Control In Visual Search Research Articles

Attentional development can help us understand the inattentional blindness effect in visual search

IntroductionInattentional Blindness (IB) is the failure to notice an unexpected, usually salient stimulus while immersed in a different, often demanding attentional task. More than just a laboratory curiosity, IB is an important phenomenon to understand because it may be related to real-world errors such as missed “incidental findings” in medical image or security searches. Interest in individual differences in susceptibility to IB has produced a number of studies showing inconclusive results.MethodsHere, we tested IB in a sample of 277 participants, 4-25 years old performing a visual search task. On two critical trials, an unexpected letter and an unexpected word were presented among photorealistic objects.ResultsThere was a clear age effect with younger individuals showing higher IB levels. IB correlated with attentional control in visual search and with Continuous Performance Test-CPT for d-prime, response times and attentional shifting measures. These effects disappeared if age was controlled. There were no general effects of intelligence (IQ; RIST) or gender. Younger observers showed a negative correlation of IB for the word with the verbal components of the RIST IQ-proxy (no effect for the letter).DiscussionThese results support a relationship between IB and cognitive-developmental changes, showing that maturation of attention and executive processes can help us understand the intriguing phenomenon of (sometimes) missing what is in front of our eyes.

An EEG study of the combined effects of top-down and bottom-up attentional selection under varying task difficulty.

We examined the effect of combined top-down and bottom-up attentional control sources, using known attention-related EEG components that are thought to reflect target selection (N2pc) and distractor suppression (PD ). We used endogenous cues (valid vs. neutral) for top-down attentional control, and salience in the form of color singletons (either the target or a distractor) for bottom-up attentional control in visual search. Crucially, in two experiments, the task was of increasing difficulty, reporting the orientation of a tilted target (Experiment 1), or the position of a small gap within the target among tilted non-targets (Experiment 2). Our results showed strong cueing effects on RT and accuracy in both experiments, demonstrating a general facilitation of responses to validly cued targets. Whereas the processing of salient targets was not improved compared with non-salient targets, the presence of a salient distractor consistently worsened performance. The N2pc and PD were only observed in trials where targets were preceded by neutral cues in Experiment 1, and for validly cued targets and salient neutrally cued targets in Experiment 2. A cueing effect was found on the PD in Experiment 1, showing an amplitude reduction in trials where the target was validly cued. These results support the idea that bottom-up attentional allocation occurs only when top-down allocation of attention is absent or inefficient. Therefore, these results indicate that attentional selection and suppression during visual search are both influenced by top-down cueing and give support to theories that focus on the interaction between the two types of attention.

Why signal suppression cannot resolve the attentional capture debate

ABSTRACT Luck et al. (2021, Progress toward resolving the attentional capture debate. Visual Cognition, 29(1), 1–21. https://doi.org/10.1080/13506285.2020.1848949) propose that proactive suppression can help to resolve the long-standing attentional capture debate. They argue that salient but task-irrelevant stimuli automatically generate a priority signal, which leads to attentional capture if it is not suppressed. While this signal suppression framework provides a refreshing new perspective on attentional capture, it cannot fully resolve this debate. To do this, it would have to be demonstrated that task-contingent capture effects in spatial cueing tasks are linked to proactive feature-based suppression preventing attentional capture by salient but irrelevant objects. I argue that there is little evidence if any evidence for such a link. I consider possible reasons why suppression does not seem to play a major role in spatial cueing tasks, and also highlight important general limitations of proactive inhibitory control in visual search.

Out with the old: New target templates impair the guidance of visual search by preexisting task goals.

Representations of known target features (attentional templates) guide attention toward target objects during visual search. Recent research has shown that templates for different target-defining attributes can be maintained simultaneously, but interactions between multiple templates have not yet been studied systematically. Here, we investigated the competition between long-term (sustained) and short-term (transient) search goals in tasks where participants searched for targets defined by 1 of 2 possible colors. One target color remained constant across blocks or runs of trials, while the other changed on every trial. Both colors were indicated at the start of each trial by cue displays. To assess the efficiency of target selection processes guided by sustained and transient color templates, RTs and N2pc components were measured in Experiment 1 for search displays that contained a target in the constant or variable color. Results revealed robust sustained-template costs. RTs were slower and N2pc components emerged later and were smaller for sustained-color as compared to transient-color target objects. Experiments 2 and 3 demonstrated that this cost emerged rapidly, within 2 trials after a new constant color template had been established. These findings suggest that the activation of a new top-down search goal impairs the ability of a preexisting template in working memory to guide attention toward target objects, reflecting a new type of retroactive interference in the control of visual search. These findings also have implications for our understanding of interactions between short-term task goals and longer-term attentional biases associated with the affective or motivational valence of objects. (PsycInfo Database Record (c) 2020 APA, all rights reserved).

Target-nontarget similarity decreases search efficiency and increases stimulus-driven control in visual search.

Some points of criticism against the idea that attentional selection is controlled by bottom-up processing were dispelled by the attentional window account. The attentional window account claims that saliency computations during visual search are only performed for stimuli inside the attentional window. Therefore, a small attentional window may avoid attentional capture by salient distractors because it is likely that the salient distractor is located outside the window. In contrast, a large attentional window increases the chances of attentional capture by a salient distractor. Large and small attentional windows have been associated with efficient (parallel) and inefficient (serial) search, respectively. We compared the effect of a salient color singleton on visual search for a shape singleton during efficient and inefficient search. To vary search efficiency, the nontarget shapes were either similar or dissimilar with respect to the shape singleton. We found that interference from the color singleton was larger with inefficient than efficient search, which contradicts the attentional window account. While inconsistent with the attentional window account, our results are predicted by computational models of visual search. Because of target-nontarget similarity, the target was less salient with inefficient than efficient search. Consequently, the relative saliency of the color distractor was higher with inefficient than with efficient search. Accordingly, stronger attentional capture resulted. Overall, the present results show that bottom-up control by stimulus saliency is stronger when search is difficult, which is inconsistent with the attentional window account.

Modeling Lag-2 Revisits to Understand Trade-Offs in Mixed Control of Fixation Termination During Visual Search.

An important question about eye-movement behavior is when the decision is made to terminate a fixation and program the following saccade. Different approaches have found converging evidence in favor of a mixed-control account, in which there is some overlap between processing information at fixation and planning the following saccade. We examined one interesting instance of mixed control in visual search: lag-2 revisits, during which observers fixate a stimulus, move to a different stimulus, and then revisit the first stimulus on the next fixation. Results show that the probability of lag-2 revisits occurring increased with the number of target-similar stimuli, and revisits were preceded by a brief fixation on the intervening distractor stimulus. We developed the Efficient Visual Sampling (EVS) computational model to simulate our findings (fixation durations and fixation locations) and to provide insight into mixed control of fixations and the perceptual, cognitive, and motor processes that produce lag-2 revisits.

EPS Mid-Career Award 2014. The control of attention in visual search: Cognitive and neural mechanisms.

In visual search, observers try to find known target objects among distractors in visual scenes where the location of the targets is uncertain. This review article discusses the attentional processes that are active during search and their neural basis. Four successive phases of visual search are described. During the initial preparatory phase, a representation of the current search goal is activated. Once visual input has arrived, information about the presence of target-matching features is accumulated in parallel across the visual field (guidance). This information is then used to allocate spatial attention to particular objects (selection), before representations of selected objects are activated in visual working memory (recognition). These four phases of attentional control in visual search are characterized both at the cognitive level and at the neural implementation level. It will become clear that search is a continuous process that unfolds in real time. Selective attention in visual search is described as the gradual emergence of spatially specific and temporally sustained biases for representations of task-relevant visual objects in cortical maps.

Activation of new attentional templates for real-world objects in visual search.

Visual search is controlled by representations of target objects (attentional templates). Such templates are often activated in response to verbal descriptions of search targets, but it is unclear whether search can be guided effectively by such verbal cues. We measured ERPs to track the activation of attentional templates for new target objects defined by word cues. On each trial run, a word cue was followed by three search displays that contained the cued target object among three distractors. Targets were detected more slowly in the first display of each trial run, and the N2pc component (an ERP marker of attentional target selection) was attenuated and delayed for the first relative to the two successive presentations of a particular target object, demonstrating limitations in the ability of word cues to activate effective attentional templates. N2pc components to target objects in the first display were strongly affected by differences in object imageability (i.e., the ability of word cues to activate a target-matching visual representation). These differences were no longer present for the second presentation of the same target objects, indicating that a single perceptual encounter is sufficient to activate a precise attentional template. Our results demonstrate the superiority of visual over verbal target specifications in the control of visual search, highlight the fact that verbal descriptions are more effective for some objects than others, and suggest that the attentional templates that guide search for particular real-world target objects are analog visual representations.

Functional brain organization of preparatory attentional control in visual search

Looking for an object that may be present in a cluttered visual display requires an advanced specification of that object to be created and then matched against the incoming visual input. Here, fast event-related fMRI was used to identify the brain networks that are active when preparing to search for a visual target. By isolating the preparation phase of the task it has been possible to show that for an identical stimulus, different patterns of cortical activation occur depending on whether participants anticipate a ‘feature’ or a ‘conjunction’ search task. When anticipating a conjunction search task, there was more robust activation in ventral occipital areas, new activity in the transverse occipital sulci and right posterior intraparietal sulcus. In addition, preparing for either type of search activated ventral striatum and lateral cerebellum. These results suggest that when participants anticipate a demanding search task, they develop a different advanced representation of a visually identical target stimulus compared to when they anticipate a nondemanding search.

Reward and attentional control in visual search.

It has long been known that the control of attention in visual search depends both on voluntary, top-down deployment according to context-specific goals, and on involuntary, stimulus-driven capture based on the physical conspicuity of perceptual objects. Recent evidence suggests that pairing target stimuli with reward can modulate the voluntary deployment of attention, but there is little evidence that reward modulates the involuntary deployment of attention to task-irrelevant distractors. We report several experiments that investigate the role of reward learning on attentional control. Each experiment involved a training phase and a test phase. In the training phase, different colors were associated with different amounts of monetary reward. In the test phase, color was not task-relevant and participants searched for a shape singleton; in most experiments no reward was delivered in the test phase. We first show that attentional capture by physically salient distractors is magnified by a previous association with reward. In subsequent experiments we demonstrate that physically inconspicuous stimuli previously associated with reward capture attention persistently during extinction--even several days after training. Furthermore, vulnerability to attentional capture by high-value stimuli is negatively correlated across individuals with working memory capacity and positively correlated with trait impulsivity. An analysis of intertrial effects reveals that value-driven attentional capture is spatially specific. Finally, when reward is delivered at test contingent on the task-relevant shape feature, recent reward history modulates value-driven attentional capture by the irrelevant color feature. The influence of learned value on attention may provide a useful model of clinical syndromes characterized by similar failures of cognitive control, including addiction, attention-deficit/hyperactivity disorder, and obesity.

Trial-by-trial adjustments of top-down set modulate oculomotor capture

The role of top-down control in visual search has been a subject of much debate. Recent research has focused on whether attentional and oculomotor capture by irrelevant salient distractors can be modulated through top-down control, and if so, whether top-down control can be rapidly initiated based on current task goals. In the present study, participants searched for a unique shape in an array containing otherwise homogeneous shapes. A cue prior to each trial indicated the probability that an irrelevant color singleton distractor would appear on that trial. Initial saccades were less likely to land on the target and participants took longer to initiate a saccade to the target when a color distractor was present than when it was absent; this cost was greatly reduced on trials in which the probability that a distractor would appear was high, as compared to when the probability was low. These results suggest that top-down control can modulate oculomotor capture in visual search, even in a singleton search task in which distractors are known to readily capture both attention and the eyes. Furthermore, the results show that top-down distractor suppression mechanisms can be initiated quickly in anticipation of irrelevant salient distractors and can be adjusted on a trial-by-trial basis.

Sources of Top–Down Control in Visual Search

Endogenous control of visual search can influence search guidance at the level of a supradimensional topographic saliency map [Wolfe, J. M. Guided Search 2.0: A revised model of visual search. Psychonomic Bulletin & Review, 1, 202-238, 1994], and modulate nonspatial mechanisms coding saliency in dimension-specific input modules [Müller, H. J., Reimann, B., & Krummenacher, J. Visual search for singleton feature targets across dimensions: Stimulus- and expectancy-driven effects in dimensional weighting. Journal of Experimental Psychology: Human Perception and Performance, 29, 1021-1035, 2003]. The current experiment used fMRI to dissociate these mechanisms in a singleton feature search task in which the likely target dimension (color or orientation) was semantically precued and target saliency in each dimension was varied parametrically. BOLD signal increases associated with increased demands for top-down guidance were observed within the fronto-parietal attention network and in the right anterior middle frontal gyrus. Decreasing requirements for top-down control led to BOLD signal increases in medial anterior prefrontal cortex, consistent with a gating mechanism in favor of stimulus-related processing [Burgess, P. W., Dumontheil, I., & Gilbert, S. J. The gateway hypothesis of rostral prefrontal cortex (area 10) function. Trends in Cognitive Sciences, 11, 290-298, 2007]. Another network of brain areas consisting of left lateral fronto-polar cortex, the left supramarginal gyrus, and the cerebellum, as well as a bilateral network consisting of the posterior orbital gyrus, the inferior frontal gyrus, and the pre-SMA were associated with top-down dimensional (re-) orienting. These data argue in favor of distinct endogenous control systems for visuospatial and dimension-based attentional processing. Finally, cue validity modulated saliency processing in the left temporo-parietal junction (TPJ), pointing to a crucial role of the left TPJ in integrating an endogenous dimension-based attention set with bottom-up saliency signals.

The importance of being expert: Top-down attentional control in visual search with photographs

Two observers looking at the same picture may not see the same thing. To avoid sensory overload, visual information is actively selected for further processing by bottom-up processes, originating within the visual image, and top-down processes, reflecting the motivation and past experiences of the observer. The latter processes could grant categories of significance to the observer a permanent attentional advantage. Nevertheless, evidence for a generalized top-down advantage for specific categories has been limited. In this study, bird and car experts searched for face, car, or bird photographs in a heterogeneous display of photographs of real objects. Bottom-up influences were ruled out by presenting both groups of experts with identical displays. Faces and targets of expertise had a clear advantage over novice targets, indicating a permanent top-down preference for favored categories. A novel type of analysis of reaction times over the visual field suggests that the advantage for expert objects is achieved by broader detection windows, allowing observers to scan greater parts of the visual field for the presence of favored targets during each fixation.

Bottom-up and Top-down Control in Visual Search

Previous research suggests that the allocation of attention is largely controlled either in a stimulus-driven or in a goal-driven manner. To date, few studies have systematically manipulated variables affecting stimulus-driven and goal-driven selection independently in order to investigate how both manners of control interrelate and affect performance in visual search. In the present study observers were presented with search displays consisting of an array of line segments rotated at various orientations. The task of observers was to indicate the presence or absence of a vertical line segment (the target) presented amongst a series of nontargets and possibly one distractor. By varying the absolute differences in orientation between the target, nontargets, and distractors, relative target-distractor salience and target-distractor similarity were independently manipulated to investigate the contribution of stimulus-driven and goal-driven control. The major result was that relative target-distractor salience and target-distractor similarity affected search performance independently. Performance was better in cases where the irrelevant distractor was not a salient item in the search display and did not look similar to the target. The results are discussed in terms of models of attentional control.

Anterior Prefrontal Cortex Contributions to Attention Control

In a series of event-related functional magnetic resonance studies, we consistently found activation in anterior prefrontal cortex related to visual dimension changes in singleton search tasks. I review these data and discuss possible contributions of anterior prefrontal cortex to attention control in visual search. It is proposed that anterior prefrontal cortex may detect task-relevant stimulus changes when the target is ambiguously defined. This process may occur in the absence of awareness and may support visual dimension weighting by inhibition of the old relevant dimension in favor of the new dimension.

Parietal activation during visual search in the absence of multiple distractors.

Search for a target object embedded in a visual scene involves the posterior parietal cortex. This region is thought to play a role in visual attention by counteracting the effects of distractors on targets or by inhibiting distractors. Using fMRI, we investigated whether the parietal cortex is also engaged in visual search without distractors. Cortical activation was compared between two 'single object' search tasks differing only in difficulty. Activation differences between both tasks were found in the anterior and inferior part of the intraparietal sulcus, but in neither its posterior part nor the frontal eye fields. Thus a subset of parietal regions participates in the control of visual search even in the absence of distractors.

On the role of blank spaces for eye-movement control in visual search.

The present experimental data demonstrate that in a simple letter-search task using a highly repetitive spatial pattern, the use of a block structure similar to the one we are familiar with in a reading situation (blocks of characters separated by blank spaces) does not facilitate scanning behavior. The presence of blank spaces interspersed irregularly within lines ofxs which have to be scanned in search of a target letter causes a decrease in fixation durations but also decreases saccade size. The results can be understood in terms of an inhibition of visual processing by the presence of the blank spaces: the visual span for the different target letters was found to be significantly smaller when blank spaces were present within the background than when they were absent. Saccade sizes adapt to this change in visual span and become smaller, confirming the visual-span-control hypothesis for scanning eye movements (Jacobs, 1986). When saccades become smaller, less information is extracted at each fixation, causing a decrease in processing times and shorter fixation durations.

Eye-movement control in visual search: how direct is visual span control?

In order to distinguish between the effects of low-level sensory mechanisms and those of higher level factors on eye-movement control processes, a simple letter search task was used in which cognitive load was reduced to the very minimum. The special purpose of this study was to test the visual span control hypothesis, which considers that, in such a task, eye movements are controlled as a direct function of spatial visibility limits (O’Regan, Levy-Schoen, & Jacobs, 1983). In a first psychophysical experiment, three methods were used to manipulate the spatial visibility limits (visual span), as measured by a psychophysical procedure: changing viewing distance, interletter spacing, and target-background similarity. The results of this experiment then were used as a reference for predicting mean saccade sizes and fixation durations in a visual search task in which the same visibility changes were made. About 80% of the variance of mean saccade sizes could be accounted for by adjustment of saccades to changes in visual span, so the visual span control hypothesis was confirmed. As to the temporal characteristics of scanning behavior, less than 50% of fixation duration variance seemed to be determined by visual span changes. Other, higher level factors, possibly related to decisional processes intervening in the triggering of saccades and the computation of their spatial parameters, might play an important role in determining fixation durations in a simple search task. The results are interpreted in relation to recent models of eye-movement control by two largely independent subsystems functioning in parallel.