Salient distractor processing: inhibition following attentional capture.

Salient objects often capture attention in a purely exogenous way, followed by inhibition of their locations after a period. Yet, the neural circuits underlying the exogenous attention remain underspecified. Seidel Malkinson et al. explore this by uncovering large-scale cortical gradients associated with exogenous attention within the human cortex.

Neural evidence for attentional capture by salient distractors.

Salient objects often capture our attention, serving as distractors and hindering our current goals. It remains unclear when and how salient distractors interact with our goals, and our knowledge on the neural mechanisms responsible for attentional capture is limited to a few brain regions recorded from non-human primates. Here we conducted a multivariate analysis on human intracranial signals covering most brain regions and successfully dissociated distractor-specific representations from target-arousal signals in the high-frequency (60-100 Hz) activity. We found that salient distractors were processed rapidly around 220 ms, while target-tuning attention was attenuated simultaneously, supporting initial capture by distractors. Notably, neuronal activity specific to the distractor representation was strongest in the superior and middle temporal gyrus, amygdala and anterior cingulate cortex, while there were smaller contributions from the parietal and frontal cortices. These results provide neural evidence for attentional capture by salient distractors engaging a much larger network than previously appreciated.

Long-term memory retrieval bypasses working memory.

For decades, it has been assumed that when humans retrieve information from long-term memory (LTM), information need first to be brought back into working memory (WM). However, as WM capacity is limited, it is unclear what happens if information from LTM needs to be retrieved while WM is fully engaged? To address this question, observers had to retrieve colors from LTM while WM storage capacity was fully engaged. The behavioral results showed that retrieving information from LTM is possible even when WM capacity is fully occupied. Additional evidence from electroencephalogram (EEG) confirmed that WM was fully engaged as the suppression of alpha oscillation reached its maximum when memorizing the maximum amount of information into WM; yet the suppression in alpha oscillation was even further amplified when items were retrieved simultaneously from LTM, providing a neural signature of additional LTM retrieval capacity above and beyond the maximum WM capacity. Together, our findings indicate that information retrieved from LTM does not always have to be brought back into WM, but instead might be accessed through a different mechanism when WM is fully engaged.

Visual Working Memory Adapts to the Nature of Anticipated Interference.

Visual working memory has been proven to be relatively robust against interference. However, little is known on whether such robust coding is obligatory, or can be flexibly recruited depending on its expected usefulness. To address this, participants remembered both the color and orientation of a grating. During the maintenance, we inserted a secondary color/orientation memory task, interfering with the primary task. Crucially, we varied the expectations of the type of interference by varying the probability of the two types of intervening task. Behavioral data indicate that to-be-remembered features for which interference is expected are bolstered, whereas to-be-remembered features for which no interference is expected are left vulnerable. This was further supported by fMRI data obtained from visual cortex. In conclusion, the flexibility of visual working memory allows it to strengthen memories for which it anticipates the highest risk of interference.

Spatial enhancement due to statistical learning tracks the estimated spatial probability.

It is well known that attentional selection is sensitive to the regularities presented in the display. In the current study we employed the additional singleton paradigm and systematically manipulated the probability that the target would be presented in one particular location within the display (probabilities of 30%, 40%, 50%, 60%, 70%, 80%, and 90%). The results showed the higher the target probability, the larger the performance benefit for high- relative to low-probability locations both when a distractor was present and when it was absent. We also showed that when the difference between high- and low-probability conditions was relatively small (30%) participants were not able to learn the contingencies. The distractor presented at a high-probability target location caused more interference than when presented at a low-probability target location. Overall, the results suggest that attentional biases are optimized to the regularities presented in the display tracking the experienced probabilities of the locations that were most likely to contain a target. We argue that this effect is not strategic in nature nor the result of repetition priming. Instead, we assume that through statistical learning the weights within the spatial priority map are adjusted optimally, generating the efficient selection priorities.

Automatically binding relevant and irrelevant features in visual working memory.

It is generally assumed that, to save storage space, features are stored as integrated objects in visual working memory (VWM). Although such an object-based account does not always hold because features can be processed in parallel, a previous study has shown that different features can be automatically bound with their locations (task-irrelevant feature) into an integrated unit, resulting in improved memory performance. The present study was designed to further explore this phenomenon by investigating whether other features, which are not spatial in origin, can act as the binding cue to form such automatic binding. To test this, we used three different features as binding cues (i.e., colour, spatial frequency, and shape) over multiple separate experiments. The results consistently showed that when two features shared the same binding cue, memory performance was better relative to when each of those features had their own binding cue. We conclude that any task-irrelevant feature can act as a binding cue to automatically bind with task-relevant features even across different objects, resulting in memory enhancement.

Across-trial spatial suppression in visual search.

In order to focus on objects of interest, humans must be able to avoid distraction by salient stimuli that are not relevant to the task at hand. Many recent studies have shown that through statistical learning we are able to suppress the location that is most likely to contain a salient distractor. Here we demonstrate a remarkable flexibility in attentional suppression. Participants had to search for a shape singleton while a color distractor singleton was present. Unbeknown to the participant, the color distractor was presented according to a consistent pattern across trials. Our findings show that participants learn this distractor sequence as they proactively suppressed the anticipated location of the distractor on the next trial. Critically, none of the participants were aware of these hidden sequences. We conclude that the spatial priority map is highly flexible, operating at a subconscious level preparing the attentional system for what will happen next.

Spatial suppression due to statistical learning tracks the estimated spatial probability.

People are sensitive to regularities in the environment. Recent studies employing the additional singleton paradigm showed that a singleton distractor that appeared more often in one specific location than in all other locations may lead to attentional suppression of high-probability distractor locations. This in turn effectively reduced the attentional capture effect by the salient distractor singleton. However, in basically all of these previous studies, the probability that the salient distractor was presented at this specific location was relatively high (i.e., 65%; or a ratio of 13:1 between high- and low-probability locations). The question we addressed here was whether participants still can learn the regularities in the display even when these regularities are quite subtle. We systematically manipulated the ratio of the distractor appearing at the high- and low-probability location from 2:1 to 8:1. We asked the question whether the suppression effect would depend on the probabilities of the distractor appearing in the high-probability location. The results showed that the suppression of the high-probability location was linearly related to the high-low-probability ratio. In other words, the more evidence that a distractor appears more often at a particular location, the stronger the suppression. This indicates that the distribution of attention is optimally adapted to the statistical regularities present in the display.

Salience determines attentional orienting in visual selection.

Recently the signal-suppression account was proposed, positing that salient stimuli automatically produce a bottom-up salience signal that can be suppressed via top-down control processes. Evidence for this hybrid account came from a capture-probe paradigm that showed that while searching for a specific shape, observers suppressed the location of the irrelevant color singleton. Here we replicate these findings but also show that this occurs only for search arrays with 4 elements. For larger array sizes when both target and distractor singleton are salient, there is no evidence for suppression; instead and consistent with the stimulus-driven account, there is clear evidence that the salient distractor captured attention. The current study shows that the relative salience of items in the display is a crucial factor in attentional control. In displays with a few heterogeneous items, top-down suppression is possible. However, in larger displays in which both target and distractor singletons are salient, no top-down suppression is observed. We conclude that the signal-suppression account cannot resolve the long-standing debate regarding stimulus-driven and goal-driven attentional capture. (PsycInfo Database Record (c) 2020 APA, all rights reserved).

Proactively location-based suppression elicited by statistical learning.

Recently, Wang and Theeuwes used the additional singleton task and showed that attentional capture was reduced for the location that was likely to contain a distractor [1]. It is argued that due to statistical learning, the location that was likely to contain a distractor was suppressed relative to all other locations. The current study replicated these findings and by adding a search-probe condition, we were able to determine the initial distribution of attentional resources across the visual field. Consistent with a space-based resource allocation ("biased competition") model, it was shown that the representation of a probe presented at the location that was likely to contain a distractor was suppressed relative to other locations. Critically, the suppression of this location resulted in more attention being allocated to the target location relative to a condition in which the distractor was not suppressed. This suggests that less capture by the distractor results in more attention being allocated to the target. The results are consistent with the view that the location that is likely to contain a distractor is suppressed before display onset, modulating the first feed-forward sweep of information input into the spatial priority map.

Visual memory benefits from prolonged encoding time regardless of stimulus type.

It is generally assumed that the storage capacity of visual working memory (VWM) is limited, holding about 3-4 items. Recent work with real-world objects, however, has challenged this view by providing evidence that the VWM capacity for real-world objects is not fixed but instead increases with prolonged encoding time (Brady, Störmer, & Alvarez, 2016). Critically, in this study, no increase with prolonged encoding time was observed for storing simple colors. Brady et al. (2016) argued that the larger capacity for real-world objects relative to colors is due to the additional conceptual information of real-world objects. With basically the same methods of Brady et al., in Experiments 1-3, we were unable to replicate their basic findings. Instead, we found that visual memory for simple colors also benefited from prolonged encoding time. Experiment 4 showed that the scale of the encoding time benefit was the same for familiar and unfamiliar objects, suggesting that the added conceptual information does not contribute to this benefit. We conclude that visual memory benefits from prolonged encoding time regardless of stimulus type. (PsycInfo Database Record (c) 2020 APA, all rights reserved).

Implicit attentional biases in a changing environment.

The current study investigates whether statistical regularities that change over time affect attentional selection. While searching for a target singleton, the distractor singleton was presented much more often in one location than in all other locations. Crucially, the location that had a distractor much more often, changed to new locations during the course of the experiment. Here we established exactly how the bias of attention followed these changes in the display. Unlike previous studies, we show that selection was remarkably flexible as the attentional bias followed the changes in the environment incorporating contributions of previous contingencies to the current attentional bias. Importantly, the initial learning experience had a lingering and enduring effect on subsequent attentional biases. We argue that the weights within the spatial priority map of selection are adjusted to changing environments, even though observers are unaware of these changes in the environment.

Statistical regularities induce spatial as well as feature-specific suppression.

[Correction Notice: An Erratum for this article was reported in Vol 45(10) of Journal of Experimental Psychology: Human Perception and Performance (see record 2019-57445-001). In the article, Figure 1 was an older version and has been updated. All versions of this article have been corrected.] We are constantly extracting regularities from the visual environment to optimize attentional orienting. Here we examine the phenomenon that recurrent presentation of distractors in a specific location leads to its attentional suppression. Specifically, we address the question whether suppression is specific to the spatial regularities of distractors or also extends to visual features bearing statistical regularities. To that end, we used a visual search task with two high-probability locations, each showing one of two distractor types more often than the other. At these high-probability locations, target processing was impaired and attentional capture by either distractor was reduced, consistent with feature-unspecific spatial suppression. However, suppression was more facilitated when the distractor feature was presented at the high-probability location that matched its features, suggesting feature-specific suppression. Interestingly, feature-unspecific spatial suppression only spread between locations when distractors varied within a feature dimension (e.g., red and green) but not when they varied across feature dimensions (e.g., red and square). Our findings thus demonstrate a joint influence of implicitly learned spatial and feature regularities on attention and reveal how the visual system can benefit from complex statistical regularities. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Anticipatory Distractor Suppression Elicited by Statistical Regularities in Visual Search.

Salient yet irrelevant objects often capture our attention and interfere with our daily tasks. Distraction by salient objects can be reduced by suppressing the location where they are likely to appear. The question we addressed here was whether suppression of frequent distractor locations is already implemented beforehand, in anticipation of the stimulus. Using EEG, we recorded cortical activity of human participants searching for a target while ignoring a salient distractor. The distractor was presented more often at one location than at any other location. We found reduced capture for distractors at frequent locations, indicating that participants learned to avoid distraction. Critically, we found evidence for "proactive suppression" as already "prior to display onset," there was enhanced power in parieto-occipital alpha oscillations contralateral to the frequent distractor location-a signal known to occur in anticipation of irrelevant information. Locked to display onset, ERP analysis showed a distractor suppression-related distractor positivity (PD) component for this location. Importantly, this PD was found regardless of whether distracting information was presented at the frequent location. In addition, there was an early PD component representing an early attentional index of the frequent distractor location. Our results show anticipatory (proactive) suppression of frequent distractor locations in visual search already starting prior to display onset.

Spatial suppression due to statistical regularities is driven by distractor suppression not by target activation.

Where and what we attend to is not only determined by what we are currently looking for but also by what we have encountered in the past. Recent studies suggest that biasing the probability by which distractors appear at locations in visual space may lead to attentional suppression of high-probability distractor locations, which effectively reduces capture by a distractor but also impairs target selection at this location. However, in many of these studies introducing a high-probability distractor location was equivalent to increasing the probability of the target appearing in any of the other locations (i.e., the low-probability distractor locations). Here, we investigate an alternative interpretation of previous findings according to which attentional selection at high-probability distractor locations is not suppressed but selection at low-probability distractor locations is facilitated. In two visual search tasks, we found no evidence for this hypothesis: there was no evidence for spatial suppression when only target probabilities were biased (Experiment 1), nor did the spatial suppression disappear when only the distractor probabilities were biased while the target probabilities were equal (Experiment 2). We conclude that recurrent presentation of a distractor in a specific location leads to attentional suppression of that location through a mechanism that is unaffected by any regularities regarding the target position.

Statistical regularities bias overt attention.

A previous study employing the additional singleton paradigm showed that a singleton distractor that appeared more often in one specific location interfered less with target search than when it appeared at any other location. These findings suggested that through statistical learning the location that was likely to contain a distractor was suppressed relative to all other locations. Even though feasible, it is also possible that this effect is due to faster disengagement of attention from the high-probability distractor location. The present study tested this hypothesis using a variant of the additional singleton task adapted for eye tracking in which observers made a speeded saccade to a shape singleton and gave a manual response. The singleton distractor was presented more often at one location than all other locations. Consistent with the suppression hypothesis, we found that fewer saccades landed at the high-probability distractor location than any other location. Also, when a target appeared at the high-probability location, saccade latencies towards the target were higher than latencies towards the target when it was presented at other locations. Furthermore, in addition to suppression, we also found evidence for faster disengagement from the high-probability distractor location than the low-probability distractor location; however, this effect was relatively small. The current findings support the notion that through statistical learning plasticity is induced in the spatial priority map of attentional selection so that the high-probability distractor location is suppressed compared to any other location.

Statistical regularities modulate attentional capture independent of search strategy.

An earlier study using the additional singleton task showed that statistical regularities regarding the distractor location can cause an attentional bias that affects the amount of attentional capture by distractors and the efficiency of selection of targets. The distractor singleton was systematically present more often in one location than in all other locations. The present study investigated whether this bias also occurs when observers adopt a feature search mode, i.e., when they search for a specific feature (circle) between elements with different shapes, while ignoring a colored distractor singleton. It is assumed that in feature search, observers can ignore distractors in a top-down way and as such one expects that statistical regularities about the distractor location should not play a role. Contrary to this prediction, we found that even in feature search, both attentional capture by the distractors and the efficiency of selecting the target were impacted by these statistical regularities. Moreover, statistical regularities regarding the feature value of the distractor (its color) had no effect on the amount of capture or the efficiency of selection. We claim that statistical regularities cause passive lingering biases of attention such that on the priority map, the location containing a high probability distractor competes less for attention than locations that are less likely to contain distractors.

How to inhibit a distractor location? Statistical learning versus active, top-down suppression.

Recently, Wang and Theeuwes (Journal of Experimental Psychology: Human Perception and Performance, 44(1), 13-17, 2018a) demonstrated the role of lingering selection biases in an additional singleton search task in which the distractor singleton appeared much more often in one location than in all other locations. For this location, there was less capture and selection efficiency was reduced. It was argued that statistical learning induces plasticity within the spatial priority map such that particular locations that are high likely to contain a distractor are suppressed relative to all other locations. The current study replicated these findings regarding statistical learning (Experiment 1) and investigated whether similar effects can be obtained by cueing the distractor location in a top-down way on a trial-by-trial basis. The results show that top-down cueing of the distractor location with long (1,500 ms; Experiment 2) and short stimulus-onset symmetries (SOAs) (600 ms; Experiment 3) does not result in suppression: The amount of capture nor the efficiency of selection was affected by the cue. If anything, we found an attentional benefit (instead of the suppression) for the short SOA. We argue that through statistical learning, weights within the attentional priority map are changed such that one location containing a salient distractor is suppressed relative to all other locations. Our cueing experiments show that this effect cannot be accomplished by active, top-down suppression. Consequences for recent theories of distractor suppression are discussed.

Statistical regularities modulate attentional capture.

The present study investigated whether statistical regularities can influence visual selection. We used the classic additional singleton task in which participants search for a salient shape singleton while ignoring a color distractor singleton. The color distractor singleton was systematically presented more often in 1 location than in all other locations. For this high-probability location, we found that both the amount of attentional capture by distractors and the efficiency of selecting the target were reduced. There was a spatial gradient of suppression, as the attentional capture effect and the efficiency of selecting the target scaled with the distance from the high-probability location. Some participants were aware of the statistical regularities, but this did not affect the results whatsoever. We interpret these findings as evidence that spatially statistical regularities that are unknown to the observer can influence attention such that locations that have a high probability of containing a distractor are suppressed relative to all other locations. (PsycINFO Database Record

Inhibition of return revisited: Localized inhibition on top of a pervasive bias.

An inhibitory after-effect of attention, frequently referred to as inhibition of return (IOR), operates at a previously attended location to discourage perseverative orienting. Using the classic cueing task, previous work has shown that IOR is not restricted to a previously attended location, but rather spreads to adjacent visual space in a graded manner. The present study expands on this earlier work by exploring a wider visual region and a broader range of cue-target onset asynchronies (CTOAs) to characterize the temporal dynamics of the IOR gradient. The results reveal that the magnitude of IOR generated by cueing decreases exponentially as the CTOA increases. The width of the IOR gradient first increases and then decreases, with a temporal profile that is well captured by an alpha function. Importantly, the present study reveals that in addition to its rapidly decaying local properties, cue-induced IOR can include a pervasive inhibitory bias, which remains relatively stable across IOR's lifetime.