frings and wentura - negative priming with masked distractor-only prime trials - 2002¿

awareness in negative priming tasks 1

Running head: AWARENESS IN NEGATIVE PRIMING PARADIGMS

Negative priming with masked distractor-only prime trials: Awareness moderates Negative

Priming

Christian Frings & Dirk Wentura

Saarland University Christian Frings Saarland University Faculty of Behavioral Sciences Department of Psychology Building 1 P.O. Box 15 11 50 D-66041 Saarbrücken [email protected]

-------- Experimental Psychology, in press -----------


Abstract

The literature yields inconsistent evidence for negative priming (NP) following

masked distractor-only prime trials. We contrast two different hypotheses on the inconsistent

findings, one – which is most compatible with the temporal discrimination theory – that

relates the sign of priming effects to the absence vs. presence of prime awareness and one –

which is most compatible with the inhibition and episodic retrieval accounts – that relates the

sign of priming effects to the prime event being categorized as a to-be-attended vs. to-be-

ignored event. In two experiments it turned out that participants’ awareness of the masked

stimuli caused the different results (with participants being not aware of the primes showing

NP), whereas the factor ‘prime color = probe target color’ vs. ‘prime color = probe distractor

color’ (i.e., the prime contains the to-be-attended vs. the to-be-ignored signal) did not

moderate NP. These findings are discussed with regard to theories of negative priming and the

debate on conscious versus unconscious perception.


Negative priming with masked distractor-only prime trials: Awareness moderates Negative

Priming

Since its introduction by Dalrymple-Alford and Budayr (1966), Neill (1977), and

Tipper (1985), the Negative Priming (NP) phenomenon has been a widely researched topic in

cognitive psychology. The original finding was that responses to a previously ignored

stimulus were retarded if the same stimulus was subsequently repeated as a target. Usually,

this effect is demonstrated in selective attention tasks, where target stimuli are accompanied

by distractor-stimuli. Thus, if a stimulus is to be ignored in the first trial (the prime trial) and

then presented as the target in the consecutive trial (the probe; this condition is called the

ignored-repetition condition) responses are slower compared to a control condition with

unrepeated stimuli (i.e., the unrepeated condition). Despite extensive evidence in favor of the

NP-effect, the underlying mechanisms continue to be hotly debated today. The two most

popular theories about NP are the inhibition account (e.g., Tipper, 1985; Houghton & Tipper,

1994; Tipper, 2001) and the episodic retrieval account (e.g., Neill & Valdes, 1996). The

inhibition account focuses on active inhibition of the prime-distractor during the process of

selecting the prime target; inhibition is assessed by presenting prime distractors as probe-

targets in the consecutive trial. The episodic retrieval account highlights the ability of a

stimulus to retrieve its latest appearance: Thus, if a probe target retrieves its latest appearance

as the prime distractor, a do-not-response tag will hamper response generation.

Recently, Milliken, Joordens, Merikle, and Seifert (1998) developed an alternative

perspective on NP, the temporal discrimination theory. They assume a comparison process

that detects discontinuities or mismatches between the mental representation of the prime trial

and the perception of the probe trial. If the quality of match is high as in the case of the prime

target being identical to the probe target (i.e., the attended repetition condition of NP

experiments), no mismatch is detected and any response facilitation due to the fact that the

same stimulus was just processed before will lower response time (compared to the


unrepeated condition). If the quality of match is poor as in the case of the unrepeated

condition of NP experiments, a quick mismatch detection occurs, immediately starting a

process of generating a response to the probe target. If, however, the quality of match is

intermediate as in the case of the ignored repetition condition of NP experiments the

mismatch process needs more time to arrive at the final mismatch decision such that the

process of generating a response to the probe target is delayed compared to the unrepeated

condition, resulting in a NP-effect.

NP as a function of prime awareness

In this regard, one important finding was that NP even occurs after distractor-only

prime trials, that is, even without a selection process in the prime-trial (Milliken et al., 1998;

see also Milliken & Joordens, 1996). In an experimental series (Milliken et al. 1998, Exp. 2a-

2c & Exp. 3) a distractor was presented very briefly (33 ms) during the prime trial and was

masked by a forward and backward mask. Nevertheless, NP was observed when the probe

trial contained a distractor. These results fitted with predictions of temporal discrimination

theory: Probe targets could neither be identified as ‘old’ nor as ’new’ if they immediately

followed masked and briefly displayed distractors; thus, a delayed response to the probe target

will occur and cause NP. Furthermore, participants in Milliken et al.’s experiments stated that

they were not aware of the masked primes. Recently, Healy and Burt (2003) yielded further

evidence for this masked NP-effect. They found slower responses to targets in a Stroop-color

naming task if the same stimuli were – directly before the Stroop-display – briefly presented

and followed by a backward mask. These results are interesting because the findings of

Milliken et al. (1998) and Healy and Burt (2003) contrast findings of similar experiments by

Allport, Tipper and Chmiel (1985, Exp. 4 & 5). In these experiments Allport et al. (1985)

varied the SOA (stimulus onset asynchrony) of the prime display and backward mask. For

short SOAs participants of Allport and colleagues yielded a positive priming effect whereas

for long SOAs NP occurred. As in the experiments of Milliken and colleagues, participants


seemed not to be fully aware of the prime stimuli (their identify-accuracy of masked stimuli

was not better than chance). Allport et al. concluded that NP depends on selection of a target

against a distractor. Thus, if a prime display is presented only at short SOAs no NP will occur

because participants could not select a target against a distractor. Milliken et al., however,

argued that the masked distractors in their experiments can not be identified as ‘old’ or as

‘new’ because the quality of match of a masked distractor is ‘intermediate’ (see above). For a

new theoretical approach to NP it seems important to elaborate on this inconsistency1.

However, the literature yields even more puzzling findings for masked NP. Recently,

in an attempt to replicate the distractor-only NP effect Neill and Kahan (1999, Exp. 1a & Exp.

1b) reported inconsistent results with masked distractor-only-prime trials. In fact, in their

Experiment 1b they found – as one would expect from the broader literature on priming –

positive priming effects following distractor-only prime trials with masked distractors (this

result parallels the findings of Allport et al., 1985) . In contrast, in their Experiment 1a (which

was essentially the same as Experiment 1b) they replicated the findings of Milliken et al.

(1998). Neill and Kahan (1999, p. 306) noted post hoc that the participants´ awareness of the

masked primes might be the moderator of their inconsistent results: Awareness of the prime-

distractor might be a predictor of quality of match to the probe target.

However, neither Milliken and colleagues (1998) nor Neill and Kahan (1999) nor

Healy and Burt (2003) used sensitive procedures to measure participants´ awareness of the

prime distractors. Because this phenomenon is quite central for the temporal discrimination

theory, and because the NP literature needs further research to clarify these inconsistencies,

with Experiment 1 and 2 we tried to replicate NP following masked distractor-only prime

trials while using direct tests to measure participants´ awareness of the masked stimuli (see,

e.g., Greenwald, Klinger, & Schuh, 1995). Our direct test allows for a more conservative test

of participants’ awareness (see, e.g., Merikle, Smilek, & Eastwood, 2001). If Neil and Kahan

are correct with their post hoc argument, the number of participants being aware of the single


prime distractor will predict whether a negative, a null, or a positive priming effect will be

observed. Moreover, our direct test allows for a split of the sample with regard to the prime

distractors’ visibility.

NP as a function of prime status

There might be, however, a further argument to explain the diverging results of Neil

and Kahan’s (1998) Experiments 1a and 1b, ironically one that helps to bring the inhibition

account and episodic retrieval theory again into play. The prime distractors in their

experiments (as well as those of Milliken et al., 1998, and ours in Exp. 1) were of neutral

color (i.e., they neither matched the probe-target nor the probe-distractor in color). One can

argue that the prime distractor is therefore not specified as a to-be-ignored or a to-be-attended

object because color was used for target-distractor discrimination in the probe trial. The

inhibition account assumes that a to-be-ignored stimulus can be identified by the feature of,

e.g., color, location, temporal sequence etc. Thus, if the probe display contains color as the

differentiating feature, one can argue that the prime of neutral color is neither specified as a

stimulus that should be attended-to nor as one that should be ignored. Likewise, the episodic

retrieval theory assumes that distractors are marked by a do-not-response tag. Distractors of

the probe display, however, can only be identified by color. Thus, one can argue that a prime

of neutral color is neither specified as a stimulus that should be tagged nor as one that should

not be tagged. In both cases it is at the discretion of the participants to process the prime in

either the one way or the other.

Thus, both the inhibition account and the episodic retrieval theory predict that the

number of participants who treat the prime distractor as a to-be-attended object might

determine whether the NP effect turns into a null or even a positive priming effect. This

argument fits with the observation of Neill and Kahan that part of the sample of their

Experiment 1b (i.e., the one resulting in a positive priming effect) had “previously

participated in other experiments in which they were instructed to attempt to identify a


masked word” (p. 306). This experience might have lead to adopting the stance that the brief

flicker (i.e., the prime distractor) is a to-be-attended event. Moreover, this argument is also

compatible with regard to the procedure of Allport and colleagues (1985). In their

experiments participants’ individual thresholds for masked stimuli were surveyed before they

worked through the NP task. Therefore, participants were fully aware that masked stimuli

were presented, and they should try to identify them, that is, they handled them as to-be-

attended objects.

Thus, in Experiment 2, we varied the color of the prime distractor, such that it either

matched that of the probe target or that of the probe distractor. In the former case the prime

distractor carries the to-be-attended signal, in the latter case the to-be-ignored signal. Given

the backdrop of the inhibition and episodic retrieval accounts, we would predict positive

priming after prime distractors which match the probe target in color whereas negative

priming is predicted after prime distractors which match the color of the probe distractor.

Both accounts are not very specific about the role of awareness. Thus, if color match but not

awareness will be the dominant predictor for the sign of the priming effect, we can take that

as a piece of evidence for the inhibition and episodic retrieval accounts.

However, we should hasten to add that for two reasons the temporal discrimination

account is not incompatible to a dependency of the NP effect on color match. Firstly, one can

argue that the quality of match is higher in the case of a color match of prime and probe

target. However, because the theory assumes a curvilinear relationship of quality of match and

response times, the prediction is not clearly specified. Secondly, Milliken et al. (1998)

demonstrated that even for supraliminal distractor-only-prime trials a NP effect emerged if

participants were instructed to process clearly visible distractors as to-be-ignored-objects

whereas a positive priming effect emerged if participants were instructed to process them as

to-be-attended objects. Given this, the theory would be compatible with the finding of a

positive priming effect in the case of a color match and a NP effect in the case of a mismatch.


However, the temporal discrimination account would put more weight on awareness of the

prime (as a closer associate of quality of match) than on features that signal relevance or

irrelevance of the prime. In conclusion, finding a dependence of the sign of the priming effect

on awareness but not on color match would be most compatible to the temporal

discrimination account.

Experiment 1

Experiment 1 is primarily concerned with the replication of the masked distractor-only

NP effect while assessing participants’ awareness in a more controlled way. However, we

added a further condition. As mentioned above, a single visible prime distractor is not in itself

enough to predict positive priming effects. According to Milliken and colleagues (1998), the

absence of a strategic component seems to be important. Instructing their participants to

willingly ignore the prime distractors, they found NP-effects even if a single distractor

stimulus was clearly visible (i.e., it was presented for 200 ms without a mask; Exp. 4). Up to

now, masked and “strategic ignorance” NP effects have never been tested for in a single

experiment, using a within-participants design (nevertheless, it is argued that the same process

caused these NP-effects).

Method

Participants. Seventeen undergraduate students (13 women and 4 men) of the

University of Jena (aged 19 to 27; M = 23) participated either for partial course credits or

were paid an amount of four €.

Materials. The stimuli set comprised the following high-frequency German nouns:

Palme (palm), Perle (pearl), Pulver (powder), Diener (servant), Dosis (dose rate), Donner

(thunder), Bogen (bow), Buche (beech), Becher (cup),Teller (plate) , Tenor (tenor), Tunnel

(channel). The individual letters of the words had a size of 9 x 5 mm. Distractors in the probe

display were always presented in green color whereas probe targets were presented in red

color. Both words were presented in uppercase and at close quarters in the center of the


screen, one above the other. Half of the targets were presented above the distractor, the other

half below (see Design). The distractors of the prime display were always presented in black

color.

Design. Essentially, the design comprised two within-subjects factors: (1) presentation

modus of prime distractor (subliminal vs. supraliminal) and (2) prime condition (repeated vs.

unrepeated). Additionally, the positions of probe distractor and target were counterbalanced.

As a between-subjects factor sequence of presentation modus (subliminal presentation first vs.

second) was counterbalanced.

Procedure. All participants were tested individually. The experiment was conducted

on a standard PC with a standard monitor with a resolution of 800 x 600 pixels and a refresh

rate of 75 hz. The experiment was conducted with the Inquisit-software (inquisit 1.33) and a

Labtec head-set microphone. The participant started each trial by pressing the space bar.

Following the practice block, two blocks (one subliminal and one supraliminal) consisting of

120 trials each were presented (half the trials were repeated, half the trials were unrepeated).

Roughly following Milliken and colleagues (1998) the sequence of events for the subliminal

condition was as follows: First, a fixation marker was presented for 390 ms. Then the premask

consisting of 14 @-symbols was presented for 520 ms before it was overwritten by the prime

distractor. The prime distractor appeared for 39 ms before the postmask (consisting of 14 @-

symbols as well) was shown for 520 ms. Participants were instructed to focus their attention

on the location of these strings because they would indicate the position of the probe stimuli

while simultaneously the content of the symbols was irrelevant to them. On appearance of the

probe display, participants pronounced the red word as quickly and as accurately as possible

(naming task). The probe display lasted until participants responded to it or until 5000

milliseconds have passed by. In the supraliminal condition the prime distractor was not

masked and was presented for 300 ms before it was overwritten by a blank screen which

lasted for 520 ms. Most importantly, in the supraliminal condition participants were instructed


to willingly ignore the prime distractor. The experimenter coded the correctness of responses

of the participant in each trial via another computer.

For each trial, three different words were randomly chosen from the stimulus list and

were assigned the roles of prime distractor, probe target, and probe distractor. A stimulus was

never repeated in a subsequent trial and was not chosen again before all remaining stimuli of

the list were selected. Repeated trials were created by replacing the chosen prime distractor

with the probe target.

Following the 240 experimental trials, participants were told that the flicker (in the

subliminal condition) presented before the probe (i.e., the mask-distractor-mask sequence)

contained a word. They were instructed to work through 24 prime identification trials to

obtain a direct effect of prime awareness. During this block, each stimulus was presented

twice as a prime distractor, using the same parameters as before in the subliminal condition.

However, the probe display now contained only one word out of the stimulus list that was

either identical to the prime distractor or not. Participants had to decide by key-pressing

whether probe and prime matched (which was the case in half of the trials) or not.

Results

A significance level of α = .05 was chosen for all analyses throughout the text.

Prime awareness. With the data of the direct test, we computed the non-parametric

signal detection sensitivity index A’ (Pollack, 1970; see also Goschke & Kuhl, 1993) with hits

being correctly identified words and false alarms being incorrectly identified words.2 Mean A’

was M = .53 (SD = .12) and was not significantly different from 0.50, t(16) = 1.13, p = .28, ns.

Thus, on average, participants had no access to the lexical status of the prime. Additionally,

none of them showed a significant contingency between presentation (i.e., whether prime and

probe matched or matched not) and response (yes vs. no), all χ2 < 1.51, p > .22.

Negative Priming. Correct RTs for each participant and RTs that were above 200 ms

but below 1700 ms were included in the analysis. This procedure resulted in the elimination


of 3% of all trials (error rate was < 1% and hence we did not analyze errors). The between-

participants factor sequence of blocks showed neither a main effect nor an interaction with

priming, all Fs < 1.50, ns. The factor was therefore discarded in the following analyses. Mean

RTs are shown in Table 1. A 2 (presentation condition) x 2 (prime condition) ANOVA with

mean RT as the dependent variable yielded a significant main effect for prime condition,

F(1,16) = 9.92, p < .01. On average, participants were M = 8 ms (SD = 10 ms; d = .80) slower

following repeated prime distractors, thus indicating a significant NP effect. NP did not

depend on the prime distractor being presented subliminally or (to be ignored) supraliminally,

as is shown by the lack of an interaction effect of prime and presentation conditions, F(1,16)

= .09, p = .77, ns. (There was no main effect of presentation, F[1,16] < 1, ns.).

Discussion

The results clearly replicate the finding of Milliken and colleagues (1998) and are also

in line with the results of Experiment 1a of Neill and Kahan (1999), and Experiment 1 of

Healy and Burt (2003). Furthermore, the results are consistent with the suggestions of Neill

and Kahan (1999) who argued that their positive priming effect (found in their Exp. 1b with

masked priming) might be due to participants’ awareness of masked primes. Here, we found a

NP-effect with a proven absence of prime awareness for all participants. As an aside, the

results of this experiment lend support to the claim that the same mechanism is at work given

subliminal presentation conditions as well as given instructions to willingly ignore

supraliminally presented distractors (in the studies of Milliken and colleagues, 1998, this was

only varied between experiments). This strengthens the arguments raised by Milliken et al.

(1998) for a temporal discrimination theory on NP.

Of course, just because there were no participants being aware of the masked primes,

our results are not a clear test of the hypothesis that awareness moderates this NP-effect. One

further point should be noted. The overall reaction time seems to be higher than in the

experiments of Milliken et al. (1998). Thus, with Experiment 2, we decided to try to


conceptually replicate the masked NP-effect with modest modifications to Experiment 1,

which make Experiment 2, however, more similar to the experiments of Milliken et al. (1998)

and Neil and Kahan (1999). For example, probe distractors and probe targets were now

presented with interleaved letters. It might be that these differences lead to a higher portion of

participants who are aware of the prime distractors. Moreover, a self-constructed software and

voicekey-apparatus was used which were designed especially for NP-experiments. It might be

that the longer reaction times were caused by technical reasons.

Additionally, we tested the hypothesis whether variations of the color of the prime

distractor could induce a to-be-attended or a to-be-ignored signal. As argued above (see

Introduction),if color match but not awareness would be the dominant predictor for the sign of

the priming effect, we can take that as a piece of evidence in favour of the inhibition and

episodic retrieval accounts. However, finding a dependence of the sign of the priming effect

on awareness but not on color match would be most compatible to the temporal

discrimination account.

Experiment 2

Method

Participants. Twenty undergraduate students (16 women and 4 men) of the University

of Jena (aged 19 to 26; M = 23) participated either for partial course credits or were paid an

amount of 3 €.

Design, Materials, and Procedure. Design, materials, and procedure were essentially

the same as in Experiment 1 with the following exceptions. A self-constructed software and

voicekey-apparatus was used. Presentation of prime distractor (28 ms) now was masked for

all participants. Besides manipulating the prime condition (repeated vs. unrepeated), the color

of the prime distractor was varied as a within-subjects factor. That is, the prime distractor had

either the same color (red or blue) as the probe target or the probe distractor. Whether red or

blue color served as the target color was balanced between participants. The individual letters


of the words measured 10 x 6 mm. In line with Milliken et al. (1998) and Neil and Kahan

(1999), the probe display now contained two interleaved uppercase words in the middle of the

screen, one above the other. Following the voice key task participants were told that the

flicker before the probe displays had contained a word. Then they had to work through 48

prime identifications trials. During these trials the prime distractors were presented exactly as

in the voice key task. However, participants now had to decide whether the flicker contained a

word or a non-word by pressing a key. Non-words were created by modifying words from the

stimulus set (e.g., PALME was modified to PLIME). In half of the trials the flicker contained

a word from the stimulus set, in the other half the flicker contained a non-word. Each word of

the stimulus set as well as each non-word was presented two times, once in red and once in

blue.

Results

Prime awareness. The mean non-parametric signal detection sensitivity index A’ was

M = .56 (SD = .19) and not significantly different from chance performance (i.e., .50), t(19) =

-1.32, p = .20, ns. However, a closer inspection of the distribution revealed that four

participants showed a significant contingency between word identification and response, all χ2

> 5.59, p < .05 (A’ was above .82). Thus, these participants were ‘aware’ of the subliminally

presented prime distractors. For the other participants the masking of the prime distractors

was successful, all individual χ2 < 2.75, p > .09, ns (A’ was in the range of .27 to .75).

Therefore, we could assume that these participants had no access to the lexical status of prime

distractors (in the following called ‘unaware’). A preliminary 2 (prime condition) x 2 (prime-

probe match) x 2 (prime awareness) ANOVA yielded a significant interaction effect of prime

condition and prime awareness, F(1,18) = 8.93, p < .01. Thus, the following analyses are

dominantly conducted for the subsample (N = 16) of ‘unaware’ participants. Of course, for

reasons of comparison, we will return to the subsample (N = 4) of ‘aware’ participants as


well. Additionally, color of the masked stimuli had no influence on detection performance, for

both (red and blue) distractor conditions |t|(19) < 1, ns.

Negative Priming. Correct RTs for each participant and RTs that were above 200 ms

but below 1700 ms were included in the analysis. This procedure resulted in the elimination

of 1% of the RTs (error rate was < 1% and hence we did not analyze errors). The factors

‘position of probe target’ (above or below the probe distractor) and ‘color of prime distractor’

(blue or red) showed no main effect, all Fs < 1.16, ns, nor did they interact with any other

condition, all Fs < 2.52, all ps > .13, ns. Thus, they were discarded for further analyses. Table

2 shows the mean reaction times for the prime condition (repeated vs. unrepeated) and the

color match (prime distractor having the probe target color or not). For ‘unaware’ participants,

a 2 (prime condition) x 2 (color match) ANOVA yielded a main effect for prime condition,

F(1,15) = 7.01, p < .05. Neither the main effect for color match nor the interaction between

prime condition and color match was significant, F(1,15) = .48, p = .50, ns, and F(1,15) = .18,

p = .68, ns, respectively. Thus, the prime-probe color match had no influence on the NP

effect. For both prime-probe match conditions the average NP effect was M = -12 ms (SD =

19 ms; d = .66), that is, participants were on average 12 ms slower after repeated prime

distractors – regardless of whether the prime distractor had the same color as the probe target

or the probe distractor. Both means were significantly different from zero, t(15) = -2.52, p <

.05, for the trials with the prime distractor having the same color as the probe target and t(15)

= -1.76, p < .05 (one-tailed), for the trials with the prime distractor having a different color as

the probe distractor. In contrast, the subsample (N = 4) of ‘aware’ participants showed on

average a positive priming effect of M = 16 ms (SD = 6 ms) for repeated prime distractors that

was significantly different from zero, t(3) = 5.58, p < .05.

Discussion

Again, the results confirm the finding of Milliken et al.(1998) that NP occurs after

distractor-only prime trials. More interestingly, Experiment 2 provides evidence for the


hypothesis that the contrary results of Neill and Kahan's (1999) experiments 1a and 1b were

due to differences in participants’ awareness. In our Experiment 2 the participants split into

two subsamples. The subsample of ‘unaware’ participants showed a significant NP effect

whereas the subsample of ‘aware’ participants showed a positive priming effect. In contrast to

our Experiment 1 and to Experiment 4 of Milliken et al. (1998), the subsample of ‘aware’

participants can marginally perceive the prime-distractors but lack the intention to actively

ignore them. Thus, a NP effect cannot be expected for them.

Furthermore, the color of the prime-distractor had no influence on the NP effect. We

gave the prime-distractors a clear to-be-attended or to-be-ignored signal, that is, the color of

the probe target or the probe distractor. However, it seems that participants do not use this

signal in processing the distractor. If they would have used it in the way predicted by the

inhibition and episodic retrieval accounts, the experiments with distractor-only prime trials

would have lost their power as an element in favour of the temporal discrimination account

and as a pinprick against the other theories.

General discussion

In two experiments we yielded further evidence for a specific NP-effect, namely NP

following masked distractor-only prime trials. The reassurance of this finding strengthens the

arguments raised by Milliken et al. (1998) and thus could be interpreted as further evidence

for the temporal discrimination theory. Furthermore, the inconsistent results on masked NP as

reported by different researchers can now be explained with regard to our experiments. As

mentioned above, Milliken et al. (1998) reported NP after masked distractor-only-prime trials,

as did Neill and Kahan (1999; Exp. 1a), as well as Healy and Burt (2003; Exp. 1) whereas

Neill and Kahan (1999; Exp. 1b) as well as Allport et al. (1985; Exp. 4-5) found positive

priming after masked prime trials. Against the background of our results, it seems plausible

that participants’ awareness has caused these inconsistencies: Participants must be ‘unaware’


of masked prime-distractors to show a NP effect. For participants who are ‘aware’ of masked

prime-distractors and lack the intention to ignore them, a positive priming effect will emerge.

Obviously, our results add further data to the debate on perception with and without

awareness (see, e.g., Merikle et al., 2001). One approach used to demonstrate that the

distinction between conscious and unconscious information processing is a meaningful one is

to show that participants can produce qualitatively different patterns of performance if they

are consciously aware versus unaware (see, e.g., Joordens & Merikle, 1992). Moreover, if

participants’ performance is moderated due to their level of awareness which was measured in

a discrimination test this result can be interpreted as a validation of the adequateness of the

discrimination test (Marcel, 1980). In our Experiment 2, we found qualitative different

patterns of results in dependence of participants` awareness; this suggests that our

discrimination test was an adequate measure of awareness and yields further evidence for the

dissociation of conscious versus unconscious information processing: Four participants had

access to the lexical state of the masked prime distractors (as their performance in the direct

test indicated). These participants seemed to have used the consciously processed information

of masked stimuli, that is, they may have learned that in half the trials the masked words were

directly repeated as the target. Knowing this contingency between prime and probe display, it

seems plausible that the participants had intentionally focussed their attention on the prime

distractors (and tried to identify them) and had handled them not as distractors but rather as

targets. This would explain why a positive priming effect emerged for them. In contrast,

participants who could not categorize masked stimuli during the direct test showed a NP-

effect. As Merikle and colleagues (2001) stated, information perceived without awareness

leads to more automatic reactions that cannot be controlled by the perceiver. Thus, the

perceived information of the prime display interfered with processing of the probe display:

The probe target could not be identified as ‘new’ because participants have perceived the

probe target directly before the probe display (albeit without awareness) and it could not be


identified as ‘old’ because it was not perceived with awareness. Participants could not

intentionally use the information of the prime distractors to control their reactions to the probe

display because they had no explicit or conscious access to the prime distractors. Overall, our

data can be interpreted as an example for a qualitative difference in performance due to

differences in perceiving with or without awareness.

Additionally, our results have further implications for the theories of NP. We found

that the variation of prime color in our Experiment 2 (i.e., it either matches the color of the

probe target or the probe distractor) does not moderate the NP effect. This result has some

implications for the inhibition account (Houghton & Tipper, 1994). This model would predict

that prime stimuli will be processed with regard to their color. Thus, prime distractors with the

color of the probe target should not be inhibited (because the target-color should attract

attention) whereas prime distractors with the color of the probe distractor should be inhibited

(because the distractor-color would be the signal for ignoring). The inhibition model would

therefore predict that for trials with the same color of prime distractor and probe target a

positive priming effect will emerge whereas for trials with a different color of prime distractor

and probe target a negative priming effect will emerge; our results do not suggest such an

interaction, however. 3 The same is true for episodic retrieval theory (Neill & Valdes, 1996).

Similarly to the inhibition account, episodic retrieval theory would predict that our color-

variation should moderate the NP-effect. A distractor that is specified as a to-be-attended

signal should not be encoded with a do-not-response tag. Thus, episodic retrieval would also

predict, that for trials in which color of prime distractor matches color of probe target, no NP

emerges.

However, although we interpret the results as being most compatible to the temporal

discrimination theory, they are still somewhat problematic. The theory assumes a comparison

process that detects discontinuities or mismatches between the mental representation of the

prime trial and the perception of the probe trial. In Experiment 2, the color of the prime-


distractor had either the color of the probe-target or not. This variation should influence the

quality of match of prime and probe. However, apparently this was not the case. There are

two possible explanations. First, since Milliken et al. (1998) assume a curvilinear relationship

between quality of match and response latencies, we can assume that the qualities of match in

the color match and color mismatch conditions, respectively, mark two points on the curve,

one on the ascending and the other on the descending part of the curve, with comparable y-

axis values, i.e., comparable RT-predictions. Second, we might assume that color is a

marginal feature that does not alter the quality of match. Whatever the reason might be, it

seems that the comparison process is not yet fully understood and needs a more accurate

specification. Further research about the temporal discrimination theory should therefore

concentrate on the comparison process of prime and probe, and analyse its impact on the NP

effect.

Thus we can strongly suggest that there is now strong evidence for a specific NP

effect, namely NP following masked distractor-only prime trials. The most suitable

approach to this NP seems to be the temporal discrimination account. However, it would

be crucial for this theory to further analyse the relationship between prime-probe

comparison and NP. Furthermore, inconsistent results in the literature on masked NP can

now be explained as being due to differences in level of awareness.


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Author note

Christian Frings and Dirk Wentura, Department of Psychology, Saarland University,

Germany.

Correspondence concerning this article should be addressed to Christian Frings, Saarland

University, Faculty of Behavioral Sciences, Department of Psychology, Building 1, P.O. Box

15 11 50, D-66041 Saarbrücken, Germany or via email to [email protected].

The authors would like to thank Jörg Peuckert for his technical support.


Footnotes

1 However, to be honest, there are critical differences between these experiments. In

the experiments of Milliken et al. (1998) a target stimulus was never presented in the prime

display whereas in the experiments of Allport et al. (1985) a target stimulus was always

presented in the prime display. Additionally, the time interval between prime and probe

display varied between both studies (about 500 ms compared to 1200 ms). Most importantly,

participants in the experiments of Allport et al. tried to identify the stimuli of the prime

display, that is they knew that there were stimuli presented whereas the participants of

Milliken and colleagues did not know or were not given any hint to assume that masked

stimuli were presented. It may be that these differences have caused the different priming

effects.

2 A’ is the non-parametric signal detection sensitivity index that is typically used if the number

of observations is very small or if the hit rates of some participants are perfect. Note that

chance performance yielded an A’ of 0.5, whereas perfect performance was reflected in an A´

value of 1.0.

3 Milliken et al. (1998) as well as Neill and Kahan (1999) mentioned the possibility that

participants inhibited the complete prime display (because the prime display did not match the

internally defined template of a target stimuli, that is a clear readable, red words). If one

adopts this perspective, NP with masked distractor-only prime trials can be explained with a

more general inhibition account.


Table 1

Mean Response Times for the Repeated and Unrepeated Prime Conditions as a Function of

Presentation Mode (Experiment 1)

Presentation overall

Subliminal Supraliminal

Repeated 815

810

813

Unrepeated 808

801

806

NP effecta -7*b (4)

-9* (4)

-8** (3)

* p < .05 ** p < .01 a RT(Unrepeated) minus RT(Repeated); Standard errors in Parentheses b one-tailed test


Table 2

Mean Response Times for the repeated and unrepeated prime conditions as a function of

prime-probe color match (Experiment 2)

‚Unaware’ (N = 16) ‚Aware’( N = 4)

Prime-Probe-match overall overall

Same color Different color

Repeated 642

644

643

635

Unrepeated 629

633

631

651

NP effecta -14*

(5)

-11*b

(6)

-12*

(5)

16*

(3)

* p < .05 a RT(Unrepeated) minus RT(Repeated); Standard errors in Parentheses b one-tailed test

frings and wentura - negative priming with masked distractor-only prime trials - 2002¿

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