Journal of Experimental Psychology:Human Perception and Performance1975, Vol. 1, No. 4, 339-352

Judging Up and Down

Herbert H. Clark and Hiram H. BrownellStanford University

In Experiment 1 subjects were asked to judge whether an arrow was point-ing up or pointing down at various heights inside a surrounding rectangle.They were faster on an arrow pointing up the higher it was in the rectangle,and they were faster on an arrow pointing down the lower it was in therectangle. Experiments 2, 3, and 4 were designed to test three sources forthis "congruity effect." The intrusive height information for each arrowwas assumed to facilitate or interfere with (a) the activation of the correctmotor response; (b) the maintenance of the implicit instruction "Is it point-ing up, or is it pointing down?"; or (c) the selection of the criterial per-ceptual information as a basis for the response. All three experiments wereconsistent with c, but not with a or b. Indeed, the results contrasted withprevious demonstrations of the Stroop effect in certain critical features.

In a recent experiment we found thatpeople were subject to a curious influencewhen they attempted to judge the directionin which an arrow was pointing. In thatexperiment—described later as Experiment1—we confronted subjects with a picture ofan arrow at one of several heights withina rectangle. The arrow was pointing eitherUP or DOWN/ and each subject's task was todecide as quickly as possible which way itwas pointing, up or down. What happenedwas this: When the arrow was pointing UP,the subjects were faster the higher the arrowwas in the rectangle; but when the arrowwas pointing DOWN, they were faster thelower it was in the rectangle. Simplydescribed, the subjects were faster when thearrow's "intrusive attribute" (its height)had the same value as its "criterial attribute"

This research was supported in part by GrantMH-20021 from the National Institute of MentalHealth. We thank William P. Banks, StephenMonsell, Edward E. Smith, and especially JerryBalzano, whose able suggestions on the substanceof this paper have improved it considerably.Hiram H. Brownell is now at The Johns HopkinsUniversity.

Requests for reprints should be sent to HerbertH. Clark, Department of Psychology, StanfordUniversity, Stanford, California 94305.

1 Throughout this paper we use all capitals(e.g., UP) to denote the physical direction ofarrows, italic (e.g., up} to denote words or instruc-tions, and quotation marks (e.g., "up") to denoteeither explicit or implicit responses.

(its direction). We will call this the con-grtiity effect in absolute judgments.

At first glance the congruity effect ap-pears to be identical to a phenomenon de-scribed by Shor (1970). He presented sub-jects with block arrows pointing either UPor DOWN and containing, for distraction,either the word up or the word down. He,like us, asked his subjects to say whichway the arrow was pointing, up or down.He found that subjects were faster whenthe intrusive attribute (the word up or downinside the arrow) had the same value as thecriterial attribute (the actual direction UPor DOWN). In analogous experiments, Mor-ton (1969) and Fox, Shor, and Steinman(1971) found that judgments of the posi-tion of a word within a rectangle could befacilitated or interfered with by the meaningof the word itself (up, down, left, or right;North, East, South, or West). Similarly,Dyer (1972) was able to induce facilitationand interference in judgments of the direc-tion of movement of words on an oscilloscopescreen by using the words up, down, left,and right whose meaning was either con-gruent or incongruent with their directionof movement. As Morton, Shor, and Dyernoted, these phenomena all resemble thewell-known Stroop effect, where naming thecolor of the ink in which a word is printedis facilitated or interfered with by the con-tent of the word itself (see Dyer, 1973;

339

340 HERBERT H. CLARK AND HIRAM H. BROWNELL

Hintzman, Carre, Eskridge, Owens, Shaff,& Sparks, 1972; Keele, 1972; Stroop, 1935).Morton, Shor, and Dyer argued that thesephenomena can be explained with the samemodel that explains most, if not all, otherStroop effects.

But the congruity effect we discovereddiffers from these three investigators' Stroopeffects in one important respect. In theirdisplays, and in most other Stroop demon-strations, either the criterial or the intrusiveattribute was a word, letter, or digit, some-thing linguistic in nature. In our displays,on the other hand, both attributes wereprima facie perceptual in nature. This sug-gests that the congruity effect may originatefrom a source entirely different from Mor-ton's, Shor's, and Dyer's Stroop effects, soit has the potential of telling us somethingnew about perceptual codes and their rolein perceptual judgments.

In this article we will examine three broadmodels for the congruity effect and testthem in a verification task. In this taskthe subject first reads a single-word "in-struction," up or down. Then, while timed,he looks at a display containing an UP orDOWN arrow and responds "true" if the in-struction correctly describes the directionof the arrow and "false" if it does not. Weassume that the timed part of this task con-sists roughly of three stages (see Clark &Chase, 1972). At the perceptual codingstage, the subject forms a perceptual codefor the arrow's direction, say direction (ver-tical (+polar)) for an UP arrow. At thecomparison stage, he compares this per-ceptual code against the instructional code,say direction (vertical (—polar)) for theinstruction down. If they match, he com-putes the code corresponding to the motorresponse "true," say truth (+polar); if theydon't match, he computes the code corre-sponding to "false," say truth (—polar). Atthe final motor stage, he initiates the motorresponse corresponding to the response codethat has been activated. In our task thisconsisted of a press of a "true" or "false"'button.

In this scheme the intrusive code, herethe arrow's height, can affect the true-

false judgment in only three possible ways,and this leads to the following three models.2

The motor competition model. In thismodel the intrusive attribute affects the ac-tivation of the motor response. When an UPor DOWN arrow is high, it is assumed to elicitthe additional perceptual code position (ver-tical (+polar)). Since this code overlapswith part of the response code truth ( +polar), it tends to activate the "true" re-sponse itself and thereby facilitate the re-sponse "true" and interfere with the re-sponse "false." But when an UP or DOWNarrow is low, it elicits position (vertical(—polar)), which tends to activate truth(—polar), facilitating "false" and interfer-ing with "true." So the model predicts thatresponses will be speeded up when the posi-tion (HIGH or LOW) and the response("true" or "false") have the same polarity,and they will be slowed down otherwise.

This prediction is indicated in Table 1.In a verification task like ours, there mustbe at least eight configurations: The in-struction is either up or down, the arrow'sdirection is either UP or DOWN, and its posi-tion is either-HIGH or LOW. Of these eight,four should be speeded up and four sloweddown if the motor competition model is cor-rect. The four speeded up are marked with0 in column 1, and the four slowed down aremarked with +r, indicating that the secondfour should take r longer, on the average,than the first four, regardless of other differ-ences among the configurations. Thus, ifthe motor competition model is correct,parameter r should be reliably greater than 0.Statistically, this is equivalent to predictinga significant Instruction X Direction X Posi-tion interaction, as Table 1 shows.

The instructional competition model. Inthis model the intrusive position code getsconfused with the instructional code. Im-agine a display with an UP arrow high inthe rectangle when the instruction is down.The subject viewing the display, by thismodel, mistakenly compares the directioncode direction (vertical (+polar)) first

2 Although we use the word competition innaming these models, the models are meant tocover facilitation as well as interference effects.

JUDGING UP AND DOWN 341

TABLE 1LATENCY INCREMENTS PREDICTED FOE EIGHT CONFIGURATIONS UY THE MOTOR,

INSTRUCTIONAL, AND PERCEPTUAL COMPETITION MODELS

Instruction

Updownupdown

updownupdown

Pictorial configurationDirection

UPDOWNDOWNUP

UPDOWNDOWNUP

Position

HIGHHIGHHIGHHIGH

LOWLOWLOWLOW

Motorcompetition model

00

+ r+ r

+r+ r

00

Instructionalcompetition model

0+ s

0+ s

+s0

+ s0

Perceptualcompetition model

0+t+t

0

+t00

+tNote. Parameters r, s. and f correspond to the motor competition model, instructional competition model, and perceptual com-

petition model, respectively.

against the intrusive position code position(vertical ( + polar)), finding a match andreadying the response "true." But beforehe responds, he realizes the mistake, makesthe right comparison, and comes up with thecorrect response "false." In this instance,by readying the wrong answer, he will beslowed down in giving correct response"false." In general, the model predicts thatresponses will be speeded up when the posi-tion (HIGH or LOW) and instruction (upor down) have the same polarity, and theywill be slowed down otherwise. As shownin Table 1, this predicts that parameter swill be reliably greater than 0, which isequivalent to predicting a significant Posi-tion X Instruction interaction.

The perceptual competition model. In thismodel the intrusive position code gets con-fused instead with the criterial directioncode. Imagine again a display with an UParrow high in the rectangle when the in-struction is down. The subject here, ac-cording to this model, mistakenly comparesthe intrusive position code against the in-struction code, finding a match and ready-ing the response "true." But before heresponds, he catches the error, makes theright comparison, and comes up with thecorrect response "true." Here, because hehad readied "true" by the preliminary com-parison, he is speeded up in giving the re-sponse "true." In general, the model pre-dicts that responses will be speeded up whenthe arrow's position (HIGH or LOW) and itsdirection (UP or DOWN) have the same po-

larity, and they will be slowed down other-wise. This model, then, predicts that pa-rameter t in Table 1 should be reliablygreater than 0, or equivalently that therewill be a significant Position X Directioninteraction.

In summary, the motor, instructional, andperceptual competition models predict, re-spectively, that parameters r, s, and t willbe reliably greater than 0. These param-eters represent the three possible ways theintrusive attribute can interact—both logi-cally and statistically—with the criterial at-tribute, the instruction, or both.

Seymour (1974), in effect, has alreadytested the motor and instructional competi-tion models for a Stroop task similar tothose of Morton, Shor, and Dyer. He pre-sented subjects with a word placed eitherabove or below a square; inside the squarewas the instruction above or below. Thesubjects were to say "true" when the ex-ternal word was in the place specified by theinstruction and "false" when it was not.When Seymour used as external words yesand no, and right and wrong, he expectedthem to facilitate and interfere with the re-sponses "true" and "false." Yet he foundno interference effects. In terms of ourmodels, parameters r, s, and t were 7, 14,and 25 msec for the yes/no experiment and21, 15, and —2 msec for the right/wrongexperiment, none of which were reliablygreater than 0. But when he used as ex-ternal words up and down, parameters r, s,and t were 32, 102, and 14 msec. Param-

342 HERBERT H. CLARK AND HIRAM H. BROWNELL

eter ^ was reliably greater than 0, whereasparameters r and t were not.

Seymour's experiment, then, fit the in-structional competition model. This sug-gests that the Stroop effects in Morton's,Shor's, and Dyer's tasks may also have orig-inated in a confusion of the intrusive words(e.g., up and down} with the implicit in-struction (e.g., "Is the arrow pointing up,or is it pointing down?"), not from inter-ference with the motor response or fromconfusion with the criterial perceptual code.The question that remains, then, is whetherthe congruity effect has the same explana-tion. Because the intrusive code in the con-gruity effect is perceptual rather than lin-guistic in nature, it may not have. The fourexperiments we designed were directed atthis question. Experiment 1 was plannedas a demonstration of the basic congruityeffect, and Experiments 2, 3, and 4 as testsof the three models in several variations onthe verification task.

One final point: We have denoted ourperceptual, instructional, and response codesas abstract composites like position (vertical(+ polar)} to emphasize two points. First,these codes cannot be "implicit" responses,like "up," with only phonetic or articulatoryproperties. If both position and directionwere coded alike, for example as "up" and"down," the subject could never tell the twodimensions apart; on the other hand, if posi-tion were coded as "high" and "low" anddirection as "up" and "down," there wouldbe no reason to predict selective facilitationor interference. Second, the codes must re-flect the "interpretive" character of the per-ceptual attributes. Position intrudes on di-rection only because its code has interpretiveelements in common with the code for di-rection, namely, the elements of verticalityand polarity. We would expect very littleintrusion if the arrow were varied from sideto side instead. An interpretive code is alsorequired to explain why interference in theclassic Stroop effect increases as the intru-sive attribute becomes more and more sim-ilar semantically to the criterial attribute(see Fox et al., 1971; Klein, 1964; Sey-mour, 1973a, 1973b).

EXPERIMENT 1Method

On each of 204 trials subjects were shown apictorial configuration consisting of an arrowpointing either up or DOWN within a rectangle,and they were required to indicate, while timed,which way the arrow was pointing, up or down.

The 12 distinct configurations we used each con-sisted of an arrow 1 cm long centered horizontallyin a rectangle 4 cm wide and 5 cm tall. The arrowpointed either UP or DOWN, and the midpoint of itsshaft was 1, 1.5, 2, 3, 3.5, or 4 cm from the topof the rectangle. These six positions—three abovethe center, three below the center, and none strad-dling the center—will be called, numbering fromtop to bottom, Positions 1, 2, 3, 5, 6, and 7. Eachconfiguration was drawn in india ink and presentedin the lower of two 13 X 7 cm viewing fields ina modified Iconix tachistoscope. The two viewingfields were aligned vertically with the upper field1 cm above the lower one. (The upper field wasused in Experiments 2, 3, and 4 for the presenta-tion of the single-word instruction.) Betweentrials the subjects looked at a blank 13 X 15 cmadaptation field that coincided with the area cov-ered by the two viewing fields. The displays were51 cm from the eyes.

To begin each trial, the subject pressed a "ready"button. The configuration appeared .5 sec laterand remained on until the subject pressed eitherthe "up" or the "down" button to indicate hisanswer. He was timed in milliseconds from theonset of the configuration to the press of thebutton. He pressed the "up" button with onethumb, the "down" 'button with the other, and the"ready" button, placed midway between the "up"and "down" buttons, with either thumb. The re-sponses "up" and "down" were assigned to the leftand right buttons for half the subjects and to thereverse for the other half.

Each subject went through 12 practice trials and192 experimental trials. The practice trials con-sisted of the 12 configurations in a random order.The experimental trials consisted of eight blocksof 24 trials, where each block was made up oftwo instances of the 12 configurations in an indi-vidually randomized order. In this and the re-maining experiments, the subjects were all Stan-ford University undergraduates either fulfilling acourse requirement in introductory psychology orearning $2. There were 12 subjects in Experiment1 after one was eliminated for making more than10% errors. They were instructed to respond asquickly as possible without making errors.

Results

Figure 1 plots the mean latencies for eachof the 12 configurations. Each mean is anaverage of the 12 subject means once theerror trials had been removed. As Figure 1makes plain, there was a strong congruity

JUDGING UP AND DOWN 343

effect. Roughly speaking, the higher thearrow, the faster the decision on UP arrowsand the slower the decision on DOWN arrows.The trends for the UP and DOWN arrows(13.8 and —6.0 msec/position, respectively)8

were reliably different from each other, as in-dicated by the significant Direction X Posi-

.tion interaction, F(5, 50) = 11.77, p < .001.Moreover, the difference between the twotrends was highly regular. In order, the UPminus DOWN difference scores at Positions1 through 7 were +71, +62, +25, -2, -21,and —49 msec. This trend had a slope of19.8 msec/position and linear correlation of.99, F(l, 50)= 57.76, p < .001. The resid-ual from this linear effect was not reliable.

The overall means for Positions 1 through7 (490, 471, 475, 477, 488, and 514 msec,respectively), differed reliably from eachother, F(5, 50)= 13.44, p < .001, reflectingboth a linear trend and a quadratic trend.First, there was a general increase in laten-cies from Position 1 to Position 7. Thislinear trend had a slope of 3.9 msec/posi-tion and a highly reliable correlation of .58,F(l, 50)= 22.71, p < .001. Second, therewas a general increase in latencies from themiddle positions to the outer ones. Thequadratic component among the six meanswas highly reliable, with a correlation of.77, /?(!, 50)= 40.03, p < .001. Once thelinear and quadratic trends were subtractedfrom these means, the residual variance wasnot reliable, F(3, 50)= 1.49.

In summary, the 12 means in Figure 1 areneatly described by a statistical model (adescriptive, not explanatory model) that hasonly three additive components: (a) Laten-cies increase linearly with position, (b) laten-cies increase from the middle to the outerpositions as aquadratic, and (c) UP minusDOWN decreases linearly with position. Thismodel, using 3 of the 11 degrees of freedomin the latencies, accounts for 90.0% of thevariance among the 12 means. Componentsa, b, and c account for 9.7%, 17.1%, and63.2% of the variance, so the congruityeffect, Component c, clearly accounts for thelion's share of the variance. Another 6.9%

3 All slopes reported in Experiments 1 and 2were computed from least squares linear fits of thedata.

y 5500)(T>

c

450 UP arrows

1 2 3 5 6 7Position

FIGURE 1. Mean latencies in Experiment 1 forforced-choice direction judgments of UP and DOWNarrows at six vertical positions.

of the variance is accounted for (with 1degree of freedom) by the 14-msec advantageof UP over DOWN arrows. This difference,however, was not reliable, F < 1, nor wasthe rest of the residual variance from thisstatistical model.

The overall error rate was 2.4%, rangingfrom .5% to 7.8% for individual subjects.Though few in number and hence not veryreliable, the errors generally increased fromPosition 1 to 7 for UP (1.0%, 0%, 0%,0%, 4.7%, 4.7%) and decreased for DOWN(5.7%, 5.7%, 3.1%, .5%, 2.1%, 1.0%).The errors therefore correlated highly withthe latencies ( r= .77) , ruling out anymajor speed-accuracy trade-off that mightconfound the results.

Discussion

Experiment 1 demonstrates the basic con-gruity effect. The UP arrow was judgedfaster the higher it was, and the DOWNarrow was judged faster the lower it was.Indeed, the two trends crossed in a smoothlinear trend without any discontinuities.This may be explained as follows. The far-ther an arrow is from the middle of therectangle, the more discriminably high orlow it is. And the more discriminablyhigh or low it is, the earlier the intrusiveposition code is formed and the more likelyit is to intrude on the judgment process

344 HERBERT H. CLARK AND HIRAM H. BROWNELL

900

800

700

CDI/)

03

900

800

700

DOWN-up:5^~^^-^ /-^> .̂-DOWN-down

/ UP-down

UP-up

1 2 3 5 6 7Position

FIGURE 2. Mean latencies in Experiment 2 fortrue-false direction judgments of UP and DOWN-arrows, paired with the instructions up anddown, at six vertical positions.

(regardless of the model). So the linearityof the congruity effect forcefully demon-strates that the intrusive code becomesmore effective in its facilitation or inter-ference the earlier it is formed.

The Congruity effect here reflects bothfacilitation and interference (see also Clark& Brownell, Note 1). Position 4, our un-used middle position, can be consideredneither high nor low. When the UP arrowwas above that position, there was facilita-tion ; when it was below that position, therewas interference. The DOWN arrow showedthe opposite effects. These facilitation andinterference effects were superimposed, ad-ditively, on two other trends. Judgmenttime increased slightly both the lower thearrow was in the rectangle and the fartherit was from the center of the rectangle.These two trends most likely originated in

the way subjects scanned the displays. Thesubjects probably scanned from top to bot-tom on some occasions and from the middleoutwards on others. The important pointis that these scanning effects are additive tothe congruity effect and cannot be used toexplain it away.

EXPERIMENT 2

Experiment 2 was designed to distinguishamong the three models described in theintroduction to this article.

Method

Subjects were shown on each trial a one-wordinstruction, for example, up, and then an arrowwithin a rectangle. While timed, they were toindicate "true" or "false," depending on whetheror not the word correctly described the arrow.There were two distinct tasks. In the directiontask, the subjects judged the direction of the arrow,whether it pointed up or down. The 24 displaysfor this task consisted of the instruction up ordown combined with each of the 12 configurationsused in Experiment 1. In the position task, thesubjects judged the position of the arrow, whetherit was high or low. The 24 displays used herewere the same as before but with the instructionshigh and low in place of up and down. Theinstructions were typed in elite and appeared inthe center of the upper 13 X 7 cm viewing fieldof the tachistoscope. Otherwise, the equipmentand displays were identical to those in Experi-ment 1.

There were 20 subjects, half of whom receivedthe direction task first and half of whom receivedthe position task first. The former subjects re-ceived 16 practice direction trials, 96 experimentaldirection trials (four blocks of the 24 displays).8 practice position trials, and 96 experimentalposition trials. The design was analogous forthe latter half of the subjects. The instructionappeared in the upper viewing field .5 sec afterthe start of each trial and remained on for 1 sec.When it disappeared, the configuration appearedin the lower field and remained on until the sub-ject pressed the "true" or "false" button. Thetiming, randomization, and counterbalancing wereotherwise the same as in Experiment 1.

Results

Direction task. Figure 2 plots the meanlatencies, computed as in Experiment l,.forthe 24 displays in the direction task. Itreveals a striking congruity effect of thesame form as in Experiment 1. Generally,the up arrow was judged faster the higherit was, and the DOWN arrow was judged

JUDGING UP AND DOWN 345

TABLE 2MEAN LATENCIES (IN MSEC) FOR POSITION JUDGMENTS IN EXPERIMENT 2

Arrow Instruction Kespon.se Position" MOverall

M

UPUPDOWNDOWN

M

highlowhighlow

"true""false""true""false"

743 (1.2)889 (7.5)776 (0)906 (3.8)828

741 (0)869 (3.8)847 (1.2)942 (7.5)850

894 (1.2)1048 (5.0)904 (2.5)1091 (10.0)984

792935842980887

Q<A

UP

UPDOWNDOWN

M

hjghlowhighlow

"false""true""false""true"

839 (0)852 (7.5)818 (2.5)855 (3.8)

841

803 (0)905 (13.8)884 (1.2)801 (1.2)

848

952 (0)1017 (11.2)910 (1.2)

1016 (5.0)

974

864925870891888

QQA

« Percent errors are given in parentheses.

faster the lower it was, regardless of otherfactors in the experiment. This congruityeffect was highly reliable, as shown by thesignificant Position (1 to 7) X Direction (UPvs. DOWN) interactions, F(5, 90) =7.57, p< .001. Moreover, the position of the ar-row did not interact reliably with anythingelse—either with the instruction (up vs.down), F < 1, or with the response ("true"vs. "false"), F<\. Statistically, therefore,the two UP curves in Figure 2 were parallel,as were the two DOWN curves. This is thepattern predicted by the perceptual com-petition model, not by the motor competitionmodel or by the instructional competitionmodel.

In more detail, the two UP curves, aver-aged together, increased 18.6 msec/positionwith a linear correlation of .88, F(\, 90) =34.82, p < .001. The DOWN curves decreased6.0 msec/position with a correlation of —.54,^(1, 90)= 3.54, p < .10. In order, the UPminus DOWN difference scores at Positions1 to 7 were +128, +82, +29, +10, +32,and —62 msec. These decreased 24.6 msec/position with a highly significant linear cor-relation of .90, F(l, 90)= 30.66, p < .001.The residual from this linear trend was notsignificant, F(4, 90)= 1.80. This patternfor the congruity effect looks remarkablylike that in Experiment 1.

There were four other reliable differences

in the direction judgments. UP arrowswere 36 msec faster than DOWN arrows,F(l, 18)= 8.92, p < .01. Up instructionswere 94 msec faster than down instructions,F(l, 18)= 32.86, p < .001. "True" in-structions (those for up-up and DOWN-down) were judged 100 msec faster than"false" instructions (those for up-do-wn andDOWN-M/>),F(1, 18) = 53.01, p < .001. Andthere were reliable differences across thesix vertical positions of the arrow, F'(5, 90)= 3.79, p < .005. Latencies increased anaverage of 6.3 msec/position with a correla-tion of .64. This trend was reliable, F(l,90)= 7.76, p < .01, but so also was theresidual from the linear effect, F(4, 90) =2.80, p < .05. In this experiment the quad-ratic trend was not reliable, F < 1, perhapsbecause the subjects here, unlike those inExperiment 1, had to scan from the in-struction in the upper viewing field to theconfiguration in the lower field and couldnot accurately find the center of the rec-tangle before it appeared.

In summary, the 24 means in Figure 2are adequately described by a statisticalmodel similar to the one fitted in Experi-ment 1. This one has five additive effects :(a) Latencies vary over the six positions,(b) UP arrows are faster than DOWN arrows,(c) UP minus DOWN decreases linearly withposition, (d) "true" is faster than "false,"

346 HERBERT H. CLARK AND HIRAM H. BROWNELL

and (e) up instructions are faster thandown instructions. Of the 23 degrees offreedom in the 24 means, Component a re-quires 5 and the other four componentsrequire 1 each for a total of 9 degrees offreedom. This model accounts for 95.0%of the variance. Components a, b, c, d, and eaccount for 6.8%, 5.1%, 10.8%, 38.1%, and34.2% of the variance, respectively.

The overall error rate was 2.7%, rangingfrom 0% to 7.3% for individual subjects.As before, the errors were generally cor-related with latencies by condition (r — .53).

Position task. The mean latencies forthe position judgments, listed in Table 2,reveal a 'weak congruity effect at best. Ac-cording to the perceptual competition model,judgments should have been faster in Posi-tions 1 to 3 than in Positions 5 to 7 givenan UP arrow, but just the reverse given aDOWN arrow. Overall, however, the con-gruity effect was only 31 msec in the pre-dicted direction, and this was not quitesignificant, F(l, 18) = 3.05, p < .10.

All the other trends one would expect inthe position judgments did occur. High was90 msec faster than low, F(l, 18) =24.05,p < .001. "True" was 50 msec faster than"false," F(l, 18) =13.35, p< .005. Themean latencies increased an average of 144msec from the highly discriminable outerpositions (1 and 7) to the less discriminableinner ones (3 and 5), F(2, 36)= 50.66, p< .001. So the farther an arrow was fromthe center, the easier it was to judge as highor low. Finally, there were two minorinteractions. First, the latencies increasedless from the outer to inner positions for theinstruction high than for the instructionlow, 121 to 167 msec, F(2, 36)= 3.69, p <.05. Second, the increases for the high in-struction on the UP arrow and for the lowinstruction on the DOWN arrow were notmonotonic with position as in the other in-stances. In these cases, Positions 2 and 6were fastest, not Positions 1 and 7, F(2,36)= 5.87, p < .01. We have no ready ex-planations for these two interactions.

The overall error rate was 3.8%, rangingfrom 0% to 9.4% for individual subjects.The error rates for each condition, listed inTable 2, correlated .58 with the mean

latencies. For this task, the subjects re-ceiving the position task first were reliablyslower than those receiving the directiontask first, F(l, 18)= 7.04, p < .025. Andthe former subjects were faster in Positions1 to 3 than on Positions 5 to 7, whereas thelatter yielded the reverse trend, F(l, 18) =4.72, p < .05. This last result has no readyexplanation, though it is rather small.

Discussion

Experiment 2 provided strong evidencethat the congruity effect fits the perceptualcompetition model, and not the motor com-petition or instructional competition models.The evidence is straightforward. The mo-tor, instructional, and perceptual competitionmodels predict, respectively, that parametersr, s, and t will be reliably greater than 0(see Table 1). Estimates of these para-meters in the direction judgments were —14,— 1, and 43 msec, respectively. Only t wasreliably larger than 0. There is one furtherconsideration. In Experiment 1, the con-gruity effect became stronger the farther thearrow was from the center of the rectangle,and the same occurred in Experiment 2.So whichever model is correct, its parametershould increase in monotonic steps fromthe innermost positions (3 and 5) throughthe middle positions (2 and 6) to the outer-most positions (1 and 7). Parameter t in-creased from 10 to 25 to 94 msec in ahighly reliable trend, whereas parameter rdid not increase monotonically (—7, —33,1) nor did parameter s ( — 12, 11, —2) . Theconclusion seems clear. The intrusive posi-tion code affected the direction judgmentsby increasing t, but not by increasing r or s.

In testing the three models for the con-gruity effect, we have presupposed that thephenomenon we have called the congruityeffect in Experiment 2 is the same as thecongruity effect in Experiment 1. Theparallels between Experiments 1 and 2 ap-pear to justify this .presupposition. Thecongruity effect was linear over the six posi-tions in both experiments, with correlationsof .99 and .90, respectively. The size ofthe effect was virtually the same in both ex-periments too. The advantage of UP overDOWN arrows decreased by 20 msec/posi-

JUDGING UP AND DOWN 347

tion in Experiment 1 and by 25 msec/posi-tion in Experiment 2. The difference be-tween the two trends was not significant,F < 1. These parallels strongly suggestthat the congruity effect arises from thesame source in the verification task as itdoes in the forced-choice task.

According to all three models we haveconsidered, the position code can facilitateor interfere with the direction code onlywhen it is formed prior to the comparisonor response stage. To account for Experi-ment 1 we had to assume that the positioncode would be formed earlier the more dis-criminably high or low the arrow was in therectangle. Experiment 2 confirmed this as-sumption directly. In the position task, sub-jects were faster in deciding whether an ar-row was high or low the farther it was fromthe center of the rectangle.

Taken by itself, however, the position taskwas disappointing, for it did not turn up areliable congruity effect of its own. Param-eters r, s, and t were estimated at —9, 11,and 31 msec, respectively, and althoughthere is a hint here that the perceptualcompetition model is most appropriate, the31 msec estimate for t was not quite reliable.There are two reasons t may have been soslight. First, the six positions we chosemay have been much more discriminablethan the two directions UP and DOWN, and soalthough the position codes were formedfast enough to intrude on the directionjudgments, the direction codes were notformed fast enough to intrude on the posi-tion judgments. Second, for an arrow therewere six possible positions, but only twopossible directions (UP and DOWN). Thismay have made position more salient thandirection, also leading to position codes beingmore intrusive on direction judgments thanvice versa. We designed Experiments 3 and4 with these two points in mind.

EXPERIMENTS 3 AND 4

Experiments 3 and 4 consisted of a forced-choice task and a verification task, respec-tively, but with the arrows varying overonly two positions, Positions 3 and 5 fromExperiment 1. These two positions were

chosen from a pilot experiment because posi-tion judgments took at least as long to makefor them alone as did direction judgments.The idea was, then, that the direction codeswould be formed early enough to intrude onthe position judgments and yield a con-gruity effect. Experiment 3 was designedto measure the relative speeds of "pure"position and direction judgments. Experi-ment 4 was designed to uncover the con-gruity effects, if present, in both positionand direction judgments. Experiments 3and 4 were carried out on the same subjects,with Experiment 3 first and Experiment 4second.

Method

Experiment 3. On each trial subjects wereshown an arrow within a rectangle and wererequired to indicate, while timed, which of twoarrows had been presented. On any block oftrials the arrow varied on only one attribute,position or direction. So subjects went throughthe following four blocks of trials in a counter-balanced order: (a) direction judgments with allarrows at Position 3, (b) direction judgmentswith all arrows at Position 5, (c) position judg-ments with all arrows pointing UP, and (d)position judgments with all arrows pointingDOWN. The four blocks each consisted of 8practice trials (four of each configuration) and16 experimental trials (eight of each configura-tion), giving a total of 96 trials. For the direc-tion judgments subjects pressed an "up" and"down" button for UP and DOWN arrows, respec-tively, and for position judgments they pressed"high" and "low" buttons for arrows at Positions 3and 5, respectively. All subjects used their righthand for the "high" and "up" responses and theirleft for the "low" and "down" responses. Experi-ment 3 was like Experiment 1 in all other pertinentrespects.

Experiment 4. Experiment 4 was essentiallythe same as Experiment 2 except that there wereonly four configurations (an UP or DOWN arrowat Position 3 or 5). As a consequence, there wereeight direction displays (the instructions wp anddown combined with the four configurations) andeight position displays (high and low combinedwith the four configurations). The direction taskconsisted of 8 practice trials (the eight displays)and two blocks of 16 experiments trials (twoeach of the eight displays) for a total of 40 trials.The position task was analogous. When a subjecterred on a display, it was repeated later in thatblock unless it was missed before. In all otherrelevant respects, the procedure, apparatus, random-ization, counterbalancing, and instructions werethe same as in Experiment 2.

348 HERBERT H. CLARK AND HIRAM H. BROWNELL

TABLE 3MEAN LATENCIES (IN MSEC) FOR POSITION AND DIRECTION JUDGMENTS IN EXPERIMENT 3

Judgment required Intrusive dimension Criteria! dimension Stimulus Block M Judgment M

Position

Position

Direction

Direction

UP arrow

DOWN arrow

Position 3

Position 5

Position 3Position 5Position 3Position 5UP arrowDOWN arrowUP arrowDOWN arrow

454 (1.6)508 (.8)460 (0)464 (0)435 (0)454 (0)429 (1.6)438 (0)

481^O 1

471

. . -439

a Percent errors are given in parentheses.

There were 16 subjects in Experiments 3 and 4after one was eliminated for making more than10% errors in Experiment 4.

Results for Experiment 3

As the mean latencies in Table 3 show,the direction judgments were 32 msec fasterthan the position judgments, F(\, 15) =15.14, p < .005. The position judgmentsyielded a reliable 25-msec congruity effect,.F(l, 15)= 6.75, p < .025, although the di-rection judgments yielded only a small, un-reliable 5-msec congruity effect, F < 1. Thecongruity effect was reliably larger for theformer than for the latter, F(\, 15)= 11.67,p < .005. Finally, subjects were 29 msecfaster on Position 3 than Position 5 in theirposition judgments, F(\, 15) =7.50, p<.025. The overall error rate was A%.

We therefore succeeded in finding fourconfigurations with this property: The codesfor the directions UP and DOWN were formedat least as quickly as the codes for the twopositions. The difference was 32 msec. Butthere was an unexpected twist. We variedonly one dimension—either position or di-rection—at a time within any one blockof trials in an attempt to look at judgmentsuncontaminated by an intruding dimension.Nevertheless, the direction of the arrows

TABLE 4MEAN LATENCIES (IN MSEC) FOR DIRECTION

JUDGMENTS IN EXPERIMENT 4

Arrowdirection

UPUPDOWNDOWN

Arrow positiona

Instruction Response

up "true"down "false"up "false"dawn "true"

3

566 (0)804 (4.7)770 (1.6)802 (9.4)

5

660 (0)872 (4.7)716 (1.6)787 (4.7)

M

613838743794

R Percent errors are given in parentheses.

affected the speed of the position judgments,with Position 3 judged faster for UP arrowsand Position 5 judged faster for DOWNarrows. So even these "pure" discrimina-tion trials do not provide an uncontaminatedmeasure of speed of position and directionjudgments.

Results for Experiment 4

Direction task. The direction judgmentsin Experiment 4 yielded a congruity effectof 58 msec. As the latencies in Table 4show, subjects judged UP arrows 81 msecfaster in Position 3 than in Position 5, butjudged DOWN arrows 34 msec faster in Posi-tion 5 than in Position 3. This 58 msecinteraction was reliable, F(l, 15)= 5.64, p< .05. Furthermore, the position of the ar-row did not interact reliably with either theinstruction, F < 1, or the response, F < 1.Thus, as before, the latencies fit the per-ceptual competition model and did not fitthe motor competition or instructional com-petition models.

There were other parallels with Experi-ment 2. UP arrows were judged faster thanDOWN arrows, by 43 msec, F(l, 15)= 2.34,ns. The instruction up was responded tofaster than down, by 138 msec, F(l, 15)= 60.29, p < .001. "True" judgments weremade faster than "false" ones, by 87 msec,F(l, 15)= 12.79, p < .005. As in Experi-ment 2, the UP curves increased with posi-tion (81 msec) more than the DOWN curvesdecreased with position (34 msec), makingPosition 3 faster overall than Position 5 by24 msec, which was not reliable. The statis-tical model considered in Experiment 2(here using 5 of the 7 degrees of freedom)

JUDGING UP AND DOWN 349

accounts for 99.2% of the variance amongthe eight means in Table 4.

Position task. The position judgments inExperiment 4 yielded a congruity effect of69 msec. The mean latencies are listed inTable 5. As they reveal, subjects judgedUP arrows 53 msec faster than DOWN arrowswhen in Position 3 but they judged DOWNarrows 86 msec faster than UP arrows whenin Position 5. This 69-msec interaction washighly significant, F(l, 15) =15.95, p<.005, As before, the direction of the arrowdid not interact reliably with either the in-struction, F(l, 15)— 3.35, or the response,.F < 1. So here again, the congruity effectfit only the perceptual competition model.

In addition, high instructions were re-sponded to 151 msec faster than low instruc-tions, F(l, 15) = 29.21, p < .001. "True"was an average of 65 msec faster than"false," F(l, 15) =3.35, ns. A statisticalmodel analogous to the one applied to thedirection judgments (using 5 of the 7 de-grees of freedom) accounts for 97.1% ofthe variance among the mean latencies inTable 5. The deviations from the modelare not significant.

The direction judgments were 27 msecfaster on the average than the position judg-ments, F(l, 15) =2.05, ns. Though un-reliable, this difference is almost identicalto the 32 msec difference in Experiment 3.There were no other reliable differences be-tween the direction and position judgments.Overall, the error rates on the direction andposition tasks (shown in Tables 4 and-5)were respectively, 3.3% and 5.5%, cor-relating .68 and .70 with mean latencies.

Discussion

In Experiment 4 there were congruityeffects in both the direction and positionjudgments, and they had a special form.The motor, instructional, and perceptualcompetition models predict, respectively,that r, s, and t will be reliably greater than 0.For the direction judgments, estimates ofr, s, and t were 16, —3, and 58 msec, andonly t was reliably greater than 0. Like-wise, for the position judgments, estimatesof r, s, and t were —4, 31, and 69 msec, andagain only t was reliably greater than 0.

TABLE SMEAN LATENCIES (IN MSEC) FOR POSITION

JUDGMENTS IN EXPERIMENT 4

Arrowposition

3355

Instruc-tion

highlowhighlow

Arrow direction"Response

"true""false""false""true"

UP

627 (0)870 (4.7)756 (4.7)877 (18.8)

DOWN

706 (0)896 (6.2)70S (3.1)756 (6.2)

M

666883730817

& Percent errors are given in parentheses*.

So like Experiment 2, Experiment 4 yieldedstrong evidence for the perceptual competi-tion model as an account for the congruityeffect.

We argued earlier that if the directioncodes were formed early enough, they wouldintrude on the position judgments. Experi-ments 3 and 4 bear out this argument. Inthe pure discrimination trials of Experiment3, direction judgments were 32 msec fasterthan position judgments. From this, onecould conclude that the direction codes forUP and DOWN are formed earlier than theposition codes for Positions 3 and 5, andthat direction should therefore intrude onposition judgments more than positionshould intrude on direction judgments. In-deed, the average congruity effect wasslightly larger for the position judgments(69 msec) than for the direction judgments(58 msec), though not reliably so. Thelogic here, however, relies on the assump-tion that Experiment 3 provided a puremeasure of discriminability for the two posi-tions and the two directions. This assump-tion may not be entirely correct. As wesaw, the directions UP and DOWN intrudedon the position judgments even in Experi-ment 3, perhaps contaminating them as apure measure of discriminability. If so,Positions 3 and 5 may be more discriminablethan Experiment 3 showed, and then thenear equality of the two congruity effects inExperiment 4 would follow.

GENERAL DISCUSSION

We found in Experiment 1 that people,while deciding whether an arrow was point-ing up or down, were influenced by anotherof the arrow's characteristics. The higherthe arrow was, the faster people could decide

350 HERBERT H. CLARK AND HIRAM H. BROWNELL

that it pointed up, and the lower it was, thefaster they could decide that it pointed down.To get at the locus of this congruity effect,we posed three models—the motor, in-structional, and perceptual competitionmodels—and tested for their respectiveparameters r, s, and t in four verificationtasks. The findings were most consistentwith the perceptual competition model.Parameter t was reliable in three of thefour tasks, whereas parameters r and s werenot reliable in any. And in parallel with thecongruity effect in Experiment 1, param-eter t in Experiment 2 got larger the fartherthe arrow was from the center of the rec-tangle, whereas parameters r and s did not.The evidence for the perceptual competitionmodel seems quite solid.

Our findings are in striking contrast withthose of Seymour (1974) on a very similartask. Compare the position task in ourExperiment 4 with his Experiment 3. Inboth tasks the subjects were required todecide whether or not a figure was high, orlow, in a rectangle. But the two tasksdiffered in the figure whose height was beingjudged. In our task it was an arrow, andits direction was intrusive; in his task it wasa word (up or down), and its meaning wasintrusive. In our task the latencies fit theperceptual competition model with a reli-able t. In his they fit the instructionalcompetition model with a reliable s. So thenature of the intrusive attribute may becritical.

One is tempted to reason as follows.When the intrusive attribute is perceptualin nature, it intrudes on the perceptual code;when it is linguistic in nature, it intrudeson the instructional code. And this holdsfor the whole range of Stroop effects. So,for example, the present congruity effecthas a different origin from Shor's Stroopeffect (1970), despite their similar ap-pearance. But without further empiricalsupport, this is just a conjecture, thoughsurely an interesting one. Instead, onecould follow an alternative line of reasoning.The three models we tested are not mutuallyexclusive: More than one could be true ata time. Indeed, in the position task of Ex-periment 4, there was a hint in the data that

parameter s, in addition to t, might be reli-ably greater than 0. It is possible, then, thatthe intrusive attribute affects the perceptualcode, the instructional code, or both, depend-ing on other factors in the experiment. InSeymour's task, for example, the instruc-tion and intrusive word were presentedsimultaneously (in ours, they were pre-sented successively), and that may explainwhy they were so easily confused.

In any case our findings raise the pos-sibility that there are multiple loci of facilita-tion and interference in the traditionalStroop effects discussed in the literature(see Dyer, 1973). If so, models of theStroop effect must allow for this possibility,and none we are aware of do. It seemsnatural, for example, to view our congruityeffect and Seymour's (1974) Stroop effectsimply as two varieties of the same phe-nomenon. But then not one of the Stroopmodels we know of (e.g., Dalrymple-Alford& Azkoul, 1972; Dyer, 1973; Morton &Chambers, 1973; Seymour, 1974) is able tohandle both simultaneously. Seymour'smodel, for example, appears to predict thatour task would yield the same congruityeffect, if any, as his. Yet it did not. Oursuccessive stage model, on the other hand,accommodates these contrasting results byallowing the intrusive code to enter atseveral points in the process.

We have been rather vague so far aboutthe exact workings of the perceptual compe-tition model; now we will consider two spe-cific ways of characterizing it. In the first,the perceptual delay model, the intrusiveattribute speeds up or slows down the orig-inal formation of the criterial perceptualcode, and all this happens at the perceptualstage. The code direction (vertical (+polar)) is formed quickly when the UParrow is high, but slowly when the UParrow is low. In the second model, theperceptual confusion model, the action is allat the comparison stage. This stage hasto compare the criterial perceptual code withthe instruction code while ignoring the in-trusive perceptual code. Sometimes, how-ever, the intrusive code is inadvertently com-pared first, and this facilitates the later cor-rect comparison when the intrusive code is

JUDGING UP AND DOWN 351

congruent with the criterial code, but inter-feres with it when it is not.

The available evidence gives a slight edgeto the perceptual delay model. In thismodel the intrusive attribute affects theperceptual stage and therefore cannot inter-act with the instruction or response. In theother model, the intrusive attribute affectsthe comparison stage, and so it can inter-act with the instruction or response since thecomparison stage makes use of the instruc-tion code and computes the response code.But as we saw, the congruity effect did notinteract reliably with the instruction or re-sponse in any of the four verification tasks.Nor did the congruity effect change sizeor shape from Experiment 1 to Experiment2, where there was a radical change in thecomparison stage from a forced-choiceprocess to a verification process. All thisevidence, admittedly negative evidence, addssome plausibility to the perceptual delaymodel.

The perceptual delay model, if correct,may have quite a concrete interpretation.Consider the congruity effect in the direc-tion judgments. At its base, direction issimply change of position, and so codingdirection consists of coding change of posi-tion. For example, the UP arrow is codedas having a potential position that is highrelative to its present position. It is easyto see, then, how facilitation or interferencecould occur. When the UP arrow is high,its actual position is coded as high relative tothe middle, and this is somehow confusedwith the coding of its potential position ashigh relative to its actual position. Facilita-tion would result. When the UP arrow islow, its actual position is coded as lowrelative to the middle, and in an analogousway this would lead to interference. Thepoint is that both the direction and positioncodes embody implicit comparisons of phys-ical position, and in these comparisons them-selves the facilitation and interference mayoccur.

In Experiments 1 through 4 we alsohappened to find in the latencies a consistentadvantage of UP over DOWN, up over down,high over low, and "true" over "false."These differences are summarized in Table

TABLE 6SIZES OF FOUR DIFFERENCES (IN MSEC) ACROSS

EXPERIMENTS 1 THROUGH 4

DifferenceDirection tasks1 3 2 4

Position tasks3 2 4

UP over DOWN 14 14 36 43 — 1 9 17 — 1 6up over down „ _ 94 138 — — —high over low — •— — — — 90 151"true" over "false" — — 100 87 — SO 65

6. The "true"-"false" difference is con-sistent with the Clark and Chase (1972)model for verification, which posits an extramental operation for detecting a mismatchand computing "false" over detecting amatch and computing "true." The advan-tage of high over low is consistent with aconsiderable literature (see Clark, 1969)that shows that unmarked adjectives (likehigh) are easier to encode and compare thanmarked adjectives (like low). Similarly,the advantage of up over down fits previousfindings (Clark, 1973, 1974; Clark, Car-penter, & Just, 1973; Clark & Chase, 1972)that positive preposition (e.g., above, on topof, in front of, ahead of, and before) arenormally easier to encode and compare thanimplicitly negative ones (e.g., below, under-neath, in back ojt behind, and after). As forUP and DOWN, UP was faster than DOWN inthose tasks where direction was a criterialattribute (the direction tasks), but not inthose tasks where it was not (the positiontasks). Speculatively, then, UP is fasterthan DOWN, just as up is faster than downand high faster than low, when it takes partin the comparison process, but not when itdoes not.

What we have found here fits neatly withthe congruity effects in comparative judg-ments as illustrated in a recent experimentby Clark, Banks, and Lucy (Note 2; seeBanks, Clark, & Lucy, 1975, for a review).When subjects were shown two UP arrows,they were faster at deciding which washigher; but when shown two DOWN arrows,they were faster at deciding which waslower. As Banks et al. explained it, thetwo UP arrows tended to be coded in termsof highness, and the two DOWN arrows interms of lowntss. Consequently, the codesfor the UP arrows matched the instruction

35-2 HERBERT H. CLARK AND HIRAM H. BROWNELL

Which is higher?, and those for the DOWNarrows matched Which is lower?, yieldingthe congruity effect in comparative judg-ments. What remains to be explained iswhy UP and DOWN* arrows are coded thisway. From our findings we suggest thatup arrows elicit intrusive direction codesthat make it easier, because of congruence,to code the arrows in terms of how highthey are; DOWN arrows elicit the opposite-direction codes facilitating the coding interms of how low they are. Thus, we viewthe congruity effects in absolute and com-parative judgments as pieces of the samecloth.

REFERENCE NOTES

1. Clark, H. H., & Brownell, H. H. Direction,position and their perceptual integrality. Manu-script submitted for publication, 1975.

2. Clark, H. H., Banks, W. P., & Lucy, P. Onthe nature of the English comparative. Un-published manuscript, 1974. (Available fromH. H. Clark, Department of Psychology, Stan-ford University, Stanford, California.)

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Clark, H. H. Sface, time, semantics, and the child.In T. E. Moore (Ed.), Cognitive developmentand the acquisition of language. New York:Academic Press, 1973.

Clark, H. H. Semantics and comprehension. InT. A. Sebeok (Ed.), Current trends in linguistics,Vol. 12: Linguistics and adjacent arts and sci-ences. The Hague, Netherlands: Mouton, 1974.

Clark, H. H., Carpenter, P. A., & Just, M. A. Onthe meeting of semantics and perception. InW. G. Chase (Ed.), Visual informat:on proc-essing. New York: Academic Press, 1973.

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(Received March 3, 1975)