Automatic and Controlled Semantic Processing: a Masked Prime-Task Eﬀect

Consciousness and Cognition Consciousness and Cognition 14 (2005) 278–295 www.elsevier.com/locate/concog

Automatic and controlled semantic processing: A masked prime-task eﬀect

B. Valde´sa,*, A. Catenab, P. Marı´-Beﬀaa

a University of Wales, Bangor, Adeilad Brigantia, Penrallt Road, Gwynedd LL57 2AS, UK b University of Granada, Spain

Received 5 February 2004 Available online 26 October 2004

Abstract

A classical definition of automaticity establishes that automatic processing occurs without attention or consciousness, and cannot be controlled. Previous studies have demonstrated that semantic priming can be reduced if attention is directed to a low-level of analysis. This finding suggests that semantic processing is not automatic since it can be controlled. In this paper, we present two experiments that demonstrate that semantic processing may occur in the absence of attention and consciousness. A negative semantic priming effect was found when a low-level prime-task was required and when a masked lexical decision prime-task was performed (Experiment 1). This paper also discusses the limitations of the inhibitory mechanism involved in negative semantic priming effect. 2004 Elsevier Inc. All rights reserved.

Keywords: Automaticity; Consciousness; Attention; Semantic priming; Negative Priming; Word processing

1. Introduction

When confronted with printed words, skilled readers have the subjective impression that reading is an automatic process that does not requires attentional control or eﬀort. For decades this

* Corresponding author. Fax: +44 1248 38 2599. E-mail address: [email protected] (B. Valde´s).

1053-8100/$ - see front matter 2004 Elsevier Inc. All rights reserved. doi:10.1016/j.concog.2004.08.001 B. Valde´s et al. / Consciousness and Cognition 14 (2005) 278–295 279 idea has guided the research on word recognition (see Rayner, Foorman, Perfetti, Pesetsky, & Seidenberg, 2001, for a recent review) and has served to explain some experimental phenomena such as Stroop interference (Stroop, 1935; see also MacLeod, 1991, for a review) and semantic priming (Neely, 1991). There is evidence that words are processed up to semantic levels even though participants are not instructed to attend to them (Fuentes, Carmona, Agis, & Catena, 1994), or after attending to a non-semantic, physical dimension of the word (i.e., the ink colour) instead of the meaning (MacLeod, 1991, 1992). Processing of words is assumed to proceed without explicit intention but also without consciousness. Merely presenting words either under a subjective conscious threshold (Marcel, 1983) or under an objective one (Dehaene et al., 1998; Naccache & Dehaene, 2001) triggers a processing stream that cannot be prevented. The complete processing of words involves the processing of multiple dimensions or levels (McClelland & Rumelhart, 1981; Seidenberg & McClelland, 1989): a letter level, at which features are integrated to form the letters that compose a particular word; an orthographic level, at which letters are integrated to form orthographic patterns; a lexical level, at which the orthography of the word is activated; and a semantic level, at which the meaning of the word is accessed (Bentin, Mouchetant-Rostaing, Giard, Echallier, & Pernier, 1999). Event-related potentials and cerebral blood flow studies (Posner, Abdullaev, McCandliss, & Sereno, 1999; Posner & Petersen, 1990) have suggested that these levels are reached following a clear sequence. These stages of processing are commonly believed to occur in a bottom-up manner that proceeds automatically (Neely, 1991). Despite such automaticity, recent studies have suggested that both unattended and unconscious information can be controlled (Carr & Dagenbach, 1990; Dagenbach, Carr, & Wilhelmsen, 1989; Tzelgov, Henik, & Berger, 1992). To test the automaticity of word processing, several researchers have modified the traditional procedure of semantic priming by manipulating the level of representation at which attention is directed to during the prime display. The effect obtained with this procedure is known as Prime-Task Effect (Marı´-Beffa, Fuentes, Catena, & Houghton, 2000). In traditional semantic priming experiments, pairs of semantically related and unrelated words are presented in a sequen- tial manner. Participants are instructed to perform a task that demands explicit awareness of the meaning of the word (i.e., lexical decision, categorization, naming; see Neely, 1991 for a review). This task can be performed, or not, in the first word (prime) and the effect is measured in the reaction time to the second word (probe) task. It is assumed that the presentation of the first word produces the activation of its internal representation in memory, sending also activation to the representations of those words that are more closely associated with it. Thus, when an associated word appears as a probe stimulus, the previous activation of its representation due to the presence of the prime related word facilitates any response to it. In Prime-Task effect experiments the most common procedure is to compare the semantic priming effect, when participants are instructed to perform a lower level task on prime display (i.e. letter search), with another condition in which a higher or deeper level task is required (e.g. naming, lexical decision, categorisation, etc.). In both cases, participants generally perform a lexical decision task on the probe word. It has been shown that if the prime-task requires attention to be allocated to a lower level of analysis, like in a letter search task, then the semantic priming effect is reduced (Chiappe, Smith, & Besner, 1996; Henik, Friedrich, & Kellogg, 1983; Henik, Friedrich, Tzelgov, & Tramer, 1994; Kaye & Brown, 1985; Parkin, 1979; Smith, 1979; Smith, Theodor, & Franklin, 1983; Stolz & Besner, 1996). These results seem to challenge the idea of automaticity 280 B. Valde´s et al. / Consciousness and Cognition 14 (2005) 278–295 of word processing since they may suggest that the orientation of attention to a deep level of representation is necessary for the processing of meaning. Although there are some disagreements in the theoretical explanation of this effect, most authors assume that the allocation of attention to a low level feature impairs or interrupts the flow of processing to further stages. For example, Henik et al. (1994) suggested that dedicating all the processing resources to the low level features could exert this kind of attentional control. As a result, there are not enough resources left to activate semantic properties, and semantic priming is reduced or eliminated. Alternatively, the lack of semantic processing could also be modelled by blocking the feedback loops between lexical and semantic levels in a neural network, as attention is oriented to lower levels (Stolz & Besner, 1996). In addition, Duscherer and Holender (2002) claim that semantic processing requires the awareness of the meaning of the prime word. Thus, the reduction of semantic priming when attention is oriented to low level features would be the logical consequence of deploying awareness away from the semantic level. In any case, all these theoretical accounts assume that semantic processing can be interrupted before it is completed if attention is not directed to a semantic level. However, using this basic paradigm, the results are not always consistent. One of the patterns of results most problematic, for the ‘‘lack of semantic processing’’ accounts, is that some studies have shown a negative semantic priming effect when a letter search task is performed on the prime display. If semantic processing was never completed, then no semantic effect at all, positive or negative, would be expected. The presence of a negative semantic priming effect suggests that the control mechanism responsible for the reduction of positive semantic priming may act once the semantic representations have been already processed, bringing down their level of activation, even below resting levels, in order to better control the goal of the task (Catena, Fuentes, & Tu- dela, 2002; Hoffman & MacMillan, 1985; Marı´-Beffa et al., 2000; Tipper, Weaver, & Houghton, 1994). Orienting attention to a low level of processing probably does not block the further processing of the semantic attributes of the prime. Rather, the prime word is automatically fully processed, but those dimensions that are not relevant for the task have to be inhibited to prevent them from reaching the control of the response (Marı´-Beffa et al., 2000). Interestingly, most models incorporating an inhibitory mechanism (see Tipper, 2001 for a review) assume that the development of inhibition requires certain time to be effective. Supporting this idea, Yee (1991) has found positive priming when prime-probe onset asynchrony (SOA) was 500 ms, but negative semantic priming when the SOA was increased to 600 ms. Indeed, some models (Houghton & Tipper, 1994; Houghton, Tipper, Weaver, & Shore, 1996) assume that inhibition cannot develop until the offset of the stimuli. Here, we addressed this issue in two experiments displaying words for a very short time (25 ms), and increasing the prime-response to probe interval in order to allow the development of inhibition of the prime words. A second line of evidence favouring the automaticity of semantic processing from words comes from masking experiments where the prime display is presented under the conscious threshold. In these experiments the prime stimuli were presented during a brief period of time. To avoid participants becoming aware of them, prime stimuli were followed and/or preceded by a pattern mask. The probe was presented after a blank interval. Typically, the response to a word that is preceded by another semantically related word is facilitated in comparison to an unrelated word condition (Marcel, 1983). There is now abundant evidence supporting the idea that the prime word does not need to be consciously processed to obtain semantic priming effects (Abrams, Klinger, & Greenwald, 2002; B. Valde´s et al. / Consciousness and Cognition 14 (2005) 278–295 281

Brown & Hagoort, 1993; Dehaene et al., 1998; DellÕAcqua & Grainger, 1999; Draine & Green- wald, 1998; Greenwald, Klinger, & Liu, 1989; Kemp-Wheeler & Hill, 1992; Klinger, Burton, & Pitts, 2000; Naccache & Dehaene, 2001). It seems, at this point in our review of the literature, that neither attention nor consciousness is necessary for the complete processing of words. But can this unconscious or unattended information be controlled? Previous studies investigating this question suggest that unconscious and unattended information are affected by the same underlying mechanisms (Merikle & Joordens, 1997). Furthermore, Dagenbach et al. (1989) have demonstrated that the effect of an unconsciously processed word on a subsequent related target is affected also by the goals of the task. Then, if a word is presented under a conscious threshold and performance demands a superficial analysis of its characteristics, a reduced or absent semantic priming effect is observed on a related target. Nev- ertheless, if a high level of analysis is required negative semantic priming can be observed. Con- trary to those effects occurring with consciously processed words, Dagenbach et al. (1989) obtained the opposite pattern of results. The authors explained this effect as evidence of a ‘‘centre-surround’’ attentional mechanism that needs to suppress those active representations that may compete for the response in order to highlight the properties of the stimulus that are relevant for the task. In this case, due to the automatic spreading of activation, active and competing related words have to be inhibited. As a result, negative semantic priming is observed on a subsequent task on those words. The existence of unconscious negative semantic priming may suggest that, similarly to what happens with unattended information, unconscious information can also be controlled. Nevertheless, the question remains, is it the same control mechanism underlying all of these effects? Our rationale for the current study is that a stronger test of non-automaticity of word processing can be obtained in conditions where neither attention nor consciousness are expected to be devoted to word meaning. Thus, stronger evidence favouring the automaticity principle will be obtained if non-attended and non-conscious words are found to prime the processing of related probes. In this paper, we compare semantic priming effects produced by attended conscious information, unattended conscious information, attended unconscious information, and unattended unconscious information. We assume that even when the prime words are masked, attention can be directed to them because we warned participants that a word should be displayed before the mask. Our prediction is that, if attention and consciousness have a common underlying mechanism, then unconscious and unattended information will be controlled in the same way depending on the goal of the task.

2. Experiment 1

In this experiment, we manipulated the nature of the prime task and the awareness of the prime stimuli. Participants were presented with a prime display composed of a single stimulus followed by a probe display containing a single stimulus. In one block of trials participants had to indicate whether a pre-designated target letter was a component of the prime word or not (Letter search task). As in previous prime-task studies we assume that the completion of this task requires attention to be allocated to a low level of analysis (letter level). In another block of trials participants had to indicate if the prime stimulus was a word or not (a lexical decision task). We assumed that 282 B. Valde´s et al. / Consciousness and Cognition 14 (2005) 278–295 the lexical decision demanded a deep (lexical-semantic) level of processing. Any effects on the processing of related probes in the letter search block would support the idea of automaticity of semantic processing. Furthermore, the direction of this effect may indicate the action of a control mechanism upon it. To facilitate the action of a possible mechanism of control we simply allowed some preparation for the prime-task by presenting the target letter in advance. If this control mechanism blocks the higher processing of words, a reduction of positive priming will be observed. But, if meaning has been fully processed and causes any interference with the task, we ex- pect to find evidence of its inhibition in the related probes task. When primes are displayed below the conscious threshold, the predicted pattern of priming is rather imprecise, as no references were found in the literature regarding the effect of allocating attention to a low-level of processing with masked presentations. In any case, any inhibitory action would depend on the level of interference of semantic properties with the task. On the other hand, it could be predicted that the level of activation reached by masked words might not be strong enough to interfere with the task, and therefore neither negative nor positive priming would be observed.

2.1. Method

2.1.1. Participants Twenty-two students of the University of Granada, aged between 18 and 45-years-old, participated in the experiment and received course credit for their participation. All of them were native Spanish speakers with normal or corrected-to-normal vision.

2.1.2. Stimuli and materials Stimuli consisted of 180 (4–8 letter, 1–3 syllabi) Spanish word-pairs (Mean Associative Strength: 28.28), extracted from the Spanish word database of Soto, Sebastian, Garcıá, and Del Amo (1982). The 180 pairs of related words were divided in to three different lists (A–C) of 60 related pairs of words in each. The word-pairs of each list were then mixed to construct three different sets of stimuli with three conditions in each one: related (60 trials), unrelated (60 trials), and non-word (60 trials). The resulting sets were counterbalanced across subjects. In this way, all the word-pairs were presented in all conditions across subjects. For example, if BOCA (mouth) and LENGUA (tongue) appeared related in one set, they were separated to appear as unrelated in another set (MESA-LENGUA, table-tongue). The non-word condition was created by chang- ing one letter in order to make it orthographically correct, but with no meaning in Spanish, for example, MESA (table) was changed to MEPA (tatle). For masked conditions, the mask consisted of an array of capital letters of the same length as its respective prime word (i.e., GTRD). Stimuli were displayed in white on a black background. For the visual search task, the target letter was presented at the centre of the display at fixation. In half of trials the letter was present in the prime array (for positive visual search), and the other half absent (for negative visual search). In masked trials, the letter was contained in the mask in the same position as in the masked prime-word. For probe displays a ‘‘+’’ was used as a fixation point and a lexical decision was required. Thus, in visual search trials, participants had to switch between a letter search task (to the prime) and a lexical decision task (to the probe). An IBM compatible personal computer was used to display the stimuli (via a S-VGA monitor 800 · 600), and to record responses using a custom written program. The monitor was located B. Valde´s et al. / Consciousness and Cognition 14 (2005) 278–295 283

60 cm in front of the participant. All participants were required to use one hand to respond to the prime task and the other hand for the probe task. Hand responses were counterbalanced across subjects. The ‘‘C’’ and ‘‘V’’ keys from the keyboard were assigned to the left hand and the ‘‘N’’ and ‘‘M’’ keys were assigned to the right hand. The ‘‘YES’’ or ‘‘NO’’ mapping of the response keys were counterbalanced across subjects.

2.1.3. Design and procedure A 2 (Task: letter search, lexical decision) · 2 (Masking: masked, unmasked) · 2 (Relatedness: related, unrelated) within subjects factorial design was used. The factor Task was manipulated between blocks while the other two factors were manipulated within blocks. Within the visual search block, half of the trials contained a positive search and the other half a negative search. In the Visual Search literature it has being proposed that negative and positive trials could be completed using different strategies (Chun & Wolfe, 1996). Therefore, for the analysis of results, Positive and Negative trials were treated as separate levels of the Task factor. It is important to indicate that the non-word condition was used only to induce the lexical decision task and was not included in the analysis. The prime task was counterbalanced across subjects: half of the subjects performed first the Visual Search task and then the Lexical decision, and the other half, the reverse order. Each pair of words was presented masked and unmasked in a random order making a total of 360 trials per block, (180 masked and 180 unmasked: 60 related, 60 unrelated, and 60 non-words for each mask condition). Each block was preceded by a practice block of 48 trials. To obtain masked presentations with an objective threshold criterion, the parameters employed were based on a previous pilot experiment with a different group of participants from those who participated in the current study (Catena, Valdes, & Fuentes, submitted). In this experiment, each trial started with a fixation point presented at the centre of the visual display for 500 ms. This was followed by a sequence of two stimuli presented at the centre of the display: a word (BARBA, beard) or a non-word (BARTA, beald) was followed by a 70 ms pattern mask. The interval between stimuli and mask onsets (SOA) was randomly selected in each trial from one of the following pool: 13.39, 26.78, 40.17, 53.56, 107.12, and 187.6 ms. Each stimulus (words and pseudo- words) was presented once in each SOA condition. Participants were asked to press a key if the stimulus was a word and another key if was a non-word (lexical decision task). Analysis of discrimination signal detection theory index (d0) showed that under a 40.17 ms SOA d0 was not different from zero (see Table 1), indicating that subjects were unable to discriminate between words and non-words when the two shortest SOAs were used. Therefore, for all the masking conditions of Experiments 1 and 2 a SOA of 25ms was employed. In Experiment 1, each trial started with a letter presented in the centre of the visual display, and displayed for 250 ms, that served as fixation (lexical decision block) or indicated the target to

Table 1 Experimental measure of word awareness Prime duration (ms) 13.36 26.78 40.17 53.56 66.95 107.12 d0 0.042 0.317 1.033* 1.692* 2.605* 2.769* SD 0.293 0.574 0.699 0.698 0.766 0.808 Asterisks indicate that discrimination performance began to deviate significantly from zero (p < 0.025). 284 B. Valde´s et al. / Consciousness and Cognition 14 (2005) 278–295 search for in the prime display (visual search block). After a blank interval of 10 ms the prime display was presented for 25 ms. In masked trials (M), immediately after the prime word, a pattern mask was presented for 70 ms. The same interval was blank in unmasked trials (UM). The first response (prime task) was required within 1500 ms. Participants had to indicate whether the target letter was in the prime display (letter search) or whether a word was presented in the prime display (lexical decision), depending on the block of trials. An inter response-stimuli interval was fixed on 250 ms. After this period, a ‘‘+’’ sign was presented, in the centre of the display for 250 ms, which acted as a fixation point for the probe stimuli. After a further 10 ms, the probe display appeared for 25 ms. Participants were required to respond within 1500 ms of the presentation of the probe by indicating whether the probe was a word or not (see Fig. 1). There were separate sets of written instructions for each block (visual search and lexical decision). Participants sat in front of the computer monitor and the experimenter provided further explanations after the participants fully read the instructions. Participants were told that a mask could follow some words, though the response should be based on the conscious stimulus. This meant that in masked conditions the response should be based on the mask. With this procedure it is guarantied that accuracy would be similar in both masked and unmasked conditions. In both blocks a lexical decision was required for probe displays. In the continuous presentation of trials, participants could distinguish between prime and probe displays because of the different cues presented at fixation. In the case of prime displays, the letter appearing at fixation served both as a fixation point and as a cue indicating the letter to search for next. For probe displays the cross ‘‘+’’ was used for all the trials and served both as a fixation point and as a reminder for the lexical decision task happening next. This arrangement was especially informative for the Visual Search block because in the Lexical Decision block only lexical decisions were required for both prime

Fig. 1. Stimuli sequence in masked and unmasked conditions of Experiment 1. B. Valde´s et al. / Consciousness and Cognition 14 (2005) 278–295 285 and probe displays. At the beginning of each block the participants performed 48 practice trials under the supervision of the researcher. At the end of the ﬁrst block, the researcher explained the instructions for the second block, highlighting the new task to perform with the prime. The response keys were identical for both blocks. After every 120 trials there was a short rest period in each block

2.2. Results

Separate analyses were performed for the RT and errors data for prime and probe tasks responses. Two subjects were discarded due to the corruption of their data ﬁles.

2.2.1. Prime task Mean reaction times of correct responses were submitted to a two way 3 · 2 repeated measures analysis of variance (ANOVA) for the factors Task (PVS, NVS, and LD) and Masking (M and UM). The analysis showed a significant effect for the Task · Masking interaction, F(2,38) = 27.78, MSE = 958.55, p < .01, and also a main effect of Task F(2,38) = 23.84, MSE = 5382.93, p < .01 (See Table 2). The simple effects analysis of the two-way interaction showed significant effects of Task in both masked, F(2,38) = 36.98, MSE = 3535.34, p < .01, and unmasked trials, F(2,38) = 8.62, MSE = 2806.13, p < .01, but no effect of Masking factor on any task. Post-hoc LSD analysis indicated that in unmasked conditions Negative Visual

Table 2 Mean reaction time (in milliseconds) and error rates (%) for prime responses at masked and unmasked trials of Experiments 1 and 2 Task Unmasked Masked Experiment 1 PVS RT 821 844 % Error 14.4 14.7 NVS RT 862 857 % Error 15.7 14.2 LD RT 789 761 % Error 19.0 19 Experiment 2 PVS RT 939 969 % Error 28.5 29.3 NVS RT 1029 1012 % Error 28.8 26.7 LD RT 895 730 % Error 19.3 19.2 Note. PVS, Positive Visual Search; NVS, Negative Visual Search; LD, Lexical Decision. 286 B. Valde´s et al. / Consciousness and Cognition 14 (2005) 278–295

Search responses were significantly slower that in the other two tasks, and that Lexical Decision responses were faster than Positive Visual Search responses. On the other hand, in masked trials, Lexical Decision responses were significantly faster than in the other two tasks (See Table 2). The same 3 · 2 (Task · Masking) repeated measures analysis of variance on percentage of errors showed only a significant main effect of Task F(2,38) = 14.36, MSE = 17.00, p < .01. Post hoc LSD test showed that there were more errors in Lexical Decision than in Positive and Neg- ative Visual Search.

2.2.2. Probe task: Prime-task effect Mean correct probe reaction times greater than 200 ms and less than 1500 ms were computed for each participant and condition. Less than a 1% of trials were removed using this cut-off. Trials with a wrong response to the prime were excluded from analysis. Table 3 shows the mean reaction times and percentage of errors for lexical decisions at 18 target conditions. Data were submitted to a3· 2 · 2 within subjects ANOVA, for the factors Task (Positive Search, Negative Search, and Lexical Decision), Masking (Masked and Unmasked) and Relatedness (Related and Unrelated). The analysis showed a reliable Task by Masking interaction, F(2,38) = 5.09, MSE = 1232.25, p < .01, and Task by Masking by Relatedness interaction, F(2,38) = 8.52, MSE = 1004.97, p < .01. The simple effects analysis of the three-way interaction showed significant effects of

Table 3 Mean reaction time (in milliseconds) and error rates (%) for target responses at all experimental conditions of Experiments 1 and 2 Task Unmasked Masked R UR NW UR-R R UR NW UR-R Experiment 1 PVS RT 699 681 870 18* 671 691 850 +20* % Error 2.8 4.4 22 +1.6 3.7 5.1 21.6 +1.4 NVS RT 713 716 880 +3 703 690 885 13 % Error 6.9 9.9 18.9 +3 6.3 7 21.4 +.7 LD RT 663 690 883 +27* 701 685 903 16* % Error 7.5 7.7 24.8 +.2 8.7 10.8 24 +2.1 Experiment 2 PVS RT 687 690 911 +3 685 720 913 +35* % Error 2.4 3.2 23.2 +.8 3.2 3.5 20.6 +.3 NVS RT 728 727 950 1 708 710 927 +2 % Error 7.2 9.6 18.3 +2.4 6.6 9.8 19.9 +3.2 LD RT 648 669 906 +21* 674 675 934 +1 % Error 1.9 2.9 32 +1 4.2 10.5 27.7 +6.3 Note. PVS, positive visual search; NVS, negative visual search; LD, lexical decision; R, related; UR, unrelated; NW, non-word; UR-R, amount of priming. Asterisk indicates p < .05 significance level. B. Valde´s et al. / Consciousness and Cognition 14 (2005) 278–295 287 relatedness both in Positive Visual Search Unmasked, F(1,19) = 7.27, MSE = 448.03, p < .05 (the Related condition was slower than the unrelated one), and in Lexical Decision, for both masked [F(1,19) = 9.03, MSE = 843.38, p < .05] (the Related condition was slower than the Unrelated one) and unmasked conditions, F(1,19) = 4.65, MSE = 543.42, p < .05 (the Related condition was faster than the Unrelated one) (see Table 3). No reliable effects were found on Negative Visual Search conditions. Despite no significant effect being found for the Positive Visual Search Masked condition (when using a specific error term for the analysis, p < .08) a positive priming effect was observed and clearly contrasts with the significant negative priming obtained in the unmasked condition. However, when we considered the global error from the appropriate interaction as the error term for that contrast, this positive priming effect of 20 ms reached significance (F(1,19) = 7.77, MSE = 506.71, p < .05). A3· 2 · 2 ANOVA (Task · Masking · Relatedness) of error percentages showed no significant effects of Task · Masking · Relatedness interaction, but did for the Task by Masking interaction, F(2,38) = 5.76, MSE = 20.63, p < .05, and the main effect of Task, F(2,38) = 5.02, MSE = 81.50, p < .05. Simple effects analysis of the Task by Masking interaction showed that more errors were committed in the masked than in the unmasked condition in Negative Visual Search, F(1,19) = 5.60, MSE = 10.62, p < .05, and in Lexical Decision, F(1,19) = 6.26, MSE = 31.67, p < .05. Also, more errors were found in Negative Visual Search than in Positive Visual Search both in the unmasked, F(1,19) = 13.33, MSE = 34.20, p < .05, and the masked condition, F(1,19) = 6.19, MSE = 16.35, p < .05. Finally, more errors were committed in the Lexical Decision than in the Positive Visual Search in the masked condition, F(1,19) = 8.72, MSE = 66.86, p < .05.

2.3. Discussion

The present results show that the magnitude and direction of semantic priming may depend on both, consciousness and the level of processing where attention is allocated. We have introduced an extreme test of the non-automaticity of meaning processing, in order to determine whether attention and/or consciousness are necessary to fully process a word. Regarding the standard unmasked conditions, we replicated the classical positive semantic priming effect when a lexical decision is performed both in prime and probe displays (Henik et al., 1994; Neely, 1991). However, when a visual letter search is performed and attention is directed to a low level analysis, this facilitation is inverted obtaining a negative semantic priming effect instead of the typical reduction of positive priming observed in the standard prime task effect (Henik et al., 1994; Marı´-Beffa et al., 2000). The occurrence of negative priming supports the automaticity of semantic processing and the idea of an inhibitory mechanism that suppresses, or inhibits, those activations that interfere with the goal of the task (Houghton et al., 1996). In this case, as attention is allocated to the letter level, any semantic activation has to occur automatically and, as it interferes with the low level task, has to be inhibited. To fully understand the present pattern of results, mainly in the lexical decision conditions, it is important to acknowledge that the high error rates can be due, first, to the very small presentation time (25 ms), and, second, to the fact that subjects can be still processing the search letter when the prime display is presented. Although semantic priming did not reach significance following negative search, the opposite pattern deserves some consideration. The positive search is self-terminated, because it finishes 288 B. Valde´s et al. / Consciousness and Cognition 14 (2005) 278–295 when the participant finds the target letter. In the negative search, however, the participant needs to exhaust all the possibilities before reaching the ‘‘no’’ response as can be confirmed by the slower reaction times upon the prime task. According with The Activation Threshold Mechanism, proposed by Chun and Wolfe ‘‘Unsuccessful searches are terminated when no remaining items have probabilities above a termination threshold’’ (Chun & Wolfe, 1996, p. 71). Possibly, in this experiment, due to the high error rates the activation threshold is low and search is terminated after using the word representation as a secondary source of information about the presence of a letter. Thus, the pattern of results resembles more the pattern showed in a high level prime task, such as lexical decision. In any case only positive search trials could be unambiguously used to claim that a low level of representation is used to complete the prime task. Considering the results obtained in the masked conditions, where prime words were presented below the conscious threshold, first, the masked priming effects are clearly opposite to the unmasked ones. When a lexical decision task is performed on prime displays, instead of a typical positive semantic priming effect (Marcel, 1983) we found a robust negative one (28 ms.) As suggested by Dagenbach et al. (1989) we interpret this data as the result of a ‘‘centre-surround’’ mechanism that according with the task-goal is trying to enhance the semantic properties of the prime display. Once, the prime display is present, this mechanism acts inhibiting the activation of semantic associates of the prime in order to increase the signal-to-noise ratio of the attended stimuli. On the other hand, and very interestingly, when a letter search task is performed upon the mask, the identification of the word is not required and no inhibition is observed. Then, we obtained automatic semantic priming in the absence of attention and consciousness. In summary, the results obtained in this experiment confirm the automaticity of semantic processing. Our results also support the idea of a control mechanism that may inhibit all the information that is interfering with the task-goal.

3. Experiment 2

The main aim of the second experiment was to determine if the lack of preparation for a task could inﬂuence the control mechanisms that are responsible for the negative priming observed in Experiment 1. The main idea was that the preparation for a task allows the development of the inhibitory processing because this requires some time to work eﬃciently (Houghton et al., 1996). In the present experiment both the letter to be searched for and the prime word were presented simultaneously. Thus, participants did not know in advance the target letter. If inhibition has no time to develop, then it is expected that negative priming will disappear in those conditions were it was obtained in Experiment 1.

3.1. Method

3.1.1. Participants Twenty two undergraduate students at the University of Granada, aged between 18 and 45 years, participated in the experiment and received course credit for their participation. All of them were native Spanish speakers with normal or corrected-to-normal vision. B. Valde´s et al. / Consciousness and Cognition 14 (2005) 278–295 289

Fig. 2. Stimuli sequence for Experiment 2.

3.1.2. Stimuli design and procedure The stimuli and visual parameters were identical to those employed in Experiment 1, except that the target letter of the letter search task was displayed simultaneously with the prime word, just above it. A cross (+) was now presented at fixation before each display. The experimental design and temporal parameters used in this experiment were identical to those used in Experi- ment 1. As previously mentioned, the only modification affected the prime display, where the letter to search for was presented simultaneously with the prime word but slightly above (0.5 cm) and was always visible. The trial sequence in this case was as follows: Each trail started with a ‘‘+’’ at fixation for 250 ms. Then, the prime display appeared after a 10 ms blank interval, (see Fig. 2). The prime display consisted of a single letter and a word below, both displayed at the centre of the screen. All other procedural details were as in Experiment 1.

3.2. Results

As in Experiment 1, two separate analyses on the RT data and on the error data were performed for prime and probe tasks responses. Two subjects were discarded due to the corruption of their data ﬁles. 290 B. Valde´s et al. / Consciousness and Cognition 14 (2005) 278–295

3.2.1. Prime task Mean reaction times of correct responses were submitted to a two way 3 · 2 repeated measures analysis of variance (ANOVA) for the factors Task (PVS, NVS, and LD) and Masking (M and UM). The analysis showed a significant effect for Task · Masking interaction, F(2,38) = 8.09, MSE = 2806.13, p < .01, and a main effect of the factor Task F(2,38) = 90.07, MSE = 7965.80, p < .01 (see Table 2). These differences across tasks were found for both unmasked F(2,38) = 55.18, MSE = 5060.46, p < .01, and masked F(2,38) = 80.70, MSE = 5711.46, p < .01, trials. Post hoc LSD analysis indicates that once again, in Lexical Decision task responses were significantly faster than in the other two tasks both in unmasked and masked trials. Also, Positive Visual Search responses were faster than negative ones. Responses to the masks were slower than to unmasked words in Positive Visual Search, but faster in Lexical Decision. The 3 · 2 (Task · Masking) repeated measures analysis of variance on percentage of errors showed significant effects of Task only, F(2,38) = 28.49, MSE = 38.09, p < .01. Post hoc LSD test indicated that there were more errors in Positive and Negative visual search than in Lexical Decision.

3.2.2. Probe task: The prime-task effect Mean reaction times of correct responses longer than 200 ms and shorter than 1500 ms (see Table 3) were submitted to a three-way 3 · 2 · 2 repeated measures analysis of variance (ANOVA) for the factors Task (PVS, NVS, and LD) Masking (M and UM) and Relatedness (R, Related; UR, Unre- lated). Only trials with a correct response to the prime were included in the analysis. The analysis showed a significant Task by Masking, F(2,38) = 4.82, MSE = 1605.63, p < .05, and Task · Mask- ing · Relatedness interaction, F(2,38) = 3.17, MSE = 1045.42, p = .053. Also the main effects of Task and Relatedness reached significance, F(2,38) = 4.88, MSE = 11077.64, and F(1,19) = 7.18, MSE = 894.89, respectively. Detailed analysis of the three-way interaction demonstrated a significant positive priming effect in the unmasked lexical decision (21 ms, F(1,19) = 8.12, MSE = 524.86, p < .05) and the masked positive visual search conditions (35 ms, F(1,19) = 7.14, MSE = 1754.02, p < .05). No significant priming effects were found in the other conditions (all FÕs < 1). The 3 · 2 · 2 (Task · Masking · Relatedness) repeated measures analysis of variance on percentage of errors showed reliable main effects of Task, F(2,38) = 26.05, MSE = 21.12, p < .01 (percentages were 3.1, 7.9, and 3.5, respectively for Positive Visual Search, Negative Visual Search, and Lexical Decision), and Masking, F(1,19) = 4,86, MSE = 9.09, p < .05 (percentages were 4.4 and 5.2, respectively for Unmasked and Masked condition). Also the Task by Masking interaction reached significance, F(2,38) = 3.78, MSE = 7.94, p < .05. Simple effects analysis of this interaction showed that the percentage of errors was greater in masked than in unmasked conditions only in the Lexical Decision task, F(1,19) = 18.54, MSE = 5.22, p < .01. Also, a greater percentage of errors was found in Negative Visual Search than in Lexical Decision and Positive Visual Search, both in unmasked and masked conditions (min F = 17.74, p < .01).

3.3. Discussion

In this experiment, we have obtained three important results. First, consistent with previous work described in prime-task effect literature, we have replicated the reduction of semantic priming in unmasked visual search trials: the traditional prime-task effect. Second, in spite of the dif- B. Valde´s et al. / Consciousness and Cognition 14 (2005) 278–295 291 ference between Experiment 1 and 2, the magnitude of the positive semantic priming found in masked positive letter search trials is consistent. Once again, as in Experiment 1 we observed semantic priming independent of consciousness and attention. And finally, negative priming effects present in experiment 1 completely disappeared. These results show that the prime task effect can be modulated by the pre-cueing of the search letter. Reduction of semantic priming is mainly observed when there is no time to prepare for the letter search. When this time is available, negative priming emerges. This pattern of results cannot be fully predicted by a theory that solely assumes that semantic processing can be interrupted at early stages of word processing. If the interruption of semantic processing is still a plausible control mechanism, it seems to work only when the letter to search appears simultaneously with the target. When there is more time to prepare for the letter search, inhibition can be observed (see Section 4). As we indicated in the discussion section of Experiment 1, the high error rates to the prime in lexical decision can be explained considering the amount of time the prime is displayed, and also, that attention can be captured by the letter above the prime. To summarize, there are two main conclusions to be drawn from this experiment. Lack of time to prepare for the next task affects inhibitory mechanisms of control, while excitatory mechanisms remain intact. And second, this mechanism of control can operate upon unattended and unconscious representations. In the next section, we will further discuss the parallelism between attention and consciousness in the context of the prime task effect.

4. General discussion

The study presented here has extremely tested the automaticity theory of word processing. To ensure this, it was necessary to obtain evidence of semantic processing in three circumstances. First, when attention was allocated to a low level of processing (word letters instead of meaning). Second, when words were presented below an objective conscious threshold, and third, and even stricter, a condition in which the previous two conditions were combined, resulting in no consciousness and no attention directed to word meaning. In order to achieve these goals we used a Prime-task paradigm in combination with masking procedures. Comparison between Experi- ment 1 and 2 helps clarify some inconsistencies across Prime-task studies and also to explain some aspects about the cognitive control in word processing. The pattern of results obtained in the present study contributes in several ways to the debate about the automaticity of semantic processing. First, regarding the Unmasked Letter Search Con- ditions, in Experiment 2 we replicate previous studies (Chiappe et al., 1996; Henik et al., 1983; Henik et al., 1994; Kaye & Brown, 1985; Parkin, 1979; Smith, 1979; Smith et al., 1983; Stolz & Besner, 1996) which have shown a reduction of semantic priming effect when a letter search task is performed on the prime display. However, in Experiment 1, when the target letter was presented 250 ms before the prime word, we found significant negative priming. This result indicates that allocation of attention to the letter levels does not prevent the processing of word meaning, and instead, is completed automatically. Two main explanations of the prime-task effect have been put forward. First, it has been proposed that attention interrupts the higher processing of a word if it is directed to a low level of 292 B. Valde´s et al. / Consciousness and Cognition 14 (2005) 278–295 processing (Henik et al., 1983; Henik et al., 1994; Stolz & Besner, 1996). Second, it has been also proposed that semantic representation of a word must be inhibited depending on its level of interference with the goal task (Marı´-Beffa et al., 2000). The present study supports the second idea. If semantic processing were interrupted at the letter level, no priming at all should be observed. Rather, it appears that meaning has been processed, but it interferes with the goal of the task, and therefore it has to be inhibited. Comparisons between Experiment 1 and 2 indicate that preparation time is a relevant factor for obtaining negative priming. The lack of negative priming fre- quently observed in the literature may be accounted for this factor. We assume that the presentation of the letter in advance helps to establish an attentional task-set which includes excitatory and inhibitory control mechanisms (Marı´-Beffa et al., 2000; Milliken, Joordens, Merikle, & Seiffert, 1998; Tipper et al., 1994). Therefore, by increasing the time participants had to prepare for the task, we allowed a more effective inhibition of those properties of the word that could interfere with the task-goal (Tipper, 2001; Tipper et al., 1994). We are not assuming that inhibition starts before the onset of the stimulus, but that it is more effective if enough time is given for the mechanism of control to prepare. The results of the present study do not allow us to discern the way this preparation proceeds. However, it can be assumed, for example, that some kind of orientation to the processing level where inhibition has to operate can be done in advance. Positive semantic priming obtained in masked letter search trials confirmed the automaticity of semantic processing even in these extreme conditions (no attention to meaning plus no word consciousness). It appears that the meaning of the masked word is automatically activated but does not interfere with the task. We assume that interference occurs when activation levels of a distracter are strong enough to compete for the response. In contrast with the positive priming observed when subjects searched for a letter in the prime- task, when a lexical decision was required, negative priming (Experiment 1) and no priming at all (Experiment 2) was observed. This pattern of results can be explained by assuming the idea of a ‘‘center-surround’’ mechanism that, in order to pop-out the relevant properties for the task needs to inhibit those active representations that may compete for the response (Dagenbach et al., 1989) even if they are unconsciously activated. In Experiment 1 of the current study, the letter at fixation indicated that a prime (not probe) would be presented next. Although a lexical decision was performed in both cases, this discrimination is important because primes were either words or non- words (mask), while probes were either words or pseudo-words. Therefore, the completion of a lexical decision may ask for different strategies in prime versus probe displays. While it is clear how pre-cueing the letter search task can influence the emergence of negative semantic priming, it might be less clear how this pre-cueing can affect semantic priming from the Lexical Decision prime-task. In Experiment 1, there were different cues for the prime and the probe displays. A letter always signalled that a prime trial (containing probably a mask) would come next, and the probe display (that was always unmasked) was cued by a plus sign. In Exper- iment 2, all the displays were cued with a plus sign (‘‘+’’). The differential cueing from Experiment 1 not only affected the way participants performed the letter search prime-task, but also seems to have affected the execution of the lexical decision prime-task for masked trials. With differential cueing (Experiment 1), participants clearly know whether a mask might appear in the next display. This will help to prepare the operations of the ‘‘centre-sourround’’ mechanism, which is believed to be responsible for negative semantic priming in masked situations (Dagenbach et al., 1989). In Experiment 2, as the cue was the same for prime and probe displays, it was not possible B. Valde´s et al. / Consciousness and Cognition 14 (2005) 278–295 293 for the participants to predict whether a possible masked display was coming next, therefore making it more difficult for attention to be ready for a masked trial. This lack of prediction is reflected in the longer reaction times in the second experiment.1 And, because the control mechanisms have more time to prepare, more efficient inhibition (and negative priming) would be expected in the first experiment than in the second experiment. In summary, our results indicate that semantic properties of a word can be processed when words are presented under an objective threshold of awareness, and also when attention is not allocated to semantic but to low-level features of the word. We conclude that word processing is fully automatic. However, automatism should not imply that no control mechanism can operate. Our results indicate that a putative inhibitory like control mechanism (Posner & DiGirolamo, 1998; Posner & Snyder, 1975) is operating even when neither attention nor consciousness is directed to meaning. Therefore, we support the idea of a redefinition of automaticity as a process that occurs without intention or without conscious monitoring (see Tzelgov, 1997 for an extensive theoretical discussion). However, in no-attention and no-consciousness situations, inhibitory control mechanisms are working, as in attended and conscious situations, in order to allow participants to fulfil the task requirements. Words are processed automatically, but the destiny of their mental representations will depend on subjectÕs task-goals.

Acknowledgments

This study was supported by a Ph.D. grant from the Consejo Nacional de Ciencia y Tecnologıá (CONACyT), Me´xico (National Council of Science and Technology) to Berenice Valde´s Conroy, No.:110866/110994. This research was also partially supported by a project grant from Biotech- nology and Biological Sciences Research Council (BBSRC) to Dr. Paloma Marı´-Beffa (5/S16740) and by BBSRC Underwood Fund to Dr. Andre´s Catena and Dr. Paloma Marı´-Beffa. We thank Jason Lauder and three anonymous reviewers for constructive comments on earlier versions of the manuscript.

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