Differential effects of exogenous and endogenous attention on second-order texture contrast sensitivity

When temporal attention interacts with expectation

Temporal attention is voluntarily deployed at specific moments, whereas temporal expectation is deployed according to timing probabilities. When the target appears at an expected moment in a sequence, temporal attention improves performance at the attended moments, but the timing and the precision of the attentional window remain unknown. Here we independently and concurrently manipulated temporal attention-via behavioral relevance-and temporal expectation-via session-wise precision and trial-wise hazard rate-to investigate whether and how these mechanisms interact to improve perception. Our results reveal that temporal attention interacts with temporal expectation-the higher the precision, the stronger the attention benefit, but surprisingly this benefit decreased with delayed onset despite the increasing probability of stimulus appearance. When attention was suboptimally deployed to earlier than expected moments, it could not be reoriented to a later time point. These findings provide evidence that temporal attention and temporal expectation are different mechanisms, and highlight their interplay in optimizing visual performance.

Attention relieves visual crowding: Dissociable effects of peripheral and central cues

Visual crowding can be reduced when attention is directed to the target by peripheral cues. However, it is unclear whether central cues relieve visual crowding to the same extent as peripheral cues. In this study, we combined the Posner cueing task and the crowding task to investigate the effect of exogenous and endogenous attention on crowding. In Experiment 1, five different stimulus-onset asychronies (SOAs) between the cue and the target and a predictive validity of 100% were adopted. Both attentional cues were shown to significantly reduce the effect of visual crowding, but the peripheral cue was more effective than the central cue. Furthermore, peripheral cues started to relieve visual crowding at the shortest SOA (100 ms), whereas central cues worked only at later SOAs (275 ms or above). When the predictive validity of the cue was decreased to 70% in Experiment 2, similar results to Experiment 1 were found, but the valid cue was less effective in reducing crowding than that in Experiment 1. In Experiment 3, when the predictive validity was decreased to 50%, a valid peripheral cue improved performance but a valid central cue did not, suggesting that endogenous attention but not exogenous attention can be voluntarily controlled when the cues are not predictive of the target's location. These findings collectively suggest that both peripheral and central cues can alleviate crowding, but they differ in terms of strength, time dynamics, and flexibility of voluntary control.

Exogenous temporal attention varies with temporal uncertainty

Temporal attention is the selection and prioritization of information at a specific moment. Exogenous temporal attention is the automatic, stimulus driven deployment of attention. The benefits and costs of exogenous temporal attention on performance have not been isolated. Previous experimental designs have precluded distinguishing the effects of attention and expectation about stimulus timing. Here, we manipulated exogenous temporal attention and the uncertainty of stimulus timing independently and investigated visual performance at the attended and unattended moments with different levels of temporal uncertainty. In each trial, two Gabor patches were presented consecutively with a variable stimulus onset. To drive exogenous attention and test performance at attended and unattended moments, a task-irrelevant, brief cue was presented 100 ms before target onset, and an independent response cue was presented at the end of the trial. Exogenous temporal attention slightly improved accuracy, and the effects varied with temporal uncertainty, suggesting a possible interaction of temporal attention and expectations in time.

Effects of involuntary and voluntary attention on critical spacing of visual crowding

Visual spatial attention can be allocated in two distinct ways: one that is voluntarily directed to behaviorally relevant locations in the world, and one that is involuntarily captured by salient external stimuli. Precueing spatial attention has been shown to improve perceptual performance on a number of visual tasks. However, the effects of spatial attention on visual crowding, defined as the reduction in the ability to identify target objects in clutter, are far less clear. In this study, we used an anticueing paradigm to separately measure the effects of involuntary and voluntary spatial attention on a crowding task. Each trial began with a brief peripheral cue that predicted that the crowded target would appear on the opposite side of the screen 80% of the time and on the same side of the screen 20% of the time. Subjects performed an orientation discrimination task on a target Gabor patch that was flanked by other similar Gabor patches with independent random orientations. For trials with a short stimulus onset asynchrony between cue and target, involuntary capture of attention led to faster response times and smaller critical spacing when the target appeared on the cue side. For trials with a long stimulus onset asynchrony, voluntary allocation of attention led to faster reaction times but no significant effect on critical spacing when the target appeared on the opposite side to the cue. We additionally found that the magnitudes of these cueing effects of involuntary and voluntary attention were not strongly correlated across subjects for either reaction time or critical spacing.

Spatial attention in encoding letter combinations

Reading requires the correct identification of letters and letter positions within words. Selective attention is, therefore, required to select chunks of the text for sequential processing. Despite the extensive literature on visual attention, the well-known effects of spatial cues in simple perceptual tasks cannot inform us about the role of attention in a task as complex as reading. Here, we systematically manipulate spatial attention in a multi-letter processing task to understand the effects of spatial cues on letter encoding in typical adults. Overall, endogenous (voluntary) cue benefits were larger than exogenous (reflexive). We show that cue benefits are greater in the left than in the right visual field and larger for the most crowded letter positions. Endogenous valid cues reduced errors due to confusing letter positions more than misidentifications, specifically for the most crowded letter positions. Therefore, shifting endogenous attention along a line of text is likely an important mechanism to alleviate the effects of crowding on encoding letters within words. Our results help set the premise for constructing theories about how specific mechanisms of attention support reading development in children. Understanding the link between reading development and attention mechanisms has far-reaching implications for effectively addressing the needs of children with reading disabilities.

No effect of spatial attention on the processing of a motion ensemble: Evidence from Posner cueing

The formation of ensemble codes is an efficient means through which the visual system represents vast arrays of information. This has led to the claim that ensemble representations are formed with minimal reliance on attentional resources. However, evidence is mixed regarding the effects of attention on ensemble processing, and researchers do not always make it clear how attention is being manipulated by their paradigm of choice. In this study, we examined the effects of Posner cueing - a well-established method of manipulating spatial attention - on the processing of a global motion stimulus, a naturalistic ensemble that requires the pooling of local motion signals. In Experiment 1, using a centrally presented, predictive attentional cue, we found no effect of spatial attention on global motion performance: Accuracy in invalid trials, where attention was misdirected by the cue, did not differ from accuracy in valid trials, where attention was directed to the location of the motion stimulus. In Experiment 2, we maximized the potential for our paradigm to reveal any attentional effects on global motion processing by using a threshold-based measure of performance; however, despite this change, there was again no evidence of an attentional effect on performance. Together, our results show that the processing of a global motion stimulus is unaffected when spatial attention is misdirected, and speak to the efficiency with which such ensemble stimuli are processed.

Voluntary attention improves performance similarly around the visual field

Performance as a function of polar angle at isoeccentric locations across the visual field is known as a performance field (PF) and is characterized by two asymmetries: the HVA (horizontal-vertical anisotropy) and VMA (vertical meridian asymmetry). Exogenous (involuntary) spatial attention does not affect the shape of the PF, improving performance similarly across polar angle. Here we investigated whether endogenous (voluntary) spatial attention, a flexible mechanism, can attenuate these perceptual asymmetries. Twenty participants performed an orientation discrimination task while their endogenous attention was either directed to the target location or distributed across all possible locations. The effects of attention were assessed either using the same stimulus contrast across locations or equating difficulty across locations using individually titrated contrast thresholds. In both experiments, endogenous attention similarly improved performance at all locations, maintaining the canonical PF shape. Thus, despite its voluntary nature, like exogenous attention, endogenous attention cannot alleviate perceptual asymmetries at isoeccentric locations.

Inter-individual variations in internal noise predict the effects of spatial attention

Individuals differ considerably in the degree to which they benefit from attention allocation. Thus far, such individual differences were attributed to post-perceptual factors such as working-memory capacity. This study examined whether a perceptual factor - the level of internal noise - also contributes to this inter-individual variability in attentional effects. To that end, we estimated individual levels of internal noise from behavioral variability in an orientation discrimination task (with tilted gratings) using the double-pass procedure and the perceptual-template model. We also measured the effects of spatial attention in an acuity task: the participants reported the side of a square on which a small aperture appeared. Central arrows were used to engage sustained attention and peripheral cues to engage transient attention. We found reliable correlations between individual levels of internal noise and the effects of both types of attention, albeit of opposite directions: positive correlation with sustained attention and negative correlation with transient attention. These findings demonstrate that internal noise - a fundamental characteristic of visual perception - can predict individual differences in the effects of spatial attention, highlighting the intricate relations between perception and attention.

Contrasting effects of exogenous and endogenous attention on size perception

Although neuroimaging studies have shown that exogenous and endogenous attention are dissociable, only a few behavioural studies have explored their differential effects on visual sensitivity, and none have directly focused on visual appearance. Here, we show that exogenous and endogenous attention produces contrasting effects on apparent size. Participants performed a spatial pre-cueing comparative judgement task that had been frequently used to test the attentional effects on visual perception. The results showed that a smaller stimulus within the focus of exogenous attention was perceived to be equal in size as a larger unattended stimulus, whereas a larger stimulus within the focus of endogenous attention was perceived to be equal in size as a smaller unattended stimulus. In other words, exogenous attention increased the perceived size while endogenous attention decreased the perceived size. The contrasting effects may be attributed to the mechanism that exogenous attention favours parvocellular processing for which more neurons with smaller receptive fields (RFs) are activated for a given size, whereas endogenous attention favours magnocellular processing for which fewer neurons with larger RFs are activated. This finding shows that exogenous and endogenous attention acts differentially on size perception, and provides supportive evidence for the distinct mechanisms underlying the two types of attentional processing.

An image-computable model of how endogenous and exogenous attention differentially alter visual perception

Attention alters perception across the visual field. Typically, endogenous (voluntary) and exogenous (involuntary) attention similarly improve performance in many visual tasks, but they have differential effects in some tasks. Extant models of visual attention assume that the effects of these two types of attention are identical and consequently do not explain differences between them. Here, we develop a model of spatial resolution and attention that distinguishes between endogenous and exogenous attention. We focus on texture-based segmentation as a model system because it has revealed a clear dissociation between both attention types. For a texture for which performance peaks at parafoveal locations, endogenous attention improves performance across eccentricity, whereas exogenous attention improves performance where the resolution is low (peripheral locations) but impairs it where the resolution is high (foveal locations) for the scale of the texture. Our model emulates sensory encoding to segment figures from their background and predict behavioral performance. To explain attentional effects, endogenous and exogenous attention require separate operating regimes across visual detail (spatial frequency). Our model reproduces behavioral performance across several experiments and simultaneously resolves three unexplained phenomena: 1) the parafoveal advantage in segmentation, 2) the uniform improvements across eccentricity by endogenous attention, and 3) the peripheral improvements and foveal impairments by exogenous attention. Overall, we unveil a computational dissociation between each attention type and provide a generalizable framework for predicting their effects on perception across the visual field.

Time-dependent inhibition of covert shifts of attention

Visual transients can interrupt overt orienting by abolishing the execution of a planned eye movement due about 90 ms later, a phenomenon known as saccadic inhibition (SI). It is not known if the same inhibitory process might influence covert orienting in the absence of saccades, and consequently alter visual perception. In Experiment 1 (n = 14), we measured orientation discrimination during a covert orienting task in which an uninformative exogenous visual cue preceded the onset of an oriented probe by 140-290 ms. In half of the trials, the onset of the probe was accompanied by a brief irrelevant flash, a visual transient that would normally induce SI. We report a time-dependent inhibition of covert orienting in which the irrelevant flash impaired orientation discrimination accuracy when the probe followed the cue by 190 and 240 ms. The interference was more pronounced when the cue was incongruent with the probe location, suggesting an impact on the reorienting component of the attentional shift. In Experiment 2 (n = 12), we tested whether the inhibitory effect of the flash could occur within an earlier time range, or only within the later, reorienting range. We presented probes at congruent cue locations in a time window between 50 and 200 ms. Similar to Experiment 1, discrimination performance was altered at 200 ms after the cue. We suggest that covert attention may be susceptible to similar inhibitory mechanisms that generate SI, especially in later stages of attentional shifting (> 200 ms after a cue), typically associated with reorienting.

Desenvolvimento e validação de medidas psicofísicas de sensibilidade ao contraste de segunda-ordem

A medida de sensibilidade ao contraste (SC) de primeira ordem é frequentemente utilizada para avaliação da percepção espacial. Nosso objetivo foi desenvolver e validar um teste de SC de segunda ordem para aplicação clínica. Modificações metodológicas foram realizadas na rotina psicofísica para redução do tempo de testagem e no primeiro experimento validamos a nova metodologia. Em um segundo experimento, dezesseis participantes foram testados nas mesmas condições do primeiro experimento. As medidas de consistência interna por alfa de Cronbach foram robustas para a medida de primeira ordem sendo α= 0,788, segunda ordem por ruído branco α= 0,668 e por ruído rosa α= 0,717. O desenvolvimento e validação deste novo experimento para medidas de SC de segunda ordem permitirá avançar nos estudos dos mecanismos básicos da percepção de espaço para estímulos complexos, assim como a aplicação clínica em diversas doenças.

Differential impact of endogenous and exogenous attention on activity in human visual cortex

How do endogenous (voluntary) and exogenous (involuntary) attention modulate activity in visual cortex? Using ROI-based fMRI analysis, we measured fMRI activity for valid and invalid trials (target at cued/un-cued location, respectively), pre- or post-cueing endogenous or exogenous attention, while participants performed the same orientation discrimination task. We found stronger modulation in contralateral than ipsilateral visual regions, and higher activity in valid- than invalid-trials. For endogenous attention, modulation of stimulus-evoked activity due to a pre-cue increased along the visual hierarchy, but was constant due to a post-cue. For exogenous attention, modulation of stimulus-evoked activity due to a pre-cue was constant along the visual hierarchy, but was not modulated due to a post-cue. These findings reveal that endogenous and exogenous attention distinctly modulate activity in visuo-occipital areas during orienting and reorienting; endogenous attention facilitates both the encoding and the readout of visual information whereas exogenous attention only facilitates the encoding of information.

Differential impact of exogenous and endogenous attention on the contrast sensitivity function across eccentricity

Both exogenous and endogenous covert spatial attention enhance contrast sensitivity, a fundamental measure of visual function that depends substantially on the spatial frequency and eccentricity of a stimulus. Whether and how each type of attention systematically improves contrast sensitivity across spatial frequency and eccentricity are fundamental to our understanding of visual perception. Previous studies have assessed the effects of spatial attention at individual spatial frequencies and, separately, at different eccentricities, but this is the first study to do so parametrically with the same task and observers. Using an orientation discrimination task, we investigated the effect of attention on contrast sensitivity over a wide range of spatial frequencies and eccentricities. Targets were presented alone or among distractors to assess signal enhancement and distractor suppression mechanisms of spatial attention. At each eccentricity, we found that exogenous attention preferentially enhanced spatial frequencies higher than the peak frequency in the baseline condition. In contrast, endogenous attention similarly enhanced a broad range of lower and higher spatial frequencies. The presence or absence of distractors did not alter the pattern of enhancement by each type of attention. Our findings reveal how the two types of covert spatial attention differentially shape how we perceive basic visual dimensions across the visual field.

The coordinate system of endogenous spatial attention during smooth pursuit

A central question in vision is whether spatial attention is represented in an eye-centered (retinotopic) or world-centered (spatiotopic) reference-frame. Most previous studies on this question focused on how coordinates are modulated across saccades. In the present study, we investigated the reference-frame of attention across smooth pursuit eye-movements using a goal-directed saccade task. In two experiments, participants were asked to pursue a moving target while attending to one or two grating stimuli. On each trial, one stimulus was constant in its retinal position and the other was constant in its spatial position. Upon detection of a slight change in stimulus orientation, participants were asked to stop pursuing and perform a fast saccade toward the modified stimulus. In the focused attention condition, they attended one, predefined, stimulus, and in the divided attention condition they attended both. In Experiment 1 the angle of the orientation change marking the target event was constant across participants and conditions. In Experiment 2, the angle was individually adapted to equate performance across participants and conditions. Findings of the two experiments were consistent and showed that the enhancement of mean visual sensitivity in the focused relative to the divided attention condition was similar in magnitude for both retinotopic and spatiotopic targets. This indicates that during smooth pursuit, endogenous attention was proportionally divided between targets in retinotopic and spatiotopic frames of reference.

In search of exogenous feature-based attention

Visual attention prioritizes the processing of sensory information at specific spatial locations (spatial attention; SA) or with specific feature values (feature-based attention; FBA). SA is well characterized in terms of behavior, brain activity, and temporal dynamics-for both top-down (endogenous) and bottom-up (exogenous) spatial orienting. FBA has been thoroughly studied in terms of top-down endogenous orienting, but much less is known about the potential of bottom-up exogenous influences of FBA. Here, in four experiments, we adapted a procedure used in two previous studies that reported exogenous FBA effects, with the goal of replicating and expanding on these findings, especially regarding its temporal dynamics. Unlike the two previous studies, we did not find significant effects of exogenous FBA. This was true (1) whether accuracy or RT was prioritized as the main measure, (2) with precues presented peripherally or centrally, (3) with cue-to-stimulus ISIs of varying durations, (4) with four or eight possible target locations, (5) at different meridians, (6) with either brief or long stimulus presentations, (7) and with either fixation contingent or noncontingent stimulus displays. In the last experiment, a postexperiment participant questionnaire indicated that only a small subset of participants, who mistakenly believed the irrelevant color of the precue indicated which stimulus was the target, exhibited benefits for valid exogenous FBA precues. Overall, we conclude that with the protocol used in the studies reporting exogenous FBA, the exogenous stimulus-driven influence of FBA is elusive at best, and that FBA is primarily a top-down, goal-driven process.

Specific Visual Subregions of TPJ Mediate Reorienting of Spatial Attention

The temporo-parietal junction (TPJ) has been associated with various cognitive and social functions, and is critical for attentional reorienting. Attention affects early visual processing. Neuroimaging studies dealing with such processes have thus far concentrated on striate and extrastriate areas. Here, we investigated whether attention orienting or reorienting modulate activity in visually driven TPJ subregions. For each observer we identified 3 visually responsive subregions within TPJ: 2 bilateral (vTPJant and vTPJpost) and 1 right lateralized (vTPJcent). Cortical activity in these subregions was measured using fMRI while observers performed a 2-alternative forced-choice orientation discrimination task. Covert spatial endogenous (voluntary) or exogenous (involuntary) attention was manipulated using either a central or a peripheral cue with task, stimuli and observers constant. Both endogenous and exogenous attention increased activity for invalidly cued trials in right vTPJpost; only endogenous attention increased activity for invalidly cued trials in left vTPJpost and in right vTPJcent; and neither type of attention modulated either right or left vTPJant. These results demonstrate that vTPJpost and vTPJcent mediate the reorientation of covert attention to task relevant stimuli, thus playing a critical role in visual attention. These findings reveal a differential reorienting cortical response after observers' attention has been oriented to a given location voluntarily or involuntarily.

Spatial attention alters visual appearance

It is well established that attention improves performance on many visual tasks. However, for more than 100 years, psychologists, philosophers, and neurophysiologists have debated its phenomenology-whether attention actually changes one's subjective experience. Here, we show that it is possible to objectively and quantitatively investigate the effects of attention on subjective experience. First, we review evidence showing that attention alters the appearance of many static and dynamic basic visual dimensions, which mediate changes in appearance of higher-level perceptual aspects. Then, we summarize current views on how attention alters appearance. These findings have implications for our understanding of perception and attention, illustrating that attention affects not only how we perform in visual tasks, but actually alters our experience of the visual world.

Towards a Dynamic Exploration of Vision, Cognition and Emotion in Alcohol-Use Disorders

Abstract: Visuoperceptive impairments are among the most frequently reported deficits in alcohol-use disorders, but only very few studies have investigated their origin and interactions with other categories of dysfunctions. Besides, these deficits have generally been interpreted in a linear bottom-up perspective, which appears very restrictive with respect to the new models of vision developed in healthy populations. Indeed, new theories highlight the predictive nature of the visual system and demonstrate that it interacts with higher-level cognitive functions to generate top-down predictions. These models nota-bly posit that a fast but coarse visual analysis involving magnocellular pathways helps to compute heuristic guesses regard-ing the identity and affective value of inputs, which are used to facilitate conscious visual recognition. Building on these new proposals, the present review stresses the need to reconsider visual deficits in alcohol-use disorders as they might have cru-cial significance for core features of the pathology, such as attentional bias, loss of inhibitory control and emotion decoding impairments. Centrally, we suggest that individuals with severe alcohol-use disorders could present with magnocellular dam-age and we defend a dynamic explanation of the deficits. Rather than being restricted to high-level processes, deficits could start at early visual stages and then extend and potentially intensify during following steps due to reduced cerebral connec-tivity and dysfunctional cognitive/emotional regions. A new research agenda is specifically provided to test these hypotheses.

Attention enhances apparent perceptual organization

Perceptual organization and selective attention are two crucial processes that influence how we perceive visual information. The former structures complex visual inputs into coherent units, whereas the later selects relevant information. Attention and perceptual organization can modulate each other, affecting visual processing and performance in various tasks and conditions. Here, we tested whether attention can alter the way multiple elements appear to be perceptually organized. We manipulated covert spatial attention using a rapid serial visual presentation task, and measured perceptual organization of two multielements arrays organized by luminance similarity as rows or columns, at both the attended and unattended locations. We found that the apparent perceptual organization of the multielement arrays is intensified when attended and attenuated when unattended. We ruled out response bias as an alternative explanation. These findings reveal that attention enhances the appearance of perceptual organization, a midlevel vision process, altering the way we perceive our visual environment.

Endogenous spatial attention during perceptual learning facilitates location transfer

Covert attention and perceptual learning enhance perceptual performance. The relation between these two mechanisms is largely unknown. Previously, we showed that manipulating involuntary, exogenous spatial attention during training improved performance at trained and untrained locations, thus overcoming the typical location specificity. Notably, attention-induced transfer only occurred for high stimulus contrasts, at the upper asymptote of the psychometric function (i.e., via response gain). Here, we investigated whether and how voluntary, endogenous attention, the top-down and goal-based type of covert visual attention, influences perceptual learning. Twenty-six participants trained in an orientation discrimination task at two locations: half of participants received valid endogenous spatial precues (attention group), while the other half received neutral precues (neutral group). Before and after training, all participants were tested with neutral precues at two trained and two untrained locations. Within each session, stimulus contrast varied on a trial basis from very low (2%) to very high (64%). Performance was fit by a Weibull psychometric function separately for each day and location. Performance improved for both groups at the trained location, and unlike training with exogenous attention, at the threshold level (i.e., via contrast gain). The neutral group exhibited location specificity: Thresholds decreased at the trained locations, but not at the untrained locations. In contrast, participants in the attention group showed significant location transfer: Thresholds decreased to the same extent at both trained and untrained locations. These results indicate that, similar to exogenous spatial attention, endogenous spatial attention induces location transfer, but influences contrast gain instead of response gain.

Attention alters spatial resolution by modulating second-order processing

Endogenous and exogenous visuospatial attention both alter spatial resolution, but they operate via distinct mechanisms. In texture segmentation tasks, exogenous attention inflexibly increases resolution even when detrimental for the task at hand and does so by modulating second-order processing. Endogenous attention is more flexible and modulates resolution to benefit performance according to task demands, but it is unknown whether it also operates at the second-order level. To answer this question, we measured performance on a second-order texture segmentation task while independently manipulating endogenous and exogenous attention. Observers discriminated a second-order texture target at several eccentricities. We found that endogenous attention improved performance uniformly across eccentricity, suggesting a flexible mechanism that can increase or decrease resolution based on task demands. In contrast, exogenous attention improved performance in the periphery but impaired it at central retinal locations, consistent with an inflexible resolution enhancement. Our results reveal that endogenous and exogenous attention both alter spatial resolution by differentially modulating second-order processing.

How visual spatial attention alters perception

Visual attention is essential for visual perception. Spatial attention allows us to grant priority in processing and selectively process information at a given location. In this paper, I explain how two kinds of spatial attention: covert (allocated to the target location, without accompanying eye movements) and presaccadic (allocated to the location of the upcoming saccade's target) affect performance and alter appearance. First, I highlight some behavioral and neuroimaging research on covert attention, which alters performance and appearance in many basic visual tasks. Second, I review studies showing that presaccadic attention improves performance and alters appearance at the saccade target location. Further, these modulations change the processing of feature information automatically, even when it is detrimental to the task at hand. We propose that saccade preparation may support transsaccadic integration. Systematically investigating the common and differential characteristics of covert attention and presaccadic attention will continue to further our understanding of the pervasive selective processing of information, which enables us to make sense of our complex visual world.

On spatial attention and its field size on the repulsion effect

We investigated the attentional repulsion effect-stimuli appear displaced further away from attended locations-in three experiments: one with exogenous (involuntary) attention, and two with endogenous (voluntary) attention with different attention-field sizes. It has been proposed that differences in attention-field size can account for qualitative differences in neural responses elicited by attended stimuli. We used psychophysical comparative judgments and manipulated either exogenous attention via peripheral cues or endogenous attention via central cues and a demanding rapid serial visual presentation task. We manipulated the attention field size of endogenous attention by presenting streams of letters at two specific locations or at two of many possible locations during each block. We found a robust attentional repulsion effect in all three experiments: with endogenous and exogenous attention and with both attention-field sizes. These findings advance our understanding of the influence of spatial attention on the perception of visual space and help relate this repulsion effect to possible neurophysiological correlates.

Endogenous attention improves perception in amblyopic macaques

Amblyopia, a developmental disorder of vision, affects many aspects of spatial vision as well as motion perception and some cognitive skills. Current models of amblyopic vision based on known neurophysiological deficiencies have yet to provide an understanding of the wide range of amblyopic perceptual losses. Visual spatial attention is known to enhance performance in a variety of detection and discrimination tasks in visually typical humans and nonhuman primates. We investigated whether and how voluntary spatial attention affected psychophysical performance in amblyopic macaques. Full-contrast response functions for motion direction discrimination were measured for each eye of six monkeys: five amblyopic and one control. We assessed whether the effect of a valid spatial cue on performance corresponded to a change in contrast gain, a leftward shift of the function, or response gain, an upward scaling of the function. Our results showed that macaque amblyopes benefit from a valid spatial cue. Performance with amblyopic eyes viewing showed enhancement of both contrast and response gain whereas fellow and control eyes' performance showed only contrast gain. Reaction time analysis showed no speed accuracy trade-off in any case. The valid spatial cue improved contrast sensitivity for the amblyopic eye, effectively eliminating the amblyopic contrast sensitivity deficit. These results suggest that engaging endogenous spatial attention may confer substantial benefit to amblyopic vision.

Visual working memory capacity increases between ages 3 and 8 years, controlling for gains in attention, perception, and executive control

Research in adults has aimed to characterize constraints on the capacity of Visual Working Memory (VWM), in part because of the system's broader impacts throughout cognition. However, less is known about how VWM develops in childhood. Existing work has reached conflicting conclusions as to whether VWM storage capacity increases after infancy, and if so, when and by how much. One challenge is that previous studies did not control for developmental changes in attention and executive processing, which also may undergo improvement. We investigated the development of VWM storage capacity in children from 3 to 8 years of age, and in adults, while controlling for developmental change in exogenous and endogenous attention and executive control. Our results reveal that, when controlling for improvements in these abilities, VWM storage capacity increases across development and approaches adult-like levels between ages 6 and 8 years. More generally, this work highlights the value of estimating working memory, attention, perception, and decision-making components together.

Attention Modifies Spatial Resolution According to Task Demands

How does visual attention affect spatial resolution? In texture-segmentation tasks, exogenous (involuntary) attention automatically increases resolution at the attended location, which improves performance where resolution is too low (at the periphery) but impairs performance where resolution is already too high (at central locations). Conversely, endogenous (voluntary) attention improves performance at all eccentricities, which suggests a more flexible mechanism. Here, using selective adaptation to spatial frequency, we investigated the mechanism by which endogenous attention benefits performance in resolution tasks. Participants detected a texture target that could appear at several eccentricities. Adapting to high or low spatial frequencies selectively affected performance in a manner consistent with changes in resolution. Moreover, adapting to high, but not low, frequencies mitigated the attentional benefit at central locations where resolution was too high; this shows that attention can improve performance by decreasing resolution. Altogether, our results indicate that endogenous attention benefits performance by modulating the contribution of high-frequency information in order to flexibly adjust spatial resolution according to task demands.

Deconstructing Interocular Suppression: Attention and Divisive Normalization

In interocular suppression, a suprathreshold monocular target can be rendered invisible by a salient competitor stimulus presented in the other eye. Despite decades of research on interocular suppression and related phenomena (e.g., binocular rivalry, flash suppression, continuous flash suppression), the neural processing underlying interocular suppression is still unknown. We developed and tested a computational model of interocular suppression. The model included two processes that contributed to the strength of interocular suppression: divisive normalization and attentional modulation. According to the model, the salient competitor induced a stimulus-driven attentional modulation selective for the location and orientation of the competitor, thereby increasing the gain of neural responses to the competitor and reducing the gain of neural responses to the target. Additional suppression was induced by divisive normalization in the model, similar to other forms of visual masking. To test the model, we conducted psychophysics experiments in which both the size and the eye-of-origin of the competitor were manipulated. For small and medium competitors, behavioral performance was consonant with a change in the response gain of neurons that responded to the target. But large competitors induced a contrast-gain change, even when the competitor was split between the two eyes. The model correctly predicted these results and outperformed an alternative model in which the attentional modulation was eye specific. We conclude that both stimulus-driven attention (selective for location and feature) and divisive normalization contribute to interocular suppression.

In interocular suppression, a visible target presented in one eye can be rendered invisible by a competing image (the competitor) presented in the other eye. This phenomenon is a striking demonstration of the discrepancy between physical inputs to the visual system and perception, and it also allows neuroscientists to study how perceptual systems regulate competing information. Interocular suppression has been explained by mutually suppressive interactions (modeled by divisive normalization) between neurons that respond differentially to the two eyes. Attention, which selects relevant information in natural viewing condition, has also been found to play a role in interocular suppression. But the specific role of attentional modulation is still an open question. In this study, we proposed a computational model of interocular suppression integrating both attentional modulation and divisive normalization. By modeling the hypothetical neural responses and fitting the model to psychophysical data, we showed that interocular suppression involves an attentional modulation selective for the orientation of the competitor, and covering the spatial extent of the competitor. We conclude that both attention and divisive normalization contribute to interocular suppression, and that their impacts are distinguishable.

How Attention Affects Spatial Resolution

We summarize and discuss a series of psychophysical studies on the effects of spatial covert attention on spatial resolution, our ability to discriminate fine patterns. Heightened resolution is beneficial in most, but not all, visual tasks. We show how endogenous attention (voluntary, goal driven) and exogenous attention (involuntary, stimulus driven) affect performance on a variety of tasks mediated by spatial resolution, such as visual search, crowding, acuity, and texture segmentation. Exogenous attention is an automatic mechanism that increases resolution regardless of whether it helps or hinders performance. In contrast, endogenous attention flexibly adjusts resolution to optimize performance according to task demands. We illustrate how psychophysical studies can reveal the underlying mechanisms of these effects and allow us to draw linking hypotheses with known neurophysiological effects of attention.

The effects of stimulus-driven competition and task set on involuntary attention

It is well established that involuntary attention—the exogenous capture of attention by salient but task-irrelevant stimuli—can strongly modulate target detection and discrimination performance. There is an ongoing debate, however, about how involuntary attention affects target performance. Some studies suggest that it results from enhanced perception of the target, whereas others indicate instead that it affects decisional stages of information processing. From a review of these studies, we hypothesized that the presence of distractors and task sets are key factors in determining the effect of involuntary attention on target perception. Consistent with this hypothesis, here we found that noninformative cues summoning involuntary attention affected perceptual identification of a target when distractors were present. This cuing effect could not be attributed to reduced target location uncertainty or decision bias. The only condition under which involuntary attention improved target perception in the absence of distractors occurred when observers did not adopt a task set to focus attention on the target location. We conclude that the perceptual effects of involuntary attention depend on distractor interference and the adoption of a task set to resolve such stimulus competition.

Perceptual awareness and its neural basis: bridging experimental and theoretical paradigms

Understanding consciousness is a major scientific challenge of our times, and perceptual awareness is an integral part of that challenge. This Theme Issue aims to provide a timely focus on crucial insights from leading scientists on perceptual awareness and its neural basis. The issue refers to key research questions and findings in perceptual awareness research and aims to be a catalyst for further research, by bringing together the state-of-the-art. It shows how bridges are being built between empirical and theoretical research and proposes new directions for the study of multisensory awareness and the role of the states of the body therein. In this introduction, we highlight crucial problems that have characterized the development of the study of perceptual awareness. We then provide an overview of major experimental and theoretical paradigms related to perceptual awareness and its neural basis. Finally, we present an overview of the Theme Issue, with reference to the contributed articles and their relationships.

Angular declination and the dynamic perception of egocentric distance

The extraction of the distance between an object and an observer is fast when angular declination is informative, as it is with targets placed on the ground. To what extent does angular declination drive performance when viewing time is limited? Participants judged target distances in a real-world environment with viewing durations ranging from 36-220 ms. An important role for angular declination was supported by experiments showing that the cue provides information about egocentric distance even on the very first glimpse, and that it supports a sensitive response to distance in the absence of other useful cues. Performance was better at 220-ms viewing durations than for briefer glimpses, suggesting that the perception of distance is dynamic even within the time frame of a typical eye fixation. Critically, performance in limited viewing trials was better when preceded by a 15-s preview of the room without a designated target. The results indicate that the perception of distance is powerfully shaped by memory from prior visual experience with the scene. A theoretical framework for the dynamic perception of distance is presented.

The attentional effects of single cues and color singletons on visual sensitivity

Sudden changes in the visual periphery can automatically draw attention to their locations. For example, the brief flash of a single object (a "cue") rapidly enhances contrast sensitivity for subsequent stimuli in its vicinity. Feature singletons (e.g., a red circle among green circles) can also capture attention in a variety of tasks. Here, we evaluate whether a peripheral cue that enhances contrast sensitivity when it appears alone has a similar effect when it appears as a color singleton, with the same stimuli and task. In four experiments we asked observers to report the orientation of a target Gabor stimulus, which was preceded by an uninformative cue array consisting either of a single disk or of 16 disks containing a color or luminance singleton. Accuracy was higher and contrast thresholds lower when the single cue appeared at or near the target's location, compared with farther away. The color singleton also modulated performance but to a lesser degree and only when it appeared exactly at the target's location. Thus, this is the first study to demonstrate that cueing by color singletons, like single cues, can enhance sensory signals at an early stage of processing.

Perceptual learning of second order cues for layer decomposition

Luminance variations are ambiguous: they can signal changes in surface reflectance or changes in illumination. Layer decomposition-the process of distinguishing between reflectance and illumination changes-is supported by a range of secondary cues including colour and texture. For an illuminated corrugated, textured surface the shading pattern comprises modulations of luminance (first order, LM) and local luminance amplitude (second-order, AM). The phase relationship between these two signals enables layer decomposition, predicts the perception of reflectance and illumination changes, and has been modelled based on early, fast, feed-forward visual processing (Schofield et al., 2010). However, while inexperienced viewers appreciate this scission at long presentation times, they cannot do so for short presentation durations (250 ms). This might suggest the action of slower, higher-level mechanisms. Here we consider how training attenuates this delay, and whether the resultant learning occurs at a perceptual level. We trained observers to discriminate the components of plaid stimuli that mixed in-phase and anti-phase LM/AM signals over a period of 5 days. After training, the strength of the AM signal needed to differentiate the plaid components fell dramatically, indicating learning. We tested for transfer of learning using stimuli with different spatial frequencies, in-plane orientations, and acutely angled plaids. We report that learning transfers only partially when the stimuli are changed, suggesting that benefits accrue from tuning specific mechanisms, rather than general interpretative processes. We suggest that the mechanisms which support layer decomposition using second-order cues are relatively early, and not inherently slow.