport, 1999). An alternative hypothesis supports the idea of language-specific selection in bilingual lexical access (Costa, Miozzo & Caramazza, 1999) which also involves some kind of attentional control mechanism (Costa, Hernndez & Sebastin-Galls, 2008). Another important step has been Bialystok’s distinction between control and representational processes. The functions contributing to control processes include selective attention to relevant aspects of a problem, inhibition of attention to misleading information, and switching between competing alternatives. The functions involved with representation processes include encoding problems in sufficient detail, accessing relevant knowledge, and making logical inferences about relational information. Bilingualism seems to be associated with more effective controlled processing in children; the assumption is that the constant management of two competing languages enhances executive functions while

Address for correspondence: Paola Bonifacci, Dipartimento di Psicologia, Universit degli Studi di Bologna, Viale Berti Pichat n.5, 40127 Bologna, Italy; e-mail: [email protected]

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Bilingualism and anticipation 257

no relevant difference seems to emerge in representational tasks based more heavily on analytic knowledge or detailed representations of knowledge (Bialystok, 2001; Bialystok & Martin, 2004). The possible bilingualism advantage in cognitive control has been evaluated by means of different tasks. The first relevant observation refers to the ability of children to shift between different task criteria. For example, Bialystok (1999) asked children to perform a sorting task (Zelazo, Frye & Rapus, 1996) in which they had to sort cards according to a criterion that changed at a certain point in the task. The change of criterion usually elicits a number of incorrect responses. It was observed that bilingual children outperformed monolingual children when the second criterion was introduced, suggesting a better ability at shifting between task rules. The paradigm most widely used to demonstrate the existence of a bilingual advantage is the Simon task (Simon & Ruddell, 1967). In this task, stimuli are presented with a rule that requires participants to ignore the position and respond only to a relevant target feature (for example, if red, press the left key; if green, press the right key). When the stimulus appears on the same display side as the correct response key (congruent trials), both position and response information converge in the correct response. When the stimulus appears on the opposite side (incongruent trials), a greater effort at processing is required to resist the prepotent tendency to respond to the position cue. The increment in response time for the last condition, usually between 20 and 30 ms, is the Simon effect (review in Lu & Proctor, 1995). Bilingual advantages in the Simon task have been reported for young adults (Bialystok, 2006), and middleaged and older adults (Bialystok, Craik, Klein & Viswanathan, 2004). However, bilingual advantages seem to be confined to complex tasks requiring control over attention to competing cues (interference suppression) and not to tasks requiring control over competing responses (response inhibition) (Martin-Rhee & Bialystok, 2008). Moreover, it seems that bilinguals do not differ from monolinguals in terms of active inhibition but do have a better ability to maintain action goals and to use them to bias goal-related information (Colzato, Bajo, van den Wildenberg, Paolieri, Nieuwenhuis, La Heij & Hommel, 2008). Recently, the possible control advantage in bilingualism has been evaluated in terms of conflict resolution abilities using the Attentional Network Task (ANT; Fan, McCandliss, Sommer, Raz & Posner, 2002; Rueda, Fan, McCandliss, Halparin, Gruber, Pappert-Lercari & Posner, 2004) both on samples of adult (Costa et al., 2008) and kindergarten bilinguals (Carlson & Meltzoff, 2008). This task is a combination of a cue reaction time task (Posner, 1980) and a flanker task (Eriksen & Eriksen, 1974) exploring attentional abilities divided into three components: executive control (conflict resolution), alerting and orienting. Participants are asked to indicate whether a central arrow is oriented to the right or left. 2010 Blackwell Publishing Ltd.

The arrow is presented between flanker arrows pointing either in the same direction (congruent condition) or in different directions (incongruent condition) from the target. Responses are slower for incongruent than for congruent conditions, showing that more cognitive effort is needed to resolve the conflict. The alerting network is explored by showing that faster responses occur when a cue is presented before the target stimulus than when it is not. Finally, orienting is studied by showing that responses are faster when a cue indicates the position of a target stimulus than when it is not. Both the ANT and the Simon task appear to involve inhibitory control as a common component but, as suggested by Costa and colleagues (2008), the ANT paradigm relies minimally on linguistic and memory processes that may interact with bilingualism. Specifically, while in the Simon task participants are required to hold the stimulus–response rule in working memory (if it is red press left, if it is blue press right), this working memory component is not required in the flanker task. Costa and colleagues found that the difference between congruent and incongruent trials was larger for monolinguals than for bilinguals. That is, bilinguals suffered less interference from incongruent flankers than monolinguals, suggesting that the mechanisms involved in conflict resolution are more efficient for the former group. Moreover, bilinguals showed a greater benefit from the alerting cue compared to monolinguals. Carlson and Meltzoff (2008) found that, when controlling for socioeconomic status (SES), age and verbal ability, bilinguals performed better than monolinguals on a subset of tasks involving conflicting attention, which included the ANT task, but there were no differences in the other subset of tasks involving impulse-control executive functions. These latter abilities were explored by delay-of-gratification tasks in which children needed to wait while the experimenter was out of the room and not peek inside a gift box; this task also assessed children’s skills to delay food reward in order to receive a larger amount. Despite the majority of studies that report evidence supporting the existence of a bilingual advantage, recent reports seem controversial and some findings have led to the emergence of new questions. With particular reference to the repeatedly observed advantage on the Simon task, Morton and Harper (2007) did not replicate the advantage of bilinguals over monolinguals when controlling for SES and ethnicity. What they found was that bilingual and monolingual children performed identically, whereas children from higher SES families were advantaged compared to children from lower SES families. In another recent study of the bilingual advantage in the Simon task, the differences between monolinguals and bilinguals disappeared after a few blocks of practice (Bialystok et al., 2004, Experiment 3). Controversial results emerged also with reference to the developmental dimension, specifically the extent to

258 Paola Bonifacci et al.

which the bilingual advantage impacts on cognitive development and persists throughout life. Recent evidence showed that bilingualism delays cognitive decline (see Craik & Bialystok, 2006, for a review), whereas the research conducted with younger adults has not led to such strong results. It has been suggested that the bulk of positive effects associated with bilingualism is present in those developmental stages in which the attentional system of the individual is not at its maximum level of performance (Costa et al., 2008), while these differences become smaller or disappear when individuals are at the peak of their attentional capabilities. For example, Bialystok, Craik and Ruocco (2006) and Bialystok (2006) found small differences in dual-task processing and in the magnitude of the Simon effect, respectively, between bilingual and monolingual university undergraduate students. Finally, studies directed towards the evaluation of the bilingual advantage, as highlighted by the literature reviewed above, have been mainly focused on the evaluation of control and executive functions. However, these are complex cognitive functions whose performance might be confounded by other variables such as speed of processing, working memory and, to different extents according to the task used, linguistic processes. Speed of Information Processing (SIP) refers to the rate at which sensory information passing into the nervous system can be operated upon and it is a very basic component of intellectual functioning (Jensen, 1998). Speed of information processing is a useful construct for differentiating between domain-specific and domain-general cognitive processes, and this has been applied in the study of learning disabilities (Bonifacci & Snowling, 2008). Speed of processing has been considered since early research in bilingual studies although few studies have addressed the question directly. Somewhat inconsistent with the notion that bilingualism selectively benefits cognitive control, several studies reported that bilinguals were overall faster than monolinguals. In order to rule out the possibility that bilinguals were generally better in ‘speed of processing’, Bialystok, Martin and Viswanathan (2005) included in a Simon task a neutral condition. This neutral condition did not require executive control, but mainly measured ‘speed of processing’ and the authors did not find any differences between bilinguals and monolinguals. That is, bilinguals and monolinguals were equally fast in the neutral condition, but bilinguals were still faster in the experimental conditions of the Simon task. These results led Bialystok and colleagues to propose, for the first time, that bilinguals could be better in an executive control component different from inhibition, namely monitoring (the ability to constantly monitor the need to engage conflict resolution mechanisms such as inhibitory processes). Alternatively, it could have been that the neutral condition used by Bialystok and colleagues was not demanding enough to show the bilingual advantage in speed of processing. Consequently, some studies were specifically designed to 2010 Blackwell Publishing Ltd.

address this issue of the bilingual advantage in overall RTs. For example, Martin-Rhee and Bialystok (2008, Study 1) and Costa, Hernndez, Costa-Faidella and Sebastin-Galls (2009) addressed this issue. Costa and colleagues hypothesized that the overall speed advantage observed in bilinguals might reveal an impact of bilingualism on the efficiency of the conflict monitoring system, and that consequently, its detectability would depend on the extent to which the experimental conditions tax the monitoring system. These conditions were re-created by manipulating parametrically the percentage of congruent and incongruent trials in the experiment and, consistent with their hypothesis, the authors found that bilinguals were faster than monolinguals in the condition in which the monitoring system is maximally recruited (50% congruent version). The first aim of the present study was therefore to assess if the so-called bilingual advantage refers to domain-general skills, such as speed of processing, or to domain-specific skills, and if this is the case, which basic cognitive functions are involved. In particular, the main focus of the present study was to introduce the evaluation of anticipation skills in bilinguals, whereas speed of processing, inhibition and working memory were considered control measures for the former. We tested SIP through Choice Reaction Time tasks (CRT), which can be considered an example of the tasks commonly referred to as Elementary Cognitive Tasks (ECT) (Neubauer & Knorr, 1997). ECT are characterized by a minimum level of complexity where performance is primarily dependent on speed of processing. It is assumed that accuracy can reach a ceiling effect if participants perform the tasks without time constraints (Jensen, 1998). If bilingual participants were to show faster RTs on this simple measure of SIP, it would mean that the bilingual advantage is active at a low level of cognitive processing and is widespread across cognitive functions. In other words, this would suggest that bilingualism improves general cognitive abilities and this would offer new insights for bilingual literature. On the other hand, if bilinguals and monolinguals did not differ in SIP on ECTs, this would allow us to assume that an eventual bilingual advantage is specific only to those particular tasks where specific skills are manipulated and in which bilinguals outperform monolinguals. In order to evaluate speed of information processing and basic cognitive skills in bilingual and monolingual participants, we developed a battery of elementary cognitive tasks of increasing complexity such as choice reaction time, inhibition (go ⁄ no-go task), verbal (numbers) and non-verbal (symbols) working memory and anticipation tasks. Inhibition skills refer to the ability to voluntarily suppress irrelevant stimuli and responses and focus on goaldirected actions. It was included since it is one of the most frequent dimensions referred to the bilingual advantage studied in literature. We chose a go ⁄ no-go task instead of a Simon task because it is freer from linguistic interference. Working memory tasks were included both


to test for differences in this domain between monolingual and bilingual participants, but also to evaluate the role of working memory capacity when analysing performances in the other cognitive tasks. In fact, a good working memory allows for the maintenance of information (verbal or non-verbal) until the optimal time for its use arrives. The potential advantage of bilingualism on working memory has been an object of debate. For example, Bialystok et al. (2004) increased the working memory load of the Simon effect and showed that bilingual participants responded more rapidly to conditions that involved greater demands on working memory. However, the difference between monolinguals and bilinguals does not seem to be in memory ability, or even in short-term or simple working memory; rather, it is in conditions that include stringent demands for control and inhibition (Bialystok, 2009). To our knowledge, the ability to anticipate incoming events has received little attention in bilingual studies and the present study would offer a new insight into this topic posing a new question concerning the so-called bilingual advantage: do bilingual speakers develop more efficient anticipation skills in non-linguistic tasks? Anticipation is a highly multidisciplinary theme, and a growing interest is emerging in empirical, theoretical and computational literature (Pezzulo, Hoffmann & Falcone, 2007). There is now a converging body of evidence in psychology and neurobiology indicating the presence of several anticipatory mechanisms in the brain and highlighting the crucial role of anticipation in a large array of cognitive functionalities such as planning, imitation, theory of mind, and language use (Pezzulo et al., 2007). Anticipation can be defined as a cognitive process that requires the knowledge of regularities in the temporal unfolding of external events to perform a predictive behaviour (Posada, Franck, Georgieff & Jeannerod, 2001). In this perspective, response anticipation is supported by executive control functions (MacDonald, Cohen, Stenger & Carter, 2000). According to this model, to anticipate an incoming event (as colour in Posada and colleagues’ paradigm, see below for a detailed description of the task) participants must use simultaneously some components (know the notion of repetitive sequence, store in memory the sequence and the instruction to anticipate) which are integrated by working memory (WM). During the task, participants also have to refresh the mental representation at each trial. Updating, which represents the active component of WM, is considered as one of the most frequently postulated executive functions (EF) in recent literature (Collette & Van der Linden, 2002; Friedman, Miyake, Corley, Young, DeFries & Hewitt, 2006; Miyake, Friedman, Emerson, Witzki, Howerter & Wager, 2000). However, the ability to anticipate cannot be completely explained as the sum of good working memory and cognitive control, although these are basic determinants. Anticipation involves a portion of probabilistic reasoning which is the result of the information available in the 2010 Blackwell Publishing Ltd.

short- or long-term memory in terms of patterns of regularities and the use we make of it while predicting what is more likely to come next. Predictions can be either explicit or implicit and allow for selective and focused processing (Corbetta, Miezin, Dobmeyer, Shulman & Petersen, 1991; Posner & Petersen, 1990). If a subject is able to make accurate predictions, the time and accuracy of responses are improved and more pertinent reactions are allowed. In this view, anticipation is seen as relatively independent from working memory skills, and as a specific cognitive capacity which can be fostered by experience such as bilingualism. Our hypothesis follows the rationale adopted in other studies on bilingual advantage: extensive training increases efficiency in a wide range of abilities and not only in those more closely related to the training itself (Green & Bavelier, 2003). Since it has been proposed that inhibition skills are improved in bilinguals because this group is used to suppressing the non-relevant language, it might also be hypothesized that anticipation skills are improved in bilinguals because they have practice in anticipating the upcoming element of a sentence in two or more languages, each characterized by specific syntactic and pragmatic rules. Bilinguals are faced with at least two verbal codes that they use in everyday language processes. In discourse processing, anticipation occurs as an ongoing activity of language unfolding and reflects what, given the current input, is likely to be referred to next (Otten & Van Berkum, 2008). However, what is to be expected depends both on the linguistic content and on the grammar, syntax and pragmatic structures of the language used. In other words we suggest that anticipation skills should be enhanced in bilinguals due to the continuous practice they exert in predicting upcoming events (words, sentences, meaning) according to different regularities in language structures and pragmatics. A considerable body of literature on monolingual language processing suggests that people anticipate upcoming syntactic structure (e.g. Kamide, Altmann & Haywood, 2003) and can make predictions about the grammatical role of an upcoming word (e.g. Lau, Stroud, Plesch & Phillips, 2006). Moreover, previous research has shown that readers make predictions about upcoming meaning (inferences). In text comprehension research the emerging consensus is that readers do not rigidly infer everything logically possible all the time but do make predictive inferences under particular circumstances, such as when the text is sufficiently constraining and world knowledge makes the inference sufficiently available (Weingartner, Guzmn, Levine & Kline, 2003). A very recent study has shown that 7-month-old bilingual infants succeeded in redirecting their anticipatory looks more correctly than monolinguals (Kovcs & Mehler, 2009). The authors refer to anticipatory look as an eye movement performed to one side of the screen within 1 second of the end of the word and before the appearance of the visual reward. Since bilinguals are better at overcoming a previously learned response, authors


interpreted these results as a domain-general enhancement of the cognitive control system. This indicates that perceiving and processing utterances from two languages improves the ability to make predictions even in preverbal infants. This extensive practice in anticipating elements in discourse practice, together with better executive control and more efficient alerting (see also Bialystok & Feng, 2009), should improve the ability to update predictions on what is to be expected. In the present paper, we explore anticipation in an adapted version of the anticipation task developed by Posada and colleagues (2001). Specifically, in the task developed by Posada and colleagues participants are required to anticipate the colour of upcoming geometrical shapes, after having learned their order. Hence, we can consider this paradigm a non-linguistic task which may allow us to evaluate whether the ability to anticipate is fostered by the mastering of two languages and extends to non-verbal tasks. The second aim of the study was to compare two different age groups (children and adolescents) of monolinguals and bilinguals in order to evaluate the impact of bilingualism on the developmental trajectories of cognitive functions. As mentioned above, the developmental dimension is of crucial importance when studying control abilities. Attentional skills continue to develop during adolescence (Anderson, Anderson & Garth, 2001; Gomez-Perez, Ostrosky-Solis & ProsperoGarcia, 2003; Siegler, 1978; see also Ridderinkhof & Van der Stelt, 2000, for a review) as documented by brain imaging studies reporting significant decreases in cortical grey matter and increases in white matter in adolescent years (Giedd, Blumenthal, Jeffries, Castellanos, Liu, Zijdenbos, Paus, Evans & Rapoport, 1999; Jernigan, Trauner, Hesselink & Tallal, 1991; see also Durston & Casey, 2006, for a review). In fact, the improvement of executive and control abilities is supported by development in specific core cognitive processes that are still immature in late childhood, including processing speed (Hale, 1990), voluntary response suppression (Diamond & Goldman-Rakic, 1989; Fischer, Biscaldi & Gezeck, 1997), and working memory (Zald & Iacono, 1998).

activity for the evaluation of learning and cognitive functioning, and from an association of bilingual parents situated in Bologna. The monolingual group was recruited from the same schools as the bilingual children. The ‘Youth’ group consisted of 32 participants aged between 14 and 22 years (15 females, 17 males); 16 were monolinguals (mean age 19.06 yrs, SD: 1.84) and 16 were bilinguals (mean age 18.06 yrs, SD: 3.6). The relatively wide age range of the sample does not suffer from developmental factors since it is known that executive control abilities seem to reach a plateau after puberty (Rueda et al., 2004). For both the Children and the Youth group, the monolingual participants were matched to the bilingual subjects for age, sex and non-verbal IQ, tested with the Italian version of the K-BIT (Kaufmann Brief Intelligence Test; Kaufman & Kaufman, 1990; Bonifacci, Santinelli & Contento, 2007). The experimental group was characterized by a proficiency in two languages: Italian and another language, practiced both at school and at home. The languages spoken, other than Italian, were English (12), German (9), Chinese (4), Tagalog (1), Moroccan Arabic (1), Albanian (1), Polish (1), Slovack (1) and Russian (1). Due to the variety of languages other than Italian, it was difficult to establish the level of proficiency in both languages accurately. Instead of a linguistic assessment we used criteria based on the type of bilingualism and the age of language acquisition. All bilingual participants had either a familiar bilingualism (they had an Italian parent with whom they spoke Italian and a parent whose L1 was not Italian and who was used to speaking in their mother-tongue language with the child) or spoke an L1 which was not Italian and had attended an Italian school for at least 6 years. However, it is important to underline that none of our tasks included linguistic material except for the instructions; the main aim of the present study was to evaluate the impact of bilingualism on non-verbal skills. Design and materials A battery of four tasks was written in E-Prime software (Schneider, Eschman & Zuccolotto, 2002) and presented on a laptop computer:

Method Choice Reaction Time Participants The total sample of the study consisted of 68 participants divided into different age and language knowledge groups. The ‘Children’ group consisted of 36 children aged between 6 and 12 years (16 females, 20 males); 18 were monolinguals (mean age 9.61 yrs, SD: 2.06) and 18 were bilingual children (mean age 9.28 yrs, SD: 2.3). Bilingual participants were recruited from mainstream schools where the Department of Psychology, University of Bologna, was conducting a collaborative screening 2010 Blackwell Publishing Ltd.

The icons of a hand and of a foot were presented for 1 sec in random sequence (with a 1 sec white screen interval). Subjects were required to press the H key for the hand and the F key for the foot (stickers with the Italian capital letters were used). After six practice trials, 60 experimental trials followed. Go ⁄ No-go task The Go ⁄ No-go task was based on the same stimuli used for the choice reaction time task (hand and foot).


Participants were required to follow the same instructions as for the previous task, but not to press any key when the images were presented together with a sound. The sound appeared at image onset. After 10 practice trials, 60 experimental trials followed, 40 in the ‘go’ and 20 in the ‘no-go’ condition, thus in a 2:1 ratio. The number of errors and omissions was recorded together with reaction times for both go and no-go tasks. Memory with number This task required the subject to detect if a target digit appeared in a string of digits. After a 1 sec blank screen, a sequence of numbers (between 1 and 9) was presented for 3 sec. The length of the sequence varied between one and seven digits. Next, a blank screen appeared for 1 second, followed by a target number which remained on the screen until the subject gave a response. Children were instructed to look at the number that came after the sequence and then answer ‘Yes’ or ‘No’ depending on whether the target was in the previous sequence. Two stickers with ‘Yes’ and ‘No’ labels were put over two adjacent keys on the keyboard (Keys V and N). Numbers were written in 32-point font and double-spaced. Fourteen number-string sequences (two of one number, two of two numbers, two of three numbers, two of four numbers, two of five numbers, two of six numbers, two of seven numbers) were repeated randomly four times for a total of 56 target trials preceded by four practice trials. For every sequence length, half of the trials were positive and half negative. Memory with symbol The symbol memory task was developed as a non-verbal version of the number memory task and the procedure was similar except that the stimuli were letters taken from the Gurmukhi alphabet (Malherbe & Rosenberg, 1995) (Figure 1). These characters were chosen because they resemble neither geometric shapes nor Latin letters and it is therefore quite hard to name them using verbal labels. None of the bilingual participants knew this alphabet. In the Symbol memory task, the maximum sequence length was five (rather than seven as for digits) because of the complexity of the symbols. Eight symbol-string sequences were repeated randomly six times for a total of 48 target trials preceded by six practice trials. As before, half of the trials were positive and half negative. Anticipation In this task sequences of coloured (yellow, green or blue) rectangles were displayed in the middle of the screen. The task involved three conditions each divided into several

blocks. In the first condition (Sequence learning), participants were informed that the colours were distributed in a fixed sequence, and they were instructed to try to disclose the sequence. After disclosing the sequence they had to press the Q key and tell the experimenter which was the colour sequence. The number of items needed to disclose the sequence was measured and was called the Learning Score. The sequences involved four tokens made by three colours (blue, blue, green, yellow) and were repeated until a response was given or until nine sequences had been displayed. All participants identified the correct sequence before reaching the maximum trials available. After the sequence was learned, participants were required to perform three Anticipation tasks (of increasing difficulty) and three Reaction Time tasks. In the Anticipation blocks, coloured rectangles appeared in a fixed order and the participant was instructed to try to push the correct colour button before the rectangle appeared, in other words to anticipate the next element of the sequence. In the Reaction Time tasks, performed after each anticipation sequence, the same coloured rectangles appeared in random order and participants were required to press the corresponding colour key after the rectangle appeared. In the first Anticipation sequence, rectangles appeared in the same order as in the learning sequence (blue, blue, green, yellow) for a total of nine blocks (36 trials). In the second Anticipation sequence, participants were instructed on a new sequence (yellow, green, blue, blue) which they had to repeat aloud, and they were again requested to anticipate the upcoming stimulus for nine blocks (36 trials). Finally, in the third Anticipation block, a third sequence was created, which was the combination of the first two (blue, blue, green, yellow, yellow, green, blue, blue) and subjects were instructed to repeat the sequence aloud and then perform the anticipation task. The sequence was repeated four times for a total of 32 trials. In each Anticipation block a black slide stayed on the monitor for 1500 msec, and this was the time interval for the participants to anticipate the upcoming stimulus. After 1500 msec or after a response was given, a coloured rectangle appeared for 1000 msec and feedback was given with a ‘correct’, ‘incorrect’ or ‘out of time’ response displayed for 500 msec. Procedure All subjects were tested individually in a session that lasted approximately 40 minutes, with appropriate breaks. The instructions for each task appeared on the screen in Italian and were read aloud by the experimenter. Ethical clearance1 and parental permission were obtained before administering the tests. The tasks were presented in a randomized order.

1

Figure 1

Example of a trial from the memory symbol task.

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This study was carried out according to the ethical guidelines laid down by AIP (Associazione Italiana di Psicologia).


Results Characteristics of the groups In Table 1 a summary of the characteristics of the groups is displayed, including intellectual functioning measures and age. As expected, considering intellectual functioning as indexed by IQ values measured with the adapted Italian version of the K-BIT (Kaufmann Brief Intelligence Test; Kaufman & Kaufman, 1990; Bonifacci et al., 2007), no differences emerged considering either Group (monolinguals, bilinguals) (F(1, 65) = 0.1; p = ns), or Age (Children, Youths) (F(1, 65) = 36.32; p = ns). As far as age was concerned, there was a clear significant difference between the Children and Youth groups (F(1, 67) = 217.8; p < .01), but no difference emerged for Group (F(1, 67) = 1.16; p = ns). Data analyses Measures of accuracy and Reaction Times (RTs) or Anticipation Times (ATs) were recorded for each task and analyses were conducted on mean RTs of correct

Table 1 Youths)

responses only. We use the term ATs to refer to the time needed to anticipate the response which is different from the standard RTs needed to answer to a stimulus. Reaction times under 100 msec were excluded because they were considered to be ‘anticipatory errors’ and they might to be too fast to reflect a real stimulus processing. For CRT and Inhibition tasks, ANOVAs were conducted for each of the speed of information processing tasks with Group (Monolinguals, Bilinguals) and Age (Children, Youths) as the between-subjects factors, and means, medians and standard deviations for correct RTs or ATs as dependent variables. Afterwards, for WM and Anticipation tasks, repeated measures analyses of variance (ANOVAs) were run with Task or Sequence as the within-subjects factors and with Group (Monolinguals, Bilinguals) and Age (Children, Youth) as between-subjects factors. When analyses based on median values did not differ from means they were not reported. ANOVAs with accuracy as the dependent variable were also run for each task. Table 2 reports mean RTs and task accuracy scores for each group.

Sample size, mean age and non-verbal IQ of monolingual and bilingual participants, divided by age group (Children, Children

Monolinguals Bilinguals

Youths

Age (years)

KBIT (std.scores)

n

Mean (SD)

Mean (SD)

18 18

9.61 (2.1) 9.27 (2.3)

110.38 (12.5) 111.76 (14.1)

Age (years)

KBIT (std.scores)

n

Mean (SD)

Mean (SD)

16 16

19.06 (1.84) 18.06 (3.66)

108.93 (11.1) 109.86 (14.7)

Table 2 Mean RT parameters and accuracy (percentage of errors) in the reaction time and anticipation time tasks for monolingual and bilingual participants, divided by age group (Children, Youths) Children

Choice RT means (msec) Choice RT errors % Go ⁄ No-go means (msec) Go ⁄ No-go errors % Memory numbers means (msec) Memory numbers errors % Memory symbols means (msec) Memory symbols errors % Anticipation Learning Score Anticipation 1st seq. means (msec) Anticipation 1st seq. errors % Anticipation 2nd seq. means (msec) Anticipation 2nd seq. errors % Anticipation 3rd seq. means (msec) Anticipation 3rd seq. errors % Anticipation random RT means (msec) Anticipation random RT errors %

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Youths

Monolinguals

Bilinguals

Monolinguals

Bilinguals

Mean (SD)

Mean (SD)

Mean (SD)

Mean (SD)

665.65 4.25 809.04 11.01 1593.80 9.42 1625.51 14.08 16.33 744.15 9.56 616.38 7.56 714.67 18.51 814.515 2.88

(177.76) (4.32) (136.53) (10.57) (475. 43) (12.29) (473.6) (10.45) (8.4) (217.52) (14.58) (183.85) (15.00) (204.44) (14.54) (141.39) (3.08)

620.79 5.93 742.65 13.42 1457.86 9.52 1446.84 16.46 14.611 601.66 2.46 506.08 6.01 535.74 12.19 767.98 3.94

(151.32) (4.3) (138.03) (16.49) (422.10) (11.88) (324.45) (12.80) (7.59) (172.64) (5.30) (168.68) (11.12) (202.41) (15.04) (144.21) (4.04)

460.92 4.37 550.27 9.58 1005.93 2.34 1069.98 8.03 14.68 585.14 1.04 518.80 1.56 524.56 13.02 571.79 1.56

(93.73) (4.12) (95.83) (22.59) (237.91) (2.33) (202.08) (6.32) (6.90) (172.01) (2.24) (412.92) (2.68) (267.58) (14.83) (98.04) (1.31)

430.10 6.25 533.19 5.42 1050.32 3.90 1099.55 8.81 17.75 448.76 2.43 369.84 3.47 458.45 8.85 532.35 4

(71.35) (3.42) (72.40) (4.85) (152.78) (8.61) (257.50) (13.42) (8.82) (93.01) (5.64) (156.19) (5.96) (198.94) (9.95) (51.28) (3.65)


Group differences Choice Reaction Times Considering the RT means there was a significant effect of Age (F(1, 65) = 36.32; p < .01), but there was no effect for Group (F(1, 65) = 1.32; p = ns), or for the interaction Group · Age (F(1, 65) = 0.46; p = ns). The same trend was observed for standard deviations [Age: (F(1, 65) = 34.67; p < .01); Group: (F(1, 65) = 0.120; p = ns), Group · Age: (F (1, 65) = 0.738; p = ns)]. The Youth group had faster RTs and was less variable than the Children group. No difference was observed when considering Accuracy scores (all ps > .05). Inhibition In the Go trials of the Inhibition task, a significant effect of Age emerged (F(1, 65) = 69.335; p < .01.), but no effect for Group (F(1, 65) = 2.2; p = ns), or for the interaction Group · Age was evident (F(1, 65) = 0.769; p = ns). The same trend was observed for standard deviations [Age: (F(1, 65) = 55.8; p < .01); Group: (F(1, 65) = 0.45; p = ns), Group · Age: (F(1, 65) = 0.184; p = ns)]. Again, the Children group was found to have slower RTs and to be more variable in comparison to the Youth group. Considering the No-go trials in terms of accuracy (percentage of false hits) no difference was observed (all ps >. 05). Working memory As far as the Memory tasks were concerned, a repeated measures analysis of variance (ANOVA) was run with Task (two levels: verbal and non-verbal) as a withinsubjects factor and with Group (Monolinguals, Bilinguals) and Age (Children, Youth) as between-subjects factors. Mean (median and SD) RTs for numbers and symbols constituted the dependent variables. A significant effect of Age emerged (F(1, 64) = 37.26; p < .001), but no effects for Group (F(1, 64) = 0.59; p = ns) and no interaction for Age · Group was observed (F(1, 64) = 1.56; p = ns). Moreover, neither Task effect (F(1, 64) = 1.12; p = ns) nor interactions Task · Group (F(1, 64) = 0.21; p = ns) and Task · Age (F(1, 64) = 0.53; p = ns) were revealed. Considering standard deviations, neither Age effect (F(1, 64) = 1.5; p = ns) nor Group effect (F(1, 64) = 0.46; p = ns) and Group · Age (F(2, 63) = 1.359; p = ns) emerged. However, a Task effect was observed (F(1, 64) = 80.47; p