Perceptual Learning Induces Persistent Attentional Capture by Nonsalient Shapes

Different neural mechanisms for nonsalient trained stimuli and physically salient stimuli in visual processing

Previous studies have shown that nonsalient trained stimuli could capture attention and would be actively suppressed when served as distractors. However, it was unclear whether nonsalient trained stimuli and physically salient stimuli operate through the same attentional neural mechanism. In the current study, we investigated this question by recording event-related potentials (ERPs) of searching for the two stimuli separately after matching the difficulty. The present results provided additional evidence for the function of the suppression in that it may terminate a shift of attention. For the N1 component, the nonsalient trained stimuli had a shorter latency and larger amplitude than the physically salient stimuli whether presented as targets or distractors. It indicated that the nonsalient trained stimuli had an earlier sensory processing and greater visual attention orienting. The N2 posterior-contralateral (N2pc) amplitude of the physically salient target was larger than the nonsalient trained target. This suggested that physically salient stimuli had a stronger ability to capture attention. However, when they presented as distractors, only the nonsalient trained stimuli could elicit the PD component. Therefore, active suppression of the physically salient stimuli was more difficult than the nonsalient trained stimulus with the same difficulty. For the P3 component, the amplitude of the physically salient stimuli was larger than that of the nonsalient trained stimuli, both as targets and distractors, which indicated that the top-down controlled process of outcome evaluation for the salient triangle was stronger. Overall, these results suggested that they were processed via different neural mechanisms in the early sensory processing, attentional selection, active suppression, and the outcome-evaluation process.

Distinct roles of theta and alpha oscillations in the process of contingent attentional capture

Introduction

Visual spatial attention can be captured by a salient color singleton that is contingent on the target feature. A previous study reported that theta (4-7 Hz) and alpha (8-14 Hz) oscillations were related to contingent attentional capture, but the corresponding attentional mechanisms of these oscillations remain unclear.

Methods

In this study, we analyzed the electroencephalogram data of our previous study to investigate the roles of capture-related theta and alpha oscillation activities. Different from the previous study that used color-changed placeholders as irrelevant cues, the present study adopted abrupt onsets of color singleton cues which tend to elicit phase-locked neural activities. In Experiment 1, participants completed a peripheral visual search task in which spatially uninformative color singleton cues were inside the spatial attentional window and a central rapid serial visual presentation (RSVP) task in which the same cues were outside the spatial attentional window. In Experiment 2, participants completed a color RSVP task and a size RSVP task in which the peripheral color singleton cues were contingent and not contingent on target feature, respectively.

Results

In Experiment 1, spatially uninformative color singleton cues elicited lateralized theta activities when they were contingent on target feature, irrespective of whether they were inside or outside the spatial attentional window. In contrast, the same color singleton cues elicited alpha lateralization only when they were inside the spatial attentional window. In Experiment 2, we further found that theta lateralization vanished if the color singleton cues were not contingent on target feature.

Discussion

These results suggest distinct roles of theta and alpha oscillations in the process of contingent attentional capture initiated by abrupt onsets of singleton cues. Theta activities may reflect global enhancement of target feature, while alpha activities may be related to attentional engagement to spatially relevant singleton cues. These lateralized neural oscillations, together with the distractor-elicited N2pc component, might consist of multiple stages of attentional processes during contingent attentional capture.

Is a new feature learned behind a newly efficient color-orientation conjunction search?

It is well known that feature search is efficient, whereas conjunction search is usually inefficient. However, prior studies have shown that some conjunction search could become very efficient through perceptual learning, behaving like a traditional feature search. An unanswered question is whether a new feature is learned when an inefficient conjunction search become efficient after extensive training. A popular view is that the trained conjunction has been successfully unitized into a new feature and thus could pop out from neighboring distractors. Here, by using stimulus specificity and transfer of perceptual learning as an approach, we investigate whether a new feature is learned when an initially inefficient conjunction search becomes highly efficient after extensive training. In two experiments, we consistently found that long-term perceptual learning over days could induce an inefficient-to-efficient pattern change in a color-orientation conjunction search. Moreover, the learning effect of the conjunction target could partly transfer to a new target that shared a same color or a same orientation with the trained target. Remarkably, the total amount of the learning effect was approximately equal to the sum of the transfer effects of individual features. Such additive learning pattern could last for at least several months, although the learning of separate features showed different patterns of persistence. These results do not support that the trained conjunction is unitized into a new and inseparable feature after learning. Instead, our findings point to a feature-based attention enhancement mechanism underlying long-term perceptual learning and its persistence of color-orientation conjunction search.

Inhibition of return as a foraging facilitator in visual search: Evidence from long-term training

Inhibition of return (IOR) discourages visual attention from returning to previously attended locations, and has been theorized as a mechanism to facilitate foraging in visual search by inhibitory tagging of inspected items. Previous studies using visual search and probe-detection tasks (i.e., the probe-following-search paradigm) found longer reaction times (RTs) for probes appearing at the searched locations than probes appearing at novel locations. This IOR effect was stronger in serial than parallel search, favoring the foraging facilitator hypothesis. However, evidence for this hypothesis was still lacking because no attempt was made to study how IOR would change when search efficiency gradually improves. The current study employed the probe-following-search paradigm and long-term training to examine how IOR varied following search efficiency improvements across training days. According to the foraging facilitator hypothesis, inhibitory tagging is an after-effect of attentional engagement. Therefore, when attentional engagement in a visual search task is reduced via long-term training, the strength of inhibitory tagging decreases, thus predicting a reduced IOR effect. Consistent with this prediction, two experiments consistently showed that IOR decreased while search efficiency improved through training, although IOR reached the floor more quickly than search efficiency. These findings support the notion that IOR facilitates search performance via stronger inhibitory tagging in more difficult visual search.

Learned low priority of attention after training to suppress color singleton distractor

Allocating attention to significant events, such as a salient object, is effortless. Our brain is effective on this type of processing because doing so is generally beneficial for survival. However, a salient object could also be distracting and ignoring it costs a large amount of cognitive resource. In the present study, we conducted two behavioral experiments to investigate the effect of learned suppression of a salient color. Particularly, we were interested in the effect of learning in a new task context in which the previously suppressed color was task irrelevant. In Experiment 1, we trained the participants for five days with explicit instruction to suppress a color singleton distractor in a visual search task. We measured the effect of training with a dot probe task before and after the training. Colors in the dot probe task only served as the background and were not associated with the position of the target dot. However, we found that attention was involuntarily biased away from the previously suppressed color. In Experiment 2, the color singleton could either be the target or distractor in the visual search task, making the suppression of the color singleton inefficient for task performance. The results showed no training effect in the dot probe task after this manipulation. These findings provided direct evidence for the learned low priority of attention after training to suppress the color singleton distractor.

Spatial task relevance modulates value-driven attentional capture

Attention tends to be attracted to visual features previously associated with reward. To date, nearly all existing studies examined value-associated stimuli at or near potential target locations, making such locations meaningful to inspect. The present experiments examined whether the attentional priority of a value-associated stimulus depends on its location-wise task relevance. In three experiments we used an RSVP task to compare the attentional demands of a value-associated peripheral distractor to that of a distractor associated with the top-down search goal. At a peripheral location that could never contain the target, a value-associated color did not capture attention. In contrast, at the same location, a distractor in a goal-matching color did capture attention. The results show that value-associated stimuli lose their attentional priority at task-irrelevant locations, in contrast to other types of stimuli that capture attention.

Gotcha: Working memory prioritization from automatic attentional biases

Attention is an important resource for prioritizing information in working memory (WM), and it can be deployed both strategically and automatically. Most research investigating the relationship between WM and attention has focused on strategic efforts to deploy attentional resources toward remembering relevant information. However, such voluntary attentional control represents a mere subset of the attentional processes that select information to be encoded and maintained in WM (Theeuwes, Journal of Cognition, 1[1]: 29, 1-15, 2018). Here, we discuss three ways in which information becomes prioritized automatically in WM-physical salience, statistical learning, and reward learning. This review integrates findings from perception and working memory studies to propose a more sophisticated understanding of the relationship between attention and working memory.

Combined influence of valence and statistical learning on the control of attention: Evidence for independent sources of bias

Selection history exerts a powerful influence on the control of attention. Stimuli signalling reward and punishment capture attention even when physically non-salient and task-irrelevant. Repeated presentation of a salient distractor at a particular location generates learned suppression, resulting in reduced attentional processing at that location. A debate in the field concerns whether different components of selection history influence attention via a common underlying mechanism of learning-dependent control or via distinct, independent mechanisms. We probed this question with a particular focus on reward/punishment history and learned suppression. Participants were trained to suppress a particular location (high probability distractor location) and associate colours with reward or no outcome (no-reward). In a subsequent task, reward and no-reward distractors appeared in all locations equally often. In a separate experiment, we replaced reward with electric shocks. Reward and shock distractors captured attention more strongly than no-reward and no-shock distractors irrespective of their location. Distractors appearing in the high probability location showed reduced capture irrespective of their type. The results imply that reward and punishment learning and learned suppression have independent influences on the attentional system.

Selection history is relative

Visual attention can be tuned to specific features to aid in visual search. The way in which these search strategies are established and maintained is flexible, reflecting goal-directed attentional control, but can exert a persistent effect on selection that remains even when these strategies are no longer advantageous, reflecting an attentional bias driven by selection history. Apart from feature-specific search, recent studies have shown that attention can be tuned to target-nontarget relationships. Here we tested whether a relational search strategy continues to bias attention in a subsequent task, where the relationally better color and former target color both serve as distractors (Experiment 1) or as potential targets (Experiment 2). We demonstrate that a relational bias can persist in a subsequent task in which color serves as a task-irrelevant feature, both impairing and facilitating visual search performance. Our findings extend our understanding of the relational account of attentional control and the nature of selection history effects on attention.

Selection history in context: Evidence for the role of reinforcement learning in biasing attention

Attention is biased towards learned predictors of reward. The influence of reward history on attentional capture has been shown to be context-specific: When particular stimulus features are associated with reward, these features only capture attention when viewed in the context in which they were rewarded. Selection history can also bias attention, such that prior target features gain priority independently of reward history. The contextual specificity of this influence of selection history on attention has not been examined. In the present study, we demonstrate that the consequences of repetitive selection on attention robustly generalize across context, such that prior target features capture attention even in contexts in which they were never seen previously. Our findings suggest that the learning underlying attention driven by outcome-independent selection history differs qualitatively from the learning underlying value-driven attention, consistent with a distinction between associative and reinforcement learning mechanisms.

Automatic Detection of Orientation Contrast Occurs at Early but Not Earliest Stages of Visual Cortical Processing in Humans

Orientation contrast is formed when some elements orient differently from their surroundings. Although orientation contrast can be processed in the absence of top-down attention, the underlying neural mechanism for this automatic processing in humans is controversial. In particular, whether automatic detection of orientation contrast occurs at the initial feedforward stage in the primary visual cortex (i.e., V1) remains unclear. Here, we used event-related potentials (ERPs) to examine the automatic processing of orientation contrast in humans. In three experiments, participants completed a task at fixation while orientation contrasts were presented in the periphery, either in the upper visual field (UVF) or the lower visual field (LVF). All experiments showed significant positive potentials evoked by orientation contrasts over occipital areas within 100 ms after stimulus onset. These contrast effects occurred 10-20 ms later than the C1 components evoked by identically located abrupt onset stimuli which indexes the initial feedforward activity in V1. Compared with those in the UVF, orientation contrasts in the LVF evoked earlier and stronger activities, probably reflecting a LVF advantage in processing of orientation contrast. Even when orientation contrasts were rendered almost invisible by backward masking (in Experiment 2), the early contrast effect in the LVF was not disrupted. These findings imply that automatic processing of orientation contrast could occur at early visual cortical processing stages, but was slightly later than the initial feedforward processing in human V1; such automatic processing may involve either recurrent processing in V1 or feedforward processing in early extrastriate visual cortex. Highlights -We examined the earliest automatic processing of orientation contrast in humans with ERPs.-Significant orientation contrast effect started within 100 ms in early visual areas.-The earliest orientation contrast effect occurred later than the C1 evoked by abrupt onset stimuli.-The earliest orientation contrast effect was independent of top-down attention and awareness.-Automatic detection of orientation contrast arises slightly after the initial feedforward processing in V1.

On the distinction between value-driven attention and selection history: Evidence from individuals with depressive symptoms

When predictive of extrinsic reward as targets, stimuli rapidly acquire the ability to automatically capture attention. Attentional biases for former targets of visual search also can develop without reward feedback but typically require much longer training. These learned biases towards former targets often are conceptualized within a single framework and might differ merely in degree. That is, both are the result of the reinforcement of selection history, with extrinsic reward for correct report of the target providing greater reinforcement than correct report alone. A direct test of this shared mechanisms hypothesis is lacking, however. Recent evidence demonstrates that depressed individuals present with blunted value-driven attentional biases. Based on the shared mechanisms hypothesis, we predicted that depressed individuals would similarly show blunted attentional biases for former targets following unrewarded training. To the contrary, however, we found that the effects of selection history on attention were robust and equivalent between individuals experiencing depressive symptoms and control participants, whereas attentional capture by previously reward-associated stimuli was blunted in depressed individuals. Our results suggest a qualitative distinction between the effects of reward history and the effects of selection history on attention, with depressive symptoms impairing the former while leaving the latter unaffected.

On the value-dependence of value-driven attentional capture

Findings from an increasingly large number of studies have been used to argue that attentional capture can be dependent on the learned value of a stimulus, or value-driven. However, under certain circumstances attention can be biased to select stimuli that previously served as targets, independent of reward history. Value-driven attentional capture, as studied using the training phase-test phase design introduced by Anderson and colleagues, is widely presumed to reflect the combined influence of learned value and selection history. However, the degree to which attentional capture is at all dependent on value learning in this paradigm has recently been questioned. Support for value-dependence can be provided through one of two means: (1) greater attentional capture by prior targets following rewarded training than following unrewarded training, and (2) greater attentional capture by prior targets previously associated with high compared to low value. Using a variant of the original value-driven attentional capture paradigm, Sha and Jiang (Attention, Perception, and Psychophysics, 78, 403-414, 2016) failed to find evidence of either, and raised criticisms regarding the adequacy of evidence provided by prior studies using this particular paradigm. To address this disparity, here we provided a stringent test of the value-dependence hypothesis using the traditional value-driven attentional capture paradigm. With a sufficiently large sample size, value-dependence was observed based on both criteria, with no evidence of attentional capture without rewards during training. Our findings support the validity of the traditional value-driven attentional capture paradigm in measuring what its name purports to measure.