Processing multidimensional objects under different perceptual loads: The priority of bottom-up perceptual saliency

Bottom-up perceptual salience and top-down retro-cues concurrently determine state in visual working memory

Recent studies have demonstrated that in visual working memory (VWM), only items in an active state can guide attention. Further evidence has revealed that items with higher perceptual salience or items prioritised by a valid retro-cue in VWM tend to be in an active state. However, it is unclear which factor (perceptual salience or retro-cues) is more important for influencing the item state in VWM or whether the factors can act concurrently. Experiment 1 examined the role of perceptual salience by asking participants to hold two features with relatively different perceptual salience (colour vs. shape) in VWM while completing a visual search task. Guidance effects were found when either colour or both colour and shape in VWM matched one of the search distractors but not when shape matched. This demonstrated that the more salient feature in VWM can actively guide attention, while the less salient feature cannot. However, when shape in VWM was cued to be more relevant (prioritised) in Experiment 2, we found guidance effects in both colour-match and shape-match conditions. That is, both more salient but non-cued colour and less salient but cued shape could be active in VWM, such that attentional selection was affected by the matching colour or shape in the visual search task. This suggests that bottom-up perceptual salience and top-down retro-cues can jointly determine the active state in VWM.

Differential brain mechanisms for processing distracting information in task-relevant and -irrelevant dimensions in visual search

A crucial function of our goal-directed behavior is to select task-relevant targets among distractor stimuli, some of which may share properties with the target and thus compete for attentional selection. Here, by applying functional magnetic resonance imaging (fMRI) to a visual search task in which a target was embedded in an array of distractors that were homogeneous or heterogeneous along the task-relevant (orientation or form) and/or task-irrelevant (color) dimensions, we demonstrate that for both (orientation) feature search and (form) conjunction search, the fusiform gyrus is involved in processing the task-irrelevant color information, while the bilateral frontal eye fields (FEF), the cortex along the left intraparietal sulcus (IPS), and the left junction of intraparietal and transverse occipital sulci (IPTO) are involved in processing task-relevant distracting information, especially for target-absent trials. Moreover, in conjunction (but not in feature) search, activity in these frontoparietal regions is affected by stimulus heterogeneity along the task-irrelevant dimension: heterogeneity of the task-irrelevant information increases the activity in these regions only when the task-relevant information is homogeneous, not when it is heterogeneous. These findings suggest that differential neural mechanisms are involved in processing task-relevant and task-irrelevant dimensions of the searched-for objects. In addition, they show that the top-down task set plays a dominant role in determining whether or not task-irrelevant information can affect the processing of the task-relevant dimension in the frontoparietal regions.

Decomposing experience-driven attention: Opposite attentional effects of previously predictive cues

A central function of the brain is to track the dynamic statistical regularities in the environment - such as what predicts what over time. How does this statistical learning process alter sensory and attentional processes? Drawing upon animal conditioning and predictive coding, we developed a learning procedure that revealed two distinct components through which prior learning-experience controls attention. During learning, a visual search task was used in which the target randomly appeared at one of several locations but always inside an encloser of a particular color - the learned color served to direct attention to the target location. During test, the color no longer predicted the target location. When the same search task was used in the subsequent test, we found that the learned color continued to attract attention despite the behavior being counterproductive for the task and despite the presence of a completely predictive cue. However, when tested with a flanker task that had minimal location uncertainty - the target was at the fixation surrounded by a distractor - participants were better at ignoring distractors in the learned color than other colors. Evidently, previously predictive cues capture attention in the same search task but can be better suppressed in a flanker task. These results demonstrate opposing components - capture and inhibition - in experience-driven attention, with their manifestations crucially dependent on task context. We conclude that associative learning enhances context-sensitive top-down modulation while it reduces bottom-up sensory drive and facilitates suppression, supporting a learning-based predictive coding account.

The neural correlates of perceptual load induced attentional selection: an fMRI study

The neural correlates of perceptual load induced attentional selection were investigated in an functional magnetic resonance imaging (fMRI) experiment in which attentional selection was manipulated through the variation of perceptual load in target search. Participants searched for a vertically or horizontally oriented bar among heterogeneously (the high load condition) or homogeneously (the low load condition) oriented distractor bars in the central display, which was flanked by a vertical or horizontal bar presented at the left or the right periphery. The search reaction times were longer when the central display was of high load than of low load, and were longer when the flanker was incongruent than congruent with the target. Importantly, the flanker congruency effect was manifested only in the low load condition, not in the high load condition, indicating that the perceptual load in target search determined whether the task-irrelevant flanker was processed. Imaging analyses revealed a set of fronto-parietal regions having higher activations in the high than in the low load condition. Anterior cingulate cortex (ACC) was more activated for the incongruent than for the congruent trials. Moreover, ACC and bilateral anterior insula were sensitive to the interaction between perceptual load and flanker congruency such that the activation differences between the incongruent and congruent conditions were significant in the low, but not in the high load condition. These results are consistent with the claim that ACC and bilateral anterior insula may exert executive control by selectively biasing processing in favor of task-relevant information and this biasing depends on the resources currently available to the control system.

Response inhibition and attentional control in anxiety

Traditionally, anxiety has been associated with a selective attentional bias for threat and a decreased capacity in attentional control. In two different experiments, we investigated whether individuals with different levels of self-reported state anxiety (Experiment 1) and induced anxiety (Experiment 2) had impaired response inhibition processes (attentional control deficit) as characterized by a different response style in the presence of negative stimuli under low and high perceptual load conditions. A go/no-go paradigm with emotional distractors (angry, happy, and neutral faces) was used to provide measures of perceptual sensitivity, inhibition, and response style. Our findings showed that perceptual sensitivity, as assessed by the d′ parameter of signal detection theory, was reduced in all participants for angry faces under low perceptual load, where enough perceptual resources were available to be attracted by distractors. Importantly, despite similar perceptual sensitivity, the beta parameter indicated that high state anxiety individuals in both experiments were less flexible at adjusting to task demands in the presence of angry face distractors by adopting a stricter criterion. Implications of findings are discussed within current models of attentional control in anxiety.

Biasing the organism for novelty: A pervasive property of the attention system

Although the functional and anatomical independences between the orienting and the executive attention networks have been well established, surprisingly little is known about the potential neural interaction between them. Recent studies point out that spatial inhibition of return (IOR), a mechanism associated with the orienting network, and nonspatial inhibition of return, a mechanism associated with the executive network, might bias the organism for novel locations and objects, respectively. By orthogonally combining the spatial and the nonspatial IOR paradigms in this fMRI study, we demonstrate that the orienting and the executive networks interact and compensate each other in biasing the attention system for novelty. Behaviorally, participants responded slower to the target at the old location only when the color of the target was novel, and participants responded slower to the old color representation only when the target appeared at a novel spatial location. Neurally, the orienting network was involved in slowing down responses to the old location only when the nonspatial IOR mechanism in the executive network was not operative (i.e., when the color of the target was novel); the prefrontal executive network was involved in slowing down responses to the old color representation only when the spatial IOR mechanism in the orienting network was not functioning (i.e., when the target appeared at a novel location).

Target-target similarity on the attentional blink: Task-relevance matters!

Studies of the attentional blink (AB) indicate that similarity modulates the magnitude of the impairment in reporting the second of two masked targets. The present experiments tested whether similarity-based modulations of the AB are determined by all object dimensions or by task-relevant dimensions only. Similarity between target faces was manipulated on two dimensions, only one of which was task-relevant. The results indicated that similarity on the task-relevant dimension modulated the AB, while similarity on task-irrelevant dimension did not. These results suggest that selection during the AB can occur on the level of task-relevant dimensions.

Low-level information and high-level perception: the case of speech in noise

Auditory information is processed in a fine-to-crude hierarchical scheme, from low-level acoustic information to high-level abstract representations, such as phonological labels. We now ask whether fine acoustic information, which is not retained at high levels, can still be used to extract speech from noise. Previous theories suggested either full availability of low-level information or availability that is limited by task difficulty. We propose a third alternative, based on the Reverse Hierarchy Theory (RHT), originally derived to describe the relations between the processing hierarchy and visual perception. RHT asserts that only the higher levels of the hierarchy are immediately available for perception. Direct access to low-level information requires specific conditions, and can be achieved only at the cost of concurrent comprehension. We tested the predictions of these three views in a series of experiments in which we measured the benefits from utilizing low-level binaural information for speech perception, and compared it to that predicted from a model of the early auditory system. Only auditory RHT could account for the full pattern of the results, suggesting that similar defaults and tradeoffs underlie the relations between hierarchical processing and perception in the visual and auditory modalities.

Effects of spatial distribution of attention during inhibition of return (IOR) on flanker interference in hearing and congenitally deaf people

This study explored the interaction between the spatial distribution of attention during inhibition of return (IOR) and different levels of flanker interference in congenitally deaf subjects as compared with hearing subjects. Color (Experiment 1) and alphanumeric (Experiment 2) flanker interference effects were differentiated into the pre-response and the response levels. The spatial distribution of attention was manipulated through IOR. Subjects were asked to either make color or letter/digit discriminations to the central targets or detect the abrupt-onset peripheral targets. Deaf subjects were significantly faster than hearing subjects at detecting peripheral targets irrespective of the cue validity, while the two groups had comparable sizes of IOR. In the central discrimination tasks, deaf subjects showed significant response level, but not pre-response level, flanker effects irrespective of the type of stimuli and the spatial location of the flanker. For hearing subjects, however, spatial attention interacted with the pre-response and response flanker effects in different ways. While flankers at the cued location caused interference effects at the response level and facilitatory effects at the pre-response level, those at the uncued location caused different effects depending on the type of stimuli. Moreover, increasing the peripheral attention for hearing subjects, by increasing the proportion of peripheral detection trials, made hearing subjects behave like deaf subjects. These results demonstrate that deaf people possess enhanced peripheral attentional resources as compared with hearing people. The spatial distribution of attention modulates mainly the resolution of the pre-response flanker interference in hearing people, but affects neither the pre-response nor the response level interference in deaf people.