due to the limited capacity of our visual system , selective attention needs to efficiently filter relevant stimuli from the incoming stream of visual information .
which stimuli are selected for further processing is a complex process that depends on various factors such as physical salience ( e.g. , [ 1 , 2 ] ) , task - relevance [ 3 , 4 ] , threat relevance [ 5 , 6 ] , or learning experience .
current visual attention theories , modeling which information is selected under which circumstances , often assume that the visual system weights such factors and assigns priority to each stimulus in the visual field , determining the probability with which it is selected [ 811 ] . naturally , as observers , we desire to attend to those stimuli that correspond to our current intentions and goals . by means of a search template that directly refers to a mental image of the desired object we can efficiently find such stimuli and deploy our attentional resources to it [ 1214 ] .
high weights for features corresponding to current goals of the observer can also have detrimental effects , impairing performance .
for example ,  contingent capture  describes the effect that visual attention is captured by task - irrelevant stimuli that match the search template in one or more features [ 15 , 16 ] .
it was argued that attention deployment towards stimuli that partially match the search template , regardless of its actual task - relevance , is mediated by working memory ( wm ) which may store the search template so that the observer can constantly match incoming information in ongoing tasks [ 8 , 1720 ] . a study by woodman & arita   provided neurophysiological evidence that attentional templates are maintained in wm and that the strength of template representations in wm predicts the performance in a visual search task .
as wm has a limited capacity , search templates maintained in wm for a search task at hand may sometimes compete with other information maintained in wm .
more recent research has indeed suggested that visual selection can be closely intertwined with visual working memory processes [ 2225 ] , for example , by showing memory - driven attentional capture .
for example , olivers and eimer   presented observers colored items they had to maintain in wm before they were being probed for correct retrieval . during maintenance , observers performed a visual search task .
when distractors shared the colors of items maintained in wm , search was slowed down compared to distractors of neutral colors , suggesting attentional capture by features in wm ( see also [ 24 , 26 ] ) .
although it seems plausible that our perception can be biased towards stimuli that match our goals and intentions , perception as such is never a self - purpose ; we intend to perceive something so that we can act upon the perceived .
action as the purpose of selection has been brought forward by allport 's selection - for - action theory allport   and a large body of literature has pointed towards a close interrelation of selection and action since ( e.g. , [ 2834 ] ) .
's   study , participants had to prepare a grasping or pointing movement according to a cue presented in the beginning of each trial . for grasping ,
size is a relevant dimension because grasping requires the specification of size - related parameters to control grip aperture . for pointing ,
luminance is a relevant dimension because pointing crucially requires the localization of to - be - pointed objects  and this localization
before participants executed the movement , they were shown a search display with various filled grey circles .
either all circles were identical , or one circle was a size singleton ( smaller circle ) or one circle was a luminance singleton ( brighter circle ) .
after the search task , participants executed the previously prepared movement towards one among various , real objects in front of them .
it was found that preparing a grasping movement facilitated detection of size singletons , whereas preparing a pointing movement facilitated detection of luminance singletons .
the authors concluded that planning an action biases visual perception towards dimensions that deliver important information for controlling that action .
the large overlaps between visual attention and wm have been attributed to attentional control mechanisms being in some way common with those recruited in the service of wm maintenance [ 23 , 25 ] .
similarly , the overlaps between visual attention and action planning have been ascribed to a common coding of perception and action [ 29 , 32 , 36 ] .
it seems economically plausible that a common mechanism allows the visual system ( a ) to deploy attention to the relevant information currently available to the senses , ( b ) to maintain information not present to the senses anymore , and ( c ) to plan action related to the present / maintained visual information .
this study aimed at investigating such interactions of visual attention , visual wm , and action planning .
more specifically we were interested in whether attention is particularly biased towards dimensions that are both action relevant and wm relevant , for example , towards a red circle if red is to be held in wm and a grasping movement is to be executed towards a circular item . 

the present study combined a visual search task with a working memory ( wm ) task and a motor task .
participants had to prepare a pointing or grasping movement but withhold execution until the end of a trial .
participants also had to memorize a color hue until the end of a trial . at the end of a trial
, participants performed the planned movement towards the memorized ( circular ) item , thus combining wm and motor planning .
while participants planned the movement and held the color in their wm , they had to perform a visual search task in which they always had to respond to a diamond - shaped target among circle distractors .
note that , for grasping , shape was a relevant dimension because the to - be - grasped objects were circles and thus required the specification of circle - related parameters ( e.g. , [ 37 , 38 ] ) . in some of the trials , one of the distractors could be colored ; the color could be related or unrelated to the color in wm .
we hypothesized that the additional color singletons will capture attention and slow down response times ( c.f .
, ) , even more so when they are related to wm content ( c.f . , ) .
memory - relevance and action - relevance coincided when the additional singleton in the search task was of a color related to wm and when a grasping movement was being prepared .
thus we expected the capture effect to be most pronounced when the color singleton both matches the wm content and is congruent to the action - relevant dimension , because , for such stimuli , task - relevance and action - relevance coincided .
21 volunteers ( aged 1927 years ) naive to paradigm and objective of the experiment participated for course credit . all but two were right - handed and all had normal or corrected - to - normal vision ( tested with landolt ring test , visus  1 ) .
participants were seated in a comfortable chair in a dimly lit room at 50  cm distance from an lcd - tn screen ( samsung syncmaster 2233 ) .
participants had a customizable keyboard ( ergodex dx1 ) on their left side in front of them with two buttons that were labeled 
n  and were operated by the middle and index finger of the left hand .
stimulus presentation and response collection were controlled by a windows pc using e - prime 2 routines .
the examiner sat approximately 2  m behind the participant with a standard keyboard on her lap to register participants ' movement .
movement cues were color photos taken from a female volunteer showing a forearm / hand on a black background that performs a pointing or grasping movement ( see figure 1(b ) ) .
the numbers of pixels for the pointing and grasping hands were approximately identical ( ~20% of the screen ; ~80% were black pixels ) .
memory items were filled circles ( diameter : 3.6 visual angle ) colored in one of nine shades of four colors ( blue , green , yellow , and red ) , that is , 36 different hues in total .
rgb values were identical to those used by olivers & eimer ; see the appendix for rgb and cie(x , y ) values .
search displays consisted of eight items placed on an imaginary circle with a diameter of 10.6 ( see figure 1(a ) ) .
colors were taken from the same pool of colors as memory items ( see above ) .
targets were grey diamonds ( 3 ) with an embedded stylized black m or n. m and n were made by removing two lines from the hourglass ; that is , m , n , and hourglass were superposable . in
the target was presented equally often in each of the eight positions . in memorized color trials and neutral color trials , there was one target , one color distractor , and six grey distractors .
target and color singleton were presented equally often in each of the eight positions but never in neighboring positions .
each trial started with a central fixation , shown for 500  ms ( see figure 1(c ) ) , and was replaced with a movement cue shown for 1500  ms .
participants were instructed to prepare the indicated movement but withhold movement execution until the end of the trial .
a display followed for 1000  ms that randomly showed one of the 36 color hues .
participants were instructed to memorize this hue until it was probed in the end of the trial . after a blank display showing only a fixation cross , the search display was shown . in one - third of the trials ( 320 trials ) ,
, a color distractor was presented that had a hue from the same color category as the memorized item but never the exact same hue ( memorized color ) . in the remaining third of the trials
, a color distractor was presented that had a hue from a different color category as the memorized item ( neutral color ) .
participants were instructed to respond as fast as possible ( while avoiding errors ) to the letter embedded in the target ( 50% m , 50% n ) by pressing the according button on the keyboard .
after participants responded , the search display was replaced by another blank display for 500  ms .
subsequently , a memory probe display appeared with three ( circular ) memory items arranged in a pyramid arrangement .
participants were instructed to execute the planned movement towards the item with the memorized hue .
the two other items were always from the same color category as the memorized hue ( e.g. , if the memorized items were from the category  red , 
two out of the remaining eight hues were randomly selected to appear together with the memorized hue ) .
all items being from the same color category was thought to discourage verbalization of the color and encourage a visual memory representation .
for pointing movements participants had to touch the screen with the tip of their right index finger . for the grasping movement participants had to make a claw - like gesture with their right hand , touching the screen with all five fingers along the outlines of the respective memory item .
after participants performed the movement , the examiner pressed one out of two buttons to register which movement had been executed by the participant ( point versus grasp ) and pressed one out of three buttons to register towards which item the movement was made ( first , second , and third colored circle within the pyramid arrangement ) .
only trials in which participants performed the correct movement and towards the correct object were counted as correct trials .
after an intertrial interval of 1000  ms ( black screen ) , a new fixation cross announced the beginning of a new trial . there were six experimental conditions : three color conditions ( color absent , memorized color , and neutral color ) and two movement conditions ( pointing and grasping ) .
target position ( or target - color distractor position combination , resp . ) was counterbalanced with each of the six experimental conditions across the experiment .
the experiment comprised 960 trials ( + 30 practice trials ) divided in 40 blocks of 48 trials , that is , 160 trials per experimental condition .
after each block a pause of at least 10  sec followed and performance feedback ( rts and accuracy for the search task and accuracy for the motor task ) was provided to participants on the screen .
mean response times ( rt ) and error rates were calculated for each participant separately for each of the six experimental conditions . for  memorized color  trials , rts were collapsed across all hues from the same category as the memory item . for 
neutral colors ,  rts were collapsed across all hues from all categories to which the memory item did not belong . only trials in which all three tasks ( search task , motor task , and memory task ) were performed correctly and trials without exceedingly long search rts ( > 2000  ms ) or short rts ( < 300  ms ) remained in the rt analyses .
these criteria were reached in 64.5 % ( sd = 8.8% ) of the trials .
data were submitted to a 2  3 anova with the factors color ( absent versus memorized versus neutral ) and movement ( pointing versus grasping ) .
greenhouse - geisser correction was applied when appropriate . as measures of effect size , partial eta squared (  )
is reported for anovas , and epsilon (  ) is reported for t - tests .
search rts depended on the presence of a color distractor , f(2,40 ) = 32.96 , p < 0.001 ,  = 0.622 .
rts were shortest when color was absent ( m = 789  ms ) followed by distractors with neutral colors ( m = 830  ms ) and distractors with memorized colors ( m = 854  ms ) , all p < 0.001 ( contrasts ) ; see figure 2 .
how much search rts were modulated by color singleton depended on preparation of a movement , f(2,40 ) = 5.44 , p = 0.008 ,  = 0.214 .
follow - up t - test for dependent measures showed that differential movement preparation ( pointing versus grasping ) did not affect neither trials without color distractors ( m = 6  ms ) , t(21 ) = 0.79 , p = 0.440 ,  = 0.24 nor trials with neutral color distractors ( m = 4  ms ) , t(21 ) = 0.61 , p = 0.548 ,  = 0.19 . in trials with memorized color distractors , however , preparing a grasping movement increased search rts compared to preparing a pointing movement ( m = 19  ms ) , t(21 ) = 2.85 , p = 0.010 ,  = 0.88 . to confirm that the 2-way interaction is not a merely additive effect of wm and action planning ,
an additional anova was calculated in which the capture effect was taken as a dependent measure ( mean rts for  color absent  were subtracted from mean rts for  memorized color  and  neutral color  , resp . ) . a 2  2 anova with the factors color ( memorized versus neutral ) and movement ( pointing versus grasping )
results showed that the capture effect was not modulated by the preparation of a movement ( p = 0.084 ) but was modulated by the distractor type ( mmem = 65  ms versus mneutr = 41  ms ) , f(1,40 ) = 22.59 , p < 0.001 ,  = 0.530 .
the increase in attentional capture for memorized colors was more pronounced for grasping ( m = 35  ms ) than for pointing ( m = 13  ms ) , f(1,40 ) = 7.72 , p = 0.012 ,  = 0.279 .
the correct movement according to the movement cue was executed equally often for grasping ( 93.3% ) as for pointing ( 92.3% ) , p > 0.5 .
the memory items were correctly identified ( in terms of executing the movement towards the item of the hue that was shown in the beginning of the trial ) in 71.0% of the trials ( sd = 2.1% ) . to reveal whether those participants that were best in memorizing were also
the ones that were most distracted by memorized color distractors , pearson 's product - moment correlation was computed for memory accuracy and rt difference for color absent versus memorized color ( across movement conditions ) .
results showed a strong correlation (  = 0.44 ; p = 0.024 ) ; that is , the better memory performance , the more rt impairment due to memorized colors ; see figure 3 .
no such correlation was found for memory performance and rt impairment due to neutral colors ( p = 0.127 ) .
the key result of the present study is an interrelation of action planning and maintenance in working memory ( wm ) .
attention was particularly biased towards colors matching wm content when participants prepared a grasping movement compared to a pointing movement .
when no color distractor was presented or the color distractor had a color unrelated to wm content , the preparation of the movement did not affect attention deployment .
the presence of a color distractor impaired visual search even though colors were entirely search - irrelevant .
even though the task could be solved and the target be found most of the times ( overall error rates ~3% ) , response times were slowed down .
this is a replication of earlier findings showing that salient stimuli can capture attention against the intention of an observer [ 2 , 3941 ] .
apparently , salient distracting information needs to be rejected before attention can be directed towards the task - relevant stimulus , a time demanding process .
current visual attention models account for attentional capture , for example , by assuming that the weight of any bottom - up feature map can not be set to zero by the observer , regardless of the task - relevance of the feature dimension ( guided search , [ 11 , 14 ] ) . by this means
, salient stimuli will always project on the master map of activations ( or , priority map , ) , based on which attention deployment is being made .
the present study also showed that the attentional capture was particularly pronounced when the color distractor matched the color category that was held in wm .
this suggests that stimuli matching information maintained in wm are given more priority in visual processing than stimuli of equal salience that were not maintained in wm .
it should be noted that the longer response times for trials in which task - irrelevant color distractors were present do not necessarily indicate that those distractors were processed in a bottom - up manner . according to bacon and egeth ,
two search modes would have been applicable in the present search task : singleton detection mode in which observers search for anything that stands out from the background and feature search mode in which observers search for a predefined feature ( here , diamond ) , a search mode only possible when the target feature is known and does not change between trials . as in the present paradigm observers searched for a diamond - shape target throughout the experiment while ignoring color both search modes could have been used .
applying the feature search mode ( rather than singleton detection ) would have been particularly beneficial to color - present trials as distraction by the irrelevant color singleton would have been minimized . in color
absent trials , however , observers could have applied the simpler singleton detection mode as this search mode was sufficient to efficiently find the target .
if this was the case longer rts for color - present trials may have been due to differences in search strategy and not to bottom - up attentional capture .
different search modes in color - absent and color - present trials seem , however , rather unlikely as the trial types were completely randomized between trials .
this makes it unlikely that observers switched their search mode between trials because they could not predict which trial type would follow .
only as soon as stimuli showed up on the screen could observers know whether a color was present or not .
regardless of the applied search mode , more priority to wm - related stimuli is well in line with the notion that visual attention and wm may rely on the same mechanism of prioritization of items [ 5254 ] and replicates earlier results showing that guidance of attention from wm occurs even when it is detrimental to performance [ 13 , 23 , 25 , 55 ] .
for example , olivers and colleagues [ 13 , 23 ] argue that search templates and other representations in wm compete for resources . as a search template ,
items have full access to the sensory input and can bias selection towards matching objects . maintaining an item in wm (
e.g. , because it will be probed in the end of a trial ) is similar to adopting a search template ( or an  attentional set  ; ) .
such representations ( so - called  accessory memory items  ) have a passive status after being encoded into wm to not interfere with an ongoing task ( here , the search task ) and can be reactivated to regain the status of a search template when they become relevant ( here , when memory probes are presented ) .
reactivation of accessory memory items may also happen involuntarily , for example , when a wm matching distractor is presented during the search task .
this leads to prioritization of features held in wm , attentional capture results which may impair performance ( see also [ 24 , 25 ] ) . in the present study this was the case in the
, it seems that weights for features in the wm task spill over to visual search and bias attention accordingly ( e.g. , [ 53 , 56 ] ) . the increased attentional capture by color distractors matching the item held in wm could also be due to color priming from the wm displays to the search displays [ 7 , 57 ] .
previous studies using a similar paradigm , however , could rule out the possibility of priming effects ( e.g. , [ 24 , 26 , 58 ] ) .
those studies showed that attentional capture during a search task occurred only when previously presented items had to be remembered .
when observers were merely exposed to the crucial features , no such effects were found .
additional evidence comes from an imaging study   when wm content was repeated in a search task , enhanced activity in a variety of brain regions known to be sensitive to the prior history of events was found .
conversely , when items only had to be identified but not held in wm , their repetition elicited a suppressed response in the same regions .
given the similar paradigm it seems likely that , also in the present experiment , visual search costs were due to wm content rather than repetition effects .
interestingly , the present results indicate that guidance of attention from wm was most pronounced when participants prepared a grasping movement .
this indicates that apart from overlaps between visual attention and wm there may also be a connection between wm and action planning ; see wm model in figure 4 .
there is quite some evidence that action planning has a strong impact on perceptual processes , even in situations when action and perception are not directed to the same objects but merely overlap in time ( e.g. , [ 2834 ] ) .
for example , when observers have the intention to perform an action , such as grasping or pointing , their attention can be biased towards simultaneously presented yet unrelated visual objects .
this leads to faster target detection when the target is congruent to the planned action compared to incongruent targets [ 32 , 34 ] . in the present study , the feature dimension
shape  was crucial to the search task ; the feature  diamond  was task - relevant as targets were diamond - shaped ; the feature  circle  was task - irrelevant as distractors were circle - shaped .
shape is a dimension also relevant to grasping as grasping requires the specification of shape - related parameters .
for example , for a safe grip of an object , an agent needs to know the properties of its surface ; a ball is grasped differently than a cube ( e.g. , [ 37 , 38 ] ) . in the present study , participants had to grasp circular items in the memory probe display , rendering the feature  circle  particularly crucial for action planning .
conversely , when participants had to point at the circular items , no feature should have been rendered more crucial because none of the features in the search task ( shape , color ) were particularly relevant for pointing .
it appears that when circles were made relevant through planning of a grasping movement , circular distractors captured more attention than when a pointing movement was planned but only if their color matched wm content .
thus wm might be a mediating process involved in the relation of action planning and attention . in terms of the wm model by olivers and colleagues the planning of an action such as a grasping movement might increase the demand on wm and thus cause additional interference in wm because it requires the maintenance of information for subsequent action execution ( see figure 3 ) . in the present study preparing a grasping movement may have needed the maintenance of an action - relevant feature  circle shape  in wm .
this action - relevant feature may have prioritized processing of circle distractors in memorized colors in the search task , thus increasing interference with target processing and impairing performance .
our data show that action planning only modulated search performance when participants prepared a grasping movement and one of the distractors was in a memorized color .
this suggests that only when both circle prioritization by action - planning and color prioritization by wm maintenance coincided did attentional capture by the color singleton particularly impair search performance .
this is strong evidence for a common mechanism underlying selective attention , wm , and action planning .
the present results thus add to the previous literature showing that action planning is a rather dominant source of top - down control in selection and not only can modulate attention deployment but also can interact with wm content .
even though nine hues had to be distinguished within one color category , participants correctly remembered the hue in ~71% of the cases ( chance level 1/3 ) .
if the ability to discriminate hues was as good for color distractors as for memory probes , one would expect no distraction away from the target as the color singleton never exactly matched the hue of the memorized color .
however , hues within the same color category induced a significant increase in target search time compared to a neutral color category .
this indicates that , whereas participants were able to keep a relatively precise representation of the memory item in wm , a much broader variety of hues , actually the entire color category , was able to involuntarily capture attention .
perception of similar hues as one color category is a basic mechanism of the visual system [ 60 , 61 ] and is , for example , crucial to perceive a constant surface under varying lighting conditions . in the present study , whether hues were perceived as belonging to one category or not might have been due to varying time pressure or processing strategies .
for example , observers may have been biased towards the entire wm - relevant color category under the time pressure of the search task ( rt was stressed for the search task ) that did not allow the visual system to differentiate between hues . when the memory probe was shown in the end of a trial
, however , observers were able to make more precise color judgments ( precision was stressed for the memory task ) .
moreover , the visual system may have relied on color categories when no explicit incentive to differentiate between hues was present ( such as for task - irrelevant distractors during search ) ; thus attention was biased towards the entire category .
this may in fact be an adaptive strategy of the visual system to cope with the invariance of physical features in real world settings .
for example ,  color constancy  describes the effect that observers perceive the color of an object constant even though the exact wavelength may change drastically as a function of environmental variables such as illumination , perspective , shading , and distance [ 63 , 64 ] .
more recently it was found that attention deployment can be biased towards perceptual categories that typically share very few low - level features , even when this is detrimental to performance .
the present results may provide an example in which attention deployment is biased towards a color category even though only one subset of that category ( a specific hue ) was task - relevant . a strategy to more thoroughly process colors ,
however , might have been used when observers had the incentive to correctly identify one hue among similar ones ( such as for the memory probe ) .
this notion is in line with findings suggesting that how prominent the effect of color category on hue perception is relies on various factors such as the specific task , cognitive demands , and strategies of the observer . in the present study
it should be noted that some studies suggest that longer response times for distractor - present trials in additional singleton paradigms are due to nonspatial filtering costs [ 4245 ] whereas other studies suggest they are due to attentional capture by the distractor [ 39 , 4648 ] .
one reason for the diverging results may be that singletons only capture attention when they match the observer 's goal . although the present study can not contribute to answering this open question
, we assume that in the present study attentional capture accounts for the longer response times for distractor - present trials .
even though color distractors never matched the target category , they did match the wm content , namely , in the 
memorized color  condition . as it was the observers ' goal to maintain items in wm , attentional capture by items matching wm content
may therefore be considered attentional capture due to matching of the observer 's goal . in line with this , in a study using a similar paradigm as the present study , an n2pc component contralateral to the memory - matching distractor ( i.e. , a distractor negativity ) was found , suggesting that indeed stimuli sharing features of wm content capture attention .
to sum up , the present results showed that action planning not only determines the way we perceive our visual environment but also determines how working memory ( wm ) drives attention deployment .
observers were distracted from target search when a salient color item was presented concurrently to the target .
this distraction was more pronounced when the colored item was related to a color held in wm , indicating attention guidance by wm content . preparing a grasping movement enhanced wm guided attention deployment .
we conclude that target templates , action plans , and wm maintenance have common underlying mechanisms and compete for processing capacity .
 visual search is impaired when a salient task - irrelevant stimulus is presented together with the target . 
 recent research has shown that this attentional capture effect is enhanced when the salient stimulus matches working memory ( wm ) content , arguing in favor of attention guidance from wm . 
 visual attention was also shown to be closely coupled with action planning . 
 preparing a movement renders action - relevant perceptual dimensions more salient and thus increases search efficiency for stimuli sharing that dimension . the present study aimed at revealing common underlying mechanisms for selective attention , wm , and action planning . 
 participants both prepared a specific movement ( grasping or pointing ) and memorized a color hue . before the movement was executed towards an object of the memorized color , a visual search task ( additional singleton ) 
 was performed . 
 results showed that distraction from target was more pronounced when the additional singleton had a memorized color . 
 this wm - guided attention deployment was more pronounced when participants prepared a grasping movement . 
 we argue that preparing a grasping movement mediates attention guidance from wm content by enhancing representations of memory content that matches the distractor shape ( i.e. , circles ) , thus encouraging attentional capture by circle distractors of the memorized color . we conclude that templates for visual search , action planning , and wm compete for resources and thus cause interferences . 