Event-based prospective memory across the lifespan: Do all age groups benefit from salient prospective memory cues?

Cognitive Development 39 (2016) 103–112

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Cognitive Development

Event-based prospective memory across the lifespan: Do all age groups benefit from salient prospective memory cues? Anett Kretschmer-Trendowicz a,∗ , Mareike Altgassen a,b a b

Department of Psychology, Technische Universität Dresden, Germany Donders Institute for Brain, Cognition and Behaviour, Radboud University Nijmegen, The Netherlands

a r t i c l e

i n f o

Article history: Received 18 February 2015 Received in revised form 11 April 2016 Accepted 19 April 2016 Keywords: Prospective memory Lifespan development Perceptual saliency Cognitive control

a b s t r a c t The present study investigated effects of cognitive control demands on prospective memory (PM) performance across the lifespan. Four different age groups (children, adolescents, young adults, old adults) worked on a computer-based picture categorization task as ongoing activity, while PM cue salience was varied within-subjects. Results revealed significant main effects of age group and salience. The children group was outperformed by all other age groups, while those groups’ PM performance did not differ significantly. Except for old adults, all age groups benefited from the presentation of salient PM cues. Further, age group and salience interacted significantly, indicating that the children group benefited most from the presentation of salient PM cues, while surprisingly the oldest group showed better results when PM cues were low-salient. Thus, results suggest that cognitive control demands differentially impact children’s and old adults’ PM and that different mechanisms seem to underlie PM development at both ends of the lifespan. © 2016 Elsevier Inc. All rights reserved.

1. Introduction Remembering to pass by the dry cleaning to pick up a dress on the way home or to attend a meeting in the afternoon are typical examples of everyday prospective memory (PM) tasks. In contrast to retrospective memory, which describes the memory for past events, PM represents the memory for future intentions and is defined as the ability to initiate and implement an intended action at an appropriate future time-point (time-based PM) or when a certain event is presented (event-based PM; e.g., Brandimonte, Einstein, & McDaniel, 1996). PM is crucial to develop independence across childhood and adolescence, and is essential to maintain an independent life in old age (e.g., Kliegel, Jäger, Altgassen, & Shum, 2008a; Kvavilashvili, Kyle, & Messer, 2008). Various studies investigated factors that influence successful prospective remembering and found cognitive control functions to be important correlates (e.g., Kliegel, Martin, McDaniel, & Einstein, 2002; Marsh & Hicks, 1998). Cognitive control refers to the ability of flexibly adapting one’s own behavior to current task demands or internal goals (e.g., Botvinick, Braver, Barch, Carter, & Cohen, 2001). Typical examples of cognitive control functions are inhibition, updating and task switching (e.g., Miyake et al., 2000). Relations between cognitive control functions and PM have been found in a large number of correlative studies in different age groups (children: e.g., Atance & Jackson, 2009; Shum, Cross, Ford, & Ownsworth, 2008; adolescents: e.g., Ward, Shum, McKinlay, Baker-Tweney, & Wallace, 2005; older adults: e.g., Schnitzspahn, Stahl, Zeintl, Kaller, & Kliegel, 2013). For instance, Shum et al. (2008) found working memory,

∗ Corresponding author at: Department of Psychology, Technische Universität Dresden, Zellescher Weg 17, D-01062 Dresden, Germany. E-mail address: [email protected] (A. Kretschmer-Trendowicz). http://dx.doi.org/10.1016/j.cogdev.2016.04.005 0885-2014/© 2016 Elsevier Inc. All rights reserved.

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inhibition, switching and verbal fluency to significantly predict PM in children. Ford, Driscoll, Shum, and Macaulay (2012) reported inhibition, but not working memory to significantly impact PM in children aged 4–6 years, whereas Mahy and Moses (2011) found the reversed pattern in a sample of the same age groups. Also studies focusing on the other end of the lifespan found cognitive control functions to correlate with PM performance and to serve as significant predictors in regression analyses. For instance, Schnitzspahn et al. (2013) reported inhibition and switching, but not updating/working memory to be significant predictors of PM in older adults. Thus, while there is ample evidence that cognitive control functions are needed for prospective remembering, the extent to which specific functions are involved may depend on the respective task demands and the cognitive characteristics of the target population (Kliegel, Altgassen, Hering, & Rose, 2011). 1.1. Framework to address influences of cognitive control on PM An influential theoretical model that systematically describes the role of cognitive control resources (and cognitive control demands) for event-based PM performance is the multiprocess framework by McDaniel and Einstein (2000). According to this model, the involvement of cognitive control functions in event-based prospective remembering depends on various factors such as characteristics of the PM and the ongoing task (e.g., focality of PM cues, difficulty of the ongoing task), the quality of intention formation (e.g., planning) and personal variables (e.g., personality traits, reduced cognitive resources). Thus, PM tasks can be initiated rather automatically (e.g., when PM cues are focal to the ongoing task and PM cue features are automatically processed while working on the ongoing task) or retrieval of the intended action may depend more on resource-demanding cognitive control functions (e.g., when non-focal PM cues are presented and processing of PM cue features is not involved in the ongoing task; here more monitoring for the PM cue is needed). Another factor that impacts PM performance is the salience of the PM cue relative to items of the ongoing task (McDaniel & Einstein, 2000). In previous PM studies salience has mostly been manipulated in terms of perceptual distinctiveness of the cue (e.g., Cohen, West, & Craik, 2001; Einstein, McDaniel, Manzi, Cochran, & Baker, 2000). According to the multiprocess framework highly salient PM cues require less cognitive control resources to be detected, as the delayed intention “pops into mind” due to the PM cue being distinct and standing out from ongoing task items. In contrast, low-salient PM cues blend in with ongoing task items and require more monitoring to be detected. 1.2. PM development and influences of cognitive control across the lifespan Previous research tested the predictions of the multiprocess framework in various age groups. However, in contrast to the number of studies employing correlational designs, only few studies experimentally varied cognitive control demands of PM tasks. This was mainly done in older adults (e.g., D’Ydewalle, Bouckaert, & Brunfaut, 2001; Kidder, Park, Hertzog, & Morrell, 1997; Martin & Schumann-Hengsteler, 2001), while research in younger age groups only recently started to systematically manipulate the extent to which cognitive control resources are needed for PM task performance (preschoolers: Mahy, Moses, & Kliegel, 2014b; school-aged children: Kliegel et al., 2013; adolescents: Wang et al., 2011; Ward et al., 2005). Even though the vast majority of studies point to an increase of PM across childhood (e.g., Guajardo & Best, 2000; Kliegel et al., 2013; Kvavilashvili, Messer, & Ebdon, 2001; Mahy & Moses, 2011; Shum et al., 2008; Wang, Kliegel, Liu, & Yang, 2008; Yang, Chan, & Shum, 2011; for a review see Mahy, Moses, & Kliegel, 2014a) until adolescence (e.g., Ward et al., 2005), the specific pattern of results seems to depend on certain task characteristics. For instance, Kliegel et al. (2013) compared 6and 7-year-old with 9- and 10-year-old children and found ongoing task absorption, PM cue salience and the location of the PM cue (i.e., whether the PM cue appeared in the focus of attention or not) to affect age differences. In both age groups PM performance was found to be improved when the PM task was embedded in a less absorbing ongoing task and when PM cues were presented perceptually salient compared to ongoing task items. Importantly, when varying the location of the PM cue, age differences only appeared when the cue was presented outside of the center of attention. The authors explained this pattern with higher cognitive control resources (e.g., monitoring for the cue) needed to detect the PM cue in the latter condition. Ward et al. (2005) manipulated stimulus presentation times of ongoing task items, and with this varied the extent to which cognitive resources were available to perform the PM task. In the high-demanding condition stimuli were presented for 600 ms, in the low-demanding condition for 850 ms. Age differences in PM performance between children (7- to 10-year-olds), adolescents (13- to 16-year-olds) and young adults (18- to 21-year-olds) were more pronounced in the highly demanding condition. In general, studies point to an increase of event-based PM across childhood, but also show inconsistencies in this development, which might be due to differences in cognitive control demands of the specific PM tasks being used. In line with predictions of the multiprocess framework, age differences seem to be more pronounced in tasks requiring more cognitive control resources for successful prospective remembering as compared to tasks with low cognitive control requirements. These findings are in line with ample empirical evidence showing an increase of cognitive control functions across childhood (e.g., Huizinga, Dolan, & van der Molen, 2006; Lehto, Juujärvi, Kooistra, & Pulkkinen, 2003). Continuing in development, research shows that PM seems to increase throughout adolescence to young adulthood. Wang, Kliegel, Yang, and Liu (2006) compared 13- with 22-year-olds in their event-based PM performance and found young adults to perform significantly better than adolescents. Consistently, Altgassen, Vetter, Phillips, Akgün, and Kliegel (2014) reported significant age effects in PM when comparing adolescents with adults, and found switching to significantly predict adolescents’ PM performance. However, not all studies found this pattern of increasing PM across adolescence. For instance, Ward et al. (2005) only found children to differ from adolescents and young adults, while there were no differences between

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the adolescent and the young adult group (for another study reporting no significant age differences between adolescents and young adults in event-based PM, see Zimmermann & Meier, 2006). Wang et al. (2011) only reported age differences between adolescents and adults when PM cues were presented non-focally and not when they were presented in the focus of the ongoing task. Thus, taken together in line with the multiprocess view and evidence of an ongoing development of cognitive control resources across adolescence (e.g., Luciana, Conklin, Hooper, & Yarger, 2005), the appearance of PM age differences between adolescents and young adults seems to depend on the cognitive control demands of the specific PM task. Focusing on PM research in old adults, studies have more consistently found age-related impairments in time-based as compared to event-based PM tasks (e.g., Jäger & Kliegel, 2008; Park, Hertzog, Kidder, Morrell, & Mayhorn, 1997) and explained them with higher demands on cognitive control resources in time- as compared to event-based tasks (e.g., Bastin & Meulemans, 2002). Results on event-based PM performance are mixed (studies reporting age-related declines in PM: e.g., Bisiacchi, Tarantino, & Ciccola, 2008; Maylor, 1998; studies reporting spared event-based PM in old adults: e.g., Einstein & McDaniel, 1990; Jäger & Kliegel, 2008; Reese & Cherry, 2002). Interestingly, in their meta-analysis, Henry, MacLeod, Phillips, and Crawford (2004) showed that age-related declines in event-based PM in old adults are mainly evident in PM tasks that strongly rely on cognitive control processes such as inhibition, updating and switching; all functions that are known to decline in old age (for a study reporting age-related declines in these functions and relating them to PM see Schnitzspahn et al., 2013). Consistently, previous studies reported beneficial effects of presenting highly salient PM cues on old adults’ PM performance (e.g., Cohen, Dixon, Lindsay, & Masson, 2003, Exp. 2; Einstein et al., 2000, Exp. 1) and thus pointed to the boosting effect of reduced cognitive control demands on old adults’ ability to initiate delayed intentions. 1.3. The current study Taken together, previous research on different age groups indicates that cognitive control resources influence PM performance. However, whether this influence is similar across the lifespan when one and the same paradigm is applied to a lifespan sample remains unknown. In general, studies on PM development targeting lifespan samples are scarce. The few existing studies indicate that PM develops in an inverted U-shaped function across the lifespan (Kliegel, Mackinlay, & Jäger, 2008c; Mattli, Schnitzspahn, Studerus-Germann, Brehmer, & Zöllig, 2014; Zöllig et al., 2007; Zimmermann & Meier, 2006, 2010). An increase of PM from childhood to young adulthood is followed by a decrease in old age. For instance, Kliegel et al. (2008c) applied a complex PM task to two groups of children (7- and 10-year-olds), a group of younger adults (about 25 years old) and a group of old adults (about 67 years old). The authors found a PM increase until adulthood and a decline from younger to old adulthood (for similar developmental patterns in event-based PM tasks see Zimmermann & Meier, 2006, 2010; Zöllig et al., 2007). Moreover, Kliegel et al. (2008c) showed that the inverted U-shaped pattern was more pronounced in a condition where individuals had to actively interrupt the ongoing task to execute the PM task compared to a no interruption condition. The authors concluded that inhibitory control might be one factor underlying PM development from childhood to old age. However so far, no study investigated the influence of cognitive control demands on PM in a lifespan sample by manipulating PM cue characteristics while simultaneously using the same paradigm for all age groups. This approach would allow (1) to directly compare PM performance in different age groups independent of task-related differences and (2) to test for possible differential effects of varying cognitive control demands on PM across different age groups, which may help clarify whether similar mechanisms underlie the rise and fall of PM across the lifespan. The present study set out to test the effects of varying cognitive control demands on PM performance in a lifespan sample by experimentally manipulating PM cue salience. As indicated above, following the multiprocess framework perceptually salient PM cues are assumed to reduce the need for active monitoring due to them “popping out” and capturing attention more automatically (McDaniel & Einstein, 2000). This should reduce the need for cognitive control resources to detect the PM cue and to shift from the ongoing to the PM task. Studies on both ends of the lifespan point to beneficial effects of PM cue salience (preschoolers: Mahy et al., 2014b; school children: Kliegel et al., 2013; old adults: e.g., Cohen et al., 2003, Exp. 2). However, so far no study has targeted the influence of PM cue salience in adolescence, a group where prospective remembering is especially important as it is necessary to develop independence and to successfully perform in school and build social relations. Furthermore, nothing is known about possible differential effects of salience manipulations across the lifespan. As for our predictions, we expected to replicate the inverted U-shaped pattern of PM development with increasing PM performance from child- to adulthood and a decline from young adulthood to old age. Consistent with predictions of the multiprocess framework, we hypothesized generally better PM performance when PM cues are presented highly salient compared to a non-salient task condition. Moreover, we expected to find a significant interaction between age and PM cue salience, indicating that children, adolescents and old adults benefit most from the presentation of salient PM cues due to their still developing or already decreasing cognitive control resources. If increasing the salience of PM cues would effectively improve PM performance, this finding may have important implications for the design of delayed intentions in the home, school or work environment of children, adolescents and (old) adults. For instance, perceptually highlighting PM cues as compared to stimuli of the ongoing task could be employed as a strategy for remembering important everyday prospective tasks.

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Table 1 Sample characteristics.

N Age range in years Age M(SD) in years Gender Verbal abilities M(SD)

Children

Adolescents

Young adults

Old adults

20 5 5.00 (−) 10 F, 10 M –

20 12–15 13.60 (1.05) 13 F, 7 M 12.30 (2.08)

20 21 − 25 22.60 (1.19) 7 F, 13 M 11.90 (2.07)

20 55 − 74 64.60 (5.75) 9 F, 11 M 12.65 (2.52)

Note: F = female, M = male. Because the Wechsler Intelligence Scale for Children (Petermann & Petermann, 2008) does not provide norms for children younger than 6 years, no age-normalized verbal abilities scores could be calculated for the group of 5-year-olds.

2. Method 2.1. Participants Overall, 80 participants divided into four age groups were included in this study (for details see Table 1). Children and adolescents were recruited through schools and child care centers, young adults through educational institutions and old adults through retirement homes. All participants spoke German as their first language, showed no severe health problems or psychiatric conditions and no memory deficits. Age groups were parallel for age-normalized scores of verbal abilities (F(2,57) = 0.56, p = 0.57) as measured by the German version of the Wechsler Intelligence Scale for Children (WISC-IV, Petermann & Petermann, 2008) resp. the Wechsler Adult Intelligence Scale (WAIS-III, Von Aster, Neubauer, & Horn, 2006) and for gender (X2 (3) = 3.75, p = 0.29; see also Table 1). 2.2. Materials and procedure The PM task was adopted from a previous study (Altgassen, Kliegel, Rendell, Henry, & Zöllig, 2008) and modified to present pictures instead of words (see Altgassen, Ariese, Wester, & Kessels, 2015 for a similar approach). The ongoing task consisted of a computer-based picture categorization task. For each trial, two pictures were simultaneously presented on the screen and individuals had to indicate via button press, if both pictures belonged to the same category (i.e., animals, food, instruments, locomotive objects or body parts) or not. Pictures were presented for 3 s or until a response was made. If no response was made during this time period, the picture pair disappeared and the next one was presented. Pictures were black and white line drawings of familiar and easy-to-name objects selected randomly from the Snodgrass and Vanderwart (1980) picture system. To adapt ongoing task difficulty to the children group, the maximal picture presentation time for this age group was extended to 6 s. Adapting ongoing task difficulty is an appropriate method to isolate age effects in PM (e.g., Einstein, Smith, McDaniel, & Shaw, 1997; Kvavilashvili et al., 2008). The PM task was to press a predefined key whenever one of the specific PM targets (e.g., a crown) was presented. Cognitive control load of the prospective task was varied within participants (low- vs. high-salient cues). For the low salience condition, participants were asked to press the pink key whenever one of four PM cues (belt, sea horse, vase, crown) was presented on the screen. The target pictures were presented in the same format as the ongoing task items. For the high salience condition four different PM cues were used and participants had to press the pink key whenever a picture of a jacket, a sock, a bug or a fork was presented. Target pictures were surrounded by a red frame (opposed to black-framed ongoing task items). Using a colored frame to manipulate PM cue salience has already been successfully applied in previous studies (Hicks, Cook, & Marsh, 2005; Mahy et al., 2014b). Order of task blocks was counterbalanced across participants. The high-salient task block consisted of 65 ongoing task items (37 showed two pictures of different categories, 28 pictures of the same categories) and four PM cues, the low-salient task block comprised 66 ongoing task items (37 showed two pictures of different categories, 29 pictures of the same categories) and four PM cues. Dependent measures were proportions of PM hits (PM accuracy), proportions of correct ongoing task responses (ongoing task accuracy) as well as reaction times of correct PM and correct ongoing task responses (in ms). After explaining the general procedure of the task, the ongoing task was instructed. An ongoing task practice block was followed by a single ongoing task block (consisting of 20 trials with 12 items showing two pictures of the same category and 8 displaying two pictures of different categories) to assess baseline performance. Thereafter the (high- or low-salient) PM task was introduced and a filled delay of about 5 min with the vocabulary test (first half) followed. After working on the PM test block, participants had a short break. Hereafter the second PM task block was instructed followed by another filled delay of approximately 5 min with the vocabulary test (second half). After finishing both PM blocks individuals were asked to describe what they had to do during the computer tasks (i.e., ongoing task and PM task). Thereafter, participants were asked to recall all PM cues. If they were not able to recall all 8 cues, a recognition test followed, including the PM cues and distractor items. Participants were tested individually. Overall, testing took about one hour. Only individuals who had given written informed consent were allowed to participate. For children and adolescents, parents had to sign the consent form additionally. The study was conducted in accord with the declaration of Helsinki and was approved by the local ethics committee.

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Table 2 Mean proportions of PM and ongoing task hits. PM task

Children Adolescents Young adults Old adults

Ongoing task

Low-salient M(SD)

High-salient M(SD)

Baseline M(SD)

Low-salient M(SD)

High-salient M(SD)

0.31 (0.38) 0.80 (0.21) 0.84 (0.19) 0.85 (0.32)

0.56 (0.43) 0.89 (0.24) 0.95 (0.13) 0.73 (0.36)

0.82 (0.12) 0.94 (0.05) 0.96 (0.05) 0.90 (0.12)

0.80 (0.16) 0.93 (0.04) 0.96 (0.02) 0.91 (0.10)

0.83 (0.15) 0.95 (0.03) 0.95 (0.04) 0.92 (0.09)

Table 3 Outlier-corrected PM and ongoing task reaction times. PM task

Children Adolescents Young adults Old adults

Ongoing task

Low-salient M(SD)

High-salient M(SD)

Baseline M(SD)

Low-salient M(SD)

High-salient M(SD)

2592.32 (425.34) 1140.73 (206.34) 1182.69 (296.18) 1426.00 (227.37)

2665.94 (951.07) 1099.52 (341.79) 1171.64 (429.34) 1345.56 (246.98)

2426.67 (539.08) 862.49 (97.03) 838.99 (123.26) 1321.52 (217.99)

2463.35 (480.27) 1170.71 (156.43) 1221.24 (215.26) 1496.61 (205.82)

2271.03 (528.72) 1099.56 (141.91) 1141.34 (174.15) 1464.53 (170.67)

Note: Reaction times are displayed in ms. Stimulus presentation times for children were longer (6 s) compared to the other age groups (3 s). Reaction times were corrected for outliers using boxplot analyses within each age group. For PM reaction times in the low-salient task condition two outliers were excluded from the children group, one from the adolescent and one from old adults group. There were no outliers in the group of young adults. For PM reaction times in the high-salient task condition one outlier was excluded from the group of old adults. Regarding ongoing task reaction times, in the baseline condition two outliers were excluded from the group of adolescents, while there were no outliers within the other age groups. For ongoing task reaction times in the low-salient condition two outliers were excluded from both the group of children and adolescents and one from the group of old adults. In the high-salient task condition respectively one outlier was excluded from the children and the adolescent group and three from the group of old adults.

3. Results Table 2 provides an overview over PM and ongoing task hits.

3.1. PM performance A mixed measures ANOVA with the between-subject factor age group and the within-subject factor PM cue salience was applied to investigate the effects of age group and PM cue salience on PM accuracy as well as their interactions. Results revealed significant main effects for age (F(3,76) = 11.89, p = 0.00, ␩2 p = 0.32) and salience (F(1,76) = 7.78, p = 0.01, ␩2 p = 0.09). Planned post hoc tests showed that the children group differed significantly from the other three age groups in their PM accuracy (ps < 0.01), whereas those three age groups did not differ significantly (all ps = 1). In addition to the two significant main effects, a significant interaction between the two variables was found (F(3,76) = 7.08, p = 0.00, ␩2 p = 0.22). With the exception of the oldest age group, all age groups performed better when high- as compared to low-salient PM cues were presented (see Table 2). Paired-samples t-tests showed that the children group (t(19) = 2.94, p = 0.01) and the young adult sample (t(19) = 3.33, p = 0.00) performed significantly better in the high- compared to the low-salient condition, whereas old adults showed the reverse pattern with higher PM accuracy in the low-salient condition (t(19) = −2.52, p = 0.02). In the adolescent group accuracy did not differ significantly between both conditions (t(19) = 1.68, p = 0.11). A second mixed measures ANOVA with the between-subject factor age group and the within-subject factor PM cue salience was used to examine the effects of age group and PM cue salience on PM reaction times as well as their interactions.1 Before conducting the ANOVA, reaction time measures were corrected for outliers using boxplot analyses for each age group. A significant main effect was revealed for age (F(2,50) = 4.01, p = 0.02, ␩2 p = 0.14), but not for salience or the interaction between age group and salience (both Fs < 0.38; for descriptive details see Table 3). Post hoc comparisons indicated significantly faster reaction times in the adolescent compared to the old adult group (p = 0.03), but no reaction time differences between the other age groups (all ps > 0.09). In addition to between group comparisons, reaction times for the two salience conditions were also analyzed within age groups using t-tests for dependent samples. For all age groups, results revealed no significant PM reaction time differences between the two task conditions (ts < 2.17, ps > 0.08).

1 Note that reaction times of the children group were not included due to extended stimulus presentation times as compared to the other three age groups.

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Table 4 Mean number of recalled and recognized PM cues. Low salience

Children Adolescents Young adults Old adults

High salience

Recall M(SD)

Recognition M(SD)

Recall M(SD)

Recognition M(SD)

2.15 (1.46) 3.75 (0.55) 3.55 (0.69) 2.85 (1.53)

3.24 (1.25) 4.00 (0.00) 4.00 (0.00) 3.75 (1.00)

2.30 (1.49) 3.60 (0.68) 3.05 (1.15) 2.50 (1.70)

3.24 (1.20) 3.88 (0.35) 4.00 (0.00) 3.56 (1.09)

Note: Mean number of recognized PM cues only includes numbers of those individuals who failed to recall all PM cues (children: N = 17, adolescents: N = 8, young adults: N = 17, old adults: N = 16).

3.2. Ongoing task performance To address possible group effects in ongoing task accuracy a mixed measures ANOVA with ongoing task block (baseline vs. dual task low salience vs. dual task high salience) as within subject factor was conducted. Significant age group differences were revealed (F(3,76) = 14.57, p = 0.00, ␩2 p = 0.37), whereas the main effect for ongoing task block (F(2,152) = 1.16, p = 0.32) as well as the interaction between age group and ongoing task block (F < 1) were not significant. Planned post hoc comparisons revealed that only the children group was significantly outperformed by the other three age groups (p < 0.01), while these groups did not show any significant differences in ongoing task accuracy (ps > 0.19; for descriptive details see Table 2).2 After outlier correction using boxplot analyses, the mixed measures ANOVA for ongoing task reaction times revealed significant main effects for age group (F(2,49) = 48.48, p = 0.00, ␩2 p = 0.66) and ongoing task block (F(2,98) = 61.74, p = 0.00, ␩2 p = 0.58) as well as a significant interaction between both variables (F(4,98) = 3.56, p = 0.01, ␩2 p = 0.13; for descriptive details see Table 3).1 Post hoc comparisons revealed significantly faster reaction times in adolescents and young adults compared to old adults (ps = 0.00), but no reaction time differences between the adolescent and the young adult group (p = 1). For ongoing task blocks results showed significant reaction time differences between all three blocks with overall fastest reaction times in the baseline and slowest reaction times in the low-salient task block (ps < 0.008; see also Table 3). Within group comparisons for the children group revealed neither significant reaction time differences between baseline and the dual task conditions nor between the two salience conditions (ts < 1.2, ps > 0.28). Adolescents responded significantly faster in the baseline as compared to the low- or high-salient task condition (baseline vs. low-salient: t(16) = −9.93, p = 0.00; baseline vs. high-salient: t(17) = −8.16, p = 0.00), while differences between the two salience conditions only approached significance (t(17) = 1.90, p = 0.08). Similarly, faster reaction times in the baseline compared to the low- and high-salient task conditions were found in young adults (baseline vs. low-salient: t(18) = −8.20, p = 0.00; baseline vs. high-salient: t(19) = −7.15, p = 0.00). The difference between the two salience conditions approached significance (t(18) = 2.08, p = 0.05). Old adults responded significantly faster in the baseline compared to the low-salient task condition (t(17) = −2.90, p = 0.01), while the difference between the baseline and the high-salient condition approached significance (t(16) = −2.10, p = 0.05) with a trend to faster reaction times in the baseline condition. The difference between the two salience conditions was not significant (t(15) = 0.90, p = 0.38). 3.3. Retrospective memory analysis Table 4 displays the number of recalled and recognized PM cues for each age group and task condition. A mixed measures analysis of recalled PM cues revealed a significant main effect of age (F(3,76) = 11.05, p = 0.001, ␩2 p = 0.30), but no main effect of salience condition (F(1,76) = 1.18, p = 0.28) and no significant interaction (F(3,76) = 0.52, p = 0.67). Post hoc comparisons revealed significant differences between children and adolescents (p = 0.00) as well as between the children and the young adult group (p = 0.00), indicating that adolescents and young adults recalled significantly more PM cues correctly than children. Moreover, adolescents recalled significantly more PM cues correctly than old adults (p = 0.00). Children and old adults (p = 0.63) as well as adolescents and young adults (p = 1) did not differ in their number of correctly recalled PM cues. The non-significant main effect of salience indicates that numbers of correctly recalled low- and high-salient PM cues did not differ. Analysis of recognized PM cues revealed a significant main effect of age (F(3,54) = 3.02, p = 0.04, ␩2 p = 0.14), but no main effect of salience condition (F(1,54) = 0.59, p = 0.45) and no significant interaction (F(3,54) = 0.25, p = 0.86). Post hoc analyses showed that only children and young adults differed significantly in the number of recognized PM cues (p = 0.04) with young adults recognizing more PM cues correctly than children, while all other age group differences were not significant (ps > 0.25).

2 To test whether age differences in ongoing task accuracy may impact PM results, baseline ongoing task accuracy was added as a co-variate to the mixed measures ANOVA. Results revealed a significant age effect (F(3,75) = 4.94, p = 0.00, ␩2 p = 0.17), whereas the main effect for salience was no longer significant (F(1,75) = 0.25, p = 0.62, ␩2 p = 0.00). However, the interaction between age group and salience was also still significant (F(3,75) = 7.23, p = 0.00, ␩2 p = 0.22). Post hoc analyses showed that only the children group differed significantly from all other age groups (p < 0.014), while those groups did not differ significantly in their PM accuracy (p = 1). Thus, except for the non-significant main effect for PM cue salience, results did not change when controlling for baseline ongoing task accuracy.

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Finally, we analysed PM performance while including only those individuals who recognized all PM cues correctly. There were significant main effects of age (F(1,54) = 9.24, p = 0.00, ␩2 p = 0.34) and salience (F(1,54) = 4.77, p = 0.03, ␩2 p = 0.08) as well as a significant interaction between both variables (F(3,54) = 4.00, p = 0.01, ␩2 p = 0.18). Thus, the pattern of results did not change when controlling for retrospective memory deficits for PM cues. 4. Discussion The present study was the first to investigate the influence of cognitive control demands on PM performance across a lifespan sample by manipulating PM cue characteristics. Until to date, several studies investigated effects of PM cue salience in various age groups, but none of them applied one and the same paradigm to samples of the entire lifespan and tested possible differential effects of cue salience. Furthermore, no study focussed on the critical period of adolescence when manipulating PM cue salience. Including different age groups of the entire lifespan and applying the same paradigm, allows us to test whether similar mechanisms underlie the rise and fall of PM performance across the lifespan independent of certain characteristics of the PM paradigm. The first hypothesis of the present study was to replicate the inverted U-shaped developmental pattern of PM with an increase from childhood to young adulthood followed by a decrease from young to old adulthood (e.g., Kliegel et al., 2008c; Zöllig et al., 2007). Results indicated indeed an increase of PM from childhood to adolescence, whereas from adolescence onwards PM performance seems to be relatively stable until old age. Similarly, PM reaction times did not differ between the adolescent and the young adult group and not between the young and the old adult group. The developmental increase from childhood to adolescence is in line with several children studies (e.g., Guajardo & Best, 2000; Kliegel et al., 2013; Mahy et al., 2014b; Shum et al., 2008). The missing PM increase from adolescence to adulthood contrasts with our hypothesis, but is consistent with studies reporting similar effects (Wang et al., 2011; Ward et al., 2005; Zimmermann & Meier, 2006). For instance, in the study of Wang et al. (2011) age differences between a young adolescent (11- to 14-year-olds) and a young adult group (17- to 21-year-olds) were only evident in a non-focal PM condition. In the present study, PM cues were presented focally. The focal character of the cues might have facilitated self-initiated retrieval processes and thus enhanced adolescents’ PM performance. Possibly, adolescents’ cognitive abilities are sufficiently developed to perform PM tasks with focal PM cues comparably to young adults. These findings support the assumption of the multiprocess framework that focality of the PM cue is a central factor to impact PM (McDaniel & Einstein, 2000). The latter is also supported by the missing age-related decline from young adulthood to old age (at least within the low-salient condition), which may indicate that despite old adults’ cognitive impairments, they succeed in performing focal PM tasks. The second hypothesis of this study was that overall individuals would show better PM performance when PM cues were perceptually salient compared to a non-salient condition following the reduced cognitive control demands of high-salient cues (McDaniel & Einstein, 2000). Consistent with this notion, there was a significant main effect of PM cue salience with regards to PM accuracy, which is in line with previous studies reporting salience to affect PM performance (e.g., Cohen et al., 2003, Exp. 2; Kliegel et al., 2013). Targeting our third hypothesis, namely that developing populations such as children, adolescents and old adults benefit most from the presentation of highly salient PM cues, results revealed a significant interaction between age group and salience. Post hoc analyses indicated that especially young children’s PM performance improved upon presentation of highsalient PM cues, which is consistent with two studies that targeted salience effects in similar age groups (Kliegel et al., 2013; Mahy et al., 2014b). Interestingly, this performance increase of young children was only reflected in PM accuracy, but not in their reaction times. Moreover, compared to the baseline condition, ongoing task accuracy and reaction times did not significantly deteriorate when the PM task was added to the ongoing task (an ongoing task performance decrease could have pointed to costs due to the added PM task). Thus, for young children, results indicate that highlighting PM cues directly influences PM accuracy, but does not affect PM reaction times or any parameters of the ongoing task. Even when providing PM cues of high salience, children’s performance did not improve to the level of adolescents, indicating that highlighting the PM cues did not fully compensate for reduced cognitive control resources that are, however, necessary to succeed in PM tasks. Importantly, the positive effects of presenting high-salient PM cues in children cannot be explained by differences in retrospective memory for PM cues across salience conditions, as no significant differences between correctly recalled highand low-salient PM cues were revealed. Taken together, on a conceptual level results indicate that high-salient PM cues may indeed capture children’s attention automatically (in line with predictions of the multiprocess framework, McDaniel & Einstein, 2000) and enhance PM accuracy while not affecting cognitive resources needed to perform the ongoing task. In contrast, children’s cognitive resources do not seem to be sufficiently developed to intentionally allocate (enough) attention to PM cues, which are not distinctive from ongoing task items, as indicated by worse PM but spared ongoing task performance in the low-salient task condition. Focussing on PM of the adolescent group shows that the PM accuracy level was already close to ceiling in the low-salient task condition. Thus, it is not surprising that the presentation of highly salient PM cues only slightly improved performance.3 As indicated above, presenting PM cues focally may enable adolescents to achieve adult levels of PM performance. Consis-

3 Importantly, even though PM accuracy is at a high level, it differs significantly from the maximum of four PM hits in the low- as well as the high-salient condition (low-salient: p = 0.00, high-salient: p = 0.046).

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tently, PM reaction times did not differ between the two salience conditions in the adolescent sample indicating that focally presented PM cues lead to fast reaction times which are not improved by an additional salience manipulation. Interestingly, when focussing on ongoing task reaction times, the differences between the two salience conditions approached significance, indicating that adolescents responded faster to ongoing task items when PM cues were presented highly salient as compared to the non-salient condition. While manipulating salience of the PM cues did not directly affect PM performance, in line with prediction of the multiprocess framework, it may have released resources and thus influenced parameters of the ongoing task. On a conceptual level, however, when comparing the two most prominent theories on event-based PM, results support the preparatory attentional and memory processes (PAM) theory of Smith (2003), and Smith and Bayen (2004), which assumes that all PM tasks need cognitive resources (at least to some extent) as opposed to the multiprocess view. In the present study, high-salient PM cues seemed to reduce the need for cognitive control in adolescents, but did not lead to an automatization of PM task execution as proposed by the multiprocess theory (McDaniel & Einstein, 2000); indicated by significant ongoing task reaction time differences between the baseline and not only the low-salient but also the high-salient dual task condition. Similarly, Smith, Hunt, McVay, and McConnell (2007) showed that not only low-salient but also high-salient PM cues lead to ongoing task costs. This was interpreted in terms of a need for cognitive resources to execute the PM task in both conditions which are in turn not available to work on the ongoing task. However, since research that explicitly tested different theoretical accounts on event-based PM in adolescents is still scarce, future studies need to address different PM theories under a developmental point of view covering not only older adults but also populations at the other end of the lifespan. One aspect limiting the interpretation of salience effects on PM performance in adolescents, is the already high performance in the low-salient PM condition. Thus, future studies should apply PM paradigms with higher ongoing task difficulty levels or should even manipulate ongoing task demands to test whether salience variations may show differential effects. Focussing on the group of old adults revealed a surprising result. Compared to the non-salient PM condition, old adults performed worse when PM cues of high salience were presented. This result contrasts with previous studies that consistently reported beneficial effects of salient PM cues in old adults and even a reduction of age-related PM differences (Cohen et al., 2003, Exp. 2; Einstein et al., 2000, Exp. 1; see e.g., Altgassen, Phillips, Henry, Rendell, & Kliegel, 2010 for a study on older adults manipulating PM cue saliency through differences in emotional valance). PM reaction times did not differ between the two salience conditions. Interestingly, even though highly salient PM cues led to fewer PM hits, they did not negatively affect any parameters of the ongoing task (neither accuracy nor reaction times). Moreover, results showed no significant difference between the numbers of correctly recalled/recognized high- and low-salient PM cues. Thus, the performance decline in the high-salient task condition cannot be explained by retrospective memory deficits. While in children presenting highly salient PM cues was found to enhance PM performance (see also Kliegel et al., 2013 for similar results), performance in old adults deteriorated. How can these age-related differences in salience effects be explained? The present study manipulated salience by adding a red border to the PM cues in the high-salient condition, whereas, all ongoing task items had a black border. Possibly, this change in colour was less noticeable for old adults. Exploring visual processing in old adults. Rubin, Roche, Prasada-Rao, and Fried (1994) reported a reduced contrast sensitivity in older adults (aged 65–90 years). Moreover, Park and Puglisi (1985) showed a decline of color memory in old age. Thus, even though the (specific depicted objects of the) PM cues of both salience conditions seem to have been encoded similarly well (as indicated by equal retrospective memory for cues of both conditions; see also Cohen et al., 2003 for a similar effect), old adults may have not been able to make use of the colored border of PM cues. However, if old adults would have not or only less well been able to perceive the red border, they should have still shown a similar performance across both salience conditions. Thus, neither difficulties in perceiving visual contrasts nor in color memory can fully account for the surprising decline of old adults’ PM when presenting highly salient cues. Another possibility is that the red border somehow irritated old adults, which should be reflected in increased reaction times in the high-salient condition. However, old adults’ PM reaction times did not significantly differ between both salience conditions. More research is needed to explore under which task conditions PM cue salience reduces cognitive control demands and benefits old adults’ PM. Considering old adults’ results from a conceptual point of view, findings indicate that in contrast to children and young adults, variations of PM cue salience do not automatically capture old adults’ attention and lead to an improvement in PM performance. Thus, mechanisms that underlie the decrease of PM performance in old age seem to differ from mechanisms that drive the increase of PM at the other end of the lifespan (see also Zöllig et al., (2007) for differences in neural correlates underlying PM development across the lifespan). Future studies should also include eye tracking and event-related potentials to better understand how salience manipulations affect (or do not) PM performance across different age groups. Taken together, we found a developmental increase in PM from childhood to adolescence but no further developmental changes until old age, which might be due to the focal presentation of PM cues that already seems to enhance adolescents’ and young adults’ but not young children’s PM. Moreover, findings of the present study showed that different age groups, especially at the two ends of the lifespan, were differently affected by saliency manipulations of the PM task when one and the same paradigm is applied. Children’s PM was enhanced by presenting high-salient PM cues, whereas old adults’ PM was impaired, indicating that both groups are sensitive to manipulations of cognitive control demands of PM tasks. To benefit old adults’ PM performance different manipulations might be needed that do not interfere with their intention to initiate the PM task.

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Acknowledgements This research was supported by the German Research Foundation (DFG grant SFB 940/1 2013). We thank Andrea Bünermann, Nick Grandjean, Jana Schröder and Kira Tönnes for their help with data collection and all our study participants.

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