Qu cooperation influences inhibition 2011

Journal of Experimental Child Psychology 108 (2011) 549–566

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Journal of Experimental ChildPsychology

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Two is better than one, but mine is better than ours:Preschoolers’ executive function during co-play

Li Qu ⇑Division of Psychology, School of Humanities and Social Sciences, Nanyang Technological University, 637332 Singapore, Singapore

a r t i c l e i n f o

Article history:Available online 27 September 2010

Keywords:Executive functionPreschoolersSocial contextFacilitationCooperationCulture

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a b s t r a c t

The current study investigated how playing with another individ-ual may influence 3- and 4-year-olds’ executive function in theLess-Is-More (LIM) task, where children point to the tray withthe smaller amount of treats so as to obtain the larger amount oftreats in the other tray. In Experiment 1, 35 Singaporean childrenwere tested with a self version and a co-player–split version ofthe LIM task. Results showed that children appeared to be lessimpulsive when playing with a co-player than when playing indi-vidually. Experiment 2 further investigated how the intention ofthe co-player, collective profit oriented versus individual profit ori-ented, may influence children’s executive function. In total, 96 chil-dren were tested with a self version, a co-player–share version, anda co-player–opponent version. Results showed that the co-playingfacilitation effect appeared in only the co-player–opponent ver-sion. Together, the results of the current study showed that whenpreschoolers play with an individual who shares a common goalwith them, they may become more efficient in executive control.

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Introduction

Executive functions (EFs) refer to the processes required for the conscious control of thought, emo-tion, and action (e.g., Zelazo, Qu, & Müller, 2005). From a functional perspective, EF can be described asa problem-solving process that includes problem representation and goal establishment, plan con-struction, plan and rule execution, and outcome evaluation (Zelazo, Carter, Reznick, & Frye, 1997).The development of EF is associated with the development of the brain, especially the prefrontal

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550 L. Qu / Journal of Experimental Child Psychology 108 (2011) 549–566

cortex (see review in Tsujimoto, 2008). EF develops rapidly during the preschool years (e.g., Carlson,2005). For instance, based on a reversed reinforcement paradigm (Boysen & Berntson, 1995), the Less-Is-More (LIM) task measures children’s EF involving conflicts (Carlson, Davis, & Leach, 2005). In thistask, children are presented with two trays: one with a larger amount of treats and the other witha smaller amount of treats. Children are supposed to point to the tray with the smaller amount oftreats so as to win the larger amount of treats. Across 16 test trials, most 3-year-olds had difficultyin pointing to the smaller amount of treats, whereas 4-year-olds performed much better (Carlsonet al., 2005, Study 1). Young preschoolers’ performance was improved when real treats such as jelly-beans were replaced with neutral symbols such as a mouse versus an elephant (Carlson et al., 2005,Study 2). This implies that young children’s EF can be improved when their attention is directed to-ward the essential goal of the task instead of the attractive feature of the stimuli (Carlson et al.,2005; Metcalfe & Mischel, 1999; Zelazo, Qu, & Kesek, 2009).

The early development of EFs has been linked to theory of mind, emotion regulation, and socialcapabilities. EF influences children’s social competence and their social interaction in daily life (e.g.,Ciairano, Visu-Petra, & Settanni, 2007). For instance, most 3-year-olds fail to deceive a competitoras measured via the windows task, in which children are supposed to point to an empty box forthe competitor instead of the box that contains a treat (Russell, Mauthner, Sharpe, & Tidswell,1991). Russell and his colleagues found that children’s performance can be improved when the de-mands to inhibit predominant responses are removed. For example, instead of asking children to pointto a box, they asked children to use a tool such as a pointer to indicate which box they want the exper-imenter to have or a button that releases a sweet from an automated machine. When responding withthese new methods, children’s performance improved (Hala & Russell, 2001; Russell, Hala, & Hill,2003; see also Carlson, Moses, & Hix, 1998). Thus, young children’s failure in the windows task isdue not only to their difficulty in simultaneously representing competitors’ mental states and theirown mental states but also to their lack of executive control (Hala & Russell, 2001; Russell et al., 2003).

EF, similar to other cognitive functions, develops within social contexts (Vygotsky, 1978). Childrenprofit from being with an adult, an older child, or a peer in a variety of social contexts (e.g., Burton,1941; Foley & Ratner, 1998; Garton & Pratt, 2001; Perlmutter, Behrend, Kuo, & Muller, 1989). Workingwith another person can improve a number of children’s abilities, including categorization, free recall,use of strategies, and understanding of questions (Manion & Alexander, 1997; Ratner, Foley, & Gim-pert, 2002). For instance, collaborating on a block-sorting task with a child with higher sorting abilitiescan improve the scores of 4- to 7-year-olds with lower sorting abilities (Garton & Pratt, 2001).

Teaming up with another person may facilitate children’s performance both cognitively and affec-tively. Cognitively, working with another person may increase children’s awareness of the essentialgoal as well as the other individual’s perspectives and problem-solving methods. Such awarenessmay be integrated into children’s own awareness and further facilitate their behavioral control. Affec-tively, working with another person may increase children’s enjoyment of the activity. Such sugges-tions are consistent with functional magnetic resonance imaging (fMRI) studies in adults. Comparedwith playing a game independently, playing with another person seems to be associated with morebrain activity in the frontoparietal network, which is related to EF and theory of mind, and the anteriorinsula, suggesting higher levels of autonomic arousal and feelings of reward (e.g., Decety, Jackson,Sommerville, Chaminade, & Meltzoff, 2004; Rilling et al., 2002).

The facilitation effect may be due to the emphasis on the essential goal. During cooperation, indi-viduals are working toward the same goal, which may help them to realize the essential goal and focuson it. For instance, Gräfenhain, Behne, Carpenter, and Tomasello (2009) asked 3-year-olds to play withan experimenter jointly or in parallel and then had the experimenter suddenly stop playing the gamewhen it was her turn. The researchers found that children exhibited clear signs to encourage theexperimenter to reengage in the game in the joint play condition but not in the parallel play condition.During co-play, preschoolers not only realize the joint goal but also want to fulfill the joint goal.

The facilitation effect may also be due to an exchange of ideas and perspectives (e.g., Fawcett &Garton, 2005). Co-playing, even without communication, may make children more aware of and morewilling to adopt different perspectives and problem-solving methods. Such a process may help chil-dren to reflect and internalize the knowledge and, hence, to regulate their behaviors accordingly(e.g., Kuhn, Garcia-Mila, Zohar, & Anderson, 1995). According to Rogoff (1998), while physically

L. Qu / Journal of Experimental Child Psychology 108 (2011) 549–566 551

observing their partners’ actions, children mentally perform the same actions themselves. For in-stance, 3- and 4-year-olds tend to show a self-efficiency bias after accomplishing a task with a morecapable partner (Foley & Ratner, 1998; Kushnir, Wellman, & Gelman, 2009; Sommerville & Hammond,2007). After the task, when asked to describe the problem-solving process, young children more oftenreported that ‘‘I did it” even though it was the partner who actually did it. It is not surprising thatyoung children make a source memory mistake given that during the cooperation the responsibilityand duty may have been ambiguous and contingent. However, most important, such bias reflectsthe fact that young children are integrating the capable partner’s behavior into their own behaviors.Such an integration process involves learning and will eventually increase children’s cognitiveabilities.

Co-playing can also increase children’s task engagement, enjoyment, and motivation, which mayfurther facilitate children’s performance. For instance, Burton (1941) asked a preschooler to play apegboard game until the child felt bored, at which point a second child was brought in to play thegame with the first child. In this situation, it was found that the previously bored child continuedto play the game for one third of the initial playtime. Similarly, compared with playing alone, a pre-schooler would play with a set of toys for a longer period of time and play with the toys in a greatervariety of manners when teaming up with another child (Perlmutter et al., 1989; Simmel, Baker, & Col-lier, 1969). This is possibly because, compared with playing alone, the mildly increased positive moodfrom the co-play may facilitate children’s flexibility and problem-solving abilities (e.g., Isen, 2003),and the enhanced intrinsic motivation associated with the co-play may make children more able toconcentrate on the task (e.g., Chang & Burns, 2005; Qu, Liberman, Lim, Loh, & Leong, 2010).

The current study focused on the cognitive aspect of the facilitation effect associated with cooper-ation. In particular, it aimed to investigate the impact that sharing task goals had on EF during passivecooperation (i.e., without communication or exchange of ideas between team members).

It is not surprising that during cooperation, preschoolers are able to perceive the goals of the part-ner given that even 18-month-olds are sensitive to others’ intention (e.g., Meltzoff, 1995). However, itis not a simple process for children to understand another person’s intention and integrate it with theirbehavioral control. As Johnson and Johnson (1974) stated, children need to identify and realize (a) theexistence of the other person, (b) the action of the other person, and (c) the nature and implication ofeach person’s goal. Compared with the ability to understand competitive intention, children seem totake a longer time to develop the ability to understand other people’s cooperative intention. For exam-ple, Herrmann and Tomasello (2006) found that 24-month-olds were more responsive to an informingcooperator, whereas 18-month-olds were more responsive to a prohibiting competitor. Furthermore,it is only after 5 years of age that children are able to engage in real cooperation (e.g., Tomasello,Kruger, & Ratner, 1993) when they are able to ignore distractions, coordinate attention, communicatewith partners, understand the perspectives of the partner, and integrate their goals with the partner’sgoals. In particular, children need to understand false beliefs (i.e., that other people’s beliefs can bewrong) so as to develop such collective intentionality or to understand other people’s intention duringcooperation (Tomasello, Carpenter, Call, Behne, & Moll, 2005; Tomasello & Rakoczy, 2003).

Thus, it is important to examine how young preschoolers integrate their own goals with their part-ner’s goals during cooperation. The current study used a passive cooperation approach to investigatethis question. Unlike active cooperation, during which the partner is actively involved and even servesas the leader of the team (e.g., Fawcett & Garton, 2005), during passive cooperation, the partner mainlyhelps to create an atmosphere of cooperation instead of engaging in any real essential activities. It isstill the child who eventually makes the decision and solves the problem. This passive cooperation ap-proach should provide more insight into the initial stage of cooperation compared with an activecooperation approach.

Indeed, such a method has been used in the past and has shown some interesting results, althoughthe studies in the past were not designed to examine the impact of cooperation. The previous resultshave illustrated that behaviorally the presence of a collaborator may improve 3-year-olds’ perfor-mance in deception. For instance, Chandler, Fritz, and Hala (1989) engaged young children to play ahide-and-seek board game with the first experimenter in which children were supposed to coverthe footprints of a puppet so that the second experimenter was not able to find the treats. In additionto the ability of deception, this task required children to inhibit their impulse to reveal the truth,


which should be very challenging for 3-year-olds. Surprisingly, 60% of the 3-year-olds in that studywere able to conceal the footprints or even change the footprints to deceive the second experimenter.These findings were replicated by Sodian, Taylor, Harris, and Perner (1991, Study 1), who engaged chil-dren to help a truck driver hide. To clarify whether young children are indeed able to deceive, Sodianet al. (1991, Study 2) further manipulated the intention of the second experimenter (i.e., the personthe children were supposed to deceive) by introducing her as either a cooperator, a generous king pup-pet who would give the treasure to children if he found it, or a competitor, a greedy robber who wouldkeep the treasure for himself. They found that the 3-year-olds behaved the same way regardless of theintention of the second player; they covered the footprints of the first puppet regardless of whetherthe second puppet was the collaborator or the competitor. This suggests that when co-playing withthe first experimenter and the puppet, young children are able to deceive and control their behaviors,although mentally they do not understand the function of deception.

One way to explain such results is to analyze the goals of each player in these studies. In the studyof Chandler et al. (1989) and the first study of Sodian et al. (1991), the essential and common goal forchildren and the first experimenter was to help the puppet hide the target and stop the second exper-imenter from finding the target. The method associated with this goal was to remove the evidence. Inthe second study of Sodian and colleagues, the general goal of children and the first experimenter wasstill to help the puppet hide the treasure. Depending on the condition, the second experimenter’s gen-eral goal could either be giving the children the treasure or not giving the children the treasure. Nev-ertheless, the specific goal of the second experimenter was to find the treasure. It seems that theyoung children focused on the specific goal of the second experimenter and failed to integrate the sec-ond player’s general goal with their own goal. Hence, the young children did not change their behav-iors accordingly.

These findings suggest that the involvement of a co-player, although passive, may influence youngpreschoolers’ EF. Russell and colleagues have provided further evidence to support this proposal in aseries of studies on deception. These researchers showed that an ally could facilitate 3-year-olds’ per-formance in the windows task (Hala & Russell, 2001; Russell, Jarrold, & Potel, 1994; Russell et al.,1991). Across all conditions, Experimenter 1, mainly as the narrator and treat distributor, sat besidea child and Experimenter 2, as the competitor of the child, sat facing them. In the standard condition,the child made the decision and action (i.e., pointing to a box) alone and received a biscuit as a reward.In the ally condition, Experimenter 1 was the teammate of the child, and during each trial each ofthem could win a biscuit as a reward. In the experimenter–player condition, the child told Experi-menter 1 where to point, Experimenter 1 conducted the pointing action, and only the child receivedthe biscuit, as in the standard condition. The researchers found that 3-year-olds were more able to de-ceive Experimenter 2 in the ally condition than in the experimenter–player condition and the standardcondition (Hala & Russell, 2001, Study 1). Hala and Russell (2001, Study 2) further found that the allycondition improved children’s performance regardless of the presence of an opponent (i.e., Experi-menter 2) during children’s pointing. These findings suggest that the involvement of an ally whoshares the same goals as the child (i.e., winning treats ‘‘for us and for me”), although functioning pas-sively, may make the goal of winning treats salient, which may further facilitate children’s inhibitorycontrol. To explain why the experimenter–player condition did not facilitate children’s performance,the authors argued that children might not understand the intention of Experimenter 1, who con-ducted the pointing action. The experimenter–player is similar to the generous king in Study 2 of So-dian et al.’s (1991) study. A young child might not perceive that the goal of this player (i.e., winning atreat for you – the child) is the same as the child’s goal. The essential task goal might not be clearlyemphasized in this case.

Thus, how children perceive and integrate the goal of a collaborator during passive cooperation candetermine the outcomes of the cooperation. It seems that when children perceive that the co-playerhas the same goal as theirs, the essential task goal is emphasized, which may be beneficial for chil-dren’s EF. To verify this proposal, the current study first examined whether the presence of a co-playerwho has the same goal as children would facilitate children’s executive control in the LIM task (Carl-son et al., 2005), a relatively pure EF task. Second, the current study aimed to investigate whether thetype of goal the co-player has – an individual profit-oriented goal or a collective profit-oriented goal –facilitates children’s executive control.


Similar to the hide-and-seek board game, the windows task, and the deception task, in the LIM taskchildren are not told the winning rule of the game explicitly. Instead, children are supposed to learnfrom practice that the treat(s) in the tray to which they point will be taken away (in the standard ver-sion used by the Carlson group, the treats are given to a naughty monkey puppet). In terms of exec-utive control, these tasks are also similar because children need to inhibit their impulse for the desiredtarget and select the less desirable object. However, unlike the other aforementioned tasks, the LIMtask does not require children to deceive. Also, unlike the other tasks in which children may win notreats if they point to the wrong side, children in the LIM task receive some treats regardless of theirresponses during each trial.

To simplify the procedure, the current study modified the standard version of the LIM task to a selfversion in which children are tested alone instead of with a naughty puppet (see Fig. 1A). A child isasked to point to a tray to win a reward, but the tray to which the child points is taken back by theexperimenter and the child is rewarded with the treats from the other tray. Previous work has shownthat children’s performance on this nonsocial version is similar to the standard version of the LIM task(Sapienza, Carlson, & Hobson, 2009). In addition, three co-player versions were modified from thestandard version: co-player–split (see Fig. 1B), co-player–share (see Fig. 1C), and co-player–opponent.

Fig. 1. Sample stimuli used in the self version (A), the co-player–split version and co-player–opponent version (B), and the co-player–share version (C). For demonstration, the cartoon figure in white is the child, the cartoon figure in gray with long hair isExperimenter 1, and the cartoon figure in gray with short hair is Experimenter 2.


In the co-player versions, two experimenters are involved and their roles are fixed. Experimenter 1serves as the instructor and operator of the game, sitting opposite the child, and Experimenter 2 isthe co-player of the game, sitting next to the child. This setting is different from the setting in the stan-dard and opponent versions of the windows task and the standard LIM task because in the currentstudy the co-player is presented as a partner who plays the game with the child instead of as a com-petitor from whom the child wins rewards.

Experiment 1 aimed to investigate whether the inclusion of a co-player would facilitate children’sperformance in the LIM task. In the co-player–split version, the co-player presents herself as the onewho shares the goal with the child – who wants to play the game and wants to win lots of treats. Thechild and the co-player then team up to play the game and win rewards together, but each of them hasan individual treasure box in which to store rewards. During each trial, the child makes the decision bypointing to a tray, whereas the co-player is only passively involved by asking the child, ‘‘Which tray oftreats do WE want to point to?” The rewards are split in half, and both the child and the co-player winhalf of the prizes. This version is similar to the ally version designed by Hala and Russell (2001). Basedon their previous findings, it was hypothesized that children who had the co-player–split versionwould outperform children who had the self version.

Given that in the co-player–split version both individual profit (winning treats ‘‘for me”) and col-lective profit (winning treats ‘‘for us”) are emphasized, Experiment 2 aimed to further investigatewhether an emphasis on either goal may contribute to the facilitation effect. Thus, two other co-playerversions were designed: co-player–share and co-player–opponent. The co-player–share version issimilar to the co-player–split version except that only the collective goal (winning treats for us) isemphasized because during each trial the child and the co-player share the rewards and the rewardsare stored in their common treasure box. This is similar to the experimenter–player version in Halaand Russell’s (2001) study.

The co-player–opponent version is similar to the co-player–split version except that (a) the co-player intends to keep all of the treats herself but is told to play the game together with the child,(b) the opponent receives the rewards from the box to which the child pointed, and (c) instead of ask-ing, ‘‘Which tray of treats do WE want to point to?” the opponent asks, ‘‘Which tray of treats do YOUwant to point to?” (See a comparison of the four versions in Table 1.) In this case, only the individualgoal (winning treats ‘‘for me”) is emphasized. The co-player–opponent version is similar to the stan-dard LIM task (Carlson et al., 2005) except that in the current version (a) the naughty monkey was re-placed with a second experimenter and (b) instead of sitting opposite the child, the opponent (thesecond experimenter) sat beside the child to play the game together with the child. This co-player–opponent version is also similar to the standard/opponent version of the windows task (Russellet al., 1994) except that in the current version (a) children were not told to win treats from the oppo-nent but were told that the opponent wants to have all the treats and that they are going to play thegame together, (b) the opponent sat beside the child instead of opposite the child, and (c) both playersreceived some treats (a large amount or a small amount) regardless of the child’s responses. Thus, theco-player–opponent version of the LIM task is less competitive than the opponent version of the win-dows task.

In both experiments, a between-participant design was used. To control for individual differences,children’s vocabulary, memory span, EF, and ability to understand false beliefs were tested as well.

Experiment 1

Experiment 1 aimed to verify whether playing with another individual may improve children’sexecutive control with the modified LIM tasks.

Method

ParticipantsIn total, 16 younger preschoolers (mean age = 41.3 months, SD = 4.6, range = 35–47, 8 girls) and 19

older preschoolers (mean age = 51.1 months, SD = 2.1, range = 48–56, 11 girls) participated in this

Table 1Comparison of the modified Less-Is-More task.

Version Co-playerasking

Treats distribution Child’s goal Co-player’sgoal

Commongoal

Self – The treats in the box towhich the child did notpoint are given to thechild

Winningrewards ‘‘for me”

– –

Co-player–split

‘‘Which tray oftreats do WEwant to pointto?”

The treats in the box towhich the child did notpoint are split in half;the child and the co-player each receiveshalf

Winning rewards‘‘for us and forme”



Co-player–share

‘‘Which tray oftreats do WEwantto point to?”

The treats in the box towhich the child did notpoint are given to thechild and the co-player.

Winning rewards‘‘for us”



Co-player–opponent

‘‘Which tray oftreats do YOUwant to pointto?”

The treats in the box towhich the child did notpoint are given to thechild; the treats in thebox to which the childpointed are given tothe co-player

Winning rewards‘‘for me”




experiment. The results were the same with or without a 2-year-old (n = 1), so the 2-year-olds’ datawere combined with the 3-year-olds’ data and the results were reported accordingly. The children, re-cruited through Singaporean day care centers, were from various ethnic backgrounds. In all cases, par-ents were provided with a written description of the experiment, and they granted informed consentallowing their children to participate.

MaterialsStickers and marbles were used. In the self version, three transparent boxes were used: two for the

experimenter to display the stimuli and one for children to store the rewards they won. In addition, asupply bin was used for the experimenter to store these treats. In the co-player–split version, one ex-tra transparent box was used for the co-player (Experimenter 2) to store the rewards.

Design and procedureA mixed design was used where children were randomly assigned to one of the versions, the self

version or the co-player–split version, and during each version they were given 16 trials.Each child was tested by one or two female experimenters in a quiet corner of the child’s day care

center. In both versions, first children were shown two different types of treats (e.g., stickers vs. mar-bles) and were asked to choose their favorite one. The chosen type was used as stimuli throughout thewhole task. Then children were presented a two-treat array and a six-treat array in shallow trays andwere asked which amount they preferred. If children indicated that they preferred the two-treat array(usually because they liked a specific stimulus in the two-treat array), the experimenter asked chil-dren to choose between a one-treat array and a two-treat array. After such clarification, all childrenindicated that they preferred the larger amount.

In the self version, the experimenter asked children whether they wanted to win a lot of treats, andall children confirmed that they did. The experimenter then gave children a box and told them, ‘‘This isyour treasure box.” Then the experimenter put the other two boxes in front of children within equaldistance. The experimenter told children how to play the game: ‘‘Every time you point to a tray, I willtake back the tray, then I will give you the other tray, and you are going to get the treats in that tray,and you can put the treats into your treasure box.” Next the experimenter put two treats in one boxand six treats in the other box. The rule was repeated and children were asked, ‘‘Which tray of treats


do you want to point to?” After children made their selection, the experimenter pulled back both trays,removed the treats from the selected tray, and put them back in her supply box. She then placed thetreats from the nonselected tray in children’s treasure box, saying, ‘‘See, you get this many treats.”Children were given two practice trials, followed with a verbal rule check as in Carlson et al.’s(2005) study: ‘‘If you point to this tray, do you get the treats in the tray?” The experimenter gave feed-back and repeated the questions as needed (up to three times). Then children received 16 trials with-out any feedback from the experimenter. The number of treats in each tray was counterbalanced. After8 trials, regardless of performance, the experimenter emptied the two display trays and gave childrena verbal rule reminder.

In the co-player–split version, before the game was explained, the second experimenter showed upand announced that she wanted to play the game as well. The first experimenter asked the secondexperimenter to choose, and the second experimenter wanted to have the treats from the larger array.The first experimenter then said, ‘‘You two want to have the same. You two can become a team andplay the game together.” The first experimenter then asked children whether they wanted to have anytreats, and all children confirmed that they wanted to have some treats. Then the first experimenterput a treasure box in front of the children and the second experimenter, within equal distance, andtold children the rule: ‘‘Every time you point to a tray, I will take back the tray, then I will give youand Sally [Experimenter 2] the other tray, and you two are going to get the treats in that tray, andyou two are going to split the treats and each of you can put the treats into your own treasure box.”The procedure of the co-player–split version was similar to that of the self version except that Exper-imenter 2, the co-player, was the passive partner of children, having the same interests as children andsplitting the treats from the tray to which children did not point. During each trial, Experimenter 2asked children, ‘‘Which tray of treats do WE want to point to?” Similar to the self version, childrenmade the response by pointing to a tray.

After the modified LIM task, children were given the Peabody Picture Vocabulary Test–Third Edi-tion (PPVT) (Dunn & Dunn, 1997), the Digit Span task (Davis & Pratt, 1996), the Dimensional ChangeCard Sort (DCCS) (Zelazo, Müller, Frye, & Marcovitch, 2003), and the Contents False Belief task (Well-man & Liu, 2004). The PPVT measures the development of receptive vocabulary. Children were askedto select the picture that best represents the meaning of a stimulus word presented orally. The DigitSpan task measures short-term memory span. Children were asked to repeat a set of numbers after theexperimenter. The DCCS is a measure of rule switch and EF. Children were asked to sort cards that canbe sorted by two dimensions: color and shape. Children who successfully sorted five of six trials dur-ing both pre- and postswitch phases were considered to have successfully switched sorting dimen-sions and were scored as ‘‘passing.” The Contents False Belief task measures whether childrenunderstand that other people’s beliefs can be wrong. Children were shown a cookie box and askedwhat they thought was inside. After discovering that the box actually contains something different(e.g., tissue), children were asked about what another person would think if this person had neveropened the box. Children were considered to have passed the task only when they successfully an-swered a control reality question on what was inside the box and the target question on the false be-liefs. For each child, the total testing time was less than 45 min. The LIM version and the DCCSdimension were counterbalanced between the participants.

Results

Preliminary analysis did not show any significant difference with regard to sex (F < 1). Most chil-dren (91%) gave the correct answers during rule check, and all answered correctly following feedback.There were no significant dimension differences on the DCCS (Z = 1.586, p = .113). Versions did not dif-fer according to age, rule check, PPVT, Digit Span, DCCS, or Contents False Belief (see Table 2), suggest-ing that there were no systematic differences between groups on these other nonmanipulatedvariables.

Following the method used in Carlson et al.’s (2005) study, with the probability of optimal response(the proportion of trials in which children chose the smaller amount of treats) as the dependent var-iable, a 2 (Age) � 2 (Version) analysis of variance (ANOVA) showed a significant age improvement, F(1,31) = 9.943, p = .004, g2

p = .243, indicating that the 3-year-olds (M = .49, SD = .23) performed worse

Table 2Descriptive statistics for children’s performance as a function of age, version, and task in Experiment 1.

Task Self Co-player–split

M SD M SD F/Z p

3-year-olds (n = 8) (n = 8)Less-Is-MoreRule check .88 .35 .88 .35 0.000 1.000Probability of optimal response .35a .11 .63 .23 9.713 .008Peabody Picture Vocabulary Test 87.6 18.1 83.3 11.1 0.285 .603Digit span 3.13 0.23 3.50 0.53 3.316 .090Dimensional change card sortNumber of correct trials during postswitch 1.88 2.64 2.57 3.21 0.213 .652Number of children who passed 2 3 0.522 .602Contents false beliefNumber of children who passed 0 0 0.000 1.000

4-year-olds (n = 9) (n = 10)Less-Is-MoreRule check 1.00 .00 .90 .32 0.895 .357Probability of optimal response .67b .18 .73c .21 0.412 .530Peabody Picture Vocabulary Test 95.0 20.8 93.6 20.7 0.022 .885Digit Span 4.00 1.25 3.70 0.67 0.437 .518Dimensional Change Card SortNumber of correct trials during postswitch 2.44 2.96 3.22 3.07 0.299 .592Number of children who passed 3 5 0.715 .475Contents False BeliefNumber of children who passed 1 1 0.180 .850

Combined (n = 17) (n = 18)Less-Is-MoreRule check .94 .24 .89 .32 0.290 .594Probability of optimal response .52 .22 .68b .22 5.010 .032Peabody Picture Vocabulary Test 91.8 19.4 89.4 17.8 0.137 .714Digit Span 3.59 1.00 3.61 0.61 0.007 .935Dimensional Change Card SortNumber of correct trials during postswitch 2.20 2.83 2.94 3.04 0.486 .491Number of children who passed 5 6 1.043 .297Contents False BeliefNumber of children who passed 1 1 0.544 .586

a Children’s performance was significant below the chance level (.50) at p < .01.b Children’s performance was significant above the chance level at p < .05.c Children’s performance was significant above the chance level at p < .01.


than the 4-year-olds (M = .70, SD = .19), which replicated the previous findings (Carlson et al., 2005).Separate one-sample t tests showed that the 4-year-olds, but not the 3-year-olds, performed signifi-cantly above chance (.50), t(18) = 4.431, p < .001. There was a significant version difference, F(1,31) = 6.912, p = .013, g2

p = .182, showing that the children who had the co-player–split version(M = .68, SD = .22) outperformed the children who had the self version (M = .52, SD = .22). One-samplet tests showed that the children who had the co-player–split version, t(17) = 3.580, p = .002, but notthe children who had the self version, performed significantly above chance. In particular, the 3-year-olds performed significantly below chance in the self version, t(7) = 3.800, p = .007, butperformed at chance level in the co-player–split version, t(7) = 1.633, p = .147, and the 4-year-oldsperformed significantly above chance in the self version, t(8) = 2.744, p = .025, and in the co-player–split version, t(9) = 3.375, p = .008. The age and version interaction was not significant, F(1,31) = 2.978, p = .094, g2

p = .088.A repeated measure with age and version as the between-participant dependent variables and time

as the within-participant dependent variable was used to examine learning across the 16 trials. Theresults (see Fig. 2) showed that there was a significant interaction between time and version, F(15,465) = 1.725, p = .043, g2

p = .053. Further analysis showed that the learning effect across the 16 trials

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Fig. 2. Probabilities of optimal response on the Less-Is-More task across trials by the function of version in Experiment 1.


appeared only in the co-player–split version, F(15, 240) = 2.165, p = .008, g2p = .119, and not in the self

version, F(15, 225) = 1.003, p = .453, g2p = .063.

Discussion

Similar to the results reported by Carlson et al. (2005, Study 1) with the standard version of the LIMtask, in the current study the 4-year-olds performed significantly better than the 3-year-olds in themodified LIM task. The 4-year-olds’ selection of the tray with the small amount of treats was signif-icantly above chance level. Unlike the 3-year-olds who performed at chance level in Carlson and col-leagues’ study, but similar to the results of the windows task (Russell et al., 1991), the 3-year-olds inthe current study performed significantly below chance level. The performance difference between thechildren in Carlson and colleagues’ study and those in the current study may be due to the fact that the3-year-olds in the current study were on average 2 months younger than those in Carlson and col-leagues’ study.

The results of the current study showed that the children in the co-player–split version outper-formed those in the self version. In addition, across 16 trials, learning appeared only in the co-player–split version and not in the self version. This finding is consistent with the studies using thehide-and-seek board game and the windows task (Chandler et al., 1989; Hala & Russell, 2001; Sodianet al., 1991). Furthermore, the current study has extended the previous finding by showing that it isexecutive control that co-playing with another person facilitates.

During the passive cooperation, in which an experimenter sits beside a child without providing anyexplicit suggestions or feedback, the co-player is able to influence the child’s EF. The co-player has thesame goal as the child – winning a lot of treats. The presence of such a co-player may make the childmore aware of the goal of the game compared with playing alone. According to Munakata’s (2001)graded representation account, goal representation can be graded in terms of strength or ‘‘how ‘clean’they are for signaling the appropriate information” (p. 309). When the task goal becomes salient, thechild may be more able to focus on it and resist other temptations. This mechanism is similar to thefacilitation effect of the symbol LIM task. In the symbol LIM task (Carlson et al., 2005, Study 2), theattractive treats are replaced with neutral symbols and children are more able to focus on the task goal


– winning treats – instead of being distracted by the treats presented in front of them, as occurs in thestandard version.

Experiment 2

The results of Experiment 1 showed that, compared with playing the game by themselves, playingthe game with another person who shared the same interests in rewards could improve preschoolers’performance on the LIM task. This facilitation effect is possibly due to sharing and emphasizing thetask goal of winning treats. In the co-player–split version, the co-player’s goals are winning treats‘‘for us,” or collective profit oriented, as well as ‘‘for me,” or individual profit oriented. It is unclearwhether it is essential to have both collective and individual profits emphasized for children to im-prove their executive control.

Whether young preschoolers perceive the co-player’s collective profit-oriented goal and integratesuch a goal with their own goal is related to their development of social understanding, in particulartheory of mind such as false belief (e.g., Tomasello & Rakoczy, 2003). In false belief tasks, children aretested on whether they can identify another person’s beliefs, which may be wrong and may be differ-ent from children’s own beliefs at the current moment (Gopnik & Astington, 1988). If children fail toidentify the other person’s beliefs, this suggests that children do not fully understand the other per-son’s perspectives or intention. Given that most of the children in Experiment 1 failed the ContentsFalse Belief task, it was assumed that these young preschoolers were not able to understand the co-player’s collective profit-oriented goal of winning treats ‘‘for us” even though they understood theco-player’s individual profit-oriented goal of winning treats ‘‘for me.” Hence, the facilitation effectwas possibly due to the co-player’s individual profit-oriented goal of winning treats ‘‘for me.”

Thus, in Experiment 2, the co-player’s goals were separated. In particular, the co-player–share ver-sion and the co-player–opponent version were used to examine the consequences of a collective prof-it-oriented goal of winning treats ‘‘for us” and an individual profit-oriented goal of winning treats ‘‘forme,” respectively. It was hypothesized that the facilitation effect, if it appeared, would appear in theco-player–opponent version instead of the co-player–share version.

Method

ParticipantsIn total, 44 younger preschoolers (mean age = 42.3 months, SD = 4.0, range = 33–47, 22 girls) and

52 older preschoolers (mean age = 53.5 months, SD = 4.4, range = 48–63, 26 girls) participated in thisexperiment. The results were the same with or without a 2-year-old (n = 1) and 5-year-olds (n = 2), sothe 2-year-old’s data were combined with the 3-year-olds’ data, the 5-year-olds’ data were combinedwith the 4-year-olds’ data, and the results were reported accordingly. An additional four children (oneboy and three girls) were excluded from the final sample because they did not understand English. Thechildren, recruited via the same procedure, were from similar backgrounds as those in Experiment 1.

MaterialsThe materials were similar to those used in Experiment 1. In the co-player–share version, a com-

mon treasure box was used for children and the second experimenter to store their rewards. In the co-player–opponent version, children and the second experimenter both had their own treasure box inwhich to store the rewards.

Design and procedureThe design was similar to that used in Experiment 1. Children were randomly assigned to one of the

three versions: the self version, the co-player–share version, or the co-player–opponent version.The procedure of the self version was the same as that used in Experiment 1.The procedure of the co-player–share version was the same as that used for the co-player–split ver-

sion in Experiment 1 except that the rewards were put into the common treasure box for children andthe co-player to share.


In the co-player–opponent version, after children selected their favorite type of treat and demon-strated that they wanted to win lots of treats, the second experimenter came in and said that shewanted to play the game as well. The first experimenter asked the second experimenter to choose,and the second experimenter claimed that she would want to have all of the treats from both arrays.The first experimenter immediately disapproved by saying, ‘‘You cannot have all the treats. This childwants to have some too.” The first experimenter then asked children whether they wanted to havesome treats, and all children confirmed that they wanted to have some treats. Then the first experi-menter gave children and the second experimenter each a treasure box similar to that in the co-player–split version and said, ‘‘You both want to have treats, but I cannot give all the treats to youor to Sally [Experimenter 2]. Let’s play this game and win the treats in this way.” Then the first exper-imenter told them the rule: ‘‘Every time you point to a tray, Sally gets the treats in that tray and they’llgo into her treasure box, and you’ll get the treats in the other tray and they’ll go into your treasurebox.” The rest of the procedure was the same as that in the self version except that during each trialExperimenter 2 (the opponent) asked children in a forced tone, ‘‘Which tray of treats do YOU want topoint to?” Similar to the self version, children made the response by pointing to a tray.

After the modified LIM, children were given the four control tasks. The whole assessment tookapproximately 45 min.

Results

Preliminary analysis did not show any significant difference with regard to sex (F < 1). Most children(83%) gave the correct answers during rule check, and all answered correctly following feedback. Therewere no significant dimension differences on the DCCS (Z = 1.118, p = .264). Versions did not differaccording to age, rule check, PPVT, Digit Span, DCCS, or Contents False Belief (see Table 3), suggestingthat there were no systematic differences between groups on these other nonmanipulated variables.

With the probability of optimal response as the dependent variable, a 2 (Age) � 3 (Version) ANOVAshowed a significant age effect, F(1, 90) = 6.995, p = .010, g2

p = .072. Separate one-sample t testsshowed that the 4-year-olds, but not the 3-year-olds, performed significantly above chance,t(51) = 3.213, p = .002. There was a significant version effect, F(2, 90) = 3.634, p = .030, g2

p = .075.Tukey’s post hoc analysis showed that the children in the co-player–opponent version (M = .59,SD = .16) performed significantly better than the children in the self version (M = .49, SD = .16). Theresults of the co-player–share version (M = .52, SD = .16) did not differ significantly from those ofthe other two versions. Separate one-sample t tests showed that the children who had the co-player–opponent version, t(31) = 3.260, p = .003, but not the children who had the self version orthe co-player–share version, performed significantly above chance. In particular, the 3-year-olds per-formed significantly below chance in the self version, t(15) = �2.506, p = .024, but performed at chancelevel in the co-player–opponent version, t(14) = 2.134, p = .051, and the co-player–share version,t(12) = �0.237, p = .817. The 4-year-olds performed at chance in the co-player–share version,t(18) = 0.804, p = .432, but significantly above chance in the self version, t(15) = 2.835, p = .013, andin the co-player–opponent version, t(16) = 2.451, p = .026. The age and version interaction was notsignificant, F(1, 90) = 2.058, p = .134, g2

p = .044. A repeated measure with age and version as thebetween-participant dependent variables and time as the within-participant dependent variablewas used to examine learning across the 16 trials. The results did not show any significant time effect,F(15, 1350) = 1.356, p = .182, g2

p = .015, or any interaction between time and version, F(15, 1350) =1.101, p = .335, g2

p = .024.

Discussion

Consistent with Carlson et al.’s (2005, Study 1) findings and the results of Experiment 1, the 4-year-olds outperformed the 3-year-olds on the standard version of the LIM task.

The results showed that, compared with the self version, the 3- and 4-year-olds performed better inthe co-player–opponent version but not in the co-player–share version. Children’s performance in theself version was at chance level, whereas their performance in the co-player–opponent version wasabove chance level. In the co-player–opponent version, both the co-player and children aimed for

Table 3Descriptive statistics for children’s performance as a function of age, version, and task in Experiment 2.

Self Co-player–share Co-player–opponent F/Z p

M SD M SD M SD

3-year-olds (n = 16) (n = 13) (n = 15)Less-Is-MoreRule check .75 .45 .85 .38 .73 .46 0.861 .430Probability of optimal response

.41a .15 .49 .15 .58 .14 5.306 .009

Peabody Picture Vocabulary Test85.4 17.5 83.5 17.4 80.7 17.0 0.243 .786

Digit Span 3.36 1.15 3.55 1.51 3.05 0.90 0.443 .646

Dimensional Change Card SortNumber of correct trials during postswitch 3.33 3.00 2.73 3.13 1.00 2.34 2.183 .129Number of children who passed 6 5 2 3.771 .152

Contents False BeliefNumber of children who passed 0 1 1 1.187 .553

4-year-olds (n = 16) (n = 19) (n = 17)Less-Is-MoreRule check .88 .34 .84 .38 .94 .24 0.634 .535

Probability of optimal response.58b .12 .53 .18 .61b .19 1.026 .366


Digit Span 3.79 0.58 3.31 1.34 3.53 0.87 0.771 .469Dimensional Change Card SortNumber of correct trials during postswitch 2.19 2.83 2.38 2.94 3.38 2.83 0.793 .459Number of children who passed 5 6 8 0.935 .626


Combined (n = 32) (n = 32) (n = 32)Less-Is-MoreRule check .81 .40 .84 .37 .84 .37 0.073 .970

Probability of optimal response.49 .16 .52 .16 .59b .16 3.340 .040


Digit Span 3.56 0.94 3.41 1.39 3.35 0.89 0.255 .776

Dimensional Change Card SortNumber of correct trials during postswitch 2.68 2.91 2.52 2.97 2.36 2.84 0.086 .918Number of children who passed 11 11 10 1.899 .389


a Children’s performance was significant below the chance level (.50) at p < .05.b Children’s performance was significant above the chance level at p < .05.


individual profit – winning treats ‘‘for me.” This indicates that the emphasis on individual profit canimprove young preschoolers’ executive control.

These findings are different from those of Sapienza et al. (2009), who found that children per-formed similarly on the standard LIM task with a naughty monkey puppet as the opponent and theindividual version of the LIM task without the puppet. The individual version of the LIM task is similarto the self version of the LIM task in the current study. However, the co-player–opponent version isdifferent from the standard version in that the co-player sat beside children as a co-player insteadof sitting opposite children as a competitor. It is possible that having a puppet as an opponent is dif-ferent from having the second experimenter as a co-player and opponent.


These findings seem to be different from the results of the original reversal learning study of chim-panzees (Boysen & Berntson, 1995). In Boysen and Berntson’s (1995) study, two chimpanzees weretested together. They sat on either side of the test apparatus, opposite each other. One chimpanzeeselected a tray, and the candies in the selected tray were given to the other chimpanzee. After nearly400 trials, these chimpanzees were still unable to select the tray with the smaller amount of candies soas to win the larger amount of candies for themselves. Unlike the structure used in Boysen and Bernt-son’s study, in the co-player–opponent version of the current study the opponent as a co-player satbeside, instead of opposite to, children and shared common interests with children – play the gameand win more treats. Furthermore, language was used in the current study, and this clearly conveyedthe intention of the co-player–opponent. In addition, the relationship between the two chimpanzeesin Boysen and Berntson’s study was unclear. Hare, Call, Agnetta, and Tomasello (2000) put food eithervisible to both chimpanzees or visible solely to the subordinate chimpanzee. They found that the sub-ordinate chimpanzee would seek the food only when the food was not visible to the dominant chim-panzee. These results suggest that even chimpanzees are sensitive to the social context and theintention of other chimpanzees and are able to regulate their behaviors accordingly.

In addition, the facilitation effect shown in the co-player–opponent version of the LIM task seemsto be contrary to Russell et al’s (1991, 1994) results in the windows task, where young preschoolersperformed the same regardless of whether the opponent was present or not. This is possibly becausethe two tasks are different. As outlined earlier, first, in the windows task the opponent sits oppositechildren, whereas in the co-player–opponent version of the LIM task the opponent, as a co-player, sitsbeside children. Second, in the original (and opponent) windows task, the first experimenter keptreminding children where they needed to point so that the second experimenter would not get thechocolate (Russell et al., 1991). However, in the co-player–opponent version of the LIM task, childrenwere told to play the game with the second experimenter. Third, the windows task is a zero-sum com-petition task (Stanne, Johnson, & Johnson, 1999), meaning that the winner takes all of the rewards andthe loser gets nothing. However, in the co-player–opponent version of the LIM task, both players canreceive some treats, although one receives a larger amount and one receives a smaller amount. Thus,the competition atmosphere in the co-player–opponent version of the LIM task is not as strong as inthe opponent windows task. In fact, the idea of ‘‘playing together” is suggested in the co-player–oppo-nent version of the LIM task. The goal that focuses on individual profit – winning lots of treats ‘‘for me”– is emphasized and shared by both players. Such an emphasis may make children more able to con-trol their behaviors.

In contrast to the facilitation effect associated with the co-player–split version, there was no learn-ing effect in the co-player–opponent version. This implies that the facilitation effect of the co-player–opponent version might not be as strong as that of the co-player–split version. In the co-player–oppo-nent version, the common goal between children and the co-player was winning treats ‘‘for me,”which was similar to the goal that children would have in the self version. However, in the co-player–split version, the common goal between children and the co-player was winning treats ‘‘forus and for me,” which emphasized not only the goal that children would have in the self versionbut also the more general goal ‘‘for us.” This double emphasis may be better able to direct children’sattention toward the final goal of the task compared with an emphasis on a single goal. A direct com-parison between the co-player–split and the co-player–opponent may help to answer this question.

The co-player–share version of the LIM task did not show any facilitation effect. This suggests thatthe co-player’s goal focusing on collective profit – winning treats ‘‘for us” – might not be integratedinto children’s goal. This finding is consistent with the result of the generous king condition in Sodianand colleagues’ (1991, Experiment 1) study and the result of the experimenter–player condition inHala and Russell’s (2001, Experiment 1) study in that the preschoolers did not take the co-player’scooperative intention into consideration. In these conditions, the co-player does not receive any treatsspecifically for herself. An unselfish intention such as this might not strengthen the goal of the youngchildren; thus, these conditions did not help children’s behavioral control. It is possible that children’sgoal was winning treats ‘‘for me” and the co-player’s intention might not have been perceived as rel-evant to their own, as in Benjamin Franklin’s (1756/2004) observation that ‘‘mine is better than ours”(p. 252). Furthermore, children’s cooperation ability is closely associated with their social understand-ing (e.g., Tomasello et al., 2005; Tomasello & Rakoczy, 2003). Most of the children in the current study


failed the Contents False Belief task, suggesting that they had not fully developed the understanding ofother people’s mental states. This is possibly the main reason why these children’s performance didnot improve in the co-player–share version.

General discussion

Preschoolers develop EFs rapidly (see Zelazo, Carlson, & Kesek, 2008, for a review). Nevertheless,they are easily distracted by the attractive features of stimuli and fail to focus on the essential goalof the task (e.g., Carlson et al., 2005; Russell et al., 1991). Previous work has shown that it is possibleto increase children’s EF by directing their attention to the main goal of the task. For instance, pre-schoolers were able to wait for a longer period of time when they concentrated on the similarities be-tween marshmallows and clouds or imagined rewards as pictures than when they focused on thesweet taste of the marshmallows or imagined rewards as real (Mischel & Baker, 1975; Moore, Mischel,& Zeiss, 1976). Similarly, young preschoolers were less impulsive in the LIM task when real treats suchas jelly beans were replaced with neutral symbols such as a mouse versus an elephant (Carlson et al.,2005, Study 2).

The current study continues this line of research by aiming to improve preschoolers’ EF with theemphasis on the main task goal. Instead of directing children’s attention by manipulating the physicalappearance of the stimuli or the mental representation of the stimuli, the current study included a co-player who shares the same goal as children. It was expected that the presence of a co-player whoshares the goal with children would allow children to concentrate on the common goal and furtheruse the joint goal to guide their behaviors.

The current results support such a proposal. Consistent with previous findings (Chandler et al.,1989; Hala & Russell, 2001; Sodian et al., 1991), the results of Experiment 1 showed that when playingwith another individual, children’s behavioral control can be improved. As opposed to the tasks usedin previous studies, which require the ability to deceive as well as executive control, the current studyused the LIM task, which is a relatively pure measure of EFs for 3- and 4-year-olds. Thus, the currentstudy provided direct evidence for the facilitation effect of co-playing on executive control.

In the co-player–split version of Experiment 1, the goal of the co-player was both collective andindividual oriented – winning treats ‘‘for us and for me.” Experiment 2 further investigated how apartner’s intention may influence children’s behavioral control. In the co-player–share version, thegoal of the co-player was winning treats ‘‘for us,” focusing on collective profit. In the co-player–oppo-nent version, the goal of the co-player was winning treats ‘‘for me,” focusing on individual profit. Theresults showed that, compared with the self version, the facilitation effect of the co-player appearedonly in the co-player–opponent version and not in the co-player–share version. These findings implythat the individual profit-oriented goal may be integrated with children’s own goal, which may help todirect children’s attention to the essential goal of the task. The failure to share the collective profit-ori-ented goal with the co-player, as in the co-player–share version, was possibly due to the fact that the3- and 4-year-olds in the current study had not fully developed false belief or collective intentionality,or were not able to take the other person’s different perspective and integrate it with their own goal.Follow-up studies should examine the performance of older preschoolers who have passed false belieftasks. In addition, the current study did not directly examine how children perceive the other player’sintention. Interviews and observation of children’s interaction with the other player during free playshould be used to investigate this issue in the future.

In addition, although co-playing with another person improved 3-year-olds’ performance on theLIM task in the current study, the facilitation effect does not seem to be unlimited. In Experiment 1,the co-player–split version improved the 3-year-olds’ performance from below chance to chance level.In Experiment 2, the co-player–opponent version improved the 3-year-olds’ performance from belowchance to barely above chance level. This seems unlike the facilitation effect caused by the dot andmouse-versus-elephant versions of the LIM task, which improved the 3-year-olds’ performance fromchance level to above chance level (Carlson et al., 2005, Study 2).

Such differences may be due to several issues. First, as mentioned earlier, the baseline of the 3-year-olds in the current study, below chance, was much lower than that of the 3-year-olds in Carlsonand colleagues’ (2005) study, whose performance was at chance level. The facilitation effect may be


the same, but the outcomes were different. Second, the facilitation effect may vary in degree. Accord-ing to Carlson and colleagues, even the facilitation effect associated with various types of symbols canbe different. Symbols may vary in terms of the degree of abstractness, as does the facilitation effect.For instance, compared with the real treats version, the mouse-versus-elephant version significantlyimproved young children’s performance, but the rocks version and the dot version did not. This pro-posal is also consistent with the graded representation account (e.g., Munakata, 2001). Finally, thefacilitation effect may differ in nature. From the perspective of EF as the problem-solving framework(Zelazo et al., 1997), although co-playing with another person may help preschoolers to establish thegeneral task goal and keep focusing on this goal, it might not help children to construct and executeplans or evaluate the outcome. It is possible that the symbol versions may encourage children to uselanguage during the whole problem-solving process and may facilitate their EF in general (Müller, Zel-azo, Leone, Hood, & Rohrer, 2004). In the future, other task paradigms specific for each problem-solv-ing stage should be used to examine the effect of co-playing.

The long-term effect of facilitation associated with co-playing is another aspect that deserves fur-ther examination. In addition, the current study was conducted in Singapore, an Asian country withintermingled Eastern and Western cultures. The samples may be unique. Cross-cultural studies areneeded to examine this aspect further.

Conclusion

The current study has documented a co-playing facilitation effect on preschoolers’ EF, namely thatwhen playing with another individual who shares a common goal with them, preschoolers becomemore efficient in executive control. These findings are consistent with the proposal that the develop-ment of EFs is sensitive to social context and affective context (Qu & Zelazo, 2007; Zelazo et al., 2005).Moreover, presenting the LIM task in different social and affective contexts provides an innovative toolto examine the link among EF, social context, and affective processing.

Acknowledgments

This research was supported by a grant from the School of Humanities and Social Sciences, Nany-ang Technological University. Portions of the study were presented at the annual meeting of the JeanPiaget Society, Quebec City, Canada, 2008. The author thanks the children, parents, and day care cen-ters for their participation as well as Khairiyah Binte Kassim, Koh See Leng Hope, Nur Izyan Binte Is-mail, Sim Lit Wee, Lim Sim Ping Rachel, Tan Xueling Crystal, and Wu Jing Hang for their assistance indata collection and coding. The author also thanks Dr. David Crystal, Dr. Stephanie M. Carlson, and thetwo reviewers for comments on an earlier draft of the manuscript.

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