Automatic semantic processing of unattended words

JOURNAL OF VERBAL LEARNING AND VERBAL BEHAVIOR 18, 413--426 (1979)

Automatic Semantic Processing of Unattended Words WILLIAM

O. SHAf'FER AND DAVID

LABERGE

University of Minnesota

In a two-choicereactiontimeexperiment,subjectsidentifiedsinglewordsas belongingto one of four semanticcategories.Each target word had flankingwords placed above and belowit which belongedto the same or a differentcategoryas the target. Responselatencieswereelevatedwhen the category of the flanking words was assigned to a responsedifferentthan the target category, replicatingthe pattern reported by Eriksenand Eriksen (1974)in a letter identificationtask. It is concluded that semanticinformation of the flankingwords is processedautomatically.The data also suggest that some interferencemay occur at an earlier categorizationstage independent of response assignment. The main question which motivated these been simplified in studies by Eriksen and experiments concerns how a reader may pro- Eriksen (1974) and Taylor (1977). Using letters cess unattended words. Stated another way, as target items, these authors instructed subthis question asks how well a subject can jects to respond to a letter positioned at the isolate a target word from closely neighboring center of a string of letters, and to ignore the letters placed to the right and left of this words in a display. Willows and MacKinnon (1973) showed central letter. Eriksen and Eriksen (1974) that skilled readers sometimes semantically placed three letters on each side of the target process words that are placed between the letter in most of their conditions, and Taylor lines of text. This implies that, for these (1977) placed only one letter to the right and readers, words occurring near the momentary left of this central letter. Although subjects point of eye fixation may be processed simul- were instructed to ignore these flanking taneously with the words falling at the point of letters, it was clear from the results that closely fixation. The issue of parallel processing of placed flanking letters were being processed several words in a display or in text is of along with the target letter. The critical considerable interest to the investigator of measure of the processing ofthe flanking items reading, because in reading normal text, other was the rise in latency to a target letter when words are positioned close to the momentary flanking letters were assigned to competing point of fixation, both to the right and left of responses, as compared to the latencies the target word(s), and above and below it. obtained when the flanking letters were The general methodology of investigating assigned to the same response as the target parallel processing of symbolic material has letter. We will refer to this latency difference as the incompatible flanker effect. This manner of measuring the processing of This research was supported by United States Public distracting patterns is analogous to that used Health Service grants: National Institute of Mental in the well-known Stroop task (1935) in which Health (5-R01-MHI6270), National Institute of Child the two types of patterns presented simulHealth and Human Development (5-R01-HD06730), and taneously are words and colors. Recently, Center for Research in Human Learning Grant (T01several experiments have paired words with HD-00098). Requests for reprints should be sent to Dr. pictures of common objects, e.g., the word William O. Shaffer, Department of Psychology, University of Arkansas, Fayetteville, Arkansas 72701. "radio" placed within the outline of a picture 413

0022~5371/79/040413-14S02.00/0 Copyright©1979 by Academic Press, Inc. All rights of reproduction in any form reserved. Printed in Great Britain

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of a horse (Rayner & Posnansky, 1978). In these examples of Stroop-type tests, the automatic processing of the word is assessed in terms of its interference with the processing of the pictorial pattern. The method used in the present experiment may be considered a type of Stroop test in which both classes of patterns are words. Therefore the subjects were always in the mode of reading words as opposed to identifying colors, letters, or pictures. Like the Eriksen and Eriksen (1974) and Taylor (1977) studies, both target and flanker items are Of the same format. For their experiments the items were letters; for the present study, the items were words. For example, a typical display in the present study showed the target item DESK along-with the flanking item SHOE positioned above and below the target. A particularly hoteworthy difference between the present study and the studies of Eriksen and Eriksen (1974) and Taylor (1977) is the way that responses were assigned to the stimulus items. Instead of assigning each item directly to a response, we assigned categories of items to a response. For example, names of metals and furniture were assigned to one response and names of clothing and trees were assigned to the other response. This simplified the learning task for the subjects, since they needed only to learn four category-response associations to perform the task accurately. We assumed that the typical subject had already learned the assignments of the word items to the four categories of metals, furniture, clothing, and trees. In fact, the association of these words to the appropriate category should have been automatic if the word was processed semantically in the unattended flanker position. • This procedure of assigning categories to responses also permitted us to use a large number of different words. On the other hand, Eriksen and Eriksen (1974) used only four target letters. Had we used only four words, two to a response, one might well argue that the semantic processing of a flanker word was

bypassed by direct associations of the word to an overt response. Moreover, with only four words, the relatively high frequency of occurrence of a word within a block of trials would maintain the activation of processing mechanisms of the four words at a relatively high level, with the result that a minimum of stimulus input would initiate processing. This would not offer as strong test of the main hypothesis as the case in which the words were presented infrequently, so that individual word processing mechanisms would be at a relatively low level at the onset of a display, much as is the case in a typical reading task. The critical measure of processing of unattended flanking words in this study involved a comparison of response latencies to displays of two types: a display in which the flanking item was assigned to a different response than the one assigned to the target (incompatible condition); and a display in which the flanking item was assigned to the same response as the one assigned to the target (compatible condition). In short, the critical question is whether an incompatible flanker effect can be demonstrated in a semantic processing task. If the latencies under the incompatible conditions exceed the latencies under the compatible condition, then there is support for the hypothesis that unattended flanking words are processed semantically.

EXPERIMENT 1

Method Subjects. The subjects were 12 college-age, right-handed, native speakers of English who were given the option of two dollars or two points for extra credit in an introductory psychology class at the Minneapolis campus of the University of Minnesota. One additional subject was eliminated for exceeding a 10~ error rate. Materials. Four semantic categories, metals (M), furniture (F), clothing (C), and trees (T), were selected from the Battig and Montague

AUTOMATIC SEMANTIC PROCESSING

(1969) production norms for categorized words. These categories were selected to include at least eight frequent exemplars of lengths of three to six letters. An additional constraint on item selection was that four of the words contained three or four letters and were designated "short" words, whereas the remaining four words contained five or six letters and were designated "long" words. Although there exist only a few categories whose eight most frequently generated examples offer these distributional properties, all but three of the 32 words used in this study ranked in the top 10 in the Battig and Montague norms. The complete word list for Experiment 1 is provided in the Appendix. Apparatus. Three words were displayed one above another in upper-case black letters on a white background. The middle word was designated the target, and the upper and lower words were designated flankers. On any given trial the two flanking words were always the same word. The displays were presented on a 38-cm diagonal television screen, driven from a Tektronix 4501 scan converter. A Data General 1220 computer controlled all aspects of stimulus presentation, timing, and response collection. Each letter was presented within a 7 x 11 dot matrix which measured 11 x 17 mm on the screen, subtending visual angles of 32' and 49'. The space between letters was 7 mm and the space between lines was 13mm, subtending visual angles of 20' and 37'. Subjects were tested individually or in pairs seated in individual booths in a dimly lighted room. The television screen was mounted at eye level and positioned 125 cm from the edge of the table where the subject was seated. On the table in front of each subject were two 25mm-diameter response buttons mounted on an inclined plane. Soft white noise bursts were presented through earphones as response feedback for fast responses. A card diagramming the assignment of semantic categories to the left- and right-hand buttons was placed on the table in view of the subject throughout the experiment.

415

Metals and furniture items were assigned to one hand and clothes and trees items to the other hand. It was stressed that subjects would find the task much easier when they had memorized which categories went with each hand. The phrases "clothes tree" and "metal furniture" were suggested as mnemonic aids. Design. The most important independent variable was the relationship between the center or target word and the peripheral or flanking word. Each word appeared with four types of flankers: Identical (same response), Same Category (same response), Different Category (same response), and Different Response (different category). For the first three types of flankers, the response to the flanking word was compatible with the response to the target word; only in the Different Response Condition was the flanking word associated with an incompatible or opposite hand response. In the Identical Condition, the target word was flanked by itself, i.e., the same word was presented three times simultaneously. In the Same Category Condition, the target word was flanked by a different word from the same semantic category. For example, a name of a metal was flanked by a different metal name. Because the target and the flanker word were both chosen from the same semantic category, they both necessarily were associated with the same response. In the Different Category Condition, flanker words were selected from the other category associated with the same response. For example, since metals and furniture were paired together, a word from the category of metals was flanked by a word from the category of furniture, or vice versa. Finally, in the Different Response Condition, the flanker was from a different category and associated with a different response. For example, a name of a metal was flanked by a name of a tree. Within each of the four categories and two word lengths, half of these Different Response flanker words were selected from each of the two opposite response categories. In pairing target and flanker words, several

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SHAFFER AND LABERGE

additional constraints were added. "Long" and "short" words never occurred together; occasionally a four-letter word appeared with a three-letter word as a flanker (both were considered "short" words), but word length was usually the same and, at most, differed by one letter. Second, each of the 32 words was used exactly once as a targe t and once as a flanker in each of the four flanker types. Obtaining this equality was facilitated by adding the constraint that each flanker-target pair was also reversed to form a corresponding pair in which the previous target was now the flanker and vice versa. Third, no flanking word began with the same first letter as the target word (except for the identical word flankers, of course). An effort was made to minimize the repetition of a letter in the same serial position in both the target and flanker word. In the nonidentical conditions, the proportion of these letter repetitions in the same serial position was .019. An effort was also made to minimize the repetition of a letter from the target word anywhere in the flanking word. In the nonidentical conditions, the proportion of letters repeated regardless of serial position was .169. A complete list of the pairings of target and flanker words appears in the Appendix. Each subject was shown all words under all four flanker conditions. Thus, with respect to this major factor, the design was both withinsubjects and within-words. The 32 words included 8 words from each of the four categories. In each category, half of the words were three or four letters in length (called "short" words) and the other half of the words were five or six letters in length (called "long" words). The presentation of 32 words under each of the four flanker types constituted a complete replication of 128 trials. Each subject received two of these replications or blocks. A right-hand response was required for two of the categories (e.g., metals and furniture) and a left-hand response was required for the other two (e.g., clothing and trees). Response assignments were balanced

across the subjects. In summary, the complete design included the following variables: four flanker types; four semantic categories (two for each hand), eight words per category, four short and four long words, two replications or blocks per subject, and 12 subjects who served in one of two groups of response assignment conditions (metals and furniture on right or left hand). The six factors evaluated by an analysis of variance were: flankers, categories, hands, word length, blocks, and groups. Subjects and words were treated as random factors while all other factors were considered fixed (Clark, 1973). Another candidate for a random factor was categories; however, we decided to treat categories as a fixed factor and not claim generalizability to all possible semantic categories on the basis of this small sample of four categories. Procedure. Each experimental session consisted of instructions, three or four practice blocks, and two test blocks. Subjects were first told informally that their task would be to identify the semantic category of common words by pushing a button, and then were asked to study a card indicating the categories that went with each button. It was explained that this card would remain in front of them throughout the experiment in case they got confused, but they should memorize this information and not rely on the card. After subjects studied the response assignments for a few minutes, formal instructions were read to them. Subjects were told that this study concerned the speed with which people recognize the meaning of a word and was part of a series of experiments on reading. It was explained that three words would be presented on the screen and that they were to read only the middle word and then push one of the two buttons to identify which of the four categories that word belonged to. It was emphasized that they should ignore the top and bottom words in making their decision. Instructions also included a few example words from each category, an explanation of

AUTOMATIC SEMANTIC PROCESSING

the visual feedback for errors and auditory feedback for speed, details of the timing of the various parts of each triM, encouragement to use the periodic rest opportunities, and encouragement to ask questions at various places throughout the instructions. Both speed and accuracy were encouraged by telling subjects to "respond as quickly as you can while still trying not to make errors." Additional emphasis was given to processing only the center word by explaining that the warning signal would always indicate where the center word would appear and by asking subjects to focus on that area "so that you will be able to read the middle word at the instant that it appears." The sequence of events on each trial began with the display of a plus sign for a half second as a warning signal indicating that the trial was about to start. Next, the screen went blank for a half second. Then, three words appeared simultaneously until the subject responded or until 2.5 seconds had elapsed without a response. A response or expiration of the deadline immediately terminated the display. If an error or omission occurred, a small red light above the screen flashed on for a half second. If a subject responded within 1 second, a soft burst of white noise was presented on the head-phones. Finally, there was a 1-second pause before the warning signal appeared to start the next trial. Regardless of the speed of a subject's response or the type of feedback presented, the total interval from the initiation of one trim to the initiation of the following trial was always 4.9 seconds. Each practice block consisted of 32 trials one presentation of each word. All aspects of display presentation, timing, and feedback were identical to the experimental blocks except for more frequent rest periods (every eight trials) and the use of strings of X's as flankers. The practice blocks provided a general warm-up to our apparatus, exposure to the word list, and an opportunity to learn which categories were assigned to each response button. Results of the practice blocks

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were monitored; after some of the practice blocks, some subjects were given "speed encouragement" or "accuracy encouragement" which usually succeeded in quickly bringing them in line with our 10~o error criterion and the criterion of responding within 1 second. Occasionally, a fourth practice block was needed to reach these criteria. Instructions and practice blocks usually took 15-20 minutes. The ensuing test blocks added 20 minutes for a total session length of about 40 minutes. Each of the two test blocks consisted of t28 trials formed by presenting each of the 32 words for a semantic category decision in each of the four flanker conditions. Each subject or pair of subjects received two unique random permutations of the 128 combinations. After every 16 trials, a rest opportunity was provided which lasted until subjects pushed a button to indicate that they were ready to begin again. Results

The mean latencies for correct responses and the error rates are presented in Table 1. These means were computed by averaging the latencies of correct responses for the four items in each of the experimental combinations of word length, word category, flanker conditions, and test block combinations. The analysis of variance program then averaged scores across all factors except flanker type. Considering first the mean response times, there was a highly significant main effect for the flanker manipulation, rain F'(3, 70) = 8.26, p < .001, M S e = 18,300.14. Implications of this main effect were examined by Scheff6 post hoc comparisons. The Different Response Condition took 43 milliseconds longer than the Same Category Condition, min F'(3, 70) = 3.22, p < .05, MS~ = 18,300.14. Thus, analogous to the results of Eriksen and Eriksen (1974) and Taylor (1977) using a letter identification task, our semantic category identification task did produce a latency increase for targets flanked by items associated with an

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SHAFFER AND LABERGE TABLE 1 FOUR TYPES OF FLANKERS, MEAN RESPONSE TIMES, AND ERROR RATES

Same response Type of flanker Example Block 1 mean Block 2 mean Overall mean

Different response

Identical

Same category

Differentcategory

DESK DESK DESK

LAMP DESK LAMP

GOLD DESK GOLD

COAT DESK COAT

635 (2.6) 592 (3.1) 613 (2.9)

655 (2.3) 598 (3.1) 626 (2.7)

687 (1.8) 644 (4.2) 666 (3.0)

693 (6.8) 645 (3.4) 669 (5.1)

Note. Mean response times are expressedin milliseconds. Error rates are in parentheses. incompatible response. In short, there was an incompatible flanker effect. A second important aspect of the flanker results concerned whether the Different Category Condition would be treated like a compatible condition (because flankers were associated with the same response) or an incompatible condition (because flankers were not associated with the same category). The Different Category Condition took 40 milliseconds longer than the Same Category Condition. This difference was significant using a Scheff6 post hoc comparison, minF'(3,70)=2.77, p<.05, MSe=18,300.14. A similar comparison of the Different Category and Different Response Conditions indicated the 3 millisecond difference was not significant, min F' < 1. In addition to the significant main effect for types of flanker, there was a significant practice effect, min F'(1, 60)=23.65, p<.001, MSe=18,608.81. Response times were 49 milliseconds faster on the second replication. There was also a highly significant main effect for semantic categories, rain F'(2, 32)= 14.99, p < .001, MS~--36,470.54. In the latency data, there were no other significant main effects, and none of the interactions was significant. A similar six-factor analysis of variance on the error rates indicated that there were no significant interactions, and the only significant main effect was semantic categories,

min F'(2, 40) = 4.02, p < .05, MSe = .3345. The pattern of results for categories was the same for both the error and response time data (r = .998), Items from the metals category were easiest and fastest while items from the furniture category were the most difficult and slowest. Several factors could be responsible for this pattern, such as, word frequency, and "typicality" or "goodness" of category instances. However, since this result did not interact with flanker results (or any other factor), it need not concern us further.

Discussion Experiment ] produced two important results. First, response times for semantic decisions took longer when the target word was flanked by a word from a semantic category which was paired with the opposite response button. Thus, our word classification task, analogous to the Eriksen and Eriksen (1974) and Taylor (1977) letter classification-task, indicated that information from the flanker items is being processed by the subjects. In our semantic task, information about the category of the flanking word(s) is being processed despite the fact that the task required subjects to process only the center or target word in order to respond accurately, and also despite our explicit instructions to subjects to "read only the center line" and to "ignore the words on the top and bottom lines in making your

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decision." Apparently, the subjects cannot prevent themselves from processing the meanings of the flanking words. This property of being unable to prevent a process from occurring is a central aspect of automaticity (LaBerge & Samuels, 1974). Thus, we suggest that this procedure may be used to assess automatic processing and that this first result provides evidence for automatic semantic processing of words. A second important result from Experiment 1 focuses on the question of whether the latency elevation found for the incompatible Different Response Condition should be attributed to response confusion or category confusion. The semantic task could conceivably require the subject to make two responses: a covert category identification response (e.g., saying "furniture" to themselves when the target is "desk") and an overt button selection response (e.g., recalling the association between "furniture" and the left button). If the locus of the latency elevation is only at the category identification stage, then the Different Response and Different Category Conditions should produce equally elevated latencies because both of these conditions used flankers associated with a different semantic Category than the target word. On the other hand, if the locus of the effect is only at the response button selection stage, then only the Different Response Condition should have produced elevated latencies because this condition was the only one in which the semantic categories of the target and flanker words were associated with different response buttons. Finally, if the effect occurs at both stages, then latencies for the Different Category Condition and the Different Response Condition should both be elevated but more so for the Different Response Condition. The pattern of results of Experiment 1 clearly supported category identification and not response button selection as the critical factor in the latency elevation. Response times for the Different Category and Different Response Conditions were only 3 milliseconds

apart. Further, each of these conditions took significantly longer than the condition using flankers from the same semantic category. These results seem quite trustworthy since they were tested using conservative Scheff6 post hoc comparisons and also the conservative error terms suggested by Clark (1973) to allow generalizing results across samples of subjects and words. As further support of the importance of category identification over response button selection, it is important to consider the extreme differences in the amount of experience that subjects have had with these two processes. When subjects enter the laboratory, they are assumed to be proficient at category identification due to their many years of experience with these common words. However, to learn the relationship between category names and response buttons as required for the resp'onse selection process, subjects must be given instructions and a considerable number of practice trials. Consistent with current notions of automaticity, the results suggest that it is not the newly learned button selection process that is automatic, rather it is the initial processing up to and including accessing the category name which appears to be automatic. EXPERIMENT 2

Although the results of Experiment 1 apparently place the locus of the incompatible flanker effect at an earlier stage than the Eriksen and Eriksen experiment (1974), neither Experiment 1 nor the Eriksens' original experiment answers the question of whether this latency difference is an interference or a facilitation effect. Taylor (1977), however, did provide an answer by using a neutral condition in which some flanking letters were not assigned to either response. Comparing latencies from this condition with the condition of compatible and incompatible flankers, Taylor showed both facilitation and inhibition by these kinds of flankers. When

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flanking letters were presented simultaneously letter word was used as the last letter of a fivewith the target letter, the amount of inhibition letter nonword). In addition, some effort was given by incompatible flankers was about 42 made toward separating groups of letters that milliseconds and the amount of facilitation had appeared side by side in the target words. due to compatible flankers was about 15 However, this was not always achieved, but milliseconds. each nonword did consist of letters from at The main purpose of Experiment 2 was to least three different words. Some of the most determine to what extent the latency differ- pronounceable nonwords resulting from this ences with word materials of Experiment 1 procedure were BATA, TAMM, BRIST, and were due t o interference, facilitation, or a APESTS. Among the least pronounceable combination of both. To answer this question, were DLO, PIOD, MIBKS, and DAPVER. Design. As in Experiment 1, the most a fifth type of flanker, namely, nonwords, was added in order to provide a neutral important independent variable was the type comparison for assessing the relative con- of flanker, i.e., the type of relationship between tributions of interference and facilitation. the center or target word and the peripheral or Experiment 2 also used other pairings of the flanking words. The major difference between four categories used in Experiment 1 in order Experiments 1 and 2 was the addition of to pursue greater generalizability of results. nonword flankers to the four flanker types used in Experiment 1. Method A second design change was the use of Subjects. The subjects we~-e36 college-aged, additional pairings of the four semantic right-handed, native speakers of English who categories with respect to common response were given the option of two dollars or two assignments. A total of six of these pairings points for extra credit in an introductory exhausted all possible combinations of ways psychology class at the Minneapolis campus to assign two categories to each hand. Using a of the University of Minnesota. Six subjects notational system which tells which two cateserved in each of the six combinations of Hand gories were assigned to the right hand, the six and Category pairings. Two additional sub- conditions will be designated as follows: MF jects were excluded from the analyses: one for (metals and furniture), CT (clothes and trees), exceeding a 10~ error criterion, and one who MT, CF, MC, and FT. Six subjects were run in had latencies over one second on 16~o of the each of the six conditions. Of these six possibiresponses (compared to less than 1~ for other lities, there are three pairs which turn out to be reversals or counterbalancings of the left and subjects). Materials. The target words were identical right hand assignments. For example, the MF to the words used in Experiment 1. The subjects had metals and furniture assigned to nonword flankers were generated using the their right hand (leaving clothing and trees for same letters used in the target words. These their left hand) while the CT subjects had nonwords were intended to be as pronounce- clothing and trees assigned to their right hand able as possible while still meeting several (leaving metals and furniture for their left constraints on the positioning of letters. Each hand). This equivalence was utilized in confirst letter of a target word also appeared as structing lists. Thus, for purposes of analysis, the first letter of a nonword. Corresponding subjects were considered to be in one of three permutations were made for the letters in groups: MF-CT, MC-FT, and MT-CF. In pairing target and flanker combinations, positions two through six of the target words with minor exceptions made for the final letter the same general procedures were used as in or final pair of letters from five- and six-letter Experiment 1. In fact, the MF and CT conwords (e.g., sometimes the last letter of a six- ditions reused the pairings of Experiment 1

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and the Appendix. Thus, except for the addition of nonword flankers, these two conditions provided an exact replication of the first experiment. For the MC-FT and MTCF lists, new pairings were necessary in the Different Category and Different Response Conditions. Although not logically necessary, new pairings were also assigned in Nonword and Same Category Conditions for each new list. Each subject responded to all words under all five flanker conditions. Thus, as in Experiment 1, the design was both within subjects and within words with respect to the type of flanker. Because many of the factors in the analysis of Experiment 1 produced nonsignificant main effects or produced significant but uninteresting main effects, and because these factors did not interact with flankers or with each other, no effort was made to separate data according to hands, word length, categories, or blocks. In summary, the only distinctions examined in Experiment 2 were differences among the five types of flankers and the three groups of subjects (MFCT, MC-FT, and MT-CF). Procedure. All aspects of the instructions, practice blocks, and test blocks were identical to Experiment 1 with the single exception that adding the 32 nonword flankers to each test block increased the length of the experimental session to 50 minutes.

Results The mean latencies and error rates are presented in Table 2. The means for each

flanker type were computed by averaging the correct latencies for each of the 64 possible items for each flanker type. The main effect of flanker type was highly significant, min F'(4, 243) = 28.70, p <.001, MSe=844.17. The differences among the three groups were also significant, minF'(2,35)=4.78, p<.01, MSe=23,960.18, due primarily to subjects assigned to the M T CF condition responding more than 50 milliseconds faster than subjects in the other two conditions. The overall interaction between flankers and groups was not significant, min F'(8,342)= 1.20, MS~ =906.68. As in Experiment 1 Scheff6 post hoc comparisons, using the conservative error term suggested by Clark (1973), were used to explore the significant overall differences among types of flankers. The Different Response Condition took 43 milliseconds longer than the Same Category Condition, min F'(4, 243) = 19.42, p < .001; MS~ = 844.17 (for this and all other post hoc tests). Thus, again the semantic category identification task produced a latency increase for targets flanked by items associated with an opposite button response. This result replicates the 43 millisecond difference of Experiment 1. The Different Category Condition was also significantly longer than the Same Category Condition, min F'(4, 243)-- 4.23, p <.005. However, unlike Experiment 1, the Different Category Condition was significantly faster than the Different Response Condition, min F'(4, 243) = 5.53, p < .001. This result did not replicate the findings of Experiment 1.

TABLE 2 MEAN RESPONSE TIMES AND ERROR RATES FOR FIVE TYPES OF FLANKERS IN EXPERIMENT 2 Same response Type of flanker Response time (msec) Error rate

Identical

Same category

Different category

572 3.4

575 2.9

595 2.9

Different response

Neutral

618 6.6

587 3.1

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Reasons for this latency decrease for the to the flanker category lead to an erroneous Different Category Condition will be explored response. in the discussion. The main new information sought in Discussion Experiment 2 was whether the latency differBy using nonwords as a neutral comparison ences reflect interference effects, facilitation point, Experiment 2 established that the effects, or both, Additional post hoc compari- flanker effect reflects a latency difference sons analyzed the effect of the neutral or attributable to approximately two-thirds nonword flankers in relation to the Different interference and one-third facilitation. ExperiResponse Condition and the more rapidly ment 2 also replicated the incompatible processed Same Category Condition. The flanker effect. It took 44 milliseconds longer to Nonword Condition was 31 milliseconds respond to items flanked by words associated faster than the Different Response Condition, with different responses than to items in the min F'(4, 243)-- 9.87, p < .001. However, two conditions associated with the same comparing the Nonword Condition with the response. Same Category Condition produced< a Experiment 2 did not replicate the findings min F'(4, 243) = 1.60, which was not significant of Experiment 1 with respect to the relationby this conservative test. Using nonword ship of the Different Category Condition and flankers as a neutral comparison point, it the other conditions, as shown in Figure 1. appears that the 43 milliseconds latency in- Items in this condition were 22 milliseconds crease for different response flankers can be separated into a 31 millisecond interference effect and a 12 millisecond facilitation effect. The interference effect covers about 72~o of the difference and is highly significant while the 650 facilitation effect covers the remaining 12 milliseconds but fails of significance. However, • J ",, these latency values compare quite favorably with Taylor's (1977) values of approximately 40 and 15 milliseconds for inhibition and ~ e O 0 facilitation, respectively, using letter items as .c_E / X stimuli. / X / X Analysis of the error rates indicated that the / X / \ only significant result was a main effect for /..¢' " :~ 5 5 0 f./ flanker type, minF'(4,234)=9.22, p<.001, MS¢ = 2.0353. By inspecting the error data in Table 2, it is obvious that the error rate of 6.6}/o in the Different Response Condition was .#~---* M C - - F ~ ~00--" MF --CT nearly twice the rate of any of the other four I ~--, MTconditions which ranged from 3.4 to 2.9~o. In fact, this contrast accounted for 98.4~o of the I I I [ I ID SC DC DR N flanker variance. A similar pattern occurred in Flanker Type Experiment 1, but was not significant. The FIG. 1. Mean latency of categorization of target words most likely explanation for this pattern is that as a function of type of flanking words. The four category names for the flanker items are being categor!es were Metals (M), Clothing (C), Furniture (F), activated in all conditions, but only in the and Trees (T). Each curve represents an assignment of Different Response Condition did responding pairs of categories to left and right responses.

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AUTOMATIC SEMANTIC PROCESSING

longer than the Same Category Condition and 24 milliseconds faster than the Different Response Condition. Both differences were highly significant in Experiment 2 while only the former was significant in Experiment 1. Since the near equality of the Different Category and Different Response Conditions in Experiment 1 was the crucial piece of data for concluding that interference occurred at the point of category identification and not response selection, this failure to replicate deserves some further scrutiny. Recall that the 12 subjects in the MF-CT group provided an exact replication of Experiment 1 except for the addition of nonword flankers. These subjects even received the same word list. Looking only at the data for these subjects, was the pattern of Experiment 1 replicated? Mean response times for each of the three groups of subjects are presented in Figure 1. Data for each group were reanalyzed separately (analogous to an analysis of simple main effects). Results of these separate group analyses are summarized in Table 3. For the

MF-CT group, the main effect of flankers was highly significant, min F'(4,130)=8.14, p<.001, MS~=1121.31. A series of Scheffb post hoc comparisons, using the same error term as the main effect, indicated that the Different Response Condition took 40 milliseconds longer than the Same Category Condition, rain F'(4, 130) = 4.39, p < .005; the Different Category Condition took 34 milliseconds longer than the Same Category condition, min F'(4, 130) = 3.07, p < .025, and the 7 millisecond difference between the Different Category and Different Response Conditions was not significant, min F'(4, 130) = .12. Thus, for the MF-CT group, the pattern of results of Experiment 1 was replicated in all essential details--especially with respect to the equivalence of the Different Response and Different Category Conditions. Table 3 shows a different pattern of results for the other two groups. The Different Category flankers were 25 and 37 milliseconds faster than the Different Response flankers. What is different about these other two

TABLE 3 RESPONSETIME DIFFERENCESFOR THE FLANKER EFFECTS, SCHEFFI~POST HOC COMPARISONS,AND OVERALL f TESTS FOR THREE GROUPS WITH DIFFERENT PAIRINGSOF CATEGORIES

Flanker main effect

Different response vs same category

Different category vs same category

Different response vs different category

MF-CT a Difference (msec) rain F'(4, 130) Probability

8.14 < .001

40.5 4.39 < .005

33.9 3.07 < .025

6.6 .12 ns

MC-FT b Difference (msec) rain F'(4, 140) Probability

6.79 < .001

35,6 4.25 < .005

10.7 .38 ns

24.9 2.08 ns

MT-CF c Difference (msec) rain F'(4,127) Probability

16.72 < .001

51.9 12.08 < .001

15.2 1.03 ns

36.8 6.05 < .001

a Metals and Furniture on one hand and Clothing and Trees on the other. MS~= 1121.31 for all tests. bMetals and Clothing on one hand and Furniture and Trees on the other. MSe=892.78 for all tests. CMetals and Trees on one hand and Clothing and Furniture on the other. MSe=670.05 for all tests.

424

SHAFFER AND LABERGE

groups? New pairings of flanker and target appear to allow the combininO of the two words were generated for these lists. However, categories under one superordinate category. similar results were obtained for three of the In the MF-CT condition, two of the subjects four flanker types repeated from Experiment spontaneously volunteered that they thought 1; tiopefully, this difference is not crucial, The other combinations of categories would be other major difference among groups was the easier to learn. Although it would have been instructions concerning which categories were more desirable to have anticipated these difto be associated with the right and left hands. ferences and kept systematic records of the We suspect that the crucial difference was a strategies and verbal reports from all subjects strategy difference in how the subjects re- in all conditions, the fragments of evidence all sponded to the instructions on the pairing or seem consistent with the view that subjects can grouping of categories. and do use superordinate category labels in Consider, for example, the MT-CF group, some instances. This strategy factor could in which subjects were instructed to push one conceivably have altered the pattern of results button if the target word belonged to the obtained by changing the experiment from a category of Metals or Trees, and the other four-category study to one in which the subbutton if the category was Furniture or jects used only two categories. Clothing. Subjects could reduce their memory Another possible interpretation of the reload by redefining these categories as "out- sults of the three groups combined is that door things" and "indoor things." With these interference takes place both at the category new subject-defined categories, the condition and response selection locations. The points where targets were flanked by a different for the Different Category Condition appear (experimenter-defined) category would now on the average to lie between the average be a Same Category Condition to the subject. values for the Same Category and Different Similarly, in the MC-FT group, where Response Conditions, and this general result subjects were instructed to push one button is supported statistically. Thus, the conservatfor Metals or Clothing and the other for ive conclusion, based on the reasoning in the Furniture or Trees, subjects could reduce the Discussion Section of Experiment 1, is that at memory load by redefining the categories as least some interference occurs at the location "nonwood" and "wood." If some proportion of category processing. Whether or not all of it of the subjects did this, it would tend to reduce occurs here or whether some occurs also at the latency in the Different Category Condi- the response selection stage depends on the tion toward the level of the Same Category resolution of the category combination issue Condition, which is the trend shown in Figure already discussed. 1 for the MT-CF and MC-FT groups. PartCONCLUSION way through the data collection, we became The results from both Experiments 1 and 2 aware of these different patterns in the different groups and began postexperimental replicate and extend the findings of Eriksen interviews when time permitted. When asked and Eriksen (1974) and Taylor (1977). what, if any, strategy they used to remember Decision times for their letter items and our the category assignments, several of the sub- word items can be increased by changing the jects mentioned reinterpreting the categories response assignments to an item flanking the into higher level pairs such as the ones target. The Eriksens interpreted their results mentioned above. Suggesting the mnemonics in terms of response competition or inter"metal furniture" and "clothes tree," as in the ference: That is, conflicting information from instructions for Experiment 1, encouraged a the display is assumed to produce longer 9roupin 9 of the two category labels but did not processing times at the response selection

425

AUTOMATIC SEMANTIC PROCESSING

stage. The present results suggest that interference may also occur earlier at the categorization stage. We interpret the Eriksens' and Taylor's results and the present findings as supporting the notion of automatic processing of certain types of information of the flanking stimulus,

even if this information is detrimental to performance. Additionally the present findings are consistent with those of Willows and MacKinnon (1973), in that single unattended words positioned above and below a target word are processed automatically in terms of their semantic characteristics.

APPENDIX: ITEMS, FLANKERS,AND MEAN RESPONSETIMES BY CONDITION

Word

Same category

Compatible different category

Incompatible category

Same word

Same category

Compatible different category

Incompatible category

Zinc Tin Gold Iron Silver Brass Copper Steel

Lamp Desk Bed Sofa Table Chair Chest Stool

Palm Shoe Oak Belt Spruce Pants Dress Maple

543 586 600 555 593 545 592 630

581 585 565 540 526 568 540 575

618 636 589 562 575 630 657 608

687 609 614 571 594 664 724 708

Desk Lamp Sofa Bed Chest Stool Table Chair

Iron Gold Tin Zinc Copper Steel Silver Brass

Pine Coat Hat Elm Shirt Socks Apple Birch

649 661 723 719 655 615 630 657

708 709 675 736 660 668 722 668

827 744 696 735 786 727 720 655

694 677 719 743 700 751 697 696

Shoe Belt Hat Coat Pants Dress Shirt Socks

Pine Elm Oak Palm Maple Apple Birch Spruce

Desk Bed Zinc Gold Table Chair Steel Silver

616 585 603 630 583 583 572 600

636 581 651 615 646 624 617 639

680 726 642 670 645 650 60l 649

682 593 747 694 658 584 672 663

Elm Pine Palm Oak Spruce Birch Apple Maple

Coat Hat Belt Shoe Shirt Socks Pants Dress

Lamp Sofa Tin Iron Brass Chest Stool Copper

628 622 607 613 595 626 615 613

692 587 619 608 605 622 580 624

617 627 762 658 658 65: 665 621

646 633 672 698 621 649 658 709

Metals Iron Gold Tin Zinc Copper Steel Silver Brass Furniture

Lamp Desk Bed Sofa Table Chair Chest Stool

Clothing Coat Hat Belt Shoe Shirt Socks Pants Dress Trees

Pine Elm Oak Palm Maple Apple Birch Spruce

426

SHAFFER A N D LABERGE

REFERENCES BATTIG, W. F., & MONTAGUE,W. E. Category norms for verbal items in 56 categories: A replication and extension of the Connecticut Norms. Journal of Experimental Psychology, 1969, 80, (3, Pt. 2). CLARK, H. H. The language-as-fixed-effect-fallacy: A critique of language statistics in psychological research. Journal of Verbal Learning and Verbal Behavior, 1973, 12, 335-359. ERIKSEN, B. A., & ERIKSEN, C. W. Effects of noise letters upon the identification of a target letter in a nonsearch task. Perception & Psychophysics, 1974, 16, 143-149. LABERGE, n., & SAMUELS, S. J. Toward a theory of automatic information processing in reading. Cognitive Psychology, 1974, 6, 293-323.

RAYNER,K., & POSNANSKY,C. Stages of processing in word identification. Journal of Experimental Psychology: General, 1978, 107, 64-80. STROOP, J. R. Studies of interference in serial verbal reactions. Journal of Experimental Psychology, 1935, 18, 643-662. TAYLOR, D. A. Time course of context effects, Journal of Experimental Psychology: General, 1977, 106, 404-426. WILLOWS, D. M., & MACKINNON, G. E. Selective reading: Attention to the "unattended" lines. Canadian Journal of Psychology, 1973, 27, 292-304.

(Received November 30, 1978)