Preemptive control of attentional capture by colour: evidence from trial-by-trial analyses and orderings of onsets of capture effects in reaction time distributions

Top-down suppression of negative features applies flexibly contingent on visual search goals

Visually searching for a frequently changing target is assumed to be guided by flexible working memory representations of specific features necessary to discriminate targets from distractors. Here, we tested if these representations allow selective suppression or always facilitate perception based on search goals. Participants searched for a target (i.e., a horizontal bar) defined by one of two different negative features (e.g., not red vs. not blue; Experiment 1) or a positive (e.g., blue) versus a negative feature (Experiments 2 and 3). A prompt informed participants about the target identity, and search tasks alternated or repeated randomly. We used different peripheral singleton cues presented at the same (valid condition) or a different (invalid condition) position as the target to examine if negative features were suppressed depending on current instructions. In all experiments, cues with negative features elicited slower search times in valid than invalid trials, indicating suppression. Additionally, suppression of negative color cues tended to be selective when participants searched for the target by different negative features but generalized to negative and non-matching cue colors when switching between positive and negative search criteria was required. Nevertheless, when the same color - red - was used in positive and negative search tasks, red cues captured attention or were suppressed depending on whether red was positive or negative (Experiment 3). Our results suggest that working memory representations flexibly trigger suppression or attentional capture contingent on a task-relevant feature's functional meaning during visual search, but top-down suppression operates at different levels of specificity depending on current task demands.

Priming effect of individual similarity and ensemble perception in visual search and working memory

Perceptual priming is a well-known phenomenon showing that the repetition of an object's feature can facilitate subsequent detection of that item. Although the priming effect has been rigorously studied in visual search, less is known about its effect on working memory and it is unclear whether the repetition of similar features, and furthermore, ensemble perception created by a large set of similar features, can induce priming. In this study, we investigated the priming effects of individual similarity and ensemble perception in visual search and visual working memory (VWM). We replicated the classic perceptual priming effect (Experiment 1a) and found that visual search was enhanced when the current target had a similar color to the previous target (Experiment 1b), but not when the similar color had been shown as a distractor before (Experiment 1c). However, if the target and distractors of similar colors formed ensemble perception, the search efficiency was again promoted even when the current target shared the same color with the previous distractor (Experiment 1d). For VWM, repeating the ensembles of the target- and nontarget-color subsets did not significantly affect the memory capacity, while switching the two harmed the memory fidelity but not capacity (Experiment 2). We suggest different underlying mechanisms for priming in visual search and VWM: in the former, the perception history of individual similarity and stimuli ensemble exert their effects on through the priority map, by forming a gradient distribution of attentional weights that peak at the previous target feature and diminish as stimulus diverges from the previously selected one; while in the latter, perception history of memory ensemble may influence the deployment of existing memory resources across trials, thereby affecting the memory fidelity but not its capacity.

EXPRESS: Don't blame yourself: Conscious source monitoring modulates feedback control during speech production

Sensory feedback plays an important role in speech motor control. One of the main sources of evidence for this are studies where online auditory feedback is perturbed during ongoing speech. In motor control, it is therefore crucial to distinguish between sensory feedback and externally generated sensory events. This is called source monitoring. Previous altered feedback studies have taken non-conscious source monitoring for granted, as automatic responses to altered sensory feedback imply that the feedback changes are processed as self-caused. However, the role of conscious source monitoring is unclear. The current study investigated whether conscious source monitoring modulates responses to unexpected pitch changes in auditory feedback. During a first block, some participants spontaneously attributed the pitch shifts to themselves (self-blamers) while others attributed them to an external source (other-blamers). Before block 2, all participants were informed that the pitch shifts were experimentally induced. The self-blamers then showed a reduction in response magnitude in block 2 compared with block 1, while the other-blamers did not. This suggests that conscious source monitoring modulates responses to altered auditory feedback, such that consciously ascribing feedback to oneself leads to larger compensation responses. These results can be accounted for within the dominant comparator framework, where conscious source monitoring could modulate the gain on sensory feedback. Alternatively, the results can be naturally explained from an inferential framework, where conscious knowledge may bias the priors in a Bayesian process to determine the most likely source of a sensory event.

Capacity limitations in template-guided multiple color search

Visual selection of target objects relies on representations of their known features in visual working memory. These representations are referred to as attentional templates. We asked how the capacity of visual working memory relates to the maximal number of attentional templates that can simultaneously guide visual selection. To measure the number of active attentional templates, we used the contingent capture paradigm where cues matching the attentional template have larger effects than cues in a non-matching color. We found larger cueing effects for matching than non-matching cues in one-, two-, and also three-color searches, suggesting that participants can establish up to three attentional templates. However, scrutiny of matching cue trials showed that with three attentional templates, larger cueing effects only occurred when the matching cue had the same color as the actual target. When the matching cue had a possible target color that was different from the actual target color, cueing effects were similar to non-matching cue colors. We assume that processing of a matching cue activates one of the three templates, which inhibits the remaining templates to the level of non-matching colors. With two colors, the inhibition from the activated template is less complete because the initial template activation is higher. Overall, only a maximum of two attentional templates can operate successfully in the contingent capture paradigm. The capacity of template-guided search is therefore far below the capacity of visual working memory.

Procedural Control Versus Resources as Potential Origins of Human Hyper Selectivity

In the current review, we argue that experimental results usually interpreted as evidence for cognitive resource limitations could also reflect functional necessities of human information processing. First, we point out that selective processing of only specific features, objects, or locations at each moment in time allows humans to monitor the success and failure of their own overt actions and covert cognitive procedures. We then proceed to show how certain instances of selectivity are at odds with commonly assumed resource limitations. Next, we discuss examples of seemingly automatic, resource-free processing that challenge the resource view but can be easily understood from the functional perspective of monitoring cognitive procedures. Finally, we suggest that neurophysiological data supporting resource limitations might actually reflect mechanisms of how procedural control is implemented in the brain.

Testing the top-down contingent capture of attention for abrupt-onset cues: Evidence from cue-elicited N2pc

Many studies using N2pc as a marker of attentional capture have demonstrated top-down contingent capture for salient color singletons: Among all salient cues that are not predictive of the target location, only cues similar to searched-for target features, and thus, matching to the top-down attentional control settings capture attention. This is reflected in matching cue's elicitation of an N2pc and a cueing effect in behavior, and the absence of the corresponding effects for non-matching cues (with features dissimilar to that of the searched-for targets). Yet, with abrupt-onset cues, corresponding evidence is missing, inviting speculations about the potential of abrupt-onset cues to capture attention followed by quick suppression within the target displays. Here, we used two types of abrupt-onset cues to test if capture by such cues also adheres to the contingent-capture principle: matching abrupt-onset cues with a color similar to the top-down control settings and non-matching abrupt-onset cues with a color different from all searched-for targets. With the help of these cues, top-down contingent capture was supported. Only matching abrupt-onset cues elicited an N2pc and a behavioral cueing effect. Depending on the exact side conditions, non-matching cues either elicited no N2pc or a P_D (i.e., evidence of active suppression). Results are discussed against the background of competing theories on attention capture by abrupt-onset cues.

Investigating the role of verbal templates in contingent capture by color

To investigate if top-down contingent capture by color cues relies on verbal or semantic templates, we combined different stimuli representing colors physically or semantically in six contingent-capture experiments. In contingent capture, only cues that match the top-down search templates lead to validity effects (shorter search times and fewer errors for validly than for invalidly cued targets) resulting from attentional capture by the cue. We compared validity effects of color cues and color-word cues in top-down search for color targets (Experiment 1a) and color-word targets (Experiment 2). We also compared validity effects of color cues and color-associated symbolic cues during search for color targets (Experiment 1b) and of color-word cues during search for both color and color-word targets (Experiment 3). Only cues of the same stimulus category as the target (either color or color-word cues) captured attention. This makes it unlikely that color search is based on verbal or semantic search templates. Additionally, the validity effect of matching color-word cues during search for color-word targets was neither changed by cue-target graphic (font) similarity versus dissimilarity (Experiment 4) nor by articulatory suppression (Experiment 5). These results suggested either a phonological long-term memory template or an orthographically mediated effect of the color-word cues during search for color-words. Altogether, our findings are in line with a pronounced role of color-based templates during contingent capture by color and do not support semantic or verbal influences in this situation.

Bottom-up attention capture with distractor and target singletons defined in the same (color) dimension is not a matter of feature uncertainty

In visual search, attention capture by an irrelevant color-singleton distractor in another feature dimension than the target is dependent on whether or not the distractor changes its feature: Capture is present if the irrelevant color distractor can take on different features across trials, but absent if the distractor takes on only one feature throughout all trials. This influence could be due to down-weighting of the entire color map. Here we tested whether a similar effect could also be brought about by down-weighting of specific color channels within the same maps. We investigated whether a similar dependence of capture on color certainty might hold true if the distractor were defined in the same (color) dimension as the target. At odds with this possibility, in the first and third blocks—in which feature uncertainty was absent—an irrelevant distractor of a certain color captured attention. In addition, in a second block, varying the distractor color created feature uncertainty, but this did not increase capture. Repeating the exact same procedure with the same participants after one week confirmed the stability of the results. The present study showed that a color distractor presented in the same (color) dimension as the target captures attention independent of feature uncertainty. Thus, the down-weighting of single irrelevant color channels within the same feature map used for target search is not a matter of feature uncertainty.

Testing a priming account of the contingent-capture effect

In the contingent-capture protocol, singleton cues that have a target's searched-for feature capture attention, but cues that do not have the target's searched-for feature do not, a result labeled the contingent-capture effect. The contingent-capture effect is usually regarded as evidence for the observers' ability to establish search settings for certain nonspatial features in a top-down manner. However, in recent years it has become increasingly clear that selection history is also a powerful mediator of attentional capture. In this vein, it has been suggested that contingent-capture effects could emerge as a result of (intertrial) priming: The idea is that features that have been encountered previously in the target are primed, so that cues that have these features automatically capture attention in a subsequent encounter. Here we tested a strong version of the priming account of the contingent-capture effect. We wanted to know whether cues that had target features would capture attention when the corresponding features were not part of the instructions (i.e., when the corresponding features were task-irrelevant). The results suggested that a strong version of the priming account of contingent capture is not supported. In five experiments, we found little evidence that the contingent-capture effect could be explained by (intertrial) priming of task-irrelevant features alone. These results show that processes beyond priming through task-irrelevant features are critical for contingent-capture effects.

Capture of attention by target-similar cues during dual-color search reflects reactive control among top-down selected attentional control settings

We investigated the origin of attention capture in the contingent-capture protocol during a search for two colors. When searching for the target color, cues similar to the target capture attention but cues dissimilar to the target do not capture attention. The results are typically explained by top-down contingent capture, a form of proactive control where participants set up attentional control settings (ACSs) for the target and cues matching the ACSs capture attention. However, based on recent research, we hypothesized that the situation could be more complicated during search for several features. Here, reactive control in the form of (cue) color-elicited selection of one of several separate pre-activated ACSs, one for each single searched-for feature, could contribute to performance. With the help of mixing and switch costs, we demonstrated that participants searched for two colors by separate pre-activated ACSs, and a closer inspection of the capture effects of the cues confirmed that reactive control contributed to ACS selection.

A meta-analysis of contingent-capture effects

The present meta-analyses investigated the widely used contingent-capture protocol. Contingent-capture theory postulates that only top-down matching stimuli capture attention. Evidence comes from the contingent-capture protocol, in which participants search for a predefined target stimulus preceded by a spatial cue. The cue is typically uninformative of the target's position but either presented at target position (valid condition) or away from the target (invalid condition). The common finding is that seemingly only top-down matching cues capture attention as shown by a selective cueing effect (faster responses in valid than invalid conditions) for cues with a feature similar to the searched-for target only, but not for cues without target-similar feature. The origin of this "contingent-capture effect" is, however, debated. One alternative explanation is that intertrial priming-the priming of attention capture by the cue in a given trial by attending to a feature-similar target in the preceding trial-mediates the contingent-capture effect. Alternatively, the rapid-disengagement account argues that all salient stimuli capture attention initially, but that the disengagement from non-matching cues is rapid. The present meta-analyses shed light on this debate by (a) identifying moderators of the size of reported contingent-capture effects (64 experiments) and (b) analyzing pure (blocked) versus mixed presentation of different targets as well as summarizing results of published intertrial priming studies (12 experiments) in the contingent-capture protocol. We found target-singleton versus non-singleton status and pure versus mixed presentation of different targets to be reliable moderators. Furthermore, results indicated the presence of publication bias. Otherwise, the contingent-capture theory was supported, but we discuss additional factors that must be taken into account for a full account of the results.

Attention capture is temporally stable: Evidence from mixed-model correlations

Studies on domain-specific expertise in visual attention, on its cognitive enhancement, or its pathology require individually reliable measurement of visual attention. Yet, the reliability of the most widely used reaction time (RT) differences measuring visual attention is in doubt or unknown. Therefore, we used novel methods of analyses based on linear mixed models (LMMs) and tested the temporal stability, as one index of reliability, of three attentional RT effects in the popular additional-singleton research protocol: (1) bottom-up, (2) top-down, and (3) memory-driven (intertrial priming) influences on attention capture effects. Participants searched for a target having one specific color in most (Exp. 1) or all (Exp. 2) trials. Together with the target, in half (Exp. 1) or two thirds (Exp. 2) of the trials, a distractor was presented that stood out by the target's (Exp. 1) or a target-similar (Exp. 2) color, therefore matching a top-down search set, or by a different color, capturing attention in a bottom-up way. Also, matching distractors were primed or unprimed by the target color of the preceding trial. We analyzed all three attention capture effects in manual and target fixation RTs at two different times, separated by one (Exp. 1 and 2) or four weeks (only in Exp. 1). Random slope correlations of LMMs and standard correlation coefficients computed on individual participants' effect scores showed that RT capture effects were in general temporally stable for both time intervals and dependent variables. These results demonstrate the test-retest reliability necessary for looking at individual differences of attentional RT effects.

Choosing attentional control settings in a dynamically changing environment

Goal-directed attentional control supports efficient visual search by prioritizing relevant stimuli in the environment. Previous research has shown that goal-directed control can be configured in many ways, and often multiple control settings can be used to achieve the same goal. However, little is known about how control settings are selected. We explored the extent to which the configuration of goal-directed control is driven by performance maximization (optimally configuring settings to maximize speed and accuracy) and effort minimization (selecting the least effortful settings). We used a new paradigm, adaptive choice visual search, which allows participants to choose one of two available targets (a red or a blue square) on each trial. Distractor colors vary predictively across trials, such that the optimal target switches back and forth throughout the experiment. Results (N = 43) show that participants chose the optimal target most often, updating to the new target when the environment changed, supporting performance maximization. However, individuals were sluggish to update to the optimal color, consistent with effort minimization. Additionally, we found a surprisingly high rate of nonoptimal choices and switching between targets, which could not be explained by either factor. Analysis of participants' self-reported search strategy revealed substantial individual differences in the control strategies used. In sum, the adaptive choice visual search enables a fresh approach to studying goal-directed control. The results contribute new evidence that control is partly determined by both performance maximization and effort minimization, as well as at least one additional factor, which we speculate to include novelty seeking.

Visual search for emotional expressions: Effect of stimulus set on anger and happiness superiority

Prior reports of preferential detection of emotional expressions in visual search have yielded inconsistent results, even for face stimuli that avoid obvious expression-related perceptual confounds. The current study investigated inconsistent reports of anger and happiness superiority effects using face stimuli drawn from the same database. Experiment 1 excluded procedural differences as a potential factor, replicating a happiness superiority effect in a procedure that previously yielded an anger superiority effect. Experiments 2a and 2b confirmed that image colour or poser gender did not account for prior inconsistent findings. Experiments 3a and 3b identified stimulus set as the critical variable, revealing happiness or anger superiority effects for two partially overlapping sets of face stimuli. The current results highlight the critical role of stimulus selection for the observation of happiness or anger superiority effects in visual search even for face stimuli that avoid obvious expression related perceptual confounds and are drawn from a single database.

There is more to trial history than priming in attentional capture experiments

We used contingent attentional capture to investigate whether capture in a given trial n was affected by the cue-target position relations in a preceding trial n-1. Typically, attentional capture by a cue facilitates reaction times for targets in valid conditions (with the cue and target at the same position) relative to invalid conditions (with the cue and target at different positions). Also, this validity effect holds for cues with a feature similar to the searched-for target features (i.e., matching cues), but not for cues dissimilar to the searched-for target features (i.e., nonmatching cues), a pattern termed contingent capture because capture is assumed to be contingent on the match between the cue and top-down control settings. Here, we replicated this contingent-capture pattern with cues that were nonpredictive of the target position. In addition, we showed that during search for white onset targets, red nonmatching color cues also created a validity effect if the same nonmatching cue had been used as a valid cue in trial n-1 (Exps. 1 and 2). This intertrial contingency of the nonmatching cue's validity effect was also found if the cues and targets both changed their positions from trial to trial, rendering position priming unlikely (Exp. 2). A similar intertrial contingency was found for nonmatching white onset cues, but not for matching red color cues during search for red color targets (Exp. 3). These results are discussed in light of explanations of the contingent-capture effect and of intertrial contingencies.

Unconscious vision and executive control: how unconscious processing and conscious action control interact

Research on unconscious or unaware vision has demonstrated that unconscious processing can be flexibly adapted to the current goals of human agents. The present review focuses on one area of research, masked visual priming. This method uses visual stimuli presented in a temporal sequence to lower the visibility of one of these stimuli. In this way, a stimulus can be masked and even rendered invisible. Despite its invisibility, a masked stimulus if used as a prime can influence a variety of executive functions, such as response activation, semantic processing, or attention shifting. There are also limitations on the processing of masked primes. While masked priming research demonstrates the top-down dependent usage of unconscious vision during task-set execution it also highlights that the set-up of a new task-set depends on conscious vision as its input. This basic distinction captures a major qualitative difference between conscious and unconscious vision.

Attentional capture and inhibition of saccades after irrelevant and relevant cues

Attentional capture is usually stronger for task-relevant than irrelevant stimuli, whereas irrelevant stimuli can trigger equal or even stronger amounts of inhibition than relevant stimuli. Capture and inhibition, however, are typically assessed in separate trials, leaving it open whether or not inhibition of irrelevant stimuli is a consequence of preceding attentional capture by the same stimuli or whether inhibition is the only response to these stimuli. Here, we tested the relationship between capture and inhibition in a setup allowing for estimates of the capture and inhibition based on the very same trials. We recorded saccadic inhibition after relevant and irrelevant stimuli. At the same time, we recorded the N2pc, an event-related potential, reflecting initial capture of attention. We found attentional capture not only for, relevant but importantly also for irrelevant stimuli, although the N2pc was stronger for relevant than irrelevant stimuli. In addition, inhibition of saccades was the same for relevant and irrelevant stimuli. We conclude with a discussion of the mechanisms that are responsible for these effects.

Using response time distributions to examine top-down influences on attentional capture

Three experiments examined contingent attentional capture, which is the finding that cuing effects are larger when cues are perceptually similar to a target than when they are dissimilar to the target. This study also analyzed response times (RTs) in terms of the underlying distributions for valid cues and invalid cues. Specifically, an ex-Gaussian analysis and a vincentile analysis examined the influence of top-down attentional control settings on the shift and skew of RT distributions and how the shift and the skew contributed to the cuing effects in the mean RTs. The results showed that cue/target similarity influenced the size of cuing effects. The RT distribution analyses showed that the cuing effects reflected only a shifting effect, not a skewing effect, in the RT distribution between valid cues and invalid cues. That is, top-down attentional control moderated the cuing effects in the mean RTs through distribution shifting, not distribution skewing. The results support the contingent orienting hypothesis (Folk, Remington, & Johnston, Journal of Experimental Psychology: Human Perception and Performance, 18, 1030-1044, 1992) over the attentional disengagement account (Theeuwes, Atchley, & Kramer, 2000) as an explanation for when top-down attentional settings influence the selection of salient stimuli.

Top-down search for color prevents voluntary directing of attention to informative singleton cues

Visuo-spatial attention can be directed in a top-down controlled way to search for color targets and it can be captured by color contrasts, regardless of color identity. Here we tested whether participants can both search for a particular color target (e.g., red) and make use of a color-contrast cue that predicted the target's most likely position to direct their attention voluntarily. Our results show that this was impossible for the participants. Results support that top-down search for particular colors is incommensurate with directing attention to just any color contrast. The results are discussed in light of the current debates concerning the roles of color and color contrast for visuo-spatial attention.

The costs of switching attentional sets

People prioritize those aspects of the visual environment that match their attentional set. In the present study, we investigated whether switching from one attentional set to another is associated with a cost. We asked observers to sequentially saccade toward two color-defined targets, one on the left side of the display, the other on the right, each among a set of heterogeneously colored distractors. The targets were of the same color (no attentional set switch required) or of different colors (switch of attentional sets necessary), with each color consistently tied to a side, to allow observers to maximally prepare for the switch. We found that saccades were less accurate and slower in the switch condition than in the no-switch condition. Furthermore, whenever one of the distractors had the color associated with the other attentional set, a substantial proportion of saccades did not end on the target, but on this distractor. A time course analysis revealed that this distractor preference turned into a target preference after about 250–300 ms, suggesting that this is the time required to switch attentional sets.

Executive control over unconscious cognition: attentional sensitization of unconscious information processing

Unconscious priming is a prototypical example of an automatic process, which is initiated without deliberate intention. Classical theories of automaticity assume that such unconscious automatic processes occur in a purely bottom-up driven fashion independent of executive control mechanisms. In contrast to these classical theories, our attentional sensitization model of unconscious information processing proposes that unconscious processing is susceptible to executive control and is only elicited if the cognitive system is configured accordingly. It is assumed that unconscious processing depends on attentional amplification of task-congruent processing pathways as a function of task sets. This article provides an overview of the latest research on executive control influences on unconscious information processing. I introduce refined theories of automaticity with a particular focus on the attentional sensitization model of unconscious cognition which is specifically developed to account for various attentional influences on different types of unconscious information processing. In support of the attentional sensitization model, empirical evidence is reviewed demonstrating executive control influences on unconscious cognition in the domains of visuo-motor and semantic processing: subliminal priming depends on attentional resources, is susceptible to stimulus expectations and is influenced by action intentions and task sets. This suggests that even unconscious processing is flexible and context-dependent as a function of higher-level executive control settings. I discuss that the assumption of attentional sensitization of unconscious information processing can accommodate conflicting findings regarding the automaticity of processes in many areas of cognition and emotion. This theoretical view has the potential to stimulate future research on executive control of unconscious processing in healthy and clinical populations.

Attentional sensitization of unconscious visual processing: Top-down influences on masked priming

Classical theories of automaticity assume that automatic processes elicited by unconscious stimuli are autonomous and independent of higher-level cognitive influences. In contrast to these classical conceptions, we argue that automatic processing depends on attentional amplification of task-congruent processing pathways and propose an attentional sensitization model of unconscious visual processing: According to this model, unconscious visual processing is automatic in the sense that it is initiated without deliberate intention. However, unconscious visual processing is susceptible to attentional top-down control and is only elicited if the cognitive system is configured accordingly. In this article, we describe our attentional sensitization model and review recent evidence demonstrating attentional influences on subliminal priming, a prototypical example of an automatic process. We show that subliminal priming (a) depends on attentional resources, (b) is susceptible to stimulus expectations, (c) is influenced by action intentions, and (d) is modulated by task sets. These data suggest that attention enhances or attenuates unconscious visual processes in congruency with attentional task representations similar to conscious perception. We argue that seemingly paradoxical, hitherto unexplained findings regarding the automaticity of the underlying processes in many cognitive domains can be easily accommodated by our attentional sensitization model. We conclude this review with a discussion of future research questions regar-ding the nature of attentional control of unconscious visual processing.

Top-down contingent feature-specific orienting with and without awareness of the visual input

In the present article, the role of endogenous feature-specific orienting for conscious and unconscious vision is reviewed. We start with an overview of orienting. We proceed with a review of masking research, and the definition of the criteria of experimental protocols that demonstrate endogenous and exogenous orienting, respectively. Against this background of criteria, we assess studies of unconscious orienting and come to the conclusion that so far studies of unconscious orienting demonstrated endogenous feature-specific orienting. The review closes with a discussion of the role of unconscious orienting in action control.

Neuro-cognitive mechanisms of conscious and unconscious visual perception: From a plethora of phenomena to general principles

Psychological and neuroscience approaches have promoted much progress in elucidating the cognitive and neural mechanisms that underlie phenomenal visual awareness during the last decades. In this article, we provide an overview of the latest research investigating important phenomena in conscious and unconscious vision. We identify general principles to characterize conscious and unconscious visual perception, which may serve as important building blocks for a unified model to explain the plethora of findings. We argue that in particular the integration of principles from both conscious and unconscious vision is advantageous and provides critical constraints for developing adequate theoretical models. Based on the principles identified in our review, we outline essential components of a unified model of conscious and unconscious visual perception. We propose that awareness refers to consolidated visual representations, which are accessible to the entire brain and therefore globally available. However, visual awareness not only depends on consolidation within the visual system, but is additionally the result of a post-sensory gating process, which is mediated by higher-level cognitive control mechanisms. We further propose that amplification of visual representations by attentional sensitization is not exclusive to the domain of conscious perception, but also applies to visual stimuli, which remain unconscious. Conscious and unconscious processing modes are highly interdependent with influences in both directions. We therefore argue that exactly this interdependence renders a unified model of conscious and unconscious visual perception valuable. Computational modeling jointly with focused experimental research could lead to a better understanding of the plethora of empirical phenomena in consciousness research.

Novelty and saliency in attentional capture by unannounced motion singletons

The present study examined attentional capture by an unannounced motion singleton in a visual search task. The results showed that a motion singleton only captured attention on its first unannounced occurrence when the observers had not encountered moving items before in the experiment, whereas it failed to capture when observers were familiar with moving items. This indicates that motion can capture attention independently of top-down attentional control settings, but only when motion as a feature is unexpected and new. An additional experiment tested whether salient items can capture attention when all stimuli possess new and unexpected features, and novelty information cannot guide attention. The results showed that attention was shifted to the location of the salient item when all items were new and unexpected, reinforcing the view that salient items receive attentional priority. The implications of these results for current theories of attention are discussed.

Controlling the Unconscious

Are unconscious processes susceptible to attentional influences? In two subliminal priming experiments, we investigated whether task sets differentially modulate the sensitivity of unconscious processing pathways. We developed a novel procedure for masked semantic priming of words (Experiment 1) and masked visuomotor priming of geometrical shapes (Experiment 2). Before presentation of the masked prime, participants performed an induction task in which they attended to either semantic or perceptual object features designed to activate a semantic or perceptual task set, respectively. Behavioral and electrophysiological effects showed that the induction tasks differentially modulated subliminal priming: Semantic priming, which involves access to conceptual meaning, was found after the semantic induction task but not after the perceptual induction task. Visuomotor priming was observed after the perceptual induction task but not after the semantic induction task. These results demonstrate that unconscious cognition is influenced by attentional control. Unconscious processes in perceptual and semantic processing streams are coordinated congruently with higher-level action goals.

Attentional capture by masked colour singletons

We tested under which conditions a colour singleton of which an observer is unaware captures attention. To prevent visual awareness of the colour singleton, we used backward masking. We find that a masked colour singleton cue captures attention if it matches the observer's goal to search for target colours but not if it is task-irrelevant. This is also reflected in event-related potentials to the visible target: the masked goal-matching cue elicits an attentional potential (N2pc) in a target search task. By contrast, a non-matching but equally strong masked colour singleton cue failed to elicit a capture effect and an N2pc. Results are discussed with regard to currently pertaining conceptions of attentional capture by colour singletons.

Specifying attentional top-down influences on subsequent unconscious semantic processing

Classical theories assume that unconscious automatic processes are autonomous and independent of higher-level cognitive influences. In contrast, we propose that automatic processing depends on a specific configuration of the cognitive system by top-down control. In 2 experiments, we tested the influence of available attentional resources and previously activated task sets on masked semantic priming in a lexical decision task. In Experiment 1, before masked prime presentation, participants were engaged in an easy or hard primary task that differentially afforded attentional resources. Semantic priming was attenuated when the primary task was hard, that is, when only little attentional resources were available. In Experiment 2, a semantic or perceptual induction task differentially modulated subsequent masked semantic priming. Hence, unconscious automatic processing depends on the availability of attentional resources and is susceptible to top-down control.

Sensorimotor supremacy: Investigating conscious and unconscious vision by masked priming

According to the sensorimotor supremacy hypothesis, conscious perception draws on motor action. In the present report, we will sketch two lines of potential development in the field of masking research based on the sensorimotor supremacy hypothesis. In the first part of the report, evidence is reviewed that masked, invisible stimuli can affect motor responses, attention shifts, and semantic processes. After the review of the corresponding evidence - so-called masked priming effects - an approach based on the sensorimotor supremacy hypothesis is detailed as to how the question of a unitary mechanism of unconscious vision can be pursued by masked priming studies. In the second part of the report, different models and theories of backward masking and masked priming are reviewed. Types of models based on the sensorimotor hypothesis are discussed that can take into account ways in which sensorimotor processes (reflected in masked priming effects) can affect conscious vision under backward masking conditions.

Top-down modulation of unconscious 'automatic' processes: A gating framework

In classical theories of automaticity, automatic processes are usually thought to occur autonomously and independently of higher level top-down factors (e.g., Posner & Snyder, 1975). However, already Neumann (1984) pointed out that the cognitive system has to be configured in a certain way for automatic processes to occur. In extension of his work, I propose a gating framework to account for the influence of top-down factors such as attention, intention and task set on automatic processes such as masked response or semantic priming. It is assumed that task representations held in prefrontal cortex regulate the gain of neurons in visual and sematic association cortex thereby modulating the effects of unconsciously perceived masked stimuli on further 'automatic' information processing steps. In support of the postulated gating framework, recent studies demonstrated a top-down modulation of automatic processes. Behavioral and electrophysiological studies with the masked response priming and semantic priming paradigms show that masked priming effects crucially depend (i) on temporal attention to the masked prime, (ii) on intentions or action plans and (iii) on the task set active immediately before masked prime presentation. For instance, masked semantic priming was only observed when the preceding task set required the orientation to semantic word features, but not when it required orientation to perceptual word features. These results support the view that unconscious automatic processes are modulated by top-down factors. They are suggestive of a gating mechanism which orchestrates the conscious and unconscious information processing streams.