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Classic change blindness is the phenomenon where seemingly obvious changes that coincide with visual disruptions (such as blinks or brief blanks) go unnoticed by an attentive observer. Some early work into the causes of classic change blindness suggested that any pre-change stimulus representation is overwritten by a representation of the altered post-change stimulus, preventing change detection. However, recent work revealed that, even when observers do maintain memory representations of both the pre- and post-change stimulus states, they can still miss the change, suggesting that change blindness can also arise from a failure to compare the stored representations. Here, we studied slow change blindness, a related phenomenon that occurs even in the absence of visual disruptions when the change occurs sufficiently slowly, to determine whether it could be explained by conclusions from classic change blindness. Across three different slow change blindness experiments we found that observers who consistently failed to notice the change had access to at least two memory representations of the changing display. One representation was precise but short lived: a detailed representation of the more recent stimulus states, but fragile. The other representation lasted longer but was fairly general: stable but too coarse to differentiate the various stages of the change. These findings suggest that, although multiple representations are formed, the failure to compare hypotheses might not explain slow change blindness; even if a comparison were made, the representations would be too sparse (longer term stores) or too fragile (short-lived stores) for such comparison to inform about the change.

Change blindness is the phenomenon that occurs when an observer fails to notice what would seem to be obvious changes in the features of a visual stimulus. Researchers can induce this experimentally by including visual disruptions (such as brief blanks) that coincide with the changes in question. However, change blindness can also occur in the absence of these disruptions if a change occurs sufficiently slowly. This "slow" or "gradual" change blindness phenomenon has not been extensively researched. Two plausible practical reasons for this are that there are few slow-change stimuli available, and that it is difficult to collect trial-specific responses without affecting expectations on later trials. Here, we describe a novel, semi-automatic procedure for quickly generating many slow-change stimuli. This procedure creates stimuli that have been specifically designed to allow assessment of change blindness on individual trials without influencing subsequent trials. We include the results of three validation experiments that demonstrate that these stimuli are effective and suitable for use in systematic studies of slow change blindness., Competing Interests: The authors have no competing interests to declare that are relevant to the content of this article., (© The Author(s) 2024. Published by Oxford University Press.)

An altered use of context and experience to interpret incoming information has been posited to explain schizophrenia symptoms. The visual system can serve as a model system for examining how context and experience guide perception and the neural mechanisms underlying putative alterations. The influence of prior experience on current perception is evident in visual aftereffects, the perception of the "opposite" of a previously viewed stimulus. Aftereffects are associated with neural adaptation and concomitant change in strength of lateral inhibitory connections in visually responsive neurons. In a previous study, we observed stronger aftereffects related to orientation (tilt aftereffects) but not luminance (negative afterimages) in individuals diagnosed with schizophrenia, which we interpreted as potentially suggesting altered cortical (but not subcortical) adaptability and local changes in excitatory-inhibitory interactions. Here, we tested whether stronger tilt aftereffects were specific to individuals with schizophrenia or extended to individuals with bipolar disorder. We measured tilt aftereffects and negative afterimages in 32 individuals with bipolar disorder, and compared aftereffect strength to a previously reported group of 36 individuals with schizophrenia and 22 healthy controls. We observed stronger tilt aftereffects, but not negative afterimages, in individuals with schizophrenia as compared to both controls and individuals with bipolar disorder, who did not differ from each other. These results mitigate concerns that stronger tilt aftereffects in schizophrenia are a consequence of medication or of the psychosocial consequences of a severe mental illness., Competing Interests: Declaration of competing interest No authors have any potential conflicts of interest to disclose., (Copyright © 2023 Elsevier B.V. All rights reserved.)

The self-generation effect refers to the finding that people's memory for information tends to be better when they generate it themselves. Counterintuitively, when proofreading, this effect may make it more difficult to detect mistakes in one's own writing than in others' writing. We investigated the self-generation effect and sources of individual differences in proofreading performance in two eye-tracking experiments. Experiment 1 failed to reveal a self-generation effect. Experiment 2 used a studying manipulation to induce overfamiliarity for self-generated text, revealing a weak but non-significant self-generation effect. Overall, word errors (i.e., wrong words) were detected less often than non-word errors (i.e., misspellings), and function word errors were detected less often than content word errors. Fluid intelligence predicted proofreading performance, whereas reading comprehension, working memory capacity, processing speed, and indicators of miserly cognitive processing did not. Students who made more text fixations and spent more time proofreading detected more errors., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

When faced with ambiguous visual input, observers may experience various perceptual interpretations of the same input. Indeed, such input can cause perception to unpredictably switch between interpretations over time. Theories of such so-called multistable perception broadly fall into two categories: top-down theories that emphasize dependence on higher-level cognitive factors such as knowledge, and bottom-up theories that suggest more vital involvement of aspects of lower-order information processing such as adaptation in the visual system. Most present-day accounts hold that both factors play a role, so that perceptual reversals arise inevitably due to factors like adaptation, yet can be delayed or hastened by higher-level cognitive influences. We revisited a body of work that shows the occurrence of perceptual reversals to depend dramatically on the observer's knowledge that the input is, indeed, ambiguous: without such knowledge many observers in that work did not experience any reversals, in apparent conflict with the idea that reversals are inevitable. We used an ambiguous animation that allowed subjects to report perceptual reversals without realizing the ambiguity. We found that subjects who were aware of the animation's ambiguity reported slightly more perceptual reversals than uninformed subjects, but that this between-group difference was small, and was overshadowed by inter-observer variability within each group. These findings suggest that knowledge of ambiguity can influence perception of ambiguous stimuli, but only mildly, in keeping with most present-day accounts. We discuss potential explanations for the discrepancy with the earlier work., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Two largely separate lines of research have documented altered pupillary dynamics in individuals diagnosed with schizophrenia. An older set of studies has demonstrated reductions in the pupillary light reflex (PLR) in individuals with schizophrenia; however, clinical and cognitive correlates of this blunted PLR have been relatively unexplored. More recently, a large body of work has demonstrated reductions in pupillary dilation in response to cognitive demands in individuals with schizophrenia, and the degree of this blunted pupil dilation has been related to more severe cognitive deficits and motivational negative symptoms. These clinically relevant alterations in the cognitive modulation of pupil size have been interpreted as reflecting insufficient information processing resources or inappropriate effort allocation. To begin to bridge these two lines of work, we investigated the PLR in 34 individuals with schizophrenia and 30 healthy controls and related the amplitude of the PLR to motivational negative symptoms and cognitive performance. Consistent with prior work, we found that the PLR was reduced in individuals with schizophrenia, and furthermore, that these measurements were highly reliable across individuals. Blunted constriction was associated with more severe motivational negative symptoms and poorer working memory among individuals with schizophrenia. These observed correlates provide a bridge between older literature documenting an altered PLR and more recent work reporting associations between negative symptoms, cognition, and blunted pupillary dilation in response to cognitive demands in individuals with schizophrenia. We provide possible mechanistic interpretations of our data and consider a parsimonious explanation for reduced cognitive- and light-related modulation of pupil size., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Some images evoke bistable percepts: two different visual experiences seen in alternation while continuously viewing an unchanged stimulus. The Necker Cube and Rubin's Vase are classic examples, each of which gives alternating percepts of different shapes. Other bistable percepts are alternating colors or directions of motion. Although stimuli that result in salient bistability are rare and sometimes cleverly constructed to emphasize ambiguity, they have been influential for over 150 years, since the work of von Helmholtz, who considered them to be evidence for perceptual visual processes that interpret retinal stimuli. While bistability in natural viewing is uncommon, the main point of this review is that implicit ambiguity in visual neural representations is pervasive. Resolving ambiguity, therefore, is a fundamental and ubiquitous process of vision that routinely affects what we see, not an oddity arising from cleverly crafted images. This review focuses on the causes of widespread ambiguity, historical perspectives on it, and modern knowledge and theory about resolving it.

The pupil provides a rich, non-invasive measure of the neural bases of perception and cognition and has been of particular value in uncovering the role of arousal-linked neuromodulation, which alters both cortical processing and pupil size. But pupil size is subject to a multitude of influences, which complicates unique interpretation. We measured pupils of observers experiencing perceptual multistability-an ever-changing subjective percept in the face of unchanging but inconclusive sensory input. In separate conditions, the endogenously generated perceptual changes were either task-relevant or not, allowing a separation between perception-related and task-related pupil signals. Perceptual changes were marked by a complex pupil response that could be decomposed into two components: a dilation tied to task execution and plausibly indicative of an arousal-linked noradrenaline surge, and an overlapping constriction tied to the perceptual transient and plausibly a marker of altered visual cortical representation. Constriction, but not dilation, amplitude systematically depended on the time interval between perceptual changes, possibly providing an overt index of neural adaptation. These results show that the pupil provides a simultaneous reading on interacting but dissociable neural processes during perceptual multistability, and suggest that arousal-linked neuromodulator release shapes action but not perception in these circumstances., Competing Interests: JB, Gd, MW, AD, TK No competing interests declared, (© 2021, Brascamp et al.)

There are clear benefits to using an online environment for human subjects' research, for instance, rapid data collection and access to a diverse body of potential participants. One distinct drawback of online environments as compared to laboratory environments is the relative lack of control over experiment conditions. For research into human vision, a specific concern is the relative lack of control over angular stimulus dimension in an online setting. This paper examines three approaches to estimating a participant's viewing distance online, and quantifies the magnitude of the error in angular stimulus size associated with each method. For each method, the average expected error is smaller than 20% of the intended stimulus size, and for the best method it is close to 10%. This paper provides a discussion of the benefits and drawbacks of each of the three methods, as well as parameter values and computer code that will facilitate the use of these methods in future online studies.

Aerobic fitness is consistently and robustly associated with superior performance on assessments of cognitive control. One potential mechanism underlying this phenomenon is activation of the locus-coeruleus. Specifically, individuals with greater aerobic fitness may be better able to sustain engagement in a cognitively demanding task via a superior ability to meet the metabolic demands of this neural system. Accordingly, the present investigation examined 1) the relationship between aerobic fitness and phasic activation of the locus-coeruleus (indexed using pupillometry) and 2) the potential mediating influence of locus-coeruleus activity on the relationship between aerobic fitness and cognitive task performance. Participants performed an inhibition task while their pupillary responses were measured using an infrared eye tracker. A VO 2max test was then performed to determine individuals' aerobic fitness levels. Consistent with previous research, higher levels of aerobic fitness were related to shorter reaction time. However, phasic activity of the locus-coeruleus did not mediate this relationship - nor did it relate to aerobic fitness level. These results suggest that aerobic fitness does not relate to differences in locus-coeruleus activity in the context of cognitive control in college-aged adults., (Copyright © 2021 Elsevier B.V. All rights reserved.)

When observers view a perceptually bistable stimulus, their perception changes stochastically. Various studies have shown across-observer correlations in the percept durations for different bistable stimuli including binocular rivalry stimuli and bistable moving plaids. Previous work on binocular rivalry posits that neural inhibition in the visual hierarchy is a factor involved in the perceptual fluctuations in that paradigm. Here, in order to investigate whether between-observer variability in cortical inhibition underlies correlated percept durations between binocular rivalry and bistable moving plaid perception, we used center-surround suppression as a behavioral measure of cortical inhibition. We recruited 217 participants in a test battery that included bistable perception paradigms as well as a center-surround suppression paradigm. While we were able to successfully replicate the correlations between binocular rivalry and bistable moving plaid perception, we did not find a correlation between center-surround suppression strength and percept durations for any form of bistable perception. Moreover, the results from a mediation analysis indicate that center-surround suppression is not the mediating factor in the correlation between binocular rivalry and bistable moving plaids. These results do not support the idea that cortical inhibition can explain the between-observer correlation in mean percept duration between binocular rivalry and bistable moving plaid perception., Competing Interests: Declaration of Conflicting Interests: The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article., (© The Author(s) 2021.)

Individuals with schizophrenia may fail to appropriately use temporal context and apply past environmental regularities to the interpretation of incoming sensory information. Here we use the visual system as a test bed for investigating how prior experience shapes perception in individuals with schizophrenia. Specifically, we use visual aftereffects, illusory percepts resulting from prior exposure to visual input, to measure the influence of prior events on current processing. At a neural level, visual aftereffects arise due to attenuation in the responses of neurons that code the features of the prior stimulus (neuronal adaptation) and subsequent disinhibition of neurons signaling activity at the opposite end of the feature dimension. In the current study, we measured tilt aftereffects and negative afterimages, 2 types of aftereffects that reflect, respectively, adaptation of cortical orientation-coding neurons and adaptation of subcortical and retinal luminance-coding cells in persons with schizophrenia (PSZ; n = 36) and demographically matched healthy controls (HC; n = 22). We observed stronger tilt aftereffects in PSZ compared to HC, but no difference in negative afterimages. Stronger tilt aftereffects were related to more severe negative symptoms. These data suggest oversensitivity to recent regularities, in the form of stronger visual adaptation, at cortical, but not subcortical, levels in schizophrenia. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Binocular rivalry suppression is thought to necessarily require local interocular conflict: the presence of incompatible image elements, such as orthogonal contours, in retinally corresponding regions of two monocular displays. Whether suppression can also be driven by conflict at the level of spatially nonlocal surface or object representations is unclear. Here, we kept local contour conflict constant while varying global conflict, defined by the gestalt formed by the two monocular displays. Specifically, each eye was presented with a grid of image elements (crosses or plusses), placed such that the two eyes' individual grid elements did not directly overlap but the grids as a whole did. In a "shared motion" condition, all elements moved in unison, inviting a gestalt made up of all elements across both eyes; in a "different motions" condition, the elements' trajectories differed between eyes, inviting a gestalt of two overlapping surfaces, each associated with one eye. Perceptual disappearances of image elements occurred more readily in the different motions condition, an observation that could not be explained by any between-condition differences in local contour conflict. In a second experiment, we furthermore established that, whereas perceptual disappearances in the shared motion condition tended to involve a single element at a time, in the different motions condition, multiple elements belonging to the same gestalt often disappeared together. These findings indicate that, even though binocular rivalry may critically rely on inhibition due to locally incompatible image elements, this inhibition also depends on the global gestalt to which these elements contribute.

Research in radiology and visual cognition suggest that finding one target during visual search may result in increased misses for a second target, an effect known as subsequent search misses (SSM). Here, we demonstrate that the common method of calculating second-target detection performance is biased and could produce spurious SSM effects. We describe the source of that bias and document factors that influence its magnitude. We use a modification of signal-detection theory to develop a novel, unbiased method of calculating the expected value for dual-target performance under the null hypothesis. We then apply our novel method to two of our data sets that showed modest SSM effects when calculated in the traditional manner. Our correction reduced the effect size to the point that there was no longer a significant SSM effect. We then applied our method to a published data set that had a larger effect size when calculated using the traditional calculation as well as when using an alternative calculation that was recently proposed to account for biases in the traditional method. We find that both the traditional method and the recently proposed alternative substantially overestimate the magnitude of the SSM effect in these data, but a significant SSM effect persisted even with our calculation. We recommend that future SSM studies use our method to ensure accurate effect-size estimates, and suggest that the method be applied to reanalyze published results, particularly those with small effect sizes, to rule out the possibility that they were spurious.

Priming of attention shifts involves the reduction in search RTs that occurs when target location or target features repeat. We used functional magnetic resonance imaging to investigate the neural basis of such attentional priming, specifically focusing on its temporal characteristics over trial sequences. We first replicated earlier findings by showing that repetition of target color and of target location from the immediately preceding trial both result in reduced blood oxygen level-dependent (BOLD) signals in a cortical network that encompasses occipital, parietal, and frontal cortices: lag-1 repetition suppression. While such lag-1 suppression can have a number of explanations, behaviorally, the influence of attentional priming extends further, with the influence of past search trials gradually decaying across multiple subsequent trials. Our results reveal that the same regions within the frontoparietal network that show lag-1 suppression, also show longer term BOLD reductions that diminish over the course of several trial presentations, keeping pace with the decaying behavioral influence of past target properties across trials. This distinct parallel between the across-trial patterns of cortical BOLD and search RT reductions, provides strong evidence that these cortical areas play a key role in attentional priming., (© The Author(s) 2019. Published by Oxford University Press.)

Although binocular rivalry is different from other perceptually bistable phenomena in requiring interocular conflict, it also shares numerous features with those phenomena. This raises the question of whether, and to what extent, the neural bases of binocular rivalry and other bistable phenomena overlap. Here we examine this question using an individual-differences approach. In a first experiment, observers reported perception during four binocular rivalry tasks that differed in the features and retinal locations of the stimuli used. Perceptual dominance durations were highly correlated when compared between stimuli that differed in location only. Correlations were substantially weaker, however, when comparing stimuli comprised of different features. Thus, individual differences in binocular-rivalry perception partly reflect a feature-specific factor that is not shared among all variants of binocular rivalry. Our second experiment again included several binocular rivalry variants, but also a different form of bistability: moving plaid rivalry. Correlations in dominance durations between binocular rivalry variants that differed in feature content were again modest. Moreover, and surprisingly, correlations between binocular rivalry and moving plaid rivalry were of similar magnitude. This indicates a second, more general, factor underlying individual differences in binocular rivalry perception: one that is shared across binocular rivalry and moving plaid rivalry. We propose that the first, feature-specific factor corresponds to feature-tuned mechanisms involved in the treatment of interocular conflict, whereas the second, general factor corresponds to mechanisms involved in representing surfaces. These latter mechanisms would operate at a binocular level and be central to both binocular rivalry and other forms of bistability.

When the two eyes' processing streams meet in visual cortex, two things can happen: sufficiently similar monocular inputs are combined into a fused representation, whereas markedly different inputs engage in rivalry. Interestingly, the emergence of rivalry appears to require attention. Withdrawing attention causes the alternating monocular dominance that characterizes rivalry to cease, apparently allowing both monocular signals to be processed simultaneously. What happens to these signals in this case, however, remains something of a mystery; are they fused into an integrated representation? In a set of experiments, we show this not to be the case: visual aftereffects are consistent with the simultaneous yet separate presence of two segregated monocular representations, rather than a joint representation. These results provide evidence that dichoptic vision without attention prompts a third and previously unknown mode, where both eyes' inputs receive equal processing, but escape interocular fusion.

Single bouts of exercise have been observed to enhance numerous domains of cognition including inhibitory aspects of cognitive control and neuroelectric indices of attention. Given that the locus-coeruleus norepinephrine system regulates alertness and attention, this system may underlie these exercise-induced enhancements. The present study used pupillometry to examine the extent to which a single bout of exercise induces changes in aspects of locus-coeruleus activation, as well as the extent to which changes in locus-coeruleus activation were associated with changes in inhibition and neuroelectric indices of attention. Using a within-participants crossover design, behavioral, neuroelectric, and pupillometric measures were assessed in response to an inhibitory control task before and after 20-min of either aerobic exercise or an active-control condition during two separate, counterbalanced sessions. The aerobic exercise condition consisted of walking/jogging on a motor driven treadmill at an intensity of approximately 70% of age-predicted maximum heart rate. The active control condition consisted of walking on the treadmill at 0.5 mph and 0% grade. Replicating prior findings, enhancements in both reaction time and neuroelectric indices of attention were observed in response to the exercise condition. However, neither the exercise nor the active control conditions were observed to induce changes in activation of the locus-coeruleus as indexed by pupil size, and changes in activation of the locus-coeruleus were not associated with exercise-induced changes in inhibition and neuroelectric indices of attention. Accordingly, these findings provide evidence to suggest that activation of the locus-coeruleus is not a mechanism underlying exercise-induced enhancements in cognition., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Psychosis-a cardinal symptom of schizophrenia-has been associated with a failure to appropriately create or use stored regularities about past states of the world to guide the interpretation of incoming information, which leads to abnormal perceptions and beliefs. The visual system provides a test bed for investigating the role of prior experience and prediction, as accumulated knowledge of the world informs our current perception. More specifically, the strength of visual aftereffects, illusory percepts that arise after prolonged viewing of a visual stimulus, can serve as a valuable measure of the influence of prior experience on current visual processing. In this paper, we review findings from a largely older body of work on visual aftereffects in schizophrenia, attempt to reconcile discrepant findings, highlight the role of antipsychotic medication, consider mechanistic interpretations for behavioral effects, and propose directions for future research., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Abnormalities in synaptic plasticity are argued to underlie the neural dysconnectivity observed in schizophrenia. One way to measure synaptic plasticity is through sensory adaptation, whereby sensory neurons exhibit reduced sensitivity after sustained stimulus exposure. Evidence for decreased adaptation in individuals with schizophrenia is currently inconclusive, possibly due to heterogeneity in clinical and medication status across samples. Here we circumvent these confounds by examining whether altered adaptation is represented sub-clinically in the general population. To test this we used three paradigms from visual perception research that provide a precise and non-invasive index of adaptation in the visual system. Two paradigms involve a class of illusory percepts termed visual aftereffects. The third relies on a visual phenomenon termed binocular rivalry, where incompatible stimuli are presented to the two eyes and observers alternate between perceiving exclusively one stimulus or a combination of the two (i.e. mixed perception). We analyzed the strength and dynamics of visual adaptation in these paradigms, in relation to schizotypy. Our results showed that increased schizotypal traits were related to reduced orientation, but not luminance, aftereffect strength (Exp. 1). Further, increased schizotypy was related to a greater proportion of mixed perception during binocular rivalry (Exp. 1 and 2). Given that visual adaption is well understood at cellular and computational levels, our data suggest that short-term plasticity in the visual system can provide important information about the disease mechanisms of schizophrenia., (Copyright © 2018 Elsevier B.V. All rights reserved.)

In primates, the two eyes offer substantially overlapping views of the world. The information they provide is merged into a single, integrated, representation in visual cortex. New evidence changes long-standing ideas about how and where in the processing stream this happens., (Published by Elsevier Ltd.)

During visual search, selecting a target facilitates search for similar targets in the future, known as search priming. During bistable perception, in turn, perceiving one interpretation facilitates perception of the same interpretation in the future, a form of sensory memory. Previously, we investigated the relation between these history effects by asking: can visual search influence perception of a subsequent ambiguous display and can perception of an ambiguous display influence subsequent visual search? We found no evidence for such influences, however. Here, we investigated one potential factor that might have prevented such influences from arising: lack of retinal overlap between the ambiguous stimulus and the search array items. In the present work, we therefore interleaved presentations of an ambiguous stimulus with search trials in which the target or distractor occupied the same retinal location as the ambiguous stimulus. Nevertheless, we again found no evidence for influences of visual search on bistable perception, thus demonstrating no close relation between search priming and sensory memory. We did, however, find that visual search items primed perception of a subsequent ambiguous stimulus at the same retinal location, regardless of whether they were a target or a distractor item: a form of perceptual priming. Interestingly, the strengths of search priming and this perceptual priming were correlated on a trial-to-trial basis, suggesting that a common underlying factor influences both.

Simultaneously showing an observer two incompatible displays, one to each eye, causes binocular rivalry, during which the observer regularly switches between perceiving one eye's display and perceiving the other. Observers differ in the rate of this perceptual cycle, and these individual differences have been reported to correlate with differences in the perceptual switch rate for other bistable perception phenomena. Identifying which psychological or neural factors explain this variability can help clarify the mechanisms underlying binocular rivalry and of bistable perception generally. Motivated by the prominent theory that perceptual switches during binocular rivalry are brought about by neural adaptation, we investigated whether perceptual switch rates are correlated with the strength of neural adaptation, indexed by visual aftereffects. We found no compelling evidence for such correlations. Moreover, we did not corroborate previous findings that switch rates are correlated between binocular rivalry and other forms of bistable perception. This latter nonreplication prompted us to perform a meta-analysis of existing research into correlations among forms of bistable perception, which revealed that evidence for such correlations is much weaker than is generally believed. By showing no common factor linking individual differences in binocular rivalry and in our other paradigms, these results fit well with other work that has shown such common factors to be rare among visual phenomena generally.

Impairments in cognitive control-the ability to exert control over thoughts and actions and respond flexibly to the environment-are well-documented in schizophrenia. However, the degree to which experimental task performance reflects true cognitive control impairments or more general alterations in effort, arousal and/or task preparedness is unclear. Pupillary responses can provide insight into these latter factors, as the pupil dilates with degree of cognitive effort and response preparation. In the current study, 16 medicated outpatients with schizophrenia (SZP) and 18 healthy controls performed a task that measures the ability to reactively inhibit and modify a planned action-the double-step task. In this task, participants were required to make a saccade to a visual target. Infrequently, the target jumped to a new location and participants were instructed to rapidly inhibit and change their eye movement plan. Applying a race model of performance, we have previously shown that SZP require more time to inhibit a planned action. In the current analysis, we measured pupil dilation associated with task preparation and found that SZP had a shallower increase in pupil size prior to the onset of the trial. Additionally, reduced magnitude of the pupil response was associated with negative symptom severity in patients. Based on primate neurophysiology and cognitive neuroscience work, we suggest that this blunted pupillary response may reflect abnormalities in a general orienting response or reduced motivational significance of a cue signifying the onset of a preparatory period and that these abnormalities might share an autonomic basis with negative symptoms., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Human visual cortex does not represent the whole visual field with the same detail. Changes in receptive field size, population receptive field (pRF) size and cortical magnification factor (CMF) with eccentricity are well established, and associated with changes in visual acuity with eccentricity. Visual acuity also changes across polar angle. However, it remains unclear how RF size, pRF size and CMF change across polar angle. Here, we examine differences in pRF size and CMF across polar angle in V1, V2 and V3 using pRF modeling of human fMRI data. In these visual field maps, we find smaller pRFs and larger CMFs in horizontal (left and right) than vertical (upper and lower) visual field quadrants. Differences increase with eccentricity, approximately in proportion to average pRF size and CMF. Similarly, we find larger CMFs in the lower than upper quadrant, and again differences increase with eccentricity. However, pRF size differences between lower and upper quadrants change direction with eccentricity. Finally, we find slightly smaller pRFs in the left than right quadrants of V2 and V3, though this difference is very small, and we find no differences in V1 and no differences in CMF. Moreover, differences in pRF size and CMF vary gradually with polar angle and are not limited to the meridians or visual field map discontinuities. PRF size and CMF differences do not consistently follow patterns of cortical curvature, despite the link between cortical curvature and polar angle in V1. Thus, the early human visual cortex has a radially asymmetric representation of the visual field. These asymmetries may underlie consistent reports of asymmetries in perceptual abilities., (Copyright © 2017 Elsevier Inc. All rights reserved.)

The presentation of different stimuli to the two eyes, dichoptic presentation, is essential for studies involving 3D vision and interocular suppression. There is a growing literature on the unique experimental value of pupillary and oculomotor measures, especially for research on interocular suppression. Although obtaining eye-tracking measures would thus benefit studies that use dichoptic presentation, the hardware essential for dichoptic presentation (e.g. mirrors) often interferes with high-quality eye tracking, especially when using a video-based eye tracker. We recently described an experimental setup that combines a standard dichoptic presentation system with an infrared eye tracker by using infrared-transparent mirrors 1 . The setup is compatible with standard monitors and eye trackers, easy to implement, and affordable (on the order of US$1,000). Relative to existing methods it has the benefits of not requiring special equipment and posing few limits on the nature and quality of the visual stimulus. Here we provide a visual guide to the construction and use of our setup.

In several research contexts it is important to obtain eye-tracking measures while presenting visual stimuli independently to each of the two eyes (dichoptic stimulation). However, the hardware that allows dichoptic viewing, such as mirrors, often interferes with high-quality eye tracking, especially when using a video-based eye tracker. Here we detail an approach to combining mirror-based dichoptic stimulation with video-based eye tracking, centered on the fact that some mirrors, although they reflect visible light, are selectively transparent to the infrared wavelength range in which eye trackers record their signal. Although the method we propose is straightforward, affordable (on the order of US$1,000) and easy to implement, for many purposes it makes for an improvement over existing methods, which tend to require specialized equipment and often compromise on the quality of the visual stimulus and/or the eye tracking signal. The proposed method is compatible with standard display screens and eye trackers, and poses no additional limitations on the quality or nature of the stimulus presented or the data obtained. We include an evaluation of the quality of eye tracking data obtained using our method, and a practical guide to building a specific version of the setup used in our laboratories.

Binocular rivalry is an important phenomenon for understanding the mechanisms of visual awareness. Here we assessed the functional locus of binocular rivalry relative to blind spot filling-in, which is thought to transpire in V1, thus providing a reference point for assessing the locus of rivalry. We conducted two experiments to explore the functional order of binocular rivalry and blind spot filling-in. Experiment 1 examined if the information filled-in at the blind spot can engage in rivalry with a physical stimulus at the corresponding location in the fellow eye. Participants' perceptual reports showed no difference between this condition and a condition where filling-in was precluded by presenting the same stimuli away from the blind spot, suggesting that the rivalry process is not influenced by any filling-in that might occur. In Experiment 2, we presented the fellow eye's stimulus directly in rivalry with the 'inducer' stimulus that surrounds the blind spot, and compared it with two control conditions away from the blind spot: one involving a ring physically identical to the inducer, and one involving a disc that resembled the filled-in percept. Perceptual reports in the blind spot condition resembled those in the 'ring' condition, more than those in the latter, 'disc' condition, indicating that a perceptually suppressed inducer does not engender filling-in. Thus, our behavioral data suggest binocular rivalry functionally precedes blind spot filling-in. We conjecture that the neural substrate of binocular rivalry suppression includes processing stages at or before V1., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

When visual input is ambiguous, perception spontaneously alternates between interpretations: bistable perception. Studies have identified two distinct sites near the right intraparietal sulcus where inhibitory transcranial magnetic stimulation (TMS) affects the frequency of occurrence of these alternations, but strikingly with opposite directions of effect for the two sites. Lesion and TMS studies on spatial and sustained attention have also indicated a parcellation of right parietal cortex, into areas serving distinct attentional functions. We used the exact TMS procedure previously employed to affect bistable perception, yet measured its effect on spatial and sustained attention tasks. Although there was a trend for TMS to affect performance, trends were consistently similar for both parietal sites, with no indication of opposite effects. We interpret this as signifying that the previously observed parietal fractionation of function regarding the perception of ambiguous stimuli is not due to TMS-induced modification of spatial or sustained attention., (Copyright © 2016 Elsevier Inc. All rights reserved.)

Trial-to-trial feature repetition speeds response times in pop-out visual search tasks. These priming effects are often ascribed to a short-term memory system. Recently, however, it has been reported that a 'build-up' sequence of repetitions could facilitate responses over 16 trials later - well beyond twice the typically reported time course (Vision Research, 2011, 51, 1972-1978). Here, we first report two replication attempts that yielded little to no support for such long-term priming of pop-out. The results instead fell in line with the predictions of a previously proposed computational model that describes priming as short-lived facilitation that decays over approximately eight trials (Vision Research, 2010, 50, 2110-2115). In the second part of this study, we show that these data are consistent with a simple formulation of decay with a single timescale, and that there is no significant priming beyond eight trials., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Attentional selection in visual search paradigms and perceptual selection in bistable perception paradigms show functional similarities. For example, both are sensitive to trial history: They are biased toward previously selected targets or interpretations. We investigated whether priming by target selection in visual search and sensory memory for bistable perception are related. We did this by presenting two trial types to observers. We presented either ambiguous spheres that rotated over a central axis and could be perceived as rotating in one of two directions, or search displays in which the unambiguously rotating target and distractor spheres closely resembled the two possible interpretations of the ambiguous stimulus. We interleaved both trial types within experiments, to see whether priming by target selection during search trials would affect the perceptual outcome of bistable perception and, conversely, whether sensory memory during bistable perception would affect target selection times during search. Whereas we found intertrial repetition effects among consecutive search trials and among consecutive bistable trials, we did not find cross-paradigm effects. Thus, even though we could ascertain that our experiments robustly elicited processes of both search priming and sensory memory for bistable perception, these same experiments revealed no interaction between the two.

It has been fifty years since Levelt's monograph On Binocular Rivalry (1965) was published, but its four propositions that describe the relation between stimulus strength and the phenomenology of binocular rivalry remain a benchmark for theorists and experimentalists even today. In this review, we will revisit the original conception of the four propositions and the scientific landscape in which this happened. We will also provide a brief update concerning distributions of dominance durations, another aspect of Levelt's monograph that has maintained a prominent presence in the field. In a critical evaluation of Levelt's propositions against current knowledge of binocular rivalry we will then demonstrate that the original propositions are not completely compatible with what is known today, but that they can, in a straightforward way, be modified to encapsulate the progress that has been made over the past fifty years. The resulting modified, propositions are shown to apply to a broad range of bistable perceptual phenomena, not just binocular rivalry, and they allow important inferences about the underlying neural systems. We argue that these inferences reflect canonical neural properties that play a role in visual perception in general, and we discuss ways in which future research can build on the work reviewed here to attain a better understanding of these properties., (Copyright © 2015 The Authors. Published by Elsevier Ltd.. All rights reserved.)

When perceptually ambiguous stimuli are presented intermittently, the percept on one presentation tends to be the same as that on the previous presentation. The role of short-term, acute biases in the production of this perceptual stability is relatively well understood. In addition, however, long-lasting, chronic bias may also contribute to stability. In this paper we develop indices for both biases and for stability, and show that stability can be expressed as a sum of contributions from the two types of bias. We then apply this analytical procedure to binocular rivalry, showing that adjustment of the monocular contrasts can alter the relative contributions of the two biases. Stability is mainly determined by chronic bias when the contrasts are equal, but acute bias dominates stability when right-eye contrast is set lower than left-eye contrast. Finally, we show that the right-eye bias persists in continuous binocular rivalry. Our findings reveal a previously unappreciated contribution of chronic bias to stable perception.

Only part of the visual information that impinges on our retinae reaches visual awareness. In a series of three experiments, we investigated how the task relevance of incoming visual information affects its access to visual awareness. On each trial, participants were instructed to memorize one of two presented hues, drawn from different color categories (e.g., red and green), for later recall. During the retention interval, participants were presented with a differently colored grating in each eye such as to elicit binocular rivalry. A grating matched either the task-relevant (memorized) color category or the task-irrelevant (nonmemorized) color category. We found that the rivalrous stimulus that matched the task-relevant color category tended to dominate awareness over the rivalrous stimulus that matched the task-irrelevant color category. This effect of task relevance persisted when participants reported the orientation of the rivalrous stimuli, even though in this case color information was completely irrelevant for the task of reporting perceptual dominance during rivalry. When participants memorized the shape of a colored stimulus, however, its color category did not affect predominance of rivalrous stimuli during retention. Taken together, these results indicate that the selection of task-relevant information is under volitional control but that visual input that matches this information is boosted into awareness irrespective of whether this is useful for the observer.

The way we perceive the present visual environment is influenced by past visual experiences. Here we investigated the neural basis of such experience dependency. We repeatedly presented human observers with an ambiguous visual stimulus (structure-from-motion) that can give rise to two distinct perceptual interpretations. Past visual experience is known to influence the perception of such stimuli. We recorded fast dynamics of neural activity shortly after stimulus onset using event-related electroencephalography. The number of previous occurrences of a certain percept modulated early posterior brain activity starting as early as 50 ms after stimulus onset. This modulation developed across hundreds of percept repetitions, reflecting several minutes of accumulating perceptual experience. Importantly, there was no such modulation when the mere number of previous stimulus presentations was considered regardless of how they were perceived. This indicates that the effect depended on previous perception rather than previous visual input. The short latency and posterior scalp location of the effect suggest that perceptual history modified bottom-up stimulus processing in early visual cortex. We propose that bottom-up neural responses to a given visual presentation are shaped, in part, by feedback modulation that occurred during previous presentations, thus allowing these responses to be biased in light of previous perceptual decisions., (Copyright © 2014 the authors 0270-6474/14/349970-12$15.00/0.)

Binocular rivalry refers to the unstable perceptual experience that arises when an observer views a different image with each eye: Each image reaches awareness in turn as the other becomes temporarily invisible. Using a novel experimental paradigm, we provide the first direct, perceptual evidence that binocular rivalry occurs only in the presence of attention. Observers in our experiment withdrew attention from a binocular rivalry stimulus shortly after one of the eyes' images was forced to visibility. Seconds later, they shifted attention back to the stimulus to report their perception. For all observers, reported perception strongly and significantly deviated from the results that would be expected if binocular rivalry continued during inattention. Strikingly, reports instead exactly matched those obtained when the stimulus was physically removed for seconds rather than left unattended. These results show that disregarding a binocular rivalry stimulus is equivalent to having it removed from view. Thus, inattention abolishes binocular rivalry.

With attention and eye-movements humans orient to targets of interest. This orienting occurs faster when the same target repeats: priming of pop-out (PoP). While reaction times (RTs) can be important, PoP's real function could be to steer where to orient, a possibility underexposed in many current paradigms, as these predesignate a target to which to orient. In a novel procedure we intermixed pop-out trials (one oddball target, two identical distractors) with choice trials (one item of each kind) where observers freely chose an item to attend to. Pop-out trials strongly drove subsequent choice: observers typically chose the preceding target. Conversely, choice trials affected subsequent pop-out RTs. Conventional PoP measures correlated positively with our choice measures among observers, suggesting common mechanisms. Our results support PoP accounts centered on altered target priority, and underscore PoP's importance for visual exploration.

When target-color repeats in pop-out visual search performance is faster than otherwise. While various characteristics of such priming of pop-out (PoP) are well known, relatively little is known about the temporal character of the memory traces underlying the effect. Recent findings on the perception of ambiguous stimuli show that the percept at any given moment is affected by perception over a long period, as well as by immediately preceding percepts. Intrigued by the existence of various parallels between this perceptual priming phenomenon and PoP, we here investigate whether similar multiplicity in timescales is seen for PoP. We contrasted long-term PoP build-up of a particular target color against shorter-term build-up for a different color. The priming effects from the two colors indeed reflect memory traces at different timescales: long-term priming build-up results in a more gradual decay than brief buildup, which is followed by faster decay. This is clearly demonstrated in Experiment 2 where sustained repetition of one target color is followed by a few repetitions of a second color. Following such a sequence, priming is initially stronger for the second target color, which was primed most recently; however, as more time passes longer-term priming starts to dominate, resulting in better search performance for the first color later on. Our results suggest that priming effects in visual search contain both transient and more sustained components. Similarities between the time courses of attentional priming and perception of ambiguous stimuli are striking and suggest compelling avenues of further research into the relation between the two effects., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

The elements most vivid in our conscious awareness are the ones to which we direct our attention. Scientific study confirms the impression of a close bond between selective attention and visual awareness, yet the nature of this association remains elusive. Using visual afterimages as an index, we investigate neural processing of stimuli as they enter awareness and as they become the object of attention. We find evidence of response enhancement accompanying both attention and awareness, both in the phase-sensitive neural channels characteristic of early processing stages and in the phase-insensitive channels typical of higher cortical areas. The effects of attention and awareness on phase-insensitive responses are positively correlated, but in the same experiments, we observe no correlation between the effects on phase-sensitive responses. This indicates independent signatures of attention and awareness in early visual areas yet a convergence of their effects at more advanced processing stages.

Experience-driven neuronal plasticity allows the brain to adapt its functional connectivity to recent sensory input. Here we use binocular rivalry, an experimental paradigm in which conflicting images are presented to the individual eyes, to demonstrate plasticity in the neuronal mechanisms that convert visual information from two separated retinas into single perceptual experiences. Perception during binocular rivalry tended to initially consist of alternations between exclusive representations of monocularly defined images, but upon prolonged exposure, mixture percepts became more prevalent. The completeness of suppression, reflected in the incidence of mixture percepts, plausibly reflects the strength of inhibition that likely plays a role in binocular rivalry. Recovery of exclusivity was possible but required highly specific binocular stimulation. Documenting the prerequisites for these observed changes in perceptual exclusivity, our experiments suggest experience-driven plasticity at interocular inhibitory synapses, driven by the correlated activity (and also the lack thereof) of neurons representing the conflicting stimuli. This form of plasticity is consistent with a previously proposed but largely untested anti-Hebbian learning mechanism for inhibitory synapses in vision. Our results implicate experience-driven plasticity as one governing principle in the neuronal organization of binocular vision., (Copyright 2010 Elsevier Ltd. All rights reserved.)

When faced with inconclusive or conflicting visual input human observers experience one of multiple possible perceptions. One factor that determines perception of such an ambiguous stimulus is how the same stimulus was perceived on previous occasions, a phenomenon called perceptual memory. We examined perceptual memory of an ambiguous motion stimulus while applying transcranial magnetic stimulation (TMS) to the motion-sensitive areas of the middle temporal cortex (hMT+). TMS increased the predominance of whichever perceptual interpretation was most commonly reported by a given observer at baseline, with reduced perception of the less favored interpretation. This increased incidence of the preferred percept indicates impaired long-term buildup of perceptual memory traces that normally act against individual percept biases. We observed no effect on short-term memory traces acting from one presentation to the next. Our results indicate that hMT+ is important for the long-term buildup of perceptual memory for ambiguous motion stimuli.

When viewing a stimulus that has multiple plausible real-world interpretations, perception alternates between these interpretations every few seconds. Alternations can be halted by intermittently removing the stimulus from view. The same interpretation dominates over many successive presentations, and perception stabilizes. Here we study perception during long sessions of such intermittent presentation. We demonstrate that, rather than causing truly stable perception, intermittent presentation gives rise to a perceptual alternation cycle with its own characteristics and dependencies, different from those during continuous presentation. Alternations during intermittent viewing typically occur once every few minutes--much less frequently than the seconds-scale alternations during continuous viewing. Strikingly, alternations during intermittent viewing occur at fairly regular intervals, making for a surprisingly periodic alternation cycle. The duration of this cycle becomes longer as the blank duration between presentations is increased, reaching dozens of minutes in some cases. We interpret our findings in terms of a mathematical model that describes a neural network with competition between alternative interpretations. Network sensitivities depend on prior dominance, thus providing a memory for past perception. Slow changes in sensitivity produce both perceptual stabilization and the regular but infrequent alternations, meaning that the same memory traces are responsible for both. This model provides a good description of psychophysical findings, and offers several indications regarding their neural basis.

When visual input is inconclusive, does previous experience aid the visual system in attaining an accurate perceptual interpretation? Prolonged viewing of a visually ambiguous stimulus causes perception to alternate between conflicting interpretations. When viewed intermittently, however, ambiguous stimuli tend to evoke the same percept on many consecutive presentations. This perceptual stabilization has been suggested to reflect persistence of the most recent percept throughout the blank that separates two presentations. Here we show that the memory trace that causes stabilization reflects not just the latest percept, but perception during a much longer period. That is, the choice between competing percepts at stimulus reappearance is determined by an elaborate history of prior perception. Specifically, we demonstrate a seconds-long influence of the latest percept, as well as a more persistent influence based on the relative proportion of dominance during a preceding period of at least one minute. In case short-term perceptual history and long-term perceptual history are opposed (because perception has recently switched after prolonged stabilization), the long-term influence recovers after the effect of the latest percept has worn off, indicating independence between time scales. We accommodate these results by adding two positive adaptation terms, one with a short time constant and one with a long time constant, to a standard model of perceptual switching.

We show that previewing one half image of a binocular rivalry pair can cause it to gain initial dominance when the other half is added, a novel phenomenon we term flash facilitation. This is the converse of a known effect called flash suppression, where the previewed image becomes suppressed upon rivalrous presentation. The exact effect of previewing an image depends on both the duration and the contrast of the prior stimulus. Brief, low-contrast prior stimuli facilitate, whereas long, high-contrast ones suppress. These effects have both an eye-based component and a pattern-based component. Our results suggest that, instead of reflecting two unrelated mechanisms, both facilitation and suppression are manifestations of a single process that occurs progressively during presentation of the prior stimulus. The distinction between the two phenomena would then lie in the extent to which the process has developed during prior stimulation. This view is consistent with a neural model previously proposed to account for perceptual stabilization of ambiguous stimuli, suggesting a relation between perceptual stabilization and the present phenomena.

When our two eyes view incongruent images, we experience binocular rivalry: An ongoing cycle of dominance periods of either image and transition periods when both are visible. Two key forces underlying this process are adaptation of and inhibition between the images' neural representations. Models based on these factors meet the constraints posed by data on dominance periods, but these are not very stringent. We extensively studied contrast dependence of dominance and transition durations and that of the occurrence of return transitions: Occasions when an eye loses and regains dominance without intervening dominance of the other eye. We found that dominance durations and the incidence of return transitions depend similarly on contrast; transition durations show a different dependence. Regarding dominance durations, we show that the widely accepted rule known as Levelt's second proposition is only valid in a limited contrast range; outside this range, the opposite of the proposition is true. Our data refute current models, based solely on adaptation and inhibition, as these cannot explain the long and reversible transitions that we find. These features indicate that noise is a crucial force in rivalry, frequently dominating the deterministic forces.

We studied distributions of perceptual rivalry reversals, as defined by the two fitted parameters of the Gamma distribution. We did so for a variety of bi-stable stimuli and voluntary control exertion tasks. Subjects' distributions differed from one another for a particular stimulus and control task in a systematic way that reflects a constraint on the describing parameters. We found a variety of two-parameter effects, the most important one being that distributions of subjects differ from one another in the same systematic way across different stimuli and control tasks (i.e., a fast switcher remains fast across all conditions in a parameter-specified way). The cardinal component of subject-dependent variation was not the conventionally used mean reversal rate, but a component that was oriented-for all stimuli and tasks-roughly perpendicular to the mean rate. For the Necker cube, we performed additional experiments employing specific variations in control exertion, suggesting that subjects have to a considerable extent independent control over the reversal rate of either of the two competing percepts.

Studying the temporal dynamics of bistable perception can be useful for understanding neural mechanisms underlying the phenomenon. We take a closer look at those temporal dynamics, using data from four different ambiguous stimuli. We focus our analyses on two recurrent themes in bistable perception literature. First, we address the question whether percept durations follow a gamma distribution, as is commonly assumed. We conclude that this assumption is not justified by the gamma distribution's approximate resemblance to distributions of percept durations. We instead present two straightforward distributions of reciprocal percept durations (i.e., rates) that both easily surpass the classic gamma distribution in terms of resemblance to empirical data. Second, we compare the distributions arising from binocular rivalry with those from other forms of bistable perception. Parallels in temporal dynamics between those classes of stimuli are often mentioned as an indication of a similar neural basis, but have never been studied in detail. Our results demonstrate that the distributions arising from binocular rivalry and other forms of bistable perception are indeed similar up to a high level of detail.

Fractal properties of arterial trees are analysed using the cascade model of turbulence theory. It is shown that the branching process leads to a non-uniform structure at the micro-level meaning that blood supply to the tissue varies in space. From the model it is concluded that, depending on the branching parameter, vessels of a specific size contribute dominantly to the blood supply of tissue. The corresponding tissue elements form a dense set in the tissue. Furthermore, if blood flow in vessels can get obstructed with some probability, the above set of tissue elements may not be dense anymore. Then there is the risk that, spread out over the tissue, nutrient and gas exchange fall short., (Copyright 2003 Elsevier Science Ltd.)