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Test–retest consistencyof Virtual Week: A task toinvestigate prospective memoryGiovanna Mioniab, Peter G. Rendellc, Franca Stablumb,Luciano Gamberinib & Patrizia S. Bisiacchiba École de Psychologie, Université Laval, Quebec, QC,Canadab Department of General Psychology, University ofPadova, Padova, Italyc School of Psychology, Australian Catholic University,Melbourne, AustraliaPublished online: 28 Jul 2014.

To cite this article: Giovanna Mioni, Peter G. Rendell, Franca Stablum, LucianoGamberini & Patrizia S. Bisiacchi (2014): Test–retest consistency of Virtual Week: A taskto investigate prospective memory, Neuropsychological Rehabilitation: An InternationalJournal, DOI: 10.1080/09602011.2014.941295

To link to this article: http://dx.doi.org/10.1080/09602011.2014.941295

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Test–retest consistency of Virtual Week: A task to

investigate prospective memory

Giovanna Mioni1,2, Peter G. Rendell3, Franca Stablum2,Luciano Gamberini2, and Patrizia S. Bisiacchi2

1Ecole de Psychologie, Universite Laval, Quebec, QC, Canada2Department of General Psychology, University of Padova, Padova, Italy3School of Psychology, Australian Catholic University, Melbourne,

Australia

(Received 23 October 2013; accepted 2 July 2014)

The present study reports test–retest consistency of Virtual Week, a well-known measure of prospective memory (PM) performance. PM is thememory associated with carrying out actions at a specific moment in thefuture. Patients with neurological disorders as well as healthy older adultsoften report PM dysfunctions that affect their everyday living. In Experiment1, 19 younger and 20 older adults undertook the standard version of VirtualWeek (version A). Older adults showed lower performance compared toyounger participants. However, the discrepancy between groups was elimi-nated at retest. Experiment 2 was conducted to investigate if remembering ofPM content determined the improvement observed in older adults at retest inExperiment 1. To this end we created a parallel version (version B) in whichwe varied the content of the PM actions. Fifty older adults were assigned toone of the two experimental conditions: Version A at test and version B atretest or vice versa (25 participants in each condition). Results showed nogroup differences in PM performance between version A and version B; more-over, no effect of test–retest was found. The study confirmed that Virtual Week

Correspondence should be addressed to Giovanna Mioni, Ecole de Psychologie, Pavillon

Felix-Antoine-Savard, 2325, rue des Bibliotheques, Universite Laval, Quebec G1 V 0A6,

Canada. E-mail: mioni.giovanna@gmail.com

Peter Rendell’s contribution was supported by an Australian Research Council Discovery

Grant. The authors gratefully acknowledge all the participants who kindly participated in the

study and Chiara Seminati, Veronica Rossetti, Rosita Garbuio and Irene Scarpa who cooperated

with the present study. The authors also acknowledge the help of Trevor Daniels with program-

ming Virtual Week and the help of Kathryn Biernacki in analysing the data.

Neuropsychological Rehabilitation, 2014

http://dx.doi.org/10.1080/09602011.2014.941295

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is a reliable measure of PM performance and also provided a new parallelversion that can be useful in clinical setting.

Keywords: Prospective memory; Virtual Week; Test–retest; Ageing.

INTRODUCTION

Prospective memory (PM) is the memory associated with carrying outintended actions at a specific moment in the future (Ellis & Kvavilashvili,2000; Kliegel, McDaniel, & Einstein, 2008; McDaniel & Einstein, 2000). Itis a highly complex process that requires formulating plans and intentions,retaining the information, and then executing the planned intention at theappropriate future moment (Kliegel, McDaniel et al., 2008; McDaniel &Einstein, 2000). According to the Einstein and McDaniel’s model (1990),there are two types of PM targets called event-based and time-based. If thetarget is event-based PM, a person performs an action when a specificevent occurs (i.e., passing a message when your friend calls); while if thetarget is time-based PM, a person forms a self-generated intention toperform an action at a specific time in the future (i.e., remembering theappointment with a friend at 4:00 p.m.). Event-based PM tasks are consideredto be less cognitively demanding than time-based PM tasks because theyrequire less self-initiated retrieval with the event providing an intrinsic exter-nal cue to help recall the task to be performed (McDaniel & Einstein, 1993;McDaniel, Guynn, Glisky, & Routhieaux, 1999; McFarland & Glisky, 2009).PM relies on retrospective memory for learning and retaining the “content” oftasks to be remembered (i.e., “what”), but also involves executive functions(i.e., initiation, planning, monitoring, and inhibition of ongoing activities)(Groot, Wilson, Evans, & Watson, 2002; McDaniel et al., 1999).

Adequate PM abilities have functional and safety implications for manyactivities of everyday living such as remembering to take medication,turning up to a meeting at a specific time, or remembering to pass on aphone message. Patients as well as healthy older adults rated PM dysfunctionsas their most salient area of concern compared to other memory problems indaily activities. PM failures have the potential to limit the personal indepen-dence causing the necessity to rely on a carer for prompting (Fleming, Shum,Strong, & Lightbody, 2005).

Researchers have extensively investigated the effects of ageing on PM(Bisiacchi, Tarantino, & Ciccola, 2008; Cona, Arcara, Tarantino, & Bisiac-chi, 2012; Henry, MacLeod, Phillips, & Crawford, 2004; McDaniel, Einstein,& Rendell, 2008; Phillips, Henry, & Martin, 2008; Mioni & Stablum, 2014)and the impact of PM impairment on activities of daily living in various clini-cal populations such as traumatic brain injury patients (Mioni, Stablum,

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McClintock, & Cantagallo, 2012; Mioni, Rendell, Henry, Cantagallo, &Stablum, 2013; Shum, Levin, & Chan, 2011), people with Parkinson’sdisease (Foster, Rose, McDaniel, & Rendell, 2013; Katai, Maruyama, Hashi-moto, & Ikeda, 2003; Kliegel, Altgassen, Hering, & Rose, 2011), mild cogni-tive impairment and Alzheimer’s disease (Kixmiller, 2002; Thompson,Henry, Rendell, Withall, & Brodaty, 2010), and multiple sclerosis (Rendell,Jensen, & Henry, 2007; West, McNerney, & Krauss, 2007)1.

However, there have been limited researches into the assessment of PMimpairment, particularly in terms of the psychometric properties of assess-ment tools. Reliable and valid PM assessments with normative data arenecessary for health professionals working with people with these types ofneurological disorders as well as working with older adults. Below, webriefly review the most common tools to assess PM in clinical settings (seealso Mioni, McClintock, & Stablum, 2014), as well as presenting the potenti-ality and psychometric characteristics of a well-known PM task, the VirtualWeek (Rendell & Craik, 2000), which is the subject of the present study.

The Rivermead Behavioural Memory Test (RBMT; Wilson, Cockburn, &Baddeley, 1985, 2003) is probably the most commonly used tool to assess PMand includes three event-based tasks. Although the RBMT has been widelyused in clinical settings and in several neuropsychological studies, it providesonly a limited range of scores and is unlikely to be sensitive to deficits inmoderate or mild patients (Mills et al., 1997; Shum, Fleming, & Neulinger,2002; Mathias & Mansfield, 2005); moreover, the test has the limitation ofnot investigating time-based PM performance (Wilson et al., 1985). TheCambridge Behavioural Prospective Memory Test (CBPMT; Groot et al.,2002) includes four time-based and four event-based tasks to be administratedover a 40-minute period. Participants were allowed to use any strategy toremember the tasks. The CBPMT showed significant correlation with a PMquestionnaire (Everyday Memory Questionnaire; Sunderland, Harris, &Baddeley, 1983) as well as with executive and neuropsychological measures(Groot et al., 2002); also, good reliability and validity were observed (Wilson,Emslie, & Foley, 2004). Wilson and colleagues revised the CBPMT andcreated the CAMPROMPT, which has three time-based and three-eventbased tasks to be completed in 30 minutes (Wilson, Emslie, Watson,Hawkins, & Evans, 2005). Delprado and colleagues (2012) used theCAMPROMPT with people with mild cognitive impairments and showedmoderate inter-item reliability, with a Cronbach alpha coefficient of .75, indi-cating good internal consistency. However, the CAMPROMPT is still limitedin the number of PM trials included and no alternative versions were devel-oped to evaluate rehabilitation interventions. The Memory for Intentions

1For a more detailed presentation of PM impairment in clinical populations please see West

(2008) and Kliegel, Jager, Altgassen, & Shum (2008).

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Screening Test (MIST; Raskin, 2004) includes four event-based and fourtime-based tasks to be performed in 30 minutes while playing a word-search puzzle that works as the ongoing task. The eight PM activities arebalanced in terms of delay interval (2 or 5 minutes delay), cue (time-basedor event-based), and response modality (verbal or physical response). TheMIST also includes an eight-item multiple-choice recognition test and amore naturalistic task or at least a task that has to be performed in dailylife and has to be performed after a 24-hour delay. The MIST has beenwidely used with healthy older adults and various clinical populations (seeRaskin, 2009, for a review). Split-half reliability was measured by Woodset al. (2008) as .70 using the Spearman-Brown coefficient. While the inter-item reliability of the individual trials was reported to be relatively poor(Cronbach’s alpha ¼ .47) the reliability of the six subscales was judged tobe better (Cronbach’s alpha ¼ .88). Finally, the Royal Prince Alfred Prospec-tive Memory Test (RPA-ProMem; Radford, Lah, Say, & Miller, 2011)includes three alternative forms, each of which had two time-based and twoevent-based tasks that have to be performed within the session or at a latertime. No differences were found between scores in the three parallel formsof the RPA-ProMem and good reliability (Spearman correlation r ¼ .71)was found between the three different forms (Radford et al., 2011).

Most of the previous PM paradigms have little resemblance to real-lifesituations and are not adequate for measuring the outcomes of rehabilitationinterventions because no alternative forms are provided (apart from RPA-ProMem). McDaniel and Einstein (2007) have pointed out that most measuresof PM lack reliability, with some tasks as low as 20%. Moreover, neuropsy-chologists need to obtain information about how patients perform in the rou-tines of everyday life, and laboratory-based PM measures may not providesuch information (Burgess et al., 2006; Knight & Titov, 2009). In fact,many neuropsychologists have realised the limitations of many conventionaltests and are looking for new approaches to measuring PM and functional dis-abilities (Knight & Titov, 2009). To solve the discrepancy between perform-ance on neuropsychological tests and performance in everyday life,researchers have developed tasks that can provide a bridge between conven-tional neuropsychological tests and behavioural observation. Virtual tasks, infact, can simulate the activity of everyday life in a controlled setting (Knight& Titov, 2009; see also Trawley, Law, & Logie, 2011; Trawley, Law, Brown,Niven, & Logie, 2013).

Virtual Week (Rendell & Craik, 2000) was developed as a laboratorymeasure of PM that closely represents PM activities in everyday life in aboard game format, where each circuit of the board represents one virtualday. As participants circuit the board they pick up cards describing events rel-evant to the time of day (e.g., meals and shopping) and they have to select anoption (e.g., what to eat and what to buy) and the choice determines the dice

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rolling consequences. The dice rolling, moving token, and event carddecisions provide the backdrop or the ongoing task, which is a definingfeature for a PM task. Participants are engaged with 10 PM tasks duringeach virtual day. Of these tasks, four are regular, four are irregular, andtwo are time-check. The regular and the time-check PM tasks are repeatedevery virtual day and simulate activities that occur as one undertakesnormal healthcare duties. The regular tasks included two event-based (i.e.,taking antibiotics at breakfast and dinner) and two time-based (i.e., takingasthma medication at 11 a.m. and 9 p.m.) tasks. In the time-check task partici-pants are required to do a lung test at 2 minutes and at 4 minutes on the chron-ometer or stop clock. The irregular tasks are different each virtual day andalso include two event-based (e.g., buying bus tickets when shopping) andtwo time-based (e.g., phone the plumber at 4 p.m.) tasks and simulate thekinds of occasional tasks that occur in everyday life.

Virtual Week is a very promising task for investigating PM performanceand it has been extensively used with normal ageing (Aberle, Rendell,Rose, McDaniel, & Kliegel, 2010; Henry, Rendell, Phillips, Dunlop, &Kliegel, 2012; Margrett, Reese-Melancon, & Rendell, 2011; Rendell &Craik, 2000; Rose, Rendell, McDaniel, Aberle, & Kliegel, 2010; Rendellet al., 2011) and different clinical populations: those with abnormal ageing(Ozgis, Rendell, & Henry, 2009; Thompson et al., 2010; Will et al., 2009),patients with multiple sclerosis (Kardiasmenos, Clawson, Wilken, &Wallin, 2008; Rendell, Jensen et al., 2007a; West et al., 2007), schizophrenics(Henry, Rendell, Kliegel, & Altgassen, 2007; Henry, Rendell, Rogers, Altgas-sen, & Kliegel, 2011), substance users (Leitz, Morgan, Bisby, Rendell, &Curran, 2009; Paraskevaides et al., 2010; Rendell, Gray, Henry, & Tolan,2007; Rendell, Mazur, & Henry, 2009), Parkinson’s patients (Foster et al.,2013), and patients with brain damage (Kim, Craik, Luo, & Ween, 2009;Mioni et al., 2013). Virtual Week has been shown to be sensitive to PM def-icits with each of these groups: normal ageing, abnormal ageing and thevarious clinical groups.

The reliability of Virtual Week was investigated by Rose et al. (2010) in astudy involving younger and older adults. Across the entire sample, reliabilityestimates of the internal consistency ranged from .84 to .94 for the regular,irregular and time-check tasks. Further, the split-half reliability for theoverall Virtual Week measure was estimated to be .74 in a clinical groupwith schizophrenia and .66 in the controls (Henry et al., 2007) and thesplit-half reliability for regular, irregular and time-check was .85, .71, and.71 for multiple sclerosis (MS) patients, and for controls was .79, .75, and.73, respectively (Rendell et al., 2012). Cronbach’s alpha for all PM taskswas .89 for traumatic brain injury (TBI) patients and .62 for controls(Mioni et al., 2013), and .89 for patients with Parkinson’s disease and .81controls (Foster et al., 2013). Thus together, evidence from clinical and

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non-clinical groups suggests that Virtual Week is a reliable indicator of PMfunction. Test–retest performance has never been investigated with VirtualWeek. This is an important feature, in particular in clinical settings, to evalu-ate the efficiency of rehabilitation training. This study primarily aimed toexamine the effect of test–retest in younger and older adults performingVirtual Week twice, one month apart. In addition, we conducted preliminaryinvestigation of the internal consistency and test–retest reliability of VirtualWeek as a measure of PM.

EXPERIMENT 1

Method

Participants

Twenty older adults (aged 65–84 years, M ¼ 73.75, SD ¼ 5.22; 16 women)and 19 younger adults (aged 22–27 years, M ¼ 23.95, SD ¼ 1.22; 9 women)took part in Experiment 1. Older adults were volunteers from the community ofPadova and were screened for visual acuity, the presence of neurologicaltrauma, use of psychoactive medication and dementia with the Mini MentalState Exam (MMSE; Folstein, Folstein, & McHugh, 1975). Older adults whoscored below 25 on the MMSE were excluded from participation. The meanMMSE of the selected older participants was 28.25 (SD ¼ 1.62).

Younger participants were volunteers recruited at the Department of GeneralPsychology, Padova, Italy. The younger adults had significantly more years ofeducation than the older adults, t(37) ¼ 9.17, p , .001, d ¼ 2.96; youngeradults, M ¼16.84, SD ¼ 1.61; older adults, M ¼ 7.90, SD ¼ 3.95.

Materials

Prospective memory task: Computer Virtual Week. Virtual Week is aboard game (Rendell & Craik, 2000; Rendell & Henry, 2009) in which par-ticipants simulate going through the course of a week (in this study weused five consecutive days from Monday to Friday). Participants movearound the board with the roll of a dice. The time of the virtual day is dis-played on a virtual time clock calibrated to the position of the token on theboard (every 2 squares the time increased 15 minutes) (e.g., Griffiths et al.,2012; Henry et al., 2012; Mioni et al., 2013; Rendell et al., 2011). As partici-pants circuit the board, they have decisions to make and things to remember toperform. Participants have to select an “Event Card” each time the tokenlands on or passes a square labelled “E”. This card describes specific activitiesand three options relevant to the virtual time of day. Each option involves

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having to roll either a set number, an even (or odd) number, or any number onthe dice. Two clocks were presented on the board (Figure 1). The clock abovethe dice was the stopclock that started at the beginning of each virtual day andrepresented the real time. The clock under the dice was a virtual clock thatmoved 15 minute every two squares. Participants completed five days with10 PM tasks per day: four regular (repeated), four irregular (non-repeated),and two time-check tasks (repeated). The four activities that occurred regu-larly every virtual day simulated health activities; two of the four regulartasks are time-based (i.e., triggered by the virtual time of day; “Use asthmainhaler at 11 a.m. and 9 p.m.”), and two tasks are event-based (i.e., triggeredby some information shown on an Event Card; “Take antibiotics at breakfastand dinner”). The four irregular tasks simulate activities that are new everyday; as for the regular tasks, half were time-based (i.e., “Pick up thelaundry at 4 p.m.”) and half were event-based (i.e., “Buy the bus tickets atlunch”). The two time-check tasks were also related to the health activitiesand were to check lung capacity when the stopclock displayed 2:00 minand 4:00 min after the start of each day.

The version used in the present study is an adaptation of the originalversion translated into Italian and already used with traumatic brain injury(TBI) patients (Mioni et al., 2013). Minor changes have been made to thestandard version to reduce some cultural differences that were evident

Figure 1. English version of Virtual Week computer screen display.

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between the Australian and Italian population (i.e., at the event card “break-fast” the Australian version required the player to select from: “crunchypeanut butter”, “porridge and apple juice” or “cereal and orange juice”.Peanut butter and porridge are not typical Italian dishes for breakfast andhave been substituted with the more familiar options of “biscuits” or“cakes”). Three event cards (on a total of 50) that referred to activities atthe university were also changed to activities that were more familiar to theItalian population (“Music store”, “Florist” and “Post office”). As inRendell and Craik (2000) and subsequent Virtual Week studies, participantswere given pre-game instructions and then a practice virtual day to ensurethey understood all features of the game. Accuracy on the PM tasks wasthe primary analysis but performance was also analysed in terms of time(minutes) to execute each virtual day at test and retest. Accuracy was calcu-lated as a proportion of correct responses. Correct scores indicated that thetarget item was remembered at the correct Event Card (event-based tasks)or at the correct virtual time (time-based tasks) and was correct before thenext roll of the dice. For time check tasks data were scored as correct if per-formed within 10 seconds in respect to the target time. Time to execute virtualdays represents the time (in minutes) to perform each virtual day.

Procedure

Older adults were tested individually in their own homes while youngerparticipants were tested at the Department of General Psychology, Padova.Each participant undertook two experimental sessions that lasted approxi-mately two hours each. During the first session (Test) participants performedVirtual Week and older adults also performed the MMSE. After one month,participants performed Virtual Week (Retest). Virtual Week was presented ona 15 inch computer screen with participants seated at a distance of approxi-mately 60 cm. Participants gave their informed consent to participate in thestudy. The study was approved by the ethical committee of psychology ofthe University of Padova and was conducted according to the principlesexpressed in the Declaration of Helsinki.

Results

Analysis of correct responses

Participants’ performance was analysed in terms of proportion of correctresponses2. This was the number correct responses, expressed as proportion

2To control for the different years of education between younger and older adults an

ANCOVA was carried out with years of education as covariate. Results showed only a main

effect of years of education, F(1, 36) ¼ 7.24, p ¼ .01, h2p ¼ .16.

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of the PM tasks scheduled for each of the four categories of tasks: regularevent, regular time, irregular event, and irregular time (Table 1). Data wereanalysed with a 2 × 2 × 2 × 2 mixed ANOVA with the between-group vari-able group (younger, older) and within-group variables PM task (regular, irre-gular), PM cue (event-based, time-based) and session (test, retest). For thisand subsequent analyses, post hoc tests were performed using the Bonferronicorrection.

Results showed a significant main effect of group, F(1, 37) ¼ 6.71, p ¼.014, h2

p¼.15; PM task, F(1, 37) ¼ 10.71, p ¼ .002, h2p ¼ .22; PM cue,

F(1, 37) ¼ 66.55, p , .001, h2p ¼ .64; and session, F(1, 37) ¼ 15.13, p ,

.001, h2p ¼ .29. There were two sets of significant interactions that were fol-

lowed up separately. Firstly, there were interactions of group × session, F(1,37) ¼ 19.16, p , .001, h2

p ¼ .34; and group × PM cue, F(1, 37) ¼ 8.28,p ¼.007, h2

p ¼ .18; and a 3-way interaction of these variables group × PMcue × session, F(1, 37) ¼ 4.92, p ¼.033, h2

p ¼ .12 (see Figure 2). Tofurther assess this three-way interaction, separate 2×2×2 ANOVAs wererun for event and time-based tasks with variables: group, session and PMtask. Secondly, there was interaction between PM task and PM cue, F(1,37) ¼ 21.44, p , .001, h2

p ¼ .37, which was followed up with tests ofsimple effects. No other interactions were significant.

The follow up of the 3-way interaction revealed, for the separate analy-sis of event-based tasks, session was a main effect, F(1, 37) ¼ 14.92, p ,

.001, h2p ¼ .29; group was not a main effect, F(1, 37) ¼ 1.17, p ¼ .286,

h2p ¼ .03; but group significantly interacted with session, F(1, 37) ¼ 8.03,

TABLE 1Experiment 1: Mean (M ) and standard deviation (SD) for PM accuracy at test and retest

session for younger and older adults

Younger adults Older adults

PM task PM target M (SD) M (SD)

Test session

Regular Event-based .91 (.09) .85 (.21)

Time-based .86 (.15) .61 (.34)

Irregular Event-based .95 (.09) .86 (.10)

Time-based .77 (.24) .45 (.23)

Time Check .58 (.26) .22 (.58)

Retest session

Regular Event-based .99 (.03) .94 (.02)

Time-based .83 (.17) .77 (.20)

Irregular Event-based .95 (.07) .96 (.07)

Time-based .73 (.23) .67 (.22)

Time Check .60 (.20) .36 (.23)

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p ¼ .007, h2p ¼ .18. Tests of simple effects revealed that in the test

session, younger adults performed significantly better on event-basedtasks than older adults, F(1, 37) ¼ 4.42, p ¼.042, h2

p ¼ .11, however,this difference was not significant in the retest session, F(1, 37) ¼ 2.32,p ¼ .136, h2

p ¼ .06. Further tests of simple effects revealed that olderadults performed better on event-based tasks in the retest session comparedto the test session, F(1, 37) ¼ 23.01, p ,.001, h2

p ¼ .38. The youngeradults did not differ between the test and retest sessions, F(1, 37) ¼0.52, p ¼ .477, h2

p ¼ .01.In time-based tasks, session was a main effect, F(1, 37) ¼ 7.49, p ¼ .009,

h2p ¼ .17; group was a main effect, F(1, 37) ¼ 7.95, p ¼.008, h2

p ¼ .18; andthere was a significant interaction between group and session, F(1, 37) ¼16.27, p , .001, h2

p ¼ .31. Tests of simple effects revealed that youngeradults performed better than older adults for time-based tasks in the testsession, F(1, 37) ¼ 15.06, p ,.001, h2

p ¼ .29. This difference was not signifi-cant for the retest session, F(1, 37) ¼ 0.95, p ¼ .336, h2

p ¼ .03. Further testsof simple effects revealed that older adults performed better for time-basedtasks in the retest session than in the test session, F(1, 37) ¼ 23.53, p ,

.001, h2p ¼ .39, however this difference was not significant for younger

adults, F(1, 37) ¼ 0.82, p ¼ .371, h2p ¼ .02.

Figure 2. Experiment 1. Mean proportion of correct prospective memory (PM) responses for PM

tasks as a function of event- and time-based cued tasks, test and retest session for the younger and

older adults. The error bars indicate +1 SE.

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The interaction between PM task and PM cue was followed up with tests ofsimple effects that showed that event-based tasks were performed more accu-rately than time-based tasks for both regular tasks, F(1, 37) ¼ 29.08, p ,

.001, h2p ¼ .44 (regular event M ¼ .92, SD ¼ .14; regular time M ¼ .77,

SD ¼ .25) and irregular tasks, F(1,37) ¼ 81.38, p , .001, h2p ¼ .67 (irregular

event M ¼ .93, SD ¼ .09; irregular time M ¼ .66, SD ¼ .26). Further tests ofsimple effects revealed that while regular time-based tasks were performedmore accurately than irregular time-based tasks, F(1, 37) ¼ 20.34, p ,

.001, h2p ¼ .36, this difference was not significant between regular event

and irregular event-based tasks, F(1, 37) ¼ 0.39, p ¼ .538, h2p ¼ .01.

Data from the time check tasks were analysed separately with a 2 × 2mixed ANOVA with between-groups variable group (younger, older) andwithin-groups variable session (test, retest)3. Results showed a significanteffect of group, F(1, 37) ¼ 17.67, p , .001, h2

p ¼ .32, where older adults(M ¼ .30, SD ¼ .27) performed less accurately than younger adults (M ¼.59, SD ¼ .23). There was also a significant effect of session, F(1, 37) ¼4.62, p ¼ .038, h2

p ¼ .11, where all participants’ performance improved inthe retest session (M ¼ .48, SD ¼ .25) compared to the test session (M ¼.40, SD ¼ .33). There was no interaction between group and session, F(1,37) ¼ 2.94, p ¼ .095, h2

p ¼ .07.In sum, the analysis of PM accuracy with regular and irregular tasks

showed that younger adults showed no test–retest effect. However, olderadults improved their performance in the retest session; older adults wereless accurate than younger adults at the test session, but the two groupswere equally accurate at the retest session. On the time check task, theyounger participants were consistently better than the older participants atboth test and retest, and all participants improved performance at retestsession.

Time to execute virtual days

Time to execute virtual days represents the time (in minutes) to performeach virtual day. Data were analysed with a 2 × 5 × 2 mixed ANOVAwith the between variable group (younger, older) and within variables ofdays (Monday, Tuesday, Wednesday, Thursday, Friday) and session (test,retest)4. Significant effects of group, F(1, 37) ¼ 91.77, p , .001, h2

p ¼.71; days, F(4, 148) ¼ 26.58, p , .001, h2

p ¼ .42; and session, F(1, 37) ¼116.92, p , .001, h2

p ¼ .76, were found. The interactions group × session,F(1, 37) ¼ 20.57, p , .001, h2

p ¼ .36; group × days, F(4, 148) ¼ 4.14,

3An ANCOVA was also carried out with years of education as covariate. The main effect of

education did not reach significance, F(1, 36) ¼ .33, p ¼ .56, h2p ¼ .01.

4An ANCOVA was also carried out with years of education as covariate. Results showed a

significant main effect of education, F(1, 36) ¼ 5.16, p ¼ .03, h2p ¼ .12.

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p ¼.003, h2p ¼ .10; and session × days, F(4, 148) ¼ 6.98, p , .001, h2

p ¼ .16,were significant. Interestingly, the interaction group × session × days wasalso significant, F(4, 148) ¼ 5.05, p , .001, h2

p ¼ .12 (Figure 3). Post-hocanalysis showed that younger adults were always faster than older adults inexecuting the virtual days. Older adults significantly decreased the time toexecute Virtual Week from Monday to Friday in the test session and theystabilised their performance after Wednesday. No differences were foundbetween days in the retest session. In younger adults no differences werefound between days either at test or retest sessions.

Reliability

The internal consistency reliability coefficients (Cronbach’s alpha) foreach of the task categories at test and retest were analysed separately foryounger and older adults and are reported in Table 2. Test–retest correlationswere also conducted separately for younger and older adults and are reportedin Table 3.

Discussion

The present study was conducted to investigate group differences in PM per-formance at test and retest in younger and older adults that performed VirtualWeek twice, one month apart. We also conducted a preliminary investigation

Figure 3. Experiment 1. Time to execute virtual days for younger and older adults at test and retest

session. The error bars indicate +1 SE.

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of test–retest reliability and internal consistency of Virtual Week (Rendell &Craik, 2000; Rendell & Henry, 2009).

Virtual Week has shown good psychometric properties when investigatedwith younger and older adults (Rose et al., 2010) and clinical populations(Henry et al., 2007; Rendell et al., 2012; Mioni et al., 2013; Foster et al.,2013), but the test–retest reliability has never been investigated. The internalconsistency at test and retest was high for both younger and older adults, andconsistent with previous Virtual Week studies (Henry et al., 2007; Mioniet al., 2013; Rendell et al., 2012; Rose et al., 2010). Importantly, this studyprovides the first test–retest correlation and it is relatively high for botholder and younger adults.

TABLE 2Reliability of Virtual Week: Cronbach’s alpha assessing internal consistency for younger

and older adults at test and re-test sessions

Regular Irregular Event-Based Time-based Time Check All tasks

Number of items 20 20 20 20 10 50

Test session

Younger adults .770 .529 .554 .822 .704 .644

Older adults .582 .900 .716 .878 .865 .915

Retest session

Younger adults .708 .704 .551 .813 .557 .830

Older adults .609 .719 .250 .761 .797 .858

TABLE 3Test–retest Person’s correlation coefficients for Virtual Week tested one month apart.

Experiment 1, versions A of Virtual Week at test and retest. Experiment 2, version A and Bof Virtual Week, completed in counterbalanced order

PM task

Test–Retest A and A

(Experiment 1) Test–Retest A and B

(Experiment 2)

Test session

Number of PM

tasks per day/total

Young

(n ¼ 19)

Old

(n ¼ 20)

All old

(n ¼ 50)

Regular 4/20 .393∗ .665∗∗ .362∗∗

Irregular 4/20 .410∗ .696∗∗ .550∗∗

Event 4/20 .128 .397∗ .305∗

Time 4/20 .581∗∗ .736∗∗ .603∗∗

Time Check 2/10 .676∗∗ .542∗∗ .564∗∗

All PM 10/50 .613∗∗ .805∗∗ .682∗∗

∗p , .05, ∗∗p , .001

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Analyses of PM performance showed that older adults were substantiallyless accurate than younger adults at test sessions, showing an age-relateddecrement in PM performance. The discrepancy between younger andolder participants was particularly evident when performing irregular tasksand when the cue was time-based. A significant effect of PM task wasfound indicating that participants were more accurate when the task wasrepeated every day (regular tasks) compared to the activities that were newevery day (irregular tasks). In regular PM tasks, the cues are presented in aconsistent routine (i.e., take medication every day at breakfast), and therefore,the preceding situational cues might provide a richer, more extensive set ofcues for triggering retrieval (Kvavilashvili & Fisher, 2007; Rose et al.,2010). A significant effect of PM cue was also found; participants wereless accurate when performing time-based compared to event-based activitiesconfirming that time-based tasks are more demanding, probably due to thehigher self-initiated retrieval to monitor the time and the absence of externalcues to help recall the PM activity (Einstein & McDaniel, 1990; McDaniel &Einstein, 2000, 2007). Analysis of time-check also showed lower perform-ance in older compared to younger adults; this might be explained by thenon-focality of the time-check task. PM cues are more focal when theongoing task involves processing features of the PM cues than whenongoing task processing is more peripheral (non-focal cues; Kliegel, Jager,& Phillips, 2008; Rendell, McDaniel, Forbes, & Einstein, 2007). Moreover,time-check tasks are related to the chronometer, which represents the realtime of the game. Time perception is reduced in older adults (Block,Zakay, & Hancock, 1998); this might have also contributed to lower perform-ance observed with older adults in time-check tasks (Mioni & Stablum, 2014).

Analysis of the time to execute Virtual Week showed no differences inyounger adults when performing Virtual Week at test or retest session, indi-cating that younger participants were familiar with the experimental pro-cedure. Older adults significantly reduced the time to execute virtual daysat test sessions from Monday to Friday. The higher time for older adults toexecute each day compared to younger adults is likely because older adultsare less familiar with technological devices (Ellis & Allaire, 1999) and arecharacterised by slower speed of processing (Salthouse, 2000; Yordanova,Kolev, Hohnsbein, & Falkenstein, 2004). Interestingly, older adults signifi-cantly reduced the time to execute each day indicating a learning effect andmore familiarity with the experimental procedure at the end of the testsession. The improvement observed in older adults (i.e., reduction in timeto complete each virtual day) was maintained at retest session; in fact olderadults were significantly faster at retest session compared to test session.

Effect of session (test vs. retest) was also found on PM accuracy. Olderadults were significantly less accurate than younger adults at test session,but, interestingly, the discrepancy between younger and older adults was

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eliminated at retest session. In particular, older adults showed a greatimprovement on irregular time-based targets. Better performance at retestsession was also observed for time-check tasks. In this case, both groups(older and younger) showed the improvement.

The improvement in PM accuracy at retest session was not expected andneeds further consideration. It is possible that, at the test session, our olderadults (with lower years of education) were less familiar with the experimen-tal procedure and the demands of a computerised task and dedicated morecognitive resources to understand the procedure; therefore, less cognitiveresources were available to implement and execute the PM activities. Onthe other hand, participants performed the same activities at test and retest.It might be possible that participants remembered or at least were more fam-iliar with the content of the PM activity at retest session. In fact, some partici-pants, before starting the retest session, clearly remembered and repeated thecontent of some of the irregular tasks with no prompt from the experimenter.This might be expected for regular tasks, which were repeated several timeswithin each session.

Therefore, we hypothesised that the higher level of accuracy observed inolder adults during the retest session was not only due to the participantsbecoming more familiar with the experimental procedure but was mainlydue to the familiarity of the content of the PM actions. To test this hypothesiswe developed two parallel versions of Virtual Week (version A and versionB) and tested two groups of older adults one month apart.

EXPERIMENT 2

Experiment 2 was conducted to investigate if the results obtained in Exper-iment 1 were due to learning of the Virtual Week procedure or due to acqui-sition of the content of the PM actions. The standard version used in theprevious study was included (version A) and we developed a second parallelversion of Virtual Week (version B). The two versions were equivalent in thenumber of PM tasks to be performed each virtual day, only the content of thePM tasks were different from version A to version B. We also investigatedreliability and internal consistency of the parallel Virtual Week version.

Methods

Participants

Fifty older adults (61–82 years, M ¼ 68.12, SD ¼ 4.98; 29 women) wereincluded in Experiment 2. Twenty-five participants performed version A (11women) and 25 version B (18 women) at test. Participants that performedversion A at test performed version B at retest and vice versa (Group A-B

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and Group B-A). Participants of group A-B were 68.40 years old (SD ¼5.07), had 11.23 years of education (SD ¼ 5.12), and had an MMSE scoreof 28.14 (SD ¼ 1.15). Participants of the group B-A were 67.84 years old(SD ¼ 4.98), had 10.56 years of education (SD ¼ 3.58) and had an MMSEscore of 28.52 (SD ¼ 1.25). No differences in age, years of education orMMSE scores were found between the two groups (all ps . .270).

Materials

Prospective memory task: Computer Virtual Week version A and versionB. A parallel version of the original Virtual Week (version A used in Exper-iment 1) was created (version B). The virtual days as presented by the 10event cards per day, had a similar structure but the specific content of theactivities in each event card differed between version A and B. RegularPM tasks were the same in version A and version B, in both versions partici-pants were required to undertake everyday health duties: “Take antibiotics atbreakfast and dinner”; “Use asthma inhaler at 11 a.m. and 9 p.m.” and “Checkthe lung capacity at 2 and 4 minutes”. New irregular PM tasks were createdfor version B. We modified only the content of the PM action not the PM cue:the time or the event card in which the PM action was to be performed was thesame in version A and version B. Thus, if participants performing version Awere required on Monday to call the bank at 12 p.m., then in version B par-ticipants were required on Monday to call the doctor at 12 p.m. (time-basedPM tasks). Similarly for the event-based PM tasks, the position of the PMcue in the virtual day was the same in each version. Thus, if participants inversion A on Monday had to return the book when at the library, which isthe sixth event card that occurred in the virtual afternoon, then in versionB, on Monday, participants are required to return the DVD at the video-store that was the sixth card that occurred in the virtual afternoon.

Recognition test of PM task content. In Experiment 2 Virtual Week hadthe added feature that immediately following each virtual day, participantscompleted a recognition test to assess their retrospective memory for thevarious PM tasks. Successful PM performance requires executing theintended action at the appropriate moment (i.e., prospective component) aswell as remembering the specific action to be performed (i.e., retrospectivecomponent) (Einstein & McDaniel, 1996). Therefore, PM failure might bedue to forgetting the content of the PM action or failing to retrieve andexecute the intended action (Einstein & McDaniel, 1996; Kliegel, Eschen,& Thone-Otto, 2005; Maylor, Smith, Della Sala, & Logie, 2002; Mioniet al., 2012; Mioni & Stablum, 2014).

The recognition test was introduced to further evaluate the source of thePM forgetting. The test required matching each intended action with its

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cue. Participants were presented with a list of the actions, some of which wererequired during the virtual day while others were distractors. For each action,there was a pull down menu listing possible PM cues (e.g., when shopping, atuniversity) displayed on the screen. Participants were required to identify therequired actions and connect each action with the right cue. Proportion ofcorrect responses in the retrospective memory test were calculated for eachPM task (regular time-based, regular event-based, irregular event-based, irre-gular time-based and time check).

Procedure

As in Experiment 1 participants were tested individually in two experimen-tal sessions that lasted approximately two hours each. Participants were testedat the Department of General Psychology, at Centre San Pio X, Padova, Italyor in their own homes. Possible effect of location was investigated and nodifferences were found (p . .05) between participants that were tested atthe two locations. During the first session (Test session) participants per-formed the MMSE and Virtual Week. After one month, participants per-formed Virtual Week (Retest session). During the test session participantswere randomly assigned to one of the two versions, A or B. The version ofVirtual Week was counterbalanced between participants, thus half of the par-ticipants first performed Virtual Week version A and half started with VirtualWeek version B. During the retest session participants that started withversion A performed version B first and vice versa. The PM task (VirtualWeek) was presented on a 15 inch computer screen with participants seatedat a distance of approximately 60 cm. Participants gave their writtenconsent to participate in the study.

Results

Preliminary analyses were conducted on PM performance (proportion ofcorrect responses) between version A and version B to investigate possibledifferences between the two versions. A mixed ANOVA of PM performanceat test session revealed PM version (A, B) was not a main effect (p ¼ .877)and did not interact with PM task (regular, irregular) or PM cue (event, time),(all ps ≥ .406). Independent t-tests on PM performance at test session for thetime-check task also showed no differences between versions A and B (p ¼.915). These analyses were repeated at retest session, and once again PMversion (A, B) was not a main effect (p ¼ .640) and did not interact withPM task or PM cue (all ps ≥.484). Independent t-tests showed the time-check task also did not vary between version A and version B at retest (p¼ .586). Further, preliminary analyses of the PM performance at test andretest were conducted including the between groups variable of versionorder (version A first, version B first); results revealed that this was not a

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main effect (p ¼ .846) and did not interact with other variables, PM task(regular, irregular), PM cue (event, time), or session (test, retest) (all ps ≥.106). In summary, PM performance did not differ between version A andversion B at either test or retest session; and the analysis of test and retest ses-sions revealed that PM accuracy did not vary according to whether complet-ing version A at test then version B at retest or the reverse order.

Analysis of correct responses. Data were analysed with a 2 × 2 × 2repeated measures ANOVA with the within-group variables PM task(regular, irregular), PM cue (event-based, time-based) and session (test,retest)5. There was a main effect of PM task, F(1, 49) ¼ 44.72, p , .001,h2

p ¼ .48, and PM cue, F(1, 49) ¼ 212.90, p , .001, h2p ¼ .81, but no

main effect of session, F(1, 49) ¼ .04, p ¼ .842, h2p ¼ .001, was found.

The only significant interaction was a two-way interaction between PMtask × PM cue, F(1, 49) ¼ 15.89, p , .001, h2

p ¼ .24. The interaction ofPM task × PM cue was analysed with tests of simple effects and it wasrevealed that event-based tasks were performed more accurately than time-based tasks for both the regular tasks, F(1, 49) ¼ 163.85, p , .001, h2

p ¼.77 (Regular event M ¼ .95, SD ¼ .01; Regular time M ¼ .64, SD ¼ .21),and irregular tasks, F(1, 49) ¼ 193.23, p , .001, h2

p ¼ .79 (Irregular eventM ¼ .89, SD ¼ .16; Irregular time M ¼ .49, SD ¼ .21). Further tests ofsimple effects also showed that regular tasks were performed more accuratelythan irregular tasks for both event-based tasks, F(1, 49) ¼ 21.73, p , .001, h2

p

¼ .31, and time-based tasks, F(1, 49) ¼ 39.84, p , .001, h2p ¼ .45. Data from

the time check tasks were analysed separately and t-test was conductedbetween accuracy at test and retest session. Results showed no significanteffect of session, t(49) ¼ 1.74, p ¼ .08, where participants were slightlyless accurate in the test (M ¼ .36, SD ¼ .23) compared to the retestsession (M ¼ .41 SD ¼ .21).

Analysis of retrospective performance. The proportion of correctresponses on the recognition test of PM content for each type of PM task attest and retest is displayed in Table 4. As for PM accuracy, the recognitiontest of PM content was analysed with a 2 × 2 × 2 repeated measuresANOVA with the within-groups variables PM task (regular, irregular), PMcue (event-based, time-based) and session (test, retest). There was no maineffect of session, F(1, 48) ¼ 2.55, p ¼ .11, h2

p ¼ .05, but there were main

5Analyses were also conducted controlling for the effect of age. Participants were divided

into two groups: old adults aged 61–67 years and old-old aged 68–82 years. No differences

on years of education or MMSE scores were found between the two groups (all ps . .360).

Results showed a significant main effect of age (p , .05) indicating that old-old adults were

less accurate than old adults. Age did not interact with any other variable (all ps . .211).

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effects of PM task, F(1, 48) ¼ 21.65, p , .001, h2p ¼ .31, and PM cue, F(1,

48) ¼ 25.05, p , .001, h2p ¼ .34. No significant interactions were found (all

ps ≥ .162).Interestingly, t-test was also conducted between PM accuracy and accu-

racy at the recognition test separately at test and retest. Participants weremore accurate on the recognition test of PM content (involving matchingthe PM action and the PM cue) than performing the PM actions (seeTable 4), except for the event-based tasks where participants were close toceiling on both PM accuracy and recognition task.

Time to execute virtual days. Data were analysed with a 5 × 2 ANOVAwith the within-groups variables of days (Monday, Tuesday, Wednesday,Thursday, Friday) and session (test, retest). There were main effects ofdays, F(4, 120) ¼ 34.43, p , .001, h2

p ¼ .53, and session, F(1, 30) ¼6.17, p ¼ .019, h2

p ¼ .17. There was also a significant interaction betweendays × session, F(4, 120) ¼ 3.56, p ¼ .009, h2

p ¼ .11. These findings indicatethat participants decreased the time to execute each virtual day at test sessionand they were stable after Wednesday; at retest their performance was stablefrom Tuesday. Participants were faster at retest session only on Monday andFriday and they performed equally the other days.

Reliability of version A and version B. The reliability coefficients(Cronbach’s alpha) were analysed separately for versions A and B at test

TABLE 4Experiment 2: Mean (M ) and standard deviation (SD) for PM accuracy and PM accuracy at

the recognition task at test and retest session; t-test values and effect size indices(Cohen’s d ) are also indicated

PM accuracy Recognition accuracy

PM task PM target M (SD) M (SD) t d

Test session

Regular Event-based .95 (.08) .98 (.14) 1.20 .26

Time-based .63 (.18) .91 (.27) 6.76∗ 1.22

Irregular Event-based .91 (.09) .95 (.10) 2.91∗ .42

Time-based .49 (.22) .82 (.23) 8.93∗ 1.46

Time Check .36 (.23) .97 (.07) 17.99∗ 3.58

Retest session

Regular Event-based .95 (.08) .98 (.05) 2.38∗ .39

Time-based .66 (.22) .91 (.16) 7.82∗ 1.29

Irregular Event-based .87 (.11) .88 (.11) .59 .90

Time-based .51 (.23) .79 (.16) 9.43∗ 1.41

Time Check .42 (.19) .93 (.15) 14.66∗ 2.97

∗p , .001

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and retest session, for each of the task categories (Table 5). The test–retestcorrelations were also calculated and reported in Table 3.

Discussion

Experiment 2 was primarily conducted to investigate if the better perform-ance obtained by older adults at retest session in Experiment 1 were due tolearning of the Virtual Week procedure or due to acquisition of the contentof the PM actions. As in Experiment 1, the internal consistency and test–retest reliability was also investigated. Two parallel versions were employed:Version A was the standard Virtual Week (Mioni et al., 2013; Rendell &Craik, 2000) and the same used in Experiment 1. In version B we changedthe content of the Event Cards and the cue of the PM tasks (either event-and time-based).

The internal consistency was high, confirming previous data (Experiment1) and consistent with previous studies of Virtual Week (Henry et al., 2007;Mioni et al., 2013; Rendell et al., 2012; Rose et al., 2010). Moreover, test–retest correlations were also sufficiently high for version A and B.

The results of PM accuracy showed that, at each testing session, version Aand version B were equivalent and no group differences were found betweenPM accuracy of participants using either version. Significant effects of PMtask and PM target were found confirming the results observed in Experiment1. Participants were less accurate when the activities were new every day(irregular tasks), in particular when the target was time-based compare toevent-based (Mioni et al., 2013; Rendell et al., 2011).

As in Experiment 1, at test session, participants reduced the time toperform each virtual day, indicating more familiarity and an acquisition of

TABLE 5Experiment 2: Reliability of Virtual Week: Cronbach’s alpha assessing internal consistencyfor older adults performing versions A and version B at test (upper part) and retest (lower

part)

Regular Irregular Event-based Time-based Time check All tasks

Number of items 20 20 20 20 10 50

Test session

Version A .37 .64 .40 .66 .64 .78

Version B .29 .76 .41 .74 .39 .71

Retest session

Version A .70 .56 .39 .21 .69 .51

Version B .80 .66 .52 .39 .79 .60

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competence with the experimental procedure. Participants were also faster inperforming Virtual Week at retest session compared to test session, indicatinga learning effect and that the confidence acquired with the experimental pro-cedure during the test session was maintained at the retest session.

Interestingly, no effect of session was found; participants were equallyaccurate at test and retest session independent of the version used. This con-firms our prediction: the improvement in PM performance observed in Exper-iment 1 was done by remembering the content of the PM action from test toretest session. In Experiment 1 the higher improvement was observed in irre-gular time-based tasks, which are the tasks that are new every day (irregularPM task with higher demands on retrospective memory) and with the targetthat required more self-initiated processes to be performed (time-based).Repeating the same task at test and retest session has increased theperformance in older adults in Experiment 1, but when participants performdifferent PM tasks at test and retest session the performance is equivalent(Experiment 2).

As in Experiment 1, an effect of session was found for time-check tasksindicating that participants were more accurate at retest compared to testsession. The time-check task is the more demanding considering that thetarget is non-focal and that is related to “real time”, but it is the task thatgains more from repetition over test and retest sessions. It is possible that par-ticipants became more familiar (and faster) with the experimental procedureand were more able to deal with the PM activity required resulting in thembeing more precise and accurate at the time-check task.

Experiment 2 also reports the results for the recognition test of PM taskcontent, assessing the retrospective memory component of the task. Theassumption is that remembering the content of the PM intention is a necessaryprerequisite for the realisation of PM actions. Interestingly, a number of pre-vious studies have found that older adults fail to carry out intentions despiteremembering their contents upon later questioning (Einstein & McDaniel,1996; Kliegel et al., 2005; Maylor et al., 2002; Mioni et al., 2012; Mioni &Stablum, 2014). Our results are in line with the results of previous findingsand confirm that PM impairment observed in older adults seems to becaused by failure in executing the PM action at the expected moment(lapses of attention; Mioni & Stablum 2014) rather than forgetting thecontent of the PM action. This conclusion is based on the finding that partici-pants were more accurate on the test of recognition of PM content and hadsuperior performance on this index of retrospective memory compared toPM. This suggests that the retrospective memory processes involved inencoding and retention of intention contents are intact, whereas the executiveprocesses underlying self-initiated intention retrieval or execution at theappropriate moment in the future are impaired (Kliegel, Martin, McDaniel,& Einstein, 2002; McDaniel & Einstein, 2000).

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GENERAL DISCUSSION

Adequate PM abilities are necessary for everyday activities such as remem-bering to buy food, attend appointments, pay bills, and take medication.PM impairment is often observed in older adults and in clinical populations(Henry et al., 2004; Kliegel, Jager, Altgassen, & Shum, 2008; Maylor,2008; McDaniel et al., 2008). PM failure can be frustrating and have thepotential to limit the independence of people and force them to rely on a care-giver for prompting. Therefore, it is important to develop reliable tools toevaluate PM performance in clinical populations as well as in healthy olderadults.

In the present study, we compared PM performance at test and retest withVirtual Week (Rendell & Craik, 2000), a well-known PM measure widelyused with healthy older adults and clinical populations (Rendell & Henry,2009). As observed by McDaniel and Einstein (2007) most of the PMmeasures have the limitation of having just a few numbers of specific PMtasks or trials and not being representative of daily life activities (see alsoBurgess et al., 2006; Knight & Titov, 2009). Virtual Week includes a rela-tively large number of PM tasks (10 for each virtual day) and there is emer-ging evidence of it being a reliable indicator of PM function in both clinicaland non-clinical populations (Rendell & Henry, 2009).

In Experiment 1, younger and older participants performed standardVirtual Week twice, 1 month apart. Older adults were less accurate thanyounger participants, confirming an age-related PM decline (Einstein, &McDaniel, 1990; Henry et al., 2004; Kliegel, Jager et al., 2008; Maylor,2008; McDaniel et al., 2008). Moreover, a significant effect of session wasfound, indicating that older adults reduced the time to execute VirtualWeek and were more accurate at retest session. We hypothesised that thehigher improvement observed in older adults was mainly due to rememberingthe content of PM actions from test to retest sessions. Thus, we developed aparallel version (version B) in which only the content of the PM activitieswere different from the standard version (version A) used in Experiment 1.

Experiment 2 was conducted on older adults, half of whom performedversion A at test session and version B at retest session and the rest performedthe reverse condition. Results showed no differences between the two ver-sions at test session indicating that both versions are equivalent, moreover,no effect of session was found, indicating that better performances obtainedin Experiment 1 were mainly due to remembering of the content of PMactions. Older adults still reduced the time to execute Virtual Week indicatingan acquisition of competence with the experimental procedure. Interestingly,in Experiment 2, analyses of retrospective memory were also conducted. Par-ticipants showed better performance when completing the recognition test atthe end of each day compared to the accuracy of completing PM tasks during

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the day. These results seem to indicate that PM dysfunction might be causedby failure to retrieve and execute the intended action at the appropriatemoment rather than forgetting the content of the PM actions (Einstein &McDaniel, 1996; Kliegel et al., 2005; Maylor et al., 2002; Mioni &Stablum, 2014).

In the present study, we found high internal consistency in line with pre-vious studies with Virtual Week (Henry et al., 2007; Mioni et al., 2013;Rendell et al., 2012; Rose et al., 2010) and moderate to high test–retestreliability. The internal consistency was very high in Experiment 1 foryounger (.64 and .83) and for older (.91 and .86) adults. In Experiment 2internal consistency was high for both version A (test ¼ .64 and retest ¼.83) and version B (test ¼ .91 and retest ¼ .86). In Experiment 1, whenusing the same version A, the older adults had a relatively high test–retestreliability (.80) while the young adults had moderate to high test–retest cor-relation (.61). In Experiment 2 that involved only older adults, the test–retestreliability was high (.68), when using versions A and B (or vice versa) at testand retest. Our results are very interesting and the trends are promising. Inlight of the moderate to high test–retest reliability when using version Aand version B, future research should consider changing the PM taskcontent as well as the PM cue for version B. In the current study, the samecue but different content for irregular PM tasks across both versions A andB of Virtual Week, may have caused some interference that reduced the con-sistency across the parallel versions.

The strength of Virtual Week as a measure of PM is the relatively highernumber of specific PM trials and the good reliability, specifically the internalconsistency. A critical feature is the inclusion of PM tasks that vary in theirrelative task demands: regular vs. irregular tasks and time-based vs. event-based. In the context of clinical practice, a differentiated profile of impair-ment on Virtual Week may therefore be informative, not only with regardto degree of PM impairment per se, but also the particular circumstances inwhich PM impairment is more likely to arise (and consequently the mannerin which rehabilitation efforts should be targeted). Also important is theinclusion of the recognition task at the end of each virtual day to investigatethe retrospective memory component of PM performance.

Limitations of Virtual Week might be the use of a computer device and theduration of the session. Regarding the use of a computer device, older partici-pants might be less familiar compared to younger adults, however, computersand technological devices are becoming more common in everyday life andmore older adults are becoming familiar with them (Torres, 2011). In thepresent study, older adults needed more time to run the first virtual days(i.e., Monday and Tuesday) but then they reduced the time to execute eachvirtual day indicating more familiarity and confidence with the experimentalprocedure. The second limitation concerns the duration of the experimental

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session. The standard version used in the present study includes five virtualdays; this version might be too long to be included in a neuropsychologicalevaluation. Clinician should consider using a reduced version (three days)that has already been used with clinical groups and demonstrated goodreliability (Henry et al., 2007; Mioni et al., 2013).

To summarise, the present study was conducted to investigate group differ-ences in PM performance at test compared to retest with Virtual Week. InExperiment 1 younger and older adults were tested with the standardVirtual Week twice, one month apart. Older adults were less accurate thanyounger participants confirming an age-related PM decline. Age-relatedPM decline was attenuated at retest session, in fact the older participantswere as accurate as younger adults. This improvement was hypothesised tobe due to remembering the content of PM action from test to retest session.To investigate this hypothesis two parallel versions were investigated withhalf of the participants undertaking version A at test and version B at retestand the other half completing each version in reverse order (Experiment 2).There were no differences in PM performance between version A and B attest session indicating that the two versions were equivalent. No effect ofsession was found, indicating that the improvement observed in olderadults in Experiment 1 was due to remembering the PM content rather thanparticipants becoming more familiar with the experimental procedure. Theanalysis of recognition task showed that PM impairment observed in olderadults is mainly due to failure in executing the PM action at the expectedmoment rather than forgetting the content of the PM action. Our resultsalso confirmed that Virtual Week is a good measure to investigatePM performance. The study also provides promising evidence of relativelyhigh internal consistency (McDaniel & Einstein, 2007; Rose et al., 2010)and test reliability.

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