Developmental Change in Working Memory Strategies: from Passive Maintenance to Active Refreshing

BRIEF REPORT Developmental Change in Working Memory Strategies: From Passive Maintenance to Active Refreshing

Vale´rie Camos Pierre Barrouillet Universite´ de Bourgogne and Institut Universitaire de France Universite´ de Gene`ve

Change in strategies is often mentioned as a source of memory development. However, though performance in working memory tasks steadily improves during childhood, theories differ in linking this development to strategy changes. Whereas some theories, such as the time-based resource-sharing model, invoke the age-related increase in use and efficiency of a strategy of active maintenance of memory broadly. traces, other theories, such as the task-switching model, do not mention strategy change. According to publishers. these models, either the cognitive load of the task or the duration of maintenance would account for recall performance. In the present study, we varied orthogonally these 2 factors. The results revealed that a allied different and unique factor affected recall performance at different ages: the duration of maintenance at disseminated its age 6 and the cognitive load at age 7. As described by the task-switching model, younger children would be of not implement any maintenance activities while performing a concurrent task, their memory traces to

one suffering from a time-based decay. This suggests that an increasing capacity of cognitive monitoring not or allows children to shift from this passive maintenance of memory traces to the active refreshing thereof is at around the age of 7, reunifying the 2 current accounts of working memory development as 2 and developmental stages. user

Association Keywords: working memory, strategy, development, maintenance individual

the One of the most striking aspects of cognitive development various factors that are classically evoked in accounting for any Psychological of during childhood is the steady improvement in working memory developmental improvement, the discovery of new strategies and use capacity (Case, 1985; Halford, 1993; Pascual-Leone, 1970), a the change in strategy use have often been suggested (Flavell, development reflected in the age-related increase in performance 1979; Siegler, 1996). Memory development is one of the main American on working memory tasks. These tasks, also called complex span domains in which these changes in strategy use have been alleged personal the tasks, are designed to evaluate the capacity of working memory by and intensively researched as an essential determinant of develop- the by requiring both the maintenance of information for subsequent ment (Bjorklund, Dukes, & Brown, 2009; Schneider & Pressley, for recall and some concurrent processing. For example, in the count- 1997). Accordingly, recent accounts of the developmental increase ing span task designed by Case, Kurland, and Goldberg (1982),

solely in working memory span such as the time-based resource-sharing copyrighted children are asked to count dots on series of cards of ascending (TBRS) model proposed by Barrouillet and Camos (2007) evoke is length and to recall the totals at the end of the series. The counting the leading role of strategy development, whereas other proposals

intended span, measured as the maximum number of totals that can be such as the task-switching model of Towse and Hitch (1995) make is recalled in correct order, strongly increases with age. Among the no reference to any change in strategy. document In their task-switching model, Towse and Hitch (1995; Hitch, article

This Towse, & Hutton, 2001; Towse, Hitch, & Hutton, 1998, 2000)

This suggested that children switch between the two functions of work- This article was published Online First March 21, 2011. ing memory (i.e., storage and processing) in a way that is isomor- Vale´rie Camos, Department of Psychology, Universite´ de Bourgogne, Dijon, France, and Institut Universitaire de France, France; Pierre Bar- phic to the design of the complex span tasks by alternating storage rouillet, Department of Psychology, Universite´ de Gene`ve, Geneva, Swit- and processing episodes. For example, when counting the arrays of zerland. dots in the counting span task, their attention would be continu- This study was supported by Agence Nationale de la Recherche Grant ously and completely devoted to processing, whereas at the end of ANR-08-BLAN-0045-01 to Vale´rie Camos and Swiss National Science their count, they would shift their attention toward storage activ- Foundation Grant 100014-118296/1 to Pierre Barrouillet. This study was ities, before turning back to processing activities when presented presented at the 2008 Advanced Course of the Archives Jean Piaget in with the next array. Towse and Hitch assumed that because the Geneva, Switzerland. We thank Francine Collet, Lucie Corbin, Prune traces of the memory items decline during processing episodes Lagner, Paula Malacz, and Armelle Moissenet for their help. Correspondence concerning this article should be addressed to Vale´rie (i.e., counting), recall performance should depend on their duration Camos, who is now at the De´partement de Psychologie, Universite´de that determines the delay between encoding and recall. As a Fribourg, Rue de Faucigny 2, 1700 Fribourg, Switzerland. E-mail: consequence, older children who perform counting tasks faster [email protected] than younger children have to maintain the information to be

898 WORKING MEMORY STRATEGIES DEVELOPMENT 899

recalled for a shorter period, explaining why they outperform switching model, whereby attention is directed by the structure of younger children at recall. In accordance with the task-switching the task, to the microlevel switching assumed by the TBRS model, hypothesis, these authors have shown in several working memory whereby attention continuously switches between processing and span tasks that increasing the duration of the processing episodes storage, even during processing episodes. This shift would arise while keeping the attentional demand of processing constant re- from the development of executive processes and a greater capac- sulted in decreased recall in both children and adults. Thus, this ity to control attention (Zelazo & Frye, 1998). Such an improve- model considers the developmental increase in working memory ment in cognitive flexibility would occur between 6 and 7 years of span as a mechanistic by-product of the increase in processing age (Diamond, 2006). Thus, the aim of the present study was to speed and the resulting reduction in delay of maintenance. test the existence of such a developmental shift around these ages. Alternatively, the TBRS model suggests that maintenance of The insufficient executive resources or inefficient executive pro- information in working memory and recall performance on span cesses in younger children would not permit them to perform such tasks depend on a specific strategy named attentional refreshing a switching of attention at a microlevel. Thus, they would perform (Barrouillet, Bernardin, & Camos, 2004; Barrouillet, Bernardin, storage and processing when required by the structure of the task Portrat, Vergauwe, & Camos, 2007; Barrouillet & Camos, 2007). without trying to actively reactivate memory traces. With gain in This strategy is the ability to switch attention during the processing attention control, older children would be able to use attentional

broadly. episodes to briefly reactivate decaying memory traces. As a con- refreshing and to interleave some bursts of reactivation of memory sequence, the more the processing component of a working mem- traces even during processing episodes. However, to the best of publishers. ory span task captures attention, the less the attention can be our knowledge, no study in children aged around 7 has ever tested switched to maintain memory items. In accordance with this this developmental shift, because the duration of maintenance and allied disseminated

its model, we have shown in adults as well as in children that recall the cognitive load of the concurrent task have not yet been orthog- be of performance depends on the proportion of time during which the onally varied at that age. Whereas studies within the task- to

one processing component captures attention, thus impeding the re- switching model varied the duration of maintenance while the not or freshing of memory traces (Barrouillet et al., 2007; Barrouillet, attentional demand of processing was held constant (Towse & is Gavens, Vergauwe, Gaillard, & Camos, 2009). This proportion of Hitch, 1995), our previous study within the TBRS theoretical and time operationalizes the cognitive load induced by the processing framework kept constant the duration of maintenance while

user component. For example, in a recent study, we asked children from manipulating the cognitive load (Barrouillet et al., 2009, Ex- Association 7 to 14 years of age to memorize letters while they read series of periment 3). digits presented after each letter (Barrouillet et al., 2009, Experi- The originality of the present study was to fill this gap by

individual ment 1). To manipulate the cognitive load of this processing manipulating both factors in the same experiment. We created

the component, we varied the number of digits presented during fixed three complex span tasks that differed in terms of either the raw Psychological of interletter intervals, with more digits to be read involving a higher duration or the attentional demand of the processing episodes.

use cognitive load. As expected, in each age group, children’s recall Children were presented with animals to be remembered, each performance decreased with the increasing number of digits. This animal being followed by a processing period consisting in naming

American suggested that children, like adults, are able to rapidly switch their the color of smileys appearing successively on-screen. A first personal the attention during processing episodes to maintain the memory condition involved the presentation of one color within a 4-s the by traces of the letters. When the number of digits to read increases, interanimal interval. A second condition was designed to involve

for this switching strategy is hindered, and forgetting can no longer be processing periods of the same raw duration but with a higher counteracted. However, the slope relating recall performance to cognitive load by presenting two colors instead of one color during solely the amount of processing to be done within each interletter interval the 4-s interval. A third condition involved the presentation of two copyrighted

is (i.e., the number of digits to be read per unit of time) was flatter in colors but during intervals of 8 s, thus resulting in longer process- younger children. This result suggested that younger children take ing periods than in first and second conditions but in the same intended

is less advantage of the increasing availability of attention when cognitive load as the first condition with a rate of one color every fewer digits have to be read. In a subsequent experiment with a 4 s. Hereafter, these three conditions are referred to as one color document

article similar design (Barrouillet et al., 2009, Experiment 3), we showed short, two color short, and two color long, respectively. In sum- This that in even younger children aged 5 recall performance was no mary, one color short and two color short had the same duration, This longer affected by variations in the number of items to be pro- which was shorter than for two color long, and one color short and cessed between two items to be remembered. This series of ex- two color long had the same cognitive load, which was smaller periments in children is consistent with the idea developed by then two color short. Bayliss, Jarrold, Baddeley, Gunn, and Leigh (2005) that younger The hypothesis of a developmental shift from a macrolevel children have a slower rate of reactivation than older children (see switching with a passive maintenance of the memoranda to a also Cowan et al., 1994). Nevertheless, we have suggested that microlevel switching and the active strategy of refreshing memory younger children may have not only a lower rate of reactivation traces during processing periods leads to contrasting predictions. If when concentrating on the memory items, but also a lower capac- young children do not use any attentional strategy to refresh ity to control their activity and switch attention to the memoranda memoranda during processing, their recall performance would for refreshing purpose, hence the absence of effect of cognitive depend only on the raw duration of the processing periods during load in 5-year-olds. which memory traces decay. Thus, their recall performance should Hitch (2006) has suggested a similar idea. He proposed that the be poorer in the two-color-long condition than in the two short development of working memory in childhood might involve a conditions, which should not differ from each other. On the con- shift from the macrolevel switching described in the task- trary, older children who use the strategy of rapid switching would 900 CAMOS AND BARROUILLET

recall fewer items when the cognitive load of processing increases, either in yellow, blue, or red appeared successively in the center of whereas the raw duration of the processing periods should not have the screen. In the one-color-short condition, each smiley was any impact. Thus, their recall performance should be poorer in the displayed on-screen for 2,667 ms and followed by a delay of 1,333 two-color-short condition than in the one-color-short and two- ms for a total 4,000 ms. In both two-color conditions, these values color-long conditions, which should not differ from each other were either of 1,334 ms and 666 ms for a total of 4,000 ms in the because both involve the same cognitive load. short duration or of 2,667 ms and 1,333 ms for a total of 8,000 ms in the long duration. Children were asked to repeat the name of Method each animal after the experimenter and to name the color of each smiley presented. They were instructed to recall in correct order Participants the name of the animals they had seen when the recall signal (a question mark) appeared on-screen. Sixty-three kindergarteners (34 boys, 29 girls; mean age ϭ 5 The experimental session was preceded by a training phase. years 8 months, SD ϭ 3.5 months) and 63 first graders (36 boys, First, children were familiarized with the color task by naming the 27 girls; mean age ϭ 6 years 9 months, SD ϭ 3.5 months) color of smileys displayed on-screen for six series. The series participated in the experiment. All the children were native French corresponded to the upcoming experimental condition with one or

broadly. speakers, and none had difficulties with perceiving or naming the two colors and a long or short duration. Then they were shown in colors. Children attended four schools in rural Burgundy, and a booklet how the different screens would follow one another and publishers. among each class they were randomly assigned to one of the three they were trained to repeat the name of each animal and to name experimental conditions. Informed consent was received from the colors of the smileys if needed. Finally, they performed on the allied

disseminated children’s carers. its computer two series of one animal and two series of two animals be of of the color-naming span task corresponding to the condition they to

one Material and Procedure were assigned to. not or is Children were presented with series of one to four colored Results and drawings of animals to be remembered (one to five for the 7-year- old group to avoid ceiling effect), with four series of each length Because no difference emerged between the schools, this factor user

Association (see Figure 1). This resulted in 16 and 20 trials for a total of 40 and was not included in the reported analysis. As far as the color- 60 memory items in 6- and 7-year-old children, respectively. Sixty naming task was concerned, the rate of errors was particularly low, animals were used to avoid between-list interferences. Because we below 2% for the three conditions. The 6-year-old children (1.2%) individual needed a large number of drawings and it would have not been made more errors than the older children (0.4%), but the effect just the ϭ ϭ ␩2 ϭ

Psychological possible to control for all potential variables that could affect failed to reach significance, F(1, 120) 3.69, p .057, .40. of p recall, we presented the same material in the same order in the The rate of errors did not differ across conditions, and the Age ϫ use three experimental conditions. Each animal was presented in an Condition interaction was not significant ( ps Ͼ .180). Moreover, invisible 6.5 ϫ 6.5-cm square in the center of the screen for 2,000 it should be noted that the following analyses on recall perfor- American

personal ms and followed by a period of 500 ms before the appearance of mance were performed on both the entire sample and a sample the the

by the first smiley. One or two smileys of 6.5-cm diameter colored restricted to the children who made no error on the color-naming for solely copyrighted is intended is document article This This

Figure 1. Illustration of trials for the one-color condition (A) and two-color-short condition (B). WORKING MEMORY STRATEGIES DEVELOPMENT 901

task (i.e., discarding fourteen 6-year-old and four 7-year-old chil- tive load but not to raw duration. When the processing component dren). Because the pattern of results was identical for both analy- was performed at the same pace (one-color-short and two-color- ses, we report below the results on the entire sample. long conditions), variations in raw duration did not result in any In recall performance, most of the errors were omissions: 40% change in recall performance (68% in both conditions; F Ͻ 1). By and 34% of the words by 6- and 7-year-old children, respectively. contrast, as we already observed in adolescents and young adults, With such a high rate of omissions, and because children did not increasing cognitive load significantly decreased recall perfor- specify in which positions these omissions occurred while they mance, and the two-color-short condition induced lower perfor- recalled orally, scoring according to correct positions would have mance (60%) than the other two conditions, F(1, 60) ϭ 8.05, p ϭ ␩2 ϭ been hazardous. We then scored recall as the percentage of animal .006, p .99. names correctly recalled whatever their position. We performed an It is interesting that this pattern of results was similar when we analysis of variance on these scores with age (6 and 7 years) and took into account the different list lengths (see Figure 3). We conditions (either one color short, two color short, or two color performed an analysis of variance on the percentage of correct long) as between-subjects factors. This analysis revealed that the recall with age, condition, and length as between-subjects factors percentage of animals correctly recalled was higher among older but excluded Length 5, which was not presented to both age than younger children (65% and 58%, respectively), F(1, 120) ϭ groups. We also discarded Length 1 because of a ceiling effect in 2 broadly. Ͻ ␩ ϭ 16.39, p .001, p .54. Although the effect of the experimental both age groups (cf. Figure 3). The effects described in the previ- conditions did not reach significance, F(2, 120) ϭ 2.30, p ϭ .105, ous analysis remained unchanged, even under this restriction on publishers. ␩2 ϭ ϭ ϭ ␩2 ϭ p .15, it interacted with age, F(2, 120) 4.59, p .012, p lengths. Older children still outperformed younger children, F(1, .30 (see Figure 2). 120) ϭ 56.48, p Ͻ .001, ␩2 ϭ .36. The effect of the conditions allied p 2 disseminated ϭ ϭ ␩ ϭ its A priori orthogonal comparisons were performed in each age failed to reach significance, F(2, 120) 2.49, p .087, p .03,

be 2 of ϭ ϭ ␩ ϭ group to test our specific predictions. As we predicted, recall but it interacted with age, F(2, 120) 4.94, p .009, p .06. to

one performance in 6-year-old children was sensitive only to the raw The percentage of correct recall decreased from Length 2 to

not 2 or duration of the color task but not to the cognitive load it involved. Length 4, F(2, 240) ϭ 115.58, p Ͻ .001, ␩ ϭ .52, and this effect is p Their percentage of correct recall did not significantly differ be- was stronger in younger than in older children, F(2, 240) ϭ 4.56, and ϭ ␩2 ϭ tween the two conditions that lasted the same duration (61% in one p .011, p .02. However, the length effect did not interact

user color short and 60% in two color short), although more distracting with conditions (F Ͻ 1), and the two-way interaction between age, Association items were presented and processed in the latter (F Ͻ 1). However, length, and condition was not significant, F(4, 240) ϭ 1.04, p ϭ ␩2 Ͻ as predicted by the hypothesis of a time-related decay of memory .39, p .01.

individual traces, increasing the duration of the processing period in the

the two-color-long condition resulted in a significant decrease in recall Discussion Psychological of (54%) compared with the two short conditions, F(1, 60) ϭ 5.51, 2

use ϭ ␩ ϭ p .022, p .98. A totally different pattern of results emerged The aim of the present study was to test the hypothesis of a in 7-year-old children whose performance was sensitive to cogni- developmental shift from a passive maintenance to an active American personal the the by for solely copyrighted is intended is document article This This

Figure 2. Mean percentage (and standard error) of animal names correctly recalled in 6- and 7-year-old children as a function of the experimental condition. 902 CAMOS AND BARROUILLET broadly. publishers. allied disseminated its be of to one

not Figure 3. Mean percentage (and standard error) of animal names correctly recalled in 6- and 7-year-old or

is children as a function of the experimental condition and list length. and

user refreshing strategy in working memory. In a complex span task in Thus, both verbal rehearsal and attentional refreshing are affected Association which the storage of animal names was interleaved with a color- by time constraints. At age 7, children could use either one or the naming task, 6-year-old children’s recall performance appeared to other, or jointly use both mechanisms. When more time is avail-

individual depend only on the raw duration of the color-naming task but not able (i.e., when the pace of the concurrent processing is low),

the on the cognitive load this task involves. On the contrary, at age 7, children could take advantage of it to rehearse or refresh the Psychological of the cognitive load of the color task, which constrains the time animal names they had to maintain. However, does this develop-

use available to refresh memory traces, determined recall performance, mental pattern reflect a qualitative change in the use of memory whereas the raw duration of the color-naming task did not have strategy between ages 6 and 7, or might it be sustained by a

American any impact. This suggests that the cognitive activities in younger quantitative change? personal the children are directly mapped onto the structure of the working Several studies have been devoted to developmental changes in the by memory span tasks. Encoding occurs during the storage episodes, the use of verbal rehearsal by investigating the onset of the

for the memory items being passively held during the processing phenomena usually considered as clues for the use of this specific periods without any attempt of active maintenance, thus suffering maintenance mechanism. They reveal that the word length effect solely from time-related decay. Recall is thus totally dependent on the on the probed recall, the speech rate/short-term memory span copyrighted

is duration of these periods, with longer periods resulting in poorer correlation, and the phonological similarity effect for visually recall. By contrast, among older children, an increased capacity to presented material all appear around age 7, suggesting a sudden intended

is control attention and monitor cognitive processes allows them to qualitative change. However, Jarrold and Tam (2011) reviewed briefly deviate attention during the processing periods to reactivate recent studies in large samples showing some evidence of the use document

article memory traces. Thus, recall performance no longer depends on the of verbal rehearsal in children younger than 7. These authors This raw duration of the processing periods but on the cognitive load of suggested that the comparison of nonadjacent small age groups This processing that determines the opportunity to refresh. would have facilitated the apparent dichotomy between children The current results do not imply that 6-year-old children never younger and older than 7, whereas microgenetic approaches on use, or do not have at their disposal, some mechanism of mainte- large samples could reveal a different picture. It must be acknowl- nance, by means of verbal rehearsal or attentional refreshing. The edged that our study falls into the former category and that the demands of the task on both attention and verbal processes could qualitative change that it shows might arise from the comparison have been strong enough to entirely block these mechanisms. of two separated points in a continuum. Concerning the attentional Conversely, the effect of cognitive load in 7-year-old children refreshing, which is a separated and independent mechanism of implies that, at least at age 7, children have and use some mech- maintenance (Camos et al., 2009; Hudjetz & Oberauer, 2007), anism to maintain verbal information. The TBRS model considers developmental studies are scarce and focused on older children the effect of cognitive load as a clue to an attentional refreshing (Barrouillet et al., 2009). However, neurophysiological studies mechanism. However, Camos, Lagner, and Barrouillet (2009) suggest that the cognitive flexibility needed to switch attention have recently shown that phonological rehearsal, as it was de- back and forth from processing to maintenance activities develops scribed in Baddeley’s (1986) model, is also sensitive to manipu- critically between ages 7 and 9 in association with maturation of lations of the pace of a verbal concurrent processing in adults. the frontal lobe (see Anderson, 2002, for review). Thus, it is WORKING MEMORY STRATEGIES DEVELOPMENT 903

possible that different strategies of maintenance exhibit different more time to counteract interference effects and restore memory developmental patterns depending on the cognitive processes and traces, for example, by elaborative rehearsal. However, such an executive functions involved. What the present study made clear is additional assumption to the interference account is contradicted that recall performance in young children aged 6 depends on the by the 6-year-olds’ pattern of results. In the two conditions with delay between encoding and recall without any effect of the the same number of distractors (two color short and long), the cognitive load of the intervening activity, suggesting that they do increase in duration did not result in better but in poorer recall not use any active maintenance strategy. Nonetheless, it should be performance. It is still possible to suppose that elaborative re- noted that our younger participants were not able to recall items in hearsal is not efficient in young children, but still leaves the correct order, and as a consequence we had to use a lenient question unanswered as to why the interference effect could be criterion that does not take serial order into account. This scoring stronger as time goes by. Moreover, the one-color-short and two- procedure, which is rather unusual to assess working memory color-short conditions, which differed in the amount of interfer- spans, could limit the scope of the present findings and make ence while lasting the same duration, did not differ in recall difficult the comparison with previous studies. However, it also performance. This leads to an inextricable puzzle for the interfer- highlights the dissociation between the maintenance of item and ence account, whereas all these results can be explained by as- order information. In adults, Nairne and Kelley (2004) showed that suming that memory traces suffer from a time-related decay the

broadly. variables such as phonological similarity affect differently item effects of which cannot be counteracted by refreshing activities in and order maintenance. In the related field of short-term memory, younger children. One would then continue to favor forgetting due publishers. several models distinguish mechanisms of maintenance for item to a temporal decay, whereas the explanatory power of the inter- from those for order (Burgess & Hitch, 1999; Gupta, 2003; Hen- ference account is restricted to the results of 7-year-old children allied disseminated

its son, 1998), and studies in young children have shown that item and with the addition of some time-related mechanism of restoration of be of order short-term memory reflects distinct capacities with different memory traces. Defenders of the interference account are left with to

one maturational rates (Majerus, 2009; Majerus, Poncelet, Greffe, & the problem of explaining how temporal decay could affect mem- not or Van der Linden, 2006). In working memory tasks, further studies ory in preschoolers and then disappear during childhood to be is are required to explore such dissociation and its developmental replaced by interference. and trajectory. In conclusion, whereas the working memory functioning exhib-

user Apart from providing some insight into the way working mem- ited by 6-year-old children was described by the task-switching Association ory strategies develop, our results are also relevant for more model as a stimuli-driven switching between processing and stor- general working memory phenomena such as the sources of for- age, the 7-year-old children’s pattern of performance reflected the

individual getting. Although the task-switching and TBRS models differ in goal-directed microlevel switching described by the TBRS model.

the their account of the development of working memory, they nev- Thus, the present study reunifies the two main current accounts of Psychological of ertheless agree on the main cause of forgetting, which is assumed working memory span tasks into a two-stage developmental

use to result from a time-based decay of the memory traces. However, model. a still ongoing debate concerning the causes of forgetting in

American working memory opposes in the literature two main conceptions:

personal References the temporal decay and representation-based interference. According the by to the former conception, memory traces would fade away with the Anderson, P. (2002). Assessment and development of executive function for mere passage of time, their activation level inescapably decreasing (EF) during childhood. Child Neuropsychology, 8, 71–82. doi:10.1076/ over time if nothing is done to reactivate them. According to the chin.8.2.71.8724 solely latter conception, time would not have any direct causal role. Baddeley, A. D. (1986). Working memory. Oxford, England: Oxford Uni- copyrighted versity Press. is Forgetting would occur through interference created by subsequent events. This interference could be provoked by the superposition Barrouillet, P., Bernardin, S., & Camos, V. (2004). Time constraints and intended resource sharing in adults’ working memory spans. Journal of Experi- is of an increasing number of items in a composite memory or by feature overwriting. When successive items share some features, mental Psychology: General, 133, 83–100. doi:10.1037/0096- document 3445.133.1.83

article these features could be deleted and the memory traces degraded Barrouillet, P., Bernardin, S., Portrat, S., Vergauwe, E., & Camos, V. This (Lewandowsky, Oberauer, & Brown, 2009). The current findings

This (2007). Time and cognitive load in working memory. Journal of Exper- might bring some insights on the debate. To favor an interference imental Psychology: Learning, Memory, and Cognition, 33, 570–585. account, one would first have to accept that the items used in the doi:10.1037/0278-7393.33.3.570 present study (animal pictures and colored smileys) might interfere Barrouillet, P., & Camos, V. (2007). The time-based resource-sharing with each other, which is possible because animals and colors model of working memory. In N. Osaka, R. H. Logie, & M. D’Esposito could have been encoded in the same format, either visually or (Eds.), The cognitive neuroscience of working memory (pp. 59–80). verbally. In line with this interference account, increasing the Oxford, England: Oxford University Press. number of distractors in an unchanged processing period (one vs. Barrouillet, P., Gavens, N., Vergauwe, E., Gaillard, V., & Camos, V. two colors in short duration) induced poorer recall performance in (2009). Working memory span development: A time-based resource- sharing model account. Developmental Psychology, 45, 477–490. doi: 7-year-old children. However, although the same number of col- 10.1037/a0014615 ored distractors was presented in both two-color conditions (short Bayliss, D. M., Jarrold, C., Baddeley, A. D., Gunn, D. M., & Leigh, E. and long), recall performance varied and was better for the long (2005). Mapping the developmental constraints on working memory condition, a result at odds with a simple interference account. To span performance. Developmental Psychology, 41, 579–597. doi: accommodate similar results, Lewandowsky and Oberauer (2009) 10.1037/0012-1649.41.4.579 have suggested that an increased duration of presentation leaves Bjorklund, D. F., Dukes, C., & Brown, R. D. (2009). The development of 904 CAMOS AND BARROUILLET

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