Verbal coding and the elimination of stroop interference in a matching task

Verbal Coding and the Elimination of Stroop Interference in a Matching Task Author(s): Michael F Mascolo and Stephen C Hirtle Source: The American Journal of Psychology, Vol 103, No (Summer, 1990), pp 195-215 Published by: University of Illinois Press Stable URL: http://www.jstor.org/stable/1423142 Accessed: 11/10/2014 15:53 Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at http://www.jstor.org/page/info/about/policies/terms.jsp JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive We use information technology and tools to increase productivity and facilitate new forms of scholarship For more information about JSTOR, please contact support@jstor.org University of Illinois Press is collaborating with JSTOR to digitize, preserve and extend access to The American Journal of Psychology http://www.jstor.org This content downloaded from 209.23.242.17 on Sat, 11 Oct 2014 15:53:34 PM All use subject to JSTOR Terms and Conditions Verbalcoding and the eliminationof Stroop interferencein a matching task MICHAEL F MASCOLO Merrimack College STEPHEN C HIRTLE University of Pittsburgh Translationalmodels of the Stroop effect (Virzi & Egeth, 1985) predict that Stroop interference can be eliminated if subjectscan be induced to process target colors using a coding system separate from the coding system used to process distractors.This hypothesiswas tested in two experiments In the first experiment, we attempted to eliminate the need for subjectsto translate target colors to verbal codes when responding to Stroop stimuli Before responding to verbal incongruent color word distractors,subjectspracticed matching colors to irregular shapes It was expected that subjectswould use nonverbal codes to mediate responding in this task After practice, subjects continued the matching task in the presence of incongruent color words Stroop interference persisted, contrary to predictions Because subjects reported adopting verbal strategiesto perform the matching task, Experiment was designed to control the verbalcoding strategiesthat subjectsemployed Before responding to Stroop distractor stimuli, subjects in the nonsense name group practiced using nonsense names to mediate the matching of shapes to colors; subjectsin the actual name group used actual color names to mediate performancein the matchingtask When incongruentcolor word distractorswere introduced, Stroop interference was eliminated for subjects in the nonsense name group, but persisted for subjects in the actual name group The results are interpreted as consistent with an outcome conflict (Navon & Miller, 1987) or a modified translational model of the Stroop effect In the Stroop (1935) color naming task, persons are asked to name the color of ink in which incongruent color words are printed (e.g., the word RED printed in blue ink) The time required to name the ink color of incongruent color words is delayed relative to the time required to name the ink color of congruent color words, non-color words, rows of X's, or color patches (Dyer, 1973; Klein, 1964; Regan, 1978) Conversely, incongruent ink colors not impede responding when subjects read the name of Stroop color words In this article, we explore the conditions under which Stroop interference can be AMERICANJOURNAL OF PSYCHOLOGY Summer 1990, Vol 103, No 2, pp 195-215 C 1990 by the Board of Trustees of the University of Illinois This content downloaded from 209.23.242.17 on Sat, 11 Oct 2014 15:53:34 PM All use subject to JSTOR Terms and Conditions 196 MASCOLO AND HIRTLE eliminated or attenuated Data pertaining to the elimination of Stroop interference can provide clues concerning the source of Stroop interference Virzi and Egeth (1985) have proposed a translational model of Stroop interference Based on recent evidence (Dunbar & MacCleod, 1984), Virzi and Egeth rejected models of the Stroop effect that maintain that Stroop interference arises as a simple function of the competition between word and color processing for access to a single centralized decision stage (Dyer, 1973; Morton & Chambers, 1973; Palef & Olson, 1975) Rather, Virzi and Egeth suggested that information is processed using several processing systems which code and process information using different decision and response stages (cf Palef, 1978) In the traditional Stroop task, a pictorial processing system codes and processes the color input To respond, the pictorial input must be translated to a verbal code Stroop interference results from the conflict between the verbal color name code associated with the target color and the incongruent color name code activated within the verbal system Virzi and Egeth's (1985) translational model of Stroop interference can be seen as a special case of Navon's outcomeconflictmodel of dualtask interference (Navon, 1984, 1985; Navon & Miller, 1987) Navon suggests that dual-task interference often results from conflicts between outputs of parallel processes, rather than from competition for limited processing resources (e.g., as in Kahneman, 1973) Outcome conflicts are analogous to interference caused by cross-talk among telephone lines, even when the number of telephone calls does not exceed the number of lines available In testing the outcome conflict model, Navon and Miller (1987) asked subjects to search for boys' names in one channel of a stimulus display, and for city names in another channel of the display When both search tasks were performed simultaneously, responses were delayed when nontargets on one channel belonged to or were related to the target category on the other channel No such effects were found when each search task was performed alone, despite identical stimulus displays These results suggest that part of the dual-task decrement observed resulted from the conflict between the outcomes of processing nontargets on one channel and targets on the other channel In Virzi and Egeth's (1985) translational model of Stroop interference, the outcome of the linguistic processing of the incongruent color word conflicts with the outcome of the translation of the target color into a linguistic color name code The translational model differs from the more general outcome conflict model only by specifying that the outcome conflict results from an obligatory translation process This content downloaded from 209.23.242.17 on Sat, 11 Oct 2014 15:53:34 PM All use subject to JSTOR Terms and Conditions ELIMINATION OF STROOP INTERFERENCE 197 between two independent processing systems (the pictorial and the linguistic) If Stroop interference results from this sort of outcome conflict, then it follows that Stroop interference can be eliminatedor attenuated by eliminating the need for the translationalstage when performing the Stroop task For example, if subjectscould be induced to use nonverbal codes exclusively to mediate target responding in the Stroop task, then Stroop interference should be eliminated, because translationof the target color to the verbal system-the system which codes distractors-would be eliminated To test the translationalmodel of Stroop interference, Virzi and Egeth (1985) asked subjects to sort Stroop color word stimuli (and control stimuli)into bins which were labeled with either a color word or with a color patch When subjectswere asked to sort the cards on the basisof the color of ink, incongruentcolor wordsproducedgreater response delays (relative to controls) when bins were labeled with color words than when bins were labeled with color patches Alternatively, when subjects were asked to sort cards on the basis of the meaningof the color words,incongruentcolor wordsproducedgreater delays (relativeto controls)when bins were labeled with color patches than when bins were labeled with color words Thus, in cases in which interference resulted, the codes activatedby target stimuliwere translated to the coding systemthat processed incongruentdistractorstimuli When no such translationoccurred, no interferencewasobserved Similarresultswere reported by Dalrymple-Alfordand Azkoul (1972) Several other studies have reported data which concur with Virzi and Egeth's (1985) findings McClain (1983b) presented the words HIGHand LOWin high and low pitches Subjectswere askedto identify either the pitch or word using either a verbal response or a pitched hum McClain found that interference occurred when the response mode and the target stimulusdimension conflicted (e.g., pitch-verbal, word-hum),but not when the response mode and stimulusdimension were compatible (e.g., pitch-hum, word-verbal).These data concur with a translationalaccount When subjects responded to pitch by humming, processing was restricted to a tonal system Because tones were not translated to the verbal system, interference from verbal distractor codes was avoided Treisman and Fearnley(1969) asked subjectsto sort cards containing either two words, two colors, or a word and a color into same or different piles Within-dimensionsorts (word-wordand color-color) proceeded more quickly than between-dimensionsorts (word-color), even when one of the words (for word-wordmatching)or colors (for color-color matching) constituted a Stroop color word Finally,Pritchatt (1968) and McClain(1983a) eliminatedStroopinterferencewhen This content downloaded from 209.23.242.17 on Sat, 11 Oct 2014 15:53:34 PM All use subject to JSTOR Terms and Conditions 198 MASCOLO AND HIRTLE subjects identified the ink colors of Stroop color words by pressing keys labeled with color patches, but not when keys were labeled with color words The results from these studies suggest that when target stimuli are processed using coding systems that are distinct from the coding systems that process distractors, interference by incongruent distractors can be eliminated Several studies have demonstrated that Stroop inteference can be created when subjects are induced to process (normally innocuous) incongruent distractors within the coding systems which mediate target responding Recall that incongruent ink colors normally not delay the reading of base words of Stroop color stimuli From a translational model, word reading never requires activation of nonverbal color codes Therefore, irrelevant colors cannot conflict with the verbal color name codes that mediate responding to base words However, if subjects were to code irrelevant colors verbally, Stroop interference might result Glaser and Glaser (1982, Exp 2) presented irrelevant color patches at various intervals prior to the presentation of color words To induce subjects to encode colors using verbal labels, congruent color words appeared with a probability of 80 The researchers found that incongruent colors impeded reading of target color words when colors appeared 300 to 500 ms before target words Thus, when encoded using the same coding system that processes target stimuli, irrelevant distractors can impede target responding Virzi and Egeth (1985) reported similar results using a spatial variant of the Stroop task Flowers and his colleagues (Compton & Flowers, 1977; Flowers & Dutch, 1976; Flowers & Stoup, 1977) have reported evidence that leads to similar conclusions For example, Flowers and Stoup (1977) asked subjects to sort shapes according to a grouping rule Either incongruent shape names (names of shapes from the opposite group) or rows of X's were printed on the shapes When a single pictorial attribute common to all shapes in a group (e.g., curved vs edged) could be used to discriminate the groups, incongruent shape names did not impede sorting However, when subjects used grouping rules which did not yield pictorial attributes that could readily discriminate the groups, incongruent shape names impeded sorting, presumably because subjects now encoded shapes verbally As long as the irrelevant distractors were processed using a different system from that used to process target stimuli, sorting proceeded without delay To garner additional support for a translational or outcome conflict model, we attempted to eliminate interference in a Stroop-like task by inducing subjects to use nonverbal codes to mediate responding to colors The study proceeded in two phases In Phase 1, subjects This content downloaded from 209.23.242.17 on Sat, 11 Oct 2014 15:53:34 PM All use subject to JSTOR Terms and Conditions ELIMINATION OF STROOP INTERFERENCE 199 learned to match color patches to irregular shapes We hypothesized that because neither colors nor irregular shapes constitute linguistic input, subjects would not employ verbal color name codes to mediate responding In Phase 2, subjects matched colors to shapes in the presence of incongruent color words, congruent color words, noncolor words, and rows of X's If subjects adopt nonverbal codes to mediate the matching of shapes to colors, then the incongruent verbal color name codes activated by distractors could not impede responding Thus, we predicted that incongruent color words would not delay responding relative to control conditions EXPERIMENT METHOD General design Experiment consisted of two phases During the learning phase, subjects performed a discrimination task in order to associate each of four colors with a different irregular shape This phase was intended to induce subjects to adopt nonverbal response codes to mediate responding to Stroop stimuli In the distractorphase, subjects continued to perform the discrimination task in the presence of various distractor stimuli Subjects Twenty undergraduates, 14 females and males, attending the State University of New York at Albany, participated Subjects were paid $3.00/ hr Stimuli and apparatus The entire experiment was conducted in a soundproof chamber An Apple 2e microcomputer controlled stimulus presentation and data collection All stimuli were presented on a 28 x 21-cm Amdek screen A black border was placed around the computer screen, limiting the subject's view to a 17.5 x 17.5-cm viewport Subjects responded using a response box containing two buttons positioned cm apart Nonfocal colors were used in the study to increase the likelihood that subjects would encode color patches using imaginal rather than verbal color name codes The hues used were brown, orange, gray, and pink The hues corresponded to the Apple 2e low-resolution color codes 8, 9, 10, and 11, respectively The names of each of these hues served as color word distractors Non-color word distractors included most, deal, wage, and best Rows of X's served as control stimuli The four shapes were constructed by arranging 13 squares into a shape such that there were no solid blocks of four squares and no blank areas enclosed by filled squares The four shapes are shown in Figure This content downloaded from 209.23.242.17 on Sat, 11 Oct 2014 15:53:34 PM All use subject to JSTOR Terms and Conditions 200 MASCOLO AND HIRTLE Figure Irregular figures used in the matching task In the learning phase, the stimulus display consisted of one of four color bars, whose lower edge was depicted 3.25 cm above the center of the viewport The color bar was 14.2 x cm One of the four shapes was centered cm below the color bar The average dimensions of the shapes were x cm In the distractor phase, the stimulus display consisted of a distractor positioned in between two color bars, each depicting the identical hue One of the four irregular shapes appeared 1.5 cm below the lower color bar The color bars and distractors were positioned on the screen such that the plus sign was always replaced with the distractor stimulus The color bars were 12.2 x cm The color words averaged 9.2 x 2.3 cm; the row of X's was 14.5 x 2.3 cm, Figure shows the arrangement of the stimuli on the computer screen for the distractor phase Design Four distractor conditions were employed: incongruent,e.g., the color word PINK surrounded by two brown color bars; congruent, e.g., the color word PINK surrounded by two pink color bars; non-colorword, e.g., the word BEST surrounded by two color bars; and rows of X's (XXX condition) The learning phase consisted of 408 trials Half the trials were distributed equally among the four types of correct color/shape pairs, and the remaining half were distributed among the 12 types of incorrect color/shape pairs The distractor phase consisted of 192 trials The incongruent condition contained 48 trials, the congruent condition contained 16 trials (for a total of 64 stimulus items containing color words), and the non-color word and XXX conditions contained 64 trials each Half the trials required a correct response and half required an incorrect response Procedure To acquaint the subject with the correct color/shape pairs, at the beginning of the learning phase, each of the four correct color/shape pairs ap- This content downloaded from 209.23.242.17 on Sat, 11 Oct 2014 15:53:34 PM All use subject to JSTOR Terms and Conditions ELIMINATION OF STROOP INTERFERENCE 201 Figure Stimulus display for distractor phases of Experiments and (subjects were asked to match the previously assigned shape to the color bars while ignoring the word) peared sequentially on the computer screen for s Subsequently, the first trial began with the presentation of a plus sign in the middle of the screen The subject was instructed to use the plus sign as a fixation point After Is, a color bar and a shape appeared on the computer screen The subject was required to determine whether or not the shape was the correct associate of the color bar The subject responded yes or no using a binary button press If the subject responded incorrectly, the word error appeared on the screen for the first second of a 3-s intertrial interval After every block of 12 trials, the subject was presented with cumulative and block accuracy scores Subjects were instructed to use the error feedback to learn the correct color/shape pairs Each trial in the distractor phase began with the presentation of the plus sign in the middle of the screen After s, the plus sign disappeared, and a color/shape/distractor combination appeared on the computer screen The subject was instructed to decide whether or not the color matched the shape, while ignoring the distractor word The subject was instructed to respond as quickly but as accurately as possible, using a button press, as in the learning phase Reaction time was recorded Error messages appeared as in the learning phase RESULTS AND DISCUSSION Error analysis For each subject, the percentage error rate for each condition was calculated Error rates were 025 for incongruent distractors, 003 This content downloaded from 209.23.242.17 on Sat, 11 Oct 2014 15:53:34 PM All use subject to JSTOR Terms and Conditions 202 MASCOLO AND HIRTLE for congruent distractors, 005 for non-color word distractors, and 008 for the XXX condition A one-way repeated measures analysis of variance (ANOVA) was significant, F(3, 51) = 6.52, MS, = 00028, p = < 01 Bonferroni t tests indicated that the error rate for the incongruent condition differed significantly from the remaining conditions No remaining comparisons proved significant time (RT) analysis The mean RTs for correct yes responses for each distractor condition were collapsed across subjects (RTs in milliseconds are shown in Table 1) A one-way repeated measures ANOVA indicated a significant effect of distractor, F(3, 51) = 11.73, p < 001 Post-hoc tests using the Bonferroni procedure indicated that subjects required significantly more RT to respond in the incongruent condition (M = 935) than in the remaining distractor conditions The RTs for the congruent (M = 778), non-color word (M = 805), and XXX (M = 785) distractor conditions did not differ significantly from each other Thus, contrary to our hypothesis, incongruent color word distractors inhibited responding relative to non-color words, congruent color words, or rows of X's Using the XXX condition as a baseline, no evidence of inhibition of non-color words nor of facilitation of congruent color words was adduced The finding that incongruent color words inhibited responding whereas non-color words produced no inhibition is consistent with the results of other Stroop studies that employ a keypress response mode (Keele, 1972; McClain, 1983a; Redding & Gerjets, 1977) The finding that congruent color words did not facilitate responding relative to an XXX baseline is consistent with the findings of McClain (1983a), but not with the findings of Redding and Gerjets Informal interviews with subjects were conducted at the completion of the experiment When asked about the strategies used to perform the task, subjects generally reported that they used actual color names to encode colors in the experiment Thus, subjects did not appear spontaneously to adopt nonverbal strategies to match colors to shapes Instead, subjects might have used verbal color name codes to mediate Reaction Table Reaction times (RTs, in ms) for Experiment RT Condition SD 935 169 Non-color word 805 135 XXX Congruent 785 778 124 183 Incongruent This content downloaded from 209.23.242.17 on Sat, 11 Oct 2014 15:53:34 PM All use subject to JSTOR Terms and Conditions ELIMINATION OF STROOP INTERFERENCE 203 responding in the task As such, incongruent color words delayed target responding Experiment was designed to control the verbal codes that subjects used to encode the color/shape displays EXPERIMENT In Experiment 1, we reasoned that if the processing of target colors in the Stroop task could proceed exclusively within the pictorial processing system, then verbal color name codes activated by incongruent color words could not impede target processing However, in Experiment 1, subjects appeared to use verbal, rather than nonverbal codes to mediate the matching of shapes to colors Thus, Experiment was designed to control the verbal codes that subjects used to mediate the matching process In so doing, we attempted to induce subjects to use nonsense names to mediate the matching of colors and shapes Experiment relied upon the assumption that pictorial codes differ qualitatively from verbal codes, and are constructed and used by separate processing systems Experiment relies upon the further assumption that distinctions can be made among different processing codes within the verbal system itself We assume that verbal processing codes differ quantitatively according to the similarity of the semantic, phonetic, or orthographic information which they represent (Keele, 1972; Klein, 1964) Our decision to induce subjects to adopt nonsense names as verbal mediates in the matching task proceeded from the assumption that unfamiliar nonsense names share the lowest degree of semantic, phonetic, or orthographic similarity possible with the verbal color name codes activated by incongruent color words We hypothesized that if subjects could be induced to use nonsense names to mediate processing of colors, then the verbal codes activated by incongruent color words would not conflict with the verbal color name codes used to match colors to shapes In so doing, Stroop interference would be eliminated To test this hypothesis, two groups of subjects were recruited Subjects in the nonsensename group were trained to encode the colors and shapes using nonsense names as verbal mediators Subjects in the actual name group were trained to encode colors and shapes using actual color names as verbal mediators Subsequently, subjects in both groups matched colors to shapes in the presence of various distractor stimuli We hypothesized that incongruent color word distractors would produce little or no delay in matching shapes to colors for subjects who encoded the colors and shapes using nonsense names We expected that incongruent color word distractors would inhibit the matching This content downloaded from 209.23.242.17 on Sat, 11 Oct 2014 15:53:34 PM All use subject to JSTOR Terms and Conditions 204 MASCOLO AND HIRTLE of colors to shapes for subjects who were encouraged explicitly to use actual color names to mediate their responses Several researchers have examined the effect of modifying the form of the verbal mediator in the Stroop task Stirling (1979) required subjects to name colors using different arbitrarily assigned letters Using this procedure, incongruent color words still delayed color naming, but to a lesser degree than did incongruent letter strings Glaser and Dolt (1977) asked participants to associate a set of color patches with one set of nonsense names, and to associate the corresponding set of color names with another set of nonsense names Subsequently, subjects were asked to provide the nonsense name for the colors of Stroop color words However, the RT to name the color of incongruent color words was still delayed in comparison to the RT to name colors of control stimuli (rows of I's) In studies of Stroop interference in bilinguals (Chen & Ho, 1986; Pyer, 1971; Magiste, 1984; Preston & Lambert, 1969), subjects were asked to use one language to name the color of ink, while the incongruent word was printed in either the same language (within-language) or in the other language (between-language) In general, these studies indicate that within-language Stroop interference is usually greater than between-language Stroop interference Chen and Ho reported evidence that between-language Stroop interference is greater when the two languages involved are similar rather than dissimilar Thus, studies that examine the effects of modifying the verbal mediators employed in the Stroop task suggest that Stroop interference can be attenuated by decreasing the similarity between the verbal color code representations activated by target and distractor stimuli in the Stroop task The present experiment differs from the studies reviewed above in several ways First, in the present experiment, subjects were not required to name colors; rather, subjects matched colors to shapes and responded via button press, as in Experiment Second, subjects engaged in a greater amount of practice in the use of nonsense names to match shapes to colors than did subjects in the Glaser and Dolt (1977) or in the Stirling (1979) studies Through practice, we intended to encourage subjects in the nonsense name group to translate target color information to a nonsense name code, and then to use the nonsense name code to mediate the matching of colors to shapes To the extent that the nonsense name code shared little similarity to the incongruent color name codes activated by incongruent color words, we predicted no outcome conflict between the matching of colors to shapes and the processing of incongruent color words Thus, in the present experiment, we predicted the elimination of Stroop interfer- This content downloaded from 209.23.242.17 on Sat, 11 Oct 2014 15:53:34 PM All use subject to JSTOR Terms and Conditions ELIMINATION OF STROOP INTERFERENCE 205 ence for subjects who used nonsense names to mediate the matching of colors to shapes, but not for subjects who used actual color names to mediate the matching of colors to shapes METHOD General design Experiment consisted of three phases, the first two of which served as preparation The first was the color name learning phase During this phase, subjects in the nonsense name group practiced naming the four colors using nonsense names Subjects in the actual name group practiced naming colors using their actual names The second was the shape learning phase During this phase, subjects learned to associate one of four irregular shapes with each of the four color/name pairs Subjects in the nonsense name group matched shapes to colors and to their assigned nonsense names, whereas subjects in the actual name group matched shapes to colors and to their actual color names Finally, in the distractorphase, both groups of subjects matched shapes to colors in the presence of various distractor stimuli Subjects Twenty-nine undergraduates, who had not participated in Experiment 1, 19 females and 10 males, attending the State University of New York at Albany, participated Subjects were paid $3.00/hr There were 14 subjects in the actual name group and 15 in the nonsense name group and apparatus The stimuli and apparatus were identical to those employed in Experiment with the following modifications Because the average length of the color word distractors exceeded the average length of the non-color word distractors in Experiment 1, the non-color word distractors were changed to most, seem, allow, and enough Each of these words was chosen from Toglia and Battig's (1978) second cluster of semantic word norms, which provides words judged to be high in familiarity, low in imaginability and concreteness, and of moderate meaningfulness In addition, these four words were chosen with the constraint that the first and last letters in each word were different from the first and last letters in any other word employed in the study Four nonsense syllables were obtained from Noble's (1961) analysis of meaningfulness of nonsense syllables Only words that were scored under 2.0 on Noble's 6-point rating scales were selected for inclusion The words were dib (1.87), heg (1.89), nem (1.89), and ruk (1.90) Each word was displayed on the computer screen in box-type letters The average dimensions of the nonsense syllables were 6.5 x 2.5 cm For the color name learning phase, the stimulus display for the nonsense name group consisted of one of four nonsense syllables surrounded by a set of color bars, each depicting the same hue For the actual name group, the nonsense names were replaced with the actual color names Stimuli were Stimuli This content downloaded from 209.23.242.17 on Sat, 11 Oct 2014 15:53:34 PM All use subject to JSTOR Terms and Conditions 206 MASCOLO AND HIRTLE displayed on the screen as they were in the distractor phase of Experiment 1, except that the shape was omitted For the shape learning and distractor phases, the basic arrangement of stimulus items on the computer screen was identical to that employed in the distractor phase of Experiment For the shape learning phase, three kinds of stimulus displays were employed For the nonsense name group, a shape was always presented on the lower half of the screen, while the upper half consisted of either (a) the associated color bars alone, (b) the associated nonsense name alone, or (c) both the associated nonsense name and the associated color bars Recall that the subject was instructed to associate the shape with both the color and the nonsense name By using these three types of displays, we attempted to prompt the subject to use the nonsense names to encode both the color and the shape pair In so doing, the subject would be discouraged form using actual color names to encode the color patch or the shape Subjects in the actual name group were presented with identical stimulus displays, except that nonsense names were replaced with actual color names The distractor phase was identical to the distractor phase in Experiment 1, except that for both groups of subjects a congruentnonsenseword distractor condition was added (For subjects in the actual name group, these words were novel and therefore had no meaning in the context of the experiment.) Thus, the distractors included (a) congruent nonsense words, (b) incongruent color words, (c) congruent color words, (d) non-color words, and (e) rows of X's Procedure The color name learning phase consisted of two segments For the first segment, subjects were acquainted with the correct color/name configurations Subjects in the nonsense name group were exposed to 10 presentations of each of the four color/nonsense name pairs for a total of 40 randomly presented trials Subjects were instructed to read the word out loud and to try to associate the word with the color bars Subjects in the actual name group performed the same task, except that the nonsense names were replaced with the actual color names In the second segment, after the presentation of an initial plus sign for s, the plus sign was replaced with a set of color bars, without the name of the color Subjects were required to name the color using the appropriate verbal associate Thus, subjects in the nonsense name group named colors using nonsense names; subjects in the actual name group named colors using their actual color names After their response, the experimenter pressed a button, and the correct verbal associate appeared in between the two color bars The color name learning phase consisted of 400 trials, 100 presentations of each color/name pair The color name learning phase required approximately hr In the shape learning phase, subjects learned to associate a shape with each of the four sets of color bars and their corresponding names After This content downloaded from 209.23.242.17 on Sat, 11 Oct 2014 15:53:34 PM All use subject to JSTOR Terms and Conditions OF STROOP INTERFERENCE ELIMINATION 207 the presentation of an initial plus sign, one of the three stimulus displays, described earlier, appeared on the computer screen To recapitulate: For subjects in the nonsense name group, the stimulus display consisted of a shape, along with either (a) the associated color bars alone, (b) the associated nonsense name alone, or (c) the associated nonsense name and color bars For subjects in the actual name group, nonsense words were replaced with actual color names Subjects were instructed to determine whether the shape matched the color, name, or color/name pair Subjects responded yes or no via button press On trials on which subjects responded incorrectly, the word error appeared at the bottom of the screen for s of a 3-s intertrial interval Subjects were instructed to use the error feedback to learn the correct color/ name/shape configurations The shape learning phase consisted of 1,020 trials, distributed equally across the three types of stimulus displays Half of the trials required a yes response and half the trials required a no response The shape learning phase required approximately 1.5 hr The procedure for the distractor phase was identical to the procedure used for the distractor phase of Experiment except for the addition of the congruent nonsense word distractor condition The distractor phase required approximately 40 The study was held over consecutive days Subjects performed the color name learning phase on Day 1, the shape learning phase on Days and 3, and the distractor phase on Day RESULTS AND DISCUSSION Error analysis For each subject, the percentage of errors made in each of the five conditions was calculated The scores for subjects in each group were analyzed separately using one-way repeated measures ANOVAS.For the actual name group, the error rates were 09, 01, 01, 02, and 01 for the incongruent non-color word, XXX, congruent color word, and nonsense word conditions, respectively For the actual name group, the main effect of condition proved significant, F(4, 52) = 14.72, MSe = 1.82, p < 01 Mean percentage error rates for the nonsense name group were 06, 01, 02, 02, and 02 for the incongruent, non-color word, XXX, congruent color word, and nonsense word conditions respectively For the nonsense name group, the main effect of condition also proved significant, F(4, 56) = 9.13, MSe = 86, p < 001 Post-hoc comparisons using the Bonferroni procedure indicated that for both groups, more errors were made in the incongruent distractor condition than in any other condition Error rates among the noncolor word, congruent, and XXX conditions did not differ significantly for either the nonsense name or the actual name groups This content downloaded from 209.23.242.17 on Sat, 11 Oct 2014 15:53:34 PM All use subject to JSTOR Terms and Conditions 208 MASCOLO AND HIRTLE Reaction time (RT) analysis Mean RTs in milliseconds and standard deviations for correct yes responses for each distractor condition for the nonsense name and actual name groups are depicted in Table These means were analyzed separately using one-way repeated measures ANOVAs For the actual name group, the main effect of condition was significant, F(4, 52) = 15.39, MSe = 45396, p < 01 For the nonsense name group, the main effect of condition also proved significant, F(4, 56) = 6.59, MSe = 3006, p < 01 For each group, all possible pairwise comparisons among the five distractor conditions were performed using the Bonferroni procedure For the nonsense name group, no differences emerged among the mean RTs for the incongruent (M = 884), non-color word (M = 879), congruent color word (M = 845), and XXX (M = 864) conditions However, the mean RT for the nonsense word condition (M = 794) proved significantly faster than the mean RT for the incongruent, non-color word, and XXX distractor conditions, but not faster than the mean RT for the congruent distractor condition For the actual name group, the picture is quite different The mean RT for the incongruent distractor condition (M = 972) was significantly slower than the mean RT for the non-color word (M = 897), congruent color word (M = 817), and XXX (M = 881) distractor conditions, but not significantly slower than the mean RT for the nonsense Table Reaction times (RTs, in ms) for Experiment Condition XXX Congruent 891 164 817 124 Mean SD Incongruent Nonsense Non-color Actual name group 897 972 924 165 146 202 Mean SD XXX Incongruent Non-color Congruent Nonsense Nonsense name group 864 884 879 845 794 160 130 137 136 136 Note Underlining indicates that means shown not differ significantly using the Bonferroni technique This content downloaded from 209.23.242.17 on Sat, 11 Oct 2014 15:53:34 PM All use subject to JSTOR Terms and Conditions ELIMINATION OF STROOP INTERFERENCE 209 word (M = 924) condition No differences emerged among the RTs for the nonsense, non-color word, and XXX conditions Congruent color words facilitated responding in comparison to the nonsense, non-color word, and incongruent conditions, but not in comparison to rows of X's One can define Stroop interference as the extent to which responding in the incongruent color word condition is delayed in comparison to control conditions Thus, subjects trained to encode colors using nonsense words eliminated interference of incongruent color words relative to the non-color word, congruent color word, and XXX conditions, whereas for subjects in the actual name group, interference persisted relative to these control conditions These data are consistent with the hypothesis that the use of nonsense names to encode colors eliminated or significantly reduced the interference caused by incongruent color words in the matching task The finding that congruent nonsense names facilitated responding in relation to the XXX and non-color word conditions for subjects in the nonsense name group, but not for subjects in the actual name group suggests that subjects in the nonsense name group did indeed encode colors using nonsense names and that congruent nonsense names facilitated responding The source of the nonsignificant difference between the RT for the incongruent and nonsense word conditions for the actual name group is not clear, although one should note that the mean RT for the nonsense word condition falls in between the means for the incongruent and non-color word conditions, yet differs significantly from neither For the nonsense name group, there is little evidence of facilitation of congruent color words relative to the XXX or non-color word conditions However, for the actual name group, congruent color words facilitated responding relative to the non-color word and nonsense word conditions The lack of facilitation of congruent color words for subjects in the nonsense name group is consistent with the proposition that nonsense names mediated responding for this group The lack of association between the nonsense name response codes and the color words precluded facilitation of congruent color words Even so, the facilitation of congruent color words for the actual name group was unexpected, given the lack of such facilitation produced in Experiment This difference between experiments might be attributed to the difference in procedures used in the two experiments Subjects in the actual name group in Experiment were prompted explicitly to use actual color names to mediate responding; subjects in Experiment received no such training Thus, the use of color This content downloaded from 209.23.242.17 on Sat, 11 Oct 2014 15:53:34 PM All use subject to JSTOR Terms and Conditions 210 MASCOLO AND HIRTLE name codes to process target stimuli may have been stronger for subjects in Experiment than for subjects in Experiment 1, which might explain the facilitation observed GENERAL DISCUSSION In Experiment 1, we attempted to encourage subjects to use nonverbal codes to respond to colors in a Stroop-like task After having practiced matching shapes to colors, subjects continued the matching task in the presence of various distractor stimuli Contrary to predictions, incongruent color words delayed the matching process Informal interviews suggested that subjects used verbal color codes to mediate responding in the task Thus, the verbal color codes activated by incongruent color words conflicted with the internal color codes used to mediate responding In Experiment 2, when nonsense names were used to mediate the matching of colors to shapes, incongruent color words did not delay responding in comparison to control conditions When subjects were prompted explicitly to use color names to mediate the matching process, incongruent color names impeded the matching process, replicating the traditional Stroop findings The finding that congruent nonsense words facilitated responding for subjects in the nonsense name group, but not for subjects in the actual name group, supports the proposition that subjects in the nonsense name group used nonsense names to mediate responding These data are consistent with the proposition that for subjects in the nonsense name group, the matching of colors to shapes did not require the translation of target colors into verbal color name codes Rather, color information was translated to a verbal nonsense name code which was distinct from the incongruent color name codes activated by distractor stimuli Thus, incongruent color name codes activated by distractors could not conflict with codes used to mediate responding As a result, Stroop interference was eliminated For subjects in the actual name group, the incongruent verbal color name codes activated by distractor stimuli conflicted with the codes that resulted from the translation of target colors to verbal color name codes One might question the extent to which verbal color name codes were not used in the processing of target colors for subjects in the nonsense name group One might expect that when learning the correct color/name/shape triads, subjects in the nonsense group translated the color input to a verbal color name code, and then This content downloaded from 209.23.242.17 on Sat, 11 Oct 2014 15:53:34 PM All use subject to JSTOR Terms and Conditions ELIMINATION OF STROOP INTERFERENCE 211 associated the color name code with a nonsense name Although this is a plausible assumption, conditions were optimal for enabling subjects to bypass or at least de-emphasize the verbal color name component when matching shapes to colors Recall that in the color name learning phase, subjects practiced naming each color word with its corresponding nonsense name for 100 trials More important, in the shape learning phase, on a given trial, subjects learned to associate shapes with either (a) a color patch alone, (b) a nonsense word alone, or (c) both the color patch and the nonsense words This procedure would make it uneconomical for subjects to use color names to code the colors and shapes With practice, many subjects reported that the matching proceeded "without thinking," or "by instinct." Thus, these conditions appear optimal for eliminating the conversion of color to verbal color name codes in the matching process for subjects in the nonsense name group Recall that Stirling (1979) reported that when asked to name the color of Stroop stimuli using arbitrarily assigned letters, incongruent color words still delayed responding in comparison to controls, but not to the extent that incongruent letter strings did Glaser and Dolt (1977) reported that incongruent color words delayed the naming of colors of Stroop color words relative to controls, even though subjects named colors with arbitrarily assigned nonsense names Unlike the results obtained in these two studies, subjects in the nonsense name group eliminated Stroop interference relative to control conditions Several factors might explain the difference in results from the present study and the results of Stirling (1979) and Glaser and Dolt (1977) First, subjects in Experiment engaged in more practice than did subjects in either of those studies Second, subjects in the present study responded via binary keypress, as opposed to verbal naming The keypress response mode might have functioned to eliminate much of the conflict created by verbal distractors (see Keele, 1972), thus enabling Stroop interference to be eliminated The results of Experiment are consistent with a modified translational model of the Stroop phenomenon The translational model (Virzi & Egeth, 1985) maintains that the processing of all information does not compete for entry into a single centralized decision or response stage; rather, different processing systems may process different information in different ways Stroop interference results when irrelevant color codes are translated to the verbal system, where they can then conflict with incongruent verbal color codes activated by distractors However, in Experiment 2, all stimuli were translated to verbal codes; both target and distractor stimuli were processed within the verbal system However, within the verbal system, the processing This content downloaded from 209.23.242.17 on Sat, 11 Oct 2014 15:53:34 PM All use subject to JSTOR Terms and Conditions 212 MASCOLO AND HIRTLE of target colors did not involve translation to verbal color codes The representations which mediated target responding were differentiated from the representations activated by color word distractors, thus preventing outcome conflict These propositions parallel the ideas put forth in the translational model, except instead of speaking of translation between two modes of processing (e.g., pictorial and verbal), we speak of translation within subsystems within a given (verbal) mode of processing This viewpoint reaffirms the contention that the modified translational model is best seen as a special case of outcome conflict (Navon, 1985; Navon & Miller, 1987): In tasks involving target and distractor processing, distractors can delay target processing insofar as the outcomes of distractor processing are incompatible with the outcomes of target processing Distractor codes can delay target processing at various points in the information processing sequence (see Eriksen & Schultz, 1979; Seymour, 1974, 1977; Stirling, 1979) as long as the distractor codes are related to the codes that mediate target responding The deleterious effects of distractors can be reduced by decreasing the relationship between the distractor codes and the target codes The codes activated by distractors are still processed; they are simply irrelevant to the processing of targets, and thus not impede processing It is important to say a word about the relationship between relative speed of processing of targets and distractors and translational models of the Stroop effect Dunbar and MacCleod (1984) have criticized models of the Stroop effect that implicate relative speed of processing of relevant and irrelevant dimensions as the primary source of interference Such models assume that in the Stroop task, word and color information is processed in parallel up to a central decision stage Because words are processed faster than colors, the word representation enters the central decision stage before the color representation, thus delaying responding Simple speed-of- processing models assume, however, that if word reading were made slower than color naming, then color naming would not be delayed by incongruent color words Dunbar and MacCleod (1984) demonstrated, however, that when word reading was made slower than color naming (by depicting color words in transformed fashion), Stroop interference persisted Thus, when word reading was made slower than color naming, the color name codes that mediated target processing must have conflicted with partially activatedincongruent color codes at some point in the processing chain These results are incompatible with simple speed-of-processing models of the Stroop effect (Morton & Chambers, 1973) Thus, the concept of differential speed of processing of relevant This content downloaded from 209.23.242.17 on Sat, 11 Oct 2014 15:53:34 PM All use subject to JSTOR Terms and Conditions ELIMINATION OF STROOP INTERFERENCE 213 and irrelevant dimensions of Stroop stimuli is not sufficient to explain the Stroop effect However, it is clear that relative speed of processing is not irrelevant to the production of Stroop inhibition (see Palef & Olson, 1975) From a translational or outcome conflict model, in order for interference to result, (a) internal codes used to process target and incongruent distractors must share some similarity or overlap, and (b) codes activated by distractors must be sufficiently activated (or available) to conflict with codes that mediate target responding Future research is needed to map out the interactions between the similarity or overlap between codes used to process targets and distractors and the availability of incongruent codes activated by distractor stimuli Notes A portion of this research was funded by a State University of New York at Albany Benevolent Research grant to Michael F Mascolo and National Science Foundation Grant BNS-8617732 to Stephen C Hirtle We would like to acknowledge our appreciation to Jay Dixon for his help in data collection and to Arthur Kramer for his helpful comments on an earlier draft of this paper Correspondence concerning this article should be addressed to Michael F Mascolo, Departmentof Psychology,MerrimackCollege, North Andover, MA 01845 Received for publicationJune 14, 1988; 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Journal of VerbalLearning and VerbalBehavior, 23, 23-38 Pritchatt, D (1968) An investigation into some of the underlying associative verbal processes