Shifts Of Visual Attention Research Articles

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.

A cognitive model of spatial path-planning

Planning a path to a destination, given a number of options and obstacles, is a common task. We suggest a two-component cognitive model that combines retrieval of knowledge about the environment with search guided by visual perception. In the first component, subsymbolic information, acquired during navigation, aids in the retrieval of declarative information representing possible paths to take. In the second component, visual information directs the search, which in turn creates knowledge for the first component. The model is implemented using the ACT-R cognitive architecture and makes realistic assumptions about memory access and shifts in visual attention. We present simulation results for memory-based high-level navigation in grid and tree structures, and visual navigation in mazes, varying relevant cognitive (retrieval noise and visual finsts) and environmental (maze and path size) parameters. The visual component is evaluated with data from a multi-robot control experiment, where subjects planned paths for robots to explore a building. We describe a method to compare trajectories without referring to aligned points in the itinerary. The evaluation shows that the model provides a good fit, but also that planning strategies may vary with task loads.

Prepare for conflict: EEG correlates of the anticipation of target competition during overt and covert shifts of visual attention

When preparing to make a saccadic eye movement in a cued direction, perception of stimuli at the target location is enhanced, just as it is when attention is covertly deployed there. Accordingly, the timing and anatomical sources of preparatory brain activity accompanying shifts of covert attention and saccade preparation tend to exhibit a large degree of overlap. However, there is evidence that preparatory processes are modulated by the foreknowledge of visual distractor competition during covert attention, and it is unknown whether eye movement preparation undergoes equivalent modulation. Here we examine preparatory processes in the electroencephalogram of human participants during four blocked versions of a spatial cueing task, requiring either covert detection or saccade execution, and either containing a distractor or not. As in previous work, a typical pattern of spatially selective occipital, parietal and frontal activity was seen in all task versions. However, whereas distractor presence called on an enhancement of spatially selective visual cortical modulation during covert attention, it instead called on increased activity over frontomedial oculomotor areas in the case of overt saccade preparation. We conclude that, although advance orienting signals may be similar in character during overt and covert conditions, the pattern by which these signals are modulated to ameliorate the behavioral costs of distractor competition is highly distinct, pointing to a degree of separability between the overt and covert systems.

Right hand presence modulates shifts of exogenous visuospatial attention in near perihand space

To investigate attentional shifting in perihand space, we measured performance on a covert visual orienting task under different hand positions. Participants discriminated visual shapes presented on a screen and responded using footpedals placed under their right foot. With the right hand positioned by the right side of the screen, mean cueing effects were significantly greater for targets presented on the right compared to the left side, at the shortest stimulus onset asynchrony. The right hand still affected attention when the left foot was used to respond and when the right hand was crossed over the midline, indicating that this effect is not restricted to the right hemifield and cannot be accounted for by greater stimulus–response compatibility with the right (responding) foot. These experiments provide preliminary evidence that the presence of the right hand can modulate shifts of visual attention but emphasise the importance of stimulus–response compatibility effects in such investigations.

Low-level fixation search in natural scenes by optimal extraction of texture-contrast information

We construct the beginnings of a low-level theory of visual fixations in natural scenes by the formulation and verification a Barlow-type hypothesis for fixation selection—where the fixation patterns are designed to maximally contrast and textural information. We first briefly overview optimum contrast-based fixation strategies in natural scenes [1] and thereafter develop an optimum texture-based fixation selection algorithm based on our computational theory of non-stationarity measurement in natural images. In particular it is shown how a simple relative coding error measure between sub-patches of a window (that defines the image scale of analysis) can effectively measure the non-stationary structure of natural scenes which subsequently can be employed for the optimal extraction of textural information. Finally we propose a simple coupling of the optimal texture-based and contrast-based fixation algorithms which exhibits robust performance for fixation selection in natural images. The performance of the fixation algorithms are evaluated for natural images by comparison to actual human fixations performed on the images. The fixation patterns thus obtained outperform randomized, Gaffe-based [2], and Itti [3] fixation strategies in terms of matching human fixation patterns in terms of mutual information. These results also demonstrate the important role that contrast and textural information play in low-level visual processes in the HVS. [1] Raj, R. G., Geisler, W. S., Frazor, R. A., & Bovik, A. C. (Oct 2005). "Contrast statistics for foveated visual systems: Fixation selection by minimizing contrast entropy," J. Opt Soc Amer A, vol. 22, pp. 2039-2049. [2] Rajashekar, U., van der Linde, I., Bovik, A. C., & Cormack, L. K. (2008). "GAFFE: A gaze-attentive fixation finding engine," IEEE Trans Image Processing, to appear. [3] Itti, L., & Koch, C. (May 2000.). A saliency-based search mechanism for overt and covert shifts of visual attention, Vision Res, vol. 40, no. 10-12, pp. 1489-1506.

Time course of visual attention with emotional faces

When a briefly presented and then masked visual object is identified, it impairs the identification of the second target for several hundred milliseconds. This phenomenon is known as attentional blink or attentional dwell time. The present study is an attempt to investigate the role of salient emotional information in shifts of covert visual attention over time. Two experiments were conducted using the dwell time paradigm, in which two successive targets are presented at different locations with a variable stimulus onset asynchrony (SOA). In the first experiment, real emotional faces (happy/sad) were presented as the first target, and letters (L/T) were presented as the second target. The order of stimulus presentation was reversed in the second experiment. In the first experiment, identification of the letters preceded by happy faces showed better performance than did those preceded by sad faces at SOAs less than 200 msec. Similarly, happy faces were identified better than sad faces were at short SOAs in Experiment 2. The results show that the time course of visual attention is dependent on emotional content of the stimuli. The findings indicate that happy faces are associated with distributed attention or broad scope of attention and require fewer attentional resources than do sad faces.

Eyes Gaze Cueing Effect: Endogenous or Exogenous Processing Mechanism?

Observing another person's averted eye gaze led to automatic shift of attention in the corresponding direction,which facilitated subsequent early visual processing. This phenomenon was termed 'eyes gaze cueing effect',in short,'gaze cueing effect' (GCE). Many researchers tried to interpret the processing mechanism underlying GCE. However,there were controversies on this topic. Friesen and Kingstone (2003) claimed that gaze cues triggered a kind of reflexive or exogenous shift of visual attention that was normally associated with the abrupt onset of a stimulus in the periphery of vision. Whereas Vecera and Rizzo (2004) found a patient EVR with frontal-lobe damage was impaired in using eye gaze cues to allocate attention,suggesting that GCE may involve frontal-lobe processes which control voluntary,not automatic,shifts of visuospatial attention. Both viewpoints have gained some evidences. Thus,whether gaze cues shifted spatial attention reflexively (exogenously) or voluntarily (endogenously) was still in debate. This issue would be clarified in the present study in two aspects. On the one hand,how gaze cues shifted observer's attention. On the other hand,how gaze cues affected the processing of the target in the corresponding direction. Two experiments were conducted in this study,which employed the spatial Stroop paradigm and the target search task respectively. In both experiments,subjects were presented with a gaze cue to the right or left visual field (VF) before the occurrence of a lateralized target to response. There were two conditions in this non-predictive cueing task:(1) targets were presented in the VF indicated by the eye gaze direction (congruent); or (2) targets were opposite to the eye gaze direction (incongruent). In the first experiment,22 subjects were required to discriminate the direction to which the peripherally presented arrow points. While in the second experiment,another 16 subjects all were instructed to finish two different tasks:One involved the detection of single feature,and the other involved the search of feature conjunction. Stimulus presentation and data collection were conducted by E-prime software. From the first experiment,it was found:(1) The lack of GCE was due to the processing conflict between gaze cue and other endogenous cues,which indicated that the two cues had similar processing mechanism; (2) Gaze cue produced larger spatial Stroop effects for valid than invalid trials,which suggested that eyes gaze led to the generation of an internal representation of the spatial location. From the second experiment,similar facilitation effects of the gaze cue for both single feature and feature conjunction search was found,which revealed that gaze cue affected feature extraction as well as later processing stages (decision and response processes),but it did not influence feature integration directly. It was concluded that the intrinsic mechanism of GCE belonged to the endogenous attention system. Eyes gaze cue may induce observers' attention shift through the generation of an internal representation of the spatial location indicated by the cue,and facilitate target feature extraction and encoding,thus speed up the response ultimately.

Fixation disengagement enhances peripheral perceptual processing: evidence for a perceptual gap effect

Temporal gaps between the offset of a central fixation stimulus and the onset of an eccentric target typically reduce saccade latencies (saccadic gap effect). Here, we test whether temporal gaps also affect perceptual performance in peripheral vision. In Experiment 1, subjects executed saccades to briefly presented peripheral target letters and reported letter identity afterwards. A central fixation stimulus either remained visible throughout the trial (overlap) or disappeared 200 ms before letter onset (gap). Experiment 2 tested perceptual performance without saccade execution, whereas Experiment 3 tested saccade execution without perceptual demands. Peripheral letter perception performance was enhanced in gap as compared to overlap conditions (perceptual gap effect) irrespective of concurrent oculomotor demands. Furthermore, the saccadic gap effect was modulated by concurrent perceptual demands. Experiment 4 ruled out a general warning explanation of the perceptual gap effect. These findings extend recent theories assuming a strong coupling between the preparation of goal-directed saccades and shifts of visual attention from the spatial to the temporal domain.

Modeling and measuring the visual detection of ecologically relevant motion by an Anolis lizard

Motion in the visual periphery of lizards, and other animals, often causes a shift of visual attention toward the moving object. This behavioral response must be more responsive to relevant motion (predators, prey, conspecifics) than to irrelevant motion (windblown vegetation). Early stages of visual motion detection rely on simple local circuits known as elementary motion detectors (EMDs). We presented a computer model consisting of a grid of correlation-type EMDs, with videos of natural motion patterns, including prey, predators and windblown vegetation. We systematically varied the model parameters and quantified the relative response to the different classes of motion. We carried out behavioral experiments with the lizard Anolis sagrei and determined that their visual response could be modeled with a grid of correlation-type EMDs with a spacing parameter of 0.3 degrees visual angle, and a time constant of 0.1 s. The model with these parameters gave substantially stronger responses to relevant motion patterns than to windblown vegetation under equivalent conditions. However, the model is sensitive to local contrast and viewer-object distance. Therefore, additional neural processing is probably required for the visual system to reliably distinguish relevant from irrelevant motion under a full range of natural conditions.

The modulation of visual orienting reflexes across the lifespan

The development of reflexive and voluntary shifts of visual attention, as well as relations between the two forms of shifting, were examined in three groups of children (5, 7, and 9 years old), one group of young adults (24 years old), and two groups of senior adults (young seniors with an average age of 69 years, and old seniors with an average age of 81 years). The task entailed response to the detection of a target (black dot) in one of four possible locations in the visual field. Relations between reflexive and voluntary shifts of attention were gauged by the degree to which flash and arrow facilitation and inhibition were observed in response to the presentation of both arrow and flash cues together in one trial. All age groups oriented reflexively in response to a flash cue and utilized the arrow cue to orient attention strategically. When flash and arrow cues were presented in quick succession and thereby competed for attention, the youngest children and oldest seniors were least efficient and flexible in their approach to the orienting task as they had difficulty modulating visual reflexes.

Temporal Coordination during Bimanual Reach-to-Grasp Movements: The Role of Vision

The performance of bimanual movements involving separate objects presents an obvious challenge to the visuo-motor system: Visual feedback can only be obtained from one target at a time. To overcome this challenge overt shifts in visual attention may occur so that visual feedback from both movements may be used directly (Bingham, Hughes, & Mon-Williams, 2008; Riek, Tresilian, Mon-Williams, Coppard, & Carson, 2003). Alternatively, visual feedback from both movements may be obtained in the absence of eye movements, presumably by covert shifts in attention (Diedrichsen, Nambisan, Kennerley, & Ivry, 2004). Given that the quality of information falls with increasing distance from the fixated point, can we obtain the level of information required to accurately guide each hand for precision grasping of separate objects without moving our eyes to fixate each target separately? The purpose of the current study was to examine how the temporal coordination between the upper limbs is affected by the quality of visual information available during the performance of a bimanual task. A total of 11 participants performed congruent and incongruent movements towards near and/or far objects. Movements were performed in natural, fixate-centre, fixate-left, and fixate-right vision conditions. Analyses revealed that the transport phase of incongruent movements was similar across vision conditions for the temporal aspects of both the transport and grasp, whereas the spatial aspects of grasp formation were influenced by the quality of visual feedback. We suggest that bimanual coordination of the temporal aspects of reach-to-grasp movements are not influenced solely by overt shifts in visual attention but instead are influenced by a combination of factors in a task-constrained way.

Time-Course of Top-Down Shifts of Covert Visual Spatial Attention

Time-Course of Top-Down Shifts of Covert Visual Spatial Attention

Increased effect of target eccentricity on covert shifts of visual attention in patients with neglect

Debate continues regarding the mechanisms underlying covert shifts of visual attention. We examined the relationship between target eccentricity and the speed of covert shifts of attention in normal subjects and patients with brain lesions using a cued-response task in which cues and targets were presented at 2° or 8° lateral to the fixation point. Normal subjects were slower on invalid trials in the 8° as compared to 2° condition. Patients with right-hemisphere stroke with neglect were slower in their responses to left-sided invalid targets compared to valid targets, and demonstrated a significant increase in the effect of target validity as a function of target eccentricity. Additional data from one neglect patient (JM) demonstrated an exaggerated validity × eccentricity × side interaction for contralesional targets on a cued reaction time task with a central (arrow) cue. We frame these results in the context of a continuous ‘moving spotlight’ model of attention, and also consider the potential role of spatial saliency maps. By either account, we argue that neglect is characterized by an eccentricity-dependent deficit in the allocation of attention.

Temporal dynamics of neuronal modulation during exogenous and endogenous shifts of visual attention in macaque area MT

Dynamically shifting attention between behaviorally relevant stimuli in the environment is a key condition for successful adaptive behavior. Here, we investigated how exogenous (reflexive) and endogenous (voluntary) shifts of visual spatial attention interact to modulate activity of single neurons in extrastriate area MT. We used a double-cueing paradigm, in which the first cue instructed two macaque monkeys to covertly attend to one of three moving random dot patterns until a second cue, whose unpredictable onset exogenously captured attention, either signaled to shift or maintain the current focus of attention. The neuronal activity revealed correlates of both exogenous and endogenous attention, which could be well distinguished by their characteristic temporal dynamics. The earliest effect was a transient interruption of the focus of endogenous attention by the onset of the second cue. The neuronal signature of this exogenous capture of attention was a short-latency decrease of responses to the stimulus attended so far. About 70 ms later, the influence of exogenous attention leveled off, which was reflected in two concurrent processes: responses to the newly cued stimulus continuously increased because of allocation of endogenous attention, while, surprisingly, there was also a gradual rebound of attentional enhancement of the previously relevant stimulus. Only after an additional 110 ms did endogenous disengagement of attention from this previously relevant stimulus become evident. These patterns of attentional modulation can be most parsimoniously explained by assuming two distinct attentional mechanisms drawing on the same capacity-limited system, with exogenous attention having a much faster time course than endogenous attention.

Repetitive transcranial magnetic stimulation over frontal eye fields disrupts visually cued auditory attention

Voluntary eye movements and covert shifts of visual attention activate the same brain regions. Specifically, the intraparietal sulcus and the frontal eye fields (FEF) appear to be involved both with generating voluntary saccades as well with attending to a peripheral spatial location. Furthermore, these regions appear to be required by both tasks--functional disruption of these regions impairs both tasks. Therefore, it appears that the targeting system that allows us to plan saccades is the same system that allows us to covertly track peripheral visual information. Recent neuroimaging studies suggest that these brain regions are also activated when participants engage in auditory spatial attention tasks. However, it remains unclear whether these regions are required by these tasks. We used repetitive transcranial magnetic stimulation (rTMS) to disrupt the FEF while participants performed an auditory localization task. On each trial, a visual cue directed attention to the probable laterality of the auditory target, and the participant decided whether the subsequent target sound came from an upper or lower speaker. In the absence of TMS, individuals were faster to respond to targets that occurred on the cued side (valid trials) than when the target appears contralaterally to the cued side (invalid side). TMS interfered with this effect, such that the costs associated with ipsilateral invalidly cued targets were substantially reduced. These results suggest that the eye-movement system is needed for normal auditory attention.

Hemispheric modulations of alpha-band power reflect the rightward shift in attention induced by enhanced attentional load

Rightward shifts in attention are a common consequence of brain injury. A growing body of evidence appears to suggest that increases in attentional load, and decreases in alertness can lead to rightward shifts in attention in healthy and patient populations. It is unclear however whether these factors affect spatial biases in attention at the level of preparatory control processes or at the level of stimulus driven expression mechanisms. Whilst such effects cannot easily be dissociated behaviourally, the robust association between changes in α-band activity and shifts in visual attention provides a neural marker by which the temporal dynamics of effects of attentional load on spatial processing might be examined. Here we use electroencephalography to examine the relationship between modulations in α-band activity and behavioural outcome on a dual task paradigm comprising a detection task (t1), closely followed by a temporal order judgment task (t2). We examine the effects of high (respond to t1 and t2) and low (t2 only) attentional load conditions on spatial bias and changes in lateralization of α-band activity over the course of the trial. As anticipated a rightward bias in detecting target onsets was observed in the temporal order judgment task (t2) under conditions of high attentional load. This rightward shift in attention was associated with changes in the lateralization of α-band activity that occurred only after the presentation of t2, suggesting that attentional load may primarily influence expression mechanisms.

Executive control of spatial attention shifts in the auditory compared to the visual modality

Voluntary orienting of visual spatial attention has been shown to be associated with activation in a distributed network of frontal and parietal brain areas. Neuropsychological data suggest that at least some of these areas should be sensitive to the direction in which attention is shifted. The aim of this study was to use rapid event-related functional magnetic resonance imaging to investigate whether spatial attention in the auditory modality is subserved by the same or different brain areas as in the visual modality, and whether the auditory and visual attention networks show any degree of hemispheric lateralisation or sensitivity to the direction of attention shifts. The results suggest that auditory and visual spatial attention shifts are controlled by a supramodal network of frontal, parietal and temporal areas. Areas activated included the precuneus and superior parietal cortex, the inferior parietal cortex and temporo-parietal junction, as well as the premotor and supplementary motor areas and dorsolateral prefrontal cortex (DLPFC). In the auditory task, some of these areas, in particular the precuneus as well as the inferior parietal cortex and temporo-parietal junction, showed 'relative' asymmetry, in that they responded more strongly to attention shifts towards the contralateral than the ipsilateral hemispace. Some areas, such as the right superior parietal cortex and left DLPFC, showed 'absolute' asymmetry, in that they responded more strongly in one than in the other hemisphere.

Art, Artists, and Perception: A Model for Premotor Contributions to Perceptual Analysis and Form Recognition

Artists, art critics, art historians, and cognitive psychologists have asserted that visual artists perceive the world differently than nonartists and that these perceptual abilities are the product of knowledge of techniques for working in an artistic medium. In support of these claims, Kozbelt (2001) found that artists outperform nonartists in visual analysis tasks and that these perceptual advantages are statistically correlated with drawing skill. We propose a model to explain these results that is derived from a diagnostic framework for object recognition and recent research in cognitive neuroscience on selective visual attention. This research demonstrates that endogenous shifts of visual attention enhance the encoding of expected features in the visual field and inhibit the perception of potential distracters. Moreover, it demonstrates complementary roles for spatial schemata and motor plans in visual attention. We argue that artists develop novel spatial schemata, which enable them to recognize and reproduce stimulus features sufficient for adequate artistic production in a medium, and that these schemata become encoded as motor plans as artists develop technical proficiency in a medium. We hypothesize that artists’ perceptual advantages can therefore, be explained by the role spatial schemata and motor plans play in selective attention.

Latency of saccades and vergence eye movements in dyslexic children

The goal of this study was to explore the latency of eye movements both in direction and in depth in dyslexic children. Sixteen dyslexic (mean age: 11.12 +/- 1.08 years) and 14 non-dyslexic children (mean age: 12.08 +/- 0.99 years) were tested. Two different paradigms (simultaneous and gap) were used to elicit pure saccades at far and at near distance, pure vergence (convergence and divergence) and combined saccade-vergence movements. Horizontal eye movements from both eyes were recorded simultaneously by a photoelectric device (Oculometer, Dr. Bouis). The mean latency of saccades at far distance (pure or combined) is significantly longer in dyslexics, regardless of the paradigm used. For both dyslexic and non-dyslexic children, latencies in the gap paradigm are shorter. Moreover, the occurrence of express latencies for divergence (pure or combined) is significantly higher for dyslexics. Difficulties in both voluntary and reflexive control shifts of visual attention from near to far distance in dyslexics could be at the origin of these findings.

Influence of Peripheral Environment Luminance and Visual Performance on Shifts of Depth Attention in Three-Dimensional Space

A series of three experiments were conducted to investigate the relation between shifts of attention in depth and subjects' visual performance or peripheral environment luminance in three-dimensional (3-D) space. Previous researchers have examined various aspects of shifts of visual attention in 3-D space. However, there were few studies to study the relationship of depth attention and peripheral environment luminance. Firstly, visual function performance of subjects was tested by means of visual measurement apparatus in experiment 1, and experimental data was divided into two groups. And then, mean reaction time (RT) of subjects was examined by changing peripheral environment luminance using a semi-realistic setting, the depth attention experiment apparatus in experiment 2. Finally, changing forecast degree examination was conducted to subjects with low visual adaptability in order to reveal the relation between delay of reaction time and forecast degree in experiment 3. The major results was shown that (1) visual performance of subjects had an individual difference; (2) shifts of attention from far space to near space was faster than the reverse under each different condition; (3) the training for visual adaptive ability can improved visual performance of subjects.