Spatial separation between targets constrains maintenance of attention on multiple objects

Humans are limited in their ability to maintain multiple attentional foci. In attentive tracking of moving objects, performance declines as the number of tracked targets increases. Previous studies have interpreted such reduction in terms of a limit in the number of attentional foci. However, increasing the number of targets usually reduces spatial separation among different targets. In this study, we examine the role of target spatial separation in maintaining multiple attentional foci. Results from a multiple-object tracking task show that tracking accuracy deteriorates as the spatial separation between targets decreases. We propose that local interaction between nearby attentional foci modulates the resolution of attention, and that capacity limitation from attentive tracking originates in part from limitations in maintaining critical spacing among multiple attentional foci. These findings are consistent with the hypothesis that tracking performance is limited not primarily by a number of locations, but by factors such as the spacing and speed of the targets and distractors.     

Irrelevant onsets cause inhibition of return regardless of attentional set

It is disputed whether onsets capture spatial attention either in a purely stimulus-driven fashion or only when they are contingent on one's attentional set. According to the latter assumption, interference from irrelevant onsets may result from nonspatial filtering costs. In the present study, we used inhibition of return (IOR) as a marker for spatial attention. IOR occurs mainly for locations that attention has visited before. Participants searched for a red object among white objects. An attentional set for redness was demonstrated by a spatial validity effect of red cues on response times. However, a stronger validity effect was found for irrelevant white onsets, which slowed responses when the onset contained a distractor, but speeded them when the onset contained a target. Most importantly, this onset benefit for targets turned into a deficit at longer SOAs, indicating IOR. We conclude that onset distractors capture spatial attention regardless of the observer's attentional set.     

Visual object agnosia as a problem in integrating parts and part relations

Current models of vision generally assume that the recognition of visual objects is achieved by encoding their component parts, as well as the spatial relations among parts. The current study examined how the processing of parts and their configurations may be affected in visual agnosia due to brain damage. Both a visual agnosic patient (AR) and healthy control subjects performed a visual search task in which they had to discriminate between targets and distractors that varied according to whether they shared their parts and/or their configuration. The results show that AR's visual search rates are disproportionally slow when targets and distractors share the same configuration than when they have different configurations. AR is also found to be disproportionately slow in discriminating targets and distractors that share identical parts when the targets and distractors share the same configuration. With differently configured targets and distractors, AR shows no part sharing effect. For controls, in contrast, the part and configuration sharing effects occur independently of one another. It is concluded that AR's object recognition deficit arises from difficulties in discriminating objects that share their configuration, and from an abnormal dependency of part information processing upon object configuration.     

工作记忆表征精度加工需求对注意引导的影响

采用注意捕获范式, 通过行为和事件相关脑电位(ERP)实验, 探讨工作记忆表征精度加工需求对注意引导的影响, 行为结果发现, 在低精度加工需求条件下, 只有一个工作记忆表征引导注意, 且处于高激活状态的工作记忆表征产生的注意捕获大于低激活状态; 而在高精度加工需求条件下, 有两个工作记忆表征引导注意, 且处于高、低激活状态的工作记忆表征产生的注意捕获没有差异。ERP结果显示, 高精度加工需求条件下诱发的NSW和LPC大于低精度加工需求条件; 在高精度加工需求条件下, 干扰项与记忆项匹配比不匹配时, 诱发更大的N2和更小的N2pc, 而在低精度加工需求条件下, 干扰项与记忆项匹配和不匹配时诱发的N2、N2pc没有差异。研究表明, 工作记忆表征精度加工需求影响注意引导的机制可能是高精度加工需求下, 工作记忆表征消耗的认知资源增加, 搜索目标获得的资源减少, 干扰项捕获的注意增加。     

Hierarchical attention in discriminating objects at different levels of specificity

An implicit assumption of studies in the attentional literature has been that global and local levels of attention are involved in object recognition. To investigate this assumption, a divided attention task was used in which hierarchical figures were presented to prime the subsequent discrimination of target objects at different levels of category identity (basic and subordinate). Target objects were identified among distractor objects that varied in their degree of visual similarity to the targets. Hierarchical figures were also presented at different sizes and as individual global and local elements in order to investigate whether attention-priming effects on object discrimination were due to grouping/parsing operations or spatial extent. The results showed that local processing primed subordinate object discriminations when the objects were visually similar. Global processing primed basic object discriminations, regardless of the similarity of the distractors, and subordinate object discriminations when the objects were visually dissimilar. It was proposed that global and local processing aids the selection of perceptual attributes of objects that are diagnostic for recognition and that selection is based on two mechanisms: spatial extent and grouping/parsing operations.     

Suppression history of distractor location biases attentional and oculomotor control

Past selection experience greatly affects the deployment of attention such that targets are more readily selected if their features or locations were more frequently selected in the past. Crucially, recent studies have shown similar experience-dependent effects also for salient task irrelevant stimuli: distractors exerted less interference if they appeared at a location where they were presented more often, relatively to other possible locations. Here we investigated the effects of such suppression history on the immediate behavioural correlates of attentional deployment, i.e., eye movements. Participants were to make saccadic eye movements to a target stimulus, while ignoring a highly distracting irrelevant visual onset appearing abruptly on the screen in a proportion of trials. Crucially, this irrelevant onset occurred more frequently in two locations on the visual display and our results showed that, relatively to distractors elsewhere, onsets presented at these locations became easier to ignore, giving rise to reduced oculomotor capture. Consistent with the notion that experience can alter attentional deployment towards spatial locations, these findings indicate that, through learning, the priority of high frequency locations becomes suppressed, attenuating the intrinsic saliency of distractors appearing therein. Traces left by individual events of attentional suppression decrease the processing priority of coordinates within topographic maps of the visual space.     

Brain activation during spatial updating and attentive tracking of moving targets

Keeping aware of the locations of objects while one is moving requires the updating of spatial representations. As long as the objects are visible, attentional tracking is sufficient, but knowing where objects out of view went in relation to one's own body involves an updating of spatial working memory. Here, multiple object tracking was employed to study spatial updating and its neural correlates. In a dynamic 3D-scene, targets moved among visually indistinguishable distractors. The targets and distractors either stayed visible during continuous viewpoint changes or they turned invisible. The parametric variation of tracking load revealed load-dependent activations of the intraparietal sulcus, the superior parietal lobule, and the lateral occipital cortex in response to the attentive tracking task. Viewpoint changes with invisible objects that demanded retention and updating produced load-dependent activation only in the precuneus in line with its presumed involvement in updating spatial working memory.     

Dividing attention between two different categories and locations in rapid serial visual presentations

When two targets are embedded in a rapid serial visual presentation (RSVP) stream of distractors, perception of the second target is impaired if the intertarget lag is relatively short (less than 500 msec). This phenomenon, called attentional blink, has been attributed to a temporal inability of attentional resources. Nevertheless, a recent study found that observers could monitor two RSVP streams concurrently for up to four items presented in close succession, suggesting a much larger visual capacity limit. However, such high-capacity performance could be obtained by a rapid shift of attention, rather than concurrent monitoring of multiple locations. Therefore, the present study examined these alternatives. Results from six experiments indicate that observers can concurrently monitor two noncontiguous locations, even when targets and distractors are from different categories, such as digits, English alphabet letters, Japanese characters, and pseudocharacters. These results can be explained in terms of a modified input-filtering model in which a multidimensional attentional set can be flexibly configured at different spatial locations.     

Time course of visual attention across perceptual levels and objects

Theories of shifts of visual attention based on attentional blink or dwell time do not directly address shifts of attention across different levels (global or local) involving multiple objects. Two experiments were conducted employing the attentional dwell time paradigm to investigate the shifts of visual attention between objects selected at same or different levels. Participants were instructed to identify two successive compound stimuli at a pre-specified level (global or local) presented at two different locations with variable SOA. The initial pair of locations in which the stimulus was presented was fixed in Experiment 1 but not in Experiment 2. Experiment 1 results showed very little impairment for second target identification when both the targets were at the global level. Attentional shift was better with both targets at the same level compared to different levels. Experiment 2 results showed that local followed by global target identification is difficult at short SOAs compared to other conditions. The results indicate that scope of attention affects the time course of visual attention. Global processing could be performed with very little capacity limitation simultaneously with distributed attention. The default mode of attention might be distributed and attention becomes focused for target identification. Different mechanisms may underlie shifts in focused attention between different locations and changes in attentional set required by changes in perceptual levels.     

Attentional enhancement during multiple-object tracking

What is the role of attention in multiple-object tracking? Does attention enhance target representations, suppress distractor representations, or both? It is difficult to ask this question in a purely behavioral paradigm without altering the very attentional allocation one is trying to measure. In the present study, we used event-related potentials to examine the early visual evoked responses to task-irrelevant probes without requiring an additional detection task. Subjects tracked two targets among four moving distractors and four stationary distractors. Brief probes were flashed on targets, moving distractors, stationary distractors, or empty space. We obtained a significant enhancement of the visually evoked P1 and N1 components (～100–150 msec) for probes on targets, relative to distractors. Furthermore, good trackers showed larger differences between target and distractor probes than did poor trackers. These results provide evidence of early attentional enhancement of tracked target items and also provide a novel approach to measuring attentional allocation during tracking.     

Attentional focus, processing load, and Stroop interference

Although the effects of attentional focus and perceptual load on selective attention when targets and distractors are distinct objects that occupy separate locations are well known, there has been little examination of their role when both relevant and irrelevant information pertains to the same object. In four experiments, participants were shown Stroop color words or strings of letters in a task of speeded color identification. When the participants' attentional focus was manipulated via cue validity or precue size, greater Stroop interference was observed when the attentional focus was narrow than when it was broad. However, when the participants were induced to adopt a comparable attentional focus in a dual-task paradigm, the differential Stroop interference was eliminated. Furthermore, contrary to the prediction of the perceptual load hypothesis, different levels of processing load did not lead to differential Stroop interference. These results emphasize the importance of stimulus structure in understanding distractor processing. They indicate that when relevant and irrelevant information pertains to the same object, narrowing attentional focus increases distractor processing, and perceptual load has a negligible effect on the extent of distractor processing.     

The spider does not always win the fight for attention: Disengagement from threat is modulated by goal set

Stimulus-driven preferential attention to threat can be modulated by goal-driven attention. However, it remains unclear how this goal-driven modulation affects specific attentional components implied in threat interference. We hypothesise that goal-driven modulation most strongly impacts delayed disengagement from threat. A spatial cueing task was used that disentangles delayed disengagement from attentional capture by tightly manipulating the locus of attention at the time of target onset. Different top-down goals were induced by instructing participants to identify bird/fish targets (Experiment 1) or spider/cat targets (Experiment 2) among animal non-targets. Delayed disengagement from a non-target spider was observed only when the spider was part of the target set, not when it was task-irrelevant. This corroborates evidence that threat stimuli do not necessarily override goal-driven attentional control and that extended processing of threatening distractors is not obligatory.     

自闭症儿童视觉动态信息的注意加工特点——来自多目标追踪任务的证据

为了考察中低功能自闭症儿童在动态条件下的多目标注意加工特点,研究采用多目标追踪实验范式,具体追踪任务采用多目标随机运动和碰撞反弹算法。实验设计为两因素混合设计,组间变量为年龄和性别匹配的中低功能自闭症和正常儿童组,组内变量为追踪目标数量（分别为1、2、3、4个目标）,因变量为被试在多目标追踪任务中的追踪正确率和追踪容量。结果发现：（1）中低功能自闭症儿童在目标数量为1到目标数量为4时的正确率均明显低于正常儿童,且标准差变异较大,中低功能自闭症儿童的多目标的持续追踪能力和稳定性存在一定的缺陷;（2）当目标数量为1时,正常组儿童与中低功能自闭症儿童的追踪容量差异不显著;目标为2、3、4时,两组追踪容量差异均显著。不同目标数量情况下中低功能自闭症儿童平均的注意容量为0.83~1.24个（平均容量约为1个）明显低于正常儿童的0.95~3.72个（最大容量接近4个）。中低功能自闭症儿童在多目标追踪上表现为单焦点注意加工的特点,存在一定程度的注意转移缺陷。     

The adaptive character of the attentional system: statistical sensitivity in a target localization task

A localization task required participants to indicate which of 4 locations contained a briefly displayed target. Most displays also contained a distractor that was not equally probable in these locations, affecting performance dramatically. Responses were faster when a display had no distractor and almost as fast when the distractor was in its frequent location. Conversely, responses were slower when targets appeared in frequent-distractor locations, even thou targets were equally likely in each location. Negative-priming effects were reliably smaller when targets followed distractors in the frequent-distractor location compared to the rare-distractor location, challenging the episodic-retrieval account Experiment 2 added a 5th location that rarely displayed distractors and never targets, yet responses slowed most when distractors appeared there. The results confirmed that the attentional system is sensitive to first- and higher-order statistical patterns and can make short- and long-term adjustments in preferences based on prior history of inspecting unsuccessful locations.     

The attentional window configures to object and surface boundaries

Attention can select items based on location or features. Belopolsky and colleagues posited the attentional window hypothesis, which theorized that spatial and featural selection interact such that featural selection occurs within a “window” of spatial selection. Kerzel and colleagues recently found that the attentional window can take complex shapes, but cannot configure around non-contiguous locations. The current experiments investigated whether perceptual grouping cues, which produce perceptual objects or surfaces, enable the attentional window to configure around non-contiguous locations. Using the additional singleton paradigm, we reasoned that observers (1) would be slowed by a colour singleton distractor that appears within the observers’ attentional window and (2) would be unaffected by distractors that do not appear within the attentional window. In separate blocks of trials, a target appeared upon one of two objects. Observers were cued to the relevant surface, and we asked if responses were affected by distractors on the cued task-relevant surface, and on the uncued irrelevant surface. Colour singleton distractors slowed responses when they appeared on the cued surface, even when those locations were non-contiguous locations. Distractors on the irrelevant surface did not affect responses. The results support a highly adaptable attentional window that is configurable to the surfaces and boundaries established by intermediate-level vision.     

Attentional resources in visual tracking through occlusion: the high-beams effect

A considerable amount of research has uncovered heuristics that the visual system employs to keep track of objects through periods of occlusion. Relatively little work, by comparison, has investigated the online resources that support this processing. We explored how attention is distributed when featurally identical objects become occluded during multiple object tracking. During tracking, observers had to detect small probes that appeared sporadically on targets, distracters, occluders, or empty space. Probe detection rates for these categories were taken as indexes of the distribution of attention throughout the display and revealed two novel effects. First, probe detection on an occluder’s surface was better when either a target or distractor was currently occluded in that location, compared to when no object was behind that occluder. Thus even occluded (and therefore invisible) objects recruit object-based attention. Second, and more surprising, probe detection for both targets and distractors was always better when they were occluded, compared to when they were visible. This new attentional high-beams effect indicates that the ability to track through occlusion, though seemingly effortless, in fact requires the active allocation of special attentional resources.     

Focal distraction: spatial shifts of attentional focus are not required for contingent capture

Contingent capture occurs when distractors that share the target's defining attribute capture attention and slow down target identification. This slowdown has been attributed to an involuntary attentional shift to the location of a pertinent distractor. The present study examined an additional source of delay: the time spent in processing pertinent distractors. In 7 experiments, distractors were presented at fixation, and targets were presented either at fixation or peripherally. Contingent capture invariably occurred when a salient distractor was presented within about 600 ms before the target, even when spatial shifts in attentional focus were ruled out. A 2-stage model is proposed in which stimuli must pass an input filter tuned to the target's defining attribute before gaining access to a high-level stage that is unavailable while a distractor is being processed.     

Target objects defined by a conjunction of colour and shape can be selected independently and in parallel

It is generally assumed that during search for targets defined by a feature conjunction, attention is allocated sequentially to individual objects. We tested this hypothesis by tracking the time course of attentional processing biases with the N2pc component in tasks where observers searched for two targets defined by a colour/shape conjunction. In Experiment 1, two displays presented in rapid succession (100 ms or 10 ms SOA) each contained a target and a colour-matching or shape-matching distractor on opposite sides. Target objects in both displays elicited N2pc components of similar size that overlapped in time when the SOA was 10 ms, suggesting that attention was allocated in parallel to both targets. Analogous results were found in Experiment 2, where targets and partially matching distractors were both accompanied by an object without target-matching features. Colour-matching and shape-matching distractors also elicited N2pc components, and the target N2pc was initially identical to the sum of the two distractor N2pcs, suggesting that the initial phase of attentional object selection was guided independently by feature templates for target colour and shape. Beyond 230 ms after display onset, the target N2pc became superadditive, indicating that attentional selection processes now started to be sensitive to the presence of feature conjunctions. Results show that independent attentional selection processes can be activated in parallel by two target objects in situations where these objects are defined by a feature conjunction.     

Spatial distribution of visual attention: Perceptual sensitivity and response latency

Studies of the spatial distribution of visual attention have shown that attentional facilitation monotonically decreases in a graded fashion with increasing distance from an attended location. However, reaction time (RT) measures have typically shown broader gradients than have signal detection (SD) measures of perceptual sensitivity. It is not clear whether these differences have arisen because the stages of information processing indexed by RT measures are different from those indexed by SD measures, or whether these differences are due to methodological confounds in the SD studies. In the present set of experiments, the spatial distribution of attention was studied by using a luminance detection task in an endogenous cuing paradigm that was designed to permit accurate calculations of SD and RT measures for targets at cued and uncued locations. Subjects made target-present/absent decisions at one of six possible cued or uncued upper visual hemifield locations on each trial. The results from three experiments suggest that the differences between broad and focal attentional distributions are not the result of different stages of information processing indexed by RT measures as opposed to SD measures. Rather, the differing distributions appear to reflect variations in attentional allocation strategies induced by the perceptual requirements typical of RT paradigms as opposed to SD paradigms. These findings support numerous prior studies showing that spatial attention affects perceptual sensitivity and that the strategic allocation of attention is a highly flexible process.     

Visual selection mediated by location: feature-based selection of noncontiguous locations.

Experiments using two different methods and three types of stimuli tested whether stimuli at non-adjacent locations could be selected simultaneously. In one set of experiments, subjects attended to red digits presented in multiple frames with green digits. Accuracy was no better when red digits appeared successively than when pairs of red digits occurred simultaneously, implying allocation of attention to the two locations simultaneously. Different tasks involving oriented grating stimuli produced the same result. The final experiment demonstrated split attention with an array of spatial probes. When the probe at one of two target locations was correctly reported, the probe at the other target location was more often reported correctly than were any of the probes at distractor locations, including those between the targets. Together, these experiments provide strong converging evidence that when two targets are easily discriminated from distractors by a basic property, spatial attention can be split across both locations.