APPLIED COGNITIVE PSYCHOLOGY
Appl. Cognit. Psychol. 19: 1177–1197 (2005)
Published online 13 September 2005 in Wiley InterScience
(www.interscience.wiley.com) DOI: 10.1002/acp.1154
The Intention Interference Effect and Aging: Similar
Magnitude of Effects for Young and Old Adults
ANNA-LISA COHEN1*, ROGER A. DIXON2
and D. STEPHEN LINDSAY3
1
New York University, USA
University of Alberta, Canada
3
University of Victoria, Canada
2
SUMMARY
In young adults, intentions have been shown to be more accessible (e.g. faster reaction times and
higher accuracy) compared to other sorts of to-be-remembered information, a result termed an
‘intention superiority effect’ (Goschke & Kuhl, 1993). In the current study, we assessed whether
older adults also demonstrate this superiority of intention-related material and we used a new
interference paradigm to examine performance. On each trial, participants performed a Stroop-like
colour-naming task on a short series of words, including words related to an intention that they
encoded at the beginning of the trial. In Experiment 1, results revealed an ‘intention interference
effect’ for both young and older adults in which performance was slower for words belonging to an
intention that participants intended to carry out versus an intention that did not have to be executed.
In Experiment 2, we tested the effect that completing an intention had on the representation of
intentions. For both groups, completing an intention led to a decrease in interference in Stroop task
performance. Copyright # 2005 John Wiley & Sons, Ltd.
Everyday life is filled with stimuli that remind us that there is a goal that needs to be
carried out (e.g. driving by the store cues the memory that we meant to buy milk). In this
example, an intention was encoded and then postponed until the time for its execution
arrived or when the appropriate conditions pertained. This is termed prospective memory.
Numerous factors are thought to contribute to the success or failure of remembering to
carry out our actions. Successful goal completion is a fundamental part of everyday
functioning and failures can undermine our competence and ability to operate independently. That is, forgetting to turn off a stove or take medication can have devastating
consequences. Therefore, prospective memory functioning is a topic of interest in older
adult populations, although results pertaining to adult age differences in prospective
memory performance are conflicting. Some studies report no deficits for older adults
*Correspondence to: Anna-Lisa Cohen, Department of Psychology, New York University, 6 Washington Place,
7th Floor, New York, NY 10003, USA. E-mail: [email protected]
Contract/grant sponsor: Natural Sciences and Engineering Research Council of Canada.
Contract/grant sponsor: National Institutes of Health (National Institute on Aging); contract/grant number:
AG08235.
Copyright # 2005 John Wiley & Sons, Ltd.
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whereas others describe significant age-related differences (e.g. see Henry, MacLeod,
Phillips, & Crawford, 2004, for a review). This conflict may partly be due to older adults’
tendency to use everyday external memory aids such as notes and reminders to
compensate for declining memory performance (Dixon, de Frias, & Bäckman, 2001).
Compensatory mechanisms from a variety of sources are potentially available in late life
which can help mitigate age differences in memory functioning (Dixon & Bäckman,
1999). However, in some situations their availability may be limited due to environmental
constraints. For this reason, it is important to examine prospective remembering in
controlled laboratory settings.
Past research (e.g. Goschke & Kuhl, 1993; Marsh, Hicks, & Bink, 1998; Marsh, Hicks,
& Bryan, 1999) showed that information related to intentions was highly accessible
compared to information that was not future-oriented. For example, results revealed that
undergraduate participants showed faster and more accurate responding to material that
was intended for some future activity compared to material that was not future-oriented.
This phenomenon was termed the ‘intention superiority effect’ (Goschke & Kuhl, 1993).
In the typical paradigm, participants are asked to memorize written descriptions of two
activities. Then, participants in an ‘execute’ condition are informed that they will have to
execute one of these activities (e.g. setting a table) later, whereas those in an ‘observe’
condition only observe the experimenter carrying out the task. Then participants from both
conditions receive a recognition memory test or lexical decision task that includes words
from both scripts. Experimenters assume that the time it takes to match a probe item with
its match in long term memory is inversely related to accessibility of that representation
(Anderson, 1983). Consistent with that idea, results have shown faster reaction times for
items related to the to-be-executed task.
As mentioned earlier, a significant number of studies show that older adults have
pronounced difficulty with remembering to carry out intentions (e.g. Cherry & Plauche,
2003; Cohen, Dixon, Lindsay, & Masson, 2003; Cohen, West, & Craik, 2001; McDaniel,
Einstein, Stout, & Morgan, 2003). Among various proposed explanations for age
differences, West and Craik (1999) suggested that after encoding, intentions may
momentarily fall below consciousness and fluctuate over the course of task performance.
They found that it was difficult for older adults to maintain the cue-action schema in an
activated state and this led to a greater proportion of instances of forgetting. Furthermore,
Maylor (1996) claimed that the retention interval may be particularly vulnerable to agerelated disruption for three reasons: (1) holding an intention in mind is more likely to
exceed the working memory capacity of older adults than of younger adults, (2) older
adults may be more vulnerable to interfering information, and (3) the retention interval can
be viewed as a type of dual task in which the intention is held in mind while other activities
are carried out. Ellis (1996) suggested that failures to carry out a previously encoded
intention were associated with a low frequency of recollections of that intention during
retention intervals. Therefore, failures in prospective memory were thought to occur due to
an inability to maintain an intention throughout the retention interval of the task. Craik and
Kerr (1996) discussed this same phenomenon in terms of momentary lapses of intentions
(MLIs). They defined MLIs as lapses that occur when intentions in short-term retention
intervals drop from awareness. Craik and Kerr suggested that during the retention interval
older adults may become more absorbed in an ongoing task than younger adults,
disrupting performance on the prospective memory task. These lapses are suggested to
occur because intentions are difficult to maintain in mind in the midst of other attention
demanding ongoing activities.
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Based on these speculations regarding older adults’ prospective memory failures, it is
plausible that older adults may have trouble maintaining intention information in a
heightened state. That is, once an intention has been encoded the representation that
there is ‘something to do’ may fall below some theoretical threshold that causes
difficulty in prospective memory performance. In the current study, we investigated
whether older adults exhibit an intention superiority effect similar to younger adults or
whether the absence of an intention superiority effect could help to further the
understanding of prospective memory functioning. The only two studies that have
explored this question is one by Maylor, Darby, and Della Sala (2000) who used a
naturalistic paradigm to examine the accessibility of naturally occurring intentions. In
their study, young and older adults were asked to generate lists of intended or completed
activities. Results showed that younger adults were able to generate more intended
activities displaying a type of superiority for this information, however older adults
failed to show superiority for this future-oriented material. In the Freeman and Ellis
(2003) study, young and old participants were told after encoding a list of action
words (e.g. bow, knock) that they would have to either verbally report or physically
enact these test items. Similar to results by Goschke and Kuhl (1993), an intervening
recognition memory test yielded faster latencies for to-be-executed items for both
young and older adults (i.e. an intention superiority effect). Therefore, these two studies
yielded conflicting results such that older adults failed to show an intention superiority
effect in the Maylor et al. (2000) study but exhibited one in the Freeman and Ellis
(2003) study.
Therefore, a first objective was to simply examine whether older adults would exhibit
superiority for intention-related information and to introduce a novel paradigm for
investigating this phenomenon. In all of the previously mentioned studies, facilitation
paradigms were used to show that attending selectively to relevant stimuli facilitates
performance on certain tasks that benefit from the processing of that information. Another
method of demonstrating attentional bias is to show that performance can suffer as a result
of attending selectively to relevant stimuli where the processing of that information leads
to disruption of performance (i.e. interference paradigms). The current research used an
interference paradigm to assess automatic influences of delayed intentions. Specifically,
we used a Stroop (1935) colour-naming task (for review, see MacLeod, 1991). If we
demonstrate that participants are influenced by the presence of the embedded words from
the intention while they are attempting to ignore their influence, we have a demonstration
of an intention interference effect.
In Experiment 1, we tested younger and older adults on a Stroop task that investigated
whether intention-related material will show more interference compared to material that
was not intention-related (i.e. an intention interference effect). The logic was that
intention-related material that has not been completed will have an increased accessibility
in mind that will lead to the activation of its semantic meaning leading to greater
interference with colour naming. In Experiment 2, we tested the effect that completing
an intention has on the representation of intentions. We were interested in testing the idea
that a completed task no longer ‘needs’ to be in a heightened state because the action has
already been executed. If older adults have difficulty discarding no-longer-relevant
information from working memory (Hasher & Zacks, 1988; Hasher, Zacks, & Rahal,
1999; Lustig, May, & Hasher, 2001), then one would expect that older adults would show
an intention interference effect because they would be unable to ‘delete’ this information
from working memory.
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EXPERIMENT 1
In this study, we tested whether words related to intentions that are to be enacted caused
more interference than control words when they are embedded within a Stroop task. On
each of a number of trials, subjects read a description of an action (e.g. ‘Place the marble
inside the plastic bag’) and were then given instructions to either prepare to ‘Do the Task’
or to ‘Forget the Task.’ Following this instruction (and before they carried out the task on
‘Do the Task’ trials), participants received a brief Stroop word list that included three
critical words from the intention (e.g. ‘marble,’ ‘plastic,’ ‘bag’). We predicted that
participants would exhibit significantly longer latencies for colour naming of critical
words belonging to ‘Do the Task’ trials versus critical words belonging to ‘Forget the
Task’ trials.1
Method
Participants
Twenty-eight young adults (range ¼ 17 to 30 years; M ¼ 19.29 years, SD ¼ 2.79) and 24
older adults (range ¼ 56 to 77 years; M ¼ 69.71 years, SD ¼ 5.83) participated in the
experiment. A one-way analysis of variance (ANOVA) revealed that older adults had
significantly more years of education (range ¼ 11 to 19 years; M ¼ 14.17, SD ¼ 2.41)
compared to young adults (range ¼ 12 to 16 years; M ¼ 12.68 years, SD ¼ 1.16),
F(50) ¼ 8.45, p < 0.05. Self-reported health was measured using a 5-point Likert
scale. Participants were asked to reflect on their health in the last month and then rate
themselves on a 5-point scale (1 ¼ very good, 2 ¼ good, 3 ¼ fair, 4 ¼ poor, 5 ¼ very poor).
Results showed that young adults (M ¼ 1.54, SD ¼ 0.58) did not differ from older adults
(M ¼ 1.54, SD ¼ 0.66) in their levels of self-reported health (F < 1).
Undergraduate students participated in exchange for optional extra credit in an
introductory psychology course. The older participants were recruited from a volunteer
pool maintained by the laboratory of Roger Dixon at the University of Victoria. These
community-dwelling participants were reimbursed for their travel expenses (e.g. bus fare,
parking). One younger adult failed to follow instructions properly and was excluded from
analyses.
Design and materials
The design was a 2 (Age: young, old) 3 (Word Type: critical, neutral, colour) 2
(Instructions: do the task, forget the task) mixed factorial design with age as the betweensubject variable and Word Type and Instructions as the within-subject variables. On each
of 24 trials, the participants (a) received an action task (e.g. ‘Place the marble inside the
plastic bag’), (b) received instructions to the effect that they would later ‘do the task’ (12
trials) or that they could ‘forget the task’ (12 trials), (c) named the colour of a series of
words presented on a computer screen, and (d) were tested on the delayed intention task.
The Stroop task used seven colours (i.e. red, blue, green, yellow, pink, white, and black). In
each 24-item Stroop list the three critical words from the action task (e.g. ‘marble,’
1
It is important to note that the participant was prompted by the experimenter to recall the intention and therefore
we cannot claim that this task is prospective in this respect. However, it was a necessary limitation to the paradigm
and did not detract from our main objective which was to observe the effect that holding an intention in mind has
on behaviour.
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Intention interference
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‘plastic,’ and ‘bag’) were embedded in a mixture of 13 novel control words and eight
congruent colour-name words (one or two tokens of each of the seven colours used in the
experiment). Control words were matched to critical words as closely as possible in terms
of frequency and concreteness (based on norms in the MRC psycholinguistic data base).
The dependent variable was response latency of correct colour-naming responses. The
stimuli were approximately 10 14 mm. Words were presented in lower case in the centre
of the screen. See Appendix A for a list of the 24 task phrases.
Procedure
Participants were tested individually in 45-min sessions. They were tested on an IBMcompatible personal computer using the Micro-Experimental Laboratory Professional
software package (Schneider, 1988). Participants were seated in front of the computer
monitor with the experimenter sitting off to one side. The study was described to
participants by the experimenter and participants also read instructions on the computer
screen outlining the requirements of the study. After giving informed consent, participants
were given a short training phase to ensure that the instructions for the primary task were
clearly understood. The instructions were as follows:
In this study, you will receive a series of short instructions to perform certain activities
(‘Peel the orange and place in trash’) and after this you will receive further instructions
to either ‘DO THE TASK’ or ‘FORGET THE TASK.’ In the trials where you are asked
to DO THE TASK, you will actually carry it out and in the trials where you are told to
FORGET THE TASK, you will not have to carry it out. In between these instruction
trials, you will receive word lists in which your task is simply to read out as quickly as
possible the colour of the font in which a word is presented. (This serves as an interlude
between the instruction trials.) Please try to repeat back to me the instructions in your
own words to show that you understand them.
The experimenter calibrated the microphone for each individual before the experiment
began so that it was sensitive to each person’s vocal responses. Participants were then
given a short training phase to ensure that they had understood the instructions. See
Appendix B for a schematic of the task procedure.
Training phase. The experimenter showed the participant a white 12.5 cm 20 cm card
on which the sentence ‘Draw a large circle on the notepad’ was printed in black size 24font. Participants were asked to read the sentence out loud. Then the card was turned over
to reveal a new card that had either of two instructions printed on it: ‘do the task’ or ‘forget
the task.’ The experimenter explained to participants that if the instruction printed on
the card was ‘do the task,’ then they would be asked to execute the task and if the
instruction printed on the card said ‘forget the task,’ then they would not have to execute
the task. (For the practice trial, participants were instructed to ‘do the task’.) Therefore, in
the practice trial participants were told that they would have to carry out the task of
‘drawing a large circle on the notepad,’ but only after they performed a short colournaming task (i.e. the Stroop task). Immediately after receiving these instructions to ‘do the
task,’ and before they carried it out, participants performed a brief Stroop task consisting
of 10 words (four colour-name words randomly intermixed with six control words). For
the Stroop task, participants were instructed say aloud into the microphone as quickly as
possible the colour of the font in which each word was presented on the computer screen
while ignoring the meaning of the words.
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Following the last word in the Stroop list of the training phase, the participant was asked,
‘is there anything you are supposed to do?’ At this point, the individual was required to
respond with ‘I am supposed to draw a large circle on the notepad’ and then carried out the
task using the relevant materials. The experimenter asked the participant if they had any
questions before the experimental phase commenced.
Experimental phase. In the experiment, there were 24 trials in total with 12 being ‘do the
task’ trials and the remaining 12 being ‘forget the task’ trials. The ordering of ‘do the task’
and ‘forget the task’ trials was in 12 random fixed orders that were counterbalanced across
participants. Immediately after the presentation of the do/forget instruction, participants
engaged in the Stroop task, which consisted of eight congruent colour-name words, 13
control items, and three task-related critical items, randomly intermixed with the
constraints that the critical items occur (a) in the order in which they appeared in the
task instruction, (b) between trials six and 19 of the Stroop task, and (c) with at least one
control item between each critical item. The assignment of trials to the ‘forget the task’
versus ‘do the task’ conditions was counterbalanced across participants.
Figure 1. Schematic for ‘Do the task’ and ‘Forget the task’ conditions
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On completion of the Stroop task, participants were asked, ‘Is there anything you are
supposed to do?’ If they had been given a ‘do the task’ instruction, participants were
required to carry out the task and if they had been given a ‘forget the task’ instruction, they
were required to respond, ‘No, there is nothing I am supposed to do.’ For each of the 25
intentions (including the practice trial) the relevant objects were placed on a table to the
right of the participant, such that the materials were within easy reach but not within direct
view of the participant. Following each Stroop list, the subject had to turn around to a table
that had over 50 objects on it. The subject’s goal was to locate the materials for the relevant
action phrase (if it were a ‘do the task’ trial) and perform the correct action phrase.
Participants rarely made mistakes remembering the short instruction (e.g. Draw a circle on
the notepad) or whether they were supposed to do/forget the task because of the short
duration of the Stroop task (i.e. only 24 words). Most participants commented, after
several trials, on the fact that task-related words were appearing on the Stroop lists; the
experimenter reminded them that their aim in the Stroop task was simply to name the
colours as quickly as possible and told them that ignoring the words and attending to
colour would help them perform well on the colour-naming task. See Figure 1 for a
schematic of the experimental design.
Results and discussion
Following Marsh et al. (1998), all incorrect responses were removed from analyses of the
Stroop data and latencies beyond three standard deviations of each participant’s mean
response or less than 300 ms were also deleted. Because Stroop lists were short in length
(24 words) and there were no incongruent colour words, accuracy was very high resulting
in little data being removed. The result was the overall removal of on average 0.43% of all
responses as errors and 0.86% as outliers. By age group, this resulted in young adults
having 0.30% as errors removed and 0.52% as outliers and older adults having 0.56% as
errors and 1.2% as outliers removed. Participants had to recall the intention after each
Stroop list, therefore, recall of intentions for both age groups was very high and
performance did not differ significantly (Young, 97%, Old ¼ 94%).
Reaction time performance was evaluated using a 2 (Age Group: young, old) 2
(Instructions: do the task, forget the task) 3 (Word Type: critical, neutral, colour)
mixed factorial ANOVA with repeated measures on the second and third factors. There
was a main effect of age group, F(1, 50) ¼ 29.01, p < 0.001, 2 ¼ 0.37, revealing that
reaction time was significantly faster for younger adults (M ¼ 651.79 ms, SD ¼ 93.50)
than for older adults (M ¼ 771.06 ms, SD ¼ 81.54). However, Age group did not
interact with any other factors (all Fs < 1.43, ps > 0.24). The cell means are displayed
in Table 1. A power analysis was conducted to determine whether there was sufficient
power to detect an effect for: (1) the age by word type interaction and, (2) the age by
instructions interaction. We used a small-to-medium effect size (f2 ¼ 0.10) in these
analyses as it would provide a more rigorous test than using a medium or large effect
size. Results revealed that the power was 0.76 to obtain a small-to-medium effect size
for an age by word type interaction with an alpha level of 0.05 indicating sufficient
power to detect this effect even with a fairly small effect size. We did a similar power
analysis to examine whether there was sufficient power to detect an interaction between
age and instructions and the analysis revealed that power was 0.67 to obtain a small-tomedium effect size with an alpha level of 0.05 indicating decent power to obtain a small
effect (Buchner, Erdfelder, & Faul, 1997).
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Table 1. Mean response latencies and standard deviations for performance on the Stroop task as a
function of instructions and word type
Do the Task
M
Young
Critical
Neutral
Colour
Old
Critical
Neutral
Colour
Forget the Task
SD
M
SD
747.05
683.29
555.24
(141.20)
(95.89)
(61.65)
702.40
671.44
551.31
(118.04)
(94.78)
(65.55)
875.10
797.41
673.14
(104.09)
(70.28)
(88.29)
836.15
792.61
651.96
(78.20)
(71.16)
(77.24)
Analyses revealed a main effect of Instructions, F(1, 50) ¼ 22.52, p < 0.001, 2 ¼ 0.31
showing that performance was slower in ‘Do the Task’ (M ¼ 721.87 ms, SD ¼ 109.57)
compared to ‘Forget the Task’ (M ¼ 700.98 ms, SD ¼ 103.87 ) trials. There was a main
effect of Word Type, F(2, 49) ¼ 144.09, p < 0.001, 2 ¼ 0.86. Pairwise comparisons
revealed that responses were faster to colour words (M ¼ 607.92 ms, SD ¼ 90.96), than
to neutral words (M ¼ 736.19 ms, SD ¼ 102.84) which were faster than critical words
(M ¼ 790.17 ms, SD ¼ 126.36). Most interestingly, the interaction between Instructions
and Word Type was significant, F(2, 49) ¼ 6.85, p < 0.01, 2 ¼ 0.22, suggesting that there
was a greater difference between latencies for critical items in the ‘Do the Task’ and
‘Forget the Task’ conditions than for control or colour items (see Figure 2). Because we
were most interested in the critical item versus neutral control item comparison for ‘do’
Figure 2. Reaction time performance on the Stroop task in Experiment 1 as a function of Word Type
and Instructions. Bars represent standard error
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versus ‘forget’ conditions, we collapsed across age group and conducted a 2 (Instructions:
do the task, forget the task) 2 (Word Type: critical, neutral) ANOVA to examine whether
an interaction would be found. The interaction was significant, F(1, 50) ¼ 14.0, p < 0.001,
2 ¼ 0.22, showing that there was a greater difference between latencies for critical items
in the ‘Do the Task’ and ‘Forget the Task’ (Critical/Do: M ¼ 811.01 ms, SD ¼ 131.62;
Critical/Forget: M ¼ 764.13 ms, SD ¼ 121.10) conditions than for neutral control items
(Neutral/Do: M ¼ 740.35 ms, SD ¼ 101.96; Neutral/Forget: M ¼ 732.03 ms, SD ¼ 103.73).
This analysis showed that words related to intentions that were to be executed were more
difficult to ignore than words from intentions that were not to be executed.
The next analysis was conducted to examine whether there was any variation in the
latencies for individual critical items for each intention. There were three critical items
belonging to an intention that always appeared in the Stroop list. We were interested in
whether response latencies for the three critical items varied as a function of their order in
the Stroop list or as a function of Instructions. Reaction time performance was evaluated
using a 2 (Age Group: young, old) 2 (Instructions: do the task, forget the task) 3
(Critical Item Order: first, second, third) mixed factorial ANOVA with repeated measures
on the second and third factors. There was the expected main effect of Age Group,
F(1, 50) ¼ 20.34, p < 0.001, 2 ¼ 0.29, revealing that reaction time was significantly faster
for younger adults (M ¼ 724.78 ms, SD ¼ 131.39) than for older adults (M ¼ 855.34 ms,
SD ¼ 111.48). There was a main effect of Instructions, F(1, 50) ¼ 21.13, p < 0.001, 2
¼ 0.30 showing that performance was slower in ‘Do the Task’ (M ¼ 810.90 ms,
SD ¼ 143.51) compared to ‘Forget the Task’ (M ¼ 769.22 ms, SD ¼ 133.56) trials. Interestingly, a significant interaction was found between Instructions and Critical Item Order,
F(1, 100) ¼ 3.64, p < 0.05, 2 ¼ 0.07, revealing that there was a greater difference
between latencies for critical item order for the ‘do the task’ instructions than for the
‘forget the task’ instructions. Pairwise comparisons showed that for ‘do the task’ trials
there was a reliable difference between latencies for critical words that appeared in the first
position (M ¼ 782.72 ms, SD ¼ 127.34) in the Stroop list compared to critical words that
appeared in the second position (M ¼ 831.14 ms, SD ¼ 157.34). There was also a
significant difference between critical words appearing in the first position compared to
those appearing in the third position (M ¼ 818.84 ms, SD ¼ 145.85).
To sum up, inspection of Figure 3 shows that reaction times on the first critical item
were comparable in the ‘Do’ and ‘Forget’ conditions, but reaction times on the subsequent
critical items increased substantially among subjects in the ‘Do’ condition (while staying
constant for those in the ‘Forget’ condition). There were no significant interactions with
age in any of the analyses. Our results imply that information that is held in mind with the
intention to be carried out has an advantage over information that is not future-oriented.
The magnitude of this effect (40 ms) was similar to the intention superiority effect found
by other researchers (e.g. Goschke & Kuhl, 1993; Marsh et al., 1998). Therefore,
enhancing critical words through linking them to an intention appears to increase their
power to interfere with colour naming. Even more interestingly, there were no interactions
with age group—older adults exhibited the same pattern of performance (albeit slower
overall) as young adults. That is, older adults displayed an intention interference effect
similar in magnitude to younger adults. This result is the first known demonstration of a
laboratory intention superiority effect in an older adult age group and its presence has
several implications for theory building in prospective memory and aging. In contrast to
our results, Maylor et al. (2000) demonstrated age differences in a naturalistic paradigm
such that younger adults exhibited an intention superiority effect but older adults did not.
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Figure 3. Reaction time performance on the Stroop task in Experiment 1 as a function of Critical
Item Order and Instructions. Bars represent standard error
However, there were several significant methodological differences in the way that item
accessibility was tested. For example, in the first study, middle aged and older aged
participants were told that they would be given a category and they were to write down as
many instances as possible of that category. The two categories were ‘performed tasks’
(i.e. jobs, appointments, things that have been done in the last few days) and ‘to-beperformed tasks’ (i.e. jobs, appointments, things you intend to do in the next few days).
Results showed that middle aged adults retrieved more to-be-performed tasks than
performed tasks (intention superiority effect) and older adults retrieved more performed
tasks than to-be-performed tasks (intention inferiority effect). Freeman and Ellis (2003)
used recognition memory latencies to examine whether this advantage for to-be-enacted
material is reduced in older adults. Similar to our findings, both young and older adults
exhibited equivalent accessibility (faster recognition latencies) for items that were to-beperformed versus items that were to be verbally reported. Thus, it may be that
methodological differences account for the different outcome (age differences) in the
Maylor et al. (2000) study compared to the current study and that of Freeman and Ellis
(2003).
A significant interaction was found between Instructions and Critical Item Order
showing a greater difference between order of critical words for ‘do the task’ than for
‘forget the task’ trials. It may be that this pattern of interference reveals a case in which the
first critical item acts as a retrieval cue for the remaining second and third critical items.
When participants believe that they will have to carry out the task, it may be that the notion
that there is ‘something to do’ is brought to mind after the first critical word acts as a cue or
intentional marker. Our results on critical item order suggest that when individuals have an
intention in mind and encounter environmental information related to that intention (e.g.
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Intention interference
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the first critical word in the list), it acts as a cue to bring other intention-relevant words to
mind in ways that slow colour-naming responses to those subsequent critical words.
The findings of Experiment 1 do not support the hypothesis that inhibition declines with
age, because older adults benefited from the ‘forget’ instructions just as much as did young
adults. Experiment 2 provided a more powerful test for an age-related inhibition deficit by
comparing Stroop colour-naming performance before versus after participants performed
tasks. Thus, on ‘before’ trials participants had not only read the task instruction (e.g. Place
the marble in the plastic bag) but had also selected the materials for and actively performed
that task immediately before doing the Stroop task. From a prospective memory
perspective, the task had been completed and could therefore be forgotten, but if older
adults have difficulty putting thoughts out of mind then the extensive processing of the task
in the ‘before’ trials should leave older adults vulnerable to interference from critical items
on the Stroop task. Therefore, in the next experiment, we were interested in examining the
effect that completing an intention had on young and older adults’ Stroop performance.
EXPERIMENT 2
A major theoretical viewpoint of normal aging posits that older adults are deficient with
respect to the ability to inhibit or ignore irrelevant information (Hasher et al., 1999). The
main thrust of this theory is that older adults have difficulty discarding no-longer-relevant
information from working memory. If this were the case, one would expect that when
older adults completed an intention and therefore no longer needed to keep it in mind—
they would still show an intention interference effect because they were unable to ‘delete’
this information from working memory. Therefore, in this experiment, we were interested
in examining the hypothesis that older adults would not show this decrease in activation
level for critical items belonging to already completed intentions due to an age-related
inhibition deficit (e.g. Hasher et al., 1999).
The procedure was similar to the procedure for Experiment 1 except that participants
read the description of the intention (e.g. place the marble in the plastic bag) and then they
were instructed to either perform the task ‘NOW’ or ‘LATER.’ In 12 of the ‘NOW’ trials,
participants completed the intention before the Stroop list. And in the 12 LATER trials,
participants completed the intention after the Stroop task. The prediction was that when
participants had to complete the intention after the Stroop task, they were required to hold
the information in mind, therefore it would be more difficult to ignore the semantic content
of critical words leading to increased interference for colour naming. In contrast, in the
NOW trials, participants complete the intention before the Stroop task; therefore they
should experience less interference because there is no need to hold the intention in mind.
Thus, the prediction was that there would be longer latencies for colour naming of critical
items in LATER trials compared to NOW trials in which participants had already executed
the intention. We were especially interested in investigating whether this effect would be
equivalent for young and older adults.
Method
Participants
Twenty-four young adults (range ¼ 18 to 34 years; M ¼ 19.67 years, SD ¼ 3.37) and 24
older adults (range ¼ 62 to 78 years; M ¼ 69.54 years, SD ¼ 4.96) participated in the
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experiment. Years of education were analysed with a one-way ANOVA to reveal that older
adults had significantly more years of education (range ¼ 10 to 20 years; M ¼ 14.83 years,
SD ¼ 2.73) compared to young adults (range ¼ 12 to 16 years; M ¼ 12.96 years,
SD ¼ 1.27), F(46) ¼ 9.32, p < 0.05. Self-reported health was once again measured using
a 5-point Likert scale. Participants were asked to reflect on their health in the last month
and then rate themselves on a 5-point scale (1 ¼ very good, 2 ¼ good, 3 ¼ fair, 4 ¼ poor,
5 ¼ very poor). Analyses revealed that young adults (M ¼ 1.88, SD ¼ 0.54) did not differ
from older adults (M ¼ 1.67, SD ¼ 0.76) in their levels of self-reported health (F < 1).
Participants were tested individually with each testing session lasting approximately
45 min. Undergraduate students participated in exchange for optional extra credit in an
introductory psychology course. Older adults were recruited from the same volunteer pool
used in Experiment 1, but those tested in the previous experiment were excluded from
participation in Experiment 2. Participants were reimbursed for any travel expenses (e.g.
bus fare, parking). One older adult failed to follow instructions and was excluded from
analyses.
Materials and procedure
The materials for Experiment 2 were exactly the same as those used in Experiment 1
except for the Instruction phase. After reading the intention, participants received
instructions to either complete the task ‘NOW’ (12 trials) or ‘LATER’ (12 trials). Across
the 24 trials, order of the ‘Now/Later’ instructions was in 12 random fixed orders that were
counterbalanced across participants.
The procedure in Experiment 2 was identical to that of Experiment 1 except for the
following change. As in Experiment 1, participants were asked to read the description of
the intention (e.g. Place the marble in the plastic bag) but then they were given instructions
to either complete the intention ‘NOW’ or ‘LATER.’ In 12 of the ‘NOW’ trials, they
completed the intention before the Stroop list. And in 12 LATER trials, they completed the
intention after the Stroop task. The instructions were as follows:
Sometimes in life, we have to remember to carry out a task immediately and at other
times we have to remember to carry out a task later. In this study, you will receive a
series of short instructions to perform certain activities (e.g. Draw a large circle on the
notepad). After this, you will receive further instructions to either do the task NOW or
do the task LATER. In the trials where you are asked to do the task NOW, you will
actually carry it out immediately. In trials where you are asked to do the task LATER,
you will actually carry out the task later after you have performed a computer task.
In the computer task, you will receive word lists in which your task is simply to read
out as quickly as possible the colour of the font in which a word is presented. (This
serves as an interlude between the instruction trials.) Please try to repeat back to me the
instructions in your own words to show that you understand them.
Results and discussion
All incorrect responses were removed from analyses of the Stroop data. Once again,
accuracy was very high resulting in little data being removed. The result was the removal
of on average 0.49% of all responses as errors (young ¼ 0.37%, old ¼ 0.61%). Latencies
beyond three standard deviations of each participant’s mean response or less than 300 ms
were also deleted, which was true for less than 0.97% of the data (young ¼ 0.63%,
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Table 2. Mean response latencies and standard deviations for performance on the Stroop task as a
function of instructions and word type
Now
M
Young
Critical
Neutral
Colour
Old
Critical
Neutral
Colour
Later
SD
M
SD
722.27
686.37
572.06
(99.12)
(83.84)
(63.48)
770.76
712.30
593.64
(132.83)
(91.42)
(70.36)
770.61
739.88
628.54
(80.99)
(70.59)
(79.71)
810.45
758.16
631.82
(109.04)
(70.08)
(84.87)
old ¼ 1.31%). Once again, recall of intentions for both age groups was high and
performance did not differ significantly (Young, 96%, Old ¼ 95%).
Response latencies were evaluated using a 2 (Age Group) 3 (Word Type) 2
(Instructions) mixed factorial ANOVA with repeated measures on the second and third
factor. Results yielded a main effect of Age Group, F(1, 46) ¼ 4.15, p < 0.05, 2 ¼ 0.08,
showing that reaction time performance was significantly faster for younger
(M ¼ 676.23 ms, SD ¼ 93.50) than for older adults (M ¼ 723.24 ms, SD ¼ 81.54). A
main effect of Word Type was observed, F(2, 92) ¼ 221.94, p < 0.001, 2 ¼ 0.83. Pairwise
comparisons showed that colour naming was fastest for colour words (M ¼ 606.52 ms,
SD ¼ 78.14), which were faster than neutral words (M ¼ 724.18 ms, SD ¼ 82.57), which
were faster than critical words (M ¼ 768.52 ms, SD ¼ 107.35). There was a main effect of
Instructions, F(1, 46) ¼ 32.20, p < 0.001, 2 ¼ 0.41 showing that performance was slower
in ‘Later’ (M ¼ 712.85 ms, SD ¼ 95.07) compared to ‘Now’ (M ¼ 686.62 ms, SD ¼ 83.63)
trials. See Table 2 for mean response latencies for all cells.
An interaction between Word Type and Instructions was observed, F(2, 92) ¼ 13.85,
p < 0.001, 2 ¼ 0.23 revealing a similar pattern of results to those found in Experiment 1
(see Figure 4). As in the previous experiment, we were most interested in the critical item
versus neutral control item comparison for ‘now’ versus ‘later’ conditions. In the next
analysis, we collapsed across age group and conducted a 2 (Instructions: now, later) 2
(Word Type: critical, neutral) ANOVA to examine whether an interaction would be found.
The interaction was significant, F(1, 47) ¼ 10.43, p < 0.01, 2 ¼ 0.18, showing that there
was a greater difference between latencies for critical items in the ‘now’ and ‘later’
(Critical/Now: M ¼ 746.44 ms, SD ¼ 92.81.62; Critical/Later: M ¼ 790.61 ms,
SD ¼ 121.88) conditions than for neutral control items (Neutral/Now: M ¼ 713.12 ms,
SD ¼ 81.30; Neutral/Later: M ¼ 735.23 ms, SD ¼ 83.84). This analysis showed that
words related to intentions that were to be executed were more difficult to ignore than
words from intentions that were not to be executed.
Inspection of the means show that there was a greater difference between latencies for
critical items in the ‘Now’ and ‘Later’ conditions than for neutral or colour items.
Therefore, results showed there were longer latencies for colour naming of critical items in
LATER trials compared to NOW trials in which participants had already completed the
intention. There were no interactions with Age Group (all Fs < 1.56, ps > 0.22). Once
again, a power analysis was conducted and it indicated that the power was 0.57 to detect a
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Figure 4. Reaction time performance on the Stroop task in Experiment 2 as a function of Word Type
and Instructions. Bars represent standard error
small-to-medium effect size for an interaction between age and word type and the power
was 0.56 to detect a small-to-medium effect size for an interaction between age and
instructions.
Additional analyses were conducted to examine whether a similar pattern of findings of
critical item order would emerge as found in Experiment 1. Reaction time performance
was evaluated using a 2 (Age Group: young, old) 2 (Instructions: Now, Later) 3
(Critical Item Order: first, second, third) mixed factorial ANOVA with repeated measures
on the second and third factor. There was no main effect of Age Group (p ¼ 0.14).
However, there was a main effect of Instructions, F(1, 46) ¼ 28.24, p < 0.001, 2 ¼ 0.38,
showing that colour naming was slower in ‘Later’ (M ¼ 790.62 ms, SD ¼ 132.51)
compared to ‘Now’ (M ¼ 746.11 ms, SD ¼ 102.54) trials. There was also a main effect
of Critical Item Order, F(2, 92) ¼ 3.56, p < 0.05, 2 ¼ 0.07. Pairwise comparisons revealed
that latencies for critical items in the first position in the Stroop list (M ¼ 754.35 ms,
SD ¼ 116.15) were significantly shorter than latencies for critical items in the second
(M ¼ 773.71 ms, SD ¼ 118.71) and third positions (M ¼ 777.02 ms, SD ¼ 117.73), with no
significant difference between second and third position critical items (see Figure 5). The
interaction between Instructions and Order was not significant (F < 1) nor were there any
interactions with Age Group (F < 1).
Our first analysis demonstrated that interference decreased when participants completed
the intention before the Stroop task relative to trials in which participants completed the
intention after the Stroop list. In a study by Marsh et al. (1998), they demonstrated an
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Figure 5. Reaction time performance on the Stroop task in Experiment 2 as a function of Critical
Item Order and Instructions. Bars represent standard error
intention superiority effect similar to Goschke and Kuhl (1993) using a lexical decision
task (LDT). In Experiment 3, participants had to perform activities from two scripts and in
one case they performed the script before the LDT and in the other case they performed the
script after the LDT. Reaction times for LDT performance were faster for information
from scripts that had not been carried out compared to information from scripts that had
been carried out. Marsh et al. (1998) explained their finding by suggesting that after an
action has already been executed, the representation of the intention is inhibited and no
longer in a heightened state. Thus, the representation loses its privileged status in memory
leading to inhibition of this material.
An important difference between results obtained in this experiment and those obtained
by Marsh et al. (1998) is that in our paradigm performance in the ‘now’ condition did not
go below the neutral baseline. That is, performance in the ‘now’ trials was characterized
by a decrease in interference but response latencies did not go below the neutral baseline.
In contrast, in the experiment conducted by Marsh et al. (1998), results showed that the
latencies for the execute script were longer than those for the neutral script when the LDT
was administered after participants had already executed the scripts. An explanation for
the absence of this inhibition result in our study may be due to the fact that critical items in
both ‘later’ and ‘now’ conditions were encountered on one occasion prior to their
presentation in the Stroop list. That is, subjects encountered the words ‘marble’, ‘plastic’,
and ‘bag’ when they read them in the task description before they appeared in the Stroop
list. Whereas, the neutral control items were only encountered once within the Stroop list.
Therefore, it may be that the critical items encountered in the ‘now’ trials resulted in some
repetition priming leading to a slight increase in interference which prevented the
possibility that they would show inhibition or a lack of interference. Therefore, we cannot
claim based on the available data that subjects are demonstrating inhibition of critical
items for ‘forgotten’ or completed intentions. Rather, the observed decrease in interference
in both experiments may reflect a decay in the activation/accessibility of critical items. In
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future studies, it would be useful to use control items that would allow us to explore
whether the inhibition effect demonstrated by Marsh et al. (1998) would be found in our
paradigm.
No interactions with age group were observed showing that older adults exhibited a
similar pattern of responding as younger adults. For both groups, completing an intention
led to a decrease in interference in Stroop task performance. This result has implications
for the inhibition deficit hypothesis. Hasher et al. (1999) argue that one of the main
functions of inhibition is to discard no-longer-relevant information from working memory
and that this ability decreases with increasing age. By this account, one would have
expected that older adults would not have shown a decrease in interference after
completing the intention before the Stroop list (Hasher et al., 1999). The reasoning is
that proponents of this account would predict that older adults are unable to delete the
contents of the intention from working memory even after they have completed it,
therefore performance in the ‘now’ and ‘later’ trials should have shown a similar amount
of interference for older adults. However, this prediction was not supported as both young
and older adults showed equivalent levels of a decrease in colour-naming interference for
critical words belonging to an intention that they had already carried out.
An important point to address from Experiment 2 is the absence of an interaction
between Critical Item Order and Instructions. In contrast to findings from Experiment 1,
results showed that there was a similar graduated pattern in response latencies for ‘now’
and ‘later’ conditions for critical item order. In Experiment 1, this differential pattern of
interference was only present for the ‘do the task’ trials but not for the ‘forget the task’
trials. The absence of this interaction in Experiment 2 may be due to the fact that
participants executed the intention in the ‘now’ trial before completing the Stroop task. It
may be that having physically interacted with the materials in this condition led to a higher
association among critical items leading to the observed pattern of response latencies.
GENERAL DISCUSSION
In the current set of experiments, results revealed that enhanced awareness of the need to
carry out an intention made it more likely that words related to that intention interfered
with colour naming when the words were later encountered in a Stroop task. Our results
imply that information that is held in mind with the intention to be carried out has an
advantage over information that is neutral or not future-oriented. A potential advantage of
using an interference paradigm, such as a Stroop task, as opposed to facilitation paradigms
lies in the fact that subjects have no reason to try to use their memories of the study
materials as a resource to help them perform such a task. As Burt (1999) stated, there are a
number of task-specific strategies that can qualify or influence the interpretation of data
from facilitation tasks such as recognition memory or LDT (see also Jacoby, 1991). In the
Stroop task, if anything, subjects have a motivation to avoid thinking about the study
materials (because thinking about them is likely to interfere with colour-naming of those
words). Consequently, one can be confident that effects of Task Instructions on Stroop
performance are spontaneous.
Our Stroop lists contained congruent colour-name words, but no incongruent colourname words. We did this to increase the extent to which participants would be open to
influence from words. That is, prior research indicates that Stroop effects increase as the
proportion of incongruent items decrease (Melara & Algom, 2003; Jacoby, Lindsay, &
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Hessels, 2003), so we speculated that including congruent (but no incongruent) colourname words would increase the extent to which participants would be sensitive to the
semantics of the task-related critical words. Thus an intention interference effect might not
be observed if, for example, most of the items in the Stroop lists were incongruent colourname words. Note, however, that it is unlikely that participants in our experiments
strategically used word meanings to perform the Stroop colour-naming task; two thirds of
the items in each list were non-colour-name words for which such a strategy would
backfire, and participants never erred by saying a non-colour-name word rather than
naming its colour.
As mention earlier, Maylor (1996) argued that the retention interval is susceptible to
age-related disruption because older adults are particularly susceptible to age-related
deficits in working memory capacity, vulnerability to interfering information, and
vulnerability in handling dual task requirements. Given this assertion, one would expect
that older adults might have been particularly vulnerable to age-related deficits, but in both
our experiments there were no interactions with age. Our findings, as well as those of
Freeman and Ellis (2003), indicate that young and older adults show equivalent item
accessibility for intentions that need to be carried out. Our findings suggest that observed
deficits in prospective memory performance may not be due to older adults’ inability to
maintain intentions in mind if the duration is relatively short between encoding and
execution. It is worth noting, that the duration of the retention interval may be a factor in
the absence of age differences in our studies. For example, an intention that needed to be
delayed for a longer duration or an intention that had to be maintained in the midst of a
demanding ongoing task might have led to a different outcome.
Our findings build upon the results found by Freeman and Ellis (2003) because we used
intentions that were more complex and we could examine how the superiority of the
intention-related material builds across items. As shown in Figure 3, the first critical cue
for ‘do the task’ items seems to act as a cue or intentional marker for the remaining
critical items. This finding suggests that intention-related representations may not enjoy
the increased activation as suggested by Goschke and Kuhl (1993). Rather, it may be that
the initial target creates some reminding of the action phrase and that this retrieval of the
remaining items slows down responding. For example, the action phrase may be
maintained in long term memory and the appearance of the first critical cue elicits
retrieval of the remaining contents of the action phrase which are transferred into working
memory where they interfere with Stroop performance. This result can benefit by
considering findings by McDaniel, Guynn, and Einstein (2004) who propose a multiprocess framework in which successful prospective memory performance is sometimes
achieved through capacity-demanding monitoring processes and in other cases via a
reflexive-associative process. Our findings seem to reflect a reflexive-associative process
because the first cue acts as a reminder (showing no interference thus no monitoring) and
causes the remaining items to be retrieved reflexively leading to the increased interference.
Research on ‘directed forgetting’ is thematically relevant to our investigation of the
intention superiority effect. In this literature, young and older adults have difficulty
‘forgetting’ information related to actions that have already been performed. For example,
in a study by Earles and Kersten (2002), participants were asked to perform an action (e.g.
break toothpick) or to read the pair and not perform the action. Following each pair, the
participants were told either to remember or to forget the pair. Younger adults intentionally
forgot verbally encoded pairs significantly better than did older adults. Interestingly,
actions that were performed were difficult for both younger and older adults to
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intentionally forget which seems to be in contrast to our results on ‘forget the task’ trials
where both young and old showed a decrease in interference. An important difference
between the paradigm described above and our paradigm is that our goal was to measure
on line item accessibility and their goal was to measure memory for 40 verb-noun pairs
(e.g. break toothpick) at the end of the experiment. The only way we could accurately
address the issue of directed forgetting would be to test both young and older adults at the
end of the study for all of the 24 do/forget phrases to examine whether the age-related
patterns observed by Earles and Kersten (2002) would be found. Unfortunately, we did not
ask our participants to perform a memory test at the end of the experiment so this remains
an interesting empirical question that we would hope to address in a future experiment.
Older adults in these experiments were healthy, community-dwelling individuals who
would probably meet criteria for ‘high functioning’ adults, and more cognitive impaired
older adults might well have revealed a different pattern of effects. Nevertheless, it is
important to note that although the magnitude of the observed intention interference effect
(approximately 40 ms) was similar for both young and older adults, we cannot assume that
the same mechanism is driving performance for both age groups. That is, the mechanism
driving the intention interference effect may not be necessarily the same for both young
and older adult groups. It would be useful to conduct a future study that would adjust
empirically for differences between young and old through making the task more difficult
for younger adults. Then reaction times would be equivalent across age groups and
comparisons could be made more easily.
In a series of three experiments, Marsh, Hicks, and Watson (2002) demonstrated that
ongoing task performance is facilitated on items related to an intention that are not
detected as prospective memory cues (failed trials) but is slowed on items related to an
intention that are detected as prospective memory cues (successful trials). Marsh et al.
(2002) isolated three components necessary for event-based prospective memory: (1)
noticing the target as relevant to a previously established intention, (2) retrieving the
intention itself, and (3) coordinating ongoing activity with the activity required to fulfil the
intention. Therefore, our results suggest that older adults have little difficulty with the first
component of prospective memory (noticing the relevant cue) but future research needs to
address the possibility that age-related decline results from difficulty with the latter two
components (retrieval and coordination).
ACKNOWLEDGEMENT
Data collection was carried out at the University of Victoria. Research was funded in part
by a PGSB scholarship from the Natural Sciences and Engineering Research Council of
Canada (NSERC) to Anna-Lisa Cohen and by a grant (AG08235) from the National
Institutes of Health (National Institute on Aging) to Roger A. Dixon.
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APPENDIX A
1.
2.
3.
4.
5.
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Place tack in the apple and place on dish
Pile blocks and place drinking straw on top
Rip sheet of paper into four pieces
Place rubber ball on top of soup can
Tie ribbon around candle and place on book
Stack pennies on top of the Kleenex box
Balance book of matches on stapler
Place cassette tape into the envelope
Put wrist watch under the picture frame
Stick the pencil and pen in the bottle
Put two stickers on the newspaper
Place the brochure in file folder
Fold the napkin three times
Put elastic around the glass
Place candy into the spoon in the bowl
Put rings onto the paint brush
Put flower inside the wool hat
Find the word ‘prosaic’ in the dictionary
Wrap the scarf around the rock
Put the beaded necklace in the teacup
Place teabag and sugar packet inside the purse
Put the spool of thread in cereal box
Put the marble in the plastic bag
Wind up the cord and tie with a piece of string
Copyright # 2005 John Wiley & Sons, Ltd.
Appl. Cognit. Psychol. 19: 1177–1197 (2005)
Intention interference
1197
APPENDIX B
Example of Stroop list
Critical items
blue
pink
beauty
good
pursuit
yellow
supper
car
blue
" marble
green
chief
pitcher
" plastic
cellar
"
bag
pink
red
white
chapter
harvest
lack
party
form
Note: Actual words from Stroop lists were displayed in seven colours: red, blue, green,
yellow, pink, white, and black on a grey background.
Copyright # 2005 John Wiley & Sons, Ltd.
Appl. Cognit. Psychol. 19: 1177–1197 (2005)