Mediated Priming in the Lexical Decision Task - Science Direct

Journal of Memory and Language 42, 314 –341 (2000) doi:10.1006/jmla.1999.2680, available online at http://www.idealibrary.com on

Mediated Priming in the Lexical Decision Task: Evidence from Event-Related Potentials and Reaction Time Dorothee J. Chwilla and Herman H. J. Kolk Nijmegen Institute for Cognition and Information, Nijmegen, The Netherlands

and Gijsbertus Mulder Institute for Experimental and Occupational Psychology, University of Groningen, Groningen, The Netherlands Mediated priming (e.g., from LION to STRIPES via TIGER) is predicted by spreading activation models but only by some integration models. The goal of the present research was to localize mediated priming by assessing two-step priming effects on N400 and reaction times (RT). We propose that the N400 priming effect mainly reflects integration processes but, in contrast with RT, does not reflect spreading activation. The results show that RT and N400 effects can dissociate. In a standard lexical decision task, we found mediated priming for N400 but not for RT. When a lexical decision to both the prime and the target was required, mediated priming was observed for both measures, but the RT effect was not influenced by list composition, whereas the N400 effect was. We conclude that two qualitatively different processes underlie the two types of mediated priming. A process of “global integration” yields an N400 effect, whereas an RT effect is evoked by spreading activation. © 2000 Academic Press Key Words: event-related potentials; N400; mediated priming; spreading activation models; compound cue models; postlexical integration.

A common finding in the psycholinguistic literature is that a word (target) is processed more efficiently when it is preceded by a related word (prime). For instance, subjects respond faster to the word TIGER when it is preceded by LION than when it is preceded by an unrelated word like RADIO. This semantic priming effect This research was supported by Grant 560-256-085 from the Netherlands Organization for Scientific Research (NWO). Portions of this research were presented at the 37th Annual Meeting of the Psychonomic Society in Chicago, 1996. We thank Phil Holcomb and two anonymous reviewers for helpful comments on earlier versions of this article. We thank Rene de Bruin of the MPI for implementing the ERP data-analysis program. We are grateful to the ERG group of the NICI for technical assistance and to Franz Gremmen for statistical advice. Special thanks to Uli Chwilla for his empathetic listening to the lion–tiger–stripes story and for preparing all figures. Address correspondence and reprint requests to Dorothee J. Chwilla, Nijmegen Institute for Cognition and Information, University of Nijmegen, P.O. Box 9104, 6500 HE Nijmegen, The Netherlands. Fax: ⫹31 24 3616066. E-mail: [email protected].

has been observed in a variety of tasks, ranging from sentence verification (e.g., Loftus, 1973) to lexical decision (e.g., Meyer & Schvaneveldt, 1971), naming (e.g., Balota & Lorch, 1986), and item recognition (e.g., Ratcliff & McKoon, 1978). The focus of this article is on mediated priming. Mediated priming refers to a facilitation in responding to a target preceded by a prime that is assumed to be only indirectly related in semantic memory [e.g., prime: LION; target: STRIPES; mediator (not presented): TIGER]. In the case of one intervening concept the facilitation is referred to as a two-step priming effect. Two-step priming effects are important because they are predicted by all spreading activation models (e.g., Anderson, 1983; Collins & Loftus, 1975), but not by expectancy models (Becker, 1980, 1985; Posner & Snyder, 1975) and by only one of the several integration models—the Gillund–Shiffrin implementation of the compound cue model (McKoon & Ratcliff, 1992). The goal of our research was to

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MEDIATED N400 AND RT PRIMING IN LEXICAL DECISION

determine whether two-step priming is achieved by spreading activation (Balota & Lorch, 1986; DeGroot, 1983; McNamara & Altarriba, 1988) or by this particular version of the compound cue model. This was accomplished by using N400, an Event-Related Potential (ERP) component, along with reaction time (RT) measures. We will argue that existing ERP evidence indicates that N400 is mainly an index of postlexical integration and, in contrast to RT, is not affected by spreading activation. A combination of the two measures, therefore, should help to establish the roles of both mechanisms in bringing about two-step priming. First, several classes of models are presented and then we discuss which of these models can explain mediated priming. SPREADING ACTIVATION MODELS According to spreading activation models (Anderson, 1983; Collins & Loftus, 1975), semantic memory consists of a network of interconnected nodes, where nodes represent concepts. It is assumed that associatively related concepts are stored close together. Presentation of a concept activates the node corresponding to this concept and, via the links to nearby nodes, part of this activation automatically spreads to the nodes of related concepts. This results in an increase in activation level for related concepts, making them temporarily more available for further processing. Spreading activation has all the characteristics of an automatic process. It is fast acting, of short duration, requires no attention or awareness, and presupposes no or minimal demands on resource capacity (Posner & Snyder, 1975; Shiffrin & Schneider, 1977). The models of Collins and Loftus (1975) and Anderson (1983) account for priming somewhat differently. Collins and Loftus (1975) assumed that the prime affects the processing of the target by increasing its activation level before the target has been presented. It is thereby assumed that: (a) the activation only spreads forward from the prime to the target and (b) only one concept can be actively processed at a time. The feature of unidirectionality does not apply to the Adaptive Control of Thought (ACT) model of Anderson (1983). According to this

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model, several words can be sources of activation simultaneously. Priming occurs because the prime node is still active when the target is presented. Because a main assumption of both models is that activation spreads to all interconnected nodes, activation should spread along the associative pathways from directly related concepts to the associates of these concepts. Spreading activation models necessarily predict two-step priming (McNamara, 1992a, b; Ratcliff & McKoon, 1988). INTEGRATION MODELS In spreading activation models, priming occurs because related concepts are connected and is, therefore, an indirect consequence of the fact that two concepts are related. In contrast, a basic feature of integration models is that the prime– target relationship is directly established and exploited in producing semantic priming. According to the integration models of DeGroot (1984, 1985) and Neely and Keefe (1989), participants match the primes and the targets for semantic similarity and use their relatedness to aid in their lexical decisions. Because a semantic match is found only on word trials, the detection of a relationship leads to a bias to respond Word, whereas the absence of such a relation invokes a bias to respond Nonword. Neely, Keefe, and Ross (1989) showed that this strategy is used more often when the nonword ratio (i.e., the proportion of trials with a nonword target and a word prime out of all trials in which targets are unrelated to their word primes) is high. These models do not predict mediated priming because there is no direct meaning relationship between the prime and the target. The comparison process therefore should bias a Nonword response, and no facilitation for two-step pairs should be observed. According to the Compound Cue model of Ratcliff and McKoon (1988), participants join the prime and the target during encoding and use the familiarity value of this combination (“compound”) when performing the lexical decision task. The idea is that words are more familiar than nonwords and that priming occurs

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because associated prime–target pairs are more familiar than unassociated pairs. To make predictions about task performance, the compound cue model must be implemented in a model of memory. Various models, such as the search of associative memory (SAM: Gillund & Shiffrin, 1984) and the theory of distributed associative memory (TODAM: Murdock, 1982), predict a boost in familiarity when the items in the compound cue are associatively related in long-term memory as opposed to when the items are unrelated. A critical assumption is that assessment of familiarity occurs very rapidly. In this way, the model—in contrast to most other integration models— can explain automatic priming effects, thereby challenging spreading activation models. The predictions for mediated priming depend on the model in which the compound cue mechanism is implemented. When the compound cue model is combined with the SAM model of Gillund and Shiffrin (1984), a boost in familiarity is found not only for directly related items but also for items that are related by one other item with high strength values to both prime and target. Therefore, the Gillund–Shiffrin implementation predicts two-step priming. In contrast, implementations with Murdock’s model (1982) or with Hintzman’s model (1986) predict priming only for directly related items. EXPECTANCY MODEL A third kind of model is the expectancy model (Becker, 1980, 1985; Posner & Snyder, 1975). According to these models, participants exploit information provided by the prime to generate an expectancy set for related target words. The resulting RT pattern depends on the size of the expectancy set. If the set is small, as for antonyms (e.g., “black–white”), then the facilitation for related primes is much larger than the inhibition for unrelated primes. If the expectancy set is large, as for category relationships (e.g., “fish–shrimp”), then the inhibition for unrelated primes is much larger than the facilitation for related primes. Expectancy models cannot explain mediated priming. First, due to the absence of a direct relationship, the target word is unlikely to be included in the expect-

ancy set. In all mediated priming experiments conducted so far, the target words were never produced as an associate of the prime in a word association task, and so we consider it highly unlikely that expectancy processes can contribute to the mediated priming effect. Second, even in the unlikely case that the target word is included in the expectancy set, then due to the subtle relationship between the indirectly related pairs we would have to assume that participants generated a large expectancy set. This should yield inhibition and not facilitation for the mediated pairs. EVIDENCE FOR MEDIATED PRIMING We may distinguish three variants of the lexical decision task which have been used in the mediated priming literature. In the standard lexical decision task, the prime and the target are presented in pairs and a word/nonword judgment to the target is required. In the double lexical decision task, the prime and the target are also presented in pairs but a word/nonword decision to both the prime and the target is required. In the single presentation lexical decision task, the prime and the target are presented singly—that is, with no obvious pairing—and a word/nonword decision to each stimulus is required. DeGroot (1983) first tested for mediated priming using the standard lexical decision task. Although some results pointed to a facilitation in the processing of two-step pairs, she concluded that activation spreads to direct associates only. Balota and Lorch (1986) argued that DeGroot’s failure to find two-step priming might be due to the use of a rather short SOA (240 ms). Because activation must cross one additional link, it could take extra prime processing time for mediated effects to emerge. They replicated the absence of two-step priming in the standard lexical decision task for both a short SOA of 250 ms and a long SOA of 500 ms, but they demonstrated mediated priming in the naming task. The results of the naming study indicated that activation spreads at least two steps deep in the semantic network. McNamara and Altarriba (1988) argued that the inclusion of direct associates might have been


responsible for the absence of two-step priming because these pairs could have induced relatedness-checking strategies. They demonstrated mediated priming when (a) a double lexical decision task was used with a list composed only of two-step pairs or (b) a single presentation lexical decision task was used which discouraged participants from using relatednesschecking strategies. In concordance with spreading activation models, the one-step priming effect in the latter task tended to be larger than the two-step priming effect. McNamara and Altarriba presented these findings as support for spreading activation models over most “nonspreading-activation models.” In addition, based on the presence of a list composition effect in the double lexical decision task, but not the single presentation lexical decision task, they concluded that the former task was affected by strategies, whereas the latter task was a pure measure of automatic processes. In this article, we test spreading activation models and the Gillund–Shiffrin implementation of the compound cue model against each other by using the N400 —an ERP component—along with RT measures. ERPs are stimulus-bound voltage fluctuations in the scalprecorded electroencephalogram (EEG). Because ERPs are much smaller than the EEG they must be extracted from it by averaging across several stimulus presentations. The ERPs elicited by a stimulus consist of a series of peaks. These peaks are typically labeled according to their polarity (P for positive, N for negative) and by their ordinal position (e.g., P3 stands for the third positive peak) or latency measured from stimulus onset (e.g., N400 is a negative peak with a mean latency of about 400 ms). It has been established that the N400 component is especially sensitive to semantic processing (see Kutas & VanPetten, 1988, 1994, for reviews) and that its amplitude is smaller when a word is preceded by a related word than when it is preceded by an unrelated word (e.g., Holcomb, 1993; Swaab, Brown, & Hagoort, 1997). This difference in amplitude is referred to as the N400 priming effect. Based on previous work (Brown & Hagoort, 1993; Chwilla, 1996; Chwilla, Brown & Ha-

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goort, 1995; Chwilla, Hagoort, & Brown, 1998; Holcomb, 1993; Kellenbach & Michie, 1996; Osterhout & Holcomb, 1995; Bentin, Kutas, & Hillyard, 1995), we assume that the N400 priming effect mainly—if not exclusively—reflects postlexical processes that arise from integrative mechanisms and, in certain situations, expectancy processes (Holcomb, 1988; Brown, Hagoort, & Chwilla, 1999). In contrast to RT, N400 does not reflect spreading activation. We maintain that N400 reflects a higher level integration process that operates on several kinds of lower level information, including lexical–semantic, syntactic, and pragmatic. Modulations in N400 amplitude appear to reflect the ease with which these different knowledge sources are integrated with the preceding context, be this a word or a sentence fragment. The better a new piece of information fits into the ongoing representation, the easier the lexical integration process and the smaller the N400 amplitude. Support for the integration view of the N400 priming effect comes from several sources. First, dissociations between RT and N400 have been observed. Brown and Hagoort (1993) did not observe an N400 priming effect when the prime was masked, but an RT priming effect was still obtained. This finding suggests that spreading activation impacts RT but not N400. Holcomb (1993) found an interaction of degradation with semantic priming for RTs but not for N400. The locus of the RT interaction has been typically claimed to be an early encoding stage, preceding or coinciding with lexical access (cf. Holcomb, 1993). Therefore, the absence of an N400 interaction has been taken to indicate that the N400 effect does not reflect lexical access. Second, selective attention studies have shown that N400 priming is obtained in the attended but not the unattended channel (Bentin et al., 1995; Kellenbach & Michie, 1996; McCarthy & Nobre, 1993). Third, the fact that N400 priming effects are found not only for associatively related pairs but also for exclusively semantically related pairs is consistent with the integration view (Hagoort, Brown, & Swaab, 1996; Kotz, 1998; for discussion of the integration view see Chwilla et al., 1998). Fourth, the integration hypothesis is bolstered

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by sentential context studies. In particular, the systematic reduction in N400 amplitude toward sentence endings for open class words (VanPetten & Kutas, 1990) fits well with this view. Taken together, the previous results support the notion that N400 mainly reflects postlexical integration but not spreading activation. In contrast, we assume that RT reflects both spreading activation and integrative mechanisms. THE PRESENT EXPERIMENTS The aim of our research was to assess the nature of mediated priming by examining twostep priming effects on N400 and RT. Based on our assumptions, the sensitivity of N400 to mediated priming has important consequences for the locus of the effect. If mediated priming is observed for RT but not for N400, this would support a spreading activation account. In contrast, if mediated priming is obtained for N400 and RT alike, this would support the Gillund– Shiffrin implementation of the compound cue model. It has been suggested that two-step priming is sensitive to list composition (McNamara & Altarriba, 1988). To assess the effects of list content and to further specify the nature of mediated priming, we compared mediated priming in a list composed of two-step pairs only (Mediated-Only List) and a list which included both one-step and two-step pairs (Mediated-and-Direct List). To avoid carryover of strategies, the Mediated-Only List was presented first. Another question was whether there are changes in mediated priming over time. Because relatedness-checking strategies may develop over time, a strategic modulation of mediated priming might be observed over different phases of the experiment. We tested this idea by comparing performance on the Mediated-Only List during the early and the later stages of the experiment. EXPERIMENT 1 Method Participants There were 42 participants (mean age, 24.17). All were native speakers of Dutch, had

no reading disabilities, were right-handed, and had normal or corrected-to-normal vision. Two participants had to be excluded from the analyses because of excessive eye-movement artifacts. Apparatus and Stimuli Participants were seated in a sound attenuating and electrically shielded chamber. A response device with two push buttons was fixed on a small table in front of the participant. The stimuli consisted of 530 prime–target pairs that were presented in uppercase black letters on a white background at moderate contrast at the center of a PC monitor (with a window 8 by 2 cm; approximately 3.0 ⫻ 0.8° of arc). The duration of both the prime and the target was 200 ms and the SOA was 550 ms. All primes were real Dutch words with the number of letters varying from 2 to 13. Half of the targets were real Dutch words and the other half were nonwords. The nonwords were constructed in accordance with the phonotactic constraints of Dutch and were derived from real words by substituting 1 or 2 letters. Letter strings of 3 to 13 letters were presented as targets. The two-step pairs were constructed on the basis of association norms (DeGroot, 1980; DeGroot & DeBil, 1987; Lauteslager, Schaap, & Schievels, 1986; VanHalen & Simons, 1992). Word triplets were built such that the first word was related to the second word but not to the third word (e.g., OORLOG–RUST, mediator VREDE; translation: WAR–QUIET, mediator PEACE), as evidenced by the fact that the target word (e.g., RUST) was not produced as an associate of the prime (e.g., OORLOG) in these norms. A possible limitation of the norms was that participants were requested to produce only one associate. Participants might have produced the target as an associate of the prime if they had been asked to produce more associates. Because it is critical for our purposes that the target is not produced as an associate of the prime, we collected additional association norms from 146 undergraduate psychology students. Students had to produce 5 associates to 78 primes that were randomly selected from the total set of 156 two-step pairs. If the mediated


target (e.g., QUIET) is not produced as an associate of the prime (e.g., WAR) then it is very unlikely that there exists a direct association from the prime to the mediated target. One possible problem when asking for multiple associates is that participants might chain their associations (i.e., produce PEACE to WAR and then produce QUIET to PEACE). We tried to discourage them from doing so by stressing that it was of great importance that they always generate associates to the first word and refrain from producing associates to previous responses. Based on the results of this association test, 16 pairs had to be removed, because the mediated target was produced as an associate of the prime. For the remaining 140 two-step pairs 1 the mediated targets were never produced as an associate of the prime despite a total of 51,100 associates produced across participants. We should mention that the validity of free association to measure distance in semantic memory has been questioned. Ratcliff and McKoon (1994) reported RT priming for word pairs that, according to free association norms, were neither directly nor indirectly related. They showed that if associative strength is measured using first-response probabilities, one spreading activation model, the ACT model (Anderson, 1983), does not predict priming for these “nonmediated” items. However, as stated by McNamara (1994), if the continued-association procedure is used, ACT predicts priming of the size obtained by Ratcliff and McKoon. The choice of any method for assessing associative strength is an implicit theoretical claim. Because Ratcliff and McKoon did not propose a model of free association in the context of a spreading activation or an integration model, it is not clear which technique is appropriate. Therefore, it seems premature to abandon the free association method until the suitability of an alternative method has been proven. Unfortunately, the methods suggested by Ratcliff and McKoon do not fulfill this criterion, because co-occurrence statistics or relatedness judgements are not yet well understood (McNamara 1

The materials are available from the first author by e-mail.

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1992b). Because there are no clear arguments for preferring one method above the other, we consider free association to be a viable method for investigating memory structure. List Composition The Mediated-Only List contained 100 twostep pairs (e.g., WAR–QUIET, mediator PEACE) and 100 unrelated pairs (e.g., PEN– QUIET). Two versions were constructed in which the targets were counterbalanced across conditions and participants, such that no participant saw a word more than once. Each version consisted of 50 two-step pairs and 50 unrelated pairs. Fifty unrelated filler pairs were included to reduce the proportion of mediated pairs. This yielded a total of 150 word prime–word target pairs. One hundred and fifty prime–target pairs with a nonword target were added to the list. The nonword ratio was .50, since in 150 of the 300 trials a nonword target was preceded by an unrelated prime word. The proportion of directly related word pairs, or relatedness proportion, was zero. The list was divided into two blocks of 150 pairs. Each block was preceded by 3 filler pairs. We used unrelated primes as a baseline instead of a neutral baseline condition. This choice was based on the work of Jonides and Mack (1984). They criticized the use of neutral primes as a baseline because they are usually not matched with informative primes in terms of physical features, ease of encoding, or ability to alert subjects. The fact that the neutral baseline is the same on all trials causes faster performance and likely leads to an underestimation of effects of facilitation and overestimation of effects of inhibition. Previous work comparing ERPs to neutral, unrelated, and related primes in lexical decision (Chwilla, 1996) has indicated that neutral primes are processed differently than unrepeated word primes. Because of these findings, we used an unrelated prime word as a baseline. The Mediated-and-Direct List contained 50 one-step pairs (e.g., MEISJE–JONGEN; translation GIRL–BOY), 50 unrelated pairs (e.g., KELDER–JONGEN; translation CELLAR– BOY), 40 two-step pairs (e.g., LION–

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STRIPES, mediator TIGER), and 40 unrelated pairs (e.g., RADIO–STRIPES). The smaller number of two-step pairs than one-step pairs was due to the fact that no more two-step pairs that fulfilled our selection criteria were available. The same target words were presented for the one-step pairs and their unrelated control pairs and for the two-step pairs and the unrelated pairs. Due to an insufficient number of two-step pairs, different target words had to be used for the one-step and the two-step pairs. Due to the use of different items, comparisons of mean RTs between the one-step and two-step pairs, as well as between the one-step control and the two-step control pairs, are inappropriate. Differences in mean RTs might be caused by specific characteristics of the two sets of items. However, comparisons of the relative size of the priming effects are appropriate, because they control for item differences. Two versions were constructed in which the targets were counterbalanced across conditions and participants, such that no participant saw a word more than once. Each version consisted of 25 one-step pairs, 25 unrelated pairs, 20 twostep pairs, and 20 unrelated pairs. Twenty-five unrelated filler pairs were included to reduce the proportion of related word pairs. This yielded a total of 115 word pairs. An equal number of prime–target pairs with a nonword target were added to the list. In the Mediated-and-Direct List, therefore, only 25 of 115 word pairs were related, yielding a relatedness proportion of .22. The nonword ratio was .56, since in 115 of 205 unrelated trials a nonword target was preceded by an unrelated prime word. The list was preceded by 3 filler pairs. Because of the shortage of two-step pairs, it was not possible to add a second block to the Mediated-and-Direct List. Electrophysiological Recording EEG was recorded with 13 tin electrodes mounted in an elastic electrode cap (Electrocap International). The electrode positions included standard International 10-20 system locations at frontal sites (F7 and F8) and three midline sites: frontal (Fz), central (Cz), and parietal (Pz). Eight electrodes were placed at nonstandard positions previously found to be sensitive to

language manipulations (e.g., Holcomb & Neville, 1990): left and right anteriortemporal sites (LAT and RAT: 50% of the distance between T3/4 and F7/8), left and right temporal sites (LT and RT: 33% of the interaural distance lateral to Cz), left and right temporoparietal (Wernicke’s area and its right hemisphere homologue, LTP and RTP: 30% of the interaural distance lateral to a point 13% of the nasion-inion distance posterior to Cz), and left and right occipital sites (OL and OR: 50% of the distance between T5/6 and O1/2). The left mastoid served as reference. Electrode impedance was less than 3 kohm. The electro-oculogram (EOG) was recorded bipolarly; vertical EOG was recorded by placing an electrode above and below the right eye and the horizontal EOG was recorded via a right to left canthal montage. The EEG and EOG signals were amplified (time constant ⫽ 10 s, bandpass ⫽ .02–30 Hz) and digitized online at 200 Hz. Procedure To avoid carryover of strategies, the Mediated-Only List was presented first. Participants were instructed to pay attention to the prime and to indicate whether the second letter string was a real Dutch word. If the second letter string was a word, they had to press the right response button with their right index finger. If not they had to press the left button with their left index finger. Participants were asked to respond quickly but to remain accurate. Similar to Balota and Lorch (1986), we used a relatively long SOA of 550 ms because it could take some time for two-step priming to develop. A set of practice trials preceded the experimental trials. Participants were trained to respond quickly (⬍1 s) and to refrain from making eye movements before the prime until approximately 1 s after the button press. Results Data Analysis EEG and EOG records were examined for artifacts and for excessive EOG amplitude (⬎100 ␮V) from 100 ms preceding the prime to 1 s after target onset. Only artifact-free trials in


which correct responses were made were included in the average. ERPs were averaged time-locked to the target, relative to a 100-ms pretarget baseline. Spreading activation models predict that twostep priming effects will be relatively small. To permit a fine-grained analysis and to increase our power to detect small but reliable changes in brain response, the ERPs were analyzed in the following way: For each participant, the mean amplitude of 50-ms epochs (i.e., the mean of 10 sample points) for the experimental conditions was computed beginning with the target onset until 900 ms after target presentation (e.g., the first epoch includes the interval of 0 to 50 ms and is a mean of the EEG amplitude at 5, 10, 15, 20, 25, 30, 35, 40, 45, and 50 ms etc.). The mean amplitudes for each of these epochs were then entered into a repeated measures analyses of variance (ANOVA). Separate ANOVAs were performed for the two lists. For the Mediated-Only List, three-way ANOVAs with repeated measures on relatedness (2 levels: twostep vs. unrelated), block (2 levels: first vs. second), and electrode (13 levels) were performed. For the Mediated-and-Direct List, three-way ANOVAs were carried out with repeated measures on distance (2 levels: one-step vs. two-step), relatedness (2 levels: related vs. unrelated), and electrode (13 levels). Based on previous visual lexical decision experiments, we expected maximal N400 effects 350 to 450 ms following target onset. We will refer to the epochs spanning this interval as the typical N400 window. Based on similar concerns about statistical power, the following supplementary analyses were conducted. First, to examine possible changes in ERPs over time, separate analyses with relatedness (2 levels) and electrode (13 levels) as factors were performed for the two blocks of the Mediated-Only List. Second, to expose possible two-step ERP effects in the Mediated-and-Direct List, separate ANOVAs with relatedness (2 levels) and electrode (13 levels) as factors were carried out for the onestep and the two-step pairs. Main effects of electrode will only be reported when they are relevant for the identi-

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fication of a particular ERP component. In those cases, main effects of electrode and interactions with relatedness were followed up by posthoc Newman–Keuls tests to assess the significance of contrasts. Where interactions with the factor electrode are reported, ANOVAs were performed after a z-score normalization procedure to equalize the mean amplitudes across experimental conditions, thus allowing effects of distribution to be examined independently of overall differences in amplitude. This normalization procedure is equivalent to that suggested by McCarthy and Wood (1985). The estimated Greenhouse and Geisser (1959) coefficient epsilon was used to correct for violations of the assumption of sphericity. All reported p values are based on corrected degrees of freedom but, to aid the reader in interpreting our statistical design, the stated degrees of freedom are uncorrected. The subject analyses were complemented by item analyses. Because the computation of by-item ERP averages is very time-consuming, we carried out by-item analyses only when the by-subject analyses were significant. In the item analyses, the mean EEG amplitudes were averaged across subjects and target items were treated as the random factor. All means presented were taken from the subject analyses. All lexical decision latencies greater than 1300 ms were counted as errors. Also, any latency that was 2.5 SD above or below the mean for both a subject or item within each condition was replaced by the mean of the means for that subject and item in that condition. Priming effects were computed by subtracting the lexical decision latencies of the critical pairs (one-step or two-step pairs, respectively) from the unrelated lexical decision times. The resulting priming effect for the onestep pairs is referred to as a one-step priming effect and the priming effect for the two-step pairs as a two-step priming effect. The RT and the error data were analyzed in the same way as the ERP data, except that in all cases by-item analyses were performed.

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CHWILLA, KOLK, AND MULDER TABLE 1

Experiment 1: Mean Reaction Times (RT), Standard Deviations (SD), and Mean Error Rates for the Different Relatedness Conditions for the Two Blocks of the Mediated-Only List and the Two Levels of Distance of the Mediatedand-Direct List Mediated-Only List Prime type

Two-step Unrelated

First block RT

SD

Errors

600 595

96 97

2.80 2.80

Second block Priming effect

⫺5

RT

SD

Errors

Priming effect

579 576

81 79

2.70 2.50

⫺3

561 561

75 78

Mediated-and-Direct List Distance Related Unrelated

One-step 539 565

70 68

1.70 2.80

Two-step 26**

1.60 2.90

0

** p ⬍ .01.

Reaction Time and Error Results The results summarized in Table 1 show that regardless of list composition, no RT two-step priming effect was obtained. Mediated-only list. No effect of relatedness was found, F1(1,39) ⫽ 1.85, p ⫽ .18; F2 ⬍ 1. A main effect of block, F1(1,39) ⫽ 12.28, p ⬍ .002; F2(1,99) ⫽ 21.38, p ⬍ .001, reflected a decrease in RTs over time. The block by relatedness interaction was not significant, F1 and F2 ⬍ 1. Separate ANOVAs for the two blocks revealed that the relatedness effect was not significant in either block, both F1s and F2s ⬍ 1. Analyses of the error data yielded no significant effects; all F1s and F2s ⬍ 1. Mediated-and-direct list. Main effects of relatedness, F1(1,39) ⫽ 13.29, p ⬍ .002; F2(1,88) ⫽ 4.39, p ⬍ .04, and an interaction with distance, F1(1,39) ⫽ 12.86, p ⬍ .002; F2(1,88) ⫽ 6.79, p ⬍ .02, were found. Separate ANOVAs showed a significant RT priming effect for the one-step pairs, F1(1,39) ⫽ 38.87, p ⬍ .001; F2(1,49) ⫽ 11.40, p ⬍ .001, but not for the two-step pairs, F1 and F2 ⬍ 0.5. Analysis of the error data showed a trend toward an effect of relatedness, F1(1,39) ⫽ 2.99, p ⬍ .10; F2(1,88) ⫽ 2.52, p ⬍ .12. Participants tended to be more accurate on the one- and two-step pairs than the

unrelated pairs. No interaction with distance was found, F1 and F2 ⬍ 1. Event-Related Potential Results The grand mean target ERPs for the midline electrodes are presented in Fig. 1, and the mean amplitudes of the waveforms for all electrodes are given in Appendix A. In this and all other figures negativity is plotted upward. Mediated-only list. Figure 1 shows that the most distinguishing features of the waveforms for the first and the second blocks were a broad centroparietally distributed negative-going wave peaking at about 370 ms which was followed by a large positivity with a parietal maximum that peaked at about 550 ms. Based on the timing and scalp distribution, we interpret the negative wave as an N400 and the positive wave as a P3. The N400 and the P3 were both widely distributed across the scalp. No effect of relatedness or block by relatedness interaction was found, both F1s ⬍ 1. Because the evaluation of the ERPs during the first and the second blocks was planned a priori, separate ANOVAs were performed for the two blocks. In the first block, no relatedness effect was found in the typical N400 window, F1s ⬍ 0.5 for the mean amplitudes for the epochs of 350 –


323

FIG. 1. Experiment 1: Grand ERP averages over subjects for the first and the second blocks of the Mediated-Only List (columns 1 and 2) and for the one-step pairs and the two-step pairs of the Mediated-andDirect List (columns 3 and 4) time-locked to the onset of the target words and separating the related pairs (solid line) and the unrelated pairs (dotted line). Fz, Cz, and Pz signify frontal, central, and parietal midline electrodes. The shaded areas indicate the time periods in which significant effects of relatedness were present. The one-step priming effects are shaded in a lighter gray.

400 and 400 – 450 ms. Although Fig. 1 suggests that N400 amplitude was somewhat more negative for the unrelated than for the two-step pairs, no reliable modulation in N400 amplitude was found. Starting at about 700 ms after target onset, differences in a centroparietally distributed Slow Wave emerged between the two-step and the unrelated pairs. Slow Wave amplitude was more negative-going for the two-step pairs than the unrelated pairs. The subject analysis yielded relatedness effects on Slow Wave amplitude in three epochs and the item analysis revealed such effects in two epochs (700 –750 ms: F1(1,39) ⫽ 5.29, p ⬍ .05; F2(1,99) ⫽ 5.41, p ⬍ .05; 750–800 ms: F1(1,39) ⫽ 4.91, p ⬍ .05; F2(1,99) ⫽ 3.71, p ⬍ .10; 800–850 ms: F1(1,39) ⫽ 6.67, p ⬍ .05; F2(1,99) ⫽ 6.06, p ⬍ .05). For the second block, the subject and item analyses yielded an effect of relatedness for the epoch of 350 – 400 ms, F1(1,39) ⫽ 4.50, p ⬍ .05; F2(1,99) ⫽ 4.92, p ⬍ .05. Thus, in the second block, a small but reliable N400-mediated priming effect was observed in the typical N400 window. Appendix A, which presents the

mean amplitudes for the two-step and the unrelated pairs, indicates that a small N400 two-step priming effect of at least 0.5 ␮V was present at all electrodes except the two frontal (Fz, F7) and the occipital electrodes. Main effects of electrode, F1(12,468) ⫽ 16.65, p ⬍ .01; F2(12,1188) ⫽ 77.33, p ⬍ .001, followed up by posthoc tests showed that N400 amplitude was smaller at F7 and F8 than at all other sites ( p ⬍ .05). Mean N400 amplitude was also larger at posterior electrodes (Cz, LTP, RTP, OL) than at the frontal midline (Fz) and the anteriortemporal sites (LAT, RAT) ( p ⬍ .05). The relatedness by electrode interactions did not approach significance, both F1s ⬍ 1.5. The late Slow Wave effect observed in the first block was absent in the second block, F1s ⬍ 1. Mediated-and-direct list. As Fig. 1 shows, the overall form of the ERPs in the Mediatedand-Direct List was similar to that of the Mediated-Only List. Appendix A shows that an N400 priming effect was clearly present for the one-step pairs [except for anterior sites (F7, F8, LAT, RAT) and the left temporal electrode

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CHWILLA, KOLK, AND MULDER TABLE 2 Experiment 1: F Values for the Subjects (F1) and Items (F2) ERP Analyses for the Mediated-and-Direct List for Those Time Periods Covering the Typical N400 Window

Degrees of freedom: Epoch (ms) 350–400 400–450

Distance

Distance ⫻ Relatedness

Relatedness

Distance ⫻ Relatedness ⫻ Electrode

F1(1,39)

F2(1,88)

F1(1,39)

F2(1,88)

F1(1,39)

F2(1,88)

F1(12,468)

F2(12,1056)

22.59** 23.04**

8.25** 12.37**

6.49* 7.56*

5.22* 5.85*

3.24 4.49*

⬍1 3.55

4.47* 3.31

3.95* 3.32

Note. The time epochs are measured from target onset. * p ⬍ .05. ** p ⬍ .01.

(LT)]. In contrast, the N400 effect was much smaller (Cz, RT, RTP) or virtually absent for the two-step pairs. The N400 one-step priming effect showed the N400 typical scalp distribution. It was largest at Cz and Pz, and there was a trend toward larger N400 priming effects over the right than the left hemisphere (see Appendix A: RT, RTP versus LT, LTP). Table 2 depicts the main results of the analyses. Main effects of distance and relatedness in the typical N400 window were found in the subject and item analyses. The effects of distance obtained because overall amplitudes were more positive for the one-step than for the twostep pairs. The effects of relatedness indicate that the mean N400 amplitude was larger for unrelated pairs than for the one-step and twostep pairs. Interactions with distance (reliable in the subject analysis and marginally significant in the item analysis) and electrode disclosed that a centroparietally distributed N400 priming effect was found for the one-step pairs but not for the two-step pairs. Posthoc tests verified this pattern. An N400 one-step priming effect was found at the midline (Fz, Cz, Pz), posterior electrodes (LTP, RTP, OL, OR), and the right temporal electrode (RT) ( p ⬍ .05). In contrast, no reliable N400 effect for the two-step pairs was found at any of the electrodes. Discussion Contrary to the results of McNamara and Altarriba (1988), no two-step RT priming effect was found in the Mediated-Only List. There

was not even a hint of more efficient processing of the two-step pairs compared to the unrelated pairs. The present failure to find two-step RT priming effects in a standard lexical decision task for a list only composed of mediated pairs is not without precedent [see DeGroot (1983: Experiment 2)]. The present results and those of DeGroot indicate that omission of direct associates is not a sufficient condition for obtaining RT two-step priming in lexical decision. Other factors, such as differences in task or presentation parameters, may be jointly responsible for the presence or the absence of RT two-step priming effects. Importantly, a reliable N400 two-step priming effect was observed in the absence of a RT effect. The two-step N400 priming effect can be accounted for by only one of the current semantic priming integration models—the Gillund– Shiffrin implementation of the compound cue model. The effect appeared to develop over time, as indicated by the presence of an N400mediated priming effect in the second block but not in the first block. Participants could have sensed that some of the word pairs are somehow related. Because the mediator was often a strong associate of the prime, they might for some pairs have detected the missing link which could have broadened the zoom lens of the meaning-integration process. This idea is compatible with the late Slow Wave effect, occurring 700 to 850 ms after the target, which was observed in the first block only. Slow Waves index sustained mental operations and their am-


325

plitude appears to reflect the difficulty of these operations (e.g., Ro¨sler, Ro¨der, Heil, & Hennighausen, 1993; Ruchkin, Johnson, Mahaffey, & Sutton, 1988). The presence of a reliable, though small and brief, N400-mediated priming effect in the second block of the pure list is taken to reflect the successful integration of the two-step pairs. The important point is that the N400 two-step priming effect appears to indicate that participants succeeded in integrating word pairs which are exclusively indirectly related. Therefore, one potentially theoretically important implication of the finding of N400mediated priming is that integrative mechanisms can cross more than one step in semantic memory, as maintained by Ratcliff and McKoon (1988). The second major finding was that a list composition effect was observed on N400. A reliable N400 two-step priming effect was found in the pure list but not in the mixed list. The disappearance of the effect in the mixed list suggests that the presence of directly related pairs invited participants to pay attention to the strongest relationships at the cost of the subtle indirect relationships. The observation of N400mediated priming in the absence of an RT effect suggests that N400 effects are not necessarily accompanied by RT effects (see also Kotz, 1998). Although the N400 two-step priming effect was significant in the subject and item analysis, one might question its validity because the effect was of short duration. Therefore, a second experiment was conducted to test the reliability of the effect.

pants can integrate indirectly related pairs of words, then the instructions might increase such integration processes. If we are correct that the N400 two-step priming effect reflects the successful integration of indirectly related pairs, then the integration instruction might affect the N400 effect.

EXPERIMENT 2

As Table 3 shows, no differences in RTs between two-step pairs and unrelated pairs were observed in the Mediated-Only List. As in Experiment 1, an RT priming effect was only found for the one-step pairs in the Mediatedand-Direct List. Mediated-only list. No effect of relatedness, block, or interaction between block and relatedness was found, all F1s and F2s ⬍ 0.5. Separate ANOVAs for the first and the second block also failed to yield an effect of relatedness, both F1s and F2s ⬍ 1. For the error data, there was a trend toward an interaction between block and

The goals of Experiment 2 were, first, to investigate the reliability of the N400-mediated priming effect and, second, to make another attempt to find two-step RT priming effects. DeGroot (1983, Experiments 3 and 4) showed that informing participants about the presence of indirectly related pairs and instructing them to use these relationships to speed their lexical decisions helps induce two-step RT priming effects. In Experiment 2, we used this integration instruction to further elucidate the nature of the N400-mediated priming effect. If partici-

Method Participants Twenty-six participants (mean age, 23.48) were recruited. They fulfilled the same criteria as those for Experiment 1. One participant had to be excluded from the analyses because of excessive eye-movement artifacts. Procedure Experiment 2 was a replication of Experiment 1, except that participants were informed about the presence of indirectly related word pairs. An example of an indirect relationship was presented and it was explained how the two words were related via the mediating word. Participants were asked to try to profit from these indirect relationships to speed their lexical decisions to the target words. Results Data Analysis The analyses performed on the ERPs and the RT and error data were identical to those of Experiment 1. Reaction Time and Error Results

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CHWILLA, KOLK, AND MULDER TABLE 3

Experiment 2: Mean Reaction Times (RT), Standard Deviations (SD), and Mean Error Rates for the Different Relatedness Conditions for the Two Blocks of the Mediated-Only List and the Two Levels of Distance for the Mediatedand-Direct List Mediated-Only List Prime type

Two-step Unrelated

First block

Second block

RT

SD

Errors

Priming effect

RT

SD

Errors

Priming effect

556 559

99 94

3.68 2.72

3

556 554

92 87

1.44 2.72

⫺2


One-step 495 526

79 86

1.44 2.56

Two-step 31***

517 520

85 78

2.80 1.40

3

*** p ⬍ .001.

relatedness, F1(1,24) ⫽ 2.84, p ⫽ .11; F2(1,99) ⫽ 2.02, p ⫽ .16. Mediated-and-direct list. The effect of distance (reflected by overall faster RTs at distance one as opposed to distance two) approached significance in the subject analysis but not in the item analysis F1(1,24) ⫽ 4.02, p ⫽ .06; F2(1,88) ⫽ 1.19, p ⫽ .28. More interestingly, main effects of relatedness, F1(1,24) ⫽ 15.35, p ⬍ .001; F2(1,88) ⫽ 4.01, p ⬍ .05, and an interaction with distance in the subject analysis, F1(1,24) ⫽ 12.34, p ⬍ .002, which was marginally significant in the item analysis, F2(1,88) ⫽ 3.11, p ⫽ .08, reflected the fact that a priming effect was present for the onestep pairs but not for the two-step pairs. Separate ANOVAs for the two levels of distance revealed a priming effect for the one-step pairs, F1(1,24) ⫽ 29.13, p ⬍ .001; F2(1,49) ⫽ 7.65, p ⬍ .008, but not for the two-step pairs, F1 and F2 ⬍ 1. Analysis of the error data yielded an interaction of distance with relatedness, F1 (1,24) ⫽ 4.69, p ⬍ .05; F2 (1,88) ⫽ 4.97, p ⬍ .03. Participants were more accurate on the one-step than the unrelated pairs, whereas they made more errors on the two-step pairs as opposed to unrelated pairs. However, posthoc tests indicated that these differences were not reliable at the 5% level.

Event-Related Potential Results The grand mean target ERPs for the midline electrodes are presented in Fig. 2, and the mean amplitudes of the waveforms, subjected to analysis for all electrodes, are given in Appendix B. Mediated-only list. The overall form of the ERPs was similar to those in Experiment 1. In the overall analysis, no effect of relatedness or interaction with block was found, both F1s ⬍ 1. The main results of the supplementary ANOVAs for the two blocks are summarized in Table 4. In the first block, the instructions yielded an early distance effect—that is, an increase in negativity for the unrelated pairs as opposed to the two-step pairs. The early negative effect showed maximal differences between conditions at Cz and Pz, where the waveforms separated already within the first 100 ms following target onset. The difference in mean amplitudes was reliable in the epochs of 200 – 250 and the 300 –350 ms. The early negative effect carried over into the N400 window and at posterior sites extended up to 900 ms after the target. However, no relatedness effect was obtained in the typical N400 window or later epochs, except for one epoch falling in the Slow Wave region (650 –700 ms: p1 and p2 ⬍ .05). In the second block of Experiment 2, as in Experiment 1, an N400 priming effect was elic-

327


FIG. 2. Experiment 2: Grand ERP averages over subjects for the first and the second blocks of the Mediated-Only List (columns 1 and 2) and for the one-step pairs and the two-step pairs of the Mediated-andDirect List (columns 3 and 4) time-locked to the onset of the target words and separating the related pairs (solid line) and the unrelated pairs (dotted line). Fz, Cz, and Pz signify frontal, central, and parietal midline electrodes. The shaded areas indicate the time periods in which significant effects of relatedness were present. The one-step priming effects are shaded in a lighter gray.

ited by the two-step pairs. Comparison of the N400-mediated priming effects between experiments (see second columns of Figs. 1 and 2) suggests that the integration instruction had two effects: First, the size of the N400 two-step priming effect at the midline, in particular at Cz and Pz, appeared to be enlarged (in the epoch of 350 – 400 ms the effect at Cz and Pz was 0.66 and 0.61 ␮V in Experiment 1 and 1.40 and 1.68 ␮V in Experiment 2). Second, the N400-medi-

ated priming effect in Experiment 2 spanned a broader time window. As Table 4 shows, relatedness effects were observed in three time windows starting at 350 to 500 ms after the target. The N400 two-step priming effect resembled the N400 one-step priming effect in terms of its timing (it’s onset was approximately 300 ms posttarget) and scalp distribution (with the largest effects at the centroparietal sites: Cz, Pz, LTP, and RTP), though the effect was much

TABLE 4 Experiment 2: F Values for the Subjects (F1) and Items (F2) ERP Analyses for the Mediated-Only List for Those Time Periods in Which Significant Relatedness Effects Were Found Separately for the First and the Second Blocks First block: Relatedness Degrees of freedom: Epoch (ms) 200–250 300–350

Second block: Relatedness

F1(1,24)

F2(1,99)

Epoch (ms)

F1(1,24)

F2(1,99)

6.93* 10.39**

4.25* 5.77*

350–400 400–450 450–500

5.78* 4.36* 6.56*

4.25* 3.96* 4.19*


328

CHWILLA, KOLK, AND MULDER TABLE 5 Experiment 2: F Values for the Subjects (F1) and Items (F2) ERP Analyses for the Mediated-and-Direct List for Those Time Periods Covering the Typical N400 Window Distance ⫻ Relatedness

Distance ⫻ Relatedness ⫻ Electrode

Degrees of freedom: Epoch (ms)

F1(1,24)

F2(1,88)

F1(1,24)

F2(1,88)

F1(1,24)

F2(1,88)

F1(12,288)

F2(12,1056)

350–400 400–450

13.06** 11.24**

12.65** 10.79**

10.87** 12.39**

6.23* 9.03**

7.83** 6.45*

4.30* 4.95*

⬍1 ⬍1

3.35* 1.81

Distance

Relatedness


smaller. Main effects of electrode in the subject and item analysis, all p values ⬍ .01, followed up by posthoc tests, indicated that N400 amplitude was larger at Cz, LT, LTP, OL, and OR than at F7 and F8 ( p ⬍ .05). A relatedness by electrode interaction in the epoch of 350 – 400 ms in the subject analysis, F1(12,288) ⫽ 4.28, p ⬍ .05, though not significant in the item test, F2 ⬍ 2, confirmed that the N400 two-step priming effect was maximal at centroparietal sites. Posthoc tests disclosed that significant N400 effects were present at Fz, Cz, Pz, LTP, and RTP ( p ⬍ .05). Mediated-and-direct list. The grand mean target ERPs for the midline electrodes are displayed in Fig. 2 (see columns 3 and 4). A large N400 priming effect was elicited by the onestep pairs. Appendix B indicates that the N400 one-step priming effect showed the typical N400 scalp distribution. It was largest at the centroparietal midline sites, virtually absent at frontal sites, and tended to be more pronounced over the right than the left hemisphere. In contrast, the N400 two-step priming effect was strongly reduced (Cz, Pz) or almost absent. Consistent with this, the analyses in the N400 window yielded effects of distance, relatedness, and interactions between the two factors (see Table 5). Posthoc tests demonstrated that an N400 one-step priming effect was present at all electrodes ( p ⬍ .05), except for three anterior sites (F7, F8, LAT). In contrast, no significant two-step priming effect was observed at any of the electrodes.

Beyond the N400 window in the 500- to 600-ms latency range, the waveforms for the two-step pairs were more negative-going than those for the unrelated pairs. Analysis of the two-step pairs disclosed relatedness effects in two time windows in the subject analyses but not in the item analysis (500 –550 ms: F1(1,24) ⫽ 4.77, p ⬍ .05; F2(1,88) ⫽ 3.01, p ⬎ .05; 550–600 ms: F1(1,24) ⫽ 6.52, p ⬍ .05; F2(1,88) ⫽ 2.35, p ⬎ .10). Across-Experiment Analyses Because the only methodological difference between Experiments 1 and 2 was one of instruction, global subject ANOVAs 2 with experiment as the between-subjects factor were carried out for N400. Mediated-only list. The global subject ANOVAs revealed relatedness effects in three consecutive time windows in the N400 latency range (350 – 400 ms: F1(1,63) ⫽ 9.89, p ⬍ .003; 400–450 ms: F1(1,63) ⫽ 5.95, p ⬍ .02; and 450 –500 ms: F1(1,63) ⫽ 5.37, p ⬍ .03), showing that a reliable N400 two-step priming effect was present. For the 450- to 500-ms window, an experiment by relatedness 2

Because all relevant ERP effects in Experiments 1 and 2 were significant in both subject and item analyses, and because the computation of by-item ERP averages is very time-consuming, only global by-subject analyses were performed. Moreover, because the N400 effects were characterized by a centroparietal distribution, the results of this subset of electrodes (Cz, Pz, LTP, RTP, OL, and OR) will be reported.


interaction was obtained F1(1,63) ⫽ 5.20, p ⬍ .05. This interaction occurred because the N400 two-step priming effect was larger in Experiment 2 (1.16 ␮V) than in Experiment 1 (0.15 ␮V). The experiment by block by relatedness interaction was not significant, Fs ⬍ 1. Mediated-and-direct list. In the global subject ANOVA, we used a broader latency window to quantify N400 effects (mean amplitude in the 300- to 550-ms epoch), which corresponds to the window typically used in the literature (e.g., Anderson & Holcomb, 1995). This ANOVA yielded main effects of experiment, F1(1,63) ⫽ 14.98, p ⬍ .001, distance F1(1,63) ⫽ 22.40, p ⬍ .001, relatedness F1(1,63) ⫽ 15.59, p ⬍ .001, and a distance by relatedness interaction, F1(1,63) ⫽ 13.29, p ⬍ .002. The main effect of experiment showed that mean amplitudes were more positive in the second (3.03 ␮V) than in the first (0.52 ␮V) experiment. The distance by relatedness interaction, followed up by posthoc tests, substantiated an N400 priming effect for the one-step pairs ( p ⬍ .01) but not for the twostep pairs. Although the one-step priming effect was larger in Experiment 2 than in Experiment 1 (1.90 and 1.12 ␮V, respectively), the experiment by distance by relatedness interaction was not significant, F1(1,63) ⫽ 2.16, p ⫽ 0.15. If, however, a directional test was used, the N400 one-step priming effect was significantly larger in Experiment 2 than in Experiment 1 ( p ⬍ .025). Discussion The integration instruction did not provoke more efficient processing of the two-step pairs. As in Experiment 1, no RT-mediated priming effect was observed. These results are inconsistent with those of DeGroot (1983). Using the same integration instruction, she found two-step RT priming effects relative to an unrelated baseline. One factor which could be responsible for the discrepancy in results is that DeGroot used a shorter SOA. However, the results of Balota and Lorch (1986) showed that SOA is not a critical factor for finding mediated priming in lexical decision. Relevant to our present argument is that the combination of list composition

329

with instructions was still not sufficient to elicit a reliable RT-mediated priming effect. The major result of Experiment 2 was the replication of N400 two-step priming in the pure list. As in Experiment 1, a reliable N400 two-step priming effect was observed only in the second block. The N400 effect was more robust in Experiment 2 in that a reliable difference between the two-step pairs and the unrelated pairs was now observed in a broader time window (350 –500 ms in Experiment 2 vs. 350 – 400 ms in Experiment 1). Moreover, the size of the N400-mediated priming effect at Cz and Pz was about 1 ␮V larger in Experiment 2 than Experiment 1. Although this difference was not significant, it suggests an effect of the integration instructions. The N400 two-step priming effect resembled the one-step N400 effect in timing and scalp distribution, though it was much smaller. In the mixed list, an N400 priming effect was present for the one-step pairs but not for the two-step pairs, as in Experiment 1. The instruction manipulation elicited a full-blown one-step priming effect which was larger than the effect observed in Experiment 1. This increase in N400 one-step priming indicates that the instructions to search for indirect relationships stimulated participants to search for relationships in general, possibly because they were uncertain about identifying the indirectly related pairs. Instructions also elicited differences in ERPs outside the N400 window. The pure list gave rise to early effects. In the first block, an increase in negativity for unrelated as opposed to two-step pairs was found in two epochs (200 – 250 and 300 –350 ms). It could be argued that this effect reflects an early onset of the N400 effect. However, the analyses do not fully support this notion, because no relatedness effect in the typical N400 window was found. Examination of Fig. 2 suggests that, in addition to the N400, an earlier negativity peaking at about 200 ms was evoked, the so-called N2. The two components are most clearly discernible at the Pz and RTP electrodes. There is abundant evidence that the N2 is very sensitive to stimulus classification processes (e.g., Mangun & Hillyard,

330


1995; Pritchard, Shappell, & Brandt, 1991). Therefore, the early negative effect might not reflect an early onset of an N400 effect but instead might reflect processes of stimulus classification. In particular, the integration instruction could have led to a different classification of unrelated word pairs, most likely an early rejection of those pairs which are obviously unrelated. The mixed list gave rise to late effects. Specifically, mean amplitudes in the 500- to 600-ms epoch were more negative-going for the twostep pairs compared to all other conditions. This increase in negativity in the P3 and Slow Wave region for the mediated pairs might reflect continued processing of these pairs. However, the absence of a reliable difference in the item test suggests that these later relatedness effects were caused by a subset of the mediated pairs. Why did we, in contrast to McNamara and Altarriba (1988), fail to demonstrate two-step RT priming effects? One possible explanation lies in task differences. In McNamara and Altarriba’s Experiments 1 and 4, a lexical decision to both the prime and the target was required, whereas in our experiments and those of others in which no mediated priming effects were reported (Balota & Lorch, 1986; DeGroot, 1983), participants performed a lexical decision only to the target. We conducted a series of experiments (Chwilla, Kolk, & Schriefers, 1997; Chwilla & Kolk, 1999) to test whether a lexical decision to both the prime and the target may be critical for establishing two-step RT priming effects. The same materials were used as in Experiments 1 and 2. With this procedure, we obtained evidence for not only two-step but even three-step RT priming effects (i.e., priming via two mediators). In Experiment 3, we therefore used the same procedure in a combined ERP/RT experiment. Based on our previous work, we predicted RT two-step priming effects. The crucial question was whether the RT effects would be accompanied by N400 effects. If the RT two-step priming effects are accompanied by N400 effects, the results would support an integration account; if not, this would support a spreading activation account of mediated priming.

EXPERIMENT 3 Method Participants Twenty-six participants (mean age, 22.50) who fulfilled the same criteria as those in Experiment 1 were employed. The data from one participant were rejected because of excessive eye-movement artifacts. Stimuli The critical items and lists were the same as those in Experiments 1 and 2. The only difference was that, in Experiment 3, some of the primes were nonwords. Specifically, half of the nonwords which were presented as targets in Experiments 1 and 2 were now presented as primes. Thus, in Experiment 3, a nonword could occur either at the prime position (left of fixation: in 25% of all cases) or at the target position (right of fixation: in 25% of all cases), yielding an equal number of correct YES and NO responses. Procedure The general procedure and the order of presentation of the lists was identical to those in Experiments 1 and 2. In Experiment 3, however, primes and targets were presented simultaneously. Specifically, the prime and the target were presented to the left and right of a fixation point and the stimulus duration was increased from 200 to 400 ms. Participants performed a double lexical decision task on both the prime and the target letter string. They indicated by pressing a button with their right index finger when both letter strings were words or pressed a button with their left index finger when they were not. If they responded incorrectly, the Dutch word for error appeared on the screen for 2 s. 3 Participants were asked to respond quickly, but to remain accurate. 3 Different ERP components, such as slow negative potentials and P3, are affected by feedback (e.g., Chwilla & Brunia, 1991; Johnson, 1988). In the present experiment only incorrect responses were followed by a feedback signal. Because incorrect trials were rejected from the analysis we consider it unlikely that the presentation of feedback on incorrect trials affected the ERPs on correct trials.


331

TABLE 6 Experiment 3: Mean Reaction Times (RT), Standard Deviations (SD), and Mean Error Rates for the Different Relatedness Conditions for the Two Blocks of the Mediated-Only List and the Two Levels of Distance of the Mediatedand-Direct List Mediated-Only List Prime type

Two-step Unrelated

First block

Second block

RT

SD

Errors

Priming effect

RT

SD

Errors

Priming effect

914 951

135 138

5.60 7.68

37***

934 976

141 157

5.92 8.80

42***


One-step 877 921

153 138

4.32 7.68

Two-step 44***

911 954

159 151

7.20 7.80

43***

*** p ⬍ .001.

Results Data Analysis The analyses performed were identical to those of Experiments 1 and 2. However, the number of ERP analyses was reduced by analyzing only the part of the waveform that included the N400. Requiring judgment of the lexical status of two instead of one letter string increased overall RT and postponed the N400 effects. The upper limit for RT was increased from 1300 ms in Experiments 1 and 2 to 2000 ms. In Experiment 3 lexical decision times greater than 2000 ms were counted as errors. Maximal N400 effects occurred in the 500- to 650-ms time window after target onset. Consequently, N400 was quantified as the mean amplitude in the following three 50-ms epochs: 500 –550, 550 – 600, and 600 – 650 ms. Reaction Time and Error Results Mediated-only list. Mean RTs and error rates are presented in Table 6. The analysis of the RT data yielded significant effects of relatedness, F1(1,24) ⫽ 27.26, p ⬍ .001; F2(1,99) ⫽ 10.23, p ⬍ .003. The block by relatedness interaction was not significant, F1 and F2 ⬍ 1. Supplementary ANOVAs revealed two-step priming effects in the first block, F1(1,24) ⫽

17.29, p ⬍ .001; F2(1,99) ⫽ 4.19, p ⬍ .05, and the second block F1(1,24) ⫽ 15.60, p ⬍ .002; F2(1,99) ⫽ 4.80, p ⬍ .04. In the error data, the effect of relatedness was significant by subjects, F1(1,24) ⫽ 8.34, p ⬍ .01, and marginally significant by items, F2(1,99) ⫽ 3.72, p ⫽ .057. Participants tended to make fewer errors on the mediated pairs than the unrelated pairs. No interaction between block and relatedness was observed, F1 and F2 ⬍ 1. Mediated-and-direct list. Main effects of distance, F1(1,24) ⫽ 20.17, p ⬍ .001; F2(1,88) ⫽ 7.68, p ⬍ .008, and of relatedness F1(1,24) ⫽ 38.81, p ⬍ .001; F2(1,88) ⫽ 11.64, p ⬍ .002, were found. The effect of distance revealed that mean RTs for the one-step and their control pairs were faster than for the two-step pairs and their control pairs. The interaction between distance and relatedness was not significant, F1 and F2 ⬍ 1. Separate ANOVAs for the two levels of distance revealed RT priming effects for the onestep pairs, F1(1,24) ⫽ 11.24, p ⬍ .004; F2(1,49) ⫽ 5.81, p ⬍ .03, and for the twostep pairs, F1(1,24) ⫽ 15.37, p ⬍ .002; F2(1,39) ⫽ 6.42, p ⬍ .02. In the error data, the effect of relatedness was significant in the subject analysis, F1(1,24) ⫽

332


FIG. 3. Experiment 3: Grand ERP averages over subjects for the first and the second blocks of the Mediated-Only List (columns 1 and 2) and for the one-step pairs and the two-step pairs of the Mediated-andDirect List (columns 3 and 4) time-locked to the onset of the prime and the target words and separating the related pairs (solid line) and the unrelated pairs (dotted line). Fz, Cz, and Pz signify frontal, central, and parietal midline electrodes. The shaded areas indicate the time periods in which significant effects of relatedness were present. The one-step priming effects are shaded in a lighter gray.

4.35, p ⬍ .05, but not in the item analysis, F2(1,88) ⫽ 2.56, p ⫽ 1.67. Collapsed across distance, participants tended to be more accurate on the related pairs than the unrelated pairs. There was no interaction between distance and relatedness, F1 and F2 ⬍ 1.

trated in Fig. 4, in which the one-step N400 priming effect at the left occipital electrode (OL) is presented for all three experiments. The

Event-Related Potential Results The grand mean ERPs for the midline electrodes are presented in Fig. 3, and the mean amplitudes for all electrodes are displayed in Appendix C. The waveforms in the double lexical decision task look somewhat different from those of Experiments 1 and 2. The N400 in Experiment 3 was broader and the relatedness effects, especially for the one-step pairs—and to a lesser extent for the two-step pairs in the second block of the pure list— extended into the P3 window. This is most likely due to the simultaneous presentation resulting in overlap of the prime and target processing and the fact that subjects had to judge the lexical status of two letter strings instead of one, which enhanced the decision-related processes. The way in which the differences in task affected N400 is illus-

FIG. 4. Grand ERP averages of the one-step priming effects at the left occipital electrode (OL), time-locked to the onset of the target words (Experiments 1 and 2) or the onset of the prime and the target words (Experiment 3), separating the related pairs (solid line) and the unrelated pairs (dotted line) for all three experiments.

333

MEDIATED N400 AND RT PRIMING IN LEXICAL DECISION TABLE 7 Experiment 3: F Values for the Subjects (F1) and Items (F2) ERP Analyses for the Mediated-Only List for Those Time Periods in Which Maximal N400 Relatedness Effects Were Found Mediated-Only List: Overall ANOVA Block ⫻ Relatedness

Relatedness Degrees of freedom: Epoch (ms)

F1(1,24)

F2(1,99)

F1(1,24)

F2(1,99)

500–550 550–600 600–650

11.57** 16.21*** 7.16*

8.30** 11.55*** 8.15**

⬍1 ⬍1 ⬍1

⬍1 ⬍1 ⬍1

First block: Relatedness Degrees of freedom: 500–550 550–600 600–650

Second block: Relatedness

F1(1,24)

F2(1,99)

Epoch (ms)

F1(1,24)

F2(1,99)

4.06 a 3.98 a 2.45 a

2.07 a 4.21* 2.99 a

500–550 550–600 600–650

9.10** 14.84** 7.93*

7.52** 6.95* 6.06*

a One-tailed: p ⬍ .025. * p ⬍ .05. ** p ⬍ .01. *** p ⬍ .001.

N400 peak at this site in Experiment 3 was delayed by about 250 ms (from 370 ms in Experiments 1 and 2 to 625 ms in Experiment 3) and the time window in which maximal N400 relatedness effects occurred was delayed by approximately 200 ms. Mediated-only list. Figure 3 shows that, in the first and the second blocks of the pure list, N400 two-step priming occurred. The results of the overall ANOVAs, exhibited in Table 7, revealed that the N400 two-step priming effect was reliable, as indicated by relatedness effects in three consecutive (500 –550, 550 – 600, 600 – 650 ms) epochs. The block by relatedness interactions were not significant. Main effects of electrode were obtained in both subjects and items analyses, all p-values ⬍ .01, for all three epochs. Posthoc tests revealed that N400 amplitude was larger at Pz than at all other electrodes ( p ⬍ .05), except from Cz, F8, and RT. Appendix C indicates that the N400 priming effect in the pure list was largest at the midline sites. The relatedness by electrode interactions, however, did not approach significance, F1 and F2 ⬍ 2.

Separate analyses were performed for the two blocks and the main results are given in Table 7. The ANOVAs for the first block yielded a relatedness effect in the 550- to 600-ms epoch in the item analysis which was marginally significant in the subject analysis. If, however, a directional test was used, then the N400 twostep priming effect in the first block was significant in three consecutive time windows in both the subjects and items analyses. The N400 twostep priming effect in the 500 to 650 latency windows was clearly significant in the second block. Mediated-and-direct list. Figure 3 shows that a large N400 priming effect was present for the one-step pairs but not for the two-step pairs. This visual impression was confirmed by the results of the analyses summarized in Table 8, which disclosed interactions between distance and relatedness for three consecutive epochs. Additional ANOVAs for the two levels of Distance indicated that N400 relatedness effects were obtained for the directly related pairs but not for the two-step pairs. The ANOVA for the one-step pairs revealed a relatedness by elec-

334

CHWILLA, KOLK, AND MULDER TABLE 8 Experiment 3: F Values for the Subjects (F1) and Items (F2) ERP Analyses for the Mediated-and-Direct List for Those Time Periods in Which Maximal N400 Relatedness Effects Were Found Mediated-and-Direct List: Overall ANOVA Distance ⫻ Relatedness

Relatedness Degrees of freedom: Epoch (ms) 500–550 550–600 600–650

F1(1,24)

F2(1,88)

F1(1,24)

F2(1,88)

2.39 5.04* 7.93**

2.99 4.99* 7.91**

11.89** 14.30** 26.88***

8.34** 9.59** 15.79***

One-step Relatedness Degrees of freedom: 500–550 550–600 600–650

Two-step Relatedness

F1(1,24)

F2(1,49)

Epoch (ms)

F1(1,24)

F2(1,39)

10.43** 19.54*** 32.63***

16.28*** 18.67*** 27.69***

500–550 550–600 600–650

⬍1 ⬍1 ⬍1

⬍1 ⬍1 ⬍1

* p ⬍ .05. ** p ⬍ .01. *** p ⬍ .001.

trode interaction. Posthoc tests demonstrated that the N400 one-step priming effect was significant at all electrodes ( p ⬍ .05), except from two anterior sites (F7, RAT). Discussion The main result of this third experiment is the demonstration of clear RT-mediated priming effects. This result stands in sharp contrast to the absence of RT-mediated priming in Experiments 1 and 2. Apparently, the double lexical decision task was successful in bringing about this effect. The size of the two-step RT priming effect was comparable to that of McNamara and Altarriba: 41 ms in our experiment versus 37 in their Experiment 4. In contrast to the results of the McNamara and Altarriba experiment, as well as one study from our laboratory (Chwilla et al., 1997, Experiment 1), the mediated priming effect occurred in both the pure and the mixed lists. However, McNamara and Altarriba (1988) also found mediated priming in a mixed list when employing a single lexical decision task. They explained this result by assuming that the single lexical decision task taps into only automatic processing and does not reflect

strategic factors. Our result suggests that the double lexical decision task can also be insensitive to strategic effects. This is also apparent from the absence of a block effect. As in Experiments 1 and 2, N400-mediated priming effects were obtained. We also replicated the list composition effect. An N400 twostep priming effect was present in the pure list but not in the mixed list. Inspection of Fig. 3 and Appendix C indicates that the absence of N400-mediated priming in the mixed list does not arise from a lack of power, because a reversed N400 effect was found for most electrodes. Again there is an indication of a block effect, but this time it is only a trend. Although N400-mediated priming is present in the first block, the effect is more robust in the second block, as indicated by the fact that (except for one time window) the effect reaches standard levels of statistical significance only in the second block. GENERAL DISCUSSION The major question addressed in this article is whether two-step priming in lexical decision is evoked by spreading activation or by an inte-


gration mechanism. We examined this issue by combining RT and N400 measures. We assumed that the N400 priming effect reflects postlexical integration but—in contrast to RT— does not reflect spreading activation. Our first major finding was a dissociation between RT and N400 effects. When a standard lexical decision task was used (Experiments 1 and 2), we found mediated priming for the N400 but not for RT. When a lexical decision to the prime as well as the target was required (Experiment 3), mediated priming occurred for both N400 and RT. 4 Second, the observed N400-mediated priming effect was sensitive to strategic effects. In all three experiments, there was a list composition effect as well as a block effect (or a trend toward a block effect). In contrast, the RT-mediated priming effect observed in Experiment 3 was not affected by strategic factors, as indicated by the absence of effects of list composition and block. We had predicted two outcomes. The finding of an RT-mediated priming effect without an N400 effect would have been clear evidence in favor of a spreading activation account. In contrast, clear support for an integration account would have been obtained if the RT effect were always accompanied by an N400 effect. The 4

A potential problem with respect to the interpretation of the ERP results concerns component overlap. A P3 is elicited in any task which requires a binary decision (for reviews see: Donchin & Coles, 1988; Johnson, 1988). Because our participants made lexical decisions, a P3 component was also evoked. The crucial question is whether the N400-mediated priming effects in the pure lists might have resulted from a shortening in latency and/or an increase in amplitude of the following P3 component. To address this issue, additional analyses of P3 peak latency and amplitude were performed. The analyses for Experiments 1 and 2 did not yield relatedness effects, F1s ⬍ 3, or interactions with electrode, F1s ⬍ 1. In contrast, in Experiment 3, the requirement of performing a double lexical decision enhanced the P3 component and effects of relatedness were also found on P3 peak amplitude ( p ⬍ .05). Therefore, it is possible that variations in P3 amplitude might have contributed to N400-mediated priming in Experiment 3. However, modulations in P3 cannot account for the N400 two-step priming effects in Experiments 1 and 2, showing that these effects reflect genuine changes in N400 amplitude. From this, we conclude that component overlap is not a critical factor for establishing N400-mediated priming effects.

335

observed pattern seems inconsistent with either model. Let us consider the two approaches in more detail to see whether such a strong conclusion is warranted. We begin with the integration approach. Implications for Integration Models of (Mediated) Priming The Gillund–Shiffrin (1984) implementation of the compound cue model is the only integration model which can explain two-step priming. This model is supported by the occurrence of N400 two-step priming in the present experiments. However, it fails to account for the absence of RT-mediated priming in Experiments 1 and 2. The occurrence of lexical integration in the absence of response facilitation is paradoxical also for the models of DeGroot (1984, 1985) and Neely (1991). The latter models assume the operation of task-related integration processes to account for response facilitation in lexical decision. Therefore, if there is no response facilitation, there should be no integration. However, there could be integration for independent reasons. Integration of lexical meaning in the context of the discourse is an essential part of normal language understanding. One possibility is that the observed priming effects are a specific example of this more global form of integration. This is the view advanced by Hess, Foss, and Carroll (1995). According to their global integration model, participants in psycholinguistic experiments search for coherence relations at the highest level that the material permits. In texts or spoken discourse, the level at which they search and discover coherence relations is much higher than that for word lists. However, when presented with lists of words, participants also attempt to create a context. This kind of integration could be exploited to facilitate lexical decision in the way described by DeGroot and Neely. Why didn’t our participants use this strategy in Experiments 1 and 2? We believe that in the present studies, the relatedness proportion (0 for the pure list and .22 for the mixed list) and the nonword ratio (.50 in the pure list and .56 in the mixed list) were too low to reinforce the use of this strategy.

336


Because the integration process is disconnected from specific decision and response-related processes in the global integration model, it can explain the occurrence of postlexical integration without response facilitation. But can the model also accommodate the effects of list composition and block? The compound cue model was designed to explain automatic priming and cannot—at least in its present form— account for these more strategic effects. The constraining assumption of the global integration model is that priming should occur only for the most coherent stimuli. The model thus predicts two-step priming, if these pairs represent the most coherent/meaningful stimuli in the list. Because the attention of the participant is captured by the most meaningful stimuli, list composition should play a critical role. The meaning relationships for the one-step pairs are obvious, whereas for the two-step pairs they are subtle. Nevertheless, indirect relationships will determine the participants’ behavior if they are the strongest relationships within a set. Therefore, the model can explain our major N400 finding—that is, the presence of N400 two-step priming in the pure list and its absence in the mixed list. Because it takes time to build up an overall representation of the coherence level, the model can also account for the block effect. So far, we have focused on the dissociation of N400 and RT effects in Experiments 1 and 2. How can integration models account for the results of Experiment 3, where mediated priming occurred for N400 and RT? This result is consistent with the Gillund–Shiffrin model. Accepting this solution, however, would imply that different forms of integration are involved: global integration in Experiments 1 and 2 and compound cue integration in Experiment 3. This should be reflected in qualitatively different N400 priming patterns. This possibility, however, is inconsistent with the finding that N400 effects of list composition and block occurred in all experiments. One argument in favor of a possible contribution of integration processes in Experiment 3 is that the error rates for the unrelated and two-step pairs in the mixed list were higher than those in Experiments 1 and 2. However, if integration processes had af-

fected the RT data, this should have been particularly advantageous for direct associates and less so for the only indirectly related pairs. Based on the absence of a list composition effect on RT, we consider it unlikely that integration processes contributed to RT-mediated priming. Implications for Spreading Activation Accounts of (Mediated) Priming Since the integration models cannot satisfactorily account for the RT results of Experiment 3, we now turn to spreading activation models. If these models could explain the RT results, this would imply that N400- and RT-mediated priming do not reflect identical processes. Closer inspection of our data provides some support for this notion. In Experiment 3, the time window in which N400-mediated priming occurred—that is, the 500- to 650-ms epoch— was some hundreds of milliseconds earlier than the mean RTs (see Table 6). Therefore, we assume that RT was affected by processes which took place after N400 integration had already taken place. But how can spreading activation models explain the absence of RT-mediated priming effects in Experiments 1 and 2? One possible explanation relates to differences in timing parameters. In Experiments 1 and 2, the prime and the target were presented sequentially with an SOA of 550 ms, whereas in Experiment 3 they were presented simultaneously. It could be argued that RT effects may depend on the simultaneous presentation and/or a shorter SOA. The literature on mediated priming does not support this idea. Although the results of DeGroot (1983) suggest that SOA might play a role, the results of Balota and Lorch (1986) clearly contradict this view. A compelling argument against the timing hypothesis is the reliable demonstration of mediated priming in the single presentation lexical decision task in which the prime and target are separated by a lexical decision response (McKoon & Ratcliff, 1992; McNamara, 1992a; McNamara & Altarriba, 1988; Shelton & Martin, 1992). A second explanation involves task demands. In Experiment 3, participants attended to the


prime and the target, but in contrast to Experiment 2, they had to overtly respond to the prime. RT-mediated priming also occurs in the single presentation lexical decision task (McKoon & Ratcliff, 1992; McNamara & Altarriba, 1988; Shelton & Martin, 1992) in which a lexical decision to the prime and the target is required as well. One could argue that, in these two task variants, more attention is given to the prime than in standard lexical decision. One possible account of the presence of RT-mediated priming in Experiment 3 is that attention to the prime was enhanced by the lexical decision response and evoked a large boost in activation, causing the automatic activation process to spread deep in the network. In contrast, if as in Experiments 1 and 2 the prime is not attended to in that no lexical decision to it is required, the amount of activation generated by the prime may be too weak or it might decay too fast to yield two-step spreading activation. There are at least two objections to the attention hypothesis: First, it could be argued that it appears contradictory that attention is needed to yield automatic activation effects. There is, however, evidence that automatic processes can be triggered by controlled processes (Shiffrin & Schneider, 1977). Second, if attention to the prime is important for yielding mediated RT effects, why were no RT effects observed when participants were instructed to use indirect relationships to speed their responses? This is a legitimate objection, but it could still be the case

337

that attending to both prime and target as long as is necessary for lexical decision is more effective in promoting spreading activation from the prime to the target than searching for indirect relationships. Whatever the critical task difference, the present and previous results (Chwilla et al., 1997) show that judging the lexicality of the prime and the target is crucial for establishing mediated RT effects in lexical decision. The fact that this is not the case for the N400mediated priming effect indicates that we are dealing with two qualitative different priming processes. Good arguments can be made that one is global integration, which leads to an N400-mediated priming effect. The evidence at hand is most compatible with the assumption that spreading activation is the other process and that this is what gives rise to RT-mediated priming. One final caveat is needed. Throughout this article, we assumed that the N400 priming effect was an index of lexical integration. It has been suggested that the N400 effect is also sensitive to lexical access (cf. Besson, Fischler, Boaz, & Raney, 1992; Kutas & Hillyard, 1989). Therefore, it might be argued that N400-mediated priming arises from spreading activation. However, although spreading activation models could explain N400 two-step priming per se, they cannot explain the more strategic effects of list composition and block. Therefore, we consider this possibility highly unlikely.

338


APPENDIX A Experiment 1: Mean N400 Amplitude within the Epoch of 350 – 400 ms Posttarget for Both Lists for the Related (First Row) and the Unrelated (Second Row) Conditions Fz

Cz

Pz

F7

F8

LAT

RAT

LT

RT

LTP

RTP

OL

OR

⫺3.74 ⫺4.40 ⫺0.66

⫺1.28 ⫺1.89 ⫺0.61

0.47 0.24 ⫺0.23

0.66 0.02 ⫺0.64

⫺1.49 ⫺2.26 ⫺0.77

⫺0.95 ⫺1.91 ⫺0.96

⫺3.46 ⫺4.60 ⫺1.14

⫺2.67 ⫺3.73 ⫺1.06

⫺4.26 ⫺5.10 ⫺0.84

⫺2.92 ⫺3.95 ⫺1.03

⫺3.31 ⫺3.41 ⫺0.10

⫺3.37 ⫺3.67 ⫺0.30

⫺0.14 ⫺2.49 ⫺2.35 ⫺3.47 ⫺3.98 ⫺0.51

2.04 ⫺0.57 ⫺2.61 ⫺1.36 ⫺1.77 ⫺0.41

1.21 2.06 0.85 0.87 0.86 ⫺0.01

1.93 1.65 ⫺0.28 1.36 0.92 ⫺0.44

⫺1.06 ⫺0.40 0.66 ⫺1.30 ⫺1.12 0.18

0.20 ⫺0.26 ⫺0.46 ⫺0.55 ⫺0.89 ⫺0.34

⫺2.36 ⫺2.58 ⫺0.22 ⫺3.39 ⫺3.63 ⫺0.24

⫺0.51 ⫺1.99 ⫺1.48 ⫺2.20 ⫺2.84 ⫺0.64

⫺2.64 ⫺3.64 ⫺1.00 ⫺4.22 ⫺4.30 ⫺0.08

⫺0.72 ⫺2.61 ⫺1.89 ⫺2.63 ⫺3.27 ⫺0.64

⫺1.68 ⫺3.11 ⫺1.43 ⫺3.16 ⫺3.17 ⫺0.01

⫺1.80 ⫺3.16 ⫺1.36 ⫺3.52 ⫺3.87 ⫺0.35

Mediated-Only List: Second block Two-step Control Difference

⫺1.61 ⫺2.04 ⫺0.43

Mediated-and-Direct List One-step Control Difference Two-step Control Difference

1.14 ⫺0.08 ⫺1.22 ⫺1.07 ⫺1.46 ⫺0.39

Note. The N400 priming effect (Difference) was computed by subtracting the mean amplitude of the related condition from the mean amplitude of the unrelated condition.

APPENDIX B Experiment 2: Mean N400 Amplitude within the Epoch of 350 – 400 ms a Posttarget for Both Lists for the Related (First Row) and the Unrelated (Second Row) Conditions Fz

Cz

Pz

F7

F8

LAT

RAT

LT

RT

LTP

RTP

OL

OR

⫺1.76 ⫺3.16 ⫺1.40

⫺0.05 ⫺1.73 ⫺1.68

1.91 1.76 ⫺0.15

2.19 1.72 ⫺0.47

⫺0.45 ⫺0.80 ⫺0.35

⫺0.10 ⫺0.33 ⫺0.23

⫺2.48 ⫺3.14 0.66

⫺1.38 ⫺2.06 ⫺0.68

⫺2.97 ⫺3.81 ⫺0.84

⫺1.65 ⫺2.66 ⫺1.01

⫺2.29 ⫺2.69 ⫺0.40

⫺2.45 ⫺2.96 ⫺0.51

2.56 ⫺1.16 ⫺3.72 ⫺1.15 ⫺1.75 ⫺0.60

5.32 0.65 ⫺4.67 1.12 0.25 ⫺0.87

3.50 3.73 0.23 2.12 3.23 1.11

3.46 3.16 ⫺0.30 1.54 1.95 0.41

0.96 1.04 0.08 ⫺0.02 0.66 0.68

2.07 0.89 ⫺1.18 ⫺0.07 0.07 0.14

⫺0.28 ⫺1.53 ⫺1.25 ⫺1.88 ⫺1.73 0.15

⫺1.74 ⫺0.68 ⫺2.42 ⫺1.13 ⫺1.18 ⫺0.05

⫺0.10 ⫺2.40 ⫺2.30 ⫺1.94 ⫺2.21 ⫺0.27

2.16 ⫺1.07 ⫺3.23 ⫺1.24 ⫺1.40 ⫺0.16

0.69 ⫺2.17 ⫺2.86 ⫺0.97 ⫺1.36 ⫺0.39

0.99 ⫺1.96 ⫺2.95 ⫺1.55 ⫺1.99 ⫺0.44


0.89 ⫺0.07 ⫺0.96


4.48 1.78 ⫺2.70 1.36 1.10 ⫺0.26

Note. The N400 priming effect (Difference) was computed by subtracting the mean amplitude of the related condition from the mean amplitude of the unrelated condition. a To facilitate a direct comparison between experiments the same time window was used as in Experiment 1.

339


APPENDIX C Experiment 3: Mean N400 Amplitude within the Epoch of 550 – 600 ms Posttarget for Both Lists for the Related (First Row) and the Unrelated (Second Row) Conditions Fz

Cz

Pz

F7

F8

LAT

RAT

LT

RT

LTP

RTP

OL

OR

3.77 2.14 ⫺1.63

⫺3.01 ⫺3.88 ⫺0.87

0.19 ⫺0.66 ⫺0.85

⫺2.43 ⫺3.00 ⫺0.57

⫺0.70 ⫺1.58 ⫺0.88

⫺1.85 ⫺2.55 ⫺0.70

⫺1.41 ⫺2.65 ⫺1.24

⫺1.46 ⫺2.33 ⫺0.87

⫺2.05 ⫺2.95 ⫺0.90

⫺1.04 ⫺2.33 ⫺1.29

⫺2.73 ⫺3.87 ⫺1.14

0.91 ⫺1.53 ⫺2.44

4.73 2.95 ⫺1.78

⫺3.11 ⫺4.39 ⫺1.28

0.55 ⫺0.80 ⫺1.35

⫺1.97 ⫺3.46 ⫺1.49

⫺0.25 ⫺1.69 ⫺1.44

⫺1.17 ⫺2.98 ⫺1.81

⫺1.22 ⫺2.37 ⫺1.15

⫺0.87 ⫺2.62 ⫺1.75

⫺1.61 ⫺2.48 ⫺0.87

⫺0.63 ⫺2.07 ⫺1.44

⫺2.16 ⫺2.81 ⫺0.65

2.94 ⫺0.15 ⫺3.09 1.26 1.48 0.22

6.76 3.51 ⫺3.25 5.16 4.37 ⫺0.79

⫺2.02 ⫺2.73 ⫺0.71 ⫺3.20 ⫺2.60 0.60

2.44 0.27 ⫺2.17 0.95 2.19 1.24

⫺0.95 ⫺1.94 ⫺0.99 ⫺2.45 ⫺1.79 0.66

1.63 ⫺0.55 ⫺0.46 ⫺0.04 1.09 1.13

⫺0.20 ⫺1.62 ⫺1.42 ⫺1.50 ⫺1.25 0.25

1.25 ⫺1.60 ⫺2.85 ⫺0.47 ⫺0.02 0.45

⫺0.02 ⫺1.51 ⫺1.49 ⫺1.05 ⫺1.21 ⫺0.16

0.95 ⫺2.01 ⫺2.96 ⫺0.96 ⫺0.79 0.17

⫺0.38 ⫺1.37 ⫺0.99 ⫺0.85 ⫺1.26 ⫺0.41

⫺0.81 ⫺2.95 ⫺2.14 ⫺1.88 ⫺2.17 ⫺0.29

Mediated-Only List: First block Two-step Control Difference

⫺2.62 ⫺3.60 ⫺0.98

0.06 ⫺1.47 ⫺1.53


⫺1.65 ⫺4.02 ⫺2.37


⫺0.31 ⫺2.70 ⫺2.39 ⫺1.22 ⫺0.99 0.23

Note. The N400 priming effect (Difference) was computed by subtracting the mean amplitude of the related condition from the mean amplitude of the unrelated condition.

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