APA CENTENNIAL FEATURE. Studies of Interference in Serial Verbal Reactions

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1 APA CENTENNIAL FEATURE Studies of Interference in Seril Verbl Rections J. Ridley Stroop George Pebody College Introduction Interference or inhibition (the terms seem to hve been used lmost indiscrimintely) hs been given lrge plce in experimentl literture. The investigtion ws begun by the physiologists prior to 1890 (Bowditch nd Wrren, J. W., 1890) nd hs been continued to the present, principlly by psychologists (Lester, 1932). Of the numerous studies tht hve been published during this period only limited number of the most relevnt reports demnd our ttention here. Miinsterberg (1892) studied the inhibiting effects of chnges in common dily hbits such s opening the door of his room, dipping his pen in ink, nd tking his wtch out of his pocket. He concluded tht given ssocition cn function utomticlly even though some effect of previous contrry ssocition remins. M tiller nd Schumnn (1894) discovered tht more time ws necessry to relern series of nonsense syllbles if the stimulus syllbles hd been ssocited with other syllbles in the mentime. From their results they deduced the lw of ssocitive inhibition which is quoted by Kline (1921, p. 270) s follows: "If is lredy connected with b, then it is difficult to connect it with k, b gets in the wy." Nonsense syllbles were lso used by Sheprd nd Fogelsonger (1913) in series of experiments in ssocition nd inhibition. Only three subjects were used in ny experiment nd the chnges introduced to produce the inhibition were so gret in mny cses s to present novel situtions. This ltter fct ws shown by the introspections. The results showed n increse in time for the response which corresponded roughly to the increse in the complexity of the sitution. The only conclusion ws stted thus: "We hve found then tht in cquiring ssocitions there is involved n inhibitory process which is not mere Editor's Note. This rticle is reprint of n originl work published in 1935 in the Journl of Experimentl Psychology, 18, The writer wishes to cknowledge the kind ssistnce received in the preprtion of this thesis. He is indebted to Dr. Joseph Peterson for encourgement, helpful suggestions, nd criticism of the mnuscript; to Mjor H. W. Fenker, grdute student in psychology, for helpful suggestions reltive to preprtion of the mnuscript; to Drs. J. Peterson, S. C. Grrison, M. R. Schneck, J. E. Cster, O. A. Simley, W. F. Smith, nd to Miss M. Nichol for id in securing subjects; to some three hundred college students who served s subjects; nd to Willim Fitzgerld of The Pebody Press for substntil ssistnce in the printing of the test mterils. result of divided pths but hs some deeper bsis yet unknown" (p. 311). Kline (1921) used 'meningful' mteril (sttes nd cpitls, counties nd county sets, nd books nd uthors) in study of interference effects of ssocitions. He found tht if the first ssocitive bond hd recll power of 10 percent or less it fcilitted the second ssocition, if it hd recll power of 15 percent to 40 percent the inhibitory power ws smll, if it hd recll power of 45 percent to 70 percent the inhibiting strength pproched mximum, if the recll power ws 70 percent to 100 percent the inhibition ws of medium strength nd in some cses might dispper or even fcilitte the lerning of new ssocition. In crd sorting Bergstrom (1893 nd 1894), Brown (1914), Bir (1902), nd Culler (1912) found tht chnging the rrngement of comprtments into which crds were being sorted produced interference effects. Bergstrom (1894, p. 441) concluded tht "the interference effect of n ssocition bers constnt reltion to the prctice effect, nd is, in fct, equivlent to it." Both Bir nd Culler found tht the interference of the opposing hbits disppered if the hbits were prcticed lterntely. Culler (1912), in the pper lredy referred to, reported two other experiments. In one experiment the subjects ssocited ech of series of numbers with striking prticulr key on the typewriter with prticulr finger; then the keys were chnged so tht four of the numbers hd to be written with fingers other thn those formerly used to write them. In the other experiment the subjects were trined to rect with the right hnd to 'red' nd with the left hnd to 'blue'. Then the stimuli were interchnged. In the former experiment n interference ws found which decresed rpidly with prctice. In the ltter experiment the interference ws overblnced by the prctice effect. Hunter nd Yrbrough (1917), Perce (1917), nd Hunter (1922) in three closely relted studies of hbit interference in the white rt in T-shped discrimintion box found tht previous hbit interfered with the formtion of n 'opposite' hbit. Severl studies hve been published which were not primrily studies of interference, but which employed mterils tht were similr in nture to those employed in this reserch, nd which re concerned with why it tkes more time to nme colors thn to red color nmes. Severl of these studies hve been reviewed recently by Telford (1930) nd by Ligon (1932). Only the vitl point of these studies will be mentioned here. Journl of Experimentl Psychology: Generl, 1992, Vol No. 1, In the public domin 15

2 16 J. RIDLEY STROOP The difference in time for nming colors nd reding color nmes hs been vriously explined. Cttell (1886) nd Lund (1972) hve ttributed the difference to 'prctice.' Woodworth nd Wells (1911, p. 52) hve suggested tht, "The rel mechnism here my very well be the mutul interference of the five nmes, ll of which, from immeditely preceding use, re 'on the tip of the tongue,' ll re eqully redy nd likely to get in one nother's wy." Brown (1915, p. 51) concluded "tht the difference in speed between color nming nd word reding does not depend upon prctice" but tht (p. 34) "the ssocition process in nming simple objects like colors is rdiclly different from the ssocition process in reding printed words." Grrett nd Lemmon (1924, p. 438) hve ccounted for their findings in these words, "Hence it seems resonble to sy tht interferences which rise in nming colors re due not so much to n equl rediness of the color nmes s to n equl rediness of the color recognitive processes. Another fctor present in interference is very probbly the present strength of the ssocitions between colors nd their nmes, lredy determined by pst use." Peterson (1918 nd 1925) hs ttributed the difference to the fct tht, "One prticulr response hbit hs become ssocited with ech word while in the cse of colors themselves vriety of response tendencies hve developed." (1925, p. 281.) As pointed out by Telford (1930), the results published by Peterson (1925, p. 281) nd lso those published by Lund (1927, p. 425) confirm Peterson's interprettion. Ligon (1932) hs published results of 'genetic study' of nming colors nd reding color nmes in which he used 638 subjects from school grdes 1 to 9 inclusive. In the light of his results he found ll former explntions untenble (He included no exmintion of or reference to Peterson's dt nd interprettion.) nd proceeded to set up new hypothesis bsed upon three fctor theory, common fctor which he never definitely describes nd specil fctors of word reding nd color nming. He points out tht the common fctor is lerned but the specil fctors re orgnic. He promises further evidence from studies now in progress. The present problem grew out of experimentl work in color nming nd word reding conducted in Jesup Psychologicl Lbortory t George Pebody College For Techers. The time for reding nmes of colors hd been compred with the time for nming colors themselves. This suggested comprison of the interfering effect of color stimuli upon reding nmes of colors (the two types of stimuli being presented simultneously) with the interfering effect of word stimuli upon nming colors themselves. In other words, if the word 'red' is printed in blue ink how will the interference of the ink-color 'blue' upon reding the printed word 'red' compre with the interference of the printed word 'red' upon clling the nme of the ink-color 'blue?' The increse in time for recting to words cused by the presence of conflicting color stimuli is tken s the mesure of the interference of color stimuli upon reding words. The increse in the time for recting to colors cused by the presence of conflicting word stimuli is tken s the mesure of the interference of word stimuli upon nming colors. A second problem grew out of the results of the first. The problem ws, Wht effect would prctice in recting to the color stimuli in the presence of conflicting word stimuli hve upon the rection times in the two situtions described in the first problem? Experimentl The mterils employed in these experiments re quite different from ny tht hve been used to study interference. 1 In former studies the subjects were given prctice in responding to set of stimuli until ssocitive bonds were formed between the stimuli nd the desired responses, then chnge ws mde in the experimentl 'set up' which demnded different set of responses to the sme set of stimuli. In the present study pirs of conflicting stimuli, both being inherent spects of the sme symbols, re presented simultneously ( nme of one color printed in the ink of nother color word stimulus nd color stimulus). These stimuli re vried in such mnner s to mintin the potency of their interference effect. Detiled descriptions of the mterils used in ech of the three experiments re included in the reports of the respective experiments. Experiment I: The Effect of Interfering Color Stimuli Upon Reding Nmes of Colors Serilly Mterils When this experiment ws contemplted, the first tsk ws to rrnge suitble tests. The colors used on the Woodworth-Wells colorsheet were considered but two chnges were deemed dvisble. As the word test to be used in comprison with the color test ws to be printed in blck it seemed well to substitute nother color for blck s n interfering stimulus. Also, becuse of the difficulty of printing words in yellow tht would pproximte the stimulus intensity of the other colors used, yellow ws discrded. After consulting with Dr. Peterson, blck nd yellow were replced by brown nd purple, hence, the colors used were red, blue, green, brown, nd purple. The colors were rrnged so s to void ny regulrity of occurrence nd so tht ech color would pper twice in ech column nd in ech row, nd tht no color would immeditely succeed itself in either column or row. The words were lso rrnged so tht the nme of ech color would pper twice in ech line. No word ws printed in the color it nmed but n equl number of times in ech of the other four colors; i.e. the word 'red' ws printed in blue, green, brown, nd purple inks; the word 'blue' ws printed in red, green, brown, nd purple inks; etc. No word immeditely succeeded itself in either column or row. The test ws printed from fourteen point Frnklin lower cse type. The word rrngement ws duplicted in blck print from sme type. Ech test ws lso printed in the reverse order which provided second form. The tests will be known s "Reding color nmes where the color of the print nd the word re different" (RCNd), 2 nd "Reding color nmes printed in blck" (RCNb). 1 Descoeudres (1914) nd lso Goodenough nd Brin (1929) presented color nd form simultneously in studying their reltive vlues s stimuli. 2 In Appendix A will be found key to ll symbols nd bbrevitions used in this pper.

3 APA CENTENNIAL: SERIAL INTERFERENCE 17 Tble I The Men Time in Seconds for Reding One Hundred Nmes of Colors Printed in Colors Different From Tht Nmed by the Word nd for One Hundred Nmes of Colors Printed in Blck nd No. Ss RCNd RCNb D PE A D/PE A Subjects nd Procedure Seventy college undergrdutes (14 mles nd 56 femles) were used s subjects. Every subject red two whole sheets (the two forms) of ech test t one sitting. One hlf of the subjects of ech sex, selected t rndom, red the tests in the order RCNb (form 1), RCNd (form 2), RCNd (Form 1) nd RCNb (form 2), while the other hlf reversed the order thus equting for prctice nd ftigue on ech test nd form. All subjects were seted so s to hve good dylight illumintion from the left side only. All subjects were in the experimentl room few minutes before beginning work to llow the eyes to djust to light conditions. The subjects were volunteers nd pprently the motivtion ws good. A ten-word smple ws red before the first reding of ech test. The instructions were to red s quickly s possible nd to leve no errors uncorrected. When n error ws left the subject's ttention ws clled to tht fct s soon s the sheet ws finished. On the signl "Redy! Go!" the sheet which the subject held fce down ws turned by the subject nd red loud. The words were followed on nother sheet (in blck print) by the experimenter nd the time ws tken with stop wtch to fifth of second. Contrry to instructions 14 subjects left totl of 24 errors uncorrected on the RCNd test, 4 ws the mximum for ny subject, nd 4 other subjects left 1 error ech on the RCNb test. As ech subject mde 200 rections on ech test this smll number of errors ws considered negligible. The work ws done under good dylight illumintion. Results Tble I gives the mens (m), stndrd devitions (), differences (D), probble error of the difference (PE A ), nd the relibility of the difference (D/PE ) for the whole group nd for ech sex. Observtion of the bottom line of the tble shows tht it took n verge of 2.3 seconds longer to red 100 color nmes printed in colors different from tht nmed by the word thn to red the sme nmes printed in blck. This difference is not relible which is in greement with Peterson's prediction mde when the test ws first proposed. The mens for the sex Tble II Showing Dt of Tble I Arrnged on the Bsis of College Clssifiction College Yer No. Ss. RCNd RCNb D D/PE A 1st d d th groups show no prticulr difference. An exmintion of the mens nd stndrd devitions for the two tests shows tht the interference fctor cused slight increse in the vribility for the whole group nd for the femle group, but slight decrese for the mle group. Tble II presents the sme dt rrnged on the bsis of college clssifiction. Only college yers one nd two contin sufficient number of cses for comprtive purposes. They show no differences tht pproch relibility. Experiment 2: The Effect of Interfering Word Stimuli Upon Nming Colors Serilly Mterils For this experiment the colors of the words in the RCNd test, described in Experiment 1, were printed in the sme order but in the form of solid squres ( ) from 24 point type insted of words. This sort of problem will be referred to s the "Nming color test" (NC). The RCNd test ws employed lso but in very different mnner from tht in Experiment 1. In this experiment the colors of the print of the series of nmes were to be clled in succession ignoring the colors nmed by the words; e.g. where the word 'red' ws printed in blue it ws to be clled 'blue,' where it ws printed in green it ws to be clled 'green,' where the word 'brown' ws printed in red it ws to be clled 'red,' etc. Thus color of the print ws to be the controlling stimulus nd not the nme of the color spelled by the word. This is to be known s the "Nming color of word test where the color of the print nd the word re different" (NCWd). (See Appendix B.) Subjects nd Procedure One hundred students (88 college undergrdutes, 29 mles nd 59 femles, nd 12 grdute students, ll femles) served s subjects. Every subject red two whole sheets (the two forms) of ech test t one sitting. Hlf of the subjects red in the order NC, NCWd, NCWd, NC, nd the other hlf in the order NCWd, NC, NC, NCWd, thus equting for prctice nd ftigue on the two sets. All subjects were seted (in their individul tests) ner the window so s to hve good dylight illumintion from the left side. Every subject seemed to mke rel effort. A ten-word smple of ech test ws red before reding the test the first time. The instructions were to nme the colors s they ppered in regulr reding line s quickly s possible nd to correct ll errors. The methods of strting, checking errors, nd timing were the sme s those used in Experiment 1. The errors were recorded nd for ech error not corrected, twice the verge time per word for the reding of the sheet on which the error ws mde ws dded to the time tken by the stop wtch. This pln of correction ws rbitrry but seemed to be justified by the sitution. There were two kinds of filures to be

4 18 J. RIDLEY STROOP Tble III The Men Time for Nming One Hundred Colors Presented in Squres nd in the Print of Words Which Nme Other Colors nd No. Ss NCWd NC D/NC D PE D/PE d ccounted for: first, the filure to see the error: nd second, the filure to correct it. Ech phse of the sitution gve the subject time dvntge which deserved tking note of. Since no ccurte objective mesure ws obtinble nd the number of errors ws smll the rbitrry pln ws dopted. Fifty-nine percent of the group left n verge of 2.6 errors uncorrected on the NCWd test (200 rections) nd 32 percent of the group left n verge of 1.2 errors uncorrected on the NC test (200 rections). The correction chnged the men on the NCWd test from to nd the men of the NC test from 63.0 to Results The mens of the times for the NC nd NCWd tests for the whole group nd for ech sex re presented in Tble III long with the difference, the probble error of the difference, the relibility of the difference, nd the difference divided by the men time for the nming color test. The comprison of the results for the whole group on the NC nd NCWd test given in the bottom line of the tble indictes the strength of the interference of the hbit of clling words upon the ctivity of nming colors. The men time for 100 responses is incresed from 63.3 seconds to seconds or n increse of 74 percent. (The medins on the two tests re 61.9 nd seconds respectively.) The stndrd devition is incresed in pproximtely the sme rtio from 10.8 to The coefficient of vribility remins the sme to the third deciml plce (/m =.171). The difference between mens my be better evluted when expressed in terms of the vribility of the group. The difference of 47 seconds is 2.5 stndrd devition units in terms of the NCWd test or 4.35 stndrd devition units on the NC test. The former shows tht 99 percent of the group on the NCWd test ws bove the men on the NC test (took more time); nd the ltter shows tht the group s scored on the NC test ws well below the men on the NCWd test. These results re shown grphiclly in Figure 1 where histogrms nd norml curves (obtined by the Gussin formul) of the two sets of dt re superimposed. The smll re in which the curves overlp nd the 74 percent increse in the men time for nming colors cused by the presence of word stimuli show the mrked interference effect of the hbitul response of clling words. The mens for the sex groups on the NCWd test show difference of 3.6 seconds which is only 1.16 times its probble error; but the mens on the NC test hve difference of 8.2 seconds which is 5.17 times its probble error. This relible sex-difference fvoring the femles in nming colors grees with the findings of Woodworm-Wells (1911), Brown (1915), Ligon( 1932), etc. The sme dt re rrnged ccording to college clssifiction in Tble IV. There is some indiction of improvement of the speed fctor for both tests s the college rnk improves. The reltive difference between the two tests, however, remins generlly the sme except for fluctutions which re probbly due to the vrition in the number of cses. Mterils Experiment 3: The Effects of Prctice Upon Interference The tests used were the sme in chrcter s those described in Experiments 1 nd 2 (RCNb, RCNd, NC, nd NCWd) with some revision. The NC test ws printed in swstiks ( ) insted of squres ( ). Such modifiction llowed white to pper in the figure with the color, s is the cse when the color is presented in the printed word. This chnge lso mde it possible to print the NC test in shdes which more nerly mtch those in the NCWd lest. The order of colors ws determined under one restriction other thn those given in section 2. Ech line contined one color whose two ppernces were seprted by only one other color. This ws done to equte, s much s 30 -to SO BO Figure 1. Showing the effect of interference on nming colors. (No interference [1]; interference [2].)

5 APA CENTENNIAL: SERIAL INTERFERENCE 19 Tble IV Showing the Dt of Tble HI Arrnged on the Bsis of College Clssifiction Clss Istyr 2dyr 3dyr 4th yr Grdutes No. Ss NCWd NC cr D D/NC D/PE* possible, the difficulty of the different lines of the test so tht ny section of five lines would pproximte the difficulty of ny other section of five lines. Two forms of the tests were printed; in one the order ws the inverse of tht in the other. Subjects nd Procedure Thirty-two undergrdutes in the University of Arizon (17 mles nd 15 femles), who offered their services, were the subjects. At ech dy's sitting 4 hlf-sheets of the sme test were red, nd the verge time (fter correction ws mde for errors ccording to the pln outlined in Experiment 2) ws recorded s the dy's score. Only few errors were left unconnected. The lrgest correction mde on the prctice test chnged the men from 49.3 to The pln of experimenttion ws s follows: D y Test RCNb RCNd NC NCWd NCWd NCWd NCWd Dy II Test NCWd NCWd NCWd NCWd NC RCNd RCNd On the 1st dy the RCNb test ws used to cquint the subjects with the experimentl procedure nd improve the relibility of the 2d dy's test. The RCNd test ws given the 2d dy nd the 13th dy to obtin mesure of the interference developed by prctice on the NC nd NCWd tests. The RCNd test ws given the 14th dy to get mesure of the effect of dy's prctice upon the newly developed interference. The NC test ws given the 3d nd 12th dys, just before nd just fter the rel prctice series, so tht ctul chnge in interference on the NCWd test might be known. The test schedule ws followed in regulr dily order with two exceptions. There were two dys between test dys 3 nd 4, nd lso two between test dys 8 nd 9, in which no work ws done. These irregulrities were occsioned by week-ends. Ech subject ws ssigned regulr time of dy for his work throughout the experiment. All but two subjects followed the schedule with very little irregulrity. These two were finlly dropped from the group nd their dt rejected. All of the tests were given individully by the uthor. The subject ws seted ner window so s to hve good dylight illumintion from the left side. There ws no other source of light. Every subject ws in the experimentl room few minutes before beginning work to llow his eyes to dpt to the light conditions. To id eye-dpttion nd lso to check for clerness of vision ech subject red severl lines in current mgzine. Every subject ws given Dr. Ishihr's test for color vision. One subject ws found to hve some trouble with red-green color vision; nd her results were discrded though they differed from others of her sex only in the number of errors mde nd corrected. Results The generl results for the whole series of tests re shown in Tble V which presents the mens, stndrd devitions, nd coefficients of vribility for the whole group nd for ech sex seprtely, together with mesure of sex differences in terms of the probble error of the difference. Tble VI, which is derived from Tble V, summrizes the prctice effects upon the respective tests. The grphicl representtion of the results in the prctice series gives the lerning curve presented in Figure 2. The Effect of Prctice on the NCWd Test Upon Itself The dt to be considered here re those given in the section of Tble V under the cption "Dys of Prctice on the NCWd Test." They re lso presented in summry in the left section of Tble VI nd grphiclly in Fig. 2. From ll three presenttions it is evident tht the time score is lowered considerbly by prctice. Reference to Tble VI shows gin of 16.8 seconds or 33.9 percent of the men of the 1st dy's prctice. The prctice curve is found to resemble very much the 'typicl' lerning curve when constructed on time units. The coefficient of vribility is incresed from.14 ±.012 to.19 ±.015. This difference divided by its probble error gives 2.60 which indictes tht it is not relible. The probbility of rel increse in vribility, however, is 24 to 1. Hence, prctice on the NCWd test serves to increse individul differences. An exmintion of the dt of the sex groups revels difference in speed on the NCWd test which fvors the femles. This is to be expected s there is difference in fvor of femles in nming colors. Though the difference is not relible in ny one cse it exists throughout the prctice series; indicting tht the reltive improvement is pproximtely the sme for the two groups. This ltter fct is lso shown by the rtio of the difference between the hlves of prctice series to the first hlf. It is. 185 for the mles nd. 180 for the femles. The Effect of Prctice on the NCWd Test upon the NC Test The middle section of Tble VI shows gin on the NC test of 4.0 seconds or 13.9 percent of the initil score. This is only 23.7 percent of the gin on the NCWd test which mens tht less thn one fourth of the totl gin on the NCWd test is due to increse in speed in nming colors. The improvement is greter for the mles, which is ccounted for by the fct tht there is more difference between nming colors nd reding nmes of colors for the mles thn for the femles.

6 20 J. RIDLEY STROOP Tble V Showing the Effects of Prctice on the NCWd Test Upon Itself, Upon the NC Test, nd Upon the RCNd Test in Terms of Men Scores, Stndrd Devitions (), nd Coefficients of Vribility (/m) for Thirty-two College Students PE A D/PE A PE< D/PE A The score is No. Ss. RCNb ± ± ±.012 No. Ss ± ± ±0.16 Initil Tests RCNd ± ± ±.013 Dys of Prctice on ± the verge time for four trils of fifty rections ech. NC Differences Coefficients of Vribility.12 ± ± ± ± ± the NCWd Test 7 8 NC Differences Coefficients of Vribility ± ± ± ± Dys of Prctice on the NCWdleA Finl Tests RCNd ff ± ± ± ± RCNd ± ± ±.022 The Effects in the RCNd Test of Prctice on the NCWd nd NC Tests The right section of Tble VI shows tht the prctice on the NCWd nd NC tests resulted in hevy loss in speed on the RCNd. A comprison of the right nd left sections of the tble shows tht the loss on the RCNd test, when mesured in bsolute units, is prcticlly equl to the gin on the NCWd test; when mesured in reltive units it is much greter. It is interesting to find tht in ten short prctice periods the reltive vlues of opposing stimuli cn be modified so gretly. There is little reltion, however, between the gin in one cse nd the loss in the other. The correltion between gin nd loss in bsolute units is.262 ±.11, while the correltion between percent of gin nd percent of loss is.016 ±. 17, or zero. This is wht one might expect. From considertion of the results of the two pplictions of the RCNd test given in the finl tests of Tble V it is evident tht the newly developed interference disppers very rpidly with prctice. From one dy to the next the men decreses from 34.8 to 22.0 seconds. This indictes tht renewing the effectiveness of old ssocitions which re being opposed by newly formed ones is esier thn strengthening new ssocitions in opposition to old well estblished ones. Tble VI A Summry of the Mens in Tble V, Showing the Effect of Prctice in the NCWd Test Upon the NCWd, the NC, nd the RCNd Tests Test M Initil Score 51.2 Finl Score 33.4 Gin 17.8 Percent Gin 34.8 Minus sign shows loss. NCWd F M NC F M RCNd F

7 APA CENTENNIAL: SERIAL INTERFERENCE 21»r **, s 40 ye so \ /\ A / Figure 2. Men scores for the group in ech of the four hlf-sheets of the NCWd test, which constituted the dily prctice. of The vribility of the group is incresed by the increse in interference due to prctice on the NCWd test. The coefficient of vribility increses from.15 ±.013 to.34 ±.031, the difference divided by its probble error being This is not surprising s the degree of the interference vries widely for different subjects. Its degree is determined by the lerning on the prctice series which is shown by the individul results to vry considerbly. One dy's prctice on the RCNd test reduced the vribility from.34 ±.031 to.25 ±.022. The decrese in vribility is 2.3 times its probble error. The dt from this experiment present interesting findings on the effect of prctice upon individul differences. The results which hve lredy been discussed seprtely re presented for comprison in Tble VII. These results show tht prctice increses individul differences where stimulus to which the subjects hve n hbitul rection pttern is interfering with rections to stimulus for which the subjects do not hve n hbitul rection pttern (the word stimulus interfering with nming colors, NCWd test); but decreses individul differences where stimulus to which the subjects do not hve n hbitul rection pttern is interfering with rections to stimulus for which the subjects hve n hbitul rection pttern (the color stimulus interfering with reding words RCNd test). There re two other vribles involved, however: initil vribility nd length of prctice. Thus in the NCWd test the initil vribility ws less, the difficulty greter, nd the prctice greter thn in the RCNd test. These findings lend some support to Peterson's hypothesis, "Subjects of norml heterogeneity would become more like with prctice on the simpler processes or ctivities, but more different on the more complex ctivities" (Peterson nd Brlow, 1928, p. 228). A sex difference in nming colors hs been found by ll who hve studied color nming nd hs been generlly ttributed to the greter fcility of women in verbl rections thn of men. There is some indiction in our dt tht this sex difference my be due to the difference in the ccustomed rection of the two sexes to colors s stimuli. In other words responding to color stimulus by nming the color my be more common with femles thn with mles. This difference Tble VII The Effects of Prctice on the NCWd Test nd the RCNd Test Upon the Coefficient of Vribility for the Group Test NCW RCNd No. Ss Coefficients of Vribility Initil Finl D

8 22 J. RIDLEY STROOP is probbly built up through eduction. Eduction in color is much more intense for girls thn for boys s observing, nming, nd discussing colors reltive to dress is much more common mong girls thn mong boys. The prctice in nming colors in the NCWd test decresed the difference between the sex groups on the NC test from difference 5.38 times its probble error to difference 2.99 times its probble error. This decrese in the difference due to prctice fvors the view tht the difference hs been cquired nd is therefore product of trining. Summry 1. Interference in seril verbl rections hs been studied by mens of newly devised experimentl mterils. The source of the interference is in the mterils themselves. The words red, blue, green, brown, nd purple re used on the test sheet. No word is printed in the color it nmes but n equl number of times in ech of the other four colors; i.e. the word 'red' is printed in blue, green, brown, nd purple inks; the word 'blue' is printed in red, green, brown, nd purple inks; etc. Thus ech word presents the nme of one color printed in ink of nother color. Hence, word stimulus nd color stimulus both re presented simultneously. The words of the test re duplicted in blck print nd the colors of the test re duplicted in squres or swstiks. The difference in the time for reding the words printed in colors nd the sme words printed in blck is the mesure of the interference of color stimuli upon reding words. The difference in the time for nming the colors in which the words re printed nd the sme colors printed in squres (or swstiks) is the mesure of the interference of conflicting word stimuli upon nming colors. 2. The interference of conflicting color stimuli upon the time for reding 100 words (ech word nming color unlike the ink-color of its print) cused n increse of only 2.3 seconds or 5.6 percent over the norml time for reding the sme words printed in blck. This increse is not relible. But the interference of conflicting word stimuli upon the time for nming 100 colors (ech color being the print of word which nmes nother color) cused n increse of 47.0 seconds or 74.3 percent of the norml time for nming colors printed in squres. These tests provide unique bsis (the interference vlue) for compring the effectiveness of the two types of ssocitions. Since the presence of the color stimuli cused no relible increse over the norml time for reding words (D/PE d = 3.64) nd the presence of word stimuli cused considerble increse over the norml time for nming colors (4.35 stndrd devition units) the ssocitions tht hve been formed between the word stimuli nd the reding response re evidently more effective thn those tht hve been formed between the color stimuli nd the nming response. Since these ssocitions re products of trining, nd since the difference in their strength corresponds roughly to the difference in trining in reding words nd nming colors, it seems resonble to conclude tht the difference in speed in reding nmes of colors nd in nming colors my be stisfctorily ccounted for by the difference in trining in the two ctivities. The word stimulus hs been ssocited with the specific response 'to red,' while the color stimulus hs been ssocited with vrious responses: 'to dmire,' 'to nme,' 'to rech for,' 'to void,' etc. 3. As test of the permnency of the interference of conflicting word stimuli to nming colors eight dys prctice (200 rections per dy) were given in nming the colors of the print of words (ech word nming color unlike the inkcolor of its print). The effects of this prctice were s follows: 1. It decresed the interference of conflicting word stimuli to nming colors but did not eliminte it. 2. It produced prctice curve comprble to tht obtined in mny other lerning experiments. 3. It incresed the vribility of the group. 4. It shortened the rection time to colors presented in color squres. 5. It incresed the interference of conflicting color stimuli upon reding words. 4. Prctice ws found either to increse or to decrese the vribility of the group depending upon the nture of the mteril used. 5. Some indiction ws found tht the sex difference in nming colors is due to the difference in the trining of the two sexes. (Mnuscript received August 15, 1934) References Bir, J. H., The prctice curve: A study of the formtion of hbits. Psychol. Rev. Monog. Suppl., 1902 (No. 19), Bergstrom, J. A., Experiments upon physiologicl memory. Amer. J. Psychol., 1893, 5, Bergstrom, J. A., The reltion of the interference of the prctice effect of n ssocition. Amer, J. Psychol., 1894, 6, Bowditch, H. P., nd Wrren, J. W., The knee-jerk nd its physiologicl modifictions. J. Physiology, 1890, 11, Brown, Wrner, Prctice in ssociting color nmes with colors. Psychol. Rev., 1915, 22, Brown, Wrner, Hbit interference in crd sorting. Univ. of Clif. Studies in Psychol., 1914, V, i, No. 4. Cttell, J. McK., The time it tkes to see nd nme objects. Mind, 1886, 11, Culler, A. J., Interference nd dptbility. Arch, of Psychol, 1912, 3 (No. 24), Descoeudres, A., Couleur, forme, ou nombre. Arch, depsychol, 1914, 14, Grrett, H. E., nd Lemmon, V. W., An nlysis of severl wellknown tests. / Appld. Psychol., 1924, 8, Goodenough, F. L., nd Brin, C. R., Certin fctors underlying the cquisition of motor skill by pre-school children. J. Exper. Psychol., 1929, 12, Hunter, W. S., nd Yrbrough, J. U., The interference of uditory hbits in the white rt. J. Animl Behv., 1917, 7, Hunter, W. S., Hbit interference in the white rt nd in the humn subject. / Comp. Physiol, 1922, 2, Kline, L. W., An experimentl study of ssocitive inhibition. J. Exper. Psychol, 1921, 4, Lester, O. P., Mentl set in reltion to retroctive inhibition. J. Exper. Psychol, 1932, 15, Ligon, E. M. A., Genetic study of color nming nd word reding. Amer. J. Psychol, 1932, 44, Lund, F. H., The role of prctice in speed of ssocition. J. Exper. Psychol, 1927, 10,

9 APA CENTENNIAL: SERIAL INTERFERENCE 23 Miiller, G. E., nd Schumnn, F., Experimentelle Beitrge zu Untersuchung des Gedchtnisses. Zsch.f. Psycho!., 1894, 6, Miinsterberg, Hugo, Gedchtnisstudien. Beitrge zur Experimentellen Psychologic, 1892, 4, 70. Perce, Bennie D., A note on the interference of visul hbits in the white rt. J. Animl Behv , 7, Peterson, J., nd Brlow, M. C, The effects of prctice on individul differences. The 27th Yer Book of Nt. Soc. Study of Educ., Prt NC 11,1928, NCWd Peterson, J., Lnier, L. H., nd Wlker, H. M., Comprisons of white nd negro children. J. Comp. Psychol, 1925, 5, RCNb Peterson, J., nd Dvid, Q. J., The psychology of hndling men in the RCNd rmy. Minnepolis, Minn. Ferine Book Co., 1918, pp Sheprd, J. F., nd Fogelsonger, H. M., Assocition nd inhibition. D Psychol. Rev, 1913, 20, D/PE d Telford, C. W., Differences in responses to colors nd their nmes. / M & F Genet. Psychol., 1930, 37, PE d Woodworth, R. S., nd Wells, F. L., Assocition tests. Psychol. Rev. Monog. Suppi, 1911, 13 (No. 57), pp. 85. /m Appendix A A Key to Symbols nd Abbrevitions Nming Colors. Nming the Colors of the Print of Word Where the Color of the Print nd the Word re Different. Reding Color Nmes Printed in Blck Ink. Reding Color Nmes Where the Color of the Print nd the Word re Different. Difference. Difference divided by the probble error of the difference. s nd s. Probble error of the difference. Sigm or stndrd devition. Stndrd devition divided by the men. Neuropsychology to Be n APA Journl In Jnury 1993, Neuropsychology, which hs been published by the Eductionl Publishing Foundtion ( subsidiry publishing progrm of the Americn Psychologicl Assocition), will be published by the Americn Psychologicl Assocition. The Publictions nd Communictions Bord of the APA hs ppointed Nelson Butters s editor of Neuropsychology. As of Jnury 1,1992, mnuscripts should be submitted to Nelson Butters Chief, Psychology Service (116B) Deprtment of Veterns Affirs Medicl Center 3350 L Joll Villge Drive L Joll.CA Mnuscripts considered by the incoming editor will be published beginning in the Jnury 1993 issue. Submitted mnuscripts should fll within the following new editoril policy sttement: The mission of Neuropsychology is to foster () bsic reserch, (b) the integrtion of bsic nd pplied reserch, nd (c) improved prctice in the field of neuropsychology, brodly conceived. The primry function of Neuropsychology is to publish originl, empiricl ppers in the field. Occsionlly, scholrly reviews nd theoreticl ppers will lso be published ll with the gol of promoting empiricl reserch on the reltion between brin nd humn cognitive, emotionl, nd behviorl function. Sought re submissions of humn experimentl, cognitive, nd behviorl reserch with implictions for neuropsychologicl theory nd prctice. Ppers tht increse our understnding of neuropsychologicl functions in both norml nd disordered sttes nd cross the lifespn re encourged. Applied, clinicl reserch tht will stimulte systemtic experimentl, cognitive, nd behviorl investigtions s well s improve the effectiveness, rnge, nd depth of ppliction is germne. Neuropsychology seeks to be the vehicle for the best reserch nd ides in the field.