The spatial resolution of visual attention

Attentional Modulation of Visual Spatial Integration: Psychophysical Evidence Supported by Population Coding Modeling

Two prominent strategies that the human visual system uses to reduce incoming information are spatial integration and selective attention. Whereas spatial integration summarizes and combines information over the visual field, selective attention can single it out for scrutiny. The way in which these well-known mechanisms-with rather opposing effects-interact remains largely unknown. To address this, we had observers perform a gaze-contingent search task that nudged them to deploy either spatial or feature-based attention to maximize performance. We found that, depending on the type of attention employed, visual spatial integration strength changed either in a strong and localized or a more modest and global manner compared with a baseline condition. Population code modeling revealed that a single mechanism can account for both observations: Attention acts beyond the neuronal encoding stage to tune the spatial integration weights of neural populations. Our study shows how attention and integration interact to optimize the information flow through the brain.

Emergent features in the crowding zone: When target-flanker grouping surmounts crowding

Crowding is the impairment of target identification when the target is surrounded by nearby flankers. Two hallmarks of crowding are that it is stronger when the flankers are close to the target and when the target strongly groups with the flankers. Here we show the opposite of both. A chevron target (pointing up or down) was presented at 8° eccentricity in the right visual field. It was surrounded by four flankers. Three of the flankers varied (pointing left or right). The fourth, the critical flanker (CF), was fixed in one orientation (left, right, up, down), yielding different configurations with the target. The CF's distance to the target was varied. Target identification depended strongly on the distance and the orientation of the CF. Remarkably, when the target and the CF grouped into a good configuration and elicited an emergent feature, performance was high if the CF was close to the target. This effect was particularly strong when participants were informed about the different CF-target configurations before the experiment. Reducing crowding and grouping by asynchronous presentation of the CF and the other items abolished the effect. When participants reported the entire configuration of the CF and the target, performance rapidly decreased with increasing spacing when the CF and the target were different but not when they were the same, indicating different spatial extents of the corresponding grouping processes. Our results show that the features emerging from the configurations of the target and a flanker strongly modulate crowding. Strong target-flanker grouping can benefit performance.

Visual crowding involves delayed frontoparietal response and enhanced top-down modulation

Crowding, the disrupted recognition of a peripheral target in the presence of nearby flankers, sets a fundamental limit on peripheral vision perception. Debates persist on whether the limit occurs at early visual cortices or is induced by top-down modulation, leaving the neural mechanism for visual crowding largely unclear. To resolve the debate, it is crucial to extract the neural signals elicited by the target from that by the target-flanker clutter, with high temporal resolution. To achieve this purpose, here we employed a temporal response function (TRF) approach to dissociate target-specific response from the overall electroencephalograph (EEG) recordings when the target was presented with (crowded) or without flankers (uncrowded) while subjects were performing a discrimination task on the peripherally presented target. Our results demonstrated two components in the target-specific contrast-tracking TRF response-an early component (100-170 ms) in occipital channels and a late component (210-450 ms) in frontoparietal channels. The late frontoparietal component, which was delayed in time under the crowded condition, was correlated with target discrimination performance, suggesting its involvement in visual crowding. Granger causality analysis further revealed stronger top-down modulation on the target stimulus under the crowded condition. Taken together, our findings support that crowding is associated with a top-down process which modulates the low-level sensory processing and delays the behavioral-relevant response in the high-level region.

Linkage between retinal ganglion cell density and the nonuniform spatial integration across the visual field

The integration of visual information over space is critical to human pattern vision. For either luminance detection or object recognition, the position of the target in the visual field governs the size of a window within which visual information is integrated. Here we analyze the relationship between the topographic distribution of ganglion cell density and the nonuniform spatial integration across the visual field. We find that the variation in the retinal ganglion cell (RGC) density across the human retina is closely matched to the variation in the extent of spatial integration. Our study suggests that a fixed number of RGCs subserves spatial integration of visual input, independent of the visual-field location.

The ability to integrate visual information over space is a fundamental component of human pattern vision. Regardless of whether it is for detecting luminance contrast or for recognizing objects in a cluttered scene, the position of the target in the visual field governs the size of a window within which visual information is integrated. Here we analyze the relationship between the topographic distribution of ganglion cell density and the nonuniform spatial integration across the visual field. The extent of spatial integration for luminance detection (Ricco’s area) and object recognition (crowding zone) are measured at various target locations. The number of retinal ganglion cells (RGCs) underlying Ricco’s area or crowding zone is estimated by computing the product of Ricco’s area (or crowding zone) and RGC density for a given target location. We find a quantitative agreement between the behavioral data and the RGC density: The variation in the sampling density of RGCs across the human retina is closely matched to the variation in the extent of spatial integration required for either luminance detection or object recognition. Our empirical data combined with the simulation results of computational models suggest that a fixed number of RGCs subserves spatial integration of visual input, independent of the visual-field location.

Color Perception and Attentional Load in Dynamic, Time-Constrained Environments

The capacity to perceive color in the peripheral field has attracted research interest for more than a decade. There is evidence that sensitivity to red-green color variations is lower than for yellow-blue in peripheral vision. Whether, and to what extent, color vision affects the visual focus of attention, which is normally much smaller than the visual field, has not yet been examined. We used a sport-specific decision-making task to assess whether the color of the jersey worn by players appearing in the periphery influences decision making by affecting the attentional and perceptual capabilities. Pairs of players wearing chromatic (blue, yellow, red, and green) and achromatic (black, white) colored jerseys were briefly presented across a range of visual angles on a 6 m concave immersive screen. Participants were required to decide to whom to pass and recall relevant information. Findings indicate that color perception changes vary with increasing visual angle, but that the focus of attention is too small to be influenced by jersey color sensitivity. Decision-making performance decreases with increasing visual angle, but is not influenced by color. The implications for decision-making processes in sport and other professional domains are discussed.

Two's company, three's a crowd: Individuation is necessary for object recognition

Object recognition is essential for navigating the real world. Despite decades of research on this topic, the processing steps necessary for recognition remain unclear. In this study, we examined the necessity and role of individuation, the ability to select a small number of spatially distinct objects irrespective of their identity, in the recognition process. More specifically, we tested if the ability to rapidly individuate and enumerate a small number of objects (subitizing) can be impaired by crowding. Crowding is flanker-induced interference that specifically impedes the recognition process. We found that subitizing is impaired when objects are close to each other (Experiment 1), and if the target objects are surrounded by irrelevant but perceptually similar flankers (Experiments 2-4). This impairment cannot be attributed to confusion between targets and flankers, wherein flankers are inadvertently included in or targets are excluded from enumeration (Experiments 3-4). Importantly, the flanker induced interference was comparable in both subitizing and crowding tasks (Experiment 4), suggesting that individuation and identification share a common processing pathway. We conclude that individuation is an essential stage in the object recognition pipeline and argue for a cohesive proposal that both crowding and subitizing are due to limitations of selective attention.

"Approximate number system" training: A perceptual learning approach

Recent research suggests that humans perceive quantity using a non-symbolic "number sense." This sense is then thought to provide a foundation for understanding symbolic numbers in formal education. Given this link, there has been interest in the extent to which the approximate number system (ANS) can be improved via dedicated training, as this could provide a route to improving performance in symbolic mathematics. However, current evidence regarding the trainability of the ANS comes largely from studies that have used short training durations, leaving open the question of whether improvements occur over a longer time span. To address this limitation, we utilized a perceptual learning approach to investigate the extent to which long-term (8,000+ trials) training modifies the ANS. Consistent with the general methodological approach common in the domain of perceptual learning (where learning specificity is commonly observed), we also examined whether ANS training generalizes to: (a) untrained locations in the visual field; (b) an enumeration task; (c) a higher-level ratio comparison task; and (d) arithmetic ability. In contrast to previous short-term training studies showing that ANS learning quickly asymptotes, our long-term training approach revealed that performance continued to improve even after thousands of trials. We further found that the training generalized to untrained visual locations. At post-test there was non-significant evidence for generalization to a low-level enumeration task, but not to our high-level tasks, including ratio comparison, multi-object tracking, and arithmetic performance. These results demonstrate the potential utility of long-term psychophysical training, but also suggest that ANS training alone (even long-duration training) may be insufficient to modify higher-level math skills.

Dynamic distractor environments reveal classic visual field anisotropies for judgments of temporal order

Numerous studies have shown that visual performance critically depends on the stimulus' projected retinal location. For example, performance tends to be better along the horizontal relative to the vertical meridian (lateral anisotropy). Another case is the so-called upper-lower anisotropy, whereby performance is better in the upper relative to the lower hemifield. This study investigates whether temporal order judgments (TOJs) are subject to these visual field constraints. In Experiments 1 and 2, subjects reported the temporal order of two disks located along the horizontal or vertical meridians. Each target disk was surrounded by 10 black and white distractor disks, whose polarity remained unchanged (static condition) or reversed throughout the trial (dynamic condition). Results indicate that the mere presence of dynamic distractors elevated thresholds by more than a factor of four and that this elevation was particularly pronounced along the vertical meridian, evidencing the lateral anisotropy. In Experiment 3, thresholds were compared in upper, lower, left, and right visual hemifields. Results show that the threshold elevation caused by dynamic distractors was greatest in the upper visual field, demonstrating an upper-lower anisotropy. Critically, these anisotropies were evident exclusively in dynamic distractor conditions suggesting that distinct processes govern TOJ performance under these different contextual conditions. We propose that whereas standard TOJs are processed by fast low-order motion mechanisms, the presence of dynamic distractors mask these low-order motion signals, forcing observers to rely more heavily on more sluggish higher order motion processes.

Lateralized Suppression of Alpha-Band EEG Activity As a Mechanism of Target Processing

Alpha-band (8-12 Hz) EEG activity has been linked to visual attention since the earliest EEG studies. More recent studies using spatial cuing paradigms have shown that alpha is suppressed over the hemisphere contralateral to a to-be-attended location, suggesting that alpha serves as a mechanism of preparatory attention. Here, we demonstrate that alpha also plays a role in active target processing. EEG activity was recorded from a group of healthy male and female human subjects in two visual search experiments. In addition to alpha activity, we also assessed the N2pc event-related potential component, a lateralized transient EEG response that has been tightly linked with the focusing of attention on visual targets. We found that the visual search targets triggered both an N2pc component and a suppression of alpha-band activity that was greatest over the hemisphere contralateral to the target (which we call "target-elicited lateralized alpha suppression" or TELAS). In Experiment 1, both N2pc and TELAS were observed for targets presented in the lower visual field but were absent for upper-field targets. However, these two lateralized effects had different time courses and they responded differently to manipulations of crowding in Experiment 2. These results indicate that lateralized alpha-band activity is involved in active target processing and is not solely a preparatory mechanism and also that TELAS and N2pc reflect a related but separable neural mechanism of visuospatial attention.SIGNIFICANCE STATEMENT The very first EEG studies demonstrated that alpha-band (8-12 Hz) EEG oscillations are suppressed when people attend to visual information and more recent research has shown that cuing an individual to expect a target at a specific location produces lateralized suppression in the contralateral hemisphere. Therefore, lateralized alpha may serve as a preparatory mechanism. In the present study, we found that a similar lateralized alpha effect is triggered by the appearance of a visual target even though the location could not be anticipated, demonstrating that alpha also serves as an active mechanism of target processing. Moreover, we found that alpha lateralization can be dissociated from other lateralized measures of target selection, indicating that it reflects a distinct mechanism of attention.

Motion prediction at low contrast

Accurate motion prediction is fundamental for survival. How does this reconcile with the well-known speed underestimation of low-contrast stimuli? Here we asked whether this contrast-dependent perceptual bias is retained in motion prediction under two different saccadic planning conditions: making a saccade to an occluded moving target, and real-time gaze interaction with multiple moving targets. In a first experiment, observers made a saccade to the mentally extrapolated position of a moving target (imagery condition). In a second experiment, observers had to prevent collisions among multiple moving targets by glancing at them through a gaze-contingent display or by hitting them with the touchpad cursor (interaction condition). In both experiments, target contrast was manipulated. We found that, whereas saccades to the imagined moving target were systematically biased by contrast, the gaze interaction performance, as measured by missed collisions, was generally unaffected - even though low-contrast targets looked slower. Interceptive actions increased at low contrast, but only when the gaze was used for interaction. Thus, perceptual speed underestimation transfers to saccades made to imagined low-contrast targets, without however necessarily being detrimental to effective performance when real-time interaction with multiple targets is required. This differential effect of stimulus contrast suggests that in complex dynamic conditions saccades are rather tolerant to visual speed biases.

Can hypnosis displace the threshold for visual consciousness?

To test the specific effects of hypnosis on the attentional components of visual awareness, we developed a posthypnotic suggestion for peripheral visual inattention inspired on the "tunnel vision" symptom of the Balint Syndrome. We constructed a dual-target visibility and discrimination paradigm, in which single-digit numerical targets were placed both on the hypnotically affected peripheral space and on the remaining undisturbed central area. Results were 3-fold: (i) when compared to participants of Low hypnotic susceptibility (Lows), highly susceptible participants (Highs) presented decreased subjective visibility; (ii) Highs did not show dual-task interference from peripheral targets (an effect of unconscious processing) during hypnotic suggestion to not attend them, but Lows did; (iii) nevertheless, when asked to execute a discrimination task over these same targets, Highs performed with the same accuracy as Lows. These results suggest that the hypnotic manipulation of visuospatial attention did produce an experiential change in Highs, but not one that could be mapped onto interference at a single (conscious or unconscious) level of processing. Rather, we posit that Highs simultaneously displayed (i) a fluctuation in awareness of peripheral targets coherent with the suggestion and (ii) a control strategy that involved removing hypnotically unattended targets from the task set whenever task instructions would allow for it. In light of these findings, we argue that hypnosis cannot be used as a tool to restrict the processing of otherwise supraliminal stimulation to subliminal levels.

Contextual-Dependent Attention Effect on Crowded Orientation Signals in Human Visual Cortex

A target becomes hard to identify with nearby visual stimuli. This phenomenon, known as crowding, places a fundamental limit on conscious perception and object recognition. To understand the neural representation of crowded stimuli, we used fMRI and a forward encoding model to reconstruct the target-specific feature from multivoxel activation patterns evoked by orientation patches. Orientation-selective response profiles were constructed in V1-V4 for a target embedded in different contexts. Subjects of both sexes either directed their attention over all the orientation patches or selectively to the target. In the context with a weak crowding effect, attending to the target enhanced the orientation selectivity of the response profile; such effect increased along the visual pathway. In the context with a strong crowding effect, attending to the target enhanced the orientation selectivity of the response profile in the earlier visual area, but not in V4. The increase and decrease of orientation selectivity along the visual hierarchy demonstrate a contextual-dependent attention effect on crowded orientation signals: in the context with a weak crowding effect, selective attention gradually resolves the target from nearby distractors along the hierarchy; in the context with a strong crowding effect, while selective attention maintains the target feature in the earlier visual area, its effect decreases in the downstream area. Our findings reveal how the human visual system represents the target-specific feature at multiple stages under the limit of attention selection in a cluttered scene.SIGNIFICANCE STATEMENT Using fMRI and a forward encoding model, we reconstructed orientation-selective response profiles for a target embedded in crowded contexts. In the context with a weak crowding effect, attention gradually resolves the target from nearby distractors along the visual hierarchy. In the context with a strong crowding effect, while the feature of the target is preserved in the early visual cortex, it degrades in the later visual processing stage. The increase and decrease of orientation selectivity along the visual hierarchy reveal how the human visual system strikes to present the target-specific feature under the limit of attention selection in a cluttered scene.

Objectively Measuring Observer Attention in Severe Thyroid-Associated Orbitopathy: A 3D Study

OBJECTIVE

Measure the attentional distraction of facial deformity related to severe thyroid-associated orbitopathy using three-dimensional (3D) images and eye-tracking technology.

METHODS

Observers recruited at an academic tertiary referral center viewed 3D facial images of patients with severe thyroid-associated orbitopathy (TAO) and controls without TAO. An infrared eye-tracking monitor recorded their eye movements and fixations in real time. Multivariate Hotelling's analysis, followed by planned posthypothesis testing, was used to compare fixation durations for predefined regions of interest, including the eyes, nose, mouth, central triangle, and remaining face without the central triangle between severe TAO patients and controls.

RESULTS

One hundred sixteen observers (mean age 26.4 years, 51% female) successfully completed the eye-tracking experiment. The majority of their attention was directed toward the central triangle (eyes, nose, mouth). On multivariate analysis, there were significant differences in the distribution of attention between control and severe TAO faces (T²  = 49.37; F(5,922) = 9.8314, P < 0.0001). On planned posthypothesis testing, observers attended significantly more to the eyes (0.77 seconds, P < 0.0001, 95% confidence interval [CI], 0.51, 1.03 seconds) and less to the nose (-0.42 seconds, P < 0.0001, 95% CI, -0.23, -0.62 seconds) in severe TAO patients. There was no significant difference in time spent on the mouth, the total time spent on the central triangle, or time spent in the remaining face between the two groups.

CONCLUSION

Severe TAO distracted observer attention toward the eyes compared to control patients. These data lend insight into how TAO may alter observers' perceptions of these patients. Future studies should investigate how these changes in observer gaze patterns may reflect the social perception of TAO patients.

LEVEL OF EVIDENCE

NA Laryngoscope, 129:1250-1254, 2019.

Neurocognitive Development of the Resolution of Selective Visuo-Spatial Attention: Functional MRI Evidence From Object Tracking

Our ability to select relevant information from the environment is limited by the resolution of attention – i.e., the minimum size of the region that can be selected. Neural mechanisms that underlie this limit and its development are not yet understood. Functional magnetic resonance imaging (fMRI) was performed during an object tracking task in 7- and 11-year-old children, and in young adults. Object tracking activated canonical fronto-parietal attention systems and motion-sensitive area MT in children as young as 7 years. Object tracking performance improved with age, together with stronger recruitment of parietal attention areas and a shift from low-level to higher-level visual areas. Increasing the required resolution of spatial attention – which was implemented by varying the distance between target and distractors in the object tracking task – led to activation increases in fronto-insular cortex, medial frontal cortex including anterior cingulate cortex (ACC) and supplementary motor area, superior colliculi, and thalamus. This core circuitry for attentional precision was recruited by all age groups, but ACC showed an age-related activation reduction. Our results suggest that age-related improvements in selective visual attention and in the resolution of attention are characterized by an increased use of more functionally specialized brain regions during the course of development.

Context mitigates crowding: Peripheral object recognition in real-world images

Object recognition is often conceived of as proceeding by segmenting an object from its surround, then integrating its features. In turn, peripheral vision's sensitivity to clutter, known as visual crowding, has been framed as due to a failure to restrict that integration to features belonging to the object. We hand-segment objects from their background, and find that rather than helping peripheral recognition, this impairs it when compared to viewing the object in its real-world context. Context is in fact so important that it alone (no visible target object) is just as informative, in our experiments, as seeing the object alone. Finally, we find no advantage to separately viewing the context and segmented object. These results, taken together, suggest that we should not think of recognition as ideally operating on pre-segmented objects, nor of crowding as the failure to do so.

Upper nasal hemifield location and nonspatial auditory tones accelerate visual detection during dichoptic viewing

Visual performance is asymmetric across the visual field, but locational biases that occur during dichoptic viewing are not well understood. In this study, we characterized horizontal, vertical and naso-temporal biases in visual target detection during dichoptic stimulation and explored whether the detection was facilitated by non-spatial auditory tones associated with the target’s location.

The detection time for single monocular targets that were suppressed from view with a 10 Hz dynamic noise mask presented to the other eye was measured at the 4° intercardinal location of each eye with the breaking Continuous Flash Suppression (b-CFS) technique. Each target was either combined with a sound (i.e., high or low pitch tone) that was congruent or incongruent with its vertical location (i.e., upper or lower visual field) or presented without a sound. The results indicated faster detection of targets in the upper rather than lower visual field and faster detection of targets in the nasal than temporal hemifield of each eye. Sounds generally accelerated target detection, but the tone pitch-elevation congruency did not further enhance performance. These findings suggest that visual detection during dichoptic viewing differs from standard viewing conditions with respect to location-related perceptual biases and crossmodal modulation of visual perception. These differences should be carefully considered in experimental designs employing dichoptic stimulation techniques and in display applications that utilize dichoptic viewing.

Discrimination of spatial phase: The roles of luminance distribution and attention

We can easily discriminate certain phase relations in spatial patterns but not others. Phase perception has been found different in the fovea vs. periphery, and for single patterns vs. textures. Different numbers of mechanisms have been proposed to account for the regularities of phase perception. In this study, I attempt to better understand the mechanisms behind discrimination of spatial phase. In order to reveal the role of luminance cues, I use histogram matching of patterns with different phases. Possible effects of attention were studied using visual search experiments with varied stimulus set size. Simple and compound Gabor patches, broadband lines and edges, and textures composed of those patterns were used as stimuli. The experiments indicate that phase discrimination is mediated by two mechanisms. The first uses luminance differences and operates pre-attentively, in parallel across the visual field. The second compares relative positions of dark and bright segments within an image, and is strictly limited by capacity of attention.

Asymmetries in Distractibility: Left Distractors Improve Reaction Time Performance

Research using the irrelevant-distractor paradigm shows perceptual load influences distractibility, such that distractors are more likely to be processed and decrease reaction times during low perceptual load. In contrast, under high load, attentional resources are limited, and the likelihood of distractibility is decreased. We manipulated distractor placement to determine whether location differentially influenced distractibility. During low load, reaction times were increased equally for all distractor locations. Under high load, left distractors speeded reaction times significantly more than right distractors. We suggest two potential explanations: (1) the central focus of attention was sufficiently large to encapsulate both the distractor and the visual array during low perceptual load, leading to increased distraction—during high load, attention was split across the two visual stimuli, allowing the distractors and array to be processed independently; (2) superior executive control for stimuli in the left visual field allowed participants to ‘catch and release’ left distractors more efficiently, ultimately decreasing distraction and providing a performance benefit. Our findings represent an intriguing development in relation to visual asymmetries in distractibility.

Those pernicious items

Hulleman & Olivers (H&O) identify a number of problems with item-based thinking and its impact on our understanding of visual search. I detail ways in which item-thought is worse than the authors suggest. I concur with the broad strokes of the theory they set out, and also clarify the relationship between their view and our recent theory of visual search.

Stimulus conflation and tuning selectivity in V4 neurons: a model of visual crowding

Visual crowding is a fundamental constraint on our ability to identify peripheral objects in cluttered environments. This study proposes a descriptive model for understanding crowding based on the tuning selectivity for stimuli within the receptive field (RF) and examines potential neural correlates in cortical area V4. For V4 neurons, optimally sized, letter-like stimuli are much smaller than the RF. This permits stimulus conflation, the fusing of separate objects into a single identity, to occur within the RF of single neurons. Flanking interactions between such stimuli were found to be limited to the RF. The response to an optimal stimulus centered in the neuron's RF, is suppressed by the simultaneous presentation of flanking stimuli within the RF. The degree of suppression is a function of the neuron's stimulus tuning properties and the position of the flanker within the RF. A single neuron may show suppression or facilitation depending on the detailed stimulus conditions and the relationship to tuning selectivity. Loss of activity in the set of neurons tuned to a particular stimulus alters its overall representation and potential identification, thus forming a basis for visual crowding effects. The mechanisms that determine the outcome of conflation are associated with object identification, and are not some other independent visual phenomena.

A recurrent neural model for proto-object based contour integration and figure-ground segregation

Visual processing of objects makes use of both feedforward and feedback streams of information. However, the nature of feedback signals is largely unknown, as is the identity of the neuronal populations in lower visual areas that receive them. Here, we develop a recurrent neural model to address these questions in the context of contour integration and figure-ground segregation. A key feature of our model is the use of grouping neurons whose activity represents tentative objects ("proto-objects") based on the integration of local feature information. Grouping neurons receive input from an organized set of local feature neurons, and project modulatory feedback to those same neurons. Additionally, inhibition at both the local feature level and the object representation level biases the interpretation of the visual scene in agreement with principles from Gestalt psychology. Our model explains several sets of neurophysiological results (Zhou et al. Journal of Neuroscience, 20(17), 6594-6611 2000; Qiu et al. Nature Neuroscience, 10(11), 1492-1499 2007; Chen et al. Neuron, 82(3), 682-694 2014), and makes testable predictions about the influence of neuronal feedback and attentional selection on neural responses across different visual areas. Our model also provides a framework for understanding how object-based attention is able to select both objects and the features associated with them.

Perceptual integration and attention in human extrastriate cortex

Visual crowding is a perceptual phenomenon with far-reaching implications in both perceptual (e.g., object recognition and reading) and clinical (e.g., developmental dyslexia and visual agnosia) domains. Here, we combined event-related fMRI measurements and wide-field brain mapping methods to investigate whether the BOLD response evoked by visual crowding is modulated by different attentional conditions. Participants underwent two sessions of psychophysical training outside the scanner, and then fMRI BOLD activity was measured simultaneously in early visual areas (including the visual word form area, VWFA), while they viewed strongly-crowded and weakly-crowded Gabor patches in attended and unattended conditions. We found that crowding increased BOLD activity in a network of areas including V1, V2, V3A, V4/V8, and VWFA. In V4/V8 and VWFA we found an increased activity related to attention. The effect of crowding in V1 was recorded only when attention was fully devoted to the target location. Our results provide evidence that some area beyond V1 might be the likely candidate for the site of crowding, thus supporting the view of visual crowding as a mid-level visual phenomenon.

The reference frame for encoding and retention of motion depends on stimulus set size

The goal of this study was to investigate the reference frames used in perceptual encoding and storage of visual motion information. In our experiments, observers viewed multiple moving objects and reported the direction of motion of a randomly selected item. Using a vector-decomposition technique, we computed performance during smooth pursuit with respect to a spatiotopic (nonretinotopic) and to a retinotopic component and compared them with performance during fixation, which served as the baseline. For the stimulus encoding stage, which precedes memory, we found that the reference frame depends on the stimulus set size. For a single moving target, the spatiotopic reference frame had the most significant contribution with some additional contribution from the retinotopic reference frame. When the number of items increased (Set Sizes 3 to 7), the spatiotopic reference frame was able to account for the performance. Finally, when the number of items became larger than 7, the distinction between reference frames vanished. We interpret this finding as a switch to a more abstract nonmetric encoding of motion direction. We found that the retinotopic reference frame was not used in memory. Taken together with other studies, our results suggest that, whereas a retinotopic reference frame may be employed for controlling eye movements, perception and memory use primarily nonretinotopic reference frames. Furthermore, the use of nonretinotopic reference frames appears to be capacity limited. In the case of complex stimuli, the visual system may use perceptual grouping in order to simplify the complexity of stimuli or resort to a nonmetric abstract coding of motion information.

Position Affects Performance in Multiple-Object Tracking in Rugby Union Players

We report an experiment that examines the performance of rugby union players and a control group composed of graduate student with no sport experience, in a multiple-object tracking task. It compares the ability of 86 high level rugby union players grouped as Backs and Forwards and the control group, to track a subset of randomly moving targets amongst the same number of distractors. Several difficulties were included in the experimental design in order to evaluate possible interactions between the relevant variables. Results show that the performance of the Backs is better than that of the other groups, but the occurrence of interactions precludes an isolated groups analysis. We interpret the results within the framework of visual attention and discuss both, the implications of our results and the practical consequences.

Selective attention within the foveola

Efficient control of attentional resources and high-acuity vision are both fundamental for survival. Shifts in visual attention are known to covertly enhance processing at locations away from the center of gaze, where visual resolution is low. It is unknown, however, whether selective spatial attention operates where the observer already looks, i.e., within the high-acuity foveola, the small, yet disproportionally important rod-free region of the retina. Using new methods for precisely controlling retinal stimulation, here we show that covert attention flexibly improves and speeds-up both detection and discrimination at loci only a fraction of a degree apart within the foveola. These findings reveal a surprisingly precise control of attention and its involvement in fine spatial vision. They show that the commonly studied covert shifts of attention away from the fovea are the expression of a global mechanism that exerts its action across the entire visual field.

Attention Increases Spike Count Correlations between Visual Cortical Areas

Visual attention, which improves perception of attended locations or objects, has long been known to affect many aspects of the responses of neuronal populations in visual cortex. There are two nonmutually exclusive hypotheses concerning the neuronal mechanisms that underlie these perceptual improvements. The first hypothesis, that attention improves the information encoded by a population of neurons in a particular cortical area, has considerable physiological support. The second hypothesis is that attention improves perception by selectively communicating relevant visual information. This idea has been tested primarily by measuring interactions between neurons on very short timescales, which are mathematically nearly independent of neuronal interactions on longer timescales. We tested the hypothesis that attention changes the way visual information is communicated between cortical areas on longer timescales by recording simultaneously from neurons in primary visual cortex (V1) and the middle temporal area (MT) in rhesus monkeys. We used two independent and complementary approaches. Our correlative experiment showed that attention increases the trial-to-trial response variability that is shared between the two areas. In our causal experiment, we electrically microstimulated V1 and found that attention increased the effect of stimulation on MT responses. Together, our results suggest that attention affects both the way visual stimuli are encoded within a cortical area and the extent to which visual information is communicated between areas on behaviorally relevant timescales.

SIGNIFICANCE STATEMENT

Visual attention dramatically improves the perception of attended stimuli. Attention has long been thought to act by selecting relevant visual information for further processing. It has been hypothesized that this selection is accomplished by increasing communication between neurons that encode attended information in different cortical areas. We recorded simultaneously from neurons in primary visual cortex and the middle temporal area while rhesus monkeys performed an attention task. We found that attention increased shared variability between neurons in the two areas and that attention increased the effect of microstimulation in V1 on the firing rates of MT neurons. Our results provide support for the hypothesis that attention increases communication between neurons in different brain areas on behaviorally relevant timescales.

The Attention Window: A Narrative Review of Limitations and Opportunities Influencing the Focus of Attention

PURPOSE

Visual attention is essential in many areas ranging from everyday life situations to the workplace. Different circumstances such as driving in traffic or participating in sports require immediate adaptation to constantly changing situations and frequently the conscious perception of 2 objects or scenes at the same time.

METHOD

The attention window task, a measure of attentional breadth, in which people must attend to 2 equally attention-demanding stimuli simultaneously, was introduced. This article provides a narrative review of studies using this task and outlines different factors that might influence the attention window.

RESULTS

Differences in the spatial distribution of attention result, for example, from effects of age or physical activities as well as from emotional processes and those affected by current motivation, while gender does not have any influence. The window is represented as an ellipse with greater attentional breadth along the horizontal axis than the vertical axis, and it is about 5 to 6 times smaller than the human visual field.

CONCLUSION

Not only everyday occurrences but also situations in sport games-for example, having an overview of the opponent, teammates, and the ball-require the ability to pay visual attention to 2 peripheral objects and continuously changing situations. Therefore, the application or avoidance of different strategies and factors is discussed to improve and adjust behavior in those situations.

Diagnosing the Periphery: Using the Rey-Osterrieth Complex Figure Drawing Test to Characterize Peripheral Visual Function

Peripheral vision is strongly limited by crowding, the deleterious influence of neighboring stimuli on target perception. Many quantitative aspects of this phenomenon have been characterized, but the specific nature of the perceptual degradation remains elusive. We utilized a drawing technique to probe the phenomenology of peripheral vision, using the Rey-Osterrieth Complex Figure, a standard neuropsychological clinical instrument. The figure was presented at 12° or 6° in the right visual field, with eye tracking to ensure that the figure was only presented when observers maintained stable fixation. Participants were asked to draw the figure with free viewing, capturing its peripheral appearance. A foveal condition was used to measure copying performance in direct view. To assess the drawings, two raters used standard scoring systems that evaluated feature positions, spatial distortions, and omission errors. Feature scores tended to decrease with increasing eccentricity, both within and between conditions, reflecting reduced resolution and increased crowding in peripheral vision. Based on evaluation of the drawings, we also identified new error classes unique to peripheral presentation, including number errors for adjacent similar features and distinctive spatial distortions. The multifaceted nature of the Rey-Osterrieth Complex Figure-containing configural elements, detached compound features, and texture-like components-coupled with the flexibility of the free-response drawing paradigm and the availability of standardized scoring systems, provides a promising method to probe peripheral perception and crowding.

Nonuniform Changes in the Distribution of Visual Attention from Visual Complexity and Action: A Driving Simulation Study

Researchers acknowledge the interplay between action and attention, but typically consider action as a response to successful attentional selection or the correlation of performance on separate action and attention tasks. We investigated how concurrent action with spatial monitoring affects the distribution of attention across the visual field. We embedded a functional field of view (FFOV) paradigm with concurrent central object recognition and peripheral target localization tasks in a simulated driving environment. Peripheral targets varied across 20-60 deg eccentricity at 11 radial spokes. Three conditions assessed the effects of visual complexity and concurrent action on the size and shape of the FFOV: (1) with no background, (2) with driving background, and (3) with driving background and vehicle steering. The addition of visual complexity slowed task performance and reduced the FFOV size but did not change the baseline shape. In contrast, the addition of steering produced not only shrinkage of the FFOV, but also changes in the FFOV shape. Nonuniform performance decrements occurred in proximal regions used for the central task and for steering, independent of interference from context elements. Multifocal attention models should consider the role of action and account for nonhomogeneities in the distribution of attention.

Towards solving the hard problem of consciousness: The varieties of brain resonances and the conscious experiences that they support

The hard problem of consciousness is the problem of explaining how we experience qualia or phenomenal experiences, such as seeing, hearing, and feeling, and knowing what they are. To solve this problem, a theory of consciousness needs to link brain to mind by modeling how emergent properties of several brain mechanisms interacting together embody detailed properties of individual conscious psychological experiences. This article summarizes evidence that Adaptive Resonance Theory, or ART, accomplishes this goal. ART is a cognitive and neural theory of how advanced brains autonomously learn to attend, recognize, and predict objects and events in a changing world. ART has predicted that "all conscious states are resonant states" as part of its specification of mechanistic links between processes of consciousness, learning, expectation, attention, resonance, and synchrony. It hereby provides functional and mechanistic explanations of data ranging from individual spikes and their synchronization to the dynamics of conscious perceptual, cognitive, and cognitive-emotional experiences. ART has reached sufficient maturity to begin classifying the brain resonances that support conscious experiences of seeing, hearing, feeling, and knowing. Psychological and neurobiological data in both normal individuals and clinical patients are clarified by this classification. This analysis also explains why not all resonances become conscious, and why not all brain dynamics are resonant. The global organization of the brain into computationally complementary cortical processing streams (complementary computing), and the organization of the cerebral cortex into characteristic layers of cells (laminar computing), figure prominently in these explanations of conscious and unconscious processes. Alternative models of consciousness are also discussed.

Can (should) theories of crowding be unified?

Objects in clutter are difficult to recognize, a phenomenon known as crowding. There is little consensus on the underlying mechanisms of crowding, and a large number of models have been proposed. There have also been attempts at unifying the explanations of crowding under a single model, such as the weighted feature model of Harrison and Bex (2015) and the texture synthesis model of Rosenholtz and colleagues (Balas, Nakano, & Rosenholtz, 2009; Keshvari & Rosenholtz, 2016). The goal of this work was to test various models of crowding and to assess whether a unifying account can be developed. Adopting Harrison and Bex's (2015) experimental paradigm, we asked observers to report the orientation of two concentric C-stimuli. Contrary to the predictions of their model, observers' recognition accuracy was worse for the inner C-stimulus. In addition, we demonstrated that the stimulus paradigm used by Harrison and Bex has a crucial confounding factor, eccentricity, which limits its usage to a very narrow range of stimulus parameters. Nevertheless, reporting the orientations of both C-stimuli in this paradigm proved very useful in pitting different crowding models against each other. Specifically, we tested deterministic and probabilistic versions of averaging, substitution, and attentional resolution models as well as the texture synthesis model. None of the models alone was able to explain the entire set of data. Based on these findings, we discuss whether the explanations of crowding can (should) be unified.

Emergence of the ability to perceive dynamic events from still pictures in human infants

The ability to understand a visual scene depicted in a still image is among the abilities shared by all human beings. The aim of the present study was to examine when human infants acquire the ability to perceive the dynamic events depicted in still images (implied motion perception). To this end, we tested whether 4- and 5-month-old infants shifted their gaze toward the direction cued by a dynamic running action depicted in a still figure of a person. Results indicated that the 5- but not the 4-month-olds showed a significant gaze shift toward the direction implied by the posture of the runner (Experiments 1, 2, and 3b). Moreover, the older infants showed no significant gaze shift toward the direction cued by control stimuli, which depicted a figure in a non-dynamic standing posture (Experiment 1), an inverted running figure (Experiment 2), and some of the body parts of a running figure (Experiment 3a). These results suggest that only the older infants responded in the direction of the implied running action of the still figure; thus, implied motion perception emerges around 5 months of age in human infants.

Saccadic Adaptation Alters the Attentional Field

It is currently unknown whether changes to the oculomotor system can induce changes to the distribution of spatial attention around a fixated target. Previous studies have used perceptual performance tasks to show that adaptation of saccadic eye movements affects dynamic properties of visual attention, in particular, attentional shifts to a cued location. In this study, we examined the effects of saccadic adaptation on the static distribution of visual attention around fixation (attentional field). We used the classic double step adaptation procedure and a flanker task to test for differences in the attentional field after forward and backward adaptation. Reaction time (RT) measures revealed that the shape of the attentional field changed significantly after backward adaptation as shown through altered interference from distracters at different eccentricities but not after forward adaptation. This finding reveals that modification of saccadic amplitudes can affect metrics of not only dynamic properties of attention but also its static properties. A major implication is that the neural mechanisms underlying fundamental selection mechanisms and the oculomotor system can reweight each other.

Temporal dissociation between the focal and orientation components of spatial attention in central and peripheral vision

Selective attention, i.e. the ability to concentrate one's limited processing resources on one aspect of the environment, is a multifaceted concept that includes different processes like spatial attention and its subcomponents of orienting and focusing. Several studies, indeed, have shown that visual tasks performance is positively influenced not only by attracting attention to the target location (orientation component), but also by the adjustment of the size of the attentional window according to task demands (focal component). Nevertheless, the relative weight of the two components in central and peripheral vision has never been studied. We conducted two experiments to explore whether different components of spatial attention have different effects in central and peripheral vision. In order to do so, participants underwent either a detection (Experiment 1) or a discrimination (Experiment 2) task where different types of cues elicited different components of spatial attention: a red dot, a small square and a big square (an optimal stimulus for the orientation component, an optimal and a sub-optimal stimulus for the focal component respectively). Response times and cue-size effects indicated a stronger effect of the small square or of the dot in different conditions, suggesting the existence of a dissociation in terms of mechanisms between the focal and the orientation components of spatial attention. Specifically, we found that the orientation component was stronger in periphery, while the focal component was noticeable only in central vision and characterized by an exogenous nature.

Are Categorical Spatial Relations Encoded by Shifting Visual Attention between Objects?

Perceiving not just values, but relations between values, is critical to human cognition. We tested the predictions of a proposed mechanism for processing categorical spatial relations between two objects-the shift account of relation processing-which states that relations such as 'above' or 'below' are extracted by shifting visual attention upward or downward in space. If so, then shifts of attention should improve the representation of spatial relations, compared to a control condition of identity memory. Participants viewed a pair of briefly flashed objects and were then tested on either the relative spatial relation or identity of one of those objects. Using eye tracking to reveal participants' voluntary shifts of attention over time, we found that when initial fixation was on neither object, relational memory showed an absolute advantage for the object following an attention shift, while identity memory showed no advantage for either object. This result is consistent with the shift account of relation processing. When initial fixation began on one of the objects, identity memory strongly benefited this fixated object, while relational memory only showed a relative benefit for objects following an attention shift. This result is also consistent, although not as uniquely, with the shift account of relation processing. Taken together, we suggest that the attention shift account provides a mechanistic explanation for the overall results. This account can potentially serve as the common mechanism underlying both linguistic and perceptual representations of spatial relations.

The crowding factor method applied to parafoveal vision

Crowding increases with eccentricity and is most readily observed in the periphery. During natural, active vision, however, central vision plays an important role. Measures of critical distance to estimate crowding are difficult in central vision, as these distances are small. Any overlap of flankers with the target may create an overlay masking confound. The crowding factor method avoids this issue by simultaneously modulating target size and flanker distance and using a ratio to compare crowded to uncrowded conditions. This method was developed and applied in the periphery (Petrov & Meleshkevich, 2011b). In this work, we apply the method to characterize crowding in parafoveal vision (<3.5 visual degrees) with spatial uncertainty. We find that eccentricity and hemifield have less impact on crowding than in the periphery, yet radial/tangential asymmetries are clearly preserved. There are considerable idiosyncratic differences observed between participants. The crowding factor method provides a powerful tool for examining crowding in central and peripheral vision, which will be useful in future studies that seek to understand visual processing under natural, active viewing conditions.

Integrating oculomotor and perceptual training to induce a pseudofovea: A model system for studying central vision loss

People with a central scotoma often adopt an eccentric retinal location (Preferred Retinal Locus, PRL) for fixation. Here, we proposed a novel training paradigm as a model system to study the nature of the PRL formation and its impacts on visual function. The training paradigm was designed to effectively induce a PRL at any intended retinal location by integrating oculomotor control and pattern recognition. Using a gaze-contingent display, a simulated central scotoma was induced in eight normally sighted subjects. A subject's entire peripheral visual field was blurred, except for a small circular aperture with location randomly assigned to each subject (to the left, right, above, or below the scotoma). Under this viewing condition, subjects performed a demanding oculomotor and visual recognition task. Various visual functions were tested before and after training at both PRL and nonPRL locations. After 6-10 hr of the training, all subjects formed their PRL within the clear window. Both oculomotor control and visual recognition performance significantly improved. Moreover, there was considerable improvement at PRL location in high-level function, such as trigram letter-recognition, reading, and spatial attention, but not in low-level function, such as acuity and contrast sensitivity. Our results demonstrated that within a relatively short time, a PRL could be induced at any intended retinal location in normally-sighted subjects with a simulated scotoma. Our training paradigm might not only hold promise as a model system to study the dynamic nature of the PRL formation, but also serve as a rehabilitation regimen for individuals with central vision loss.

Eye fixation during multiple object attention is based on a representation of discrete spatial foci

We often look at and attend to several objects at once. How the brain determines where to point our eyes when we do this is poorly understood. Here we devised a novel paradigm to discriminate between different models of spatial selection guiding fixation. In contrast to standard static attentional tasks where the eye remains fixed at a predefined location, observers selected their own preferred fixation position while they tracked static targets that were arranged in specific geometric configurations and which changed identity over time. Fixations were best predicted by a representation of discrete spatial foci, not a polygonal grouping, simple 2-foci division of attention or a circular spotlight. Moreover, attentional performance was incompatible with serial selection. Together with previous studies, our findings are compatible with a view that attentional selection and fixation rely on shared spatial representations and suggest a more nuanced definition of overt vs. covert attention.