Orthogonal stimulus–response compatibility effects emerge even when the stimulus position is task...

Orthogonal stimulus–response compatibilityeffects emerge even when the stimulus position

is task irrelevant

Akio Nishimura and Kazuhiko YokosawaThe University of Tokyo, Tokyo, Japan

The above-right/below-left mapping advantage with vertical stimuli and horizontal responses isknown as the orthogonal stimulus–response compatibility (SRC) effect. We investigated whetherthe orthogonal SRC effect emerges with irrelevant stimulus dimensions. In Experiment 1, partici-pants responded with a right or left key press to the colour of the stimulus presented above orbelow the fixation. We observed an above-right/below-left advantage (orthogonal Simon effect).In Experiment 2, we manipulated the polarity in the response dimension by varying the horizontallocation of the response set. The orthogonal Simon effect decreased and even reversed as the leftresponse code became more positive. This result provides evidence for the automatic activation ofthe positive and negative response codes by the corresponding positive and negative stimulus codes.These findings extended the orthogonal SRC effect based on coding asymmetry to an irrelevantstimulus dimension.

Performance is better when the stimulus andresponse share some features than when theydo not. This is called the stimulus–responsecompatibility (SRC) effect. SRC effects havebeen primarily studied for spatial features (seeProctor & Reeve, 1990). Responses are fasterand more accurate when the stimuli and responsesspatially correspond (e.g., right stimulus assignedto right response and left stimulus assigned toleft response) than when they do not (e.g., rightstimulus assigned to left response and left stimulusassigned to right response). Spatial SRC effects areusually attributed to the response selection beingfaster when the spatial code that specifies the

stimulus position and the spatial code thatspecifies the response position correspond thanwhen they do not (e.g., Umilta & Nicoletti, 1990).

Simon effect

Spatial SRC effects emerge even when the stimu-lus location is task irrelevant (Simon effect; forreviews, see Lu & Proctor, 1995; Simon, 1990).In a typical Simon task, participants respondwith a spatially defined right or left response tononspatial features of the stimulus, such ascolour or shape. The stimulus randomly appearsat a right or left position. When a red stimulus is

Correspondence should be addressed to Akio Nishimura, Department of Psychology, Graduate School of Humanities and

Sociology, The University of Tokyo, 7–3–1 Hongo, Bunkyo-ku, Tokyo 113–0033, Japan. Email: [email protected]

We thank Ataru Era, Ryota Takahashi, Kotomi Tanbo, and Shouhei Yonezawa for collecting the data for Experiment 1, and

Jan De Houwer and two anonymous reviewers for constructive comments.

# 2006 The Experimental Psychology Society 1021http://www.psypress.com/qjep DOI:10.1080/17470210500416243

THE QUARTERLY JOURNAL OF EXPERIMENTAL PSYCHOLOGY

2006, 59 (6), 1021–1032

assigned to the right response, and a green stimu-lus is assigned to the left response, performance isbetter when the red stimulus is presented at theright than at the left and when the green stimulusis presented at the left rather than at the right.

The Simon effect is attributed to processesoccurring at the response selection stage (Lu &Proctor, 1995; Umilta & Nicoletti, 1990).According to the dual-route account (e.g., DeJong, Liang, & Lauber, 1994; Hommel, 1993a;Kornblum, Hasbroucq, & Osman, 1990; Zorzi& Umilta, 1995), there are two stimulus–response(S–R) routes involved in the Simon effect. One isan automatic activation (or direct, unconditional)route through which irrelevant spatial stimulusinformation activates the corresponding response,and the other is an intentional translation (orindirect, conditional) route through which therelevant stimulus information (e.g., colour,shape) activates the assigned response in a con-trolled way. Because the automatic activation isfast, the appearance of the stimulus primes thespatially corresponding response. If a red stimulusassigned to a right response is presented at theright, it primes the right response. The stimuluscolour indicates the already-primed right response,so response selection is facilitated. On the otherhand, if a red stimulus appears at the left, itprimes the left response. The assigned responseis right but the left response is also activated.Therefore, there would be a response conflictbetween the primed left response and the assignedright response, and this conflict would have to beresolved. This conflict resolution is time consum-ing, so in a noncorresponding case the responseselection requires more time.

The Simon effect is not limited to spatially par-allel S–R correspondences. Any physical, struc-tural, or conceptual dimensional overlap betweenthe response set and the stimulus set could possiblyinduce a Simon effect as stimuli prime responsesautomatically when both share a common feature(Kornblum et al., 1990; Kornblum & Lee, 1995).Recently, some studies have shown Simon effectswith features other than spatially parallel S–Rfeatures. Kunde and Stocker (2002) reported aSimon effect emerging from the correspondence

of the duration of the stimulus and response.Participants responded to the stimulus colourwith a short or a long key press. The stimulusduration was either short or long. Performancewas better when the task-irrelevant stimulusduration and the required response duration corre-sponded. De Houwer (1998) obtained a semanticSimon effect. Saying “animal” or “occupation” inresponse to the nonsemantic features (Dutch vs.English, upper- vs. lower-case, noun vs. adjective)of the presented word standing for the name of ananimal or an occupation was faster when theresponse indicated the semantic category of thepresented word than when the response andthe semantic category of the presented worddiffered, even though the semantic category ofthe presented word was irrelevant to performingthe task. Mattes, Leuthold, and Ulrich (2002)replicated the compatibility effect betweenstimulus intensity and response force reported byRomaiguere, Hasbroucq, Possamaı, and Seal(1993). Moreover, Mattes et al. (2002) alsoobtained significant intensity–force correspon-dence effects with tasks where the stimulusintensity was irrelevant, and the shape of thevisual stimuli (Exp. 5) or the frequency of theauditory stimuli (Exp. 6) determined the responseforce. All of this research has shown that theSimon effect is not restricted to spatially parallelS–R correspondences, but emerges with manyS–R correspondences.

Orthogonal SRC effect

The spatial SRC effect also emerges when stimu-lus and response arrays are orthogonal, and there isno direct spatial correspondence between stimuliand responses. Bauer and Miller (1982) examinedthe SRC effects with orthogonal S–R arrange-ments (i.e., one horizontal and one vertical). Theparticipants responded to the stimulus positionby moving the index finger of their right or lefthand from a central key to the right or left keywith a horizontal response set, and to the up ordown key with a vertical response set. Withhorizontal stimulus and vertical response sets,they reported a right-up/left-down mapping

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NISHIMURA AND YOKOSAWA

preference with the right hand and a right-down/left-up mapping preference with the left hand.With vertical stimulus and horizontal responsesets, they reported an up-left/down-rightmapping preference with the right hand and anup-right/down-left mapping preference with theleft hand. They explained these results by assum-ing implicit movements toward the stimulusposition and a preference for counterclockwiserotational movements from stimulus position toresponse position for the right hand and a prefer-ence for clockwise rotational movements for theleft hand.

However, Weeks and Proctor (1990) found anoverall above-right/below-left mapping prefer-ence in their reexamination of the results ofBauer and Miller (1982) and Michaels (1989) aswell as in their own experiments with verticalstimulus and horizontal response sets. Weeksand Proctor (1990) obtained the orthogonalSRC effect (i.e., above-right/below-left advan-tage) not only with unimanual movementresponses, but also with bimanual key pressesand verbal responses. They attributed the orthog-onal SRC effect not to the preference of the motorsystem but to the cognitive coding at the S–Rtranslation stage. According to the asymmetriccoding account for the orthogonal SRC (see alsoCho & Proctor, 2004, 2005; Proctor & Cho,2003), S–R translation is more efficient whenthe structural correspondence of the polarities(i.e., positive vs. negative) of the stimulus andresponse sets is maintained in the S–R mapping.In the vertical dimension, above positions are pro-cessed faster than below positions (Chase & Clark,1971), and people put more weight on the top halfthan on the bottom half for similarity judgments(Chambers, McBeath, Schiano, & Metz, 1999).Thus, above is coded as positive, and below iscoded as negative in vertical spatial representation.In the horizontal dimension, right is coded aspositive, and left is coded as negative for right-handed people, as was demonstrated by thefinding that right positions were processed fasterthan left positions by right-handed participants(Olson & Laxar, 1973, 1974). As a consequence,an above-right/below-left mapping maintains a

structural correspondence of polarities betweenthe stimulus and response codes, and the S–Rtranslation is efficient with this mapping.The orthogonal SRC effect has been replicatedin many studies (e.g., Adam, Boon, Paas, &Umilta, 1998; Cho & Proctor, 2001; Dutta& Proctor, 1992; Lippa, 1996; Proctor, Wang, &Vu, 2002), and many researchers have acceptedthe coding asymmetry as an explanation ofthe orthogonal SRC effect (e.g., Cho & Proctor,2003; Kunde & Wuhr, 2004; Lippa, 1996;Umilta, 1991).

Orthogonal SRC with an irrelevantstimulus dimension

The asymmetric coding hypothesis restricted itsexplanation to the orthogonal SRC in which thespatial stimulus position is task relevant (Umilta,1991; Weeks & Proctor, 1990, 1991; but seeCho & Proctor, 2004). However, like other over-lapping S–R features (De Houwer, 1998; Kunde,& Stocker, 2002; Mattes et al., 2002), the rationalefor the dual-route account seems to be applicableto orthogonal SRC based on the correspondenceof the polarities to an irrelevant stimulus dimen-sion (Kornblum et al., 1990; Kornblum & Lee,1995). When irrelevant stimulus feature andresponse feature dimensionally overlap in polarity,positive and negative polarities accompanied byirrelevant stimulus positions might activate thecorresponding positive and negative polarities inrelevant response positions.

Studying orthogonal SRC with an irrelevantvertical stimulus dimension is important from amethodological perspective as well. To rule outthe spatial SRC or Simon effect with a horizontalresponse set, manipulation of the stimuli withinthe vertical dimension was often utilized regardlessof its task relevance (e.g., Duncan, 1984, Exp. 4;Hommel & Lippa, 1995; Proctor, Vu, &Marble, 2003, Exp. 4; Wallace, 1971, 1972)because at first glance there seems to be no SRCwith an orthogonal S–R arrangement. However,if SRC effects emerge with a spatially orthogonalS–R arrangement regardless of the task relevanceof the stimulus position, then orthogonal would

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not imply S–R independence, and researcherswould have to specifically design experiments torule out any SRC effects.

Although some studies included conditions inwhich participants made right or left responsesto nonspatial attributes of the stimuli presentedin an above or below position, the effect of thespatial relationship between the stimulus positionand the response position on response selectionwas not analysed (e.g., Ansorge, 2003; Hommel& Lippa, 1995). For example, in Hommel andLippa’s Experiment 2, participants responded tothe white and black circles by left or right keypresses. The circles covered either the right orthe left eye of Marilyn Monroe’s face, whichappeared upright, or tilted 45 degrees or 90degrees to the left or right. They reported theSimon effect based on the correspondencebetween the response position and the face-basedstimulus position (i.e., the stimulus position ifthe face was rotated to upright). When the facetilted 90 degrees, the stimulus appeared in eitheran above or a below position. However, theyneither analysed nor reported numerical valuesbased on the orthogonal spatial S–R relationship.

A few studies have shown a Simon-type effectwith an orthogonal S–R arrangement (orthogonalSimon effect). Wallace (1971) conducted a Simontask where stimuli appeared at the left, theright, above, or below. He obtained a nonsignifi-cant above-right/below-left advantage over theabove-left/below-right correspondence for RTs.This numerical difference was replicated with thesame conditions in his subsequent study(Wallace, 1972). Proctor et al. (2003, Exp. 4)had participants respond by pressing right or leftkeys to indicate the position of white stimuli pre-sented at the right or left and the colour of the redand green stimuli presented at the top or bottomposition. They reported a marginally significant(p ¼ .071) tendency for error rates suggestive ofthe orthogonal Simon effect. They also obtaineda similar nonsignificant trend for RTs (see theirTable 3). However, the impact of the irrelevantposition of the stimuli on the Simon task isenhanced when the location-relevant andlocation-irrelevant trials are mixed (Marble &

Proctor, 2000). Because the location-relevanttrials were intermixed with the location-irrelevanttrials within the block in their experiment, thiscontext might have activated the task-irrelevantpositional information of the stimuli.

In Experiment 1 of Cho and Proctor (2004),participants responded to the position of thestimulus above or below the fixation row bydeflecting a toggle switch to the left or right, andthe fixation row appeared randomly either aboveor below the centre of the screen before the onsetof the stimulus. Thus, the stimulus-set locationwas on either the upper half or the lower half ofthe screen. Although the participants respondednot to the stimulus-set location but to the positionof the stimulus relative to the fixation row withineach stimulus set, they obtained an orthogonalSimon-type effect between the stimulus-setlocation and the response (i.e., faster responsesfor the upper-right/lower-left correspondence)when the response set was located at the right. Incontrast, they obtained a reversed orthogonalSimon-type effect (i.e., faster responses for theupper-left/lower-right correspondence) when theresponse set was located at the left. However,there was no orthogonal Simon-type effect whenthe response set was located at the centre location.Thus, these effects with the lateralized response setcould be due to the coding of the side correspond-ing to the response set location as positive (Proctor& Cho, 2003; Weeks, Proctor, & Beyak, 1995; weconsider this issue in more detail in Experiment 2).The positive and the negative stimulus codes mightbe too weak to activate the corresponding positiveand negative response codes through an automaticactivation route with the unbiased S–R arrange-ment (i.e., the response set at the centre location).Moreover, because their task was the orthogonalSRC task where participants made left–rightresponses according to the vertical stimulus pos-ition relative to the fixation row, the verticallocation of the stimulus set might affect responseselection because of the task context even thoughthe stimulus-set location was task irrelevant (seeMarble & Proctor, 2000).

Thus although there is some evidence for anorthogonal Simon effect (Cho & Proctor, 2004;



Proctor et al., 2003; Wallace, 1971, 1972), thefindings are statistically not reliable and/ormight be by-products of the manipulations thatmade the location information active in the taskcontext (Marble & Proctor, 2000). No systematicinvestigation of the SRC effect with a horizontalresponse dimension and an irrelevant verticalstimulus dimension has been conducted. Little isknown about the orthogonal Simon effect inspite of its importance. In this study, we investi-gated the orthogonal Simon effect in a basic situ-ation where the stimulus position, which variedonly in the vertical dimension, was never contex-tually relevant to the task.

EXPERIMENT 1

In Experiment 1, we tested whether an orthogonalSRC effect emerges even when the stimulus pos-ition is task irrelevant. Participants pressed a leftor a right key in response to a nonspatial feature(i.e., colour) of vertically arrayed stimuli. If thepositive and negative codes of an irrelevantstimulus dimension are strong enough to activatethe corresponding positive and negative codes ofthe response dimension automatically even whenthe context does not make the irrelevant stimuluslocation information salient, then an orthogonalSimon effect would emerge. If, on the otherhand, the SRC based on the structural correspon-dence of the polarities emerges only when thespatial code is salient because of the task context,then no orthogonal Simon effect would beobserved.

Method

ParticipantsA total of 16 undergraduate students (7 femalesand 9 males), aged between 20 and 22 years(mean age ¼ 20.6 years), participated. All ofthem reported that they were right-handed andhad normal or corrected-to-normal vision. Theywere naıve about the purpose of the experiment.

Apparatus and stimuliThe experiment was conducted in a darkenedroom. Stimulus presentation and data acquisitionwere controlled by an AV-tachistoscope system(Iwatsu ISEL IS-703). A digital millisecondtimer measured latency from the onset of thetarget stimuli. Stimuli were presented on a 2200

display. The response apparatus (response set)consisted of right and left key boxes approximately7 cm apart from each other and approximately21 cm in front of the participants. A head-and-chin rest kept the participants’ posture and theviewing distance (approximately 58 cm) constant.

The stimuli were a white cross (5 mm width �

5 mm height) as a fixation and a red or greensquare (8 mm on a side) as a target on a black back-ground. The target colours (i.e., red and green)were matched in luminance (22.2 cd/m2). Thedistance between the fixation and the target was22 mm from edge to edge.

Task and procedureThe participants’ task was to press the left or theright key as quickly and accurately as possible inresponse to the colour of the stimulus presentedabove or below the fixation regardless of itsposition. Half the participants were instructed topress the right key in response to the red stimulusand the left key in response to the green stimulus,and vice versa with the remaining half. The rightresponses were made by the right index finger,and the left responses were made by the leftindex finger. Each experimental session consistedof three blocks, and each block consisted of 120randomly intermixed trials, consisting of 30 repli-cations for each type defined by a factorial combi-nation of stimulus colour (red or green) andstimulus position (above or below). Before thetest block, participants engaged in a practiceblock consisting of 60 trials. Participants tookshort rests between the blocks.

Each trial began with the display of the fixationcross. After 1,000 ms, the target appeared above orbelow the fixation until a response was made. Theintertrial interval was 1,500 ms. A 500-Hz tonalfeedback for 100 ms was given for error responsesduring the practice block.



Results

Reaction times (RTs) shorter than 125 ms andlonger than 1,250 ms were excluded from thedata analyses as outliers (0.017% of all the trials).The mean RTs for correct responses and percen-tages of errors were evaluated in separate analysesof variance (ANOVAs) with stimulus position(above, below) and response (left, right) aswithin-participant factors (see Table 1).

Reaction timesThe main effect of stimulus position was signifi-cant, F(1, 15) ¼ 4.67, MSE ¼ 67.92, p, .05.RTs for the stimuli presented above the fixation(M ¼ 341 ms) were shorter than those for thestimuli presented below (M ¼ 345 ms). The two-way interaction between stimulus position andresponse was significant, F(1, 15) ¼ 20.51,MSE ¼ 106.84, p, .001. Right responses(M ¼ 331 ms) were faster than left responses(M ¼ 350 ms) for the stimuli presented above thefixation. In contrast, left responses (M ¼ 343 ms)were faster than right responses (M ¼ 347 ms)for the stimuli presented below the fixation. Posthoc analyses using Tukey’s HSD test revealedthat the former difference was significant(p , .001), although the latter difference was not(p . .6). The main effect of response was not sig-nificant, F(1, 15) ¼ 3.00, MSE ¼ 271.00, p. .1.

Error rateThe main effect of stimulus position was signifi-cant, F(1, 15) ¼ 5.44, MSE ¼ 5.68, p , .05.Participants responded more accurately to thestimuli presented above the fixation (2.4%) thanto the stimuli presented below (3.8%). The two-way interaction between stimulus position and

response was significant, F(1, 15) ¼ 14.77,MSE ¼ 5.35, p, .01. Right responses (1.5%)were less error prone than left responses (3.2%)for the stimuli presented above the fixation. Incontrast, left responses (2.4%) were less errorprone than right responses (5.1%) for the stimulipresented below the fixation. Tukey’s HSD testrevealed that the latter difference was significant(p , .05), although the former difference wasnot (p . .2). The main effect of response wasnot significant, F(1, 15) ¼ 1.23, MSE ¼ 4.03,p . .2.

Discussion

The above-right/below-left advantage was mani-fest for both RTs and error rates. Above stimuliwere responded to significantly faster and numeri-cally more accurately by right responses than byleft responses, and below stimuli were respondedto numerically faster and significantly more accu-rately by left responses than by right responses.We obtained an orthogonal Simon effect of12 ms for reaction times and 2.2% for error rates.Hence, the orthogonal SRC effect emerged evenin situations where the stimulus position wastask irrelevant, and no context facilitated the useof the irrelevant stimulus position.

Although we obtained significant orthogonalSimon effects, the orthogonal Simon effects werenot reliable in previous studies (e.g., Proctoret al., 2003; Wallace, 1971, 1972). What is theexplanation for this discrepancy? The horizontalcoding of the above or below stimulus positionrelative to the previous stimulus position mighthave played some role in those previous exper-iments in which the stimuli appeared in above,below, right, or left positions in random order.For example, if the stimulus presented at anabove or below position was preceded by a stimu-lus presented at the right position, the stimulusposition is left relative to the previous stimulusposition. Thus, a horizontal attention shift fromthe previous stimulus position to the presentstimulus position (e.g., Rubichi, Nicoletti, Iani,& Umilta, 1997; Stoffer, 1991) or the horizontalcoding of the stimulus position relative to the

Table 1. Mean reaction timea and error rateb for Experiment 1

as a function of stimulus position and response

Left response Right response

Above stimulus 350 (3.2) 331 (1.5)

Below stimulus 343 (2.4) 347 (5.1)

aIn ms. bPercentage (in parentheses).



previous stimulus position (e.g., Hommel, 1993b)might make horizontal coding salient. Because theparallel SRC is stronger than the orthogonal SRC(Proctor & Wang, 1997; Weeks & Proctor, 1990),the horizontal coding of the stimulus positionmight have attenuated the orthogonal Simoneffect in Proctor et al. (2003) and Wallace (1971,1972). In our experiment, we exclusively focusedon the irrelevant SRC effect with an orthogonalS–R arrangement and obtained significantorthogonal Simon effects. The results suggestthat the above-right/below-left advantage in pre-vious studies (Cho & Proctor, 2004; Proctor et al.,2003) might not be solely due to the task context,and that positive and negative stimulus codesautomatically activate the corresponding polarityof the response codes.

EXPERIMENT 2

The location of the response set along the hori-zontal dimension is known to modulate theorthogonal SRC effect (response eccentricity effect:Cho & Proctor, 2002, 2004, 2005; Michaels,1989; Michaels & Schilder, 1991; Proctor& Cho, 2003; Weeks et al., 1995). In Proctorand Cho (2003, Exp. 1), participants engaged inan orthogonal SRC task with bimanual responses,in which the response set location varied betweenblocks. When the response set was located in theright position, a larger orthogonal SRC effectemerged than when the response set was locatedin the centre position. Moreover, when theresponse set was located in the left position, anup-left/down-right mapping preference emerged.The response eccentricity effect is explainedwithin a framework of coding asymmetry.The response eccentricity effect emerges becausethe response corresponding to the location of theresponse set is coded as positive (e.g., Proctor &Cho, 2003; Weeks et al., 1995).

In Experiment 2, we tested whether theresponse eccentricity effect emerges with anorthogonal Simon effect by varying the responseset location along the horizontal dimension. Ifthe orthogonal Simon effect is based on the

structural correspondence of polarity between thestimulus and response positions, any manipulationthat affects the coding asymmetry should alsoaffect the orthogonal Simon effect. Thus, we pre-dicted the response eccentricity effect. AlthoughCho and Proctor (2004) obtained a Simon-typeresponse eccentricity effect, the location infor-mation might be activated in some degreebecause of the orthogonal SRC task context intheir experiment (see Introduction).

Method

ParticipantsA total of 24 participants (12 females and 12males), aged between 18 and 26 years (meanage ¼ 22.5 years), took part in this experiment.All of them reported that they were right-handedand had normal or corrected-to-normal vision.None of them had participated in Experiment 1.

Apparatus, stimuli, task, and procedureThese were almost the same as those inExperiment 1 except for the following. Each testblock consisted of 180 trials. The location of theresponse apparatus was changed between blocks.Half of the participants started with the responseapparatus set 30 cm to the left of the bodymidline, followed by a centre placement, and fin-ished with the response apparatus set 30 cm tothe right of the body midline. The order of place-ment of the response apparatus was reversed forthe other half of the participants. The practiceblock consisted of 36 trials. The location of theresponse apparatus during the practice block wasidentical to that of the first test block. Betweenthe test blocks, participants left the room andtook a short break, during which time the exper-imenter moved the response apparatus to thelocation for the next test block.

Results

RTs shorter than 125 ms and longer than 1,250 mswere excluded from data analyses as outliers(0.15% of the trials). The mean RTs for correctresponses and the percentages of errors were



submitted to separate ANOVAs with responseset location (left, centre, right), compatibility(compatible: above-right/below-left; incompati-ble: above-left/below-right), and response (left,right) as within-participant factors (see Table 2).We used Tukey’s HSD test for post hoc analyses.

Reaction timesThe two-way interaction between response setlocation and compatibility was significant,F(2, 46) ¼ 18.46, MSE ¼ 196.11, p , .00001,indicating that the orthogonal Simon effectvaried with the response set location. The orthog-onal Simon effects were 16 ms (p, .001), 4 ms(ns), and –9 ms (p, .05) for the location of theresponse set at right, centre, and left, respectively.The two-way interaction between compatibilityand response was also significant, F(1, 23) ¼

6.92, MSE ¼ 287.35, p , .05. This reflected thefaster responses to the stimuli presented abovethe fixation (M ¼ 368 ms) than to the stimulipresented below the fixation (M ¼ 373 ms).Moreover, the right responses were marginallyfaster (M ¼ 366 ms) than the left responses(M ¼ 374 ms), F(1, 23) ¼ 3.37, MSE ¼ 1,498.87,p ¼ .08. Other main effects or interactions didnot reach significance (ps . .11).

Error rateThe main effect of compatibility nearly reachedsignificance, F(1, 23) ¼ 4.15, MSE ¼ 13.04, p ¼

.053. Responses tended to be more accurate witha compatible combination (1.8%) than withan incompatible combination (2.7%). This maineffect was modified by the two-way interactionbetween response set location and compatibility,F(2, 46) ¼ 7.88, MSE ¼ 6.40, p , .01, indicating

that the orthogonal Simon effect varied with thelocation of the response set. The orthogonalSimon effects were 2.2% (p , .01), 1.1% (ns),and –0.7% (ns) for the location of the responseset at right, centre, and left, respectively. Themain effect of response was also significant,F(1, 23) ¼ 11.04, MSE ¼ 5.59, p , .01.Participants made more errors with the rightresponses (2.7%) than with the left responses(1.8%). Other main effects or interactions didnot reach significance (ps . .19).

Discussion

The magnitude of the orthogonal Simon effect forboth RTs and error rates decreased as the responseset location progressed from right to left. In fact,the orthogonal Simon effect reversed when thestimulus set was located in the left position. Thisresult can be explained in terms of the asymmetriccoding hypothesis as follows. When the responseset was located in the right position, the rightresponse code became more positive, and thecoding asymmetry became more prominent. As aconsequence, the above stimuli coded as positiveprimed the positive right response code, and thebelow stimuli coded as negative primed the nega-tive left response code through an automatic acti-vation route. In contrast, when the response setwas located at the left position, the left responsecode became the positive alternative. As a result,the positive above stimuli automatically activatedthe positive left response, and the negative belowstimuli automatically activated the negative rightresponse. Consequently, the reversed orthogonalSimon effect (i.e., above-left/below-right advan-tage) emerged when the response set was located

Table 2. Mean reaction timea and error rateb for Experiment 2 as a function of response set location, compatibility, and response

Left location Centre location Right location

Left Right Left Right Left Right

Compatiblec 383 (2.3) 369 (3.2) 369 (1.5) 359 (1.7) 374 (0.8) 357 (1.3)

Incompatibled 367 (1.7) 368 (2.5) 367 (2.2) 369 (3.1) 388 (2.1) 375 (4.4)

aIn ms. bPercentage (in parentheses). cAbove-right/below-left combination. dAbove-left/below-right combination.



in the left position. Again, even though task irre-levant, the positive and negative stimulus featuresactivated the positive and negative responsefeatures, respectively. These findings confirmedthat the orthogonal Simon effect results from thestructural correspondence of coding asymmetrybetween the stimulus and response sets.

The orthogonal Simon effect was not signifi-cant for both RTs and error rates with the responseapparatus at the centre location in Experiment 2,although the S–R arrangement of this conditionwas identical to the S–R arrangement ofExperiment 1, which yielded a significant orthog-onal Simon effect for both RTs and error rates.Similarly, the orthogonal SRC effects with thecentral response set location in other responseeccentricity experiments were frequently verysmall (e.g., Cho & Proctor, 2004; Proctor &Cho, 2003; Weeks et al., 1995). In ourExperiment 2, half the participants started with aleft response set location while the other halfstarted with a right response set location, so thecentral placement of the response set alwayscame second, as was the case in other orthogonalSRC studies using the response eccentricitymethod. Thus, the order of the response setlocation might affect the coding asymmetry. Totest this, we conducted ANOVAs for RTs anderror rates with order of response set location(left first, right first) as a between-participantsfactor and response set location, compatibility,and response as within-participant factors. Theinteraction between order and compatibility wassignificant for RTs, F(1, 22) ¼ 6.71, MSE ¼

578.05, p , .05. The orthogonal Simon effectwas larger for the right-first group than for theleft-first group (see Table 3). No other effects

concerning order reached significance,Fs , 1. Although no effects concerning orderreached significance for error rates, ps . .22, theorthogonal Simon effect for error rates showed asimilar pattern to the effect for RTs (i.e., largerorthogonal Simon effects for the right-first groupthan for the left-first group, see Table 3). Theseresults indicate that an irrelevant response setlocation may influence subsequent processing.This carry-over effect of the coding asymmetryduring the first block could have attenuated theorthogonal Simon effect at the subsequent centreresponse set location in our Experiment 2 andthe orthogonal SRC effects in previous studies.

GENERAL DISCUSSION

In this study, we investigated whether the orthog-onal SRC effect emerges even when the contextdoes not make the task-irrelevant spatial stimuluscode salient. In Experiment 1, participantsresponded to the colour of the stimulus presentedabove or below the fixation by pressing a right or aleft key. We obtained an orthogonal Simon effect:Above stimuli were responded to more efficientlyby a right response than a left response, andbelow stimuli were responded to more efficientlyby a left response than a right response, in situ-ations where the stimulus position was irrelevantto the task. In Experiment 2, we manipulatedthe response set location horizontally betweenblocks to test whether the response eccentricityeffect occurred for the orthogonal Simon effect.The above-right/below-left advantage increasedfor the right response set location and reversedto an above-left/below-right advantage for theleft response set location as the polarity of the pos-ition of the response set location became morepositive. Thus, in both experiments, responseswere consistently faster and more accurate forspatially orthogonal S–R pairs that maintainedthe structural correspondence of coding asymme-try between the stimulus and response positionseven though the stimulus position was taskirrelevant.

Table 3. Orthogonal Simon effect (above-right/below-leftadvantage) as a function of response set location and order of

response set location for reaction timea and error rateb in

Experiment 2

Left location Centre location Right location

Right first 1 (20.2) 11 (1.9) 21 (2.5)

Left first 219 (21.2) 23 (0.4) 11 (1.8)

aIn ms. bPercentage (in parentheses).



We can therefore conclude that the orthogonalSimon effect based on the S–R correspondence ofcoding asymmetry is not restricted to situationswhere the task-irrelevant location information issalient because of the context. The positive stimu-lus code of the above position automatically acti-vates the positive response code, and the negativestimulus code of the below position automaticallyactivates the negative response code. This isconsistent with previous findings indicating anautomatic above-right and below-left correspon-dence (Cho & Proctor, 2004; Proctor et al.,2003; Wallace, 1971, 1972).

Although we obtained a significant orthogonalSimon effect, the magnitude of this effect (12 msin Experiment 1) was less than the typical magni-tude of the parallel Simon effect (20–30 ms; seeLu & Proctor, 1995) or the duration Simoneffect (25 ms; Kunde & Stocker, 2002, Exp. 1).The magnitude of the orthogonal Simon effectwas similar to the Simon effect between the irrele-vant brightness of the stimuli and the responseforce (8 ms; Mattes et al., 2002, Exp. 5).Although the intensity and the strength mightseem to be somewhat similar, the brightness ofthe stimuli and the response force physicallydiffer. Some transformation rather than a directS–R correspondence may be involved in the inten-sity–force Simon effect. Also, the orthogonalSimon effect is based on the structural correspon-dence of the asymmetric codes accompanied by thecoding of the physically different vertical and hori-zontal spatial positions. Thus, if there were nodirect correspondence between the irrelevantstimulus and the response dimensions, and sometransformation might have occurred, then the cor-respondence effect would be less than that for adirect S–R correspondence. This is consistentwith the dimensional overlap model (Kornblumet al., 1990) that assumes an increase of theelement-level compatibility effect (the effect ofS–R mapping within the same stimulus andresponse sets) with the increase of the set-levelcompatibility (i.e., the similarity between thestimulus and the response dimensions).Moreover, the larger effect for parallel thanorthogonal S–R arrangements is also consistent

with the orthogonal SRC paradigm in which thestimulus position is task relevant. Weeks andProctor (1990, Exp. 3; see also Proctor & Wang,1997) conducted SRC tasks with vertical or hori-zontal visual stimuli and vertical or horizontalvocal responses. They reported larger SRCeffects with parallel S–R sets (e.g., left–rightpositions of visual stimuli and “left”–“right”vocal response sets) than with orthogonal S–Rsets (e.g., left–right positions of visual stimuliand “above”–“below” vocal response sets).

Unlike other nonspatial Simon effects, theorthogonal Simon effect (i.e., above-right/below-left advantage) is nonintuitive. In fact, inthe postexperimental interviews in the presentstudies, no participants reported that the spatialS–R relationship might have affected theirresponse despite the consistent polarity correspon-dence effects. Because of this seeming lack ofcorrespondence with an orthogonal S–R arrange-ment, the experimental design with right–leftresponses and manipulation within the verticaldimension of stimuli was often adopted as a wayto control the SRC (e.g., Duncan, 1984;Hommel & Lippa, 1995; Wallace, 1971, 1972),as was mentioned in the Introduction. However,the SRC effects emerge with a spatially orthogonalS–R relationship regardless of the task relevancyof the stimulus position, as we showed in ourstudy. This result has an important methodologi-cal implication. Many studies use horizontallydefined (or horizontally varying) responses.When we adopt an orthogonal S–R arrangement,we should consider the orthogonal SRC effect andin some way control for it (such as using counter-balancing if possible), whether or not the stimulusposition is relevant to the task.

We obtained orthogonal Simon effects basedon a structural correspondence of coding asymme-try between a horizontal response position and anirrelevant vertical stimulus position. Codingasymmetry might not be confined to vertical andhorizontal spatial dimensions. Exploring otherSimon effects that may appear counterintuitive atfirst glance, as well as studying the orthogonalSimon effect in more detail, would be helpful forunderstanding better the impact of irrelevant



information on action. This could also provide con-straints for experimental designs. Research on theSimon effect based on coding asymmetry wouldbe fruitful both empirically and theoretically.

Original manuscript received 29 March 2005

Accepted revision received 15 September 2005

PrEview proof published online 31 January 2006

REFERENCES

Adam, J. J., Boon, B., Paas, F. G. W. C., & Umilta, C.(1998). The up-right/down-left advantage for verti-cally oriented stimuli and horizontally orientedresponses: A dual-strategy hypothesis. Journal of

Experimental Psychology: Human Perception and

Performance, 24, 1582–1595.Ansorge, U. (2003). Spatial Simon effects and compat-

ibility effects induced by observed gaze direction.Visual Cognition, 10, 363–383.

Bauer, D. W., & Miller, J. (1982). Stimulus–responsecompatibility and the motor system. Quarterly

Journal of Experimental Psychology, 34A, 367–380.Chambers, K. W., McBeath, M. K., Schiano, D. J., &

Metz, E. G. (1999). Tops are more salient thanbottoms. Perception & Psychophysics, 61, 625–635.

Chase, W. G., & Clark, H. H. (1971). Semantics in theperception of verticality. British Journal of Psychology,62, 311–326.

Cho, Y. S., & Proctor, R. W. (2001). Effect of aninitiating action on the up-right/down-left advan-tage for vertically arrayed stimuli and horizon-tally arrayed responses. Journal of Experimental

Psychology: Human Perception and Performance, 27,472–484.

Cho, Y. S., & Proctor, R. W. (2002). Influences of handposture and hand position on compatibility effectsfor up–down stimuli mapped to left–rightresponses: Evidence for a hand referent hypothesis.Perception & Psychophysics, 64, 1301–1315.

Cho, Y. S., & Proctor, R. W. (2003). Stimulus andresponse representations underlying orthogonalstimulus–response compatibility effects.Psychonomic Bulletin & Review, 10, 45–73.

Cho, Y. S., & Proctor, R. W. (2004). Influences of mul-tiple spatial stimulus and response codes on orthog-onal stimulus–response compatibility. Perception &

Psychophysics, 66, 1003–1017.

Cho, Y. S., & Proctor, R. W. (2005). Representingresponse position relative to display location:Influence on orthogonal stimulus–response compat-ibility. Quarterly Journal of Experimental Psychology,

58A, 839–864.De Houwer, J. (1998). The semantic Simon effect.

Quarterly Journal of Experimental Psychology, 51A,683–688.

De Jong, R., Liang, C.-C., & Lauber, E. (1994).Conditional and unconditional automaticity: Adual-process model of effects of spatial stimulus–response correspondence. Journal of Experimental


Duncan, J. (1984). Selective attention and the organiz-ation of visual information. Journal of ExperimentalPsychology: General, 113, 501–517.

Dutta, A., & Proctor, R. W. (1992). Persistence of stimu-lus–response compatibility effects with extendedpractice. Journal of Experimental Psychology:

Learning, Memory, and Cognition, 18, 801–809.Hommel, B. (1993a). The relationship between stimu-

lus processing and response selection in the Simontask: Evidence for a temporal overlap. PsychologicalResearch, 55, 280–290.

Hommel, B. (1993b). The role of attention for theSimon effect. Psychological Research, 55, 208–222.

Hommel, B., & Lippa, Y. (1995). S–R compatibilityeffects due to context-dependent spatial stimuluscoding. Psychonomic Bulletin & Review, 2, 370–374.

Kornblum, S., Hasbroucq, T., & Osman, A. (1990).Dimensional overlap: Cognitive basis for stimulus–response compatibility—A model and taxonomy.Psychological Review, 97, 253–270.

Kornblum, S., & Lee, J.-W. (1995). Stimulus–responsecompatibility with relevant and irrelevant stimulusdimensions that do and do not overlap with theresponse. Journal of Experimental Psychology: Human

Perception and Performance, 21, 855–875.Kunde, W., & Stocker, C. (2002). A Simon effect for

stimulus–response duration. Quarterly Journal of

Experimental Psychology, 55A, 581–592.Kunde, W., & Wuhr, P. (2004). Actions blind to con-

ceptually overlapping stimuli. Psychological Research,68, 199–207.

Lippa, Y. (1996). A referential-coding explanation forcompatibility effects of physically orthogonal stimu-lus and response dimensions. Quarterly Journal of

Experimental Psychology, 49A, 950–971.Lu, C.-H., & Proctor, R. W. (1995). The influence of

irrelevant location information on performance: A



review of the Simon and spatial Stroop effects.Psychonomic Bulletin & Review, 2, 174–207.

Marble, J. G., & Proctor, R. W. (2000). Mixinglocation-relevant and location-irrelevant choice-reaction tasks: Influences of location mapping onthe Simon effect. Journal of Experimental Psychology:Human Perception and Performance, 26, 1515–1533.

Mattes, S., Leuthold, H., & Ulrich, R. (2002).Stimulus–response compatibility in intensity–forcerelations. Quarterly Journal of Experimental

Psychology, 55A, 1175–1191.Michaels, C. F. (1989). S–R compatibilities depend on

eccentricity of responding hand. Quarterly Journal ofExperimental Psychology, 41A, 263–272.

Michaels, C. F., & Schilder, S. (1991). Stimulus–response compatibilities between vertically orientedstimuli and horizontally oriented responses: Theeffects of hand position and posture. Perception &

Psychophysics, 49, 342–348.Olson, G. M., & Laxar, K. (1973). Asymmetries in pro-

cessing the terms “right” and “left”. Journal of

Experimental Psychology, 100, 284–290.Olson, G. M., & Laxar, K. (1974). Processing the terms

right and left: A note on left-handers. Journal of

Experimental Psychology, 102, 1135–1137.Proctor, R. W., & Cho, Y. S. (2003). Effects of response

eccentricity and relative position on orthogonalstimulus–response compatibility with joystick andkeypress responses. Quarterly Journal of

Experimental Psychology, 56A, 309–327.Proctor, R. W., & Reeve, T. G. (Eds.). (1990).

Stimulus–response compatibility: An integrated

perspective. Amsterdam, North-Holland: ElsevierScience Publishers.

Proctor, R. W., Vu, K.-P. L., & Marble, J. G. (2003).Mixing location-relevant and irrelevant tasks: Spatialcompatibility effects eliminated by stimuli that sharethe same spatial codes. Visual Cognition, 10, 15–50.

Proctor, R. W., & Wang, H. (1997). Differentiatingtypes of set-level compatibility. In B. Hommel &W. Prinz (Eds.),Theoretical issues in stimulus–responsecompatibility (pp. 11–37). Amsterdam: Elsevier.

Proctor, R. W., Wang, H., & Vu, K.-P. L. (2002).Influences of different combinations of conceptual,perceptual, and structural similarity on stimulus–response compatibility. Quarterly Journal of

Experimental Psychology, 55A, 59–74.Romaiguere, P., Hasbroucq, T., Possamaı, C.-A., &

Seal, J. (1993). Intensity to force translation: A

new effect of stimulus–response compatibilityrevealed by analysis of response time and electromyo-graphic activity of a prime mover. Cognitive Brain

Research, 1, 197–201.Rubichi, S., Nicoletti, R., Iani, C., & Umilta, C. (1997).

The Simon effect occurs relative to the direction ofan attention shift. Journal of Experimental


Simon, J. R. (1990). The effects of an irrelevant direc-tional cue on human information processing.In R. W. Proctor & T. G. Reeve (Eds.), Stimulus–response compatibility: An integrated perspective

(pp. 31–86). Amsterdam, North-Holland: ElsevierScience Publishers.

Stoffer, T. H. (1991). Attentional focusing and spatialstimulus–response compatibility. Psychological

Research, 53, 127–135.Umilta, C. (1991). Problems of the salient-features

coding hypothesis: Comment on Weeks andProctor. Journal of Experimental Psychology: General,120, 83–86.

Umilta, C., & Nicoletti, R. (1990). Spatial stimulus–response compatibility. In R. W. Proctor & T. G.Reeve (Eds.), Stimulus–response compatibility: An

integrated perspective (pp. 89–116). Amsterdam,North-Holland: Elsevier Science Publishers.

Wallace, R. J. (1971). S–R compatibility and the idea ofa response code. Journal of Experimental Psychology,88, 354–360.

Wallace, R. J. (1972). Spatial S–R compatibility effectsinvolving kinesthetic cues. Journal of Experimental

Psychology, 93, 163–168.Weeks, D. J., & Proctor, R. W. (1990). Salient-features

coding in the translation between orthogonal stimu-lus and response dimensions. Journal of ExperimentalPsychology: General, 119, 355–366.

Weeks, D. J., & Proctor, R. W. (1991). Salient-featurescoding and orthogonal compatibility effects: A replyto Umilta. Journal of Experimental Psychology:

General, 120, 87–89.Weeks, D. J., Proctor, R. W., & Beyak, B. (1995).

Stimulus–response compatibility for verticallyoriented stimuli and horizontally oriented responses:Evidence for spatial coding. Quarterly Journal of

Experimental Psychology, 48A, 367–383.Zorzi, M., & Umilta, C. (1995). A computational

model of the Simon effect. Psychological Research, 58,193–205.



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