Copyright 1992 by the American Psvchological Association. Inc. O278-7393/92/S3.OO
Journal of Experimental PsychologyLearning. Memory, and Cognition 1992. Vol. 18. No'. 6. 1191-1210
How Semantic Is Automatic Semantic Priming? Jennifer R. Shelton and Randi C. Martin
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Rice University Priming for semantically related concepts was investigated using a lexical decision task designed to reveal automatic semantic priming. Two experiments provided further evidence that priming in a single presentation lexical decision task (McNamara & Altarriba, 1988) derives from automatic processes. Mediated priming, but no inhibition or backward priming was found in this type of lexical decision task. Experiments 3 and 4 demonstrated that automatic priming was found only for associated word pairs, as determined by word association norms, and not for word pairs that are semantically related but not associated. It is argued that automatic priming in the lexical decision task occurs at a lexical level not at a semantic level.
Meyer & Schvaneveldt (1971) first reported a semantic priming effect in the lexical decision task. They found that prime-target pairs were responded to faster when the prime was associated with the target word (e.g., coffee-cup) than when the word pairs were unassociated (e.g., dog-cup). These results have been replicated many times using different versions of the priming experiment, for example, when the prime was read and a decision was made only to the target (e.g., Balota & Lorch, 1986; Neely, 1976, 1977; Tweedy, Lapinski, & Schvaneveldt, 1977). Automatic semantic priming is often interpreted within the framework of the Collins and Loftus (1975) spreading activation model. This model consists of a network of concepts (nodes) organized in such a way that activation of a concept leads to activation of related concepts, that is, a node would activate related nodes that are nearby in the network. In the case of semantic priming, if a target word is preceded by an associated prime, the concept node for the target word is already activated to some degree when the target appears. Assuming that a certain activation level must be met to ensure recognition, the time to recognize a target word preceded by an associated prime should be less than the time to recognize a target word preceded by an unrelated prime. Although the priming effect has been referred to as semantic, most of the studies investigating semantic priming have used word pairs that are associated with one another, as This research was supported by National Institutes of Health Grant DC00218 to Randi C. Martin. Portions of this research were presented at the Annual Meeting of the Midwestern Psychological Association in Chicago, May 1990. Experiments 1 through 3 are expanded versions of experiments completed by Jennifer R. Shelton as partial fulfillment of the requirements for the MA degree at Rice University, under the direction of Randi C. Martin. We thank Henry L. Roediger III and Nancy J. Cooke who served on the MA committee. We would also like to thank James Chumbley and three anonymous reviewers for their comments on earlier versions of this article. The authors also wish to thank Alice Chu for help in collecting data for Experiment 2 and Christina Romani for providing a translation of the Burani, Tabossi, Silveri, and Monteleone (1989) article. Correspondence concerning this article should be addressed to Randi C. Martin, Department of Psychology, Rice University, Post Office Box 1892, Houston, Texas 77251.
determined by word association norms (e.g., Postman & Keppel, 1970). Only a small number of studies have looked at priming for word pairs that are not associated but are semantically related (Fischler, 1977; Hines, Czerwinski, Sawyer, & Dwyer, 1986; Hodgson, 1991; Lupker, 1984; Seidenberg, Waters, Sanders, & Langer, 1984). If activation spreads on the basis of relatedness of meaning, as argued by Collins and Loftus (1975), then one would expect to find priming for a target word preceded by a word with a similar meaning (e.g., dance-skate) even though the target word would not be produced as an associate of the prime. However, the results for priming for semantically related, unassociated pairs have been inconclusive. Fischler (1977) was the first to address the issue of priming for semantically related, unassociated words in the lexical decision task. He obtained facilitation for both semantically related, unassociated words (e.g., bread-cake) and for associated words (e.g., bread-butter). Fischler concluded that semantic priming results not only from word associations, which he argues could come about due to an "accident of contiguity" (p. 335), but from the semantic relations among words as well. However, Fischler's work was completed before a number of discoveries had been made indicating that lexical decision times reflect decision processes in addition to lexical access (Balota & Chumbley, 1984; Chumbley & Balota, 1984) and that much of the priming in a lexical decision task comes about due to subject strategies rather than to automatic processes (e.g., Balota & Lorch, 1986; Becker, 1980; Neely, Keefe, & Ross, 1989; Seidenberg et al., 1984). These strategies arise because subjects notice that some primes and targets are related and use this information to aid their word-nonword decisions. Two types of strategies have been suggested: an expectancy generation strategy and a postlexical checking strategy. Using an expectancy generation strategy, subjects read the prime and generate a possible target or targets. Subjects can respond word faster when the target matches one of the expected words than when it does not. Thus, because subjects generate related words, faster responses are obtained for related than unrelated targets. Using a postlexical checking strategy, subjects assess the semantic relation between the prime and target before making their decision to the target. Because the presence of a relation between the prime and target indicates that the target is a word (i.e., no relation 1191
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JENNIFER R. SHELTON AND RANDI C. MARTIN
would be found if the target was a nonword), subjects can use the presence of a relation to aid their word decision. Consequently, subjects are faster to respond word on related trials than on unrelated trials. One finding indicative of subject strategies is the proportion effect, that is, the finding that priming effects increase as the proportion of associated words increases (Tweedy et al., 1977; den Heyer, Briand, & Dannenbring, 1983). If priming were automatic, the amount of priming should remain constant across all proportions of associated word pairs. The proportion effect has been interpreted as resulting from strategies because the greater the proportion of related words the more likely it would be that subjects would notice that some trials are related and, hence, be motivated to use strategies in making their decisions. Another effect in the lexical decision task typically attributed to strategic effects is backward priming in which priming is seen for prime-target pairs, which are not associated in a forward direction but are associated in a backward direction (e.g., prime: hop, target: bell; Koriat, 1981; Seidenberg et al., 1984). Seidenberg et al. have argued that priming for these word pairs could only come about if subjects were using a postlexical checking strategy, because only then would the backward relation between the prime and target become obvious to the subject. (An expectancy generation strategy should not produce this effect because subjects would be unlikely to generate the backward associate.) A third effect in the lexical decision task that is argued to result from subject strategies is the inhibition effect obtained at long prime-target stimulus onset asynchronies (SOAs). Inhibition is the slower reaction time to a target primed by an unrelated word in comparison with the same target primed by a neutral prime (e.g., a rows of Xs or the word BLANK). It has been argued that inhibition results from either expectancy generation (e.g., Neely, 1977) or postlexical checking (Lorch, Balota, & Stamm, 1986). For example, if subjects generate an expected target after the prime is read, and check the presented target against the generated target, they will be slowed down when the generated target does not match the presented target. When the prime is neutral, the subject will not have any cues as to possible targets to generate. Thus, subjects will be inhibited in the unrelated condition relative to the neutral condition. If subjects are using postlexical checking, then on unrelated trials, no relation between the prime and target will be found and the subject will be biased to respond nonword. For this to result in inhibition relative to neutral prime trials, it has to be assumed that when subjects see the neutral prime, they do not check for a relation between the neutral prime and the target. Thus, it is possible that the priming that Fischler (1977) observed for semantically related, unassociated pairs was due to subject strategies rather than to automatic spreading activation. A number of other studies have used a target pronunciation task rather than a lexical decision task to examine whether automatic priming is obtained for semantically related, unassociated pairs (Hines et al., 1986; Huttenlocher & Kubicek, 1983;Lupker, 1984; Seidenberg etal., 1984). Several studies have shown that the naming task is less likely to
engage subject strategies than the lexical decision task (Balota & Lorch, 1986; de Groot, 1984; Seidenberg et al., 1984). For example, backward priming is not obtained in the naming task under the experimental conditions that result in backward priming in the lexical decision task (Seidenberg et al., 1984).1 Inhibitory effects tend to be small (Lorch, Balota, & Stamm, 1986) or nonexistent (Neely et al., 1989) in the naming task. In addition, mediated priming is obtained in the naming task but typically is not obtained in the lexical decision task (Seidenberg et al., 1984; but see McNamara & Altarriba, 1988). Mediated priming is priming between pairs of words that are connected only through a mediated association (e.g., priming of swim by winter mediated through summer). Balota and Lorch have argued that mediated priming could only come about because of automatic spreading activation, because the facilitation of the indirect target would not be expected if subjects were using strategies. That is, if subjects were using a postlexical checking strategy, then they would be unlikely to see the prime and target as related, and if subjects were using an expectancy generation strategy, then they would be unlikely to generate the mediated target. Therefore, one would not expect mediated priming when subjects are using strategies. Consequently, the presence of mediated priming can be used as an indicator of the presence of automatic semantic priming. Using the pronunciation task, Lupker (1984) and Huttenlocher and Kubicek (1983) examined priming for pairs of words from the same semantic category. Although Huttenlocher and Kubicek did not specifically check whether the pairs were associated, it is likely that many of their samecategory pairs were not associated. Lupker did specifically omit same-category pairs that were associated. Both studies found small priming effects (7 ms in Lupker's Experiment 1, and 10 ms in Huttenlocher & Kubicek's Experiment 2) that were significant in the standard analyses using subjects as a random effect but that were not significant when items were treated as a random effect (Clark, 1973). Seidenberg et al. (1984) and Hines et al. (1986) also obtained small priming effects for semantically related word pairs. However, neither of these studies carried out analyses that included items as a random effect. A test for generalization across items would 1 Koriat (1981), who first reported the backward priming effect in the lexical decision task, argued that the effect resulted from automatic spreading activation. He suggested that reading the target reactivates the prime and then the reactivated prime somehow facilitates processing of the target. As pointed out by Neely (1991), if backward priming is automatic, then one would expect to find backward priming in the naming task as well. Seidenberg et al.'s (1984) study compared backward priming in lexical decision and naming for the same stimulus materials and presentation procedures, and found backward priming for lexical decision, but not naming. Recently, Peterson and Simpson (1989) were able to demonstrate backward priming in a naming task in which a visual target was presented immediatelyfollowingan auditory prime. Backward priming decreased substantially when the visual target was delayed by 200 ms and was absent at a 300 ms interstimulus interval (ISI). Peterson and Simpson suggested that the effect occurred at very short ISIs because under these conditions, the prime had not been completely recognized when the target appeared.
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AUTOMATIC SEMANTIC PRIMING
seem particularly important in examining the issue of priming for semantically related, unassociated pairs, because a priming effect that was significant across subjects but not across items might result from a few word pairs that happened to be associated (despite attempts to rule out such pairs) or that happened to be linked through a mediated association.2 A recent study by Hodgson (1991) found no priming for semantically related pairs in a naming task, but significant priming for these same pairs in a lexical decision task. Unlike previous investigators who have assumed that effects obtained in lexical decision, but not in naming, are due to strategic processes, Hodgson argued that the significant effects in the lexical decision task could be attributed to automatic processes because they occurred at short SOAs and in the absence of inhibition (for most conditions). Thus, he argued for some type of automatic process that was engaged in lexical decision, but not in naming. However, although a short SOA may prevent expectancy generation, it would not prevent a postlexical checking strategy. The procedures in Hodgson's study may have encouraged a postlexical checking strategy, because the instructions specifically alerted subjects to the fact that some word pairs would be related and that these relations might aid them in making their lexical decision judgments. Furthermore, across testing sessions, subjects were tested on the same targets preceded by the different types of related, unrelated, and neutral primes, a procedure that may have further highlighted the fact that some pairs were related. The absence of inhibition might be accounted for because Hodgson's materials had a low nonword ratio, that is, a low proportion of nonword targets preceded by word primes out of all trials in which targets are unrelated to their word primes (Neely & Keefe, 1989). As argued by Neely and Keefe, inhibition for unrelated pairs would only be expected from a postlexical checking strategy if the absence of a relation between prime and target was informative about nonword versus word status of the target. In the materials in Hodgson's study, the number of unrelated word prime-word target trials was approximately equal to that of word prime-nonword target trials. Consequently, finding no relation between prime and target would not have biased subjects to make a nonword decision to the unrelated pairs, and hence, inhibition would not be expected based on a postlexical checking strategy. Thus, previous findings are equivocal with regard to whether automatic priming may be obtained for semantically related, unassociated pairs. In the present study, we examined again the issue of automatic priming for semantically related, unassociated words using a lexical decision task. The preceding discussion would suggest that the pronunciation task would be the preferred task for assessing automatic priming. However, recent evidence indicates that the pronunciation task is not as free from subjects strategies as previously thought. Keefe and Neely (1990) obtained a proportion effect in a naming task. Because previous research has demonstrated that postlexical effects do not appear to operate in naming (e.g., Seidenberg et al., 1984), Keefe and Neely argued that the proportion effect in the naming task is due to expectancy generation. Their results indicate that simply using a naming task does not guarantee that any priming effects that are
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obtained in this task are necessarily due to automatic processes. In fact, there was a suggestion in the Huttenlocher and Kubicek (1983) results that the significant priming for semantically related, unassociated words obtained in the analysis by subjects only occurred in the condition with a very high proportion of related pairs and not in the low proportion condition. Thus, one cannot be confident that even the marginal effects in the previous studies using the naming procedure were due to automatic processes. On the other hand, it should be noted that it is possible that the naming task underestimates the size of automatic priming effects. Recent evidence suggests that a prelexical phonological code is derived very rapidly during reading (Perfetti, Bell, & Delaney, 1988). Thus, subjects might begin to assemble a pronunciation for a target word in a prelexical fashion prior to the availability of lexical information about pronunciation (Forster, 1981). Only the speed of accessing the pronunciation on a lexical basis should be influenced by spreading activation between related concepts. Whereas Keefe and Neely's (1990) findings indicate that strategic effects may be operating in the naming task, findings from a study by McNamara and Altarriba (1988) suggest that a particular version of the lexical decision task may result in automatic priming. Experiments 2 and 3 of the McNamara and Altarriba study demonstrated mediated priming in a lexical decision task in which stimuli were presented singly (that is, with no obvious pairing between primes and targets) and subjects were required to make a decision to each stimulus. (As discussed previously, mediated priming would not be expected on the basis of subject strategies.) In a typical lexical decision task, prime-target pairs are quite obvious to the subject. For example, subjects might be asked to read the prime to themselves and only make a decision to the target (Balota & Lorch, 1986; Neely, 1976). In the McNamara and Altarriba study, because of the single-presentation procedure, subjects most likely did not engage in the generation and postlexical checking strategies that depend on an awareness of prime-target pairings. McNamara and Altarriba's finding suggests that priming can be automatic in a lexical decision 2 Schreuder, Flores d' Arcais, and Glazenborg (1984) also obtained some evidence relevant to the question of priming for semantically related unassociated pairs. In this study, the authors examined priming for word pairs that were either unrelated, perceptually related but not conceptually related (e.g. ball-orange; carrot-paintbrush), conceptually related but not perceptually related (e.g., apple-banana), or both perceptually and conceptually related (e.g., banjo-guitar). Surprisingly, when subjects were required to name the target, priming was found only for word pairs that were perceptually related. There was no evidence of priming for the conceptually related pairs if they were not also perceptually related. However, it is unclear that the priming observed in this study derived from automatic and not controlled processing. Several aspects of the design could have led subjects to use strategies, even in the naming task. For one, each subject saw the same target four times preceded by each of four types of primes. Also, the prime, although presented 400 ms prior to the target, remained on the screen while the target was presented and both prime and target remained on the screen until a response was made.
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JENNIFER R. SHELTON AND RANDI C. MARTIN
task when the task is modified in such a way as to minimize the likelihood that subjects would use strategies.3 In the present study, we used a single-presentation lexical decision procedure like that used by McNamara and Altarriba (1988) to investigate semantic priming. Although the principal aim of the present research was to test for priming for semantically related, unassociated words, our first goal was to obtain further substantiation that a single-presentation procedure would uncover automatic and not strategic priming. To increase the likelihood of obtaining automatic priming effects, we used McNamara and Altarriba's single-presentation procedure with a very low proportion of related words. Specifically, across the four experiments reported here only 9% to 26% of the word pairs were related. Experiments 1 and 2 tested this single-presentation procedure for automatic priming effects by replicating the mediated priming effect and by testing for inhibition and backward priming. Assuming that evidence for automatic priming was obtained using the single-presentation procedure, the next goal was to test (in Experiments 3 and 4) for priming for semantically related, unassociated words. In all the experiments, priming in what is termed the singlepresentation lexical decision task was compared with the priming obtained in two paired presentation conditions: a high-proportion paired condition and a low-proportion paired condition. The high-proportion condition contained 75% to 91 % related pairs (out of all word-word trials). The highproportion paired condition was included so that we could verify that the stimuli we used would produce the patterns associated with strategic priming when the testing condition was designed to maximize the probability that subjects would engage in strategies. The low-proportion paired condition (which contained the same proportion of related pairs as the single-presentation condition) was included to determine whether a paired presentation procedure with a small proportion of related trials would produce results indicative of automatic priming. As discussed earlier, smaller priming effects are obtained with lower proportions of related words (e.g., den Heyeret al., 1983; Tweedy et al., 1977). Many researchers use the paired low-proportion task under the assumption that priming derives from automatic processes when the proportion is low (e.g., Chiarello, 1988; de Groot, 1984). However, this may not be the case. That is, at least part of the priming that is observed might be due to that group of subjects who do notice the presence of related trials, despite the low proportion. It would be advantageous to have a paired procedure that did result in automatic priming. One can examine priming at very short SOAs in a paired task with no response to the prime, but not in the single-presentation task in which a response is required to each stimulus.4 Experiment 1 This experiment investigated mediated and direct priming and inhibition in all three conditions of the lexical decision task. If the single-presentation lexical decision task taps automatic priming, then we expected to replicate the finding of mediated priming (McNamara & Altarriba, 1988) and also to find no evidence of inhibition. In the high-proportion paired
task, previous results suggest that we would expect to see no mediated priming (Balota & Lorch, 1986; McNamara & Altarriba, 1988) and the presence of inhibition (de Groot, 1984). The results for the low-proportion paired task should be like those for the single presentation task if priming is automatic but like those for the high-proportion task if priming is strategic whenever paired presentation is used. To test for inhibition, it is necessary to have a neutral condition. However, controversy exists as to the choice of an appropriate neutral condition. Jonides and Mack (1984) have argued that the repeated use of the same stimulus as a neutral prime may provide a distorted estimate of facilitation and inhibition because of a number of factors such as lower processing requirements for identifying a repeated stimulus, or less of an attentional response to a repeated stimulus. However, de Groot, Thomassen, and Hudson (1982) presented evidence that although a row of crosses serving as the neutral prime appeared to overestimate facilitation and underestimate inhibition, the word BLANK as a neutral prime did not over- or underestimate these effects. Their conclusion was based on results showing that when both cross and BLANK neutral primes were included in the same experiment, reaction times to both word and nonword targets were slower after the cross primes than after the BLANK prime, and the times to the nonword targets following the BLANK prime were approximately equal to the times for nonword targets following word primes. Therefore, the neutral prime BLANK was used in the first experiment. Method Subjects. One hundred twenty Rice University undergraduate students served as subjects and received class credit for participation. There were 40 subjects in the single-presentation condition, 40 subjects in the low-proportion paired condition, and 40 subjects in the high-proportion paired condition. Materials. Thirty-six target word stimuli having both direct and mediated primes were taken from Balota and Lorch (1986). The 36 target words were divided into four sets of 9 words each. Four stimulus 3
McNamara and Altarriba (1988) also demonstrated mediated priming in an experiment using paired presentation in which the only related pairs were mediated pairs. Presumably subjects did not realize that any of the pairs were related and hence were not motivated to use strategies. 4 It might appear that our experimental design is missing one condition, that is, a high-proportion, single presentation condition. Such a condition would be useful if one were interested in determining whether the single presentation condition results in automatic priming irrespective of the proportion of related words. However, we were not interested in examining the single presentation procedure, per se, but rather in finding some combination of experimental conditions (i.e., presentation procedure and proportion) that would result in automatic and not strategic priming. Even if evidence of strategic priming were obtained in a high-proportion, single presentation condition, such would not constitute evidence that strategic effects contaminated a low-proportion, single presentation condition if the data for the low-proportion condition indicated otherwise. Consequently, the examination of priming in a high-proportion, single presentation condition was irrelevant to our aims (though of some interest for other purposes), and, hence, was not included.
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AUTOMATIC SEMANTIC PRIMING lists were created by matching each target group with direct, mediated, neutral, and unrelated primes in a Latin square design. (The unrelated primes had neither a direct nor a mediated association with the target.) The neutral prime was BLANK. Thus, for each list, there were 9 direct prime-target pairs, 9 mediated prime-target pairs, 9 neutral prime-target pairs, and 9 unrelated prime-target pairs. There were also 9 nonword-word trials using word targets different from the 36 critical word targets. In the single-presentation condition and the low-proportion paired condition, 73 filler, unrelated prime-target trials were added to each stimulus list. For the high-proportion paired condition, 73 filler, associated prime-target trials were added to each stimulus list. There were also 118 nonword targets, including 50 word primes, 9 neutral primes, and 59 nonword primes. Thus, for the single-presentation and low-proportion paired conditions, 9 of 100 word-word pairs were related (9%; if the mediated pairs are not counted as related), and for the high-proportion condition, 82 of 100 word-word pairs were related (82%). Subjects were randomly assigned to one of the four stimulus lists. Presentation of the word pairs was random within each list. Each subject received 20 practice trials prior to the experimental trials. Procedure. The stimuli were presented in a computer controlled fashion on the screen of a 512K Macintosh computer. Reaction times were recorded by the computer.5 Subjects were instructed to hit a 1 key on the number keypad with their forefinger or a 2 key on the number keypad with their middle finger to response word or nonword, respectively; the key assignments were counterbalanced across subjects. For the single-presentation lexical decision group, subjects made a decision for every letter string. A letter string was presented and stayed on the screen until a response was made. After the response, the screen was blank for 500 ms and then the next letter string was presented. Primes and targets occurred successively but subjects were not told of these pairings. Subjects were instructed to respond word to the stimulus BLANK. Stimuli were presented in obvious pairings in both paired presentation conditions. Before the presentation of each prime, a + was displayed for 750 ms on the screen indicating the next word pair was to be presented. A prime was presented for 250 ms and after a 500ms interstimulus interval, the target was presented for 250 ms. After the subjects' response, there was a 1 s delay until the next trial began. Subjects were told to read the prime to themselves and to make a decision to the target stimulus.
Results The mean reaction times for each target condition by procedure condition are summarized in Table 1. Any reaction time greater than 2,000 ms or less than 250 ms was thrown out (2%). Reaction times were analyzed only on trials in which correct responses were made. In all the experiments, analyses will be reported once in which reaction times were averaged across target items and subjects were treated as the random factor (F,, /,) and once in which reaction times were averaged across subjects and target items were treated as the random factor (F2, t2). All means presented were taken from the subject analyses. Inspection of the data in Table 1 indicates that the facilitation for the direct and mediated pairs and inhibition for the unrelated pairs varied across the three procedure types. Planned interaction comparisons were carried out assessing the interaction of procedure condition with the contrast of each of the direct, mediated, and unrelated conditions against
Table 1 Mean Response Latencies (in Milliseconds) and Proportion Errors (PE) for Direct and Mediated Priming Direct
Mediated
Neutral
Unrelated
M M PE PE M PE Condition M Single 583 .03 593 .03 613 .02 615 Low 663 .06 675 .05 683 .06 694 High 664 .05 742 .06 705 .05 751 Note. Low = low-proportion paired; high = high-proportion
PE
.03 .07 .06 paired.
the neutral condition. Facilitation of the direct word pairs relative to the neutral condition differed across the three procedure conditions, F,(2, 117) = 3.40, p < .04, MS, = 663.49 and F2(2, 70) = 3.83, p < .05, MS, = 7,046.43, as did facilitation for the mediated word pairs, F,(2, 117) = 31.65, p < .001, MSC = 587.47 and F2(2, 70) = 6.28, p < .003, MS, = 6,026.94. The inhibition for the unrelated word pairs relative to the neutral condition also differed across the three procedure conditions, /r,(2, 117)= 11.55, p < .001, MSC = 999.45 and F2(2, 70) = 3.72, p < .05, MS, = 5,508.71. To follow up these significant interactions, direct and mediated priming and inhibition were assessed separately in each of the presentation conditions and contrasted across each pair of presentation conditions. (Facilitation and inhibition were assessed against the neutral condition.) The direct priming effect was significant in each of the presentation conditions: 30-ms facilitation in the single-presentation condition, /i(39) = 3.12, p < .01 and /2(35) = 2.01, p < .05; 20-ms facilitation in the low-proportion condition, /i(39) = 2.35. p < .02 and ?2(35) = 2.27, p < .02; 41-ms facilitation in the high-proportion paired condition, /,(39) = 3.11, p < .01 and ;2(35) = 2.63, p < .01. There was no significant difference between the size of the direct priming effect in the single-presentation condition and the low-proportion paired presentation condition, /,(78) = 1.77, p > .08 and Z2(35) = 0.39, p > .70, or between the single-presentation condition and high-proportion paired presentation condition, ^(78) = 1.17, p > .25 and /2(35) = 1.75, p > .09. However, the direct priming effect was significantly larger in the high-proportion condition than the low-proportion condition, t,(l&) = 2.38, p < .02 and ?2(35) = 2.97, p .18. The inhibitory effect was significantly greater in the high-proportion paired condition than the single-presentation condition, /,(78) = 3.78, p < .001 and /2(35) = 2.84, p < .01. The inhibitory effect was significantly greater in the high-proportion paired condition than the low-proportion paired condition in the analysis by subjects, ^(78) = 3.06, p< .01, but not in the analysis by items, ?2(35) = 1.54, p > .13. The following discussion provides a summary of the results within each presentation condition. In the single-presentation condition, significant facilitation for both the direct and mediated targets was obtained, but no inhibition. Although the amount of facilitation was greater for the direct than mediated targets, the difference in the size of these two effects (10 ms) failed to reach significance, /i(39) = 1.42, p > .14 and ^(35) = 1.24, p > .17. In the high-proportion paired condition, both the direct priming effect and the inhibitory effect for unrelated pairs were significant. The mediated pairs showed significant inhibition rather than facilitation. The amount of inhibition was not significantly different for the mediated pairs and the unrelated pairs, (ts < 1). The results for the low-proportion condition were intermediate between those for the other two conditions. Significant facilitation was obtained for the direct pairs, whereas facilitation for the mediated pairs was small and nonsignificant. The inhibitory effect for the unrelated pairs was marginally significant. Unlike the case for the highproportion condition, there was a suggestion of a different pattern of responding to the mediated pairs and the unrelated pairs as the difference between the mediated and unrelated word conditions (19 ms) approached significance, ?,(39) = 1.55,p .20 and 22(17) = 0.67, p > .81, but was significant in the low-proportion paired condition (38 ms), 2,(35) = 2.04, p < .05 and 22(17) = 1.77, p < .08, and highproportion paired condition (32 ms), 2,(35) = 2.11, p < .05 and t2{ 17) = 2.64, p < .01. The forward asymmetrical priming was significantly greater in the low-proportion condition than the single-presentation condition in the analysis by subjects, 2,(70) = 2.19, p < .05, although this only approached significance in the item analysis, t2{ 17) = 1.64, p < . 12. The forward asymmetrical priming was also greater in the high-proportion paired condition than in the single-presentation condition,
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,,(70) = 1.95, p < .06 and 2,(17) = 2.64, p < .02. There was no difference in the amount of forward asymmetrical priming between the low- and high-proportion paired conditions (2s < 1). A similar pattern of results was obtained for the backward asymmetrical priming. Backward priming for the asymmetrical pairs was not significant in the single-presentation condition (-26 ms), 2,(35) = 0.79, p > .45 and 22(17) = 1.13, p > .27, but was significant in the low-proportion paired condition (19 ms), 2,(35) = 2.17, p< .05 and 22(17) = 2.31, p < .05, and in the high-proportion paired condition (25 ms), 2,(35) = 2.05, p < .05 and *2(17) = 2.03, p < .05. The amount of backward asymmetrical priming was significantly greater in the lowproportion paired condition than the single-presentation condition, 2,(70) = 3.10, p < .01 and 22(17) = 2.60, p < .02, and significantly greater in the high-proportion paired condition than the single-presentation condition, 2,(70) = 2.97, p < .01 and 22(17) = 3.94, p < .01. Backward asymmetrical priming did not differ between the two paired conditions (2s < 1). As in Experiment 1, faster mean reaction times were obtained for the single-presentation condition (546 ms) than for the low-proportion paired (647 ms) or high-proportion paired (651 ms) conditions. A statistical test revealed that these means differed significantly, F,(2, 105) = 62.86, p < .001, MS, = 15,653 and F2(2, 136) = 97.09, p < .001, MS, = 829. Post hoc tests showed that the reaction times in the singlepresentation condition were significantly faster than those in either the low- or high-proportion paired conditions, but the means of the low- and high-proportion paired conditions did not differ reliably from each other (Tukey test: dr = 11.78, qT = 3.39,/>
Journal of Experimental PsychologyLearning. Memory, and Cognition 1992. Vol. 18. No'. 6. 1191-1210
How Semantic Is Automatic Semantic Priming? Jennifer R. Shelton and Randi C. Martin
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Rice University Priming for semantically related concepts was investigated using a lexical decision task designed to reveal automatic semantic priming. Two experiments provided further evidence that priming in a single presentation lexical decision task (McNamara & Altarriba, 1988) derives from automatic processes. Mediated priming, but no inhibition or backward priming was found in this type of lexical decision task. Experiments 3 and 4 demonstrated that automatic priming was found only for associated word pairs, as determined by word association norms, and not for word pairs that are semantically related but not associated. It is argued that automatic priming in the lexical decision task occurs at a lexical level not at a semantic level.
Meyer & Schvaneveldt (1971) first reported a semantic priming effect in the lexical decision task. They found that prime-target pairs were responded to faster when the prime was associated with the target word (e.g., coffee-cup) than when the word pairs were unassociated (e.g., dog-cup). These results have been replicated many times using different versions of the priming experiment, for example, when the prime was read and a decision was made only to the target (e.g., Balota & Lorch, 1986; Neely, 1976, 1977; Tweedy, Lapinski, & Schvaneveldt, 1977). Automatic semantic priming is often interpreted within the framework of the Collins and Loftus (1975) spreading activation model. This model consists of a network of concepts (nodes) organized in such a way that activation of a concept leads to activation of related concepts, that is, a node would activate related nodes that are nearby in the network. In the case of semantic priming, if a target word is preceded by an associated prime, the concept node for the target word is already activated to some degree when the target appears. Assuming that a certain activation level must be met to ensure recognition, the time to recognize a target word preceded by an associated prime should be less than the time to recognize a target word preceded by an unrelated prime. Although the priming effect has been referred to as semantic, most of the studies investigating semantic priming have used word pairs that are associated with one another, as This research was supported by National Institutes of Health Grant DC00218 to Randi C. Martin. Portions of this research were presented at the Annual Meeting of the Midwestern Psychological Association in Chicago, May 1990. Experiments 1 through 3 are expanded versions of experiments completed by Jennifer R. Shelton as partial fulfillment of the requirements for the MA degree at Rice University, under the direction of Randi C. Martin. We thank Henry L. Roediger III and Nancy J. Cooke who served on the MA committee. We would also like to thank James Chumbley and three anonymous reviewers for their comments on earlier versions of this article. The authors also wish to thank Alice Chu for help in collecting data for Experiment 2 and Christina Romani for providing a translation of the Burani, Tabossi, Silveri, and Monteleone (1989) article. Correspondence concerning this article should be addressed to Randi C. Martin, Department of Psychology, Rice University, Post Office Box 1892, Houston, Texas 77251.
determined by word association norms (e.g., Postman & Keppel, 1970). Only a small number of studies have looked at priming for word pairs that are not associated but are semantically related (Fischler, 1977; Hines, Czerwinski, Sawyer, & Dwyer, 1986; Hodgson, 1991; Lupker, 1984; Seidenberg, Waters, Sanders, & Langer, 1984). If activation spreads on the basis of relatedness of meaning, as argued by Collins and Loftus (1975), then one would expect to find priming for a target word preceded by a word with a similar meaning (e.g., dance-skate) even though the target word would not be produced as an associate of the prime. However, the results for priming for semantically related, unassociated pairs have been inconclusive. Fischler (1977) was the first to address the issue of priming for semantically related, unassociated words in the lexical decision task. He obtained facilitation for both semantically related, unassociated words (e.g., bread-cake) and for associated words (e.g., bread-butter). Fischler concluded that semantic priming results not only from word associations, which he argues could come about due to an "accident of contiguity" (p. 335), but from the semantic relations among words as well. However, Fischler's work was completed before a number of discoveries had been made indicating that lexical decision times reflect decision processes in addition to lexical access (Balota & Chumbley, 1984; Chumbley & Balota, 1984) and that much of the priming in a lexical decision task comes about due to subject strategies rather than to automatic processes (e.g., Balota & Lorch, 1986; Becker, 1980; Neely, Keefe, & Ross, 1989; Seidenberg et al., 1984). These strategies arise because subjects notice that some primes and targets are related and use this information to aid their word-nonword decisions. Two types of strategies have been suggested: an expectancy generation strategy and a postlexical checking strategy. Using an expectancy generation strategy, subjects read the prime and generate a possible target or targets. Subjects can respond word faster when the target matches one of the expected words than when it does not. Thus, because subjects generate related words, faster responses are obtained for related than unrelated targets. Using a postlexical checking strategy, subjects assess the semantic relation between the prime and target before making their decision to the target. Because the presence of a relation between the prime and target indicates that the target is a word (i.e., no relation 1191
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JENNIFER R. SHELTON AND RANDI C. MARTIN
would be found if the target was a nonword), subjects can use the presence of a relation to aid their word decision. Consequently, subjects are faster to respond word on related trials than on unrelated trials. One finding indicative of subject strategies is the proportion effect, that is, the finding that priming effects increase as the proportion of associated words increases (Tweedy et al., 1977; den Heyer, Briand, & Dannenbring, 1983). If priming were automatic, the amount of priming should remain constant across all proportions of associated word pairs. The proportion effect has been interpreted as resulting from strategies because the greater the proportion of related words the more likely it would be that subjects would notice that some trials are related and, hence, be motivated to use strategies in making their decisions. Another effect in the lexical decision task typically attributed to strategic effects is backward priming in which priming is seen for prime-target pairs, which are not associated in a forward direction but are associated in a backward direction (e.g., prime: hop, target: bell; Koriat, 1981; Seidenberg et al., 1984). Seidenberg et al. have argued that priming for these word pairs could only come about if subjects were using a postlexical checking strategy, because only then would the backward relation between the prime and target become obvious to the subject. (An expectancy generation strategy should not produce this effect because subjects would be unlikely to generate the backward associate.) A third effect in the lexical decision task that is argued to result from subject strategies is the inhibition effect obtained at long prime-target stimulus onset asynchronies (SOAs). Inhibition is the slower reaction time to a target primed by an unrelated word in comparison with the same target primed by a neutral prime (e.g., a rows of Xs or the word BLANK). It has been argued that inhibition results from either expectancy generation (e.g., Neely, 1977) or postlexical checking (Lorch, Balota, & Stamm, 1986). For example, if subjects generate an expected target after the prime is read, and check the presented target against the generated target, they will be slowed down when the generated target does not match the presented target. When the prime is neutral, the subject will not have any cues as to possible targets to generate. Thus, subjects will be inhibited in the unrelated condition relative to the neutral condition. If subjects are using postlexical checking, then on unrelated trials, no relation between the prime and target will be found and the subject will be biased to respond nonword. For this to result in inhibition relative to neutral prime trials, it has to be assumed that when subjects see the neutral prime, they do not check for a relation between the neutral prime and the target. Thus, it is possible that the priming that Fischler (1977) observed for semantically related, unassociated pairs was due to subject strategies rather than to automatic spreading activation. A number of other studies have used a target pronunciation task rather than a lexical decision task to examine whether automatic priming is obtained for semantically related, unassociated pairs (Hines et al., 1986; Huttenlocher & Kubicek, 1983;Lupker, 1984; Seidenberg etal., 1984). Several studies have shown that the naming task is less likely to
engage subject strategies than the lexical decision task (Balota & Lorch, 1986; de Groot, 1984; Seidenberg et al., 1984). For example, backward priming is not obtained in the naming task under the experimental conditions that result in backward priming in the lexical decision task (Seidenberg et al., 1984).1 Inhibitory effects tend to be small (Lorch, Balota, & Stamm, 1986) or nonexistent (Neely et al., 1989) in the naming task. In addition, mediated priming is obtained in the naming task but typically is not obtained in the lexical decision task (Seidenberg et al., 1984; but see McNamara & Altarriba, 1988). Mediated priming is priming between pairs of words that are connected only through a mediated association (e.g., priming of swim by winter mediated through summer). Balota and Lorch have argued that mediated priming could only come about because of automatic spreading activation, because the facilitation of the indirect target would not be expected if subjects were using strategies. That is, if subjects were using a postlexical checking strategy, then they would be unlikely to see the prime and target as related, and if subjects were using an expectancy generation strategy, then they would be unlikely to generate the mediated target. Therefore, one would not expect mediated priming when subjects are using strategies. Consequently, the presence of mediated priming can be used as an indicator of the presence of automatic semantic priming. Using the pronunciation task, Lupker (1984) and Huttenlocher and Kubicek (1983) examined priming for pairs of words from the same semantic category. Although Huttenlocher and Kubicek did not specifically check whether the pairs were associated, it is likely that many of their samecategory pairs were not associated. Lupker did specifically omit same-category pairs that were associated. Both studies found small priming effects (7 ms in Lupker's Experiment 1, and 10 ms in Huttenlocher & Kubicek's Experiment 2) that were significant in the standard analyses using subjects as a random effect but that were not significant when items were treated as a random effect (Clark, 1973). Seidenberg et al. (1984) and Hines et al. (1986) also obtained small priming effects for semantically related word pairs. However, neither of these studies carried out analyses that included items as a random effect. A test for generalization across items would 1 Koriat (1981), who first reported the backward priming effect in the lexical decision task, argued that the effect resulted from automatic spreading activation. He suggested that reading the target reactivates the prime and then the reactivated prime somehow facilitates processing of the target. As pointed out by Neely (1991), if backward priming is automatic, then one would expect to find backward priming in the naming task as well. Seidenberg et al.'s (1984) study compared backward priming in lexical decision and naming for the same stimulus materials and presentation procedures, and found backward priming for lexical decision, but not naming. Recently, Peterson and Simpson (1989) were able to demonstrate backward priming in a naming task in which a visual target was presented immediatelyfollowingan auditory prime. Backward priming decreased substantially when the visual target was delayed by 200 ms and was absent at a 300 ms interstimulus interval (ISI). Peterson and Simpson suggested that the effect occurred at very short ISIs because under these conditions, the prime had not been completely recognized when the target appeared.
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AUTOMATIC SEMANTIC PRIMING
seem particularly important in examining the issue of priming for semantically related, unassociated pairs, because a priming effect that was significant across subjects but not across items might result from a few word pairs that happened to be associated (despite attempts to rule out such pairs) or that happened to be linked through a mediated association.2 A recent study by Hodgson (1991) found no priming for semantically related pairs in a naming task, but significant priming for these same pairs in a lexical decision task. Unlike previous investigators who have assumed that effects obtained in lexical decision, but not in naming, are due to strategic processes, Hodgson argued that the significant effects in the lexical decision task could be attributed to automatic processes because they occurred at short SOAs and in the absence of inhibition (for most conditions). Thus, he argued for some type of automatic process that was engaged in lexical decision, but not in naming. However, although a short SOA may prevent expectancy generation, it would not prevent a postlexical checking strategy. The procedures in Hodgson's study may have encouraged a postlexical checking strategy, because the instructions specifically alerted subjects to the fact that some word pairs would be related and that these relations might aid them in making their lexical decision judgments. Furthermore, across testing sessions, subjects were tested on the same targets preceded by the different types of related, unrelated, and neutral primes, a procedure that may have further highlighted the fact that some pairs were related. The absence of inhibition might be accounted for because Hodgson's materials had a low nonword ratio, that is, a low proportion of nonword targets preceded by word primes out of all trials in which targets are unrelated to their word primes (Neely & Keefe, 1989). As argued by Neely and Keefe, inhibition for unrelated pairs would only be expected from a postlexical checking strategy if the absence of a relation between prime and target was informative about nonword versus word status of the target. In the materials in Hodgson's study, the number of unrelated word prime-word target trials was approximately equal to that of word prime-nonword target trials. Consequently, finding no relation between prime and target would not have biased subjects to make a nonword decision to the unrelated pairs, and hence, inhibition would not be expected based on a postlexical checking strategy. Thus, previous findings are equivocal with regard to whether automatic priming may be obtained for semantically related, unassociated pairs. In the present study, we examined again the issue of automatic priming for semantically related, unassociated words using a lexical decision task. The preceding discussion would suggest that the pronunciation task would be the preferred task for assessing automatic priming. However, recent evidence indicates that the pronunciation task is not as free from subjects strategies as previously thought. Keefe and Neely (1990) obtained a proportion effect in a naming task. Because previous research has demonstrated that postlexical effects do not appear to operate in naming (e.g., Seidenberg et al., 1984), Keefe and Neely argued that the proportion effect in the naming task is due to expectancy generation. Their results indicate that simply using a naming task does not guarantee that any priming effects that are
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obtained in this task are necessarily due to automatic processes. In fact, there was a suggestion in the Huttenlocher and Kubicek (1983) results that the significant priming for semantically related, unassociated words obtained in the analysis by subjects only occurred in the condition with a very high proportion of related pairs and not in the low proportion condition. Thus, one cannot be confident that even the marginal effects in the previous studies using the naming procedure were due to automatic processes. On the other hand, it should be noted that it is possible that the naming task underestimates the size of automatic priming effects. Recent evidence suggests that a prelexical phonological code is derived very rapidly during reading (Perfetti, Bell, & Delaney, 1988). Thus, subjects might begin to assemble a pronunciation for a target word in a prelexical fashion prior to the availability of lexical information about pronunciation (Forster, 1981). Only the speed of accessing the pronunciation on a lexical basis should be influenced by spreading activation between related concepts. Whereas Keefe and Neely's (1990) findings indicate that strategic effects may be operating in the naming task, findings from a study by McNamara and Altarriba (1988) suggest that a particular version of the lexical decision task may result in automatic priming. Experiments 2 and 3 of the McNamara and Altarriba study demonstrated mediated priming in a lexical decision task in which stimuli were presented singly (that is, with no obvious pairing between primes and targets) and subjects were required to make a decision to each stimulus. (As discussed previously, mediated priming would not be expected on the basis of subject strategies.) In a typical lexical decision task, prime-target pairs are quite obvious to the subject. For example, subjects might be asked to read the prime to themselves and only make a decision to the target (Balota & Lorch, 1986; Neely, 1976). In the McNamara and Altarriba study, because of the single-presentation procedure, subjects most likely did not engage in the generation and postlexical checking strategies that depend on an awareness of prime-target pairings. McNamara and Altarriba's finding suggests that priming can be automatic in a lexical decision 2 Schreuder, Flores d' Arcais, and Glazenborg (1984) also obtained some evidence relevant to the question of priming for semantically related unassociated pairs. In this study, the authors examined priming for word pairs that were either unrelated, perceptually related but not conceptually related (e.g. ball-orange; carrot-paintbrush), conceptually related but not perceptually related (e.g., apple-banana), or both perceptually and conceptually related (e.g., banjo-guitar). Surprisingly, when subjects were required to name the target, priming was found only for word pairs that were perceptually related. There was no evidence of priming for the conceptually related pairs if they were not also perceptually related. However, it is unclear that the priming observed in this study derived from automatic and not controlled processing. Several aspects of the design could have led subjects to use strategies, even in the naming task. For one, each subject saw the same target four times preceded by each of four types of primes. Also, the prime, although presented 400 ms prior to the target, remained on the screen while the target was presented and both prime and target remained on the screen until a response was made.
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task when the task is modified in such a way as to minimize the likelihood that subjects would use strategies.3 In the present study, we used a single-presentation lexical decision procedure like that used by McNamara and Altarriba (1988) to investigate semantic priming. Although the principal aim of the present research was to test for priming for semantically related, unassociated words, our first goal was to obtain further substantiation that a single-presentation procedure would uncover automatic and not strategic priming. To increase the likelihood of obtaining automatic priming effects, we used McNamara and Altarriba's single-presentation procedure with a very low proportion of related words. Specifically, across the four experiments reported here only 9% to 26% of the word pairs were related. Experiments 1 and 2 tested this single-presentation procedure for automatic priming effects by replicating the mediated priming effect and by testing for inhibition and backward priming. Assuming that evidence for automatic priming was obtained using the single-presentation procedure, the next goal was to test (in Experiments 3 and 4) for priming for semantically related, unassociated words. In all the experiments, priming in what is termed the singlepresentation lexical decision task was compared with the priming obtained in two paired presentation conditions: a high-proportion paired condition and a low-proportion paired condition. The high-proportion condition contained 75% to 91 % related pairs (out of all word-word trials). The highproportion paired condition was included so that we could verify that the stimuli we used would produce the patterns associated with strategic priming when the testing condition was designed to maximize the probability that subjects would engage in strategies. The low-proportion paired condition (which contained the same proportion of related pairs as the single-presentation condition) was included to determine whether a paired presentation procedure with a small proportion of related trials would produce results indicative of automatic priming. As discussed earlier, smaller priming effects are obtained with lower proportions of related words (e.g., den Heyeret al., 1983; Tweedy et al., 1977). Many researchers use the paired low-proportion task under the assumption that priming derives from automatic processes when the proportion is low (e.g., Chiarello, 1988; de Groot, 1984). However, this may not be the case. That is, at least part of the priming that is observed might be due to that group of subjects who do notice the presence of related trials, despite the low proportion. It would be advantageous to have a paired procedure that did result in automatic priming. One can examine priming at very short SOAs in a paired task with no response to the prime, but not in the single-presentation task in which a response is required to each stimulus.4 Experiment 1 This experiment investigated mediated and direct priming and inhibition in all three conditions of the lexical decision task. If the single-presentation lexical decision task taps automatic priming, then we expected to replicate the finding of mediated priming (McNamara & Altarriba, 1988) and also to find no evidence of inhibition. In the high-proportion paired
task, previous results suggest that we would expect to see no mediated priming (Balota & Lorch, 1986; McNamara & Altarriba, 1988) and the presence of inhibition (de Groot, 1984). The results for the low-proportion paired task should be like those for the single presentation task if priming is automatic but like those for the high-proportion task if priming is strategic whenever paired presentation is used. To test for inhibition, it is necessary to have a neutral condition. However, controversy exists as to the choice of an appropriate neutral condition. Jonides and Mack (1984) have argued that the repeated use of the same stimulus as a neutral prime may provide a distorted estimate of facilitation and inhibition because of a number of factors such as lower processing requirements for identifying a repeated stimulus, or less of an attentional response to a repeated stimulus. However, de Groot, Thomassen, and Hudson (1982) presented evidence that although a row of crosses serving as the neutral prime appeared to overestimate facilitation and underestimate inhibition, the word BLANK as a neutral prime did not over- or underestimate these effects. Their conclusion was based on results showing that when both cross and BLANK neutral primes were included in the same experiment, reaction times to both word and nonword targets were slower after the cross primes than after the BLANK prime, and the times to the nonword targets following the BLANK prime were approximately equal to the times for nonword targets following word primes. Therefore, the neutral prime BLANK was used in the first experiment. Method Subjects. One hundred twenty Rice University undergraduate students served as subjects and received class credit for participation. There were 40 subjects in the single-presentation condition, 40 subjects in the low-proportion paired condition, and 40 subjects in the high-proportion paired condition. Materials. Thirty-six target word stimuli having both direct and mediated primes were taken from Balota and Lorch (1986). The 36 target words were divided into four sets of 9 words each. Four stimulus 3
McNamara and Altarriba (1988) also demonstrated mediated priming in an experiment using paired presentation in which the only related pairs were mediated pairs. Presumably subjects did not realize that any of the pairs were related and hence were not motivated to use strategies. 4 It might appear that our experimental design is missing one condition, that is, a high-proportion, single presentation condition. Such a condition would be useful if one were interested in determining whether the single presentation condition results in automatic priming irrespective of the proportion of related words. However, we were not interested in examining the single presentation procedure, per se, but rather in finding some combination of experimental conditions (i.e., presentation procedure and proportion) that would result in automatic and not strategic priming. Even if evidence of strategic priming were obtained in a high-proportion, single presentation condition, such would not constitute evidence that strategic effects contaminated a low-proportion, single presentation condition if the data for the low-proportion condition indicated otherwise. Consequently, the examination of priming in a high-proportion, single presentation condition was irrelevant to our aims (though of some interest for other purposes), and, hence, was not included.
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AUTOMATIC SEMANTIC PRIMING lists were created by matching each target group with direct, mediated, neutral, and unrelated primes in a Latin square design. (The unrelated primes had neither a direct nor a mediated association with the target.) The neutral prime was BLANK. Thus, for each list, there were 9 direct prime-target pairs, 9 mediated prime-target pairs, 9 neutral prime-target pairs, and 9 unrelated prime-target pairs. There were also 9 nonword-word trials using word targets different from the 36 critical word targets. In the single-presentation condition and the low-proportion paired condition, 73 filler, unrelated prime-target trials were added to each stimulus list. For the high-proportion paired condition, 73 filler, associated prime-target trials were added to each stimulus list. There were also 118 nonword targets, including 50 word primes, 9 neutral primes, and 59 nonword primes. Thus, for the single-presentation and low-proportion paired conditions, 9 of 100 word-word pairs were related (9%; if the mediated pairs are not counted as related), and for the high-proportion condition, 82 of 100 word-word pairs were related (82%). Subjects were randomly assigned to one of the four stimulus lists. Presentation of the word pairs was random within each list. Each subject received 20 practice trials prior to the experimental trials. Procedure. The stimuli were presented in a computer controlled fashion on the screen of a 512K Macintosh computer. Reaction times were recorded by the computer.5 Subjects were instructed to hit a 1 key on the number keypad with their forefinger or a 2 key on the number keypad with their middle finger to response word or nonword, respectively; the key assignments were counterbalanced across subjects. For the single-presentation lexical decision group, subjects made a decision for every letter string. A letter string was presented and stayed on the screen until a response was made. After the response, the screen was blank for 500 ms and then the next letter string was presented. Primes and targets occurred successively but subjects were not told of these pairings. Subjects were instructed to respond word to the stimulus BLANK. Stimuli were presented in obvious pairings in both paired presentation conditions. Before the presentation of each prime, a + was displayed for 750 ms on the screen indicating the next word pair was to be presented. A prime was presented for 250 ms and after a 500ms interstimulus interval, the target was presented for 250 ms. After the subjects' response, there was a 1 s delay until the next trial began. Subjects were told to read the prime to themselves and to make a decision to the target stimulus.
Results The mean reaction times for each target condition by procedure condition are summarized in Table 1. Any reaction time greater than 2,000 ms or less than 250 ms was thrown out (2%). Reaction times were analyzed only on trials in which correct responses were made. In all the experiments, analyses will be reported once in which reaction times were averaged across target items and subjects were treated as the random factor (F,, /,) and once in which reaction times were averaged across subjects and target items were treated as the random factor (F2, t2). All means presented were taken from the subject analyses. Inspection of the data in Table 1 indicates that the facilitation for the direct and mediated pairs and inhibition for the unrelated pairs varied across the three procedure types. Planned interaction comparisons were carried out assessing the interaction of procedure condition with the contrast of each of the direct, mediated, and unrelated conditions against
Table 1 Mean Response Latencies (in Milliseconds) and Proportion Errors (PE) for Direct and Mediated Priming Direct
Mediated
Neutral
Unrelated
M M PE PE M PE Condition M Single 583 .03 593 .03 613 .02 615 Low 663 .06 675 .05 683 .06 694 High 664 .05 742 .06 705 .05 751 Note. Low = low-proportion paired; high = high-proportion
PE
.03 .07 .06 paired.
the neutral condition. Facilitation of the direct word pairs relative to the neutral condition differed across the three procedure conditions, F,(2, 117) = 3.40, p < .04, MS, = 663.49 and F2(2, 70) = 3.83, p < .05, MS, = 7,046.43, as did facilitation for the mediated word pairs, F,(2, 117) = 31.65, p < .001, MSC = 587.47 and F2(2, 70) = 6.28, p < .003, MS, = 6,026.94. The inhibition for the unrelated word pairs relative to the neutral condition also differed across the three procedure conditions, /r,(2, 117)= 11.55, p < .001, MSC = 999.45 and F2(2, 70) = 3.72, p < .05, MS, = 5,508.71. To follow up these significant interactions, direct and mediated priming and inhibition were assessed separately in each of the presentation conditions and contrasted across each pair of presentation conditions. (Facilitation and inhibition were assessed against the neutral condition.) The direct priming effect was significant in each of the presentation conditions: 30-ms facilitation in the single-presentation condition, /i(39) = 3.12, p < .01 and /2(35) = 2.01, p < .05; 20-ms facilitation in the low-proportion condition, /i(39) = 2.35. p < .02 and ?2(35) = 2.27, p < .02; 41-ms facilitation in the high-proportion paired condition, /,(39) = 3.11, p < .01 and ;2(35) = 2.63, p < .01. There was no significant difference between the size of the direct priming effect in the single-presentation condition and the low-proportion paired presentation condition, /,(78) = 1.77, p > .08 and Z2(35) = 0.39, p > .70, or between the single-presentation condition and high-proportion paired presentation condition, ^(78) = 1.17, p > .25 and /2(35) = 1.75, p > .09. However, the direct priming effect was significantly larger in the high-proportion condition than the low-proportion condition, t,(l&) = 2.38, p < .02 and ?2(35) = 2.97, p .18. The inhibitory effect was significantly greater in the high-proportion paired condition than the single-presentation condition, /,(78) = 3.78, p < .001 and /2(35) = 2.84, p < .01. The inhibitory effect was significantly greater in the high-proportion paired condition than the low-proportion paired condition in the analysis by subjects, ^(78) = 3.06, p< .01, but not in the analysis by items, ?2(35) = 1.54, p > .13. The following discussion provides a summary of the results within each presentation condition. In the single-presentation condition, significant facilitation for both the direct and mediated targets was obtained, but no inhibition. Although the amount of facilitation was greater for the direct than mediated targets, the difference in the size of these two effects (10 ms) failed to reach significance, /i(39) = 1.42, p > .14 and ^(35) = 1.24, p > .17. In the high-proportion paired condition, both the direct priming effect and the inhibitory effect for unrelated pairs were significant. The mediated pairs showed significant inhibition rather than facilitation. The amount of inhibition was not significantly different for the mediated pairs and the unrelated pairs, (ts < 1). The results for the low-proportion condition were intermediate between those for the other two conditions. Significant facilitation was obtained for the direct pairs, whereas facilitation for the mediated pairs was small and nonsignificant. The inhibitory effect for the unrelated pairs was marginally significant. Unlike the case for the highproportion condition, there was a suggestion of a different pattern of responding to the mediated pairs and the unrelated pairs as the difference between the mediated and unrelated word conditions (19 ms) approached significance, ?,(39) = 1.55,p .20 and 22(17) = 0.67, p > .81, but was significant in the low-proportion paired condition (38 ms), 2,(35) = 2.04, p < .05 and 22(17) = 1.77, p < .08, and highproportion paired condition (32 ms), 2,(35) = 2.11, p < .05 and t2{ 17) = 2.64, p < .01. The forward asymmetrical priming was significantly greater in the low-proportion condition than the single-presentation condition in the analysis by subjects, 2,(70) = 2.19, p < .05, although this only approached significance in the item analysis, t2{ 17) = 1.64, p < . 12. The forward asymmetrical priming was also greater in the high-proportion paired condition than in the single-presentation condition,
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,,(70) = 1.95, p < .06 and 2,(17) = 2.64, p < .02. There was no difference in the amount of forward asymmetrical priming between the low- and high-proportion paired conditions (2s < 1). A similar pattern of results was obtained for the backward asymmetrical priming. Backward priming for the asymmetrical pairs was not significant in the single-presentation condition (-26 ms), 2,(35) = 0.79, p > .45 and 22(17) = 1.13, p > .27, but was significant in the low-proportion paired condition (19 ms), 2,(35) = 2.17, p< .05 and 22(17) = 2.31, p < .05, and in the high-proportion paired condition (25 ms), 2,(35) = 2.05, p < .05 and *2(17) = 2.03, p < .05. The amount of backward asymmetrical priming was significantly greater in the lowproportion paired condition than the single-presentation condition, 2,(70) = 3.10, p < .01 and 22(17) = 2.60, p < .02, and significantly greater in the high-proportion paired condition than the single-presentation condition, 2,(70) = 2.97, p < .01 and 22(17) = 3.94, p < .01. Backward asymmetrical priming did not differ between the two paired conditions (2s < 1). As in Experiment 1, faster mean reaction times were obtained for the single-presentation condition (546 ms) than for the low-proportion paired (647 ms) or high-proportion paired (651 ms) conditions. A statistical test revealed that these means differed significantly, F,(2, 105) = 62.86, p < .001, MS, = 15,653 and F2(2, 136) = 97.09, p < .001, MS, = 829. Post hoc tests showed that the reaction times in the singlepresentation condition were significantly faster than those in either the low- or high-proportion paired conditions, but the means of the low- and high-proportion paired conditions did not differ reliably from each other (Tukey test: dr = 11.78, qT = 3.39,/>
