EFTA01098878.pdf

IWUROPSYCHOLOGIA ELSEVIER Neuropsychologia 44 (2006) 2037-2078 www elsevier comilocateineumpsychologia Development of cognitive control and executive functions from 4 to 13 years: Evidence from manipulations of memory, inhibition, and task switching Matthew C. Davidson a'b, Dima Amso a, Loren Cruess Anderson c, Adele Diamond d,* Sackler Institutefor Developmental Psychobiologx frill Medical College of Cornell University; New York. NY. USA b Department ofPsychologx University ofMassachusetts. Amherst. MA. USA Shrive, Center. University ofMassachusetts Medical School, Waltham. MA. USA d Department ofPsychiatrx University ofBritish Columbia & Division ofChild & Adolescent Psychiatty, BC Children's Hospital. Vancouver. Canada Received 20 November 2005: received in revised form 7 February 2006: accepted 10 February 2006 Available online 31 March 2006 Abstract Predictions concerning development, interrelations, and possible independence of working memory, inhibition, and cognitive flexibility were tested in 325 panicipants (roughly 30 per age from 4 to 13 years and young adults.. 50% female). All were tested on the same computerized battery. designed to manipulate memory and inhibition independently and together. in steady state (single-task blocks) and during task-switching. and to be appropriate over the lifespan and for neuroimaging (MARI). This is one of the first studies, in children or adults, to explore: (a) how memory requirements interact with spatial compatibility and (b) spatial incompatibility effects both with stimulus-specific rules (Simon task) and with higher-level, conceptual rules. Even the youngest children could hold information in mind, inhibit a dominant response. and combine those as long as the inhibition required was steady-state and the rules remained constant. Cognitive flexibility (switching between rules), even with memory demands minimized, showed a longer developmental progression. with 13-year-olds still not at adult levels. Effects elicited only in Mixed blocks with adults were found in young children even in single-task blocks: while young children could exercise inhibition in steady state it exacted a cost not seen in adults, who (unlike young children) seemed to re-set their default response when inhibition of the same tendency was required throughout a block. The costs associated with manipulations of inhibition were greater in young children while the costs associated with increasing memory demands were greater in adults. Effects seen only in RT in adults were seen primarily in accuracy in young children. Adults slowed down on difficult trials to preserve accuracy: but the youngest children were impulsive; their RT remained more constant but at an accuracy cost on difficult trials. Contrary to our predictions of independence between memory and inhibition, when matched for difficulty RT correlations between these were as high as 0.8. although accuracy correlations were less than half that. Spatial incompatibility effects and global and local switch costs were evident in children and adults, differing only in size. Other effects (e.g.. asymmetric switch costs and the interaction of switching rules and switching response-sites) differed fundamentally over age. O 2006 Elsevier Ltd. All rights reserved. Keywords: Task switching: Inhibition: Working memory: Simon effect: Asymmetric switch costs: Global and local switch costs: Stimulus—response compatibility: Development: Children: Frontal lobe Mature cognition is characterized by abilities that include appropriately, and (c) to quickly and flexibly adapt behavior being able: (a) to hold information in mind, including compli- to changing situations. These abilities are referred to respec- cated representational structures, to mentally manipulate that tively as working memory, inhibition, and cognitive flexibility. information, and to act on the basis of it, (b) to act on the basis Together they are key components of both "cognitive control" of choice rather than impulse, exercising self-control (or self- and "executive functions" and have been studied in a wide vari- regulation) by resisting inappropriate behaviors and responding ety of experimental paradigms with diverse subject groups. Our battery of interrelated tasks enabled us to indepen- dently and systematically vary demands on these abilities and to track their development across a wider age range than hereto- • Corresponding author at: Department of Psychiatry. University of British fore investigated using the same measures at all ages. Hav- Columbia. 2255 Wesbrook Mall. Vancouver. BC. Canada V6T 2AL Tel.: +1 604 822 7220: fax: +1 604 822 7232. ing measures that span a wide age range is important given E-mail address: adele.diamondaubc.ca (A. Diamond). the protracted developmental progressions of many executive 0028-3932(8 — see front matter O 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.neuropsychologia.2006.02.006 EFTA01098878 2038 MC. Davidson e at /Neumps)rhologia 44 (2006)2037-2078 function and cognitive control skills. While some cognitive did not have to be held in mind and in another case by using abilities develop early, executive functions do not reach their stimuli (Arrows) that pointed to where to respond. We increased peak until early adulthood (DeLuca et al., 2003; Diamond, the working memory requirements by introducing conceptual 2002; Fischer, Biscaldi, & Gezeck, 1997; Harnishfeger & Pope, rules, where the correct response required mental manipulation. 1996; Kail, 1991abc; Kail & Salthouse, 1994; Luciana & Instead of a rule being "for A press left:' a rule was "for A Nelson, 2002; Luciana, Conklin, Hooper, & Yarger, 2005; Luna, press on the side opposite A:' Thus, in addition to activating Garver, Urban, Lazar, & Sweeney, 2004; Lyons-Warren, Lillie, the rules associated with the two stimuli (the memory require- & Hershey, 2004; Munoz, Broughton, Goldring, & Armstrong, ment in standard Simon tasks), participants had to instantiate the 1998; Zelazo, Craik, & Booth, 2004). Each test in our battery appropriate rule for the particular spatial location of the stimulus can be performed by children as young as 4 years; yet adults on each trial. still find many of them challenging. The entire battery takes Task-switching paradigms target the ability to flexibly shift less than 30 min to complete. These tests are also designed from one mindset to another, often times acting according to to be appropriate for testing nonhuman primates and for neu- rules that would be incompatible with the other mindset. This roimaging research using functional magnetic resonance imag- has been studied extensively in adults (e.g., Allport, Styles, & ing (fMRI) (Diamond, O'Craven, & Savoy, 1998; O'Craven, Hsieh. 1994; Jersild, 1927; Meiran, Gotler, & Perlman, 1996; Savoy, & Diamond, 1998). Monsell & Driver, 2000; Rogers & Monsell, 1995; Meiran Across this wide age span, our battery provides within- et al., 2000a,b; Meiran, 2005; Spector & Biederman, 1976; subject measures of two classic paradigms in cognitive psy- Sudevan & Taylor, 1987), including the elderly (e.g., Kramer, chology, the Simon task and task switching. In the Simon task Hahn, & Gopher, 1999; Mayr, 1996; Meimn, Gotler, & Perlman, paradigm, a non-spatial aspect of the stimulus (such as its 2001), and in various clinical groups (e.g., Aron, Sahakian, color or identity) is relevant and its spatial location is irrele- & Robbins, 2003; Brown & Marsden, 1988; Downes et al., vant. Nevertheless, the well-replicated finding in adults is that 1989; Flowers & Robertson, 1985; Hayes, Davidson, Rafal & responses are faster and more often correct when the stimu- Keele, 1998; Mecklinger, von Cramon, Springer, & Mantles- lus and response are on the same side than when they are on von Cramon, 1999; Rogers et al., 1998). However, to date, opposite sides (the Simon effect, also called spatial incompati- only a handful of studies have looked at task switching in chil- bility or stimulus—response compatibility; e.g., Craft & Simon, dren (Cepeda, Kramer, & Gonzalez de Sather, 2001; Cohen, 1970; Fitts and Seger, 1953; Hommel, 1995; Hommel, Proctor, Bixenman, Meiran, & Diamond, 2001; Crone, Bunge, Van der & Vu, 2004; Lu & Proctor, 1995; Simon & Small, 1969; Simon, Molen, & Ridderinkhof, in press; Crone, Ridderinkhof, Worm, 1990; Simon & Berbaum, 1990). This effect indicates: (a) the Somsen, & van der Molen, 2004; Reimers & Maylor, 2005; influence of an irrelevant stimulus attribute on performance and Zelazo, Craik, & Booth, 2004). (b) a prepotent tendency to respond on the same side as the Switching is fundamentally difficult and a paradigmatic stimulus (confirmed at the neuronal level [see Georgopoulos, instance of when top-down executive control is required 1994; Georgopoulos, Lurito, Petrides, Schwartz, & Massey, because generally it cannot be done "on automatic:' It taxes 19891 and with lateralized readiness potentials [Valle-Inclan, both working memory and inhibition (the newly-relevant 19961) which must be inhibited when the locations of stimu- rules and stimulus-response relations must be activated and lus and response are incompatible. It thus provides insight into the previously-relevant ones suppressed). One cannot get in the an aspect of inhibitory control. A finding that the Simon effect "groove" of repeatedly doing the same thing or staying in the decreases over a certain age range provides evidence for when same mindset because periodically one will have to change that. developmental improvement in that aspect of inhibition occurs A groove is a good analogy because it takes effort to climb over and insight into when maturational changes in the neural sys- the banks of the groove (the mindset) one is in and settle, however tem underlying that might be occurring. That neural system temporarily, into another grove. Neuroimaging studies confirm overlaps substantially with the neural system activated during that task-switching (as opposed to continuing to do the same Stroop interference and other cognitive control paradigms. It task) activates the neural system associated with executive func- includes the anterior cingulate, lateral prefrontal cortex (dorso- tion and top-down cognitive control, that is lateral prefrontal lateral and ventrolateral), pre-SMA, premotor cortex, posterior cortex (dorsolateral and ventrolateral), inferior frontal junction and superior parietal cortex, inferior temporal cortex, the insula, (IFJ) and premotor cortex, pre-SMA and the anterior cingu- and precuneus (Bush, Shin, Holmes. Rosen, & Vogt, 2003; late, and the insula and cerebellum (Brass et al., 2003; Brass, Dassonville et al., 2001; Fan, Flombaum, McCandliss, Thomas, Derrfuss,Forstmann, & von Cramon, 2005; Braver, Reynolds, & & Posner, 2003; lacoboni, Woods, & Mazziotta, 1998; Liu, Donaldson, 2003; Crone, Wendelken,Donohue, & Bunge, 2005; Banich, Jacobson, & Tanabe, 2004; Maclin Gratton, & Fabiani, DiGirolamo et al., 2001; Dove, Pollmann, Schubert, Wiggins, 2001; Peterson et al., 2002; Thomas et al., 1999; Wager & Smith, & von Cramon, 2000; Dreher & Berman, 2002; Dreher & 2003). Grafman, 2003; Kimberg, Aguirre, & D'Esposito, 2000; Meyer We investigated spatial incompatibility effects both decreas- et al., 1998; Omori et al., 1999; Pollmann, 2001; Sohn, Ursu, ing and increasing the working memory requirements tradition- Anderson, Stenger, & Carter, 2000; Sylvester et al., 2003; Wager, ally required for Simon tasks. We decreased it in one case by Reading, & Jonides, 2004). Consistent with this, patients with providing icons depicting stimuli A and B over their respective frontal cortex damage are impaired at switching between tasks response-sites so that which response goes with which stimulus (Mon,Monsell, Sahakian, & Robbins, 2004; Diedrichsen, Mayr, EFTA01098879  M.C. Davidson es nl. /Neuropsychologia 44 (2006)2037-2078 2039 Dhaliwal, Keele. & Ivry, 2000; Keele & Rafal, 2000; Owen et Finally, Diamond (1991, 2002) and others (Anderson & al., 1993; Rogers et al., 1998; Shallice & Burgess, 1991). Spellman, 1995; Gemsbacher & Faust, 1991; Hasher, Stoltzfus, We report here on the developmental progression in almost Zacks, & Rypma, 1991) have hypothesized that working mem- 300 children from 4 to 13 years of age and the performance ory and inhibition are separable functions. This is consistent of young adults for comparison, all tested on the same test with the results of the factor analyses of Miyake et al. (2000) that battery. Various manipulations exploited task switching and spa- found working memory and inhibition to be moderately corre- tial incompatibility effects, with and without an added memory lated but clearly separable. Many scholars, however, have argued component, or taxed memory without taxing inhibition or task that there is no need to postulate an inhibitory function separate switching, enabling us to test predictions concerning interre- from working memory and have produced neural network mod- lations, independence, and the developmental progressions of els consistent with that (Cohen, Dunbar, & McClelland, 1990; working memory (how much information you must hold in Kimberg & Farah, 1993; Miller & Cohen, 2001; Morton & mind and how many steps must be mentally executed using that Munakata, 2002; Munakata, 2000). Given that we hypothesized information), inhibition (resisting an incorrect response you are that working memory and inhibition are independent, we pre- inclined to make in order to make the correct response), and dicted that performance on tasks that tax primarily memory or cognitive flexibility (switching between tasks or rules). The pre- primarily inhibition would not be highly correlated, and tested dictions we tested were generated from hypotheses concerning this for relatively easy tasks and for relatively difficult tasks inhibition and working memory and hypotheses concerning cog- requiring primarily memory or primarily inhibition, matched on nitive flexibility and task switching. difficulty. 1. Hypotheses relevant to inhibition and working 2. Hypotheses relevant to cognitive flexibility and task memory switching We hypothesized that inhibition would exact a greater relative Diamond (1990, 1991, 2002) has long maintained that it is cost for young children than for older children or young adults, the conjunction of simultaneous demands on holding informa- and thus predicted that inhibitory demands would account for a tion in mind and inhibition that is truly difficult, especially if greater proportion of the variance in children's performance than one's mental settings have to be continually re-set because the in adults, and the more so the younger the child. In young adults, task changes. We thus predicted that the most difficult condition in whom inhibitory control is more mature, we hypothesized at all ages would be the one that taxes inhibition and memory in that memory demands would exact a greater cost than inhibitory a switching context, where top-down executive control is con- demands. tinually required, and that that would be even more difficult than Because we hypothesized that inhibitory control is extremely having to hold three times as much information in mind but with problematic for very young children, we predicted they would no inhibition or switching component. Further, since we hypoth- perform poorly on all trials requiring inhibition (Incongruent esized that switching is so difficult, we predicted that having to trials and switch trials) and that those effects would be addi- switch between task sets would show a long developmental pro- tive. We predicted that older children and adults would show gression even when memory demands are minimized. the same "asymmetric switch costs" (a greater relative switch Diamond has recently theorized that several seemingly inde- cost for switching to the easier [Congruent] condition) previ- pendent findings in cognitive psychology can be integrated under ously reported in adults (Allport & Wylie, 2000; Allport et al., the hypothesis that the brain and mind tend to work at a grosser 1994; De long, 1995; Kleinsorge & Heuer, 1999; Los, 19%; level, and only with effort, or more optimal functioning, work Stoffels, 1996; Wylie & Allport, 2000). Further, for slightly in a more selective manner (a theory Diamond has called "all older children, who are beginning to exercise better inhibitory or none" (Diamond, 2005, in preparation)). For example, it is control, doing so should require greater effort than in older easier to take into account all salient aspects of a stimulus than participants. Hence, we predicted that undoing that inhibition only some of its properties. Indeed, it is difficult to ignore irrele- (switching back to making a dominant response) should exact vant properties of an attended stimulus, as the Simon effect and a greater cost in those children than in adults. Thus, we pre- children's difficulties on card sorting tasks so amply demon- dicted that beginning after 6 or 7 years, asymmetric switch strate (Diamond, Carlson, & Beck, 2005; Kirkham, Cruess, & costs would be larger in younger than older participants, but Diamond, 2003). that the youngest children would show an opposite pattern of Another finding that fits under the all or none rubric is that asymmetry. it is easier to inhibit a dominant response all the time than only The ability to simply hold items in mind (without any added some of the time. One of the most demanding cognitive require- requirement to manipulate that information or exercise inhibi- ments is to switch back and forth, to overcome inertial tendencies tion) develops early, is robust even in preschoolers, and shows favoring staying in the "groove" one is in (Kirkham et al., 2003). little improvement with age (Brown, 1975; Dempster, 1985; Once in a "groove," even if it was a difficult one to settle into Diamond, 1995). Given the early maturation of the ability to (because it required resisting a tendency to act otherwise, for hold items in mind, we predicted that although it would be harder example) it is not that difficult to continue along that path. It for everyone to hold more items in mind than fewer, the relative is re-mapping stimulus—response associations, changing mind- difficulty of that would not change over age. sets, that is quite difficult (Brass et al., 2003; Fagot 1994; Los, EFTA01098880 2040 M.C. Davidson et al. /Neumpsychologia 44 (2006)2037-2078 1996, 1999; Schuch & Koch, 2003, 2004; Wannk, Hommel, & when they are presented in the context of having to periodically Allport, 2003). We thus predicted that performance at all ages switch between rules than in a block of all nonswitch trials. would be better in Incongruent-only blocks (where inhibition is Such global switch costs (the difference in performance on non- consistently required on all trials) than in Mixed blocks (where switch trials in a Mixed block versus in a single-task block; Fagot inhibition is only required on the 50% of trials that are Incon- 1994, Mar, 2000) have been shown to be greater for elders than gruent), and that this difference would be greater the younger for younger adults (Kray, Eber, & Lindenberger, 2004; Kray & the children. This might seem obvious, but most studies of the Lindenberger, 2000; Mayr, 2000; van Asselen & Ridderinkhof, classic Stroop effect still tend to administer the conditions in 2000) and higher for children than for young adults (Cepeda single-task blocks (read all the words or state the ink color of et al., 2001; Cohen et al., 2001; Reimers & Maylor, 2005), all the words), missing the most difficult condition (switching though this has not been investigated in children as young as the between having to read the words and having to state the ink youngest tested here and though some studies have not found an color). age difference in global switch costs (Crone et al., in press; Kray, A further seemingly independent finding that provides Li, & Lindenberger, 2002). We predicted that global switch costs another example of the all or none principle is that it is eas- would not only be found in our youngest participants but would ier to switch everything, or nothing, than to switch one thing be more exaggerated the younger the child. (e.g., the rule or the response) but not the other (Hommel et al., Because of floor effects (subjects should already be slower 2001; Kleinsorge, 1999; Meiran, 2000a,b; Rogers & Monsell, and more error-prone in the Incongruent-only block), the effect 1995; Schuch & Koch, 2004). Similarly, if you are supposed to of context (the Mixed block versus single-task block) should press the color opposite to a stimulus it is easier to also press the be greater on Congruent than Incongruent trials. We predicted button on the side opposite to the stimulus (rather than the typ- that this would be more evident the younger the child. Thus, ical bias to respond on the same side as the stimulus; Hedge & performance on "easy" (Congruent, nonswitch) trials should fall Marsh, 1975). Issuing a global "change" or "opposite" command closer and closer to the level of "harder" trials in the context of to all systems appears to be preferred by our neural machinery sometimes having to switch back and forth the younger the child. over a more selective command to just the action system or to just one aspect of cognition. This has been demonstrated not 3. Methods only in young adults, but also in older adults (Mayr, 2001) and children (Crone et al., in press). We predicted that we would 3.1. Participants demonstrate these effects, heretofore documented only in adults A total of 325 individuals participated. ranging in age from 4 to 45 years. and older children, even in young children. Thus, we predicted Of these. I 1 children were excluded from the analyses for failing to press any that throughout our age span, participants would do better at button or consistently pressing both. Of the remaining 314 participants. 50% switching tasks if the response-site also changed and would be were female (157 female. 157 male). Table 1 shows the number and gender of slower and less accurate on switch trials when the response-site participants in each of the age groups. Children were recruited through local preschool and elementary school programs in the suburban Boston area. Adults remained the same as on the previous trial. Another way of putting some of the above points is that con- Table 1 text matters. For example, even "easy" trials do not seem so Number of participants within each age and gender group easy when they are presented in the context of switching between those and "harder trials. Knowing that sometimes you will have Age group' Mean age S.U. N Gender (years) (years) to switch can cause you to slow down (and perhaps err more) on Female Male trials where you do not have to switch. Local context matters; it 4 4.43 0.25 30 14 16 matters what trials came before a particular trial. For example, 5 5.19 0.17 30 14 16 was the rule on the preceding trial the same as on the current 6h 6.01 0.40 30 15 15 trial? Performance is better on nonswitch than on switch tri- 6h 6.22 0.35 30 12 IS als. Was the response-site on the preceding trial the same as on 7 7.12 0.20 30 13 17 8 7.97 0.28 30 10 10 the current trial? Studies in adults have shown that performance 9 9.07 0.30 30 17 13 is better on nonswitch, same-response-site trials than on non- 10 9.92 0.30 30 13 17 switch, response-site-switch trials and on rule-switch, response- II 11.01 0.32 28 II 17 site-switch trials than on rule-switch, same-response-site trials. 13 12.89 1.21 26 17 9 We predicted a different pattern in the youngest children and a Adults 26.30 5.40 20 14 6 more exaggerated version of the adult pattern in slightly older Total number of 314 157 157 children (see above). participants Global context also matters; it matters what kind of trial block 4 The age groups were used for illustrative purposes when preparing graphs. a given trial occurs in. Performance on the same type of trial All regression analyses used the actual ages of participants and treated age as a (e.g., Congruent, Incongruent) in the same type of local con- continuous variable. b TWo groups of 6-year-old children were tested to study the effects of short text (e.g., nonswitch) varies depending on the larger context vs. long presentation time at this intermediate age. For one group. stimulus (e.g., a single-task block or Mixed block). Performance even on presentation time was 2501ms. the slower version used with younger children. "easy" nonswitch trials (where the rule on the present trial is the For the second group. stimulus presentation time was 750 nu, the faster version same as on the previous trial) is usually slower and less accurate used with older children and adults. EFTA01098881  ACC. Davidson et al. /Neumpsychologia 44 (2006) 2037-2078 2011 were recruited from within the Eunice Kennedy Shrivcr Center in Waltham. MA. pointing down like this IE demonstrated] to this button. press this button. If the The majority of participants were Caucasian and from middle to upper middle arrow is on this side. pointing down across the screen like this IE demonstrated] class families. Informed consent was obtained from all adult participants and to this button. press this button. If the arrow is on the other side. pointing down from a parent of each child participant: assent was obtained from the younger across the screen like this IE demonstrated] to this button. press this button:' children and consent from the olderones. All participants received a small, token Congruent and Incongruent trials were presented in a randomized Mixed block present for their participation. of 20 trials. This requires inhibiting the tendency to respond on the same side as the stimulus when a diagonal arrow appears. but it requires little or no working memory. as the arrow points directly to the correct response button on all trials. 3.2. Procedures common to all tests in our batten• 3.3.3. Dols All tasks were presented on a Macintosh computer using MacStim to The Dots test was designed to tax both working memory and inhibition. present the stimuli and record responses. Participants held a button box while the other tests were designed to tax primarily either working memory (10cm x 14 cm x 3 cm) with both hands and used their thumbs to press the two or inhibition, not both. Here, a large dot (diameter = 2_5 cm). was presented response buttons. For each task a horizontal rectangle (6 cm x 18 cm) with a cen- either at the left or right on each trial (sec Fig. I). Two types of Dots (striped tral fixation cross was presented on the computer screen (25cm x 33 cm). Only or solid) were used. Striped Dots contained vertical black and white stripes. one stimulus was presented per trial and participants were positioned approxi- while solid Dots were a uniform gray color. These Dots were equated for visual mately 50cm from the screen. characteristics such as size and luminance. For half of the participants a striped Participants completed a set of four related tests designed to manipulate dot indicated they should make a response on the same side as the dot while demands on working memory and inhibitor)• control (see Fig. I ). For adults and a gray dot indicated they should respond on the side opposite the dot. These older children (>7 years). stimulus presentation time was 750ms. For younger rules were reversed for the other half of the participants. An initial block of 20 children (4-6 years). stimulus presentation time was 2500ms. In all cases the Congruent trials (with all responses on the same side as the dot) was followed interstimulus interval was 500 ms. resulting in total trial durations of 1250 and by a block of 20 Incongruent trials (with all responses on the side opposite the 3000 ms. respectively. An additional group of 6-year-oldchildren was tested with dot), and then by a Mixed block of 20 trials where Congruent and opposite the short (adult) presentation time (750ms) to study the effects of presentation trials were randomly intermixed. Instructions and practice were given before time at this intermediate age. the Congruent and Incongruent blocks. Instructions alone were given before the Each task began with condition-specific instructions and a short practice Mixed block. e.g.. "Remember. gray same side: striped opposite: Memory is block consisting of four or six trials. Different numbers of trials were used to required on all trials of the Dots test to remember the rules (respond on the same allow presentation of all relevant trial types within each practice block. Partic- or opposite side as the dot I. Inhibition is required on Incongruent trials to inhibit ipants could repeat the practice trials if needed to demonstrate learning of the the prepotent response to respond on the same side as the visual stimulus. This requirements for a given task. Most children learned the task requirements with task is similar to one used by Shaffer (1965) though there each subject received one practice block and no participant needed more than two practice blocks. only one type of trial block (Congruent. Incongruent. or Mixed) and therefore The criterion for demonstrating learning was 75-80% correct on the practice subjects did not have the benefit of testing with the two easier trial blocks before trials and to be able to verbally tell the experimenter the rules. Testing blocks receiving the Mixed block. The Dots task is also similar to a task used by Vu and contained 20 trials and each participant completed 1 block for each condition Proctor (2004) but the rules for their single-task blocks did not refer to stimulus of each task. except for the 2 conditions of the Abstract Shapes task. each of appearance and so the memory demand in their Mixed condition might have which contained 2 blocks (with a shoo break in between) for a total of 40 trials been greater than in ours. for each condition. The set of tests was administered with Arrows first. then Dots. Abstract Shapes (two then six shapes). and finally Pictures. A subset of 3.3.4. Abstract Shapes participants were tested with Arrows presented last and Pictures presented first In the Abstract Shapes test. unlike all other tests.each stimulus was presented to check for order effects. but this did not affect performance. so results for both in the center of the rectangle. Participants were taught a rule for each stimulus orders of presentation are collapsed together in the results reported here. ("for this one press the left button": "for this one press right") during short prac- tice blocks before each testing condition. There were two conditions involving 3.3. Procedures specifie le individual tests two- or six-Abstract-Shapes. Participants first completed the two-shapes condi- tion (2 blocks of 20 trials) and were then taught 4 additional rules. for a total 3.3.1. Pictures of 6 shapes. and were then tested on another two blocks of 20 trials. The six- This test is a classic Simon task. Here, a color picture of either a frog or Abstract-Shapes condition taxes memory heavily (participants must hold six butterfly was presented on the left or right side of the computer screen(see Fig. I). rules in mind). but it requires little or no inhibition (as the stimuli appear at the Each stimulus had an associated right or left response. The exact instructions center of the screen and do not preferentially activate the right or left hand). given participants were: "If you sec a butterfly, press the button on the left. whether the butterfly appears on the left or right: if you see a frog. press the 4. Results: general comments button on to the right. whether the frog appears on the left of right:' Small versions of the stimuli were attached next to the correct buttons on the response box to minimize the need to remember which stimulus was associated with which The three dependent measures were percentage of correct button. The stimuli were presented randomly on the left or right of the screen responses (accuracy), speed (reaction time MTH, and percent- over the block of 20 trials, yielding Congruent (compatible) and Incongruent age of anticipatory responses (AR). Linear regressions were used (incompatible) trials. for all analyses involving age and each subject's exact age was entered, not simply the person's age grouping. Within-subject 3.3.2. Arrows ANOVAs were used for analyses comparing tasks, conditions Here. a single large arrow was presented at the left or right of the computer screen. The arrow pointed either straight down (toward the response button on within task, or trial types. All binary comparisons included the same side as the arrow) or toward the opposite side at a 45' angle (toward the Tukey corrections for multiple comparisons. Whenever the vari- response button on the opposite side: see Fig. 0.0n Congruent trials. the arrow ance structure didnot conform to the requirements for parametric pointed straight down and participants were to respond on the same side as the analyses, logarithmic or arc sine transformations of the data were arrow. On Incongruent trials. the arrow pointed diagonally toward the opposite used to obtain the required conformity. All tables and figures side and participants were to respond on the side opposite the arrow. The precise instructions participants were told were. "1want you to push the button the arrow present the raw, untransfonned data. is pointing toward. If the arrow is on the side of the box pointing down like this A response time faster than 200 ms was considered antic- IE demonstrated] to this button. press this button.If the arrow is on the other side ipatory (too fast to be in response to the stimulus). Those EFTA01098882 2012 MC. Davidson et at /Neumpsychologia 44 (2006)2037-2078 CONGRUENT TRIALS INCONGRUENT TRIALS DOTS TEST: A SPATIAL INCOMPATIBILITY TASK with ARBITRARY STIMULI ABSTRACT SHAPES TEST: • A MEMORY LOAD TASK Press Left Press Right • Press Left Press Right Press Left ARROWS TEST: A SPATIAL INCOMPATIBILITY TASK Press Right with ICONIC STIMULI Press Right Press -elf Press Left 4] Press Right Press Right Press Right PICTURES TEST: A SPATIAL INCOMPATIBILITY TASK that is a CLASSICAL SIMON TASK Press Left 4 e Press Left Press Right Press Left 4 Press Rignt Press Left INHIBITORY CONTROL DEMAND MEMORY LOAD Low Medium High Low Dots-Congruent Dots-Incongruent. Arrows Pictures Medium 2-Abstract-Shapes Dots-Mixed These 2 cells are logically possible. e.g . 6-Abstract Side (a High 6-Abstract-Shapes 'Simon" task with 3 stimuli per response button) would be High Memory! Medium Inhib. However such tasks are too difficult Fig. I. Illustration of the tasks in our battery with a table summarizing the demands of each on memory and inhibition. EFTA01098883  M.C. Davidson et at. /Neuroptychologia 44 (2006)2037-2078 2043 responses were excluded from analyses of accuracy or speed, accuracy (RT: F(1,88)=4.58, p < 0.04; anticipatory responses: but were included in analyses of anticipatory responses (ARs). F(1,88) = 6.07, p <0.02). ARs occurred when a participant was either too eager and failed to wait for the stimulus on the current trial or failed to 5.2. Arrows release the button following the previous trial. These anticipa- tory responses indicate inhibitory failures and are reported as a The Arrows test was designed to require inhibitory control percentage of all possible responses where appropriate. A trial when a response was required on the side opposite the stimulus was considered correct if: (a) the first response following a stim- but to require little or no working memory as the stimuli them• ulus was correct and (b) RT was >200 ms following stimulus selves point to the correct response button. Performance was onset. better as a function of age, with increased accuracy, increased The percentage of correct responses was calculated by divid- speed, and reduced anticipatory responses (Table 2). This was ing the number of correct responses by the sum of correct highly significant for accuracy and anticipatory responses when plus incorrect responses. Anticipatory responses were excluded all ages were included in the analyses but not significant for from that calculation. The median RI' for correct responses speed of responding (accuracy: F(1,312)=57.06; p<0.0001; only was calculated for each participant. The median value, AR: F(1,312) = 35.73, p <0.0001). When the youngest children, rather than the mean value, was used to reduce the effect of tested with a long presentation time, were removed from the outlying RI's. analyses, the age-related improvements in speed, as well as accu- The youngest children received a slower version of our tasks racy and reduced incidence of anticipatory responses, were sig- than the rest of the children and adults. The stimuli were pre- nificant at p <0.0001 (F(1,222) = 76.88 [%correct]; 36.07 MTh sented to the 4- and 5-year-olds and one group of 6-year-olds for 38.56 [AM). The youngest children (4-6 years of age) showed much longer than they were presented to the rest of the children a steady reduction in anticipatory responses, and 6-year-olds and adults (trial durations of 3000 and 1250 ms, respectively). responded correctly significantly more often than children of 4 Analyses over all ages might exaggerate RT differences over or 5 years, but there was no difference over the age range of 4-6 age (since children given longer to respond will naturally take years in response speed (accuracy: F( 1,88) = 10.69; p <0.005; longer) and might underestimate accuracy differences (since AR: F(I,88) = 6.5, p <0.02). children given longer to respond are likely to make fewer errors). Hence, analyses of age differences are reported separately for 5.3. Dots the youngest children tested with a presentation time of 2500 ms and for all other participants tested with a presentation time of In the Dots test there were three conditions (Congru- 750 ms.