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Effects of visual cue and responseassignment on spatial stimulus coding instimulus–response compatibilityAkio Nishimura a & Kazuhiko Yokosawa aa Department of Psychology, The University of Tokyo, Tokyo, JapanAccepted author version posted online: 11 Aug 2011.Published online: 22Sep 2011.
To cite this article: Akio Nishimura & Kazuhiko Yokosawa (2012) Effects of visual cue and responseassignment on spatial stimulus coding in stimulus–response compatibility, The Quarterly Journal ofExperimental Psychology, 65:1, 55-72, DOI: 10.1080/17470218.2011.611888
To link to this article: http://dx.doi.org/10.1080/17470218.2011.611888
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Effects of visual cue and response assignment on spatialstimulus coding in stimulus–response compatibility
Akio Nishimura and Kazuhiko Yokosawa
Department of Psychology, The University of Tokyo, Tokyo, Japan
Tlauka and McKenna (2000) reported a reversal of the traditional stimulus–response compatibility(SRC) effect (faster responding to a stimulus presented on the same side than to one on the oppositeside) when the stimulus appearing on one side of a display is a member of a superordinate unit that islargely on the opposite side. We investigated the effects of a visual cue that explicitly shows a superor-dinate unit, and of assignment of multiple stimuli within each superordinate unit to one response, onthe SRC effect based on superordinate unit position. Three experiments revealed that stimulus–response assignment is critical, while the visual cue plays a minor role, in eliciting the SRC effectbased on the superordinate unit position. Findings suggest bidirectional interaction between perceptionand action and simultaneous spatial stimulus coding according to multiple frames of reference, withcontribution of each coding to the SRC effect flexibly varying with task situations.
Keywords: Stimulus–response compatibility; Spatial coding; Stimulus grouping; Response selection;Perception and action.
Spatial features of perceptual and action represen-tations are important and may be fundamental forhuman information processing (e.g., Hommel,1998). The present research focuses upon ways inwhich spatial relationships between a percept anda related action affect performance. Specifically,when a stimulus and a response assigned to thatstimulus are spatially congruent (compatible con-dition), performance in certain tasks is better thanwhen stimuli and responses are not spatially con-gruent (incompatible condition). For example,
people respond to a stimulus presented on theright side more rapidly with a right response thanwith a left response (e.g., Brebner 1973). Thisphenomenon is known as the spatial stimulus–response compatibility (SRC) effect (Fitts &Deininger, 1954; Fitts & Seeger, 1953; Hommel& Prinz, 1997; Kornblum, Hasbroucq, &Osman, 1990; Proctor & Reeve, 1990; Proctor &Vu, 2006). The SRC effect emerges not onlywhen participants respond on the basis of spatialinformation, but also when they respond on the
Correspondence should be addressed to Kazuhiko Yokosawa, Department of Psychology, Graduate School of Humanities and
Sociology, The University of Tokyo, 7–3–1 Hongo, Bunkyo-ku, Tokyo 113–0033, Japan. E-mail: [email protected]
We would like to thank Ines Jentzsch and three anonymous reviewers for their helpful and constructive comments. This study was
supported by a grant from the Research Fellowships of the Japan Society for the Promotion of Science for Young Scientists to A.N. and
by a Grant-in-Aid for Scientific Research from the Japan Society for the Promotion of Science awarded to K.Y. Akio Nishimura is now
at Sophia University, Tokyo, Japan, as a Japan Society for the Promotion of Science (JSPS) Research Fellow.
# 2012 The Experimental Psychology Society 55http://www.psypress.com/qjep http://dx.doi.org/10.1080/17470218.2011.611888
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basis of other stimulus features such as colour orshape (Simon effect; Craft & Simon, 1970;Hedge & Marsh, 1975; Lu & Proctor, 1995;Simon, 1990).
A spatial coding account of stimulus andresponse positions has offered an influential expla-nation of the SRC effect (Proctor, Lu, Wang, &Dutta, 1995; Umiltà & Nicoletti, 1990; Wallace,1971). According to this account, the presentationof a stimulus elicits the formation of a spatial stimu-lus code that represents the position of this stimu-lus. Similarly, response alternatives are representedby corresponding spatial response codes. Thestimulus code automatically activates a spatiallycongruent response code. Compatible conditionsare defined as those in which the stimulus and ato-be-performed response are on the same sideand hence share a spatial feature; in this case, thestimulus code activates the correct response code,leading to a facilitation of this response. In contrast,in incompatible conditions, wherein the stimulusand a relevant response are on the opposite sides,the spatial stimulus code automatically activates aspatially congruent, but now incorrect, responsecode. This activation of an incorrect responsecode results in response conflict with the correctresponse code, which is activated by task instruc-tions. The resolution of a response conflict takestime. As a consequence, the response is delayed.
In considering the spatial coding in the SRCeffect, several reference frames are relevant to ahorizontal (left/right) encoding of stimuli atdifferent positions in a visual display. The spatialposition of an individual stimulus can be indepen-dently defined relative to a reference frame basedupon a participant’s body midline (hemispace),relative to a frame based on a participant’s fixationpoint (hemifield), and relative to a frame associatedwith another stimulus within the same display.Lamberts, Tavernier, and d’Ydewalle (1992)manipulated hemispace and hemifield, as well asthe relative position of a presented stimulus;they found that the spatial relationships betweenstimuli and responses, defined by each of these
three reference frames, independently influencedspeed of responding to targets. This finding indi-cates that spatial coding based on multiple framesof reference can occur simultaneously to impactresponse selection (see also Roswarski & Proctor,1996). In addition, other potential frames of refer-ence, associated with exogenous (Danziger,Kingstone, & Ward, 2001; Lleras, Moore, &Mordkoff, 2004) and endogenous (Abrahamse &Van der Lubbe, 2008) spatial attention, stimulatedeye (Valle-Inclán, Hackley, & de Labra, 2003), theleft/right eyes of a face with 90 degrees rotation(Hommel & Lippa, 1995), and mental imagery(Bächtold, Baumüller, & Brugger, 1998; Tlauka& McKenna, 1998), have been shown to play arole in horizontal stimulus coding.
In summary, in various visual tasks, numerouscandidate frames of reference have been identified,each of which offers a potential for influencingthe coding of an individual stimulus position.The perceived spatial position of a stimulus, as itrelates to a given frame, then may affect theeffectiveness of response that is assigned to act onthis stimulus. Furthermore, several differentframes, acting simultaneously, may contribute tooverall performance, with their relative influencebased flexibly upon task demands, environmentalfactors, instructions, and so on (e.g., Umiltà &Liotti, 1987).
Tlauka and McKenna (2000) found evidencesupporting a role for hierarchical reference framesin spatial stimulus coding associated with theSRC effect. In their study, they presented a targetstimulus randomly at one of six spatial locationsas depicted in Figure 1a.1
In their first experiment, line segments, asdepicted in Figure 1b, loosely outlined left andright portions of a larger display, thereby formingsuperordinate units. Three stimulus locations (S)within each superordinate unit were assigned,respectively, to the left or right response, using amany-to-one mapping of stimuli onto responses.For example, with separating line segmentsdepicted in the top left panel of Figure 1b,
1 Hereafter, when mentioned in the present manuscript, “Figure(s)” refer to the figure(s) in the present article, not to the figures in
the cited articles.
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Tlauka and McKenna (2000, Experiment 1)assigned S1, S2, and S3 in Figure 1a to oneresponse and S4, S5, and S6 to another response.In this design, left/right position of the superordi-nate unit (the two outlined areas) and that of anindividual stimulus could be either congruent orincongruent. The incongruent configurations aremost important to an assessment of the impact ofeach coding on performance. In this respect, thecritical stimulus locations were S3 and S6 becausethese locations of individual stimuli are incongruentwith the superordinate unit within which they areembedded. In this experiment, an SRC effect wasobserved based on the superordinate unit:
Responses were faster when they were spatiallycongruent with the superordinate unit position(and incongruent with the individual stimulus pos-ition) than when they were spatially incongruentwith the superordinate unit position (and congru-ent with the individual stimulus position).
Subsequent experiments replicated this basicSRC finding. In Experiment 2 of Tlauka andMcKenna (2000), visual cues of city names wereused (i.e., cities in UK and US) instead of percep-tual visual cues of dividing line segments toconvey a superordinate unit grouped by semanticlinks. The visual display was similar to thatdepicted in Figure 1a but city names were displayedbelow each possible stimulus location during theexperiment—for example, instead of numbers 1through 6, Bristol, York, London (cities in theUK), Miami, Boston, and Dallas (cities in theUSA) were visible, respectively. In Experiment 3of Tlauka and McKenna, city names were replacedby six letters (P, T, F, B, W, and K). Participantslearned two groups of three letters. Thus, in thiscase, the superordinate units were conveyed byvisual cues, but the groups of stimuli were initiallydefined arbitrarily with associative links acquiredthrough learning. Again, an SRC effect based onthe superordinate unit position was observed.Taken together, these findings suggest that thesuperordinate unit position, rather than the indi-vidual stimulus position, dominates spatial codingin this SRC effect. Tlauka and McKenna (2000;see also Tlauka, 2004) have assumed a hierarchicalspatial coding of stimulus position. In this view, thespatial coding of a superordinate unit conveyed byvisual cues is ranked higher in order and prioritythan the spatial coding of individual stimulus pos-itions, in terms of impact on the SRC effect.
In Tlauka and McKenna (2000), the superordi-nate units were rendered visually through use of linesegments that highlighted embedded perceptualgroups (Experiment 1), as well as use of visiblesemantic associations with American and Britishcity names (Experiment 2) and using arbitrarylinks with letters formed during a prior learningphase (Experiment 3). They attributed the for-mation of superordinate units, which dominatedthe spatial coding of embedded stimuli, to
Figure 1. (a) Illustration of a stimulus display used in Experiment
1. Note that each stimulus was numbered for reference in the main
text and that no numbers were presented on the display
throughout the experimental session. (b) Stimulus displays used in
Experiment 2. Top panels show the stimuli presented to the
experimental group. Bottom panels show the stimuli presented to
the control group.
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processes mediated by visual cues (see also Tlauka,2004). However, another factor may have beenresponsible for their pattern of findings. In all ofthese experiments, the several different stimuliembedded within each visually determined super-ordinate unit were assigned to a single response.It is possible that this many-to-one stimulus–response assignment alone is sufficient to elicitthe observed SRC effects based on a superordinateunit’s location. This is difficult to confirm in theTlauka and McKenna (2000) data because therespective contribution of perceptual cues andresponse assignments to the SRC effect based onthe superordinate unit location covary in theirexperimental design. Visual cues indicating a super-ordinate unit always accompanied a many-to-oneresponse assignment. In brief, then, we suggestthat perhaps visual cues to a superordinate unitare unnecessary, given this design.
In order to pursue the nature of spatial stimuluscoding in the interaction between perception andaction in human cognitive processing, the presentstudy was designed to disentangle the role of avisual cue to a superordinate unit—namely a per-ceptual (stimulus-related) factor—and the role ofa response assignment to stimuli within a superor-dinate unit—namely an action (response-related)factor. Experiment 1 tested the influence ofresponse assignment in the absence of any visualcue for a superordinate unit. Experiments 2 and 3tested the influence of a perceptual visual cue thatexplicitly shows superordinate units in the absenceof assigning a single response to multiple stimuliwithin a superordinate unit. In all three exper-iments, we compared performance of an experimen-tal group, in which the superordinate unit positionand the individual stimulus position were incongru-ent, with performance of a control group, in whichsuperordinate and individual positions were congru-ent. In terms of stimulus coding associated withmultiple frames of reference, this design permitsus to examine the influence of nondominant
coding in various situations, regardless of whetherthe dominant coding is based on the superordinateunit position or upon the individual stimulusposition.2
EXPERIMENT 1
Experiment 1 was designed to investigate the role ofresponse assignment in the absence of explicit visualcues showing a superordinate unit on performance inan SRC task. One goal was to ascertain the nature ofcoding dominance of the superordinate unit locationwith respect to the individual stimulus locationsembedded within this higher order unit.Accordingly, we removed the line segments thatserved as visual cues to superordinate partitioningunits (which surrounded individual stimuluslocations) from original displays that were similarto those used by Tlauka and McKenna (2000,Experiment 1); only the rectangular outer framewas presented on the screen. As in Tlauka andMcKenna’s (2000) procedure, target stimuliappeared at one of six locations. Participants wereinstructed to press either the left or the right keyin response to a target presented at three of the sixlocations and to press another key in response to atarget appearing at the remaining three locations.Three stimulus locations within each of the twosubsets were determined such that they corre-sponded, respectively, to the stimuli within each oftwo superordinate units used in Tlauka andMcKenna (2000). We defined the compatibility interms of the spatial relationship between a responselocation and the location of the superordinate unitformed by response assignment rather than thelocation of an individual stimulus.
The most important stimulus location (“targetlocation”) for an experimental group in thepresent study had a spatial code based on superor-dinate unit location that contradicted the spatialcode based on individual stimulus location. That
2 In the present study, the individual stimulus position could be coded relative to several frames of reference, as is indicated in the
previous findings (e.g., Lamberts et al., 1992). However, the aim of the present study is to examine the priority order of spatial coding of
the superordinate unit position and of the individual stimulus position. Therefore we do not discriminate among, or strictly discuss,
these frames of reference for spatial coding of individual stimulus position in the present study.
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is, target locations were S3 and S6 if S1, S2, and S3were assigned to one response and S4, S5, and S6to the other response, and S2 and S5 if S1, S5,and S6 were assigned to one response and S2, S3,and S4 to the other. If the response assignment issufficient to form the superordinate unit that dom-inates spatial coding, then the SRC effect willemerge at the target location consistent with themany-to-one response assignment in the exper-imental group. In this case, responses should befaster when the response location is spatially con-gruent with the superordinate unit location, ratherthan with the individual stimulus location.However, if a visual cue to the superordinateframe is essential, then a reversal of the SRCeffect will be observed for critical target locationsin the experimental group. In the latter case,responses should be faster when they are spatiallycongruent with the individual stimulus locationrather than with the superordinate unit location.We also introduced a control group in which thespatial codes based on the superordinate unit locationand on the individual stimulus location were alwayscongruent—that is, S1, S2, and S6 assigned to oneresponse and S3, S4, and S5 to the other. If boththe superordinate unit location and the individualstimulus location were coded, and both exerted aninfluence, then the pattern of SRC effects acrossthe locations should differ between the experimentalgroup and the control group.
Method
ParticipantsTwenty-four students (14 female and 10 male;mean age 22.3 years with a range of 20 to 26years) participated in this experiment. All the par-ticipants reported that they were right-handedand had normal or corrected-to-normal vision.They were naïve as to the purpose of the exper-iment. Half were assigned to the experimentalgroup, while the other half were assigned to thecontrol group.
Apparatus and stimuliStimulus presentation and data collection were con-trolled by anAV-tachistoscope system (Iwatsu ISEL
IS-703). Stimuli were presented on a 22-inch CRTcolour monitor (Mitsubishi Diamondtron FlatRDF22IH). A viewing distance of 46 cm was main-tained by a head-and-chin rest. Two horizontallyarrayed response keys were separated by 21 cm.The distance from a participant to response keyswas 27 cm. Participants pressed the right key withtheir right index finger and the left key with theirleft index finger. The central axis of the visualdisplay, the midline between the two responsekeys, and each participant’s body midline were line-arly aligned.
All stimuli were presented in white on a blackbackground. A large box (19 cm in width× 13 cmin height) at the centre of the display was used as aframe. The target stimulus was a square (0.5 cmon a side) that was presented in one of six locationswithin a large rectangle, as shown in Figure 1a (notethat numbers below squares were not presented toparticipants). Two locations were 2.8 cm from theleft or right vertical side of the frame and equidistantfrom the top and bottom horizontal sides (S1 andS4 in Figure 1a). Four other locations were 7.7 cmfrom the left or right vertical side and 3 cm fromthe top or bottom horizontal side (S2, S3, S5, andS6 in Figure 1a).
Tasks and procedureThe participants’ task was to press the left or rightkey as quickly and accurately as possible in responseto a target’s location.
The experimental group of 12 participants wasrandomly divided into two subgroups. Six exper-imental participants made the left response to thetarget stimuli presented at locations S1, S2, andS3 in Figure 1a, and the right response to thetarget stimuli presented at locations S4, S5, andS6 in Figure 1a, for the compatible condition,and made the opposite responses for the incompa-tible condition. The remaining experimental groupparticipants made the left response to the targetsS1, S5, and S6, and the right response to thetargets S2, S3, and S4, for the compatible con-dition. The reversed mapping was given for theincompatible condition.
Twelve participants were assigned to the controlgroup. All control participants made a left response
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to the targets S1, S2, and S6 and a right response tothe remaining targets (S3, S4, and S5), for thecompatible mapping condition. They made theright response to the targets S1, S2, and S6 andthe left response to the targets S3, S4, and S5, forthe incompatible mapping condition.
The experiment was conducted in a darkenedroom. A large rectangular frame was present onall displays throughout the experiment. The targetstimulus appeared at one of six locations, asdepicted in Figure 1a, and it remained visibleuntil a response was made. Response extinguishedthe target stimulus, and the frame remained onthe display for 1,500 ms. After this response–stimulus interval, the target for the next trialappeared.
The participants engaged in both the compatibleand the incompatible mapping conditions. Theorder of the compatibility mapping conditionswas counterbalanced across participants. To avoida potential stimulus coding strategy bias by refer-ring to spatial dimension(s), the stimulus–responsemapping was explained by the experimenter whopointed to each target on the display on which allthe possible stimulus locations were presented(Figure 1a without numbers below the targets).Each of the two mapping conditions consisted ofone practice block of 60 trials and two experimentalblocks, each of which included 132 trials. Theparticipants took short rests between the blocks.A 500-Hz tonal feedback for 100 ms was givenfor error responses during the practice block.
Results
Results are shown in Figure 2. An omnibus signifi-cance criterion was fixed at p, .05. Trials in whichresponse times (RTs) were less than 100 ms ormore than 1,000 ms (outliers; 0.40%) wereexcluded from the analyses. Both the resultingmean RTs for correct responses and the errorrates were submitted to mixed factorial analyses ofvariance (ANOVAs) with group (2; control, exper-imental) as a between-participants factor andlocation (3; see below) and compatibility (2; com-patible, incompatible) as within-participant factors.
To attain a sufficient number of trials for reliabledata summaries across all conditions, the threedifferent target locations were defined in terms oftheir relationships between the superordinate unitposition and the individual stimulus position.These are outlined below for experimental andcontrol groups.
For the experimental group, we defined a criticallocation as one in which the individual stimulusposition and the superordinate unit position wereon the opposite sides, leading to a reversed corre-spondence location. The location where the individ-ual stimulus position was the end point within asuperordinate unit side was defined as a total corre-spondence location. Finally, the location in betweenthe reversed correspondence location and the total
Figure 2. Reaction times for Experiment 1 in (a) the experimental
group and (b) the control group as a function of correspondence
location and compatibility between the superordinate unit position
and the response. Error bars represent standard errors for means.
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correspondence location was defined as a partialcorrespondence location. For example, when S1, S2,and S3 (Figure 1a) positions were mapped to oneresponse, and S4, S5, and S6 positions weremapped to another, S3 and S6 were reversed corre-spondence locations, S2 and S5 were partial corre-spondence locations, and S1 and S4 were totalcorrespondence locations. In contrast, for theparticipants with the mapping of S1, S5, and S6positions to one response and S2, S3, and S4 toanother, S2 and S5 were reversed correspondencelocations, S3 and S6 were partial correspondencelocations, and S1 and S4 were, again, total corre-spondence locations.
For the control group, the definition of total cor-respondence location was the same as that for theexperimental group (S1 and S4). However, weused different definitions concerning the innerfour stimulus locations (S2, S3, S5, and S6)because in the control group there was no reversedcorrespondence location where the superordinateunit and the individual stimulus were on the oppo-site sides. Rather these four stimulus locationsmatched the partial correspondence location inthe experimental group. Therefore, for a randomlyselected half of the participants, the S2 and S5positions were defined as Partial CorrespondenceLocation 1, and S3 and S6 as PartialCorrespondence Location 2. The S3 and S6 positionswere defined as Partial Correspondence Location 1,and S2 and S5 as Partial Correspondence Location2, for the remaining half. Thus, although this dis-tinction treats Partial Correspondence Locations1 and 2 differently, practically speaking, they didnot differ.
Concerning the location factor in theANOVAs, we treated the partial correspondencelocation for the experimental group and thePartial Correspondence Location 1 for the controlgroup as a corresponding condition, and thereversed correspondence location for the exper-imental group and the Partial CorrespondenceLocation 2 as a corresponding condition.
RTThe main effect of compatibility was significant, F(1, 22)= 43.87, p, .001. An overall SRC effect of
56 ms was obtained (335 ms vs. 391 ms). The maineffect of group was not significant, F, 1, indicat-ing comparable overall RTs for the experimental(361 ms) and the control (364 ms) groups. Theinteraction between group and compatibility wasnot significant, F, 1. The main effect of locationwas significant, F(2, 44)= 11.65, p, .001, butan interaction with group qualified this maineffect, F(2, 44)= 13.33, p, .001. The interactionbetween group and compatibility was not signifi-cant, F, 1, and that between location and compat-ibility just missed significance, F(2, 44)= 3.14,p= .053. Finally and most importantly, the three-way interaction between group, location, and com-patibility was significant, F(2, 44)= 3.78, p, .05.This indicates that the pattern of SRC effectsacross target locations differed for the two groups,experimental and control.
To analyse group differences in more detail, weconducted separate repeated measures ANOVAsfor experimental and control groups with locationand compatibility as within-participant factors.
In the experimental group, the main effect oflocation was significant, F(2, 22)= 6.11, p, .01.Response latency was shorter for the partial corre-spondence location than for the reversed corre-spondence location (347 ms vs. 374 ms; p, .01),with intermediate latency for the total correspon-dence location (362 ms). The main effect of com-patibility was also significant, F(1, 11)= 11.92,p, .01, showing a spatial SRC effect of 49 msbased on the superordinate unit location (337 msvs. 385 ms). A significant interaction betweenlocation and compatibility, F(2, 22)= 4.90,p, .05, indicated that the spatial SRC effect dif-fered in magnitude across locations (67 ms,43 ms, and 36 ms for total, partial, and reversedcorrespondence locations, respectively, ps, .001).
In the control group, the main effect of locationwas significant, F(2, 22)= 27.60, p, .001.Response latency was shorter for the total corre-spondence location (343 ms) than for the partialcorrespondence locations (1: 375 ms, 2: 376 ms;ps, .001). The main effect of compatibility wasalso significant, F(1, 11)= 46.42, p, .001,showing a spatial SRC effect of 63 ms (333 msvs. 396 ms). The interaction between location and
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compatibility was not significant, F(2, 22), 1,p= .57, indicating that the spatial SRC effectbased on superordinate unit location was compar-able in magnitude across locations (61 ms, 68 ms,and 61 ms for total, Partial 1, and Partial 2 corre-spondence locations, respectively).
Error rateThe main effect of compatibility was significant,F(1, 22)= 9.95, p, .005. An overall SRC effectof 1.2% was obtained (3.2% vs. 4.4%). The maineffect of group was significant, F(1, 22)= 7.12,p, .05, indicating that the participants in theexperimental group (4.8%) made more errors thanthose in the control group (2.9%). The maineffect of location was also significant, F(2, 44)=15.39, p, .001, and it was qualified by an inter-action with group, F(2, 44)= 5.28, p, .01. Mostimportantly, the three-way interaction betweengroup, location, and compatibility was significant,F(2, 44)= 5.39, p, .01, indicating that thepattern of SRC effects across locations differedbetween the experimental and the control groups.Other interactions were not significant, ps. .226.
To analyse the group differences in more detail(as in the RT data), we conducted separate repeatedmeasures ANOVAs for the experimental andcontrol groups with location and compatibility aswithin-participant factors.
In the experimental group, the main effect oflocation was significant, F(2, 22)= 9.81, p, .001.Participants made more errors for the reversed cor-respondence location (7.3%) than for the total orpartial correspondence locations (4.2% and 2.8%,respectively; ps, .05). Although the main effectof compatibility was not significant, F(1, 11)=2.10, p= .18, the interaction between location andcompatibility was significant, F(2, 22)= 6.28,p, .01. The significant spatial SRC effect basedon superordinate unit location was observed onlyfor the total correspondence location (3.4%,p, .05), but not for the partial (0.7%) or reversed(–1.4%) correspondence locations (ps. .71).
In the control group, the main effect of locationwas significant, F(2, 22)= 11.51, p, .001.Participants made more errors for the partial corre-spondence locations (1: 3.3%, 2: 4.3%) than for the
total correspondence location (1.1%; ps, .05). Themain effect of compatibility was also significant,F(1, 11)= 11.95, p, .01, indicating the spatialSRC effect of 1.5%. The interaction betweenlocation and compatibility was not significant,F(2, 22), 1, p= .52. The spatial SRC effectsbased on superordinate unit location were similarin magnitude across locations (0.9%, 1.3%, and2.4% for total, Partial 1, and Partial 2 correspon-dence locations, respectively).
Discussion
In the experimental group, although there was novisual cue, the many-to-one response assignmentalone permitted emergence of a spatial SRC effectbased largely on the superordinate unit locationcoding (i.e., rather than upon individual stimuluslocation coding). The spatial SRC effect was con-stant across the locations in the control group inwhich the superordinate unit location and the indi-vidual stimulus location were always congruent.However, in the experimental group, the SRCeffect was smaller with the reversed correspondencelocation where the horizontal location of the super-ordinate unit and that of the individual stimulusdiffered, than with the total correspondencelocation where these two locations were the same.This indicates that the spatial code of the superor-dinate unit location was the primary factor affectingresponses in the present task, although the spatialcode of individual stimuli also contributed to thisprocess. This finding is consistent with the notionthat spatial stimulus coding is based upon multiple,simultaneous, frames of reference (e.g., Lambertset al., 1992). The present experiment establishesthat no visual cue is necessary to elicit SRCeffects due to a superordinate reference frame;instead, simply the nature of response assignmentis sufficient to elicit an SRC effect based on thesuperordinate unit.
EXPERIMENT 2
In Experiment 2, we tested the effect of a visual cueon the spatial SRC effect based on the
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superordinate unit location, but we eliminated themany-to-one response mapping assignments usedin Experiment 1. We used a perceptual visual cuethat consisted of line segment(s), which dividedthe overall rectangular frame into largely right andleft areas (Figure 1b). This perceptual cue was thestrongest of several cues used in Tlauka andMcKenna (2000). However, in Experiment 2, thetarget stimulus appeared only at the critical targetlocations (i.e., the reversed correspondence locationin Experiment 1). In other words, each superordi-nate unit included only a single stimulus position.Consequently, in this experiment, multiplestimuli within a superordinate unit could not beassigned to a single response.
Although hierarchies are often depicted as pyra-mids in which multiple subordinate units/membersare nested within each superordinate unit, in thepresent study we focus mainly on the ordinal/subordination property of hierarchical coding, inwhich one frame of reference is ranked higher inorder and priority for spatial coding than another.Given this order/subordination perspective, it isnot necessary that a dominant frame of reference(i.e., one with a higher rank order) and a subordi-nate frame of reference realize a one-to-manyrelationship. This interpretation is consistent withthe hierarchical coding hypothesis proposed byHeister, Schroeder-Heister, and Ehrenstein(1990) to account for the horizontal spatialcoding of responses in the SRC effect. Accordingto their hierarchical coding hypothesis, the encod-ing of right or left response key position andcoding of the anatomical right or left identity ofthe responding effector are rank-ordered, with theformer being higher and the latter lower. Thelower internal coding of anatomical identitybecomes operative or influential only when ahigher rank-order of external positional codingcannot be used. To apply this perspective in thepresent study, we assumed that the term “hierarch-ical coding” is defined as follows: One frame ofreference for the spatial coding is dominant whenpotentially two or more could be available. Usingthis terminology, we investigated the hierarchicalcoding of individual stimulus locations and super-ordinate unit locations in Experiment 2. That is,
both the superordinate unit location and the indi-vidual stimulus location were potentially availableas frames of reference for the spatial coding inExperiment 2 because the visual cues (line seg-ments) formed the superordinate units.
Consistent with Experiment 1, in Experiment 2we defined compatibility in terms of a spatialrelationship between a response location and thelocation of the superordinate unit formed byvisual cues rather than between a response locationand an individual stimulus location. This conformsto the concept that the superordinate unit locationdominates the determination of compatibility, asclaimed by Tlauka (2004). Alternatively, if responseassignment is critical to performance in this task, asthe data of Experiment 1 suggest, then the SRCeffect in Experiment 2 should be based on individ-ual stimulus location. In this case, a reversed SRCeffect would emerge, given the present definitionof compatibility. On the other hand, if the visualcue is sufficient to form the superordinate unitthat dominates spatial coding, then a conventionalSRC effect should be observed in this experiment.
Method
ParticipantsThirty-two volunteers (12 female and 20 male;mean age 20.7 years, range from 20 to 25 years)participated. All reported that they were right-handed and had normal or corrected-to-normalvision. All were naïve to the purpose of the exper-iment; none had participated in Experiment1. Half were assigned to the experimental group,while the other half were assigned to the controlgroup.
Apparatus, stimuli, tasks, and procedureThese were the same as those in Experiment 1,except for the differences noted below.
The frame was divided by line segments thatloosely divided the larger rectangle into left andright parts (Figure 1b); these partitions conformedto those used in Experiment 1 of Tlauka andMcKenna (2000). For the control group, thecentral vertical line evenly divided the rectangleframe into left and the right halves as shown in
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Figure 1b (bottom row). For the experimentalgroup, the participants were presented with aframed display that was unevenly divided into twosections by three line segments. For half of theseparticipants, two line segments whose length washalf of the vertical side of the frame were drawnfrom the top and bottom sides, with the top one13.5 cm from the right vertical side and thebottom one 13.5 cm from the left vertical side.One endpoint of each line segment was on thetop or bottom horizontal side of the frame, andanother endpoint was connected by the third linesegment (Figure 1b, top left). For the remaininghalf of the experimental group, the frame was themirror image of that depicted above (Figure 1b,top right).
The target appeared at one of only two locationsin each group (see Figure 1b). For the experimentalgroup, the targets appeared only at locations corre-sponding to the reversed corresponding location inExperiment 1. For the control group, the targetsappeared at locations corresponding to those forthe experimental group. We defined the compat-ibility based on the superordinate unit location ofthe target location—that is, the location of thesuperordinate unit formed by the dividing line(s).For example, in the top left panel of Figure 1b,we defined the top-to-left/bottom-to-rightmapping as compatible and the top-to-right andbottom-to-left mapping as incompatible (notethat instructions never referred to top, bottom,left, or right in describing mapping). The oppositewas true for the top right panel of Figure 1b.
Each mapping condition consisted of one prac-tice block of 18 trials and one experimental block of150 trials.
Results
Results are shown in Figure 3. After the exclusionof outliers (0.14%) using the same criterion asthat for Experiment 1, the mean RTs for correctresponses and percentages of errors were evaluatedin separate ANOVAs with group (2; control,experimental) as a between-participants factor andcompatibility (2; compatible, incompatible) as awithin-participant factor.
RTThe main effect of group was not significant, F(1,30), 1, p= .65. The main effect of compatibilitywas significant, F(1, 30)= 4.50, p, .05. Anoverall spatial SRC effect of 8 ms was obtained.The interaction between group and compatibilitywas significant, F(1, 30)= 115.01, p, .001. Thespatial SRC effect based on superordinate unitlocation was 48 ms (p, .001) for the controlgroup, whereas it reversed to –32 ms (p, .001)for the experimental group.
Error rateNeither the main effect of group nor compatibilitywas significant, ps. .25. However, the interactionbetween group and compatibility was significant,F(1, 30)= 33.25, p, .001. As for the RT data,the significant spatial SRC effect based onsuperordinate unit location was obtained for thecontrol group (2.9%, p, .001), whereas it reversed(–1.9%, p, .05) for the experimental group.
Figure 3. Reaction times (top panel) and percentages of errors
(bottom panel) for Experiment 2 as a function of group and
compatibility between the superordinate unit position and the
response. Error bars represent standard errors for means.
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Discussion
In the absence of a many-to-one response assign-ment, the spatial SRC effect observed inExperiment 2 was not based upon the superordi-nate unit conveyed by explicit visual cues. Instead,the SRC effect depended upon the spatial positionof each stimulus. Contrary to the claim of Tlauka(2004), a visual cue was not sufficient to createsuperordinate units that determine spatial codingin the SRC effect. In accord with findings ofExperiment 1, the results of Experiment 2support the importance of response assignment asa dominant factor for determining the spatialcoding of stimuli. Although not dominant, the per-ceptual visual cue nonetheless did contribute to thespatial coding of the stimuli. The significant maineffect of compatibility indicates that the spatialSRC effect, based on the spatial coding of individ-ual stimulus position, was larger for the controlgroup than for the experimental group. In thecontrol group, spatial coding based on the locationof individual stimulus and spatial coding based onthe location of superordinate unit were congruent,whereas these were incongruent for the experimen-tal group (i.e., right for one coding and left for theother). Thus, again this pattern of results suggeststhat spatial coding is based on multiple frames ofreference.
EXPERIMENT 3
In Experiment 1, in the absence of visual cues, wefound an SRC effect that was based on superordi-nate unit location, and this functional unit appearedto be determined by response assignment alone. InExperiment 2, in the absence of many-to-oneresponse assignment, using a visual cue, we foundan SRC effect based on each stimulus positionrather than visually cued superordinate unitlocation. These results support the importance ofthe nature of response assignment in eliciting asuperordinate-unit-based SRC. However, otherdifferences between Experiments 1 and 2 mayhave contributed to the different patterns of SRCeffects in these experiments.
One factor that may have contributed to SRCeffects involves the number of stimulus positions.These differed in Experiments 1 and 2. Stimuluslocations were restricted to two (one per superordi-nate unit) in Experiment 2, whereas six locations(three per superordinate unit) were used inExperiment 1. Therefore it is difficult to arrive ata convincing conclusion based solely on theresponse assignment because in addition to theresponse assignment, the number of stimulus pos-itions (i.e., potential stimulus positions within thesuperordinate unit) also differed from that used inthe preceding experiments. It is important tomanipulate the response assignment whileholding constant stimulus number and arrange-ment in order to isolate the factors influencingSRC effects based on the superordinate unit.
Another potentially relevant considerationrelates to the fact that overall RTs were differentbetween Experiments 1 and 2. The spatial SRCeffect is known to vary as a function of RT (e.g.,Proctor & Vu, 2010; Roswarski & Proctor,1996), and the temporal property of automaticresponse activation by spatial stimulus codechanges with situations (De Jong, Liang, &Lauber, 1994; Proctor, Vu, & Nicoletti, 2003;Wascher, Schatz, Kuder, & Verleger, 2001).Specifically, the Simon effect decreases over timewhen individual stimuli and responses are arrangedhorizontally, and participants pressed the left andright buttons with their left and right hand,respectively (e.g., Wascher et al., 2001), as in thepresent designs. In other situations, the compatibil-ity effect is reported to be constant or to increaseover time. The average RT in reversed correspon-dence location for the experimental group inExperiment 1 was 374 ms, which was more than100 ms longer than that for the experimentalgroup in Experiment 2 (265 ms). Thus the differ-ent contributions of individual stimulus codingand the superordinate unit coding betweenExperiments 1 and 2 may reflect the difference intemporal property of the spatial coding based onthe superordinate unit and of the spatial coding ofeach stimulus. If the SRC effect based on thespatial coding of the individual stimulus positiondecreases with response speed, and/or if the SRC
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effect based on the spatial coding of the superordi-nate unit position increases with response speed,then we can infer that the individual stimuluscoding should be dominant for the faster RTs, asin Experiment 2, whereas the superordinate unitspatial coding should be dominant for the slowerRTs, as in Experiment 1. This pattern turns outto be consistent with what was observed in bothexperiments.
In Experiment 3, we used a visual cue butwithout response assignment, as in Experiment 2,and we presented stimuli in six locations, as inExperiment 1. We had two aims in designing thisexperiment. The first aim was to directly investigatethe effect of response assignment on the SRC effectbased on the superordinate unit with multiplestimulus positions within each superordinate unit.The second aim was to increase an overall RTlevel. To achieve these aims, we introduced no-gotrials. Participants were required to respond to thestimuli at two critical target locations, where theindividual stimulus position contradicted its super-ordinate unit position for the experimental con-dition, as in Experiment 2, whereas they wererequired not to respond to the stimuli that appearedat the other four locations. Mixing no-go trials withgo trials should also delay responses in go trials. Ifeither the number of the stimuli per each superor-dinate unit or the overall RT (or both) matter,then the SRC effect based on the superordinateunit location should replicate the findings ofExperiment 1. On the other hand, if neither vari-able is critical but response assignment is theimportant variable, then the SRC effect based onthe individual stimulus location should replicatethe findings of Experiment 2, despite the multiplestimuli per superordinate unit and the (would beobtained) RT difference between Experiments 2and 3.
Method
ParticipantsSixty-four new volunteers (36 female and 28 male;mean age 23.6 years, range from 20 to 32 years)participated in this experiment. All reported theywere right-handed and had normal or corrected-
to-normal vision. They were naïve to the purposeof the experiment. None had participated inExperiments 1 or 2. Half were assigned to theexperimental group; the others were assigned tothe control group.
Apparatus, stimuli, tasks, and procedureThese were the same as those in Experiment 2,except for the differences noted below. A stimuluscould appear at one of the six locations, as inExperiment 1. Participants were required to pressthe left or right response key only when the stimu-lus appeared at specified (i.e., target) locations thatwere used in Experiment 2. When the stimulusappeared at one of the remaining four locations(partial and total corresponding locations inExperiment 1), the participants were instructednot to press any key (no-go trials). The stimulusappeared randomly and with equal probability atone of the six locations. Thus two thirds of thetrials were the no-go trials in the present exper-iment. Either a key press or time passage of1,500 ms after the stimulus appearance eliminatedthe target. The frame and the dividing line(s)remained on the display for 1,500 ms; then thestimulus for the next trial appeared at one of thesix locations. Each mapping condition consistedof one practice block of 24 trials and two exper-imental blocks, each of which included 144 trials.No feedback was given during either the practiceor the experimental blocks.
Results
Results are shown in Figure 4. After the exclusionof outliers (0.98%) using the same criterion asthat in Experiment 1, the mean RTs for correctresponses and percentages of errors were evaluatedin separate ANOVAs with group (2; control,experimental) as a between-participants factor andcompatibility (2; compatible, incompatible) as awithin-participant factor.
RTThe main effect of group was significant,F(1, 62)= 4.42, p, .05. RT was shorter for theexperimental group (401 ms) than for the control
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group (436 ms). The main effect of compatibilitywas significant, F(1, 62)= 4.69, p, .05. Anoverall SRC effect of 14 ms was obtained. Theinteraction between group and compatibility wassignificant, F(1, 62)= 37.64, p, .001. Thespatial SRC effect based on superordinate unitlocation was 54 ms (p, .001) for the controlgroup, whereas the SRC effect reversed to –26 ms(p, .05) for the experimental group.
Error rateNeither the main effect of group nor the main effectof compatibility was significant, ps. .34.However, the interaction between group and com-patibility was significant, F(1, 62)= 20.91,p, .001. As for the RT data, the significantspatial SRC effect based on superordinate unitlocation was obtained for the control group(1.5%, p, .005), whereas the SRC effect reversed(–1.0%, p, .005) for the experimental group.
Comparison between Experiments 2 and 3
In order to directly compare the results ofExperiments 2 and 3, we conducted ANOVAsfor mean RTs and percentages of errors with exper-iment (2) and group (2) as between-participantsfactors and compatibility (2) as a within-participantfactor.
RTThe main effect of experiment was significant,F(1, 92)= 160.29, p, .001. The mean RT wasshorter in Experiment 2 (267 ms) than inExperiment 3 (418 ms). The main effect of com-patibility was significant, F(1, 92)= 5.21, p, .05.An overall SRC effect of 12 ms was obtained.The interaction between group and compatibilitywas significant, F(1, 92)= 68.63, p, .001. Thespatial SRC effect based on superordinate unitlocation was 52 ms (p, .001) for the controlgroup, whereas the SRC effect reversed to –28 ms(p, .001) for the experimental group. Othermain effects and interactions were not significant,ps. .11.
Error rateThe main effect of experiment was significant,F(1, 92)= 7.54, p, .01. Error rate was higher inExperiment 2 (2.2%) than in Experiment 3(1.5%). The interaction between group and com-patibility was significant, F(1, 92)= 55.63,p, .001. The spatial SRC effect based on superor-dinate unit location was 2.0% (p, .001) for thecontrol group, whereas the SRC effect reversed to–1.3% (p, .001) for the experimental group.Although the size of the positive effect for thecontrol group was numerically larger than that ofthe negative effect for the experimental group,this difference was not significant: the main effectof compatibility, F(1, 92)= 2.29, p= .133. Thethree-way interaction was significant, F(1, 92)=5.12, p, .05. The modulation of the SRC effectdue to group differences was more prominent inExperiment 2 (SRC effect; 2.9% for the controlgroup vs. –1.9% for the experimental group) thanin Experiment 3 (1.5% vs. –1.0%). Other main
Figure 4. Reaction times (top panel) and percentages of errors
(bottom panel) for Experiment 3 as a function of group and
compatibility between the superordinate unit position and the
response. Error bars represent standard errors for means.
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effects and interactions did not approach signifi-cance, Fs, 1.
Discussion
As in Experiment 2, the spatial SRC effectobserved in Experiment 3 was based not on thesuperordinate unit location but instead upon theindividual stimulus location. We also observed anoverall compatibility effect, which indicates thecontribution of the superordinate unit location onspatial coding. Thus the basic outcome ofExperiment 2 was replicated. A direct comparisonof experiments confirmed the similarity of thespatial compatibility effects between Experiments2 and 3 despite the fact that the overall RT forthe experimental condition in Experiment 3(401 ms) was much longer than for this conditionin Experiment 2 (265 ms).3 In fact, the overallRT of Experiment 3 is comparable to that foundin Experiment 1 (374 ms for the reversedcorrespondence location for the experimental con-dition). These results suggest that neither thenumber of potential locations for stimulus presen-tation nor overall RT difference can explain thedifference between the spatial SRC effect obtainedin Experiments 1 and 2. Instead, together withresults of Experiment 1, these findings lead to theinterpretation that the dominance of asuperordinate unit in spatial coding, and hencethe spatial SRC effect, depends upon responseassignment.
GENERAL DISCUSSION
In this study, we considered the respective roles oftwo variables on the spatial SRC effect. One vari-able addressed the role of an explicit visual cuethat outlines a superordinate unit within some
visual display. The other variable addressed thenature of requisite action patterns—namely,response assignments to the individual stimuluslocations within a superordinate unit. In thisresearch, these actions were operationalized interms of stimulus–response mappings regardingright or left responses. Specifically, these mappingswere many-to-one, as in Tlauka and McKenna(2000), or one-to-one mappings, as inExperiment 2 of the present study.
In Experiment 1, we tested the effect ofresponse assignment in the absence of a visual cueoutlining a superordinate spatial unit on SRCeffect. In this experiment, where multiple stimuluslocations were mapped onto a single response, wefound an SRC effect based on stimulus–responselocations associated with the higher order unit. InExperiment 2, we introduced a strong visual cueto convey the superordinate spatial unit, but weeliminated the many-to-one mapping of individualstimulus locations with response keys. With thisone-to-one response assignment mapping, theobserved spatial SRC effect was based on spatialcoding of individual stimulus positions ratherthan upon spatial coding related to a visible super-ordinate unit position. Experiment 3 confirmedthat the difference between Experiments 1 and 2was not due to a difference in overall RTs involvingthe two experiments, and that the absence of many-to-one stimulus–response assignment preventedthe SRC effect based on superordinate unit locationto occur even when multiple stimuli wereembedded within each superordinate unit. Takentogether, the results of these three experimentsindicate that assignment of multiple stimuliwithin a superordinate unit to a single response isessential to eliciting a dominant role for thespatial code of the superordinate unit position indetermining the representation of stimulus positionin the spatial SRC effect.
3 There was a speed–accuracy trade-off between Experiments 2 and 3: RT was shorter, but the error rate was higher in Experiment
2 than in Experiment 3. One aim of Experiment 3 was to elevate the overall RT level to a level comparable to that of Experiment 1, but
in a paradigm lacking many-to-one stimulus–response mapping, because the passage of time from the onset of the target might have
been responsible for the difference of the SRC effects between Experiments 1 and 2. From this perspective, we regard the overall RT
level as an index of the passage of time from the onset of the target, not as an index of performance or task difficulty. Thus we exclusively
focused on the RT level and disregarded an integrated task performance to which both the speed and the accuracy were related.
Therefore we are certain that the speed–accuracy trade-off is not detrimental to our claim.
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Recently the effects of action-related factors oncognitive information processing have beenbroadly acknowledged (e.g., Deubel, Schneider,& Paprotta, 1998; Müsseler & Hommel, 1997;Reed, Grubb, & Steele, 2006). In the presentstudy, an action-related factor of response assign-ment determined the coding of stimulus positionin cognitive information processing.Simultaneously this perception-related factor ofspatial coding of stimulus position affectedresponse selection, thus inducing the spatial SRCeffect. Therefore, the present study revealed bidir-ectional interaction between perception andaction, where an action-related factor (i.e., responseassignment) affected a perception-related infor-mation processing (i.e., spatial coding of stimulusposition), and the affected perceptual factor influ-enced an action (i.e., left/right key press). Thesefindings provide further support for the notion ofclose relationship between perception and actionthat induces many types of interaction (Hommel,Müsseler, Aschersleben, & Prinz, 2001).
Although a perceptual visual cue consisting ofline segments did not ensure dominance for thesuperordinate unit reference frame as a determinantof the spatial SRC effect in Experiments 2 and 3,such cues did succeed in modifying the spatialSRC effect based on individual stimulus positionin these experiments. A similar modulating effectdue to perceptual visual cueing of spatial codingwas reported by Tlauka and McKenna (2000). Intheir first experiment, the magnitude of the SRCeffect based on the superordinate unit was constantacross the target locations within a superordinateunit when the perceptual visual cue (i.e., line seg-ments) outlined the superordinate unit. On theother hand, the SRC effect varied across thetarget locations as a function of congruencybetween the superordinate unit position and theindividual stimulus position in their subsequentexperiments. In the latter experiments, the visualcues constituted semantic (city names in the UKand the USA) or acquired (through precedingtraining) arbitrary stimulus associations. Thus, ourExperiment 1, which contained no visual cues atall, successfully replicated the outcomes ofExperiments 2 and 3 in Tlauka and McKenna
(2000). Together such findings indicated that,when a distinct visual cue (line segments) ispresent, it may modulate the pattern of the SRCeffects based on the superordinate unit position.Nevertheless, in other situations it is possible thatthe superordinate-unit-based SRC effect found inTlauka and McKenna’s (2000) Experiments 2and 3 is due to response assignment alone,without contribution of visual cues indicatingsemantic or arbitrary learned associations ofstimuli, as in the present Experiment 1.
The spatial SRC effect observed in ourExperiment 1, which was based on the superordinateunit position, differed in magnitude as a function ofcorrespondence locations for the experimentalgroup. This means that individual stimulus positionswere also coded and that this coding exerted someeffects on response selection although the superordi-nate unit was the major determinant of the spatialSRC effect. The SRC effect based on the positionof individual stimuli in Experiments 2 and 3 was sig-nificantly greater for the control group, in which thesuperordinate unit position and the individualstimulus position were congruent with each other,than it was for the experimental group, in whichthese stimulus factors were on respectively oppositesides. These results indicate that the spatial rep-resentation of the superordinate unit conveyed by avisual cue also contributed to response selection.Thus, irrespective of whether the superordinateunit position or the individual stimulus positionwas the dominant frame of reference for spatialcoding of a stimulus, spatial coding based onanother frame of reference did simultaneouslyoccur and influenced the response. In this respect,the present study further supports the simultaneousspatial coding based on multiple frames of reference(e.g., Lamberts et al., 1992; Lleras et al., 2004;Roswarski & Proctor, 1996; Schankin, Valle-Inclán, & Hackley, 2010).
The contribution of each frame of reference forspatial stimulus coding and the SRC effect appearsto depend on task situations. In the present study,the SRC effect for the stimulus at exactly the sameposition on the display (reversed/partial correspon-dence location in Experiment 1 as well as stimuliin Experiments 2 and 3) varied across the
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conditions. In Experiment 1, the faster response (leftor right) to the stimulus presented at a given position(reversed correspondence location and partialcorrespondence location) varied as a function ofhow multiple stimuli were assigned to left andright responses (i.e., S–R mapping) even thoughexactly the same stimulus arrangement was usedacross the conditions. In Experiment 2, the spatialSRC effect was modulated by a subtle backgrounddifference of line segments that was entirely irrele-vant to the to-be-performed task. These findings,in conjunction with the previous findings indicatingflexible, context-dependent spatial stimulus/response coding (e.g., Hommel, 1993; Nishimura& Yokosawa, 2007, 2010a, 2010b; Rubichi, Vu,Nicoletti, & Proctor, 2006; Stevanovski, Oriet, &Jolicœur, 2002; Tlauka & McKenna, 2000; Umiltà& Liotti, 1987), strongly suggest that the contri-bution of spatial stimulus/response coding basedon each potential frame of reference in human infor-mation processing is flexibly determined dependingon stimulus/response environment, task demand,and the participants’ goal or intention.
In conclusion, the present study has revealed thatassignment of multiple stimuli within a superordi-nate unit to a single response is crucial for theemergence of a spatial SRC effect based on thesuperordinate unit position (Tlauka & McKenna,2000) when the spatial position of an individualstimulus differs from the position of the superordi-nate unit that embeds that stimulus. Perceptualvisual cues showing a superordinate unit wereneither necessary nor sufficient for this unit to bethe dominant coding factor in the SRC effect.Regardless of which type of spatial coding ofposition is dominant (superordinate or individualstimulus), the nondominant location source alsocontributes to left/right response selection. This sup-ports the notion of simultaneous spatial stimuluscoding according to multiple frames of reference.We conclude that the contribution of each potentialframe of reference for spatial coding would flexiblyvary with task environment.
Original manuscript received 10 October 2010
Accepted revision received 17 July 2011
First published online 22 September 2011
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