Signals invisible to the collicular and magnocellular pathways can capture visual attention

The retinal projection to the superior colliculus is thought to be important both for stimulus-driven eye movements and for the involuntary capture of attention. It has further been argued that eye-movement planning and attentional orienting share common neural mechanisms. Electrophysiological studies have shown that the superior colliculus receives no direct projections from short-wave-sensitive cones (S cones), and, consistent with this, we found that irrelevant peripheral stimuli visible only to S cones did not produce the saccadic distractor effect produced by luminance stimuli. However, when involuntary orienting was tested in a Posner cueing task, the same S-cone stimuli had normal attentional effects, in that they accelerated or delayed responses to subsequent targets. We conclude that involuntary attentional shifts do not require signals in the direct collicular pathway, or indeed the magnocellular pathway, as our S-cone stimuli were invisible to this channel also.     

Is Visual Selective Attention in Deaf Individuals Enhanced or Deficient? The Case of the Useful Field of View

Background

Early deafness leads to enhanced attention in the visual periphery. Yet, whether this enhancement confers advantages in everyday life remains unknown, as deaf individuals have been shown to be more distracted by irrelevant information in the periphery than their hearing peers. Here, we show that, in a complex attentional task, a performance advantage results for deaf individuals.

Methodology/Principal Findings

We employed the Useful Field of View (UFOV) which requires central target identification concurrent with peripheral target localization in the presence of distractors – a divided, selective attention task. First, the comparison of deaf and hearing adults with or without sign language skills establishes that deafness and not sign language use drives UFOV enhancement. Second, UFOV performance was enhanced in deaf children, but only after 11 years of age.

Conclusions/Significance

This work demonstrates that, following early auditory deprivation, visual attention resources toward the periphery slowly get augmented to eventually result in a clear behavioral advantage by pre-adolescence on a selective visual attention task.     

Changes in early cortical visual processing predict enhanced reactivity in deaf individuals

Individuals with profound deafness rely critically on vision to interact with their environment. Improvement of visual performance as a consequence of auditory deprivation is assumed to result from cross-modal changes occurring in late stages of visual processing. Here we measured reaction times and event-related potentials (ERPs) in profoundly deaf adults and hearing controls during a speeded visual detection task, to assess to what extent the enhanced reactivity of deaf individuals could reflect plastic changes in the early cortical processing of the stimulus. We found that deaf subjects were faster than hearing controls at detecting the visual targets, regardless of their location in the visual field (peripheral or peri-foveal). This behavioural facilitation was associated with ERP changes starting from the first detectable response in the striate cortex (C1 component) at about 80 ms after stimulus onset, and in the P1 complex (100-150 ms). In addition, we found that P1 peak amplitudes predicted the response times in deaf subjects, whereas in hearing individuals visual reactivity and ERP amplitudes correlated only at later stages of processing. These findings show that long-term auditory deprivation can profoundly alter visual processing from the earliest cortical stages. Furthermore, our results provide the first evidence of a co-variation between modified brain activity (cortical plasticity) and behavioural enhancement in this sensory-deprived population.     

Visuomotor origins of covert spatial attention

Covert spatial attention produces biases in perceptual performance and neural processing of behaviorally relevant stimuli in the absence of overt orienting movements. The neural mechanism that gives rise to these effects is poorly understood. This paper surveys past evidence of a relationship between oculomotor control and visual spatial attention and more recent evidence of a causal link between the control of saccadic eye movements by frontal cortex and covert visual selection. Both suggest that the mechanism of covert spatial attention emerges as a consequence of the reciprocal interactions between neural circuits primarily involved in specifying the visual properties of potential targets and those involved in specifying the movements needed to fixate them.     

Dissociable spatial and temporal effects of inhibition of return

Inhibition of return (IOR) refers to the relative suppression of processing at locations that have recently been attended. It is frequently explored using a spatial cueing paradigm and is characterized by slower responses to cued than to uncued locations. The current study investigates the impact of IOR on overt visual orienting involving saccadic eye movements. Using a spatial cueing paradigm, our experiments have demonstrated that at a cue-target onset asynchrony (CTOA) of 400 ms saccades to the vicinity of cued locations are not only delayed (temporal cost) but also biased away (spatial effect). Both of these effects are basically no longer present at a CTOA of 1200 ms. At a shorter 200 ms CTOA, the spatial effect becomes stronger while the temporal cost is replaced by a temporal benefit. These findings suggest that IOR has a spatial effect that is dissociable from its temporal effect. Simulations using a neural field model of the superior colliculus (SC) revealed that a theory relying on short-term depression (STD) of the input pathway can explain most, but not all, temporal and spatial effects of IOR.     

Distinct cortical and collicular mechanisms of inhibition of return revealed with S cone stimuli

Visual orienting of attention and gaze are widely considered to be mediated by shared neural pathways, with automatic phenomena such as inhibition of return (IOR)--the bias against returning to recently visited locations--being generated via the direct pathway from retina to superior colliculus (SC). Here, we show that IOR occurs without direct access to the SC, by using a technique that employs stimuli visible only to short-wave-sensitive (S) cones. We found that these stimuli, to which the SC is blind , were quite capable of eliciting IOR, measured by traditional manual responses. Critically, however, we found that S cone stimuli did not cause IOR when saccadic eye movement responses were required. This demonstrates that saccadic IOR is not the same as traditional IOR, providing support for two separate cortical and collicular mechanisms of IOR. These findings represent a clear dissociation between visual orienting of attention and gaze.     

Modulation of backward pattern masking by focal visual attention

The effect of focal visual attention on backward pattern masking was investigated using an orientation discrimination task. The results show that attention reduces primarily the effect of interruption masking, the later component of pattern masking, which occurs when the delay between the target and mask onset is about 50-150 ms. The strongest spatial cueing effect, i.e. the strongest reduction of the orientation discrimination threshold due to focal attention, was observed at intermediate (approximately 100 ms) target-to-mask stimulus onset asynchrony (SOA). There was a weak effect of cueing at shorter SOAs, and no or a very weak attentional effect was present at longer target-to-mask SOAs, where the pattern masking effect is absent. The dynamics of attentional modulation of backward pattern masking correlates closely with the dynamics of the attentional modulation of neuronal responses in the early visual cortex.     

A causal link between visual spatial attention and reading acquisition

Reading is a unique, cognitive human skill crucial to life in modern societies, but, for about 10% of the children, learning to read is extremely difficult. They are affected by a neurodevelopmental disorder called dyslexia. Although impaired auditory and speech sound processing is widely assumed to characterize dyslexic individuals, emerging evidence suggests that dyslexia could arise from a more basic cross-modal letter-to-speech sound integration deficit. Letters have to be precisely selected from irrelevant and cluttering letters by rapid orienting of visual attention before the correct letter-to-speech sound integration applies. Here we ask whether prereading visual parietal-attention functioning may explain future reading emergence and development. The present 3 year longitudinal study shows that prereading attentional orienting--assessed by serial search performance and spatial cueing facilitation--captures future reading acquisition skills in grades 1 and 2 after controlling for age, nonverbal IQ, speech-sound processing, and nonalphabetic cross-modal mapping. Our findings provide the first evidence that visual spatial attention in preschoolers specifically predicts future reading acquisition, suggesting new approaches for early identification and efficient prevention of dyslexia.     

Modality-specific control of strategic spatial attention in parietal cortex

The neural basis of selective spatial attention presents a significant challenge to cognitive neuroscience. Recent neuroimaging studies have suggested that regions of the parietal and temporal cortex constitute a "supramodal" network that mediates goal-directed attention in multiple sensory modalities. Here we used transcranial magnetic stimulation (TMS) to determine which cortical subregions control strategic attention in vision and touch. Healthy observers undertook an orienting task in which a central arrow cue predicted the location of a subsequent visual or somatosensory target. To determine the attentional role of cortical subregions at different stages of processing, TMS was delivered to the right hemisphere during cue or target events. Results indicated a critical role of the inferior parietal cortex in strategic orienting to visual events, but not to somatosensory events. These findings are inconsistent with the existence of a supramodal attentional network and instead provide direct evidence for modality-specific attentional processing in parietal cortex.     

What We Observe Is Biased by What Other People Tell Us: Beliefs about the Reliability of Gaze Behavior Modulate Attentional Orienting to Gaze Cues

For effective social interactions with other people, information about the physical environment must be integrated with information about the interaction partner. In order to achieve this, processing of social information is guided by two components: a bottom-up mechanism reflexively triggered by stimulus-related information in the social scene and a top-down mechanism activated by task-related context information. In the present study, we investigated whether these components interact during attentional orienting to gaze direction. In particular, we examined whether the spatial specificity of gaze cueing is modulated by expectations about the reliability of gaze behavior. Expectations were either induced by instruction or could be derived from experience with displayed gaze behavior. Spatially specific cueing effects were observed with highly predictive gaze cues, but also when participants merely believed that actually non-predictive cues were highly predictive. Conversely, cueing effects for the whole gazed-at hemifield were observed with non-predictive gaze cues, and spatially specific cueing effects were attenuated when actually predictive gaze cues were believed to be non-predictive. This pattern indicates that (i) information about cue predictivity gained from sampling gaze behavior across social episodes can be incorporated in the attentional orienting to social cues, and that (ii) beliefs about gaze behavior modulate attentional orienting to gaze direction even when they contradict information available from social episodes.     

Attentive mechanisms in visual search

Selective attention can be employed to a restricted region in space or to specific objects. Many properties of this attentional window or spotlight are not well understood. In the present study, we examined the question whether the putative shape of the attentional spotlight can be determined by endogenous cueing within a visual search paradigm. Participants searched for a target among distractors, which were arranged within a vertical or horizontal rectangle. The shape of this rectangle was cued endogenously in a valid or invalid way. Response times (RTs) to correct identification of target orientation were recorded. In Experiment 1, the difference between valid and invalid RTs demonstrated that cueing resulted in elongated attentional areas. This was true only for a group of experienced psychophysical participants, whereas a group of inexperienced participants were not able to use cueing in this way. In Experiment 2, the line motion illusion was used to examine the spatial properties of the attended area. The results confirmed for both experienced and inexperienced participants that attention was confined to the cued elongated area only. We present converging evidence for an attentional spotlight whose shape can be adjusted flexibly by appropriate endogenous cueing.     

线索有效性对社会性注意和外源性注意的影响

目的 眼睛注视、头朝向和生物运动方向等社会性线索,对人类的生存和社会交互极为重要.由于社会性线索和外周线索都具有反射性注意定向这一特点,社会性注意往往也被认为属于外源性注意.但是,外源性注意并不能完全解释所有的社会性注意现象.因此,两者是否具有相同的加工机制,尚存在争论.方法 本研究使用空间线索范式,系统考察了线索有效...     

An fMRI Study of the Neural Systems Involved in Visually Cued Auditory Top-Down Spatial and Temporal Attention

Top-down attention to spatial and temporal cues has been thoroughly studied in the visual domain. However, because the neural systems that are important for auditory top-down temporal attention (i.e., attention based on time interval cues) remain undefined, the differences in brain activity between directed attention to auditory spatial location (compared with time intervals) are unclear. Using fMRI (magnetic resonance imaging), we measured the activations caused by cue-target paradigms by inducing the visual cueing of attention to an auditory target within a spatial or temporal domain. Imaging results showed that the dorsal frontoparietal network (dFPN), which consists of the bilateral intraparietal sulcus and the frontal eye field, responded to spatial orienting of attention, but activity was absent in the bilateral frontal eye field (FEF) during temporal orienting of attention. Furthermore, the fMRI results indicated that activity in the right ventrolateral prefrontal cortex (VLPFC) was significantly stronger during spatial orienting of attention than during temporal orienting of attention, while the DLPFC showed no significant differences between the two processes. We conclude that the bilateral dFPN and the right VLPFC contribute to auditory spatial orienting of attention. Furthermore, specific activations related to temporal cognition were confirmed within the superior occipital gyrus, tegmentum, motor area, thalamus and putamen.     

Is Attention Based on Spatial Contextual Memory Preferentially Guided by Low Spatial Frequency Signals?

A popular model of visual perception states that coarse information (carried by low spatial frequencies) along the dorsal stream is rapidly transmitted to prefrontal and medial temporal areas, activating contextual information from memory, which can in turn constrain detailed input carried by high spatial frequencies arriving at a slower rate along the ventral visual stream, thus facilitating the processing of ambiguous visual stimuli. We were interested in testing whether this model contributes to memory-guided orienting of attention. In particular, we asked whether global, low-spatial frequency (LSF) inputs play a dominant role in triggering contextual memories in order to facilitate the processing of the upcoming target stimulus. We explored this question over four experiments. The first experiment replicated the LSF advantage reported in perceptual discrimination tasks by showing that participants were faster and more accurate at matching a low spatial frequency version of a scene, compared to a high spatial frequency version, to its original counterpart in a forced-choice task. The subsequent three experiments tested the relative contributions of low versus high spatial frequencies during memory-guided covert spatial attention orienting tasks. Replicating the effects of memory-guided attention, pre-exposure to scenes associated with specific spatial memories for target locations (memory cues) led to higher perceptual discrimination and faster response times to identify targets embedded in the scenes. However, either high or low spatial frequency cues were equally effective; LSF signals did not selectively or preferentially contribute to the memory-driven attention benefits to performance. Our results challenge a generalized model that LSFs activate contextual memories, which in turn bias attention and facilitate perception.     

Latency of visually evoked saccadic eye movements

The paper deals with the initiation of visually guided saccades, in order to break down the saccadic reaction time into functionally different periods of time. It takes into account that spatial processing of information is so basic that modelling of saccadic control properties should include spatio-temporal arrangements. The output signal of the saccadic system was measured in response to visual stimuli in which the time between the appearance of a visual stimulus in the peripheral field and the disappearance of the central fixation point was varied. The variation of the mean saccadic latency time, measured with respect to the onset of the peripheral stimulus, as a function of stimulus asynchrony was highly significant. This variation may be represented by a so-called gap-overlap curve, which is characterized here by means of five parameters. A facilitation model is introduced to fit the results of the gap-overlap experiments. The facilitation model for the initiation of visually evoked saccades incorporates a mechanism which governs the efficiency of processing of signals that arise from a stimulus presented at a particular position in space. It explains how visual information may be affected by other sensory information before it is used to command further saccades. It allows determination of saccadic system parameters, such as the peripheral and the foveal afferent processing time, the central processing time for a saccade and the degree of facilitation. These quantities were found to be characteristic for the given test subjects, and where these data could be compared with neurophysiological data, the agreement was within the experimental error.     

Effects of Multimodal Load on Spatial Monitoring as Revealed by ERPs

While the role of selective attention in filtering out irrelevant information has been extensively studied, its characteristics and neural underpinnings when multiple environmental stimuli have to be processed in parallel are much less known. Building upon a dual-task paradigm that induced spatial awareness deficits for contralesional hemispace in right hemisphere-damaged patients, we investigated the electrophysiological correlates of multimodal load during spatial monitoring in healthy participants. The position of appearance of briefly presented, lateralized targets had to be reported either in isolation (single task) or together with a concurrent task, visual or auditory, which recruited additional attentional resources (dual-task). This top-down manipulation of attentional load, without any change of the sensory stimulation, modulated the amplitude of the first positive ERP response (P1) and shifted its neural generators, with a suppression of the signal in the early visual areas during both visual and auditory dual tasks. Furthermore, later N2 contralateral components elicited by left targets were particularly influenced by the concurrent visual task and were related to increased activation of the supramarginal gyrus. These results suggest that the right hemisphere is particularly affected by load manipulations, and confirm its crucial role in subtending automatic orienting of spatial attention and in monitoring both hemispaces.     

Dynamic spatial coding within the dorsal frontoparietal network during a visual search task

To what extent are the left and right visual hemifields spatially coded in the dorsal frontoparietal attention network? In many experiments with neglect patients, the left hemisphere shows a contralateral hemifield preference, whereas the right hemisphere represents both hemifields. This pattern of spatial coding is often used to explain the right-hemispheric dominance of lesions causing hemispatial neglect. However, pathophysiological mechanisms of hemispatial neglect are controversial because recent experiments on healthy subjects produced conflicting results regarding the spatial coding of visual hemifields. We used an fMRI paradigm that allowed us to distinguish two attentional subprocesses during a visual search task. Either within the left or right hemifield subjects first attended to stationary locations (spatial orienting) and then shifted their attentional focus to search for a target line. Dynamic changes in spatial coding of the left and right hemifields were observed within subregions of the dorsal front-parietal network: During stationary spatial orienting, we found the well-known spatial pattern described above, with a bilateral hemifield representation in the right hemisphere and a contralateral preference in the left hemisphere. However, during search, the right hemisphere had a contralateral preference and the left hemisphere equally represented both hemifields. This finding leads to novel perspectives regarding models of visuospatial attention and hemispatial neglect.     

Target cueing provides support for target- and resource-based models of the attentional blink

The attentional blink (AB) describes a time-based deficit in processing the second of two masked targets. The AB is attenuated if successive targets appear between the first and final target, or if a cueing target is positioned before the final target. Using various speeds of stimulus presentation, the current study employed successive targets and cueing targets to confirm and extend an understanding of target-target cueing in the AB. In Experiment 1, three targets were presented sequentially at rates of 30 msec/item or 90 msec/item. Successive targets presented at 90 msec improved performance compared with non-successive targets. However, accuracy was equivalently high for successive and non-successive targets presented at 30 msec/item, suggesting that--regardless of whether they occurred consecutively--those items fell within the temporally defined attentional window initiated by the first target. Using four different presentation speeds, Experiment 2 confirmed the time-based definition of the AB and the success of target-cueing at 30 msec/item. This experiment additionally revealed that cueing was most effective when resources were not devoted to the cue, thereby implicating capacity limitations in the AB. Across both experiments, a novel order-error measure suggested that errors tend to decrease with an increasing duration between the targets, but also revealed that certain stimulus conditions result in stable order accuracy. Overall, the results are best encapsulated by target-based and resource-sharing theories of the AB, which collectively value the contributions of capacity limitations and optimizing transient attention in time.     

Attending to the possibilities of action

Actions taking place in the environment are critical for our survival. We review evidence on attention to action, drawing on sets of converging evidence from neuropsychological patients through to studies of the time course and neural locus of action-based cueing of attention in normal observers. We show that the presence of action relations between stimuli helps reduce visual extinction in patients with limited attention to the contralesional side of space, while the first saccades made by normal observers and early perceptual and attentional responses measured using electroencephalography/event-related potentials are modulated by preparation of action and by seeing objects being grasped correctly or incorrectly for action. With both normal observers and patients, there is evidence for two components to these effects based on both visual perceptual and motor-based responses. While the perceptual responses reflect factors such as the visual familiarity of the action-related information, the motor response component is determined by factors such as the alignment of the objects with the observer''s effectors and not by the visual familiarity of the stimuli. In addition to this, we suggest that action relations between stimuli can be coded pre-attentively, in the absence of attention to the stimulus, and action relations cue perceptual and motor responses rapidly and automatically. At present, formal theories of visual attention are not set up to account for these action-related effects; we suggest ways that theories could be expected to enable action effects to be incorporated.     

Top-Down but Not Bottom-Up Visual Scanning is Affected in Hereditary Pure Cerebellar Ataxia

The aim of this study was to clarify the nature of visual processing deficits caused by cerebellar disorders. We studied the performance of two types of visual search (top-down visual scanning and bottom-up visual scanning) in 18 patients with pure cerebellar types of spinocerebellar degeneration (SCA6: 11; SCA31: 7). The gaze fixation position was recorded with an eye-tracking device while the subjects performed two visual search tasks in which they looked for a target Landolt figure among distractors. In the serial search task, the target was similar to the distractors and the subject had to search for the target by processing each item with top-down visual scanning. In the pop-out search task, the target and distractor were clearly discernible and the visual salience of the target allowed the subjects to detect it by bottom-up visual scanning. The saliency maps clearly showed that the serial search task required top-down visual attention and the pop-out search task required bottom-up visual attention. In the serial search task, the search time to detect the target was significantly longer in SCA patients than in normal subjects, whereas the search time in the pop-out search task was comparable between the two groups. These findings suggested that SCA patients cannot efficiently scan a target using a top-down attentional process, whereas scanning with a bottom-up attentional process is not affected. In the serial search task, the amplitude of saccades was significantly smaller in SCA patients than in normal subjects. The variability of saccade amplitude (saccadic dysmetria), number of re-fixations, and unstable fixation (nystagmus) were larger in SCA patients than in normal subjects, accounting for a substantial proportion of scattered fixations around the items. Saccadic dysmetria, re-fixation, and nystagmus may play important roles in the impaired top-down visual scanning in SCA, hampering precise visual processing of individual items.