Research Report. Executive control of attentional capture by faces and eye-gaze cueing

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1 Research Report Executive control of attentional capture by faces and eye-gaze cueing Background To make effective use non-verbal information during social interaction, selective attention must be employed to focus on the most important cues. It is now well established that a number of visual attention biases operate in relation to faces and eye gaze (Frischen, Bayliss, & Tipper, 2007; Palermo & Rhodes, 2007). The research reported here focused on two particular biases: the tendency for human faces to capture visual attention when they appear in competition with other objects (Langton, Law, Burton, & Schweinberger, 2008; Ro, Russell, & Lavie, 2001; Theeuwes & van der Stigchel, 2006), and the tendency for observers visual attention to shift to spatial locations that are being gazed at by other people. This latter effect is known as gaze-cueing (for a recent review of the literature see Frischen, Bayliss & Tipper, 2007). Initial gaze-cueing studies (e.g., Friesen & Kingstone, 1998) argued that this deployment of attention was automatic or reflexive ; similarly, it has been argued that attention capture by faces is a reflexive rather than a voluntary deployment of visual attention (e.g., Theeuwes & van der Stigchel, 2006). However, the impetus for this programme of research was a series of recent indications that in fact some form of voluntary attentional control process is at work in both gazecueing (Koval, Thomas, & Everling, 2005; Ristic & Kingstone, 2005; Vecera & Rizzo, 2004, 2006) and face-capture (Bindemann, Burton, Langton, Schweinberger, & Doherty, 2007). The aim of the Fellowship was to investigate the nature of these putative control processes, using the dual-task paradigm. Dual-task methodology is used to investigate patterns of interference when performance of a primary task is combined with performance of a secondary task. Specifically, the present studies were designed to assess whether secondary tasks loading working memory (WM, the system responsible for temporary storage and processing of information) would interfere with social attention biases in primary visual attention tasks. A number of studies in the wider visual attention literature have started to use dual-task methodology to investigate the involvement of WM in selective attention. For example, it has been shown that even irrelevant information stored in WM can influence which stimuli are attended (Downing, 2000; Olivers, Meijer, & Theeuwes, 2006; Woodman, Luck, & Schall, 2007). Also, the load theory of selective attention states that WM load will modulate the amount of processing given to distracters in selective attention tasks, with a higher load leading to greater processing and therefore greater distraction, because participants are unable to keep track of task priorities (Lavie, 2005; Lavie & de Fockert, 2005). The programme of research was designed to use dual-task methodology in a systematic way, by combining three primary (social attention) tasks with two secondary (executive/wm) tasks. It was hypothesised that the face-capture and gaze-cueing effects would be modulated by dual-task demand, demonstrating that these effects are not purely reflexive, and that executive control processes in WM are at work in social attention biases. No directional predictions were made about how this modulation might occur. It was reasoned that if control processes are involved by creating and maintaining a particular attentional set during the tasks, then disruption of control processes by dualtask demand could lead to a decrease in any social attention bias. On the other hand, if attentional control processes are normally involved in social attention by suppressing (to 13

2 some extent) the distracting influence of social cues, then dual-task demand might be predicted to increase the extent of any bias. Given that it was possible to frame both these predictions, and that the direction of modulation might, in any case, turn out to differ for face-capture and gaze-cueing, it was simply predicted that dual-task demand would modulate the social attention biases. Objectives There were four objectives for this Research Fellowship the first three were researchspecific: 1) To add to the understanding of attentional capture by faces and eye-gaze cueing, by investigating the nature of top-down executive control in these social attention phenomena. 2) To use the dual-task paradigm to systematically investigate how the availability of executive resources within working memory modulates attentional capture by faces and eye-gaze cueing. 3) To investigate how characteristics of faces (such as emotional expression and facial identity) may further mediate the relationship between executive control and attentional capture by faces. These objectives have been met as outlined in the Method and Results sections below. This was a new approach to the study of social attention, and combined tasks in novel ways. The research therefore provides a solid foundation on which to build in the future study of the role of executive control in social attention. The final objective was stated as follows: 4) To develop valuable new research skills such as the use of eye-tracking methodology, and to maximise the potential for career development and training available to me as a member of the Faces Lab at the University of Stirling. The terms of this objective have to be re-framed, as by the time I received notification that the Fellowship application was successful, I had moved to take up a Lectureship at Liverpool John Moores University. I was able to keep the Fellowship as the location was not crucial to the research, and it has given me the time and resources to develop my research skills and lay the foundation for an independent research career. Thanks to the Fellowship, I have had the opportunity to establish myself as a research active member of staff in Psychology at LJMU, and I was submitted as an Early Career Researcher in the 2008 Research Assessment Exercise. I have maintained a close collaboration with the Faces Lab at Stirling, particularly with Dr Stephen Langton who remained my mentor for the Fellowship. I have visited Stirling on numerous occasions for meetings and data collection using their Tobii 1750 eyetracker. I have therefore gained experience of eye-tracking methodology through learning to use this piece of technology and the associated software 1. I also attended an eyetracking workshop at the University of Southampton, where instruction in the use of eyetracking methodology for various types of project was provided by experts such as Keith 1 I would like to thank Professor Peter Hancock for his assistance with this. 14

3 Rayner and Gerald Altmann. Working at LJMU also gave me the opportunity to be trained on a FaceLab eye-tracker which was recently purchased. In terms of additional training and career development, I have attended the British Psychological Society Media Training course as well as LJMU training on topics such as Recruitment and Selection, and Introduction to Enterprise. I have undertaken a limited amount of teaching (in accordance with the terms of the Fellowship), which gave me the opportunity to expand my experience of writing and delivering lectures, and of supervising undergraduate dissertation projects. Methods Ten experiments were outlined in the research proposal nine of these were conducted along with three additional experiments. One of the original experiments (investigating the impact of facial identity on eye-gaze cueing) was dropped on the basis of extremely unpromising pilot data. Two of the extra experiments used non-social attention cues such as arrows or colour and were intended as comparison experiments for the gazecueing studies. The third examined the impact of a further type of secondary task (manipulating visuo-spatial information) on gaze-cueing. Participants: In all experiments the participants were adults aged with normal or corrected-to-normal vision. They were mainly undergraduate and postgraduate students, but members of the community were also recruited through the Psychology Participants Panel at LJMU. All participants provided written, informed consent and were debriefed about the purpose of the study. The research was approved by the Research Ethics Committee of Liverpool John Moores University, and was conducted in accordance with LJMU and British Psychological Society ethical codes of practice. Local ethics committees at the Universities of Stirling and Edinburgh also gave approval for the studies conducted at these institutions. Primary Tasks Eye-gaze cueing: Numerous studies have demonstrated that a centrally presented face with laterally averted gaze will cause facilitation in RT to targets appearing at the side of the screen indicated by the eyes. In the variant of the task reported here, photographic representations of faces were used as non-predictive gaze-cues, and participants had to respond by indicating on which side of the screen the target appeared. It was predicted that the magnitude of the gaze-cueing effect would be modulated by WM load. In two extra experiments, the gaze cue was replaced by a non-predictive arrow cue and a predictive colour cue. Spatial cueing task: This task was adopted from Bindemann et al. (2007). Two pictures (one face and one non-face object) cued two spatial locations on the screen, and these cues were followed by an attentional probe which appeared with equal likelihood at either of the two locations. Bindemann et al. demonstrated that when participants are given no particular instructions about how to attend to the pictures, a natural face bias arises in visual attention and reaction times are faster at the location cued by the face. They also showed that participants were able to override this bias given strong instructions to attend to the non-face objects; however the aim here was to determine what would happen to the naturally-occurring face bias when participants attempted the task with a WM load. 15

4 Visual search task: This task was adopted from Langton et al. (2008). Participants were asked to search an array of pictures of natural objects for any exemplar from the category of butterflies. On half of the trials, an irrelevant face appeared amongst the distracters. Langton et al. found that, although faces were never the target of the search and were not mentioned to the participants, reaction times (RTs) were slower on trials where they occurred. In the experiments reported here, it was predicted that the imposition of a WM load would cause a modulation of this face-capture effect. Secondary Tasks Digit rehearsal: This task was chosen because variants had previously been shown to affect attention capture by colour singletons (Lavie & de Fockert, 2005) and distracter interference by both famous (De Fockert, Rees, Frith, & Lavie, 2001) and emotional (Pecchinenda & Heil, 2007) faces during selective attention tasks. In the low WM load version of the task, one digit was presented as a pre-load, which participants had to maintain in WM during one trial of the primary task. At the end of the trial they were prompted with a question mark, to which they had to respond by entering the next digit in numerical order. In the high load version, they were presented with five digits at the beginning of the trial, and at the end were given one digit from this sequence as a prompt. They then had to enter the digit that came next in the sequence. If merely having to maintain information in WM is sufficient to disrupt social attention, then facecapture and gaze-cueing should be modulated by this secondary task. Auditory N-back: Auditory N-back tasks have been shown to interfere with performance on a number of different primary tasks, for example anti-saccade tasks (Mitchell, Macrae, & Gilchrist, 2002) and attention capture (Boot, Brockmole, & Simons, 2005). It was therefore chosen as a task known to be demanding of executive resources in WM, but also because it has flexibility to vary the level of that demand. In some versions of the task, participants listen to a series of letters and respond only if and when a repetition occurrs. Here, the participants were required to make continuous responses 2. Participants listened to a stream of letters in a pseudo-random order (spaced at 2 second intervals) and had to repeat the sequence out loud. In the 0-back version of the task, participants simply repeated the letter immediately after they heard it, in the 1-back they remained one letter behind the heard sequence at all times and in the 2-back version they had to remain two letters behind. Auditory Matrix task: This task was adopted from Logie, Zucco and Baddley (1990), and was used in one of the additional experiments. Participants were asked to form a mental image of a 3 x 5 grid of squares and were then given auditory instructions as to whether each square should be filled or remain empty. The pattern of filled and empty squares in each matrix formed the shape of a digit so that, in following the instructions, participants evolved a mental image of that digit. After listening to the description they were asked to give a verbal response indicating which digit had been described. The task was therefore chosen as it involved both the manipulation and maintenance of information in visuospatial WM. 2 I would like to thank Professor Graham Hitch for this suggestion. 16

5 Results Gaze-cueing studies Gaze-cueing 1 (Digit Load): Experiment 1 combined gaze-cueing with the digit-rehearsal task. Half of the participants were allocated to a low load group (1 digit), and half to a high load group (5 digit). All participants received a block of single-task trials (gazecueing only) and a block of dual-task trials (gaze-cueing + WM load). The experiment employed three different stimulus onset asynchronies (SOAs) between the gaze cue and the target 100 milliseconds (ms), 500 ms and 1000 ms. Analyses on the data (shown in Table 1) showed an overall effect of gaze but this was not modulated by working load. Rehearsing a set of digits slowed overall RTs to the target, but the difference between cued and uncued trials was constant over both the single and dual-task blocks. Table 1: Mean reaction times for Gaze-cueing 1 (standard deviations in parentheses) Low load group (N = 26) High load group (N = 26) Single task Dual task Single task Dual task 100ms SOA Cued 370 (42) 440 (94) 357 (46) 432 (66) Uncued 371 (46) 448 (108) 370 (41) 436 (67) 500ms SOA Cued 327 (43) 370 (83) 325 (46) 361 (76) Uncued 339 (43) 388 (99) 334 (49) 372 (71) 1000ms SOA Cued 308 (36) 364 (77) 320 (43) 360 (75) Uncued 315 (43) 360 (77) 319 (47) 361 (68) Gaze-cueing 2 (N-back): The auditory N-back task was combined with the same gazecueing task used in Gaze-cueing 1. One group of participants (N=42) performed a 2- back version of the task, while a comparison group (N = 42) performed the 0-back version. Each participant performed a block of single-task (gaze-cueing) trials and a block of dual-task trials (gaze-cueing + N-back). Analyses showed that the secondary tasks slowed responses in the gaze-cueing task, but there was no clear evidence that the gaze-cueing effect was significantly modulated, even the with the executively demanding 2-back task. Gaze-cueing 3 (N-back/emotion): Experiment 3 (N = 35) investigated whether the 2-back task would have a differential impact on the cueing produced by emotional faces (fearful and happy) compared to faces with a neutral expression. Analyses showed that cued trials were again responded to faster than uncued trials, but this difference was not modulated by dual-task demand for any of the emotional expressions. However, fearful faces did enhance the cueing effect, in agreement with Tipples (2006). Gaze-cueing 4 (VS Matrix task): This additional experiment (N = 39) was conducted in order to assess the impact of a visuo-spatial secondary task on gaze-cueing. As gazecueing involves a shift in spatial attention, it was reasoned that a secondary task that made use of visuo-spatial resources in WM might have more of an impact. The gazecueing task was therefore combined with the auditory matrix task. Overall RTs were 17

6 slowed by the secondary task, but there was no evidence of any modulation in gazecueing. Arrow Cueing: This experiment (N = 31) was conducted to investigate whether arrow cueing was more susceptible to dual-task demand than eye-gaze cueing. There has been some suggestion in the literature that gaze-cueing may be more reflexive than arrow cueing (e.g., Ristic, Wright, & Kingstone, 2007). Other than the use of arrow in place of a face, the experiment was the same as Gaze-cueing 1. Analyses showed that the arrow did produce significant cueing effects despite being non-predictive of the target location. However, this cueing effect was not significantly modulated by dual-task demand. Predictive Colour Cueing: This study (N = 24) was intended as another comparison to Gazecueing 1, and the digit rehearsal secondary task. In this case however, the (colour) cue in the primary task was made 75% predictive of the appearance of the target. For half the participants a red circle in the centre of the screen predicted left, and a green circle predicted right. For the other half of the participants the opposite colour mapping was used. In other respects the materials and procedure were kept as similar to Gaze-cueing 1 as possible. The predictive central colour did produce a significant voluntary cueing effect. Although overall RTs were slower under dual-task conditions, there was no indication that the cueing effect was modulated by WM load. Eye gaze-cueing summary: In four experiments there was no evidence that the gaze-cueing effect was significantly modulated by WM demand, whether this was verbal WM load (digit rehearsal task), visuo-spatial load (matrix task) or verbal/executive load (N-back task). Arrow and colour cueing experiments were conducted in the hope that they would demonstrate modulation of cueing and provide a contrast to these null results, but these studies also showed no effect of WM load. However, the null findings are in line with recent studies that have shown no modulation of reflexive cueing to peripheral nonsocial cues by either verbal (Santangelo & Spence, 2007) or visual WM load (Santangelo, Finoia, Raffone, Belardinelli, & Spence, 2008). Attention capture by faces Spatial cueing 1 (Digit load): This experiment examined the impact of the digit rehearsal task on the spatial cueing task. Data were analysed in terms of a face bias score, calculated by subtracting the mean RT when the face cued the target from the mean RT when the object cued the target (see Table 2). Contrary to predictions, there was no overall effect of dual-task demand on the face bias; that is, the face bias was just as strong when participants completed a block of dual-task trials as when they completed a block of single task trials. However, exploration of these data demonstrated that the order in which participants attempted the single and dual-task blocks interacted with the face bias. Analyses revealed that the bias was significantly suppressed under dual-task conditions, for the dual-first group only. This would be consistent with a model whereby the singlefirst group developed a face bias in their first block of trials, which was then resistant to any disruption in a subsequent block. Meanwhile the dual-first group developed a significant face bias only once the dual-task phase of the experiment was over. Table 2: Mean face bias in milliseconds for Spatial Cueing 1 (standard deviations in parentheses) 18

7 Single First N = 16 Dual First N = 17 Total N = 33 Single task Dual task 100ms SOA 500ms SOA 100ms SOA 500ms SOA 4 (18) 7 (19) 17 (24) 11 (22) 18 (20) 17 (23) 10 (23) -6 (39) 11 (21) 12 (21) 13 (24) 2 (33) Spatial cueing 2 (N back): In this experiment the spatial cueing task was combined with a 1-back version of the N-back task (piloting demonstrated that participants were overloaded when combining spatial cueing with the 2-back version). It was predicted that the secondary task would have a significant impact on the face bias. An examination of the means in Table 3 clearly shows that participants who attempted the dual-task trials first showed a stronger bias towards the face than participants who attempted the singletask trials first. Analyses confirmed a significant effect of order on the face bias. Table 3: Mean face bias in milliseconds for Spatial Cueing 2 (standard deviations in parentheses) Single First N = 11 Dual First N = 11 Total N = 22 Single task Dual task 100ms SOA 500ms SOA 100ms SOA 500ms SOA 7 (19) 5 (19) 2 (26) 4 (18) 18 (15) 21 (18) 17 (38) 11 (40) 13 (18) 13 (20) 9 (33) 7 (31) Spatial cueing 3 (Facial familiarity): This experiment examined the impact of facial familiarity (achieved using celebrity faces for half the trials) on the face bias. Dual-task demand was manipulated between-participants in this study; one group attempted the spatial cueing task alone, while the other attempted it while performing the auditory 1-back task. What is striking (see Table 4) is that the magnitude of the face bias is weaker for the dual-task group, contrary to predictions and the results of the previous study. Analyses demonstrated no significant effects of either facial familiarity or dual-task group. This study used a sample size more than double that of the previous study, and yet failed to find any significant effect of the 1-back secondary task. Therefore, it may be safer to conclude the significant difference in the previous study was a spurious effect. Table 4: Mean face bias in milliseconds for Spatial Cueing 3 (standard deviations in parentheses) Familiar Face Unfamiliar Face Single Task 11 (22) 12 (30) N = 29 Dual Task 3 (29) 6 (27) N = 29 Total 7 (26) 9 (28) 19

8 N = 58 Spatial cueing 4/Facial emotion: This experiment investigated the impact of the digit rehearsal task on the spatial-cueing produced by emotional faces angry, happy and neutral faces were used. Analyses conducted on the face bias score, found no significant effect of dual-task demand or emotion and no interaction between these factors. However, as many previous studies have found emotional-face bias in participants with high levels of trait anxiety, the data were further analysed by dividing the participants into two groups based on their score on the State/Trait Anxiety Inventory (Spielberger et al., 1983), and including anxiety level as an extra factor in the analysis. There was a marginally non-significant trend towards an interaction between emotion and anxiety group. The means in Table 5 suggest that this trend is being driven by a tendency for the high anxiety group to avoid the angry faces (i.e., attend towards the object to a greater extent). However, there was no evidence that attention to emotional faces was more susceptible to disruption from WM load than attention to neutral faces. Table 5: Mean face bias in milliseconds for Spatial Cueing 4 (standard deviations in parentheses) Low Anxiety N = 23 High Anxiety N = 19 Total N = 42 Low WM Demand High WM Demand Neutral Happy Angry Neutral Happy Angry 3 (41) 3 (42) 6 (33) -4 (55) 6 (60) 3 (66) 11 (39) 1 (42) -10 (35) 22 (56) 11 (44) -9 (60) 6 (40) 2 (42) -1 (35) 8 (57) 8 (53) -2 (63) Spatial Cueing Summary: For the initial spatial-cueing studies, eye-tracking data were used to discard any trials where participants failed to maintain fixation, in order to ensure that the bias arose from covert attention shifts rather than eye-movements. However, removal of non-fixated trials made no difference to the pattern of data. The results of Spatial Cueing 1 suggest that having a pre-load to maintain in verbal WM depresses the tendency for attention to be captured by faces, but only if such a bias is not already established. The two studies to use the N-back secondary task showed conflicting results therefore there was no clear and consistent evidence that that the auditory N-back task significantly disrupted the face bias. There was also no evidence from this series of studies that WM load had a differential impact on emotionally expressive or familiar faces. Visual search 1 (Digit Load): This experiment (N=32) combined the visual search task with the digit rehearsal task. Participants performed a block of visual search trials with a low demand digit load (1 digit) and another block with a high demand version of the task (5 digits). Analyses revealed that the high WM demand did slow visual search RTs relative to low load, but the impact of irrelevant faces was not modulated. There was also no evidence that the presence of a face in the visual search task caused an increase in the error rate in the memory task. 20

9 Visual search 2 (N-back): This experiment (N=24) combined the visual search task with the N-back task. From piloting it was clear that participants were overloaded by performing the 2-back version of the task, therefore a 1-back version was utilised and participants performed a block of single-task trials and a block of dual-task trials. In the overall data set the basic effect of irrelevant faces demonstrated by Langton et al. did not replicate. However when examining the mean RTs from participants who performed the single block first, it appears they did show a face bias of around the usual magnitude (30ms slower when faces were present), but there was insufficient statistical power to detect this effect in the analysis. Visual search summary: It is clear that giving participants another task to perform at the same time as the visual search task leads to profound disruption to their overall performance in terms of searching for the target. The N-back task in particular rendered performance extremely slow and variable. These studies did not provide any clear evidence that the effect of irrelevant faces was modulated by the level of WM load. Conclusions Looking at the pattern of data as a whole, it seems that social attention biases are relatively resistant to attempts at disruption using dual-task methodology. Data from a series of gaze-cueing studies gave no indication that it is appropriate to reject the null hypothesis that gaze cueing is unaffected by working memory load. Interpretation of the data from the attention capture studies is less straightforward, but there is some indication that WM load can be disruptive during initial development of face biases in spatial cueing tasks. However, caution is always required in the interpretation of null results, and further research will clearly be needed to explore the boundaries of these conclusions. As this programme of experiments has used a variety of different primary and secondary tasks, it is now possible to identify the most promising way forward in the application of dual-task methodology to the study of social attention (see Future Research Priorities section below). Activities This research has been presented at the following conferences: Law, A. S., & Langton, S. R. H. (2007). Executive control of social attention. Paper presented at the Working Memory Discussion Meeting, Parcevall Hall, Yorkshire, 25 th - 27 th June. Law, A. S., & Langton, S. R. H. (2007). The role of working memory in eye-gaze cueing. Poster presented at the BPS Cognitive Section Conference, University of Aberdeen, 20 th - 22 nd August. Law, A. S., & Langton, S. R. H. (2008). The impact of working memory load on eyegaze-cueing. Paper presented at the XXIX International Congress of Psychology, Berlin, 20 th -25 th July. Law, A. S., & Langton, S. R. H. (2008). Disrupting face biases in visual attention. Poster presented at the XXIX International Congress of Psychology, Berlin, 20 th -25 th July. 21

10 Law, A. S., Langton, S. R. H., & Logie, R. H. (2009). The impact of visuo-spatial working memory load on attention to eye-gaze. Poster presented at the Experimental Psychology Society Conference, York, 8 th -10 th of July. In addition, I have taken advantage of networking opportunities in order to present some of this research at a joint Scottish face lab meeting (with attendees from universities across Scotland) and at a meeting of the Human Cognitive Neuroscience research group at the University of Edinburgh. As stated above under Objectives, I have maintained close links with the University of Stirling, but I have also been able to use the support of the Fellowship to foster collaboration with Professor Robert Logie at the University of Edinburgh, which resulted in a 2-week study visit during which additional data was gathered (Gaze-cueing 4). Outputs Datasets arising from this Fellowship have been offered to the Economic and Social Data Service. A paper focussing on a selection of the gaze-cueing studies has been submitted for publication in Visual Cognition. It is hoped that further publications acknowledging ESRC support will follow, that draw in part on this body of work, but may also be supplemented by additional data. Impacts The target audience for this research is the academic community, and the results have been disseminated as detailed in the Activities and Outputs sections. This line of research enquiry is very much theory-driven, and at an early stage, therefore there is as yet limited scope for external applications and impacts in terms of non-academic users. Future Research Priorities One aim of this Fellowship was to test a number of different combinations of primary (social attention) tasks and secondary (working memory) tasks. The pre-load (digit rehearsal) procedure was found to combine well with the primary tasks and variations of this, perhaps using visuo-spatial information instead of verbal information, would be a useful direction for future research. Further studies using the auditory matrix task may also prove fruitful. Consideration should also be given to the circumstances in which participants initially encounter the primary task although this was not an explicit aim of the Fellowship, there were indications in the data from the attention capture studies that this may be an important factor, and experiments specifically designed to investigate this issue would be welcome. Although there was little evidence here that facial identity was an important factor, facial emotion does appear to strengthen social attention biases, at least for high-anxiety participants, so there may be scope to examine the impact of different types of WM load on attention to emotional faces. The work pursued during the term of this Fellowship has provided a foundation on which to build future programmes of in-depth studies, by identifying those methods with the greatest promise 22

11 in terms of investigating the role of working memory and executive control in attention to faces and eye-gaze. 23

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13 Vecera, S. P., & Rizzo, M. (2004). What Are You Looking at? Impaired 'social Attention' Following Frontal-Lobe Damage. Neuropsychologia, 42(12), Vecera, S. P., & Rizzo, M. (2006). Eye Gaze Does Not Produce Reflexive Shifts of Attention: Evidence From Frontal-Lobe Damage. Neuropsychologia, 44(1), Woodman, G. F., Luck, S. J., & Schall, J. D. (2007). The role of working memory representations in the control of attention. Cerebral Cortex, 17, i118-i