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Subliminal access to abstract face representations does not rely on attention
Consciousness and Cognition 21 (2012) 573–583
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Consciousness and Cognition journal homepage: www.elsevier.com/locate/concog
Subliminal access to abstract face representations does not rely on attention Bronson Harry ⇑, Chris Davis, Jeesun Kim Bankstown Campus, Building 1, MARCS Auditory Laboratories, University of Western Sydney, Locked Bag 1797, Penrith NSW 2751, Australia
a r t i c l e
i n f o
Article history: Received 17 May 2011 Available online 24 December 2011 Keywords: Face identification Masked repetition priming Spatial attention
a b s t r a c t The present study used masked repetition priming to examine whether face representations can be accessed without attention. Two experiments using a face recognition task (fame judgement) presented masked repetition and control primes in spatially unattended locations prior to target onset. Experiment 1 (n = 20) used the same images as primes and as targets and Experiment 2 (n = 17) used different images of the same individual as primes and targets. Repetition priming was observed across both experiments regardless of whether spatial attention was cued to the location of the prime. Priming occurred for both famous and non-famous targets in Experiment 1 but was only reliable for famous targets in Experiment 2, suggesting that priming in Experiment 1 indexed access to view-specific representations whereas priming in Experiment 2 indexed access to view-invariant, abstract representations. Overall, the results indicate that subliminal access to abstract face representations does not rely on attention. Ó 2011 Elsevier Inc. All rights reserved.
1. Introduction Face recognition is the process of matching perceptual information with representations stored in long-term memory (e.g., Burton, Bruce, & Hancock, 1999). Previous research has focussed on what type of visual processing is associated with visual recognition, and the nature of the representations involved. However, relatively little is currently known about the role of consciousness and attention in accessing face representations. Recently, Kouider, Eger, Dolan, and Henson (2009), and Henson, Mouchlianitis, Matthews, and Kouider (2008) have shown that masked, briefly presented faces facilitate the recognition of target faces when both of these faces depict the same individual. It was proposed that this repetition priming effect indexed subliminal access to abstract representations. The claim that abstract representations were accessed was based on three findings. First, priming was shown even when primes and targets were different images of the same person, indicating that the priming involved access to view-invariant representations. Second, priming was only observed for famous targets suggesting that subliminal access was limited to pre-existing, long-term memory representations. Third, priming was not related to objective, pixel-based measures of visual similarity between targets and primes, ruling out the possibility that priming was due to low level image similarity. Evidence that face representations are accessed without consciousness does not necessarily mean that other domain general processes, such as attention, cannot modulate access to these representations. A number of studies have shown that subliminal repetition priming is not observed for masked letter and word stimuli when the primes are presented in an unattended location, indicating that subliminal access to stored representations relies on attention (Lachter, Forster, & Ruthruff, 2004; Marzouki, Grainger, & Theeuwes, 2007). Given these findings, it is possible that subliminal access to face representations also ⇑ Corresponding author. Fax: +61 2 9772 6040. E-mail address: [email protected] (B. Harry). 1053-8100/$ - see front matter Ó 2011 Elsevier Inc. All rights reserved. doi:10.1016/j.concog.2011.11.007
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require attention (although see Finkbeiner & Palermo, 2009 for evidence that unattended face produce congruency priming effects in a sex categorisation task). Alternatively, it could also be possible that attention is only required for access to particular types of face representations. Studies examining repetition priming effects in tasks with unmasked primes have shown that priming across transformed images of objects (e.g., in-plane rotations) occurs only when primes are spatially attended (Hummel, 2001; Thoma, Hummel, & Davidoff, 2004), but priming across identical images occurs regardless of whether primes are attended. These results raise the possibility that only access to abstract, view-invariant representations requires attention, a possibility that is consistent with evidence that viewing more than one face simultaneously eliminates view-invariant repetition priming effects and but not view-specific priming effects (Bindemann, Jenkins, & Burton, 2009). It is also possible that consciousness also played a role in the view-invariant priming effects reported by Kouider et al. (2009) and Henson et al. (2008). That is, since in their studies both images of an individual were used as targets in several trials throughout the experiment, it might be that the view-invariant priming effect that was observed was due to conscious exposure to each image. On this view, the view-invariant priming might not have indexed access to abstract representations, but instead indexed access to image-specific representations of the stimuli that were formed when each stimulus was viewed as a target. The present study examined the role of attention in subliminal face recognition in two experiments. Experiment 1 presented the same images as primes and as targets to examine the role of attention on access to view-specific representations and Experiment 2 presented different images as primes and targets to examine the role of attention on access to view-invariant representations. Moreover, primes in Experiment 2 were never presented consciously as targets to ensure that priming involved access to abstract representations, not image specific representations stored from repeated presentations to the target images. In each experiment, participants completed a fame judgement task similar to that used in Kouider et al. (2009) and Henson et al. (2008), however, unlike the method employed in these studies, in the current task masked primes appeared prior to targets in a spatially unattended location. Additionally an exogenous cue was presented to draw attention either to the location of the prime or to another location. If access to face representations requires attention then repetition priming should only be observed on trials where the prime was cued. 2. Experiment 1 2.1. Method 2.1.1. Participants Twenty undergraduate (Mage = 21 years, 18 female) students participated in exchange for course credit. All reported having normal or corrected to normal visual acuity. 2.1.2. Stimuli Thirty-two images of famous singers or actors and 32 images of amateur models were selected from the internet. Amateur models were chosen to ensure comparability in attractiveness and age range with the famous faces. Half of the famous and amateur model faces were female and half male. Images were cropped to include only the face region and the hairline (Fig. 1). The luminance and contrast of each image was equalised by setting the distribution of pixel intensities of the face region to a mean of 127 and a standard deviation of 50. Subsequently, the luminance and contrast of the hair was altered until there were no subjective differences between the face and hair. Each stimulus was used as a target as well as a prime. Target and prime image size was set so that the stimuli subtended 4° and 5° visual angle respectively. A stimulus that consisted of a mosaic of blurred eyes, noses and mouths from various faces was used as a forward mask and a scrambled face superimposed on a chequer-board background was used as a backward mask (vertical visual angle 5°). A cue similar to that used in Marzouki et al. (2007) was also constructed (vertical visual angle 4°; Fig. 1).
Fig. 1. Order of stimulus presentation in Experiment 1.
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2.1.3. Procedure Participants were tested individually while seated in a dimly lit booth. Head position was stabilised with a chin rest 67 cm from the monitor which had a refresh rate of 85 Hz. Stimuli were presented and reaction time and accuracy data were collected with DMDX (Forster & Forster, 2003). On each trial participants judged whether a target stimulus was famous or non-famous and indicated their response with a button press. Each trial started with the appearance of three forward masks (494 ms), one in the centre of the screen and two on each side of the central mask. After 494 ms an exogenous cue appeared in either the left or right position for 58 ms. Then a prime stimulus appeared either in the left or right locations for a another 58 ms. After the prime, the target appeared in the central location with two backward masks in the left and right locations for 494 ms (Fig. 1). On half of the trials the prime and the target were images of the same face (repetition prime trials) and on half of the trials the prime and the target were images of two different faces (control prime trials). The control primes were always the same sex (e.g., both male) to ensure that any priming effect observed was not due to between-category differences. Moreover, primes were always from the same response category as the target (e.g., both famous) to ensure that priming was not due to response congruency. That is, if the prime and targets used for baseline were associated with different response categories, priming could be based on responses made to the primes via automatic activation of stimulus-response mappings learned over the course of the experiment (Abrams & Greenwald, 2000; Damian, 2001). On half the trials the cue appeared in the same location as the prime, and on half of the trials the cue appeared on the opposite side of the display to where the prime appeared. The task consisted of four blocks of 256 trials, which meant that each target and prime appeared a total of 16 times; 128 trials had the same prime and target pairs (the repetition condition) and 128 trials had different prime and target pairs (the control condition); for 128 trials the prime was cued and for 128 trials uncued. Before the main task participants completed a practice task consisting of 36 trials. In the practice trials, eight famous and eight non-famous targets were presented that did not appear in the main task. Participants also completed a prime visibility task that consisted of a single block of 256 trials. In this task, participants determined whether the masked prime was famous or non-famous to assess how visible the primes were to each participant. However, since making a judgement about the prime would likely encourage participants to attend to the prime (thus making the primes more visible) participants also made a fame judgement to the unmasked target face to ensure participants attended to the target and prime in a similar way as in the main task. On each trial, participants first judged whether the target was famous or non-famous as quickly and as accurately as possible. Once this response was made, the words ‘‘Non-famous or famous’’ were presented on the screen to prompt participants to respond as to whether the prime was famous or non-famous. This task was identical to a single block of trials from the main task except that on half the trials the prime and target were from the same response category (i.e., both famous) and on half the trials the prime and target were from different categories (primes and targets were never the same individual). Participants completed these tasks over three days. On the first day participants completed a block of the practice trials, followed by two blocks of the main task. On the second day participants completed another two blocks of the main task and on the third day participants completed one block of the prime visibility task. 2.2. Results Two participants with error rates greater than 20% were excluded from the analysis. Incorrect responses (6.8%) were excluded from the reaction time analysis and any response greater than two standard deviations from a participants’ mean was winsorised (4.5% of the data). Table 1 presents mean reaction times and mean percent error rates across the target type (famous, non-famous), cue (prime cued, prime uncued), and prime type (repetition, control) conditions. A separate ANOVA was calculated from the participant means (F1) and the item means (F2). Participant and item means were analysed in a threeway (2 2 2) mixed repeated measures ANOVA. All factors were treated as repeated factors in the participant and item analysis, except for the target type factor (famous, non-famous) which was treated as a non-repeated factor in the item analysis.
Table 1 Mean reaction times and percent error rates across cue, target type and prime type conditions. Item type
Reaction time (ms)
Errors (%)
Cued prime
Uncued prime
Cued prime
Uncued prime
Famous targets Repetition prime Control prime Priming
538 (17) 544 (17) 6
540 (19) 547 (17) 7
4.1 (1.0) 4.8 (1.2) 0.7
5.5 (1.1) 4.8 (1.1) 0.7
Non-famous targets Repetition prime Control prime Priming
599 (20) 604 (19) 5
601 (20) 607 (20) 6
9.0 (2.2) 8.5 (2.0) 0.5
8.9 (2.5) 9.0 (2.6) 0.1
Note: Standard errors are shown in parenthesis.
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Analysis of reaction times revealed a significant main effect of prime type (F1(1,17) = 5.6, MSE = 242.6, p = 0.031, g2p ¼ 0:25; F2(1,62) = 5.0, MSE = 347.9, p = 0.030, g2p ¼ 0:07) with faster reaction times on repetition prime trials than control prime trials (M = 569 ms vs. M = 576 ms). There was a main effect of target type (F1(1,17) = 24.3, MSE = 5409.8, p < 0.001, g2p ¼ 0:59; F2(1,62) = 146.0, MSE = 1460.0, p < 0.001, g2p ¼ 0:70) with famous targets recognised faster than non-famous targets (M = 542 ms vs. M = 603 ms). The main effect of cue did not reach significance (F1(1,17) = 1.7, MSE = 129.3, p = 0.205, g2p ¼ 0:10; F2(1,62) < 1) and this factor did not interact with the other factors (all F1(1,17) < 1; all F2(1,62) < 1). Analysis of errors revealed a significant main effect of target type for the item analysis (F1(1,17) = 2.7, MSE = 219.2, p = 0.122, g2p ¼ 0:14; F2(1,62) = 7.3, MSE = 95.4, p = 0.009, g2p ¼ 0:11) with fewer errors for famous than non-famous targets (M = 4.8% vs. M = 8.9%). No other main effects or interactions were significant indicating that the reaction time results were not associated with a speed-accuracy trade-off. 2.2.1. Prime visibility Mean accuracy in the prime visibility task across famous and non-famous primes was 50.5%. A single sample t-test showed that mean performance was not significantly above chance performance (t(17) = 1.2, p = 0.24), suggesting that participants were not aware of the prime in the fame judgement task. To examine whether prime visibility was modulated either by the cue, or by response compatibility (between the prime and target), the prime visibility data was submitted to a 2 (cue) 2 (response compatibility) repeated measures ANOVA. This analysis revealed a significant main effect of response compatibility (F(1,17) = 8.62, MSE = 35639.0, p = 0.009, g2p ¼ 0:34) with better performance when the prime and target were compatible (M = 66.2%) compared to when the prime and target were incompatible (M = 34.5%). This result could indicate that participants were aware of the primes and that response interference on incompatible trials impaired performance. Alternatively, given the similar magnitude of performance enhancement for the response compatible trials and the performance impairment for the response incompatible trials, it is also possible that the effect of response compatibility is a form of a bias effect (where participants simply guessed the prime category based upon that of the target). The main effect of cue and the interaction between cue and response compatibility was not significant (Fs < 1). A linear regression was conducted to examine the relationship between priming and prime visibility across participants. Priming scores were collapsed over cue and target type conditions since these variables had no effect on priming effects. In addition, only response compatible trials were used to estimate prime visibility since there may have been an interference effect for the response incompatible trials. Fig. 2 presents the relationship between prime visibility data and the magnitude of the priming effect. There was no significant linear relationship between priming and prime visibility (R2 = 0.1, p = 0.21). To examine whether prime visibility performance was influenced by confusions between famous and non-famous targets, items that were recognised < 90% correct in the fame judgement task were removed from the prime visibility analysis (famous targets = 4; non-famous target = 8). Removing these items did not change the overall pattern of results for the prime visibility analysis as mean prime visibility was not significantly above chance (M = 51.1%, t18 = 1.3, p = 0.22) and there was no significant linear relationship between prime visibility and priming (R2 = 0.26, p = 0.53). 2.2.2. Image similarity Image similarity was calculated as the root-mean-square difference in greyscale values across each target and the respective repetition and control primes (Henson et al., 2008). This similarity measure was normalised so that identical images would have a value of zero and completely dissimilar images would have a value of one. Image similarity values were entered into a 2 2 ANOVA with prime type as a repeated factor and target type as a between factor. This analysis showed
Fig. 2. The relationship between prime visibility scores and the repetition priming effect across participants. Each point represents the data from each participant and the line represents the linear fit between the two variables.
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a significant main effect of prime type (F(1,62) = 23.5, MSE = 0.067, p < 0.001, g2p ¼ 0:28) indicating that targets and repetition primes were more visually similar than targets and control primes (M = 0.21 vs. M = 0.26). The main effect of target type (F(1,62) = 2.7, MSE = 0.007, p = 0.41, g2p ¼ 0:01) and the interaction between prime type and target type (F(1,62) = 2.7, MSE = 0.001, p = 0.407, g2p ¼ 0:01) was not significant. 2.3. Discussion Experiment 1 used a fame judgement task with masked spatially unattended repetition primes that were the same images as targets and showed repetition priming effects regardless of whether primes were attended. This result is at odds with studies showing that masked repetition priming of words and letters relies on attention (Lachter et al., 2004; Marzouki et al., 2007). Instead, the present results support studies showing that access to view-specific representations does not rely on attention (Hummel, 2001; Thoma et al., 2004). The present finding of priming for both famous and non-famous targets contrasts with the results from other studies showing masked repetition priming in a fame judgement task (Henson et al., 2008; Kouider et al., 2009).1 One possible reason why priming effects for non-famous faces is that the target stimuli were repeated 16 times whereas in previous studies the targets were only presented around 6 times. That is, priming in recognition tasks relies on the target being represented in memory (Forster, 1998) and it might be that usable representations of non-famous (i.e., unfamiliar) faces only develop with a sufficient number of repeated presentations (e.g., Tong & Nakayama, 1999). Alternatively, priming for non-famous targets in the current study might have been observed because targets and their respective repetition primes were more visually similar than the control primes. On this view, priming was not the result of activating stored representations, but was due to low level visual properties associated with the face. If so, then priming must have indexed processing at a relatively abstract stage of processing (e.g., location invariant) since the primes and targets were presented in different locations. As reported above, there was no effect of cuing on target response times (this was expected as the cues only appeared at the peripheral locations and hence there should be no main effect of cue position on reaction times to the centrally presented targets). Despite this lack of a cuing effect, it is reasonable to assume that the cuing procedure used in the present study triggered shifts in attention because the cuing procedure used in this task was similar to that used in Marzouki et al. (2007), which showed that repetition priming effects from masked letter stimuli were modulated by an exogenous cue. 3. Experiment 2 The question of whether masked faces access abstract representations even when unattended was tested in Experiment 2. Several modifications were made to the method used in Experiment 1. Firstly, the prime and target pairs were not the same images. Moreover, primes were never presented as targets (and vice versa) to ensure that the priming effect would not reflect pre-activation of the episodic representations of a particular target image formed over repeated exposures. Secondly, the cuing technique was changed to increase the chances that the cue would summon attention to the location of the prime. The cue was presented either at the central target location or in the location of the prime to ensure that a cuing effect would be observed in target reaction times. In addition, the target occasionally appeared in a cued peripheral location. This was to ensure that participants would not completely ignore the cue when it appeared in a peripheral location. 3.1. Method 3.1.1. Participants Seventeen graduate (Mage = 26.8 years, 9 female) students participated in exchange for payment. All reported having normal or corrected to normal visual acuity. None of the participants recruited for Experiment 2 participated in Experiment 1. 3.1.2. Materials Two images each of 32 famous singers or actors and 32 amateur models were selected from the internet. Images were selected so that the hairstyle, lighting conditions and pose varied across the two images of the same individuals. Two yellow bars that were similar in appearance to the cue used in previous studies (Finkbeiner & Palermo, 2009), were used to as the exogenous cue in the present experiment (see Fig. 3). 3.1.3. Procedure Fig. 2 shows the order of stimuli presentation. Each trial started with the appearance of three forward masks (for 494 ms), which was followed by an exogenous cue that appeared in one of the three locations (for 106 ms). After this, a prime stimulus appeared either in the left or right locations (for 58 ms). After the prime, the target appeared in the central location with two backward masks in the left and right locations (for 494 ms). On 40% of trials (Target cued), the cue appeared in the central location and on another 40% of trials (Prime cued), the cue appeared in the location where the prime appeared. On the
1 It should be noted that although Kouider et al. (2009) and Henson et al. (2008) did not observe a behavioural priming effect for non-famous targets, repetition-related suppression effects were observed in brain imaging data for both famous and non-famous targets.
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Fig. 3. Order of stimulus presentation in Experiment 2 for the three cuing conditions.
remaining 20% of trials (Foils), the target was presented in one of the peripheral locations and was preceded by a cue in the same location. No prime was presented on these trials. All stimuli presented in central and peripheral locations subtended 4° and 5° visual angle respectively. Given the relevance of the cue to the task (cued target location on 60% of trials) it was expected that these cuing conditions would encourage participants not to pre-focus their attention at the central location (since the target did not always appear in the central location) but attend to the cued location. All stimuli that were presented in the peripheral locations (e.g., the prime on Target and Prime cued trials, the target on Foil trials) appeared equally in the left location and the right location across trials. Participants were instructed that the cue would indicate the location of the target on the majority of trials. Moreover, it was made clear to participants that the cue always validly indicated the location of the target when the cue appeared in the central location. Thus, it is likely that the prime was unattended on target cued trials. The experiment consisted of four blocks of 320 trials that were completed over two separate days. Within a block, each target appeared five times, once in each of the prime and cuing conditions, and once in the foil condition. Participants completed a practice task consisting of 40 trials before the main task. Eight famous and eight non-famous targets were presented in this task that did not appear in the main task. Participants also completed a prime visibility task which consisted of 320 trials. All other aspects of the prime visibility task in this experiment were the same as the one used in Experiment 1. 3.2. Results Two participants with error rates greater than 20% were excluded from the analysis. Incorrect responses (8.5%) were excluded from the reaction time analysis and any response greater than two standard deviations from a participants’ mean was winsorised (4.2% of the data). 3.2.1. Analysis of the cuing effect A preliminary analysis was conducted to examine whether the cuing technique used in the present study produced a cuing effect on performance in the fame judgement task. Note that this analysis was collapsed across the prime conditions because no primes were presented in Foil trials. Separate 3 2 ANOVAs were executed with the participant means (F1) and the item means (F2) for reaction times and error rates. Analysis of reaction times showed a significant main effect of cue (F1(2,28) = 73.6, MSE = 683.0, p < 0.001, g2p ¼ 0:84; F2(2,124) = 523.45, MSE = 211.2, p < 0.001, g2p ¼ 0:89) with the fastest reaction times on Target cued trials and the slowest reaction times on Foil trials (M = 538 ms for Target cued, M = 565 ms for Prime cued, M = 619 ms for Foil). There was also a main effect of target type (F1(1,14) = 4.8, MSE = 1525.3, p = 0.045, g2p ¼ 0:26; F2(1,62) = 10.4, MSE = 1573.9, p = 0.002, g2p ¼ 0:14) with faster reaction times to famous targets than to non-famous targets (M = 565 ms vs. M = 584 ms).
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Analysis of errors showed a significant main effect of cue (F1(2,28) = 9.5, MSE = 9.9, p = 0.001, g2p ¼ 0:41; F2(2,124) = 25.2, MSE = 8.0, p < 0.001, g2p ¼ 0:29) again with fewer errors on Target cued trials and more errors on Foil trials (M = 7.3% for Target cued, M = 7.7% for prime cued, M = 10.6% for Foil). There was also a main effect of target type for the item analysis (F1(1,14) = 2.5, MSE = 124.2, p = 0.138, g2p ¼ 0:15; F2(1,62) = 4.3, MSE = 154.1, p = 0.044, g2p ¼ 0:06) with more errors for famous targets than non-famous target (M = 10.4% vs. M = 6.7%), possibly indicating that faster reaction times for famous targets might have been the result of a speed-accuracy trade-off. 3.2.2. Analysis of the priming effect Table 2 presents mean reaction times and mean percent error rates across the target type (famous, non-famous), cue (target cued, prime cued), and prime type (repetition, control) conditions. Note that this analysis omitted the foil condition because no primes were presented on these trials. Analysis of reaction times showed a main effect of cue (F1(1,14) = 66.5, MSE = 1292.6, p < 0.001, g2p ¼ 0:83; F2(1,62) = 296.0, MSE = 625.1, p < 0.001, g2p ¼ 0:83) with faster reaction times when the target was cued compared to when the prime was cued (M = 539 ms vs. M = 566 ms). There was a main effect of prime type (F1(1,14) = 40.6, MSE = 165.4, p < 0.001, g2p ¼ 0:74; F2(1,62) = 24.2, MSE = 658.0, p < 0.001, g2p ¼ 0:28) with faster reaction times to repetition trials than to control trials (M = 548 ms vs. M = 556 ms). There was also a significant main effect of target type only for the item analysis (F1(1,14) = 4.5, MSE = 7866.0, p = 0.053, g2p ¼ 0:24; F2(1,62) = 9.7, MSE = 7430.1, p = 0.003, g2p ¼ 0:14) with faster reaction times to famous targets than to non-famous targets (M = 544 ms vs. M = 561 ms). The prime type target type interaction was significant for the item analysis (F1(1,14) = 3.1, MSE = 405.2, p = 0.100, g2p ¼ 0:18; F2(1,62) = 5.2, MSE = 658.0, p = 0.027, g2p ¼ 0:08). Simple effects analysis revealed that there was a significant priming effect for famous targets (F1(1,14) = 25.1, MSE = 275.4, p < 0.001, g2p ¼ 0:64; F2(1,31) = 21.4, MSE = 795.0, p < 0.001, g2p ¼ 0:41) whereas the priming effect for non-famous targets failed to reach significance in the participant analysis (F1(1,14) = 3.7, MSE = 295.2, p = 0.077, g2p ¼ 0:21; F2(1,31) = 4.5, MSE = 521.0, p = 0.043, g2p ¼ 0:13). The reaction time analysis also revealed a marginal interaction effect between prime type and cue (F1(1,14) = 4.4, MSE = 229.0, p = 0.054, g2p ¼ 0:24; F2(1,62) = 3.5, MSE = 616.3, p = 0.065, g2p ¼ 0:05) with a larger priming effect when the target was cued compared to when the prime was cued. Simple effects analysis revealed a significant priming effect for Target cued trials (F1(1,14) = 31.6, MSE = 51.3, p < 0.001, g2p ¼ 0:64; F2(1,62) = 22.7, MSE = 657.3, p < 0.001, g2p ¼ 0:27) and for Prime cued trials (F1(1,14) = 6.6, MSE = 47.4, p = 0.022, g2p ¼ 0:32; F2(1,62) = 5.2, MSE = 617.0, p = 0.027, g2p ¼ 0:08). Analysis of errors revealed a significant main effect of target type for the item analysis (F1(1,14) = 2.9, MSE = 606.9, p = 0.112, g2p ¼ 0:17; F2(1,62) = 4.2, MSE = 884.2, p = 0.044, g2p ¼ 0:06) with more errors for famous targets than non-famous targets (M = 9.4% vs. M = 5.6%), suggesting that the faster reaction times observed for the famous targets might be due to a speed-accuracy trade-off. There was also a significant interaction between prime type and cue (F1(1,14) = 10.1, MSE = 9.2, p = 0.007, g2p ¼ 0:42; F2(1,62) = 7.5, MSE = 26.2, p = 0.008, g2p ¼ 0:11). Simple effects analysis showed a significant main effect of prime type for Target cued trials (F1(1,14) = 10.8, MSE = 2.6, p = 0.005, g2p ¼ 0:44; F2(1,62) = 9.3, MSE = 61.2, p = 0.003, g2p ¼ 0:13) with fewer errors to repetition prime trials than to control prime trials (M = 6.6% vs. M = 8.0%), whereas the priming effect failed to reach significance for Prime cued trials (F1(1,14) = 3.0, MSE = 79.7, p = 0.104, g2p ¼ 0:03; F2(1,62) < 1). 3.2.3. Prime visibility Mean accuracy in the prime visibility task across famous and non-famous primes was 48.3%. A single sample t-test showed that mean performance was not significantly above chance performance (t(14) = 1.7, p = 0.1), suggesting that participants were not aware of the prime in the fame judgement task. As in Experiment 1, the effect of cue and response compatibility on prime visibility was examined with a 2 (cue) 2 (response compatibility) repeated measures ANOVA. This analysis did not show a significant main effect for either cue or response compatibility and the interaction between these factors was also not significant (Fs < 1). Since priming varied across famous and non-famous targets, separate regression analyses between priming and prime visibility (Fig. 4) were
Table 2 Mean reaction times and percent error rates across cue, target type and prime type conditions. Item type
Reaction time (ms)
Errors (%)
Prime cued
Target cued
Prime cued
Target cued
Famous targets Repetition prime Control prime Priming
554 (19) 560 (19) 6
523 (17) 538 (18) 15
7.9 (1.6) 10.3 (1.6) 2.4
10.0 (1.8) 9.5 (1.7) 0.5
Non-famous targets Repetition prime Control prime Priming
573 (18) 576 (17) 3
544 (14) 550 (16) 6
5.3 (1.3) 5.7 (1.7) 0.4
5.9 (1.6) 5.6 (1.5) 0.3
Note: Standard errors are shown in parenthesis.
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Fig. 4. The relationship between prime visibility scores and repetition priming across participants for famous and non-famous targets. The diamond points represent data from famous target trials and the solid line represents the linear fit for this condition. The square points represent data from the non-famous target trials and the broken line represents the linear fit for this condition.
conducted (Fig. 4). The results showed that there was no significant relationship between priming and prime visibility for famous (R2 = 0.004, p = 0.83) and non-famous targets (R2 < 0.001, p = 0.97). To examine whether prime visibility performance was influenced by confusions between famous and non-famous targets, items that were recognised < 90% correct in the fame judgement task were removed from the prime visibility analysis (famous targets = 11; non-famous target = 6). Again, removing these items did not change the overall pattern of results for the prime visibility analysis as mean prime visibility was not significantly above chance (M = 50.3%, t15 = 0,28, p = 0.78) and there was no significant linear relationship between prime visibility and priming for famous (R2 = 0.01, p = 0.71) and non-famous targets (R2 = 0.03, p = 0.57). 3.2.4. Analysis of image similarity Image similarity values between targets and their respective repetition and control primes were entered into a 2 2 ANOVA with prime type as a repeated factor and target type as a between factor. This analysis showed a non-significant main effect of prime type (F(1,62) = 1.6, MSE = 0.001, p = 0.21, g2p ¼ 0:03), target type (F(1,62) = 2.7, MSE = 0.007, p = 0.41, g2p ¼ 0:01) and a non-significant interaction between these two factors (F(1,62) = 2.7, MSE = 0.001, p = 0.407, g2p ¼ 0:01), indicating that the targets and repetition primes were not more visually similar than targets and control primes for famous and non-famous items. Thus, the data from the image similarity analysis was inconsistent with the view that repetition priming effects were due to low level visual overlap between targets and repetition primes. 3.3. Discussion The primary aim of Experiment 2 was to investigate whether repetition priming effects would be observed for spatially unattended primes when targets and repetition primes were not the same images. Priming was found and occurred regardless of whether the prime was attended. This result shows that access to view-invariant representations does not rely on attention. Moreover, the primes were novel, unexposed images of the target individuals, thus the priming observed was not due to access to image specific representations. Likewise, the observed repetition priming cannot be due to the low level perceptual overlap between repetition primes and targets since the image similarity analysis did not show any evidence that the repetition primes were more similar to the targets compared to the control primes. Given the above, priming likely occurred because the prime triggered processing in a view-invariant representation that was subsequently capitalised upon by the target. In addition to showing that the repetition priming effect extended to different primes and targets, the present experiment provides strong evidence that repetition priming did not directly rely on attention. There was a clear cuing effect in the present study indicating that the cue was effective at triggering shifts in attention to the location of the prime. Given this successful manipulation of attention, the presence of a repetition priming effect provides clear evidence that access to face representations does not rely on attention. Unexpectedly, the results suggested that the priming effect was larger when the target was cued compared to when the prime was cued (although the interaction was not secure). The finding of a weaker priming effect for cued primes is counterintuitive and is at odds with previous studies examining the role of attention in masked priming (Besner, Risko, & Sklair, 2005; Finkbeiner & Palermo, 2009; Lachter et al., 2004; Marzouki et al., 2007). One explanation for the weakness of priming in the Prime cued trials is that the cue on these trials did not validly indicate the position of the target. Consequently, participants might have had to re-direct attention to the central location in order to
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make a judgement about the target presented in the central location.2 This re-directing of attention could have resulted in a resetting of any processing initiated by the prime that might have been capitalised on in processing the target (and hence no priming on those trials which would have reduced the overall priming effect). This explanation is similar to one proposed by Forster (2009) that disruptions prior to target onset, such as presenting a clearly visible item between prime and target, can result in a resetting of priming effects. It should also be noted that the presence of marginal effects (such as the one mentioned above) does not necessarily indicate that the current experiment is underpowered. The task used in the present study involved over twice as many trials as the Kouider et al. (2009) and Henson et al. (2008) studies (over 1000 trials compared to 480 trials) and we recruited a similar number of participants as these previous studies. Although the effect sizes reported in the present experiment range from weak-strong, the effect size for the priming effect was moderate-strong (g2p ¼ 0:74, participant analysis). Finally, unlike Experiment 1, in this experiment there was no priming for non-famous targets. This lack of a reliable priming effect for non-famous targets is consistent with the interpretation that the priming observed in Experiment 1 for these targets was image-specific. That is, if priming in Experiment 1 was produced because primes and targets were the same image, then the null priming effect for non-famous faces in Experiment 2 occurred because primes and targets had different poses. On the other hand, priming for famous face targets was found in Experiment 2 presumably because perceivers had pre-established, view-invariant representations for these faces. In sum, finding priming from unexposed images of famous targets provides straightforward evidence that masked face repetition priming does not rely on instance based representations. 4. General discussion The present study investigated the role of attention in unconscious access to abstract face representations by examining whether spatially unattended masked faces produce repetition priming effects in a fame judgement task. To do this, a procedure was used that built upon two separate but related masked priming paradigms. First, masked repetition priming in a fame judgement task was used to index unconscious access to face representations (Henson et al., 2008; Kouider et al., 2009). Second, as in Finkbeiner and Palermo (2009) primes were presented in a spatially unattended location to examine whether attention to the primes was necessary for access to face representations to occur. Taken together, the present results extend those of these previous studies by showing that access to view-invariant face representations does not require attention. This finding stand in clear contrast to results from studies that have used non-face stimuli (e.g., word and letter recognition tasks, Lachter et al., 2004: Marzouki et al., 2007) where it has been found that attention modulates masked repetition priming and that repetition priming across transformed images relies on attention (Hummel, 2001; Thoma et al., 2004). The conclusion that abstract representations were accessed in the present experiments is based on three findings; priming was not related to image similarity, priming was present when primes were novel, unexposed images, and priming was observed only for famous targets. However, it might be argued that priming effects were not observed for non-famous targets in Experiment 2 because of the nature of the fame judgement task. According to this view, repeating an unfamiliar stimulus (i.e., a repetition primed target) generates a false familiarity signal (Jacoby & Whitehouse, 1989) which in turn interferes with generating a ‘non-famous’ response and so eliminates priming for non-famous targets. This explanation however does not account for the priming effect found for both famous and non-famous targets in Experiment 1. One possible explanation might be based on the slight differences in demographic profile of the participants recruited for Experiments 1 and 2. For example, the participants in Experiment 2 might have been less familiar with the famous targets than the participants from Experiment 1. However, it is unclear how such differences would be related to the presence or absence of priming effects for the non-famous targets. A more general explanation for the pattern of results is that priming for non-famous targets was based on access to view-specific representations formed during the task whereas priming for famous targets was based on access to long term, view-invariant representations. This view is compatible with evidence that view-specific representations for unfamiliar faces form rapidly over a small number of presentations whereas more familiar faces are associated with long-term, view-invariant representations (Tong & Nakayama, 1999). Why might faces show masked priming (hence demonstrating they have been processed) in the absence of attention whereas other types of stimuli (words, letters) do not? In the current study, primes were presented peripherally and so would have been subject to the reduced spatial resolution that is associated with peripheral vision caused by the increased convergence of cones to retinal ganglion cells (Curcio et al., 1991; Rossi & Roorda, 2010). Priming from these peripherally presented faces shows that there is sufficient information in the periphery to trigger identification processes. In this sense, the results are consistent with the claim that identity-related information is contained in the global details (O’Toole, Abdi, Deffenbacher, & Valentin, 1993). An intriguing possibility concerning the basis of unattended masked face priming is opened up if it is assumed that such global face details can be carried by low frequency information. If priming was based on processing low spatial frequency information (the size of the current priming effects are equivalent to de Gardelle & Kouider, 2009 where primes and targets contained the same low spatial frequency face information) then this could explain why such effects can occur in the absence of attention. That is, it has been proposed that low-spatial frequency information is relayed
2 Although this explanation might seem to imply that Prime cued trials should have been the slowest trials instead of the Foil trials, this is not necessarily the case since Foil trials would have required participants to saccade to the peripherally presented targets in order to recognise them.
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by the magnocellular pathway that avoids modulation by attention either because information is relayed to face processing mechanisms via a subcortical route or by an early feedforward sweep of activity (see Vuilleumier, 2005). On this view, face processing proceeds on a coarse-to-fine basis, where the low spatial frequency information is processed automatically and then followed by conscious processing of the high spatial frequency information. In this scheme, masked priming would index the initial automatic process. Such a mechanism of face priming might go some way to explaining why faces can be primed in the absence of attention whereas other types of stimuli appear to require it (e.g., Besner et al., 2005; Fabre, Lemaire, & Grainger, 2007; Lachter et al., 2004; Marzouki et al., 2007). One possible explanation for why only faces produce priming effects is that faces may involuntarily capture attention even on trials where attention was cued elsewhere (e.g., to the target location). However, the results of studies examining the role of attention in masked priming studies suggest that this possibility is unlikely. Finkbeiner and Palermo (2009) showed no differences in task performance (in an orientation discrimination task) when masked faces appeared in an unattended location compared to attended locations, demonstrating that masked faces do not trigger exogenous shifts of attention. Moreover, even if the face prime did occasionally trigger an attention shift, such a process would (in the uncued case) take longer than the 58 ms prime display time since attentional capture has been shown to occur at least 50 ms (plus 8 ms per degree of visual angle) after the onset of a distracting stimulus (Lachter et al., 2004; Tsal, 1983). Therefore, the prime would have still been functionally unattended as it would have been replaced by the mask before attention was deployed. The current results (showing face processing in the absence of attention) appear to contradict those from search tasks that suggest that face identification requires attention (e.g., Devue, Van der Stigchel, Bredart, & Theeuwes, 2009; Tong & Nakayama, 1999). However, these sets of findings can be reconciled by taking into account domain-specific capacity-limitations. A number of studies have shown that face processing is associated with capacity-limitations, in that the identity of only one face can be processed at a time (Bindemann, Burton, & Jenkins, 2005; Breber & Macrae, 2008; Jacques & Rossion, 2007; Jenkins, Lavie, & Driver, 2003; Palermo & Rhodes, 2002). Therefore, it is likely that the findings reported in studies using search tasks reflect domain-specific capacity-limitations in face processing because search tasks involve presenting multiple faces simultaneously. The reason why search tasks show evidence that face identification requires attention is probably because spatial attention resolves the competition between multiple faces and determines which gains access to the capacity-limited face identification mechanisms. This would mean that access to face processing mechanisms is gated by attention only when multiple faces need to be identified.
References Abrams, R. L., & Greenwald, A. G. (2000). Parts outweigh the whole (word) in unconscious analysis of meaning. Psychological Science, 11, 118–124. Besner, D., Risko, E. F., & Sklair, N. (2005). Spatial attention as a necessary preliminary to early processes in reading. Canadian Journal of Experimental Psychology, 59(2), 99–108. Bindemann, M., Burton, A. M., & Jenkins, R. (2005). Capacity limits for face processing. Cognition, 98, 177–197. Bindemann, M., Jenkins, R., & Burton, A. M. (2009). A bottleneck in face identification: Repetition priming from flanker images. Experimental Psychology, 54, 192–201. Breber, J. L., & Macrae, N. C. (2008). Faces, flowers and football boots: Capacity limits in distractor processing. Cognition, 107, 718–728. Burton, A. M., Bruce, V., & Hancock, P. J. B. (1999). From pixels to people: A model of familiar face recognition. Cognitive Science, 23, 1–31. Curcio, C. A., Kimberly, A. A., Sloan, K. R., Lerea, C. L., Hurley, J. B., Klkock, I. B., et al (1991). Distribution and morphology of human cone photoreceptors stained with anti-blue opsin. Journal of Comparative Neurology, 312, 610–624. Damian, M. F. (2001). Congruity effects evoked by subliminally presented primes: Automaticity rather than semantic processing. Journal of Experimental Psychology: Human Perception and Performance, 27, 154–165. Devue, C., Van der Stigchel, S., Bredart, S., & Theeuwes, J. (2009). You do not find your own face faster: You just look at it longer. Cognition, 111, 114–122. de Gardelle, V., & Kouider, S. (2009). How spatial frequencies and visual awareness interact during face processing. Psychological Science, 21, 58–66. Fabre, L., Lemaire, P., & Grainger, J. (2007). Attentional modulation of masked repetition and categorical priming in young and older adults. Cognition, 105, 513–532. Finkbeiner, M., & Palermo, R. (2009). The role of spatial attention in nonconscious processing. Psychological Science, 20, 42–51. Forster, K. I. (1998). The pros and cons of masked priming. Journal of Psycholinguistic Research, 27, 203–233. Forster, K. I. (2009). The intervenor effect in masked priming: How does masked priming survive across an intervening word? Journal of Memory and Language, 60, 36–49. Forster, K. I., & Forster, J. C. (2003). DMDX: A windows display program with millisecond accuracy. Behaviour Research Methods, Instruments, & Computers, 35, 116–124. Henson, R., Mouchlianitis, E., Matthews, W. J., & Kouider, S. (2008). Electrophysiological correlates of masked face priming. NeuroImage, 40, 884–895. Hummel, J. E. (2001). Complementary solutions to the binding problem in vision: Implications for shape perception and object recognition. Visual Cognition, 8, 489–517. Jacoby, L. L., & Whitehouse, K. (1989). An illusion of memory: False recognition influenced by unconscious perception. Journal of Experimental Psychology: General, 118, 126–135. Jacques, C., & Rossion, B. (2007). Electrophysiological evidence for temporal dissociation between spatial attention and sensory competition during human face processing. Cerebral Cortex, 17, 1055–1065. Jenkins, R., Lavie, N., & Driver, J. (2003). Ignoring famous faces: Category-specific dilution of distractor interference. Perception & Psychophysics, 65, 298–309. Kouider, S., Eger, E., Dolan, R., & Henson, R. (2009). Activity in face-responsive brain regions in modulated by invisible, attended faces: Evidence from masked priming. Cerebral Cortex, 19, 13–23. Lachter, J., Forster, K. I., & Ruthruff, E. (2004). Forty-five years after Broadbent (1958): Still no identification without attention. Psychological Review, 111, 880–913. Marzouki, Y., Grainger, J., & Theeuwes, J. (2007). Exogenous spatial cueing modulates subliminal masked priming. Acta Psychologia, 126, 34–45. O’Toole, A., Abdi, H., Deffenbacher, K. A., & Valentin, D. (1993). Low-dimensional representation of faces in higher dimensions of the face space. Journal of the Optical Society of America A, 10, 405–411. Palermo, R., & Rhodes, G. (2002). The influence of divided attention on holistic face perception. Cognition, 82, 225–257. Rossi, E. A., & Roorda, A. (2010). The relationship between visual resolution and cone spacing in the human fovea. Nature Neuroscience, 13, 156–157.
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Tong, F., & Nakayama, K. (1999). Robust representations for faces: Evidence from visual search. Journal of Experimental Psychology: Human, Perception and Performance, 25, 1016–1035. Thoma, V., Hummel, J. E., & Davidoff, Jules. (2004). Evidence for holistic representations of ignored images and analytic representations of attended images. Journal of Experimental Psychology: Human Perception and Performance, 30, 257–267. Tsal, Y. (1983). Movements of attention across the visual field. Journal of Experimental Psychology: Human Perception and Performance, 9, 523–530. Vuilleumier, P. (2005). How brains beware: Neural mechanisms of emotional attention. Trends in Cognitive Sciences, 9, 1364–1366.
Contents lists available at SciVerse ScienceDirect
Consciousness and Cognition journal homepage: www.elsevier.com/locate/concog
Subliminal access to abstract face representations does not rely on attention Bronson Harry ⇑, Chris Davis, Jeesun Kim Bankstown Campus, Building 1, MARCS Auditory Laboratories, University of Western Sydney, Locked Bag 1797, Penrith NSW 2751, Australia
a r t i c l e
i n f o
Article history: Received 17 May 2011 Available online 24 December 2011 Keywords: Face identification Masked repetition priming Spatial attention
a b s t r a c t The present study used masked repetition priming to examine whether face representations can be accessed without attention. Two experiments using a face recognition task (fame judgement) presented masked repetition and control primes in spatially unattended locations prior to target onset. Experiment 1 (n = 20) used the same images as primes and as targets and Experiment 2 (n = 17) used different images of the same individual as primes and targets. Repetition priming was observed across both experiments regardless of whether spatial attention was cued to the location of the prime. Priming occurred for both famous and non-famous targets in Experiment 1 but was only reliable for famous targets in Experiment 2, suggesting that priming in Experiment 1 indexed access to view-specific representations whereas priming in Experiment 2 indexed access to view-invariant, abstract representations. Overall, the results indicate that subliminal access to abstract face representations does not rely on attention. Ó 2011 Elsevier Inc. All rights reserved.
1. Introduction Face recognition is the process of matching perceptual information with representations stored in long-term memory (e.g., Burton, Bruce, & Hancock, 1999). Previous research has focussed on what type of visual processing is associated with visual recognition, and the nature of the representations involved. However, relatively little is currently known about the role of consciousness and attention in accessing face representations. Recently, Kouider, Eger, Dolan, and Henson (2009), and Henson, Mouchlianitis, Matthews, and Kouider (2008) have shown that masked, briefly presented faces facilitate the recognition of target faces when both of these faces depict the same individual. It was proposed that this repetition priming effect indexed subliminal access to abstract representations. The claim that abstract representations were accessed was based on three findings. First, priming was shown even when primes and targets were different images of the same person, indicating that the priming involved access to view-invariant representations. Second, priming was only observed for famous targets suggesting that subliminal access was limited to pre-existing, long-term memory representations. Third, priming was not related to objective, pixel-based measures of visual similarity between targets and primes, ruling out the possibility that priming was due to low level image similarity. Evidence that face representations are accessed without consciousness does not necessarily mean that other domain general processes, such as attention, cannot modulate access to these representations. A number of studies have shown that subliminal repetition priming is not observed for masked letter and word stimuli when the primes are presented in an unattended location, indicating that subliminal access to stored representations relies on attention (Lachter, Forster, & Ruthruff, 2004; Marzouki, Grainger, & Theeuwes, 2007). Given these findings, it is possible that subliminal access to face representations also ⇑ Corresponding author. Fax: +61 2 9772 6040. E-mail address: [email protected] (B. Harry). 1053-8100/$ - see front matter Ó 2011 Elsevier Inc. All rights reserved. doi:10.1016/j.concog.2011.11.007
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require attention (although see Finkbeiner & Palermo, 2009 for evidence that unattended face produce congruency priming effects in a sex categorisation task). Alternatively, it could also be possible that attention is only required for access to particular types of face representations. Studies examining repetition priming effects in tasks with unmasked primes have shown that priming across transformed images of objects (e.g., in-plane rotations) occurs only when primes are spatially attended (Hummel, 2001; Thoma, Hummel, & Davidoff, 2004), but priming across identical images occurs regardless of whether primes are attended. These results raise the possibility that only access to abstract, view-invariant representations requires attention, a possibility that is consistent with evidence that viewing more than one face simultaneously eliminates view-invariant repetition priming effects and but not view-specific priming effects (Bindemann, Jenkins, & Burton, 2009). It is also possible that consciousness also played a role in the view-invariant priming effects reported by Kouider et al. (2009) and Henson et al. (2008). That is, since in their studies both images of an individual were used as targets in several trials throughout the experiment, it might be that the view-invariant priming effect that was observed was due to conscious exposure to each image. On this view, the view-invariant priming might not have indexed access to abstract representations, but instead indexed access to image-specific representations of the stimuli that were formed when each stimulus was viewed as a target. The present study examined the role of attention in subliminal face recognition in two experiments. Experiment 1 presented the same images as primes and as targets to examine the role of attention on access to view-specific representations and Experiment 2 presented different images as primes and targets to examine the role of attention on access to view-invariant representations. Moreover, primes in Experiment 2 were never presented consciously as targets to ensure that priming involved access to abstract representations, not image specific representations stored from repeated presentations to the target images. In each experiment, participants completed a fame judgement task similar to that used in Kouider et al. (2009) and Henson et al. (2008), however, unlike the method employed in these studies, in the current task masked primes appeared prior to targets in a spatially unattended location. Additionally an exogenous cue was presented to draw attention either to the location of the prime or to another location. If access to face representations requires attention then repetition priming should only be observed on trials where the prime was cued. 2. Experiment 1 2.1. Method 2.1.1. Participants Twenty undergraduate (Mage = 21 years, 18 female) students participated in exchange for course credit. All reported having normal or corrected to normal visual acuity. 2.1.2. Stimuli Thirty-two images of famous singers or actors and 32 images of amateur models were selected from the internet. Amateur models were chosen to ensure comparability in attractiveness and age range with the famous faces. Half of the famous and amateur model faces were female and half male. Images were cropped to include only the face region and the hairline (Fig. 1). The luminance and contrast of each image was equalised by setting the distribution of pixel intensities of the face region to a mean of 127 and a standard deviation of 50. Subsequently, the luminance and contrast of the hair was altered until there were no subjective differences between the face and hair. Each stimulus was used as a target as well as a prime. Target and prime image size was set so that the stimuli subtended 4° and 5° visual angle respectively. A stimulus that consisted of a mosaic of blurred eyes, noses and mouths from various faces was used as a forward mask and a scrambled face superimposed on a chequer-board background was used as a backward mask (vertical visual angle 5°). A cue similar to that used in Marzouki et al. (2007) was also constructed (vertical visual angle 4°; Fig. 1).
Fig. 1. Order of stimulus presentation in Experiment 1.
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2.1.3. Procedure Participants were tested individually while seated in a dimly lit booth. Head position was stabilised with a chin rest 67 cm from the monitor which had a refresh rate of 85 Hz. Stimuli were presented and reaction time and accuracy data were collected with DMDX (Forster & Forster, 2003). On each trial participants judged whether a target stimulus was famous or non-famous and indicated their response with a button press. Each trial started with the appearance of three forward masks (494 ms), one in the centre of the screen and two on each side of the central mask. After 494 ms an exogenous cue appeared in either the left or right position for 58 ms. Then a prime stimulus appeared either in the left or right locations for a another 58 ms. After the prime, the target appeared in the central location with two backward masks in the left and right locations for 494 ms (Fig. 1). On half of the trials the prime and the target were images of the same face (repetition prime trials) and on half of the trials the prime and the target were images of two different faces (control prime trials). The control primes were always the same sex (e.g., both male) to ensure that any priming effect observed was not due to between-category differences. Moreover, primes were always from the same response category as the target (e.g., both famous) to ensure that priming was not due to response congruency. That is, if the prime and targets used for baseline were associated with different response categories, priming could be based on responses made to the primes via automatic activation of stimulus-response mappings learned over the course of the experiment (Abrams & Greenwald, 2000; Damian, 2001). On half the trials the cue appeared in the same location as the prime, and on half of the trials the cue appeared on the opposite side of the display to where the prime appeared. The task consisted of four blocks of 256 trials, which meant that each target and prime appeared a total of 16 times; 128 trials had the same prime and target pairs (the repetition condition) and 128 trials had different prime and target pairs (the control condition); for 128 trials the prime was cued and for 128 trials uncued. Before the main task participants completed a practice task consisting of 36 trials. In the practice trials, eight famous and eight non-famous targets were presented that did not appear in the main task. Participants also completed a prime visibility task that consisted of a single block of 256 trials. In this task, participants determined whether the masked prime was famous or non-famous to assess how visible the primes were to each participant. However, since making a judgement about the prime would likely encourage participants to attend to the prime (thus making the primes more visible) participants also made a fame judgement to the unmasked target face to ensure participants attended to the target and prime in a similar way as in the main task. On each trial, participants first judged whether the target was famous or non-famous as quickly and as accurately as possible. Once this response was made, the words ‘‘Non-famous or famous’’ were presented on the screen to prompt participants to respond as to whether the prime was famous or non-famous. This task was identical to a single block of trials from the main task except that on half the trials the prime and target were from the same response category (i.e., both famous) and on half the trials the prime and target were from different categories (primes and targets were never the same individual). Participants completed these tasks over three days. On the first day participants completed a block of the practice trials, followed by two blocks of the main task. On the second day participants completed another two blocks of the main task and on the third day participants completed one block of the prime visibility task. 2.2. Results Two participants with error rates greater than 20% were excluded from the analysis. Incorrect responses (6.8%) were excluded from the reaction time analysis and any response greater than two standard deviations from a participants’ mean was winsorised (4.5% of the data). Table 1 presents mean reaction times and mean percent error rates across the target type (famous, non-famous), cue (prime cued, prime uncued), and prime type (repetition, control) conditions. A separate ANOVA was calculated from the participant means (F1) and the item means (F2). Participant and item means were analysed in a threeway (2 2 2) mixed repeated measures ANOVA. All factors were treated as repeated factors in the participant and item analysis, except for the target type factor (famous, non-famous) which was treated as a non-repeated factor in the item analysis.
Table 1 Mean reaction times and percent error rates across cue, target type and prime type conditions. Item type
Reaction time (ms)
Errors (%)
Cued prime
Uncued prime
Cued prime
Uncued prime
Famous targets Repetition prime Control prime Priming
538 (17) 544 (17) 6
540 (19) 547 (17) 7
4.1 (1.0) 4.8 (1.2) 0.7
5.5 (1.1) 4.8 (1.1) 0.7
Non-famous targets Repetition prime Control prime Priming
599 (20) 604 (19) 5
601 (20) 607 (20) 6
9.0 (2.2) 8.5 (2.0) 0.5
8.9 (2.5) 9.0 (2.6) 0.1
Note: Standard errors are shown in parenthesis.
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Analysis of reaction times revealed a significant main effect of prime type (F1(1,17) = 5.6, MSE = 242.6, p = 0.031, g2p ¼ 0:25; F2(1,62) = 5.0, MSE = 347.9, p = 0.030, g2p ¼ 0:07) with faster reaction times on repetition prime trials than control prime trials (M = 569 ms vs. M = 576 ms). There was a main effect of target type (F1(1,17) = 24.3, MSE = 5409.8, p < 0.001, g2p ¼ 0:59; F2(1,62) = 146.0, MSE = 1460.0, p < 0.001, g2p ¼ 0:70) with famous targets recognised faster than non-famous targets (M = 542 ms vs. M = 603 ms). The main effect of cue did not reach significance (F1(1,17) = 1.7, MSE = 129.3, p = 0.205, g2p ¼ 0:10; F2(1,62) < 1) and this factor did not interact with the other factors (all F1(1,17) < 1; all F2(1,62) < 1). Analysis of errors revealed a significant main effect of target type for the item analysis (F1(1,17) = 2.7, MSE = 219.2, p = 0.122, g2p ¼ 0:14; F2(1,62) = 7.3, MSE = 95.4, p = 0.009, g2p ¼ 0:11) with fewer errors for famous than non-famous targets (M = 4.8% vs. M = 8.9%). No other main effects or interactions were significant indicating that the reaction time results were not associated with a speed-accuracy trade-off. 2.2.1. Prime visibility Mean accuracy in the prime visibility task across famous and non-famous primes was 50.5%. A single sample t-test showed that mean performance was not significantly above chance performance (t(17) = 1.2, p = 0.24), suggesting that participants were not aware of the prime in the fame judgement task. To examine whether prime visibility was modulated either by the cue, or by response compatibility (between the prime and target), the prime visibility data was submitted to a 2 (cue) 2 (response compatibility) repeated measures ANOVA. This analysis revealed a significant main effect of response compatibility (F(1,17) = 8.62, MSE = 35639.0, p = 0.009, g2p ¼ 0:34) with better performance when the prime and target were compatible (M = 66.2%) compared to when the prime and target were incompatible (M = 34.5%). This result could indicate that participants were aware of the primes and that response interference on incompatible trials impaired performance. Alternatively, given the similar magnitude of performance enhancement for the response compatible trials and the performance impairment for the response incompatible trials, it is also possible that the effect of response compatibility is a form of a bias effect (where participants simply guessed the prime category based upon that of the target). The main effect of cue and the interaction between cue and response compatibility was not significant (Fs < 1). A linear regression was conducted to examine the relationship between priming and prime visibility across participants. Priming scores were collapsed over cue and target type conditions since these variables had no effect on priming effects. In addition, only response compatible trials were used to estimate prime visibility since there may have been an interference effect for the response incompatible trials. Fig. 2 presents the relationship between prime visibility data and the magnitude of the priming effect. There was no significant linear relationship between priming and prime visibility (R2 = 0.1, p = 0.21). To examine whether prime visibility performance was influenced by confusions between famous and non-famous targets, items that were recognised < 90% correct in the fame judgement task were removed from the prime visibility analysis (famous targets = 4; non-famous target = 8). Removing these items did not change the overall pattern of results for the prime visibility analysis as mean prime visibility was not significantly above chance (M = 51.1%, t18 = 1.3, p = 0.22) and there was no significant linear relationship between prime visibility and priming (R2 = 0.26, p = 0.53). 2.2.2. Image similarity Image similarity was calculated as the root-mean-square difference in greyscale values across each target and the respective repetition and control primes (Henson et al., 2008). This similarity measure was normalised so that identical images would have a value of zero and completely dissimilar images would have a value of one. Image similarity values were entered into a 2 2 ANOVA with prime type as a repeated factor and target type as a between factor. This analysis showed
Fig. 2. The relationship between prime visibility scores and the repetition priming effect across participants. Each point represents the data from each participant and the line represents the linear fit between the two variables.
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a significant main effect of prime type (F(1,62) = 23.5, MSE = 0.067, p < 0.001, g2p ¼ 0:28) indicating that targets and repetition primes were more visually similar than targets and control primes (M = 0.21 vs. M = 0.26). The main effect of target type (F(1,62) = 2.7, MSE = 0.007, p = 0.41, g2p ¼ 0:01) and the interaction between prime type and target type (F(1,62) = 2.7, MSE = 0.001, p = 0.407, g2p ¼ 0:01) was not significant. 2.3. Discussion Experiment 1 used a fame judgement task with masked spatially unattended repetition primes that were the same images as targets and showed repetition priming effects regardless of whether primes were attended. This result is at odds with studies showing that masked repetition priming of words and letters relies on attention (Lachter et al., 2004; Marzouki et al., 2007). Instead, the present results support studies showing that access to view-specific representations does not rely on attention (Hummel, 2001; Thoma et al., 2004). The present finding of priming for both famous and non-famous targets contrasts with the results from other studies showing masked repetition priming in a fame judgement task (Henson et al., 2008; Kouider et al., 2009).1 One possible reason why priming effects for non-famous faces is that the target stimuli were repeated 16 times whereas in previous studies the targets were only presented around 6 times. That is, priming in recognition tasks relies on the target being represented in memory (Forster, 1998) and it might be that usable representations of non-famous (i.e., unfamiliar) faces only develop with a sufficient number of repeated presentations (e.g., Tong & Nakayama, 1999). Alternatively, priming for non-famous targets in the current study might have been observed because targets and their respective repetition primes were more visually similar than the control primes. On this view, priming was not the result of activating stored representations, but was due to low level visual properties associated with the face. If so, then priming must have indexed processing at a relatively abstract stage of processing (e.g., location invariant) since the primes and targets were presented in different locations. As reported above, there was no effect of cuing on target response times (this was expected as the cues only appeared at the peripheral locations and hence there should be no main effect of cue position on reaction times to the centrally presented targets). Despite this lack of a cuing effect, it is reasonable to assume that the cuing procedure used in the present study triggered shifts in attention because the cuing procedure used in this task was similar to that used in Marzouki et al. (2007), which showed that repetition priming effects from masked letter stimuli were modulated by an exogenous cue. 3. Experiment 2 The question of whether masked faces access abstract representations even when unattended was tested in Experiment 2. Several modifications were made to the method used in Experiment 1. Firstly, the prime and target pairs were not the same images. Moreover, primes were never presented as targets (and vice versa) to ensure that the priming effect would not reflect pre-activation of the episodic representations of a particular target image formed over repeated exposures. Secondly, the cuing technique was changed to increase the chances that the cue would summon attention to the location of the prime. The cue was presented either at the central target location or in the location of the prime to ensure that a cuing effect would be observed in target reaction times. In addition, the target occasionally appeared in a cued peripheral location. This was to ensure that participants would not completely ignore the cue when it appeared in a peripheral location. 3.1. Method 3.1.1. Participants Seventeen graduate (Mage = 26.8 years, 9 female) students participated in exchange for payment. All reported having normal or corrected to normal visual acuity. None of the participants recruited for Experiment 2 participated in Experiment 1. 3.1.2. Materials Two images each of 32 famous singers or actors and 32 amateur models were selected from the internet. Images were selected so that the hairstyle, lighting conditions and pose varied across the two images of the same individuals. Two yellow bars that were similar in appearance to the cue used in previous studies (Finkbeiner & Palermo, 2009), were used to as the exogenous cue in the present experiment (see Fig. 3). 3.1.3. Procedure Fig. 2 shows the order of stimuli presentation. Each trial started with the appearance of three forward masks (for 494 ms), which was followed by an exogenous cue that appeared in one of the three locations (for 106 ms). After this, a prime stimulus appeared either in the left or right locations (for 58 ms). After the prime, the target appeared in the central location with two backward masks in the left and right locations (for 494 ms). On 40% of trials (Target cued), the cue appeared in the central location and on another 40% of trials (Prime cued), the cue appeared in the location where the prime appeared. On the
1 It should be noted that although Kouider et al. (2009) and Henson et al. (2008) did not observe a behavioural priming effect for non-famous targets, repetition-related suppression effects were observed in brain imaging data for both famous and non-famous targets.
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Fig. 3. Order of stimulus presentation in Experiment 2 for the three cuing conditions.
remaining 20% of trials (Foils), the target was presented in one of the peripheral locations and was preceded by a cue in the same location. No prime was presented on these trials. All stimuli presented in central and peripheral locations subtended 4° and 5° visual angle respectively. Given the relevance of the cue to the task (cued target location on 60% of trials) it was expected that these cuing conditions would encourage participants not to pre-focus their attention at the central location (since the target did not always appear in the central location) but attend to the cued location. All stimuli that were presented in the peripheral locations (e.g., the prime on Target and Prime cued trials, the target on Foil trials) appeared equally in the left location and the right location across trials. Participants were instructed that the cue would indicate the location of the target on the majority of trials. Moreover, it was made clear to participants that the cue always validly indicated the location of the target when the cue appeared in the central location. Thus, it is likely that the prime was unattended on target cued trials. The experiment consisted of four blocks of 320 trials that were completed over two separate days. Within a block, each target appeared five times, once in each of the prime and cuing conditions, and once in the foil condition. Participants completed a practice task consisting of 40 trials before the main task. Eight famous and eight non-famous targets were presented in this task that did not appear in the main task. Participants also completed a prime visibility task which consisted of 320 trials. All other aspects of the prime visibility task in this experiment were the same as the one used in Experiment 1. 3.2. Results Two participants with error rates greater than 20% were excluded from the analysis. Incorrect responses (8.5%) were excluded from the reaction time analysis and any response greater than two standard deviations from a participants’ mean was winsorised (4.2% of the data). 3.2.1. Analysis of the cuing effect A preliminary analysis was conducted to examine whether the cuing technique used in the present study produced a cuing effect on performance in the fame judgement task. Note that this analysis was collapsed across the prime conditions because no primes were presented in Foil trials. Separate 3 2 ANOVAs were executed with the participant means (F1) and the item means (F2) for reaction times and error rates. Analysis of reaction times showed a significant main effect of cue (F1(2,28) = 73.6, MSE = 683.0, p < 0.001, g2p ¼ 0:84; F2(2,124) = 523.45, MSE = 211.2, p < 0.001, g2p ¼ 0:89) with the fastest reaction times on Target cued trials and the slowest reaction times on Foil trials (M = 538 ms for Target cued, M = 565 ms for Prime cued, M = 619 ms for Foil). There was also a main effect of target type (F1(1,14) = 4.8, MSE = 1525.3, p = 0.045, g2p ¼ 0:26; F2(1,62) = 10.4, MSE = 1573.9, p = 0.002, g2p ¼ 0:14) with faster reaction times to famous targets than to non-famous targets (M = 565 ms vs. M = 584 ms).
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Analysis of errors showed a significant main effect of cue (F1(2,28) = 9.5, MSE = 9.9, p = 0.001, g2p ¼ 0:41; F2(2,124) = 25.2, MSE = 8.0, p < 0.001, g2p ¼ 0:29) again with fewer errors on Target cued trials and more errors on Foil trials (M = 7.3% for Target cued, M = 7.7% for prime cued, M = 10.6% for Foil). There was also a main effect of target type for the item analysis (F1(1,14) = 2.5, MSE = 124.2, p = 0.138, g2p ¼ 0:15; F2(1,62) = 4.3, MSE = 154.1, p = 0.044, g2p ¼ 0:06) with more errors for famous targets than non-famous target (M = 10.4% vs. M = 6.7%), possibly indicating that faster reaction times for famous targets might have been the result of a speed-accuracy trade-off. 3.2.2. Analysis of the priming effect Table 2 presents mean reaction times and mean percent error rates across the target type (famous, non-famous), cue (target cued, prime cued), and prime type (repetition, control) conditions. Note that this analysis omitted the foil condition because no primes were presented on these trials. Analysis of reaction times showed a main effect of cue (F1(1,14) = 66.5, MSE = 1292.6, p < 0.001, g2p ¼ 0:83; F2(1,62) = 296.0, MSE = 625.1, p < 0.001, g2p ¼ 0:83) with faster reaction times when the target was cued compared to when the prime was cued (M = 539 ms vs. M = 566 ms). There was a main effect of prime type (F1(1,14) = 40.6, MSE = 165.4, p < 0.001, g2p ¼ 0:74; F2(1,62) = 24.2, MSE = 658.0, p < 0.001, g2p ¼ 0:28) with faster reaction times to repetition trials than to control trials (M = 548 ms vs. M = 556 ms). There was also a significant main effect of target type only for the item analysis (F1(1,14) = 4.5, MSE = 7866.0, p = 0.053, g2p ¼ 0:24; F2(1,62) = 9.7, MSE = 7430.1, p = 0.003, g2p ¼ 0:14) with faster reaction times to famous targets than to non-famous targets (M = 544 ms vs. M = 561 ms). The prime type target type interaction was significant for the item analysis (F1(1,14) = 3.1, MSE = 405.2, p = 0.100, g2p ¼ 0:18; F2(1,62) = 5.2, MSE = 658.0, p = 0.027, g2p ¼ 0:08). Simple effects analysis revealed that there was a significant priming effect for famous targets (F1(1,14) = 25.1, MSE = 275.4, p < 0.001, g2p ¼ 0:64; F2(1,31) = 21.4, MSE = 795.0, p < 0.001, g2p ¼ 0:41) whereas the priming effect for non-famous targets failed to reach significance in the participant analysis (F1(1,14) = 3.7, MSE = 295.2, p = 0.077, g2p ¼ 0:21; F2(1,31) = 4.5, MSE = 521.0, p = 0.043, g2p ¼ 0:13). The reaction time analysis also revealed a marginal interaction effect between prime type and cue (F1(1,14) = 4.4, MSE = 229.0, p = 0.054, g2p ¼ 0:24; F2(1,62) = 3.5, MSE = 616.3, p = 0.065, g2p ¼ 0:05) with a larger priming effect when the target was cued compared to when the prime was cued. Simple effects analysis revealed a significant priming effect for Target cued trials (F1(1,14) = 31.6, MSE = 51.3, p < 0.001, g2p ¼ 0:64; F2(1,62) = 22.7, MSE = 657.3, p < 0.001, g2p ¼ 0:27) and for Prime cued trials (F1(1,14) = 6.6, MSE = 47.4, p = 0.022, g2p ¼ 0:32; F2(1,62) = 5.2, MSE = 617.0, p = 0.027, g2p ¼ 0:08). Analysis of errors revealed a significant main effect of target type for the item analysis (F1(1,14) = 2.9, MSE = 606.9, p = 0.112, g2p ¼ 0:17; F2(1,62) = 4.2, MSE = 884.2, p = 0.044, g2p ¼ 0:06) with more errors for famous targets than non-famous targets (M = 9.4% vs. M = 5.6%), suggesting that the faster reaction times observed for the famous targets might be due to a speed-accuracy trade-off. There was also a significant interaction between prime type and cue (F1(1,14) = 10.1, MSE = 9.2, p = 0.007, g2p ¼ 0:42; F2(1,62) = 7.5, MSE = 26.2, p = 0.008, g2p ¼ 0:11). Simple effects analysis showed a significant main effect of prime type for Target cued trials (F1(1,14) = 10.8, MSE = 2.6, p = 0.005, g2p ¼ 0:44; F2(1,62) = 9.3, MSE = 61.2, p = 0.003, g2p ¼ 0:13) with fewer errors to repetition prime trials than to control prime trials (M = 6.6% vs. M = 8.0%), whereas the priming effect failed to reach significance for Prime cued trials (F1(1,14) = 3.0, MSE = 79.7, p = 0.104, g2p ¼ 0:03; F2(1,62) < 1). 3.2.3. Prime visibility Mean accuracy in the prime visibility task across famous and non-famous primes was 48.3%. A single sample t-test showed that mean performance was not significantly above chance performance (t(14) = 1.7, p = 0.1), suggesting that participants were not aware of the prime in the fame judgement task. As in Experiment 1, the effect of cue and response compatibility on prime visibility was examined with a 2 (cue) 2 (response compatibility) repeated measures ANOVA. This analysis did not show a significant main effect for either cue or response compatibility and the interaction between these factors was also not significant (Fs < 1). Since priming varied across famous and non-famous targets, separate regression analyses between priming and prime visibility (Fig. 4) were
Table 2 Mean reaction times and percent error rates across cue, target type and prime type conditions. Item type
Reaction time (ms)
Errors (%)
Prime cued
Target cued
Prime cued
Target cued
Famous targets Repetition prime Control prime Priming
554 (19) 560 (19) 6
523 (17) 538 (18) 15
7.9 (1.6) 10.3 (1.6) 2.4
10.0 (1.8) 9.5 (1.7) 0.5
Non-famous targets Repetition prime Control prime Priming
573 (18) 576 (17) 3
544 (14) 550 (16) 6
5.3 (1.3) 5.7 (1.7) 0.4
5.9 (1.6) 5.6 (1.5) 0.3
Note: Standard errors are shown in parenthesis.
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Fig. 4. The relationship between prime visibility scores and repetition priming across participants for famous and non-famous targets. The diamond points represent data from famous target trials and the solid line represents the linear fit for this condition. The square points represent data from the non-famous target trials and the broken line represents the linear fit for this condition.
conducted (Fig. 4). The results showed that there was no significant relationship between priming and prime visibility for famous (R2 = 0.004, p = 0.83) and non-famous targets (R2 < 0.001, p = 0.97). To examine whether prime visibility performance was influenced by confusions between famous and non-famous targets, items that were recognised < 90% correct in the fame judgement task were removed from the prime visibility analysis (famous targets = 11; non-famous target = 6). Again, removing these items did not change the overall pattern of results for the prime visibility analysis as mean prime visibility was not significantly above chance (M = 50.3%, t15 = 0,28, p = 0.78) and there was no significant linear relationship between prime visibility and priming for famous (R2 = 0.01, p = 0.71) and non-famous targets (R2 = 0.03, p = 0.57). 3.2.4. Analysis of image similarity Image similarity values between targets and their respective repetition and control primes were entered into a 2 2 ANOVA with prime type as a repeated factor and target type as a between factor. This analysis showed a non-significant main effect of prime type (F(1,62) = 1.6, MSE = 0.001, p = 0.21, g2p ¼ 0:03), target type (F(1,62) = 2.7, MSE = 0.007, p = 0.41, g2p ¼ 0:01) and a non-significant interaction between these two factors (F(1,62) = 2.7, MSE = 0.001, p = 0.407, g2p ¼ 0:01), indicating that the targets and repetition primes were not more visually similar than targets and control primes for famous and non-famous items. Thus, the data from the image similarity analysis was inconsistent with the view that repetition priming effects were due to low level visual overlap between targets and repetition primes. 3.3. Discussion The primary aim of Experiment 2 was to investigate whether repetition priming effects would be observed for spatially unattended primes when targets and repetition primes were not the same images. Priming was found and occurred regardless of whether the prime was attended. This result shows that access to view-invariant representations does not rely on attention. Moreover, the primes were novel, unexposed images of the target individuals, thus the priming observed was not due to access to image specific representations. Likewise, the observed repetition priming cannot be due to the low level perceptual overlap between repetition primes and targets since the image similarity analysis did not show any evidence that the repetition primes were more similar to the targets compared to the control primes. Given the above, priming likely occurred because the prime triggered processing in a view-invariant representation that was subsequently capitalised upon by the target. In addition to showing that the repetition priming effect extended to different primes and targets, the present experiment provides strong evidence that repetition priming did not directly rely on attention. There was a clear cuing effect in the present study indicating that the cue was effective at triggering shifts in attention to the location of the prime. Given this successful manipulation of attention, the presence of a repetition priming effect provides clear evidence that access to face representations does not rely on attention. Unexpectedly, the results suggested that the priming effect was larger when the target was cued compared to when the prime was cued (although the interaction was not secure). The finding of a weaker priming effect for cued primes is counterintuitive and is at odds with previous studies examining the role of attention in masked priming (Besner, Risko, & Sklair, 2005; Finkbeiner & Palermo, 2009; Lachter et al., 2004; Marzouki et al., 2007). One explanation for the weakness of priming in the Prime cued trials is that the cue on these trials did not validly indicate the position of the target. Consequently, participants might have had to re-direct attention to the central location in order to
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make a judgement about the target presented in the central location.2 This re-directing of attention could have resulted in a resetting of any processing initiated by the prime that might have been capitalised on in processing the target (and hence no priming on those trials which would have reduced the overall priming effect). This explanation is similar to one proposed by Forster (2009) that disruptions prior to target onset, such as presenting a clearly visible item between prime and target, can result in a resetting of priming effects. It should also be noted that the presence of marginal effects (such as the one mentioned above) does not necessarily indicate that the current experiment is underpowered. The task used in the present study involved over twice as many trials as the Kouider et al. (2009) and Henson et al. (2008) studies (over 1000 trials compared to 480 trials) and we recruited a similar number of participants as these previous studies. Although the effect sizes reported in the present experiment range from weak-strong, the effect size for the priming effect was moderate-strong (g2p ¼ 0:74, participant analysis). Finally, unlike Experiment 1, in this experiment there was no priming for non-famous targets. This lack of a reliable priming effect for non-famous targets is consistent with the interpretation that the priming observed in Experiment 1 for these targets was image-specific. That is, if priming in Experiment 1 was produced because primes and targets were the same image, then the null priming effect for non-famous faces in Experiment 2 occurred because primes and targets had different poses. On the other hand, priming for famous face targets was found in Experiment 2 presumably because perceivers had pre-established, view-invariant representations for these faces. In sum, finding priming from unexposed images of famous targets provides straightforward evidence that masked face repetition priming does not rely on instance based representations. 4. General discussion The present study investigated the role of attention in unconscious access to abstract face representations by examining whether spatially unattended masked faces produce repetition priming effects in a fame judgement task. To do this, a procedure was used that built upon two separate but related masked priming paradigms. First, masked repetition priming in a fame judgement task was used to index unconscious access to face representations (Henson et al., 2008; Kouider et al., 2009). Second, as in Finkbeiner and Palermo (2009) primes were presented in a spatially unattended location to examine whether attention to the primes was necessary for access to face representations to occur. Taken together, the present results extend those of these previous studies by showing that access to view-invariant face representations does not require attention. This finding stand in clear contrast to results from studies that have used non-face stimuli (e.g., word and letter recognition tasks, Lachter et al., 2004: Marzouki et al., 2007) where it has been found that attention modulates masked repetition priming and that repetition priming across transformed images relies on attention (Hummel, 2001; Thoma et al., 2004). The conclusion that abstract representations were accessed in the present experiments is based on three findings; priming was not related to image similarity, priming was present when primes were novel, unexposed images, and priming was observed only for famous targets. However, it might be argued that priming effects were not observed for non-famous targets in Experiment 2 because of the nature of the fame judgement task. According to this view, repeating an unfamiliar stimulus (i.e., a repetition primed target) generates a false familiarity signal (Jacoby & Whitehouse, 1989) which in turn interferes with generating a ‘non-famous’ response and so eliminates priming for non-famous targets. This explanation however does not account for the priming effect found for both famous and non-famous targets in Experiment 1. One possible explanation might be based on the slight differences in demographic profile of the participants recruited for Experiments 1 and 2. For example, the participants in Experiment 2 might have been less familiar with the famous targets than the participants from Experiment 1. However, it is unclear how such differences would be related to the presence or absence of priming effects for the non-famous targets. A more general explanation for the pattern of results is that priming for non-famous targets was based on access to view-specific representations formed during the task whereas priming for famous targets was based on access to long term, view-invariant representations. This view is compatible with evidence that view-specific representations for unfamiliar faces form rapidly over a small number of presentations whereas more familiar faces are associated with long-term, view-invariant representations (Tong & Nakayama, 1999). Why might faces show masked priming (hence demonstrating they have been processed) in the absence of attention whereas other types of stimuli (words, letters) do not? In the current study, primes were presented peripherally and so would have been subject to the reduced spatial resolution that is associated with peripheral vision caused by the increased convergence of cones to retinal ganglion cells (Curcio et al., 1991; Rossi & Roorda, 2010). Priming from these peripherally presented faces shows that there is sufficient information in the periphery to trigger identification processes. In this sense, the results are consistent with the claim that identity-related information is contained in the global details (O’Toole, Abdi, Deffenbacher, & Valentin, 1993). An intriguing possibility concerning the basis of unattended masked face priming is opened up if it is assumed that such global face details can be carried by low frequency information. If priming was based on processing low spatial frequency information (the size of the current priming effects are equivalent to de Gardelle & Kouider, 2009 where primes and targets contained the same low spatial frequency face information) then this could explain why such effects can occur in the absence of attention. That is, it has been proposed that low-spatial frequency information is relayed
2 Although this explanation might seem to imply that Prime cued trials should have been the slowest trials instead of the Foil trials, this is not necessarily the case since Foil trials would have required participants to saccade to the peripherally presented targets in order to recognise them.
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by the magnocellular pathway that avoids modulation by attention either because information is relayed to face processing mechanisms via a subcortical route or by an early feedforward sweep of activity (see Vuilleumier, 2005). On this view, face processing proceeds on a coarse-to-fine basis, where the low spatial frequency information is processed automatically and then followed by conscious processing of the high spatial frequency information. In this scheme, masked priming would index the initial automatic process. Such a mechanism of face priming might go some way to explaining why faces can be primed in the absence of attention whereas other types of stimuli appear to require it (e.g., Besner et al., 2005; Fabre, Lemaire, & Grainger, 2007; Lachter et al., 2004; Marzouki et al., 2007). One possible explanation for why only faces produce priming effects is that faces may involuntarily capture attention even on trials where attention was cued elsewhere (e.g., to the target location). However, the results of studies examining the role of attention in masked priming studies suggest that this possibility is unlikely. Finkbeiner and Palermo (2009) showed no differences in task performance (in an orientation discrimination task) when masked faces appeared in an unattended location compared to attended locations, demonstrating that masked faces do not trigger exogenous shifts of attention. Moreover, even if the face prime did occasionally trigger an attention shift, such a process would (in the uncued case) take longer than the 58 ms prime display time since attentional capture has been shown to occur at least 50 ms (plus 8 ms per degree of visual angle) after the onset of a distracting stimulus (Lachter et al., 2004; Tsal, 1983). Therefore, the prime would have still been functionally unattended as it would have been replaced by the mask before attention was deployed. The current results (showing face processing in the absence of attention) appear to contradict those from search tasks that suggest that face identification requires attention (e.g., Devue, Van der Stigchel, Bredart, & Theeuwes, 2009; Tong & Nakayama, 1999). However, these sets of findings can be reconciled by taking into account domain-specific capacity-limitations. A number of studies have shown that face processing is associated with capacity-limitations, in that the identity of only one face can be processed at a time (Bindemann, Burton, & Jenkins, 2005; Breber & Macrae, 2008; Jacques & Rossion, 2007; Jenkins, Lavie, & Driver, 2003; Palermo & Rhodes, 2002). Therefore, it is likely that the findings reported in studies using search tasks reflect domain-specific capacity-limitations in face processing because search tasks involve presenting multiple faces simultaneously. The reason why search tasks show evidence that face identification requires attention is probably because spatial attention resolves the competition between multiple faces and determines which gains access to the capacity-limited face identification mechanisms. This would mean that access to face processing mechanisms is gated by attention only when multiple faces need to be identified.
References Abrams, R. L., & Greenwald, A. G. (2000). Parts outweigh the whole (word) in unconscious analysis of meaning. Psychological Science, 11, 118–124. Besner, D., Risko, E. F., & Sklair, N. (2005). Spatial attention as a necessary preliminary to early processes in reading. Canadian Journal of Experimental Psychology, 59(2), 99–108. Bindemann, M., Burton, A. M., & Jenkins, R. (2005). Capacity limits for face processing. Cognition, 98, 177–197. Bindemann, M., Jenkins, R., & Burton, A. M. (2009). A bottleneck in face identification: Repetition priming from flanker images. Experimental Psychology, 54, 192–201. Breber, J. L., & Macrae, N. C. (2008). Faces, flowers and football boots: Capacity limits in distractor processing. Cognition, 107, 718–728. Burton, A. M., Bruce, V., & Hancock, P. J. B. (1999). From pixels to people: A model of familiar face recognition. Cognitive Science, 23, 1–31. Curcio, C. A., Kimberly, A. A., Sloan, K. R., Lerea, C. L., Hurley, J. B., Klkock, I. B., et al (1991). Distribution and morphology of human cone photoreceptors stained with anti-blue opsin. Journal of Comparative Neurology, 312, 610–624. Damian, M. F. (2001). Congruity effects evoked by subliminally presented primes: Automaticity rather than semantic processing. Journal of Experimental Psychology: Human Perception and Performance, 27, 154–165. Devue, C., Van der Stigchel, S., Bredart, S., & Theeuwes, J. (2009). You do not find your own face faster: You just look at it longer. Cognition, 111, 114–122. de Gardelle, V., & Kouider, S. (2009). How spatial frequencies and visual awareness interact during face processing. Psychological Science, 21, 58–66. Fabre, L., Lemaire, P., & Grainger, J. (2007). Attentional modulation of masked repetition and categorical priming in young and older adults. Cognition, 105, 513–532. Finkbeiner, M., & Palermo, R. (2009). The role of spatial attention in nonconscious processing. Psychological Science, 20, 42–51. Forster, K. I. (1998). The pros and cons of masked priming. Journal of Psycholinguistic Research, 27, 203–233. Forster, K. I. (2009). The intervenor effect in masked priming: How does masked priming survive across an intervening word? Journal of Memory and Language, 60, 36–49. Forster, K. I., & Forster, J. C. (2003). DMDX: A windows display program with millisecond accuracy. Behaviour Research Methods, Instruments, & Computers, 35, 116–124. Henson, R., Mouchlianitis, E., Matthews, W. J., & Kouider, S. (2008). Electrophysiological correlates of masked face priming. NeuroImage, 40, 884–895. Hummel, J. E. (2001). Complementary solutions to the binding problem in vision: Implications for shape perception and object recognition. Visual Cognition, 8, 489–517. Jacoby, L. L., & Whitehouse, K. (1989). An illusion of memory: False recognition influenced by unconscious perception. Journal of Experimental Psychology: General, 118, 126–135. Jacques, C., & Rossion, B. (2007). Electrophysiological evidence for temporal dissociation between spatial attention and sensory competition during human face processing. Cerebral Cortex, 17, 1055–1065. Jenkins, R., Lavie, N., & Driver, J. (2003). Ignoring famous faces: Category-specific dilution of distractor interference. Perception & Psychophysics, 65, 298–309. Kouider, S., Eger, E., Dolan, R., & Henson, R. (2009). Activity in face-responsive brain regions in modulated by invisible, attended faces: Evidence from masked priming. Cerebral Cortex, 19, 13–23. Lachter, J., Forster, K. I., & Ruthruff, E. (2004). Forty-five years after Broadbent (1958): Still no identification without attention. Psychological Review, 111, 880–913. Marzouki, Y., Grainger, J., & Theeuwes, J. (2007). Exogenous spatial cueing modulates subliminal masked priming. Acta Psychologia, 126, 34–45. O’Toole, A., Abdi, H., Deffenbacher, K. A., & Valentin, D. (1993). Low-dimensional representation of faces in higher dimensions of the face space. Journal of the Optical Society of America A, 10, 405–411. Palermo, R., & Rhodes, G. (2002). The influence of divided attention on holistic face perception. Cognition, 82, 225–257. Rossi, E. A., & Roorda, A. (2010). The relationship between visual resolution and cone spacing in the human fovea. Nature Neuroscience, 13, 156–157.
B. Harry et al. / Consciousness and Cognition 21 (2012) 573–583
583
Tong, F., & Nakayama, K. (1999). Robust representations for faces: Evidence from visual search. Journal of Experimental Psychology: Human, Perception and Performance, 25, 1016–1035. Thoma, V., Hummel, J. E., & Davidoff, Jules. (2004). Evidence for holistic representations of ignored images and analytic representations of attended images. Journal of Experimental Psychology: Human Perception and Performance, 30, 257–267. Tsal, Y. (1983). Movements of attention across the visual field. Journal of Experimental Psychology: Human Perception and Performance, 9, 523–530. Vuilleumier, P. (2005). How brains beware: Neural mechanisms of emotional attention. Trends in Cognitive Sciences, 9, 1364–1366.