Running Head: WORKING MEMORY'S
on Your Mind: The Influence of the Contents of Working Memory on Choice
Starla Weaver L-SAW 2009
It is often the
case that information must be maintained until it can be applied. The active
storage and manipulation of information over short periods of time takes place
within working memory (WM). Holding information in WM can allow for successful
functioning. However, keeping information active in WM can affect other
cognitive processes. For instance, information in WM can influence processes of
selective attention. Maintaining specific information in WM can bias selective
attention toward items related to that information (Huang & Pashler, 2007).
Information in WM can also influence processes of executive attention.
Maintaining high WM loads can limit executive attention and lead to increases
in stereotypic responding (Towse & Cheshire, 2007). The current study
examined the influence of information in WM on behavioral selection. In particular
we examined whether the specific tasks one chooses to perform within a
multitasking environment would be influenced by information being maintained in
WM. We hypothesize that information in WM will influence choice through a
combination of biases to selective and executive attention.
At any given time
the amount of information available to the senses will exceed that which can be
processed perceptually. Selective attention specifies which of the available
inputs will be processed. Selection can be driven by stimulus dependent,
bottom-up processes (Treisman & Gormican, 1988) or top-down goals (Wolfe,
1998). Furthermore top-down attentional goals can bias selective attention and
allow specific features relating to one's current target to draw attention in
an automatic fashion (Serences et al., 2005; Yantis, 2000). In their biased
competition model, Desimone and Duncan (1995) propose that selective attention
can be biased toward a specific set of stimuli via attentional templates that can
specify the features, location, or identity of to-be-attended targets. A
representation of the target held active in WM is used to bias processing when
competition between multiple perceptual inputs is encountered (Chelazzi,
Miller, Duncan & Desimone, 1993; Moran and Desimone, 1985).
attention utilizes WM as a means of actively maintaining representations of
features to which attention should be biased. One consequence is that items
being maintained in WM appear to bias attention even in situations in which
selection bias is not strictly relevant to one's current goals (Downing, 2000;
Huang & Pashler, 2007; Moores & Maxwell, 2008; Olivers, Meijer &
Theeuwes, 2006; Soto & Humphreys 2007). Huang and Pashler (2007) labeled
the automatic draw of attention toward items in WM as consonance-driven
orienting. For example, in Moore and Maxwell (2008) participants presented with
a picture to remember were asked to make an identification judgment concerning
a letter that appeared in the center of either the memory picture or a neutral
picture. Although the picture being maintained was paired with the target
letter on only 20% of trials, participants were faster and more accurate at
identifying the target when it was presented on the to-be-remembered picture,
suggesting that attention was biased toward that picture. Consonance-driven
orienting has been distinguished from simple perceptual priming (Moores &
Maxwell, 2008; Olivers et al., 2006; Soto & Humphreys, 2007); has been
found for both stimuli that matched or are related to targets held in WM (Huang
& Pashler, 2007; Olivers et al., 2006); and has even been found in
situations where such orienting always impaired primary task performance (Soto
& Humphreys, 2007).
consonance-driven orienting may not be strictly automatic (Downing & Dodds,
2004; Woodman & Luck, 2007). For example Woodman and Luck (2007) found that
participants were able to inhibit items that matched the contents of WM within
visual search tasks where attentional capture would have always impaired
performance. In this case it appeared that selective attention could be biased
either toward or against items in WM depending on the functionality of such a
bias. The authors concluded that attentional capture by items in WM is not strictly
automatic. However, they noted that such capture was likely to occur in
situations where it would be beneficial to or have a neutral effect on primary
task performance, as well as in situations where an emphasis was placed on WM
accuracy. In these situations consonance-driven orienting was highly likely
because attending to stimuli that match those one is attempting to maintain in
WM allows the representation of the item to be refreshed, causing an increase
in successful storage.
consonance-driven orienting acts as a mechanism by which selective attention
aids in WM maintenance, then situations that allow shifts in selective
attention toward representations in WM ought to result in more effective
storage than situations where such shifts are prevented. Research on the
storage of locations in WM suggests that this is indeed the case (Awh, Jonides,
& Reuter-Lorenz, 1998; Lawrence, Myerson & Abrams, 2004). It seems that
locations are maintained in WM through shifts in selective attention toward
those locations (see Awh & Jonides, 2001 for review). As a result selective
attention during the retention interval appears biased toward locations in WM,
such that stimuli appearing in those locations receive preferential processing
(Awh et al., 1998).
attention and WM share a symbiotic relationship in which WM can aid selective
attention by keeping active a representation of to-be-attended targets; and
selective attention can aid WM by refreshing to-be-remembered representations.
Thus, research on selective attention and WM maintenance converge on the idea
that selective attention will be biased toward features that match those being
maintained in WM. As a result it may be expected that if information one is
maintaining in WM were to become available within a multitasking environment,
selective attention is likely to be drawn to that information.
attention has guided the perceptual processing of stimuli in an environment,
responses to those stimuli can be made. One role of executive attention is to
choose, enable, and coordinate response performance (Logan, 1985). While
habitual responses to frequently encountered stimuli can be made without the
aid of executive attention (Norman & Shallice, 1986), executive attention ensures
that actions appropriate for the current situation are able to be performed,
particularly in situations where multiple response options are available.
A number of
approaches have been used to study executive attention. One particularly
fruitful approach has been the task-switching paradigm (see Monsell, 2003 for
review). During task switching the to-be-performed task alternates periodically
between trials, such that the response appropriate for a single stimulus may vary
depending on the task required on that trial. Many accounts of task switching
assume that executive attention is needed in order to ensure that the
appropriate response is executed on each trial in accordance with changing task
demands (see for example Monsell, 2005). Nevertheless, passive processes also
contribute to task switching performance (Allport, Styles & Hsieh, 1994). For
example the speed with which a participant can respond to a stimulus is
influenced by automatic retrieval of stimulus-response bindings (Kiesel, Wendt,
& Peters, 2007; Koch & Allport, 2006; Waszak & Hommel, 2007;
Waszak, Hommel, & Allport, 2003, 2005; Wylie & Allport, 2000).
Responding to a stimulus appears to create a stimulus-response episode that is
automatically retrieved when the stimulus is presented again within the same
context (Logan, 1988). Automatic retrieval of past episodes prime previously
performed responses (Waszak & Hommel, 2007). As a result the task that has
most recently or frequently been paired with a stimulus is able to be performed
more quickly than the alternative task (Koch & Allport, 2006). Further when
a task-switching paradigm employs two sets of univalent stimuli, the
presentation of a single stimulus type can automatically activate the
associated task, making it available for performance.
of passive factors, like stimulus-response binding, in task switching has led
to debate concerning the role that executive processes play in switching
between tasks (see for example Logan, 2003). The degree of executive attention
required may depend on the specific paradigm in which the task switch takes
place (Monsell, 2005). In particular, the more environmental support offered by
a task-switching paradigm the less executive attention is likely to be required
(Arrington & Logan, 2005). For example the voluntary task-switching
paradigm provides a participant with very little environmental support
(Arrington & Logan, 2005). In this paradigm participants are instructed on
the performance of two tasks and are asked to perform each task equally often
and in a random order. Participants are then free to select the specific task
to perform on each trial. Due to the minimal amount of environmental support
provided on a trial by trial basis in this paradigm, voluntary task switching
is particularly well suited for studying executive attention.
switching performance must be driven by top-down executive processes in the
absence of explicit task instructions (Arrington & Logan, 2005; Liefooghe,
Demanet, & Vandierendonck, In Press). Nevertheless, passive processes can also
influence task choice (Arrington, 2008; Mayr & Bell, 2006). Stimulus-response
bindings are one such process. Arrington, Weaver, & Pauker (2009) found
that participants showed a preference for performing the task that had
initially been paired with a stimulus. This effect was found even when the
initial stimulus-task pairing was randomly determined by the experimenters. In
addition when the onset of two univalent stimuli was varied, participants more
often performed the task afforded by the stimulus that became available first
(Arrington, 2008). The stimulus presented first triggered the associated task
before the alternative task could be activated. The order of stimulus
presentation influenced the order of task activation leading to a bias in
In the previous
section we noted that the order in which multiple stimuli within an environment
are processed can be influenced by the contents of WM. Objects being stored in
WM are likely to receive preferential processing due to consonance-driven
orienting. Stimulus-response bindings provide a mechanism by which this
preferential processing may lead to an influence on task choice. In particular,
processing of a univalent stimulus can activate the task afforded by that
stimulus and, within the voluntary task-switching paradigm, bias performance
toward that task. If items in WM can bias selective attention toward the
processing of specific stimuli in a multitasking environment and the processing
of specific stimuli can bias responding then the contents of WM may be capable
of influencing task choice within situations where that content is not strictly
The purpose of the
present study was to determine the influence of the contents of WM on task
choice within multitasking environments. The extent to which information in WM
is able to influence task choice may depend on the type of information being
maintained. Baddeley's influential model of WM (i.e. 1992) distinguishes
between the storage of verbal information such as identities, and visual
information such as locations. These domains appear functionally and
neurologically distinct (Baddeley, 1996b; Kane et al., 2004; Sakai &
Passingham, 2003). In the current study we assessed the separate influence of
information from each type of domain on choice.
presented with a memory array displaying three characters in three locations
and were asked to maintain either the identities (identity-domain condition) or
locations (location-domain condition) of the characters in that array. Participants
then performed a series of voluntary task-switching trials on a digit affording
even/odd classification and a letter affording consonant/vowel classification.
On half of the trials one of the stimuli's identities matched the identity of a
character from the memory array. On the other half of the trials one of the
stimuli's locations matched a location from the memory array. We hypothesized
that participants would show a bias for performing tasks afforded by stimuli
that matched the memory array on the dimension they were maintaining in WM. Specifically,
participants in the identity-domain condition were expected to be more likely
to perform tasks afforded by stimuli that matched identities held in WM, while
participants in the location-domain condition were expected to be more likely
to perform tasks afforded by stimuli that appeared in locations held in WM.
While we expect participants
to show a bias toward performing tasks associated with stimuli that matched the
contents of WM, an alternative possibility should be considered. Participants
may intentionally choose not to perform the task associated with items in WM. The
voluntary task-switching paradigm instructs participants to perform two tasks
in a random order. Repeatedly performing tasks associated with information in
WM may not appear random to participants. As a result participants may choose
to override the bias associated with the contents of WM on some trials in order
to perform more randomly. In other words selective attention may be biased
toward the information in WM, but participants may choose to redirect their
attention after the initial bias in order to perform the task afforded by the
alternative stimulus. This process should take more time than simply performing
the task afforded by the stimulus to which attention had been initially drawn.
Thus in this situation increased response times (RT) would be expected on
trials where participants do not perform the task afforded by the stimulus that
matches the information they are holding in WM.
Lehigh University undergraduates participated in exchange for partial course
credit. Participants reported having normal or corrected-to-normal vision.
stimuli. The experiment was administered on a Dell Dimension computer with
a 17 inch CRT monitor running the E-prime 1.1 software package. Stimuli were
sampled randomly from the letter set A, C, E, I, R, P, M, and U and the numbers
2-9. Stimuli were presented in 18 point courier new font on a light gray
background. Characters in the memory array were blue. All other stimuli were
black. Stimuli appeared within a 5 x 5 array of locations centered on the
screen. A plus sign was always located at the center of the array. The
remaining locations within the central row and central column of the array remained
blank. Thus the stimuli appeared within the 16 remaining locations with four
possible target locations in each quadrant (see Figure 1). The array extended
approximately 6.4 cm above and below fixation and 7 cm to the left and right of
fixation. Viewing distance was not constrained.
study featured a 2x2 mixed-factor design. The first variable was WM domain or
type of information designated for retention in WM, which varied
between-subjects. The two domains were identity-domain and location-domain. The
second variable was trial type, which varied within-subjects. Trial type was
based on the relationship between the stimuli appearing in that trial and the
characters presented in that block's memory array. The two trial types were
identity-match trials, which featured one stimulus whose identity matched one
of the characters in the memory array, and location-match trials, which
featured one stimulus whose location matched one of the characters in the
memory array. The alternative stimulus was always neutral with regard to its
identity and location. The primary dependant variable of interest was the
proportion of matches performed, or the proportion of trials in which
participants performed the task associated with the stimulus that matched a
character presented in the memory array.
sessions began with a series of practice blocks each containing eight trials
intended to familiarize participants with the stimulus-response mapping for
each task and the process of selecting between tasks at random. Participants
performed one practice block in which they made even/odd judgments and one
block in which they made consonant/vowel judgments. Next participants performed
one practice block of voluntary task-switching trials. They then performed two practice
blocks that included the entire experimental procedure (see Figure 1). Each
experimental block began with the presentation of a memory array that remained
on the screen for 3000 ms. All participants saw a memory array consisting of
three alphanumeric characters. Participants in the identity-domain condition
were instructed to remember only the identity of the characters, while participants
in the location-domain condition were asked to remember only the locations
marked by the characters. Then, following a 500-ms blank screen, two voluntary
task-switching trials were completed. Each trial consisted of a letter and
number presented simultaneously. Participants had the choice of making either
an even/odd judgment concerning the number or a consonant/vowel judgment
concerning the letter. As in previous voluntary task-switching studies,
participants were instructed to attempt to perform each task equally often and
in a random order, but were given no instruction concerning the specific task to
perform on each trial (Arrington & Logan, 2004a). Responses were made using
the index and middle finger of separate hands for each task. Responses were
mapped to the "d" "f" "j" and "k" keys and were counterbalanced across
participants. Voluntary task-switching trials were separated by a 500-ms
response-stimulus interval. Each block concluded with a memory test. In the
identity-domain condition, a stimulus accompanied by a question mark was
presented in the center of the screen. In the location-domain condition, a
location was marked by a question mark. Participants pressed the "y" key for
yes if the test item or location was one that they were attempting to remember
or the "n" key for no if it was not. The correct answer for the memory test had
a 50% chance of being yes. The word correct or incorrect then
appeared on the screen indicating the accuracy of the participant's performance
on the memory test. One hundred experimental blocks were performed resulting in
200 voluntary task-switching trials.
trials were sorted into tasks based on the hand used to respond to each trial
and into task transitions based on the tasks performed on trial n-1 and trial
n. Two participants whose voluntary task switching accuracy fell below 90% were
replaced. Data from one participant who failed to switch tasks throughout the
experiment was excluded. Blocks in which the memory test was incorrect and
trials in which task performance was incorrect were not included in task choice
or RT analyses. Trials with RTs two standard deviations away from that
participant's mean RT were excluded from analysis, resulting in a loss of 4.7%
Proportion of matches. The proportions of matches performed by participants
in each WM domain condition separated by trial type and trial number are
displayed in Figure 2. Notably participants tended to perform a greater number
of matches when the stimulus matched the memory array on the dimension they
were maintaining in WM than when it matched the memory array on the
undesignated domain. Participants maintaining locations (M=.538)
performed more matches than participants maintaining identities (M=.502).
In addition the proportion of matches performed was greater on trial one (M=.554)
than on trial two (M=.486). A 2 (WM domain: identity-domain, location-domain)
x 2 (trial type: identity-match, location-match) x 2 (trial number: one, two)
mixed factor analysis of variance (ANOVA) with WM domain as a between-subject
factor found a main effect of WM domain, F(1,29)=11.23, p<.01,
ηp2=.28 and a main effect of trial number F(1,29)=22.16,
p<.001, ηp2=43. Critically for the
current hypothesis, there was also a significant WM domain x trial type
interaction, F(1,29)=4.41, p<.05, ηp2=.13.
No other effects reached significance. The results suggest that choice was
biased toward tasks associated with information in WM.
Task transitions. The task transitions between trial one and trial two were
analyzed to consider whether participants complied with the voluntary task-switching
instructions to perform the tasks in a random order. Following these
instructions would have required performing an equal number of switches and
repetitions. One-sample t-tests were used to compare the proportion of switches
performed in each WM domain condition to .5. The proportion of switches
performed did not vary from .5 for participants in either the identity-domain (M=.548)
or location-domain (M=.475) conditions, ts < 1.
Performance. Memory test accuracy and voluntary task-switching accuracy
were assessed across WM domain condition using independent sample t-tests. Memory
test accuracy was higher for participants in the identity-domain condition (M=.976)
than for participants in the location-domain condition (M=.700), t(29)=20.35,
p<.001. This finding is consistent with previous work indicating that
maintaining locations is more difficult than maintaining identities (Brisson
& Jolicoeur, 2007). Mean voluntary task-switching accuracy was high and did
not vary by WM domain condition (identity-domain: M=.974, location-domain:
M=.981), t(29)=.94, p=.36.
The speed of match
and non-match trials were compared in order to determine if participants were
actively avoiding matches on a subset of trials in order to better comply with
the instructions to perform tasks randomly. RTs are displayed in Figure 3. The
pattern of results was contrary to what would be expected if participants were
actively moving their attention on non-match trials. Match trials that involved
performing the task associated with the specific information held in WM were performed
more slowly than non-match trials. Matches and non-matches for the alternative
WM domain had similar RTs. RT was assessed with a 2(WM domain: identity-domain,
location-domain) x 2(trial type: identity-match, location-match) x 2(task
match: WM-match, non-match) mixed factor ANOVA with WM domain as a between-subjects
factor. A significant main effect of task match was found, F(1,29)=
8.00, p<.01, ηp2=.22; however, this
effect was qualified by a significant 3-way interaction, F(1,29)=4.47, p<.05,
The current study
examined the influence of the contents of WM on choice of tasks within a
multitasking environment. Previous research has noted that selective attention
tends to be captured by items being maintained in WM via consonance-driven
orienting (Downing, 2000; Huang & Pashler, 2007; Moores & Maxwell, 2008;
Soto & Humphreys, 2007). As a result these items receive preferential
processing. In addition research on executive attention has found that
responses can become activated merely by the processing of a stimulus that
uniquely affords a particular response due to stimulus-response binding (Kiesel
et al., 2007; Koch & Allport, 2006; Waszak & Hommel, 2007; Waszak, et
al., 2003; 2005; Wylie & Allport, 2000). Within the voluntary task-switching
paradigm, where participants must exert executive control in the absence of
external cues indicating which task to perform, stimulus-response bindings
appear capable of influencing task choice (Arrington, 2008; Arrington et al., 2009).
It was therefore hypothesized that within a multitasking environment the
processes of consonance-driven orienting and stimulus-response binding would
lead in increased availability of tasks associated with information in WM such
that task choice would be biased toward those tasks. The found pattern of
results supports this hypothesis. Participants in the identity-domain condition
performed a greater proportion of matches on trials that matched the memory
array on the identity dimension while participants in the location-domain
condition performed a greater proportion of matches on trials that matched the
memory array on the location dimension. The results suggest that the processes
of selective and executive attention work together to influence the tasks one chooses
to perform within environments that afford multiple tasks.
In addition to the
hypothesized bias toward performing tasks associated with the contents of WM,
the current study found a greater proportion of matches on trial one than trial
two. Task availability appears to play a large role in influencing task choice
(Arrington & Logan, 2005). The availability of a given task on any specific
trial is likely to be influenced by multiple factors. In particular, priming
from performance on the previous task appears to make the most recently
performed task especially available. This increased availability has been
proposed to contribute to switch costs within measures of task switching
performance (Allport, et al., 1994) and repetition biases in measures of
voluntary task choice (Arrington & Logan, 2005). However, the first trial
of a block lacks this source of availability, as availability of each task
appears to be essentially reset at the beginning of each new series of task-switching
trials (Schneider & Logan, 2006). Within the current study previous task
priming is likely to have contributed to the decreased influence of the memory
array on trial two.
finding of the current study was that participants in the location-domain
condition performed a greater proportion of matches than those in the
identity-domain condition. The location-domain condition was also associated
with a greater number of memory errors suggesting that maintaining locations
may have placed a greater load on WM. This finding is consistent with previous
work noting the increased load generated by maintaining spatial information in
WM (Brisson & Jolicoeur, 2007). Large WM loads appear to limit executive
processes (Baddeley, 1996a). The result is reduced ability to prioritize
selective attention (de Fockert, Rees, Firth & Lavie, 2001) and inhibit
proponent responses (Hester & Garavan, 2005). Within the current study a
reduction in executive processes, created by the load of maintaining locations,
may have lead to the increased influence of the memory array in that condition.
A similar result was found by Oberauer & Goth (2006) who noted that the
spatial but not verbal WM loads influenced primary task performance even when
that information was not needed for the primary task. Future research is needed
to determine whether the increased influence of the memory array found in the location-domain
condition is, as we have suggested, a result of the increased load created by
maintaining locations or if there is something specific about the way in which
spatial information is maintained that makes it more likely to interfere with
primary task performance.
With regard to RT
data, it had been proposed that participant's attention may be initially biased
toward stimuli that matched the information they were holding in WM but that on
a subset of trials participants may choose to move their attention to the
alternative stimulus in order to perform tasks more randomly. This movement of
attention would have increased the RT of non-match trials compared to trials
where the task afforded by the stimulus that matched the contents of WM was
performed. Unexpectedly, the opposite RT pattern was found. Match trials associated
with the contents of WM were performed more slowly than non-match trials. The
result suggests that participants were not actively moving their attention on
non-match trials. Indeed the pattern of task choice found in this study suggests
that such a strategy was hardly necessary. While a significant influence of the
contents of WM was found, the size of this influence was not large (M=.038).
Additionally, the proportion of switches performed indicated that participants
were complying with instructions to perform tasks randomly, suggesting that
executive attention was actively engaged during task choice. The RT data
suggest that this pattern was able to be obtained without sacrificing RT on
non-match trials. Instead we posit that RT was increased on WM-match trials in
the service of WM maintenance. Participants may have used WM-match trials as an
opportunity to refresh WM representations (Woodman & Luck, 2007). Indeed
memory accuracy did increase slightly as the number of match trials performed
during that block increased (zero WM-matches: M=.833, one WM-match: M=.844,
two WM-matches: M=.852) suggesting that performing the task associated
with the stimulus that matched the contents of WM allowed the representation to
be refreshed and WM storage to be enhanced. The benefit to WM maintenance
afforded by the opportunity to refresh representations in WM may have been
worth a small sacrifice of RT on those trials.
The connection between
WM and attention has been repeatedly proposed. Models of WM frequently cite the
importance of executive attention for the manipulation of information within WM
(Baddeley, 1996a; Kane, Bleckley, Conway & Engle, 2001; Norman &
Shallice, 1986). As a result, a great deal of literature has focused on the
influence that WM loads that limit executive attention can have on performance
in various situations, including task switching (Baddeley, Chincotta &
Adlam, 2001; Liefooghe, Barrouillet, Vandierendonck, & Camos, 2008; Logan,
2004). However, how the specific content of such loads may influence attention
has been considered far less often. This lack of consideration is somewhat
surprising given the potential for information in WM to guide selective
attention (Downing, 2000; Huang & Pashler, 2007; Moores & Maxwell,
2008). As demonstrated by the current study, the contents of WM may have the
potential to exert an influence on both selective and executive attention
processes. Studies of WM are likely to benefit from an integrated research
approach that considers how these processes may work together to influence the
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Figure 1. Trial line and examples
of the trial types. Gray blocks indicate all possible stimulus locations and
did not appear in the actual experiment.
Figure 2. The mean proportion of
matches performed in each WM domain as a function of trial type and trial
number. Error bars in this and all figures are 95% confidence intervals
calculated from the error term for the within-subject variable as suggested by
Masson and Loftus (2003).
Figure 3. Mean response times in
each WM domain as a function of trial type and task match.
Analysis of RTs for the second trial of each block found that task repetitions
(1114 ms) were performed significantly more quickly than task switches (1252 ms),
F(1,29)=8.12, p<.01, ηp2=.22.