Visual attention as a multilevel selection process

Natural visual scenes are cluttered and contain many different objects that cannot all be processed simultaneously. Therefore, attentional mechanisms are needed to select relevant and to filter out irrelevant information. Evidence from functional brain imaging reveals that attention operates at various processing levels within the visual system and beyond. First, the lateral geniculate nucleus appears to be the first stage in the processing of visual information that is modulated by attention, consistent with the idea that it may play an important role as an early gatekeeper in controlling neural gain. Second, areas at intermediate cortical-processing levels, such as V4 and TEO, appear to be important sites at which attention filters out unwanted information by means of receptive field mechanisms. Third, the attention mechanisms that operate in the visual system appear to be controlled by a distributed network of higher order areas in the frontal and parietal cortex, which generate top-down signals that are transmitted via feedback connections to the visual system. And fourth, the pulvinar of the thalamus may operate by integrating and coordinating attentional functions in concert with the fronto-parietal network, although much needs to be learned about its functional properties. The overall view that emerges from the studies reviewed in this article is that neural mechanisms of selective attention operate at multiple stages in the visual system and beyond and are determined by the visual processing capabilities of each stage. In this respect, attention can be considered in terms of a multilevel selection process.     

丘脑枕核参与情绪信息加工的多条通路

丘脑枕核参与多条加工情绪信息的神经通路因而在情绪信息加工中具有重要作用。第一：丘脑枕核参与到上丘-丘脑枕核-杏仁核通路。该通路可以在没有初级视觉皮层参与情况下对情绪信息进行快速加工; 第二：丘脑枕核以皮层-丘脑枕核-皮层环路和上丘-丘脑枕核-皮层通路两种形式参与到丘脑枕核-皮层通路。该通路通过控制皮层间同步化水平促进信息传递的效率; 同时通过整合皮层和皮层下情绪信号扩大其在行为输出方面的影响力。     

The effects of unilateral pulvinar damage in humans on reflexive orienting and filtering of irrelevant information

The effects of damage to the pulvinar nucleus of the thalamus in humans on reflexive orienting and selective attention were investigated. In a spatial orienting task three patients with unilateral pulvinar damage determined the location of a visual target that followed a cue that was not informative as to the targets location. Contralesional targets were responded to more slowly than ipsilesional targets. Also, at long cue target intervals patients responses to contralesional targets that appeared at previously cued locations were slower than to non-cued locations indicating that pulvinar damage does not affect inhibition of return. In the selective attention task two of the patients identified a target that appeared at one level of a global-local hierarchical stimulus while ignoring a distractor present at the other level. The distractor indicated either the same response as the target or a different response. Response times to targets in both visual fields were similar as were interference effects from the ignored distractors. These data indicate that engaging attention contralesionally is not impaired in discrimination tasks and that filtering of irrelevant information was not impaired contralesionally.     

视觉注意离散性的实验范式

注意离散性是注意间歇性地采集外界信息的特性。文章综述了视觉注意离散性的4种实验范式:(1)车轮错觉范式,刺激强度大、实验条件少、被试任务量小,较早地证实了视觉注意的离散性;(2)视觉探测范式,同时观察了被试的行为表现与电生理信号,确定了视觉注意离散性与神经振荡的关联;(3)线索靶子范式和视觉搜索范式,通过系统地变化SOA大幅提高了行为数据的时间分辨率,直观地探测到注意离散性调制的行为振荡。     

Reflexive Attention Modulates Processing of Visual Stimuli in Human Extrastriate Cortex

Attention can be oriented reflexively to a location in space by an abrupt change in the visual scene. In the present study, we investigated the consequences of reflexive attention on the neural processing of visual stimuli. The findings show that reflexively oriented attention produces modulations in early sensory analysis at the same extrastriate neural locus as the earliest effects of voluntarily focused attention. In addition, stimulus processing was found to be enhanced at later stages of analysis, which reflect stimulus relevance. As is the case with behavioral measures of reflexive attention, these physiological enhancement effects are rapidly engaged but short-lived. As time passes between the initial attention-capturing event and subsequent stimuli, the extrastriate effect reverses, and the enhancement of higher order processing subsides. These findings indicate that reflexive attention is able to affect perceptions of the visual world by modulating neural processing as early as extrastriate visual cortex.     

The distributed human neural system for face perception

Face perception, perhaps the most highly developed visual skill in humans, is mediated by a distributed neural system in humans that is comprised of multiple, bilateral regions. We propose a model for the organization of this system that emphasizes a distinction between the representation of invariant and changeable aspects of faces. The representation of invariant aspects of faces underlies the recognition of individuals, whereas the representation of changeable aspects of faces, such as eye gaze, expression, and lip movement, underlies the perception of information that facilitates social communication. The model is also hierarchical insofar as it is divided into a core system and an extended system. The core system is comprised of occipitotemporal regions in extrastriate visual cortex that mediate the visual analysis of faces. In the core system, the representation of invariant aspects is mediated more by the face-responsive region in the fusiform gyrus, whereas the representation of changeable aspects is mediated more by the face-responsive region in the superior temporal sulcus. The extended system is comprised of regions from neural systems for other cognitive functions that can be recruited to act in concert with the regions in the core system to extract meaning from faces.     

Where perception meets memory: A review of repetition priming in visual search tasks

What we have recently seen and attended to strongly influences how we subsequently allocate visual attention. A clear example is how repeated presentation of an object’s features or location in visual search tasks facilitates subsequent detection or identification of that item, a phenomenon known as priming. Here, we review a large body of results from priming studies that suggest that a short-term implicit memory system guides our attention to recently viewed items. The nature of this memory system and the processing level at which visual priming occurs are still debated. Priming might be due to activity modulations of low-level areas coding simple stimulus characteristics or to higher level episodic memory representations of whole objects or visual scenes. Indeed, recent evidence indicates that only minor changes to the stimuli used in priming studies may alter the processing level at which priming occurs. We also review recent behavioral, neuropsychological, and neurophysiological evidence that indicates that the priming patterns are reflected in activity modulations at multiple sites along the visual pathways. We furthermore suggest that studies of priming in visual search may potentially shed important light on the nature of cortical visual representations. Our conclusion is that priming occurs at many different levels of the perceptual hierarchy, reflecting activity modulations ranging from lower to higher levels, depending on the stimulus, task, and context—in fact, the neural loci that are involved in the analysis of the stimuli for which priming effects are seen.     

Selection can be performed effectively without temporal binding,but could be even more effective with it

Experiments using spatial cues and spatial probes provide strong evidence for an attention mechanism that chooses a location and selects all information at that location. This selection process can work very quickly; so quickly that selection probably begins before segmentation and grouping. It can be implemented in a neural network simply and efficiently without temporal binding. In conjunction with this spatial attention, however, temporal binding can potentially enhance visual selection in complex scenes. First, it would allow a target object to be selected without also selecting a superimposed distractor. Second, it could maintain representations of objects after attention has moved to another object. Third, it could allow multiple parts of an object or scene to be selected, segmented, and analysed simultaneously. Thus, temporal synchrony should be more likely to appear during tasks with overlapping targets and distractors, and tasks that require that multiple objects or multipart objects be analysed and remembered simultaneously.     

发展性阅读障碍的视觉注意广度技能

发展性阅读障碍在许多任务中都出现同时性加工多个视觉刺激的困难, 即视觉注意广度缺陷.本文分别综述了国内外探查阅读障碍视觉注意广度的研究.目前, 相关研究结果仍存争议, 这可能与背景语言的正字法深度以及被试年龄发展差异有关.未来研究还需利用干预,跨语言比较等方法进一步探讨阅读障碍与视觉注意广度之间的关系, 并结合脑电,脑成像技术探究汉语阅读障碍视觉注意广度的内在神经机制.     

Tracking the influence of reflexive attention on sensory and cognitive processing

Previously, we demonstrated that reflexive attention facilitates early visual processing during form discrimination (Hopfinger & Mangun, 1998). In the present study, we tested whether reflexive facilitation of early visual processing will be generated when task load is low (simple luminance detection). Target stimuli that were preceded at short cue-to-target intervals by irrelevant visual events (cues) elicited an enhanced sensory (P1) event-related potential (ERP) component as well as an enhanced longer latency, cognitive ERP component (P300). At long cue-to-target intervals, facilitation in these ERP components was no longer observed, and, although inhibition of return (IOR) was observed in reaction times, the ERPs did not show an inhibition of sensory processing. These results provide converging evidence that reflexive attention transiently facilitates neural processing of visual inputs at multiple stages of analysis (i.e., sensory processing and higher order cognitive processing) but question the view that IOR is manifest at the earliest visual cortical stages of analysis.     

Selective working memory disables inhibition of visual features

Recent research suggests that information held in working memory can facilitate subsequent attentional processing. Here, we explore the negative corollary of this conception: Under which circumstances does information in working memory disrupt subsequent processing? Seventy participants performed visual discriminations in a dual-task paradigm. They were asked to judge colors or shapes in an online attention task under three different working-memory conditions: Same, Switch, or Unknown. In the Same condition, participants selectively maintained one visual feature in working memory, from the same dimension as in the online attention task. In the Switch condition, participants selectively maintained one visual feature in working memory, but had to focus on another visual dimension in the online attention task. In the Unknown condition, participants could not predict which visual feature would be relevant for the working-memory task. We found that irrelevant features in the online attention task were particularly difficult to ignore in the Switch condition, that is, when the irrelevant features belong to a visual dimension that is simultaneously prioritized in selective working memory. The findings are consistent with accounts in terms of neural overlap between working-memory and attention circuits, and suggest that mechanisms of selection, rather than resource limitations, critically determine the extent of visual interference.     

The suppression of reflexive visual and auditory orienting when attention is otherwise engaged

Two experiments were conducted to examine whether abrupt onsets are capable of reflexively capturing attention when they occur outside the current focus of spatial attention, as would be expected if exogenous orienting operates in a truly automatic fashion. The authors established a highly focused attentional state by means of the central presentation of a stream of visual or auditory characters, which participants sometimes had to monitor. No intramodal reflexive cuing effects were observed in either audition or vision when participants performed either an exogenous visual or auditory orthogonal cuing task together with the central focused attention task. These results suggest that reflexive unimodal orienting is not truly automatic. The fact that cuing effects were eliminated under both unimodal and cross-modal conditions is consistent with the view that auditory and visual reflexive spatial orienting are controlled by a common underlying neural substrate.     

A global workspace model for phenomenal and access consciousness

Both the global workspace theory and Block’s distinction between phenomenal and access consciousness, are central in the current debates about consciousness and the neural correlates of consciousness. In this article, a unifying global workspace model for phenomenal and access consciousness is proposed. In the model, recurrent neural interactions take place in distinct yet interacting access and phenomenal brain loops. The effectiveness of feedback signaling onto sensory cortical maps is emphasized for the neural correlates of phenomenal consciousness. Two forms of top-down attention, attention for perception and attention for access, play differential roles for phenomenal and access consciousness. The model is implemented in a neural network form, with the simulation of single and multiple visual object processing, and of the attentional blink.     

视听跨通道信息的整合与冲突控制

多通道信息交互是指来自某个感觉通道的信息与另一感觉通道的信息相互作用、相互影响的一系列加工过程。主要包括两个方面：一是不同感觉通道的输入如何整合;二是跨通道信息的冲突控制。本文综述了视听跨通道信息整合与冲突控制的行为心理机制和神经机制,探讨了注意对视听信息整合与冲突控制的影响。未来需探究视听跨通道信息加工的脑网络机制,考察特殊群体的跨通道整合和冲突控制以帮助揭示其认知和社会功能障碍的机制。     

Unconscious attentional orienting to exogenous cues: A review of the literature

The present paper reviews research that focuses on the dissociation between bottom-up attention and consciousness. In particular, we focus on studies investigating spatial exogenous orienting in the absence of awareness. We discuss studies that use peripheral masked onset cues and studies that use gaze cueing. The results from these studies show that the classic biphasic pattern of facilitation and inhibition, which is characteristic of conscious exogenous cueing can also be obtained with subliminal spatial cues. It is hypothesized that unconscious attentional orienting is mediated by the subcortical retinotectal pathway. Moreover, a possible neural network including superior colliculus, pulvinar and amygdala is suggested as the underlying mechanism.     

Readout from iconic memory and selective spatial attention involve similar neural processes

Iconic memory and spatial attention are often considered separately, but they may have functional similarities. Here we provide functional magnetic resonance imaging evidence for some common underlying neural effects. Subjects judged three visual stimuli in one hemifield of a bilateral array comprising six stimuli. The relevant hemifield for partial report was indicated by an auditory cue, administered either before the visual array (precue, spatial attention) or shortly after the array (postcue, iconic memory). Pre- and postcues led to similar activity modulations in lateral occipital cortex contralateral to the cued side. This finding indicates that readout from iconic memory can have some neural effects similar to those of spatial attention. We also found common bilateral activation of a fronto-parietal network for postcue and precue trials. These neuroimaging data suggest that some common neural mechanisms underlie selective spatial attention and readout from iconic memory. Some differences were also found; compared with precues, postcues led to higher activity in the right middle frontal gyrus.     

Contributions of the human pulvinar to linking vision and action

In 3 patients with unilateral pulvinar lesions, we tested the pulvinar’s role in selective attention processing. Each patient completed four variants of a flanker interference task in which they reported the color of a square of a specified size while ignoring an irrelevant flanker that appeared either contralesionally or ipsilesionally to the target. The main finding was that when target location was not known and target and flanker were associated with competing responses, reaction times to contralesional targets were longer than those to ipsilesional targets. Our findings suggest that pulvinar damage produces a contralesional deficit in response competition.     

Top-down selective visual attention: A neurodynamical approach

We propose a system of interconnected modules consisting of populations of neurons for modelling the underlying mechanisms involved in selective visual attention. We demonstrate that it is plausible to build a neural system for visual search, which works across the visual field in parallel, but, due to the intrinsic dynamics of the system, resembles apparent modes of visual attention, namely the serial focal and the parallel spread over the space mode. Thus, neither explicit serial focal search nor saliency maps need to be assumed. A focal attentional spotlight is not included in the system but rather focal attention emerges due to the convergence of the dynamic behaviour of the neural networks. The dynamics of the system can be interpreted as a mechanism for routing information from the sensory input.     

Spectral complexity and infant attention

In two experiments, infants selectively attended to auditory stimuli that presented an increasingly complex spectral structure. Using 2- and 4-month-olds as subjects, the first study demonstrated this selectivity in comparison to the rate of acoustic change. The second study demonstrated the increased attention of 4-month-olds in response to an increasingly complex structure. Results are discussed with respect to the neural activity produced by these stimuli along the auditory pathway, and an analogy to the literature on visual attention is drawn.     

The Lower Visual Search Efficiency For Conjunctions Is Due To Noise and Not Serial Attentional Processing

Models of human visual processing start with an initial stage with parallel independent processing of different physical attributes or features (e.g. color, orientation, motion). A second stage in these models is a temporally serial mechanism (visual attention) that combines or binds information across feature dimensions. Evidence for this serial mechanism is based on experimental results for visual search. I conducted a study of visual search accuracy that carefully controlled for low-level effects: physical similarity of target and distractor, element eccentricity, and eye movements. The larger set-size effects in visual search accuracy for briefly flashed conjunction displays, compared with feature displays, are quantitatively predicted by a simple model in which each feature dimension is processed independently with inherent neural noise and information is combined linearly across feature dimensions. The data are not predicted by a temporally serial mechanism or by a hybrid model with temporally serial and noisy processing. The results do not support the idea that a temporally serial mechanism, visual attention, binds information across feature dimensions and show that the conjunction-feature dichotomy is due to the noisy independent processing of features in the human visual system.