Attentional capture by auto- and allo-cues

Attentional capture in multiple object tracking

Attentional processes are generally assumed to be involved in multiple object tracking (MOT). The attentional capture paradigm is regularly used to study conditions of attentional control. It has up to now not been used to assess influences of sudden onset distractor stimuli in MOT. We investigated whether attentional capture does occur in MOT: Are onset distractors processed at all in dynamic attentional tasks? We found that sudden onset distractors were effective in lowering probe detection, thus demonstrating attentional capture. Tracking performance as dependent measure was not affected. The attentional capture effect persisted in conditions of higher tracking load (Experiment 2) and was dramatically increased in lower presentation frequency of the onset distractor (Experiment 3). Tracking performance was shown to suffer only when onset distractors were presented serially with very short time gaps in between, thus effectively disturbing re-engaging attention on the tracking set (Experiment 4). We discuss that rapid dis- and re-engagement of the attention process on target objects and an additional more basic process that continuously provides location information allow managing strong disruptions of attention during tracking.

EEG evidence for enhanced attentional performance during moderate-intensity exercise

Research on attentional control within real-world contexts has become substantially more feasible and thus frequent over the past decade. However, relatively little is known regarding how these processes may be influenced by common naturalistic behaviors such as engaging in physical activity, which is thought to modulate the availability of neurometabolic resources. Here, we used an event-related potential (ERP) approach to determine whether various intensities of aerobic exercise might affect the concurrent performance of attentional control mechanisms. Participants performed an additional-singleton visual search task across three levels of aerobic activity while seated on a stationary bicycle: at rest, during moderate-intensity exercise, and during vigorous-intensity exercise. In addition to behavioral measures, attentional processing was assessed via lateralized ERPs referencing target selection (PCN) and distractor suppression (P_D ) mechanisms. Whereas engaging in exercise resulted in speeded response times overall, moderate-intensity exercise was found to uniquely eliminate the expression of distractor interference by the PCN while also giving rise to an unanticipated distractor-elicited Ppc. These findings demonstrate workload-specific and object-selective influences of aerobic exercise on attentional processing, providing insights not only for approaching attention in real-world contexts but also for understanding how attentional resources are used overall.

Database of Emotional Videos from Ottawa (DEVO)

We present a collection of emotional video clips that can be used in ways similar to static images (e.g., the International Affective Picture System, IAPS; Lang, Bradley, & Cuthbert, 2008). The Database of Emotional Videos from Ottawa (DEVO) includes 291 brief video clips (mean duration = 5.42 s; SD = 2.89 s; range = 3–15 s) extracted from obscure sources to reduce their familiarity and to avoid influencing participants’ emotional responses. In Study 1, ratings of valence and arousal (measured with the Self Assessment Manikins from IAPS) and impact (Croucher, Calder, Ramponi, Barnard, & Murphy, 2011) were collected from 154 participants (82 women; mean age = 19.88 years; SD = 2.83 years), in a between-subjects design to avoid potential halo effects across the three ratings (Saal, Downey, & Lahey, 1980). Ratings collected online in a new set of 124 students with a within-subjects design (Study 2) were significantly correlated with the original sample’s. The clips were unfamiliar, having been seen previously by fewer than 2% of participants on average. The ratings consistently revealed the expected U-shaped relationships between valence and arousal/impact, and a strong positive correlation between arousal and impact. Hierarchical cluster analysis of the Study 1 ratings suggested seven groups of clips varying in valence, arousal, and impact, although the Study 2 ratings suggested five groups of clips. These clips should prove useful for a wide range of research on emotion and behaviour.

The Effect of Ratio of Changing to Static Stimuli on the Attentional Capture

Studies have shown that appearing or disappearing objects attract more attention than static objects. This study examined the modulation of attention attracted by transient signals by systematically manipulating the ratio of changing (appearing/disappearing) to static stimuli. The results revealed that the effect of transient stimuli in attracting attention was diminished by simultaneously appearing (disappearing) peripheral stimuli and that the position where nothing was presented (the remaining stimulus) attracted attention when the number of appearing (disappearing) peripheral stimuli was increased. These findings suggest that the sudden change does not always capture attention, and whether changed things are attended or unchanged things are attended is determined depending on the proportion of things that change and do not change.

Testing the Attentional Dwelling Hypothesis of Attentional Capture

Researchers are strongly divided as to whether abrupt onsets capture spatial attention in a purely stimulus-driven fashion or contingent on their search goals. Recently, Gaspelin, Ruthruff and Lien (2016) offered a resolution of this debate by showing that whether spatial capture by abrupt onsets is observed in a spatial cueing search task critically depends on search difficulty. To account for these findings, they proposed an "attentional dwelling" hypothesis, according to which, following capture by a cue, attention dwells at the cued location until the object subsequently appearing at that location is identified as the target or rejected as a distractor. A critical prediction of this account is that the more similar to the target the distractor at the cued location, the longer attention should dwell at its location. Yet, Gaspelin et al. (2016) did not test this prediction because they manipulated overall search difficulty rather than the difficulty of rejecting a specific distractor. The present study provides a critical test of the attentional dwelling hypothesis, by also varying target-distractor similarity within a trial rather than only between trials. Although we closely replicated these authors' findings, the dwelling hypothesis passed the critical test in one of our two experiments. To accommodate the entire pattern of results observed here, we tentatively suggest a priority-accumulation framework, according to which cue validity effects do not necessarily index spatial shifts of attention, but instead, how much the cue speeds the resolution of the competition between the target and distractors in the search display.

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.

Collinear masking effect in visual search is independent of perceptual salience

Searching for a target in a salient region should be easier than looking for one in a nonsalient region. However, we previously discovered a contradictory phenomenon in which a local target in a salient structure was more difficult to find than one in the background. The salient structure was constructed of orientation singletons aligned to each other to form a collinear structure. In the present study, we undertake to determine whether such a masking effect was a result of salience competition between a global structure and the local target. In the first 3 experiments, we increased the salience value of the local target with the hope of adding to its competitive advantage and eventually eliminating the masking effect; nevertheless, the masking effect persisted. In an additional 2 experiments, we reduced salience of the global collinear structure by altering the orientation of the background bars and the masking effect still emerged. Our salience manipulations were validated by a controlled condition in which the global structure was grouped noncollinearly. In this case, local target salience increase (e.g., onset) or global distractor salience reduction (e.g., randomized flanking orientations) effectively removed the facilitation effect of the noncollinear structure. Our data suggest that salience competition is unlikely to explain the collinear masking effect, and other mechanisms such as contour integration, border formation, or the crowding effect may be prospective candidates for further investigation.

The role of unique color changes and singletons in attention capture

Previous studies have shown that a sudden color change is typically less salient in capturing attention than the onset of a new object. Von Mühlenen, Rempel, and Enns (Psychological Science 16: 979-986, 2005) showed that a color change can capture attention as effectively as the onset of a new object given that it occurs during a period of temporal calm, where no other display changes happen. The current study presents a series of experiments that further investigate the conditions under which a change in color captures attention, by disentangling the change signal from the onset of a singleton. The results show that the item changing color receives attentional priority irrespective of whether this change goes along with the appearance of a singleton or not.

Differential roles of the dorsal prefrontal and posterior parietal cortices in visual search: a TMS study

Although previous studies have shown that fronto-parietal attentional networks play a crucial role in bottom-up and top-down processes, the relative contribution of the frontal and parietal cortices to these processes remains elusive. Here we used transcranial magnetic stimulation (TMS) to interfere with the activity of the right dorsal prefrontal cortex (DLPFC) or the right posterior parietal cortex (PPC), immediately prior to the onset of the visual search display. Participants searched a target defined by color and orientation in “pop-out” or “search” condition. Repetitive TMS was applied to either the right DLPFC or the right PPC on different days. Performance was evaluated at baseline (no TMS), during TMS, and after TMS (Post-session). RTs were prolonged when TMS was applied over the DLPFC in the search, but not in the pop-out condition, relative to the baseline session. In comparison, TMS over the PPC prolonged RTs in the pop-out condition, and when the target appeared in the left visual field for the search condition. Taken together these findings provide evidence for a differential role of DLPFC and PPC in the visual search, indicating that DLPFC has a specific involvement in the “search” condition, while PPC is mainly involved in detecting “pop-out” targets.

Crossmodal semantic congruence can affect visuo-spatial processing and activity of the fronto-parietal attention networks

Previous studies have shown that multisensory stimuli can contribute to attention control. Here we investigate whether irrelevant audio–visual stimuli can affect the processing of subsequent visual targets, in the absence of any direct bottom–up signals generated by low-level sensory changes and any goal-related associations between the multisensory stimuli and the visual targets. Each trial included two pictures (cat/dog), one in each visual hemifield, and a central sound that was semantically congruent with one of the two pictures (i.e., either “meow” or “woof” sound). These irrelevant audio–visual stimuli were followed by a visual target that appeared either where the congruent or the incongruent picture had been presented (valid/invalid trials). The visual target was a Gabor patch requiring an orientation discrimination judgment, allowing us to uncouple the visual task from the audio–visual stimuli. Behaviourally we found lower performance for invalid than valid trials, but only when the task demands were high (Gabor target presented together with a Gabor distractor vs. Gabor target alone). The fMRI analyses revealed greater activity for invalid than for valid trials in the dorsal and the ventral fronto-parietal attention networks. The dorsal network was recruited irrespective of task demands, while the ventral network was recruited only when task demands were high and target discrimination required additional top–down control. We propose that crossmodal semantic congruence generates a processing bias associated with the location of congruent picture, and that the presentation of the visual target on the opposite side required updating these processing priorities. We relate the activation of the attention networks to these updating operations. We conclude that the fronto-parietal networks mediate the influence of crossmodal semantic congruence on visuo-spatial processing, even in the absence of any low-level sensory cue and any goal-driven task associations.

Reinstating salience effects over time: the influence of stimulus changes on visual selection behavior over a sequence of eye movements

Recently, we showed that salience affects initial saccades only in a static stimulus environment; subsequent saccades were unaffected by salience but, instead, were directed in line with task requirements (Siebold, van Zoest, & Donk, PLoS ONE 6(9): e23552, 2011). Yet multiple studies have shown that people tend to fixate salient regions more often than nonsalient ones when they are looking at images--in particular, when salience is defined by dynamic changes. The goal of the present study was to investigate how oculomotor selection beyond an initial saccade is affected by salience as derived from changing, as opposed to static, stimuli. Observers were presented with displays containing two fixation dots, one target, one distractor, and multiple background elements. They were instructed to fixate on one of the fixation dots and make a speeded eye movement to the target, either directly or preceded by an initial eye movement to the other fixation dot. In Experiment 1, target and distractor differed in orientation contrast relative to the background, such that one was more salient than the other, whereas in Experiments 2 and 3, the orientation contrast between the two elements was identical. Here, salience was implemented by a continuous luminance flicker or by a difference in luminance contrast, respectively, which was presented either simultaneously with display onset or contingent upon the first saccade. The results showed that in all experiments, initial saccades were strongly guided by salience, whereas second saccades were consistently goal directed if the salience manipulation was present from display onset. However, if the flicker or luminance contrast was presented contingent upon the initial saccade, salience effects were reinstated. We argue that salience effects are short-lived but can be reinstated if new information is presented, even when this occurs during an eye movement.

Attention capture by abrupt onsets: re-visiting the priority tag model

Abrupt onsets have been shown to strongly attract attention in a stimulus-driven, bottom-up manner. However, the precise mechanism that drives capture by onsets is still debated. According to the new object account, abrupt onsets capture attention because they signal the appearance of a new object. Yantis and Johnson (1990) used a visual search task and showed that up to four onsets can be automatically prioritized. However, in their study the number of onsets co-varied with the total number of items in the display, allowing for a possible confound between these two variables. In the present study, display size was fixed at eight items while the number of onsets was systematically varied between zero and eight. Experiment 1 showed a systematic increase in reactions times with increasing number of onsets. This increase was stronger when the target was an onset than when it was a no-onset item, a result that is best explained by a model according to which only one onset is automatically prioritized. Even when the onsets were marked in red (Experiment 2), nearly half of the participants continued to prioritize only one onset item. Only when onset and no-onset targets were blocked (Experiment 3), participants started to search selectively through the set of only the relevant target type. These results further support the finding that only one onset captures attention. Many bottom-up models of attention capture, like masking or saliency accounts, can efficiently explain this finding.

Breaking through the attentional window: capture by abrupt onsets versus color singletons

Theeuwes (Psychonomic Bulletin & Review 11:65-70, 2004) proposed that stimulus-driven capture occurs primarily for salient stimuli that fall within the observer's attentional window, such as when performing a parallel search. This proposal, which is supported by some studies, can explain many seemingly discrepant results in the literature. The present study tested this proposal using a modified precuing paradigm. Search mode was manipulated via target-distractor similarity in color space. In the parallel search condition, the orange target "popped out" from a set of distantly colored distractors (blue and green). In the serial search condition, the orange target was more difficult to find amongst a set of similarly colored distractors (yellow and red). In Experiments 1 and 2, cue validity effects for irrelevant-color singleton cues were greater under parallel than under serial search, at least partially replicating previous studies favoring the attentional-window account (e.g., Belopolsky, Zwaan, Theeuwes, & Kramer, Psychonomic Bulletin & Review 14:934-938, 2007). We found the opposite pattern, however, for capture by abrupt onsets (Experiments 3 and 4), in which case capture effects were actually greater under serial search. In sum, parallel search appears to facilitate capture by color singletons, yet to inhibit capture by abrupt onsets.

Context and competition in the capture of visual attention

Competition-based models of visual attention propose that perceptual ambiguity is resolved through inhibition, which is stronger when objects share a greater number of neural receptive fields (RFs). According to this theory, the misallocation of attention to a salient distractor--that is, the capture of attention--can be indexed in RF-scaled interference costs. We used this pattern to investigate distractor-related costs in visual search across several manipulations of temporal context. Distractor costs are generally larger under circumstances in which the distractor can be defined by features that have recently characterised the target, suggesting that capture occurs in these trials. However, our results show that search for a target in the presence of a salient distractor also produces RF-scaled costs when the features defining the target and distractor do not vary from trial to trial. Contextual differences in distractor costs appear to reflect something other than capture, perhaps a qualitative difference in the type of attentional mechanism deployed to the distractor.

A load on my mind: evidence that anhedonic depression is like multi-tasking

Multi-tasking can increase susceptibility to distraction, affecting whether irrelevant objects capture attention. Similarly, people with depression often struggle to concentrate when performing cognitively demanding tasks. This parallel suggests that depression is like multi-tasking. To test this idea, we examined relations between self-reported levels of anhedonic depression (a dimension that reflects the unique aspects of depression not shared with anxiety or other forms of distress) and attention capture by salient items in a visual search task. Furthermore, we compared these relations to the effects of performing a concurrent auditory task on attention capture. Strikingly, both multi-tasking and elevated levels of anhedonic depression were associated with increased capture by uniquely colored items, but decreased capture by abruptly appearing items. At least with respect to attention capture and distraction, depression seems to be functionally comparable to juggling a second, unrelated cognitive task.

Personally-significant information affects performance only within the focus of attention: a direct manipulation of attention

It has been suggested that personally significant (PS) information interferes with performance only when presented within the focus of attention. However, this claim was never tested by a systematic manipulation of attention, but only by using correlative measures of its locus. We addressed this issue in two experiments, utilizing a cued visual search paradigm that allowed us to directly manipulate attention and to measure behavioral and physiological responses. One of the stimuli in the search display had a higher luminance value (i.e., was cued), and, orthogonally, one of the stimuli could be a PS or neutral name. When the cue did not predict target location, PS distractors mildly interfered with task performance, regardless of the cue's location. However, when the cue predicted target location, responses were facilitated for cued targets, indicating that attention was shifted to the cue. Importantly, PS distractors interfered with task performance and elicited enhanced orienting responses only when they were cued. This implies that PS information affects performance only when presented within but not outside the focus of attention.

Interaction between stimulus-driven orienting and top-down modulation in attentional capture

The issue whether attentional capture is determined by top-down factors or can be stimulus-driven remains unsolved. To examine this, we used a spatial cueing paradigm with set size four and eight in which a color target is preceded by an uninformative cue (color or onset) that either matches or does not match the target-defining feature. The critical manipulation lies in adding no-cue trials to make the subsequent first with-cue trial unexpected, which reveals the stimulus-driven component. For the onset cue, the first-trial analysis indicated attentional capture at set size four and eight, whereas results from the average data indicated attentional capture at set size eight but not at set size four. For the color cue, attentional capture was found in the average data but not in the first trial, regardless of set size. These results can be explained by the interactive processing of early stimulus-driven activation followed by top-down modulation.

Size matters: large objects capture attention in visual search

Can objects or events ever capture one's attention in a purely stimulus-driven manner? A recent review of the literature set out the criteria required to find stimulus-driven attentional capture independent of goal-directed influences, and concluded that no published study has satisfied that criteria. Here visual search experiments assessed whether an irrelevantly large object can capture attention. Capture of attention by this static visual feature was found. The results suggest that a large object can indeed capture attention in a stimulus-driven manner and independent of displaywide features of the task that might encourage a goal-directed bias for large items. It is concluded that these results are either consistent with the stimulus-driven criteria published previously or alternatively consistent with a flexible, goal-directed mechanism of saliency detection.

Top-down and bottom-up control of visual selection

The present paper argues for the notion that when attention is spread across the visual field in the first sweep of information through the brain visual selection is completely stimulus-driven. Only later in time, through recurrent feedback processing, volitional control based on expectancy and goal set will bias visual selection in a top-down manner. Here we review behavioral evidence as well as evidence from ERP, fMRI, TMS and single cell recording consistent with stimulus-driven selection. Alternative viewpoints that assume a large role for top-down processing are discussed. It is argued that in most cases evidence supporting top-down control on visual selection in fact demonstrates top-down control on processes occurring later in time, following initial selection. We conclude that top-down knowledge regarding non-spatial features of the objects cannot alter the initial selection priority. Only by adjusting the size of the attentional window, the initial sweep of information through the brain may be altered in a top-down way.

Cognitive load modulates attentional capture by color singletons during effortful visual search

Color singletons that are irrelevant to locating a visual target do not typically capture attention if visual search is effortful. In contrast, when search is efficient color singletons are often found to capture attention. Such distraction by a color singleton can be modulated by single-task vs. dual-task manipulations when visual search is efficient. This is due, presumably, to the increased cognitive load in the dual-task condition, which interferes with top-down attentional control. This study investigated whether capture by a color singleton is also modulated by single-task vs. dual-task manipulations when visual search was effortful. The results of three experiments revealed that attentional capture effects were absent in a single-task condition and were present in a dual-task condition, but only when the identity of the color singleton is not associated with the target response-set. When the identity of the color singleton was relevant to the response-set it captured attention in both the single-task and in dual-task conditions.

Reduced attentional capture in action video game players

Recent studies indicate that playing action video games improves performance on a number of attention-based tasks. However, it remains unclear whether action video game experience primarily affects endogenous or exogenous forms of spatial orienting. To examine this issue, action video game players and non-action video game players performed an attentional capture task. The results show that action video game players responded quicker than non-action video game players, both when a target appeared in isolation and when a salient, task-irrelevant distractor was present in the display. Action video game players additionally showed a smaller capture effect than did non-action video game players. When coupled with the findings of previous studies, the collective evidence indicates that extensive experience with action video games may enhance players' top-down attentional control, which, in turn, can modulate the negative effects of bottom-up attentional capture.

Purely endogenous capture of attention by task-defining features proceeds independently from spatial attention

Attention can be focused voluntarily and effectively on spatial locations in order to enhance the processing of task-relevant events. However, work on 'attentional capture' has demonstrated that spatial biases can be temporarily reset by transient and salient stimuli, especially if they share defining characteristics with the targets of a task goal. In the current study, we investigated whether the appearance of stimuli containing task-defining features at an unattended location was sufficient to capture attention, even when these were not perceptually salient. We used event-related-potential (ERP) markers to test whether the selection of task-defining features was modulated by top-down spatial attention, and to test whether the appearance of 'unattended targets' transiently disrupted the spatial bias. Surprisingly, the results revealed that ERP markers of selection of task-defining features were equivalent for stimuli appearing at spatially attended and unattended locations. In addition, the presentation of task-defining stimuli at the spatially unattended location induced a short-lived redistribution of the pre-established spatial attention bias toward the 'capture' side. These findings show that task-defining features of a stimulus are automatically processed independently from spatial attention, and suggest the co-existence of multiple sources of top-down biasing signals, which might in part sustain the capture mechanism.

A new object captures attention--but only when you know it's new

Two hypotheses have been advanced to explain why an object appearing suddenly in an empty location captures attention. According to the first hypothesis, the visual transients that accompany an abrupt onset automatically trigger attentional orienting toward the object. The second hypothesis claims that the visual system regards the onset as an advent of a new object, and the latter's novelty causes attention to be drawn toward it. To discriminate between these two accounts, Franconeri, Hollingworth, and Simons (2005) introduced a procedure in which an object was added to the display but, crucially, the object's onset transients were concealed. Their results showed that this additional object failed to capture attention, which they interpreted as evidence against the new-object hypothesis. But the Franconeri et al. procedure could somehow have impeded the visual system from identifying the additional object as new. In three experiments, Franconeri et al.'s results were first replicated and extended. Further, it was shown that when the conditions facilitated the encoding of the locations of the old items, the new object did succeed in capturing attention.

Task-irrelevant stimulus salience affects visual search

The relative contributions of stimulus salience and task-related goals in guiding attention remain an issue of debate. Several studies have demonstrated that top-down factors play an important role, as they often override capture by salient irrelevant objects. However, Yantis and Egeth [Yantis, S., & Egeth, H. E. (1999). On the distinction between visual salience and stimulus-driven attentional capture. Journal of Experimental Psychology: Human Perception and Performance, 25, 661-676.] have made the more radical claim that salience plays no role in visual search unless the observer adopts an attentional set for singletons or "singleton-detection mode". We reexamine their claim while disentangling effects of stimulus salience from effects of attentional set and inter-trial repetition. The results show that stimulus salience guides attention even when salience is task irrelevant.

The Prioritization of Feature Singletons in the Change Detection Paradigm

Six experiments are reported investigating whether a discontinuity in colour can accrue attentional priority. In addition to a standard visual search paradigm, we examined the degree to which colour singletons and nonsingletons are susceptible to change blindness. Results showed that changes occurring at colour singletons were relatively more resistant to change blindness. Although suggestive of bottom-up marshalling of attention, no prioritization of the singleton occurred when the most stringent test of stimulus-driven attentional attraction was employed, that is, when attending to the singleton was detrimental to the task. We conclude that a discontinuity in colour will attract attention unless an attentional set is contrary to singletons.

Search time critically depends on irrelevant subset size in visual search

In order for our visual system to deal with the massive amount of sensory input, some of this input is discarded, while other parts are processed [Wolfe, J. M. (1994). Guided search 2.0: a revised model of visual search. Psychonomic Bulletin and Review, 1, 202-238]. From the visual search literature it is unclear how well one set of items can be selected that differs in only one feature from target (a 1F set), while another set of items can be ignored that differs in two features from target (a 2F set). We systematically varied the percentage of 2F non-targets to determine the contribution of these non-targets to search behaviour. Increasing the percentage 2F non-targets, that have to be ignored, was expected to result in increasingly faster search, since it decreases the size of 1F set that has to be searched. Observers searched large displays for a target in the 1F set with a variable percentage of 2F non-targets. Interestingly, when the search displays contained 5% 2F non-targets, the search time was longer compared to the search time in other conditions. This effect of 2F non-targets on performance was independent of set size. An inspection of the saccades revealed that saccade target selection did not contribute to the longer search times in displays with 5% 2F non-targets. Occurrence of longer search times in displays containing 5% 2F non-targets might be attributed to covert processes related to visual analysis of the fixated part of the display. Apparently, visual search performance critically depends on the percentage of irrelevant 2F non-targets.

Neural mechanisms of spatial- and feature-based attention: a quantitative analysis

Attentional selection can be based on spatial locations, non-spatial stimulus features, or entire objects as integrated feature ensembles. Several studies reported attentional modulations in those regions that process the constituent features of the presented stimuli. Here we employed functional magnetic resonance imaging (fMRI) to directly compare the magnitude of space- and/or feature-based attentional modulations while subjects directed their attention to a particular color (red or green) of a transparent surface and at the same time to a spatial location (left or right visual field). The experimental design made it possible to disentangle and quantify the hemodynamic activity elicited by identical physical stimuli when attention was directed to spatial locations and/or stimulus features. The highest modulations were observed when the attentional selection was based on spatial location. Attended features also elicited a response increase relative to unattended features when their spatial location was attended. Importantly, at unattended locations, a response increase upon feature-based selection was observed in motion-sensitive but not in color-related areas. This suggests that compared to color, motion stimuli are more effective in capturing attention at unattended locations leading to a competitive advantage. These results support the idea of a high biological relevance of the feature motion in the visual world.

Initial fixation placement in face images is driven by top–down guidance

The eyes are often inspected first and for longer period during face exploration. To examine whether this saliency of the eye region at the early stage of face inspection is attributed to its local structure properties or to the knowledge of its essence in facial communication, in this study we investigated the pattern of eye movements produced by rhesus monkeys (Macaca mulatta) as they free viewed images of monkey faces. Eye positions were recorded accurately using implanted eye coils, while images of original faces, faces with scrambled eyes, and scrambled faces except for the eyes were presented on a computer screen. The eye region in the scrambled faces attracted the same proportion of viewing time and fixations as it did in the original faces, even the scrambled eyes attracted substantial proportion of viewing time and fixations. Furthermore, the monkeys often made the first saccade towards to the location of the eyes regardless of image content. Our results suggest that the initial fixation placement in faces is driven predominantly by "top-down" or internal factors, such as the prior knowledge of the location of "eyes" within the context of a face.

Displaywide visual features associated with a search display’s appearance can mediate attentional capture

Whether or not the capture of visual attention is driven solely by the salience of an attention-capturing stimulus or mediated by top-down control has been a point of contention since Folk, Remington, and Johnston (1992) introduced their contingent involuntary orienting hypothesis, which states that the capture of attention by a salient stimulus depends on its relevance to a feature distinguishing the target from nontargets. Gibson and Kelsey (1998) extended Folk et al.'s (1992) hypothesis by demonstrating that features associated with the appearance of the target display also mediate capture. Although similar to Folk et al. (1992), Gibson and Kelsey's displaywide contingent orienting hypothesis makes it difficult to demonstrate stimulus-driven capture, because an observer must always use some perceptible feature as a signal of the target display's appearance; hence, such features could always be mediating capture. The present article reviews and applies the logic of Gibson and Kelsey's and Folk et al.'s (1992) hypotheses to experiments from the attentional capture literature, and assesses whether previously reported capture effects were mediated by top-down attentional control. It concludes that these capture effects were not stimulus-driven.

Color singleton pop-out does not always poop out: an alternative to visual search

Folk psychology suggests that when an observer views a scene, a unique item will stand out and draw attention to itself. This belief stands in contrast to numerous studies in visual search that have found that a unique target item (e.g., a unique color) is not identified more quickly than a nonunique target. We hypothesized that this finding is the result of task demands of visual search, and that when the task does not involve visual search, uniqueness will pop out. We tested this hypothesis in a task in which observers were presented an array of letters and asked to respond aloud, as quickly as possible, with the identity of any one of the letters. The observers were significantly more likely to respond with a uniquely colored letter than would be expected by chance. In a task in which observers blurt out the first thing that they see, unique pop-out does not poop out.

The effect of novel distractors on performance in focused attention tasks: a cognitive-psychophysiological approach

In the present study, we examined whether or not novel stimuli affect performance in a focused attention task. Participants responded to a central target while an irrelevant distractor in the visual display was occasionally changed. In Experiment 1, both target and distractor were presented centrally within the focus of attention. In Experiment 2, a central target was presented along with an irrelevant distractor at a peripheral location, outside the focus of attention. Novel distractors were associated with longer latencies and enhanced orienting responses (as measured by skin conductance responses) only when presented at an attended location. In contrast, as is demonstrated in Experiment 3, the same peripheral novel distractors interfered with task performance when they possessed task-relevant information. These results indicate that there is a fundamental difference between novel stimuli and task-relevant stimuli. Whereas the former exert influence only within the focus of attention, the latter affect performance even when positioned in an unattended location. Our findings have important implications for the operation of visual attention.

Effects of search mode and intertrial priming on singleton search

There is no consensus as to what information guides search for a singleton target. Does the most salient display element capture attention, regardless of the observer's attentional set? Do observers adopt a default salience-based search mode? Does knowledge of the target's defining featural property (when available) affect search? Finally, can intertrial contingencies account for the disparate results in the literature? We investigated search for a shape singleton when (1) the target and nontarget shapes switched unpredictably from trial to trial, (2) the target feature remained fixed, and (3) the target was a singleton on only one third of the trials. We examined overall reaction times, search slopes, errors, and the magnitude of the slowing caused by a cross-dimensional singleton distractor. Our results argue against the idea that search is guided solely by stimulus-driven factors or that subjects adopt a singleton detection mode that is blind to feature information. They show also that intertrial contingencies, although potent, cannot account for the variety of results in the literature.