Functional Brain Imaging in Development and Disorder

Tuesday, May 9, 1:00 – 2:30 pm at ARVO 2017, Baltimore, Maryland
Presenters: Geoffrey K. Aguirre, Jan Atkinson, Tessa M. Dekker, Deborah Giaschi

This symposium will feature four talks that apply functional brain imaging to the study of both visual development and visual disorders. Functional brain imaging, primarily fMRI, enables non-invasive and quantitative assessment of neural function in the human brain. The four talks in the symposium will cover topics that include the reorganization of visual cortex in blindness, studies of cortical response in children with amblyopia, the normal development of population receptive fields in visual cortex, and the effect of early cortical damage on visual development.

Post-retinal structure and function in human blindness

Speaker: Geoffrey K. Aguirre, Department of Neurology, University of Pennsylvania

Neuroimaging the typical and atypical developing visual brain: dorsal vulnerability and cerebral visual impairment

Speaker: Professor Jan Atkinson Ph.D, FMedSci; Acad. Europaea; FBA, Emeritus Professor of Psychology and Developmental Cognitive Neuroscience, University College London, Visiting Professor, University of Oxford

Development of retinotopic representations in visual cortex during childhood

Speaker: Tessa M. Dekker, Division of Psychology and Language Sciences & Institute of Ophthalmology, University College London

Neural correlates of motion perception deficits in amblyopia

Speaker: Deborah Giaschi, Department of Ophthalmology and Visual Science, University of British Columbia

S4 -The Role of Ensemble Statistics in the Visual Periphery

Time/Room: Friday, May 19, 2017, 2:30 – 4:30 pm, Pavilion
Organizer(s): Brian Odegaard, University of California-Los Angeles
Presenters: Michael Cohen, David Whitney, Ruth Rosenholtz, Tim Brady, Brian Odegaard

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The past decades have seen the growth of a tremendous amount of research into the human visual system’s capacity to encode “summary statistics” of items in the world. Studies have shown that the visual system possesses a remarkable ability to compute properties such as average size, position, motion direction, gaze direction, emotional expression, and liveliness, as well as variability in color and facial expression, documenting the phenomena across various domains and stimuli. One recent proposal in the literature has focused on the promise of ensemble statistics to provide an explanatory account of subjective experience in the visual periphery (Cohen, Dennett, & Kanwisher, Trends in Cognitive Sciences, 2016). In addition to this idea, others have suggested that summary statistics underlie performance in visual tasks in a broad manner. These hypotheses open up intriguing questions: how are ensemble statistics encoded outside the fovea, and to what extent does this capacity explain our experience of the majority of our visual field? In this proposed symposium, we aim to discuss recent empirical findings, theories, and methodological considerations in pursuit of answers to many questions in this growing area of research, including the following: (1) How does the ability to process summary statistics in the periphery compare to this ability at the center of the visual field? (2) What role (if any) does attention play in the ability to compute summary statistics in the periphery? (3) Which computational modeling frameworks provide compelling, explanatory accounts of this phenomenon? (4) Which summary statistics (e.g., mean, variance) are encoded in the periphery, and are there limitations on the precision/capacity of these estimates? By addressing questions such as those listed above, we hope that participants emerge from this symposium with a more thorough understanding of the role of ensemble statistics in the visual periphery, and how this phenomenon may account for subjective experience across the visual field. Our proposed group of speakers is shown below, and we hope that faculty, post-docs, and graduate students alike would find this symposium to be particularly informative, innovative, and impactful.

Ensemble statistics and the richness of perceptual experience

Speaker: Michael Cohen, MIT

While our subjective impression is of a detailed visual world, a wide variety of empirical results suggest that perception is actually rather limited. Findings from change blindness and inattentional blindness highlight how much of the huge amounts of the visual world regularly go unnoticed. Furthermore, direct estimates of the capacity of visual attention and working memory reveal that surprisingly few items can be processed and maintained at once. Why do we think we see so much when these empirical results suggests we see so little? One possible answer to this question resides in the representational power of visual ensembles and summary statistics. Under this view, those items that cannot be represented as individual objects or with great precision are nevertheless represented as part of a broader statistical summary. By representing much of the world as an ensemble, observers have perceptual access to different aspects of the entire field of view, not just a few select items. Thus, ensemble statistics play a critical role in our ability to account for and characterize the apparent richness of perceptual experience.

Ensemble representations as a basis for rich perceptual experiences

Speaker: David Whitney, University of California-Berkeley

Much of our rich visual experience comes in the form of ensemble representations, the perception of summary statistical information in groups of objects—such as the average size of items, the average emotional expression of faces in a crowd, or the average heading direction of point-light walkers. These ensemble percepts occur over space and time, are robust to outliers, and can occur in the visual periphery. Ensemble representations can even convey unique and emergent social information like the gaze of an audience, the animacy of a scene, or the panic in a crowd, information that is not necessarily available at the level of the individual crowd members. The visual system can make these high-level interpretations of social and emotional content with exposures as brief as 50 ms, thus revealing an extraordinarily efficient process for compressing what would otherwise be an overwhelming amount of information. Much of what is believed to count as rich social, emotional, and cognitive experience actually comes in the form of basic, compulsory, visual summary statistical processes.

Summary statistic encoding plus limits on decision complexity underlie the richness of visual perception as well as its quirky failures

Speaker: Ruth Rosenholtz, MIT

Visual perception is full of puzzles. Human observers effortlessly per-form many visual tasks, and have the sense of a rich percept of the visual world. Yet when probed for details they are at a loss . How does one explain this combination of marvelous successes and puzzling failures? Numerous researchers have explained the failures in terms of severe limits on resources of attention and memory. But if so, how can one explain the successes? My lab has argued that many experimental results pointing to apparent attentional limits instead derived at least in part from losses in peripheral vision. Furthermore, we demonstrated that those losses could arise from peripheral vision encoding its inputs in terms of a rich set of local image statistics. This scheme is theoretically distinct from encoding ensemble statistics of a set of similar items. I propose that many of the remaining attention/memory limits can be unified in terms of a limit on decision complexity. This decision complexity is difficult to reason about, because the complexity of a given task depends upon the underlying encoding. A complex, general-purpose encoding likely evolved to make certain tasks easy at the expense of others. Recent advances in understanding this encoding — including in peripheral vision — may help us finally make sense of the puzzling strengths and limitations of visual perception.

The role of spatial ensemble statistics in visual working memory and scene perception

Speaker: Tim Brady, University of California-San Diego

At any given moment, much of the relevant information about the visual world is in the periphery rather than the fovea. The periphery is particularly useful for providing information about scene structure and spatial layout, as well as informing us about the spatial distribution and features of the objects we are not explicitly attending and fixating. What is the nature of our representation of this information about scene structure and the spatial distribution of objects? In this talk, I’ll discuss evidence that representations of the spatial distribution of simple visual features (like orientation, spatial frequency, color), termed spatial ensemble statistics, are specifically related to our ability to quickly and accurately recognize visual scenes. I’ll also show that these spatial ensemble statistics are a critical part of the information we maintain in visual working memory – providing information about the entire set of objects, not just a select few, across eye movements, blinks, occlusions and other interruptions of the visual scene.

Summary Statistics in the Periphery: A Metacognitive Approach

Speaker: Brian Odegaard, University of California-Los Angeles

Recent evidence indicates that human observers often overestimate their capacity to make perceptual judgments in the visual periphery. How can we quantify the degree to which this overestimation occurs? We describe how applications of Signal Detection Theoretic frameworks provide one promising approach to measure both detection biases and task performance capacities for peripheral stimuli. By combining these techniques with new metacognitive measures of perceptual confidence (such as meta-d’; Maniscalco & Lau, 2012), one can obtain a clearer picture regarding (1) when subjects can simply perform perceptual tasks in the periphery, and (2) when they have true metacognitive awareness of the visual surround. In this talk, we describe results from recent experiments employing these quantitative techniques, comparing and contrasting the visual system’s capacity to encode summary statistics in both the center and periphery of the visual field.

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S2 – The Brain Correlates of Perception and Action: from Neural Activity to Behavior

Time/Room: Friday, May 19, 2017, 12:00 – 2:00 pm, Pavilion
Organizer(s): Simona Monaco, Center for Mind/Brain Sciences, University of Trento & Annalisa Bosco, Department of Pharmacy and Biotech, University of Bologna
Presenters: J. Douglas Crawford, Patrizia Fattori, Simona Monaco, Annalisa Bosco, Jody C. Culham

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Symposium Description

In recent years neuroimaging and neurophysiology have enabled cognitive neuroscience to identify numerous brain areas that are involved in sensorimotor integration for action. This research has revealed cortical and subcortical brain structures that work in coordination to allow accurate hand and eye movements. The visual information about objects in the environment is integrated into the motor plan through a cascade of events known as visuo-motor integration. These mechanisms allow not only to extract relevant visual information for action, but also to continuously update this information throughout action plan and execution. As our brain evolved to act towards real objects in the natural environment, studying hand and eye movements in experimental situations that resemble the real world is critical for our understanding of the action system. This aspect has been relatively neglected in the cognitive sciences, mostly because of the challenges associated with the experimental setups and technologies. This symposium provides a comprehensive view of the neural mechanisms underlying sensory-motor integration for the production of eye and hand movements in situations that are common to real life. The range of topics covered by the speakers encompasses the visual as well as the motor and cognitive neuro-sciences, and therefore are relevant to junior and senior scientists specialized in any of these areas. We bring together researchers from macaque neurophysiology to human neuroimaging and behavior. The combination of works that use these cutting-edge techniques offers a unique insight into the effects that are detected at the neuronal level, extended to neural populations and trans-lated into behavior. There will be five speakers. Doug Crawford will address the neuronal mechanisms underlying perceptual-mo-tor integration during head-unrestrained gaze shifts in the frontal eye field and superior colliculus of macaques. Patrizia Fattori will describe how the activity of neurons in the dorsomedial visual stream of macaques is modulated by gaze and hand movement direction as well as properties of real objects. Jody Culham will illustrate the neural representation for visually guided actions and real objects in the human brain revealed by functional magnetic resonance imaging (fMRI). Simona Monaco will describe the neural mechanisms in the human brain underlying the influence of intended action on sensory processing and the involvement of the early visual cortex in action planning and execution. Annalisa Bosco will detail the behavioral aspects of the influence exerted by action on perception in human participants.

Visual-motor transformations at the Neuronal Level in the Gaze System

Speaker: J. Douglas Crawford, Centre for Vision Research, York University
Additional Authors: AmirSaman Sajad, Center for Integrative & Cognitive Neuroscience, Vanderbilt University and Morteza Sadeh, Centre for Vision Research, York University

The fundamental question in perceptual-motor integration is how, and at what level, do sensory signals become motor signals? Does this occur between brain areas, within brain areas, or even within individual neu-rons? Various training or cognitive paradigms have been combined with neurophysiology and/or neuroimaging to address this question, but the visuomotor transformations for ordinary gaze saccades remain elusive. To address these questions, we developed a method for fitting visual and motor response fields against various spatial models without any special training, based on trial-to-trial variations in behavior (DeSouza et al .2011). More recently we used this to track visual-motor transformations through time. We find that superior colliculus and frontal eye field visual responses encode target direction, whereas their motor responses encode final gaze position relative to initial eye orientation (Sajad et al. 2015; Sadeh et al. 2016). This occurs both between neuron populations, but can also be observed within individual visuomotor cells. When a memory delay is imposed, a gradual transition of intermediate codes is observed (perhaps due to an imperfect memory loop), with a further ‘leap’ toward gaze motor coding in the final memory-motor transformation (Sajad et al. 2016). However, we found a similar spatiotemporal transition even within the brief burst of neural activity that accompanies a reactive, visually-evoked saccade. What these data suggest is that visuomotor transformations are a network phenomenon that is simultaneously observable at the level of individual neurons, and distributed across different neuronal populations and structures.

Neurons for eye and hand action in the monkey medial posterior parietal cortex

Speaker: Patrizia Fattori, University of Bologna
Additional Authors: Fattori Patrizia, Breveglieri Rossella, Galletti Claudio, Department of Pharmacy and Biotechnology, University of Bologna

In the last decades, several components of the visual control of eye and hand movements have been disentangled by studying single neurons in the brain of awake macaque monkeys. In this presentation, particular attention will be given to the influence of the direction of gaze upon the reaching activity of neurons of the dorsomedial visual stream. We recorded from the caudal part of the medial posterior parietal cortex, finding neurons sensitive to the direction and amplitude of arm reaching actions. The reaching activity of these neurons was influenced by the direction of gaze, some neurons preferring foveal reaching, others peripheral reaching. Manipulations of eye/target positions and of hand position showed that the reaching activity could be in eye-centered, head-centered, or a mixed frame of reference according to the considered neuron. We also found neurons modulated by the visual features of real objects and neurons modulated also by grasping movements, such as wrist orientation and grip formation. So it seems that the entire neural machinery for encoding eye and hand action is hosted in the dorsomedial visual stream. This machinery takes part in the sequence of visuomotor transformations required to encode many aspects of the reach-to-grasp actions.

The role of the early visual cortex in action

Speaker: Simona Monaco, Center for Mind/Brain Sciences, University of Trento
Additional Authors: Simona Monaco, Center for Mind/Brain Sciences, University of Trento; Doug Crawford, Centre for Vision Research, York University; Luca Turella, Center for Mind/Brain Sciences, University of Trento; Jody Culham, Brain and Mind Institution

Functional magnetic resonance imaging has recently allowed showing that intended action modulates the sensory processing of object orientation in areas of the action network in the human brain. In particular, intended actions can be decoded in the early visual cortex using multivoxel pattern analyses before the movements are initiated, regardless of whether the tar-get object is visible or not. In addition, the early visual cortex is rerecruited during actions in the dark towards stimuli that have been previously seen. These results suggest three main points. First, the action-driven modulation of sensory processing is shown at the neural level in a network of areas that include the early visual cortex. Second, the role of the early visual cortex goes well beyond the processing of sensory information for perception and might be the target of reentrant feedback for sensory-motor integration. Third, the early visual cortex shows action-driven modulation during both action planning and execution, suggesting a continuous exchange of information with higher-order visual-motor areas for the production of a motor output.

The influence of action execution on object size perception

Speaker: Annalisa Bosco, Department of Pharmacy and Biotechnology, University of Bologna
Additional Authors: Annalisa Bosco, Department of Pharmacy and Biotechnology, University of Bologna; Patrizia Fattori, Department of Pharmacy and Biotechnology, University of Bologna

When performing an action, our perception is focused towards object visual properties that enable us to execute the action successfully. However, the motor system is also able to influence perception, but only few studies reported evidence for hand action-induced visual perception modifications. Here, we aimed to study for a feature-specific perceptual modulation before and after a reaching and grasping action. Two groups of subjects were instructed to either grasp or reach to different sized bars and, before and after the action, to perform a size perceptual task by manual and verbal report. Each group was tested in two experimental conditions: no prior knowledge of action type, where subjects did not know the successive type of movement, and prior knowledge of action type, where they were aware about the successive type of movement. In both manual and verbal perceptual size responses, we found that after a grasping movement the size perception was significantly modified. Additionally, this modification was enhanced when the subjects knew in advance the type of movement to execute in the subsequent phase of task. These data suggest that the knowledge of action type and the execution of the action shape the perception of object properties.

Neuroimaging reveals the human neural representations for visually guided grasping of real objects and pictures

Speaker: Jody C. Culham, Brain and Mind Institute, University of Western Ontario
Additional Authors: Jody C. Culham, University of Western Ontario; Sara Fabbri, Radboud University Nijmegen; Jacqueline C. Snow, University of Nevada, Reno; Erez Freud, Carnegie-Mellon University

Neuroimaging, particularly functional magnetic resonance imaging (fMRI), has revealed many human brain areas that are involved in the processing of visual information for the planning and guidance of actions. One area of particular interest is the anterior intraparietal sulcus (aIPS), which is thought to play a key role in processing information about object shape for the visual control of grasping. However, much fMRI research has relied on artificial stimuli, such as two-dimensional photos, and artificial actions, such as pantomimed grasping. Recent fMRI studies from our lab have used representational similarity analysis on the patterns of fMRI activation from brain areas such as aIPS to infer neural coding in participants performing real actions upon real objects. This research has revealed the visual features of the object (particularly elongation) and the type of grasp (including the number of digits and precision required) that are coded in aIPS and other regions. Moreover, this work has suggested that these neural representations are affected by the realness of the object, particularly during grasping. Taken together, these results highlight the value of using more ecological paradigms to study sensorimotor control.

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S3 – How can you be so sure? Behavioral, computational, and neuro-scientific perspectives on metacogni-tion in perceptual decision-making

Time/Room: Friday, May 19, 2017, 2:30 – 4:30 pm, Talk Room 1
Organizer(s): Megan Peters, University of California Los Angeles
Presenters: Megan Peters, Ariel Zylberberg, Michele Basso, Wei Ji Ma, Pascal Mamassian

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Metacognition, or our ability to monitor the uncertainty of our thoughts, decisions, and perceptions, is of critical importance across many domains . Here we focus on metacognition in perceptual decisions — the continuous inferences that we make about the most likely state of the world based on incoming sensory information. How does a police officer evaluate the fidelity of his perception that a perpetrator has drawn a weapon? How does a driver compute her certainty in whether a fleeting visual percept is a child or a soccer ball, impacting her decision to swerve? These kinds of questions are central to daily life, yet how such ‘confidence’ is computed in the brain remains unknown. In recent years, increasingly keen interest has been directed towards exploring such metacognitive mechanisms from computational (e.g., Rahnev et al., 2011, Nat Neuro; Peters & Lau, 2015, eLife), neuroimaging (e.g., Fleming et al., 2010, Science), brain stimulation (e.g., Fetsch et al., 2014, Neuron), and neuronal electro-physiology (e.g., Kiani & Shadlen, 2009, Science; Zylberberg et al., 2016, eLife) perspectives. Importantly, the computation of confidence is also of increasing interest to the broader range of researchers studying the computations underlying perceptual decision-making in general. Our central focus is on how confidence is computed in neuronal populations, with attention to (a) whether perceptual decisions and metacognitive judgments depend on the same or different computations, and (b) why confidence judgments sometimes fail to optimally track the accuracy of perceptual decisions. Key themes for this symposium will include neural correlates of confidence, behavioral consequences of evidence manipulation on confidence judgments, and computational characterizations of the relationship between perceptual decisions and our confidence in them. Our principal goal is to attract scientists studying or interested in confidence/uncertainty, sensory metacognition, and perceptual decision-making from both human and animal perspectives, spanning from the computational to the neurobiological level. We bring together speakers from across these disciplines, from animal electrophysiology and behavior through computational models of human uncertainty, to communicate their most recent and exciting findings. Given the recency of many of the findings discussed, our symposium will cover terrain largely untouched by the main program. We hope that the breadth of research programs represented in this symposium will encourage a diverse group of scientists to attend and actively participate in the discussion.

Transcranial magnetic stimulation to visual cortex induces suboptimal introspection

Speaker: Megan Peters, University of California Los Angeles
Additional Authors: Megan Peters, University of California Los Angeles; Jeremy Fesi, The Graduate Center of the City University of New York; Namema Amendi, The Graduate Center of the City University of New York; Jeffrey D. Knotts, University of California Los Angeles; Hakwan Lau, UCLA

In neurological cases of blindsight, patients with damage to primary visual cortex can discriminate objects but report no visual experience of them. This form of ‘unconscious perception’ provides a powerful opportunity to study perceptual awareness, but because the disorder is rare, many researchers have sought to induce the effect in neurologically intact observers. One promising approach is to apply transcranial magnetic stimulation (TMS) to visual cortex to induce blindsight (Boyer et al., 2005), but this method has been criticized for being susceptible to criterion bias confounds: perhaps TMS merely reduces internal visual signal strength, and observers are unwilling to report that they faintly saw a stimulus even if they can still discriminate it (Lloyd et al., 2013). Here we applied a rigorous response-bias free 2-interval forced-choice method for rating subjective experience in studies of unconscious perception (Peters and Lau, 2015) to address this concern. We used Bayesian ideal observer analysis to demonstrate that observers’ introspective judgments about stimulus visibility are suboptimal even when the task does not require that they maintain a response criterion — unlike in visual masking. Specifically, observers appear metacognitively blind to the noise introduced by TMS, in a way that is akin to neurological cases of blindsight. These findings are consistent with the hypothesis that metacognitive judgments require observers to develop an internal model of the statistical properties of their own signal processing architecture, and that introspective suboptimality arises when that internal model abruptly becomes invalid due to external manipulations.

The influence of evidence volatility on choice, reaction time and confidence in a perceptual decision

Speaker: Ariel Zylberberg, Columbia University
Additional Authors: Ariel Zylberberg, Columbia University; Christopher R. Fetsch, Columbia University; Michael N. Shadlen, Columbia University

Many decisions are thought to arise via the accumulation of noisy evidence to a threshold or bound. In perceptual decision-making, the bounded evidence accumulation framework explains the effect of stimulus strength, characterized by signal-to-noise ratio, on decision speed, accuracy and confidence. This framework also makes intriguing predictions about the behavioral influence of the noise itself. An increase in noise should lead to faster decisions, reduced accuracy and, paradoxically, higher confidence. To test these predictions, we introduce a novel sensory manipulation that mimics the addition of unbiased noise to motion-selective regions of visual cortex. We verified the effect of this manipulation with neuronal recordings from macaque areas MT/MST. For both humans and monkeys, increasing the noise induced faster decisions and greater confidence over a range of stimuli for which accuracy was minimally impaired. The magnitude of the effects was in agreement with predictions of a bounded evidence accumulation model.

A role for the superior colliculus in decision-making and confidence

Speaker: Michele Basso, University of California Los Angeles
Additional Authors: Michele Basso, University of California Los Angeles; Piercesare Grimaldi, University of California Los Angeles; Trinity Crapse, University of California Los Angeles

Evidence implicates the superior colliculus (SC) in attention and perceptual decision-making . In a simple target-selection task, we previously showed that discriminability between target and distractor neuronal activity in the SC correlated with decision accuracy, consistent with the hypothesis that SC encodes a decision variable. Here we extend these results to determine whether SC also correlates with decision criterion and confidence. Trained monkeys performed a simple perceptual decision task in two conditions to induce behavioral response bias (criterion shift): (1) the probability of two perceptual stimuli was equal, and (2) the probability of one perceptual stimulus was higher than the other. We observed consistent changes in behavioral response bias (shifts in decision criterion) that were directly cor-related with SC neuronal activity. Furthermore, electrical stimulation of SC mimicked the effect of stimulus probability manipulations, demonstrating that SC correlates with and is causally involved in setting decision criteria. To assess confidence, monkeys were offered a ‘safe bet’ option on 50% of trials in a similar task. The ‘safe bet’ always yielded a small reward, encouraging monkeys to select the ‘safe bet’ when they were less confident rather than risk no reward for a wrong decision. Both monkeys showed metacognitive sensitivity: they chose the ‘safe bet’ more on more difficult trials. Single- and multi-neuron recordings from SC revealed two distinct neuronal populations: one that discharged more robustly for more confident trials, and one that did so for less confident trials. Together these finding show how SC encodes information about decisions and decisional confidence.

Testing the Bayesian confidence hypothesis

Speaker: Wei Ji Ma, New York University
Additional Authors: Wei Ji Ma, New York University; Will Adler, New York University; Ronald van den Berg, University of Uppsala

Asking subjects to rate their confidence is one of the oldest procedures in psychophysics. Remarkably, quantitative models of confidence ratings have been scarce. What could be called the “Bayesian confidence hypothesis” states that an observer’s confidence rating distribution is completely determined by posterior probability. This hypothesis predicts specific quantitative relationships between performance and confidence. It also predicts that stimulus combinations that produce the same posterior will also produce the same confidence distribution. We tested these predictions in three contexts: a) perceptual categorization; b) visual working memory; c) the interpretation of scientific data.

Integration of visual confidence over time and across stimulus dimensions

Speaker: Pascal Mamassian, Ecole Normale Supérieure
Additional Authors: Pascal Mamassian, Ecole Normale Supérieure; Vincent de Gardelle, Université Paris 1; Alan Lee, Lingnan University

Visual confidence refers to our ability to estimate our own performance in a visual decision task. Several studies have highlighted the relatively high efficiency of this meta-perceptual ability, at least for simple visual discrimination tasks. Are observers equally good when visual confidence spans more than one stimulus dimension or more than a single decision? To address these issues, we used the method of confidence forced-choice judgments where participants are prompted to choose between two alter-natives the stimulus for which they expect their performance to be better (Barthelmé & Mamassian, 2009, PLoS CB). In one experiment, we asked observers to make confidence choice judgments between two different tasks (an orientation-discrimination task and a spatial-frequency-discrimi-nation task). We found that participants were equally good at making these across-dimensions confidence judgments as when choices were restricted to a single dimension, suggesting that visual confidence judgments share a common currency. In another experiment, we asked observers to make confidence-choice judgments between two ensembles of 2, 4, or 8 stimuli. We found that participants were increasingly good at making ensemble confidence judgments, suggesting that visual confidence judgments can accumulate information across several trials. Overall, these results help us better understand how visual confidence is computed and used over time and across stimulus dimensions.

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