Similarity in motion binds and bends judgments of aspect ratio.

It is well known that objects become grouped in perceptual organization when they share some visual feature, like a common direction of motion. Less well known is that grouping can change how people perceive a set of objects. For example, when a pair of shapes consistently share a common region of space, their aspect ratios tend to be perceived as more similar (are attracted toward each other). Conversely, when shapes are assigned to different regions in space their aspect ratios repel from each other. Here we examine whether the visual system produce both attractive and repulsive distortions when the state of grouping between a pair of shapes changes on a moment-to-moment basis. Observers viewed a pair of ellipses that differed in terms of how flat or tall they were and reported the aspect ratio of one ellipse from the pair. Each ellipse was defined by a cloud of coherently-moving dots, and the dots within the two ellipses had either the same or different directions of motion, varying from trial-to-trial. We found that the cued ellipse's aspect ratio was reported to be repelled from the aspect ratio of the uncued ellipse when the shapes had different directions of motion compared to when they had the same direction of motion. These results suggest that the visual system can adaptively alter visual experience based on grouping, in particular, repelling the appearance of objects when they do not appear to go together, and it can do so quickly and flexibly.

Gaze perception from head and pupil rotations in 2D and 3D: Typical development and the impact of autism spectrum disorder.

The study of gaze perception has largely focused on a single cue (the eyes) in two-dimensional settings. While this literature suggests that 2D gaze perception is shaped by atypical development, as in Autism Spectrum Disorder (ASD), gaze perception is in reality contextually-sensitive, perceived as an emergent feature conveyed by the rotation of the pupils and head. We examined gaze perception in this integrative context, across development, among children and adolescents developing typically or with ASD with both 2D and 3D stimuli. We found that both groups utilized head and pupil rotations to judge gaze on a 2D face. But when evaluating the gaze of a physically-present, 3D robot, the same ASD observers used eye cues less than their typically-developing peers. This demonstrates that emergent gaze perception is a slowly developing process that is surprisingly intact, albeit weakened in ASD, and illustrates how new technology can bridge visual and clinical science.

Amplification in the evaluation of multiple emotional expressions over time.

Social interactions are dynamic and unfold over time. To make sense of social interactions, people must aggregate sequential information into summary, global evaluations. But how do people do this? Here, to address this question, we conducted nine studies (N = 1,583) using a diverse set of stimuli. Our focus was a central aspect of social interaction-namely, the evaluation of others' emotional responses. The results suggest that when aggregating sequences of images and videos expressing varying degrees of emotion, perceivers overestimate the sequence's average emotional intensity. This tendency for overestimation is driven by stronger memory of more emotional expressions. A computational model supports this account and shows that amplification cannot be explained only by nonlinear perception of individual exemplars. Our results demonstrate an amplification effect in the perception of sequential emotional information, which may have implications for the many types of social interactions that involve repeated emotion estimation.

The Crowd-Emotion-Amplification Effect.

How do people go about reading a room or taking the temperature of a crowd? When people catch a brief glimpse of an array of faces, they can focus their attention on only some of the faces. We propose that perceivers preferentially attend to faces exhibiting strong emotions and that this generates a crowd-emotion-amplification effect-estimating a crowd's average emotional response as more extreme than it actually is. Study 1 (N = 50) documented the crowd-emotion-amplification effect. Study 2 (N = 50) replicated the effect even when we increased exposure time. Study 3 (N = 50) used eye tracking to show that attentional bias to emotional faces drives amplification. These findings have important implications for many domains in which individuals must make snap judgments regarding a crowd's emotionality, from public speaking to controlling crowds.

Anger bias in the evaluation of crowds.

People are good at categorizing the emotions of individuals and crowds of faces. People also make mistakes when classifying emotion. When they do so with judgments of individuals, these errors tend to be negatively biased, potentially serving a protective function. For example, a face with a subtle expression is more likely to be categorized as angry than happy. Yet surprisingly little is known about the errors people make when evaluating multiple faces. We found that perceivers were biased to classify faces as angry, especially when evaluating crowds. This amplified bias depended on uncertainty, occurring when categorization was difficult, and it reached peak intensity for crowds with four members. Drift diffusion modeling revealed the mechanisms behind this bias, including an early response component and more efficient processing of anger from crowds with subtle expressions. Our findings introduce bias as an important new dimension for understanding how perceivers make judgments about crowds. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Ensemble perception includes information from multiple spatial scales.

Most visual scenes contain information at different spatial scales, including the local and global, or the detail and gist. Global processes have become increasingly implicated in research examining summary statistical perception, initially as the output of ensemble coding, and more recently as a gating mechanism for selecting which information is included in the averaging process itself. Yet local and global processing are known to be rapidly integrated by the visual system, and it is plausible that global-level information, like spatial organization, may be included as an input during ensemble coding. We tested this hypothesis using an ensemble shape-perception task in which observers evaluated the mean aspect ratios of sets of ellipses. In addition to varying the aspect ratios of the individual shapes, we independently varied the spatial arrangements of the sets so that they had either flat or tall organizations at the global level. We found that observers made precise summary judgments about the average aspect ratios of the sets by integrating information from multiple shapes. More importantly, global flat and tall organizations were incorporated into ensemble judgments about the sets; summary judgments were biased in the directions of the global spatial arrangements on each trial. This global-to-local integration even occurred when the global organizations were masked. Our results demonstrate that the process of summary representation can include information from both the local and global scales. The gist is not just an output of ensemble representation - it can be included as an input to the mechanism itself.

Integration and segmentation conflict during ensemble coding of shape.

During ensemble coding, the visual system extracts summary information from input that has been integrated, facilitating gist-level judgments about objects and features that belong together. In contrast, input can be segmented, allowing for quick categorical distinctions between objects. Integration and segmentation usually work in parallel but may sometimes conflict in the context of ensemble coding. To investigate this possibility, we examined summary perception of aspect ratio (i.e., "tallness/flatness"). Aspect ratio has a category boundary (e.g., a circle), and individual aspect ratios may be perceptually exaggerated-segmented-away from this boundary. We predicted that summary perception of multiple aspect ratios would be disrupted when, as a set, they spanned the category boundary, since integration and segmentation would then be at odds. We found that when observers reported the average aspect ratio of a set of ellipses, they were less sensitive to the mean of sets that included both tall and flat ellipses, compared to sets comprised of tall or flat ellipses. Follow-up experiments suggest this occurred because segmentation distorted the appearance of ellipses away from the category boundary, exaggerating set heterogeneity. These experiments advance understanding of how the visual system summarizes information by showing that integration and segmentation can conflict. (PsycInfo Database Record (c) 2020 APA, all rights reserved).

Is this my group or not? The role of ensemble coding of emotional expressions in group categorization.

When exposed to others' emotional responses, people often make rapid decisions as to whether these others are members of their group or not. These group categorization decisions have been shown to be extremely important to understanding group behavior. Yet, despite their prevalence and importance, we know very little about the attributes that shape these categorization decisions. To address this issue, we took inspiration from ensemble coding research and developed a task designed to reveal the influence of the mean and variance of group members' emotions on participants' group categorization. In Study 1, we verified that group categorization decreases when the group's mean emotion is different from the participant's own emotional response. In Study 2, we established that people identify a group's mean emotion more accurately when its variance is low rather than high. In Studies 3 and 4, we showed that participants were more likely to self-categorize as members of groups with low emotional variance, even if their own emotions fell outside of the range of group emotions they saw, and that this preference is seen for judgments of both positive and negative group emotions. In Study 5, we showed that this unique preference for low group emotional variance is special to group categorization and does not appear in a more basic face categorization task. Our studies reveal unexplored and important tendencies in group categorization based on group emotions. (PsycINFO Database Record (c) 2020 APA, all rights reserved).

Perceiving gaze from head and eye rotations: An integrative challenge for children and adults.

Gaze is an emergent visual feature. A person's gaze direction is perceived not just based on the rotation of their eyes, but also their head. At least among adults, this integrative process appears to be flexible such that one feature can be weighted more heavily than the other depending on the circumstances. Yet it is unclear how this weighting might vary across individuals or across development. When children engage emergent gaze, do they prioritize cues from the head and eyes similarly to adults? Is the perception of gaze among individuals with autism spectrum disorder (ASD) emergent, or is it reliant on a single feature? Sixty adults (M = 29.86 years-of-age), thirty-seven typically developing children and adolescents (M = 9.3 years-of-age; range = 7-15), and eighteen children with ASD (M = 9.72 years-of-age; range = 7-15) viewed faces with leftward, rightward, or direct head rotations in conjunction with leftward or rightward pupil rotations, and then indicated whether the face was looking leftward or rightward. All individuals, across development and ASD status, used head rotation to infer gaze direction, albeit with some individual differences. However, the use of pupil rotation was heavily dependent on age. Finally, children with ASD used pupil rotation significantly less than typically developing (TD) children when inferring gaze direction, even after accounting for age. Our approach provides a novel framework for understanding individual and group differences in gaze as it is actually perceived-as an emergent feature. Furthermore, this study begins to address an important gap in ASD literature, taking the first look at emergent gaze perception in this population.

Anisotropic visual awareness of shapes.

While object perception may feel instantaneous, it is an iterative process in which information is accumulated until ambiguity about identity and location is resolved. In theory, awareness of an object should depend on how efficiently this process occurs. Therefore, objects with inherently weak visual representations should be more susceptible to perceptual disruption. We tested this hypothesis by examining the perception of aspect ratio, a 2D feature of shapes with anisotropic representation (circular shapes are less robustly represented than elongated shapes in high-level visual areas). Observers viewed a target shape shown for 20-ms within an array of ellipses. The target, which varied from flat to tall, was either masked or unmasked. Observers indicated the target's aspect ratio and if it was visible. Observers reported seeing elongated shapes far more often than circular shapes, but only on trials with object-substitution masking. This effect replicated across five control experiments, even though the shapes were identical in basic image attributes (e.g., contrast, area). Our findings demonstrate that shapes with extreme aspect ratios are more readily available to awareness than shapes with ambiguous dimensionality. More generally, this work supports theories of object processing which suggest that strength of visual representation gates access to awareness.

Rapid visual perception of interracial crowds: Racial category learning from emotional segregation.

Drawing from research on social identity and ensemble coding, we theorize that crowd perception provides a powerful mechanism for social category learning. Crowds include allegiances that may be distinguished by visual cues to shared behavior and mental states, providing perceivers with direct information about social groups and thus a basis for learning social categories. Here, emotion expressions signaled group membership: to the extent that a crowd exhibited emotional segregation (i.e., was segregated into emotional subgroups), a visible characteristic (race) that incidentally distinguished emotional subgroups was expected to support categorical distinctions. Participants were randomly assigned to view interracial crowds in which emotion differences between (black vs. white) subgroups were either small (control condition) or large (emotional segregation condition). On each trial, participants saw crowds of 12 faces (6 black, 6 white) for roughly 300 ms and were asked to estimate the average emotion of the entire crowd. After all trials, participants completed a racial categorization task and self-report measure of race essentialism. As predicted, participants exposed to emotional segregation (vs. control) exhibited stronger racial category boundaries and stronger race essentialism. Furthermore, such effects accrued via ensemble coding, a visual mechanism that summarizes perceptual information: emotional segregation strengthened participants' racial category boundaries to the extent that segregation limited participants' abilities to integrate emotion across racial subgroups. Together with evidence that people observe emotional segregation in natural environments, these findings suggest that crowd perception mechanisms support racial category boundaries and race essentialism. (PsycINFO Database Record

Perceptual averaging of facial expressions requires visual awareness and attention.

Humans, as highly social animals, are regularly exposed to the faces of conspecifics-often more than one at a time. This feature of social living is important for understanding face perception, not just because it means that information from faces is available in bulk, but also because it changes the way individuals are perceived. For instance, when two faces are seen nearby one another, they tend to look like each other. This phenomenon of perceptual averaging is robust when both faces are seen and attended. But in everyday life, some faces may not receive the full benefit of attention, or they may not be visible at all. We evaluated whether perceptual averaging of relatively complex and simple information on faces, including facial expression and head orientation, can still occur even in these circumstances. In particular, we used object-substitution masking (OSM) and a dual-task designed to disrupt visual awareness and attention, respectively, during evaluations of briefly presented face pairs. Disruptions of awareness or attention eliminated averaging of facial expression, whereas orientation averaging persisted in spite of these challenges. These results demonstrate boundary conditions for the process of perceptual averaging. More generally, they provide insight into how the visual system processes multitudes of objects, both simple and complex, both with and without attention and awareness.

Emergent perception of gaze direction across time.

To determine where another person is looking, the visual system engages a process of emergent integration, pooling information across space from both the head and eyes. Gaze is dynamic, however, and in order to achieve a temporally stabilized metric of a person's direction of attention, this integrative process might also occur across time. Here, we tested and confirmed this prediction. Even when seen separately and in succession, the rotation of a head attracted the perceived gaze of a pair of eyes. This integration depended on temporal continuity-attraction decayed with longer delays between the face parts and prolonged viewing of the head reduced integration. Nevertheless, gaze integration persisted across delays of 2 s and even occurred against a backdrop of changing emotional expression. Gaze is a complex feature that orchestrates social interactions over time. Our results demonstrate that the representation and perception of emergent gaze is dynamic as well. (PsycINFO Database Record

Spatial cues influence the visual perception of gender.

Spatial localization is a basic process in vision, occurring reliably when people encounter an object or person. Yet the role of spatial-location in the visual perception of people is poorly understood. We explored the extent to which spatial-location distorts the perception of gender. Consistent with evidence that the perception of objects is constrained by their location in visual scenes, enhancing perception for objects in their typical location (e.g., Biederman et al., 1982), we hypothesized that people would see relatively greater femininity in faces that appeared lower in space. On each of many trials, participants briefly viewed a pair of faces that varied in gender-ambiguity. One face appeared higher than the other, and participants identified the 1 that looked more like a woman's face (Study 1) or indicated whether the 2 faces were the same (Study 2). Across 2 experiments, participants perceived greater femininity in faces seen lower (vs. higher) in space. These effects seem to be perceptual-changes to spatial location were sufficient for altering whether 2 faces looked identical or different. Thus, spatial-location modulates visual percepts of gender, providing a biased foundation for downstream processes involved in gender biases, sexual attraction, and sex-roles. (PsycINFO Database Record

Object-substitution masking weakens but does not eliminate shape interactions.

At any moment, some objects in the environment are seen clearly, whereas others go unnoticed. Whether or not these gaps in awareness are actually problematic may depend on the extent that information about unseen objects is lost. Determining when and how visual awareness and visual processing become linked is thus of great importance. Previous research using object-substitution masking (OSM) demonstrated that relatively simple visual features, such as size or orientation, are still processed even when they are not visible. Yet this does not appear to be the case for more complex features like faces. This suggests that, during OSM, disruptions of visual processing and awareness may tend to co-occur beginning at some intermediate stage along the ventral pathway. We tested this hypothesis by evaluating the extent to which OSM disrupted the perception and processing of two-dimensional objects. Specifically, we evaluated whether an unseen shape's aspect ratio would influence the appearance of another shape that was briefly visible nearby. As expected, the aspect ratios of two shapes appeared to be more similar to each other when both were visible. This averaging effect was weakened, but not eliminated, when one ellipse in each pair received OSM. These shape interactions persisted even when one ellipse from each pair was invisible. When combined with previous work, these results suggest that during object-substitution masking, disruptions of visual processing tend to strengthen with increases in stimulus complexity, becoming more tightly bound to the mechanisms of visual awareness at intermediate stages of visual analysis.

The center of attention: Metamers, sensitivity, and bias in the emergent perception of gaze.

A person's gaze reveals much about their focus of attention and intentions. Sensitive perception of gaze is thus highly relevant for social interaction, especially when it is directed toward the viewer. Yet observers also tend to overestimate the likelihood that gaze is directed toward them. How might the visual system balance these competing goals, maximizing sensitivity for discriminating gazes that are relatively direct, while at the same time allowing many gazes to appear as if they look toward the viewer? Perceiving gaze is an emergent visual process that involves integrating information from the eyes with the rotation of the head. Here, we examined whether the visual system leverages emergent representation to balance these competing goals. We measured perceived gaze for a large range of pupil and head combinations and found that head rotation has a nonlinear influence on a person's apparent direction of looking, especially when pupil rotations are relatively direct. These perceptual distortions could serve to expand representational space and thereby enhance discriminability of gazes that are relatively direct. We also found that the emergent perception of gaze supports an abundance of direct gaze metamers-different combinations of head and pupil rotations that combine to generate the appearance of gaze directed toward the observer. Our results thus demonstrate a way in which the visual system flexibly integrates information from facial features to optimize social perception. Many gazes can be made to look toward you, yet similar gazes need not appear alike.

Ensemble Perception of Dynamic Emotional Groups.

Crowds of emotional faces are ubiquitous, so much so that the visual system utilizes a specialized mechanism known as ensemble coding to see them. In addition to being proximally close, members of emotional crowds, such as a laughing audience or an angry mob, often behave together. The manner in which crowd members behave-in sync or out of sync-may be critical for understanding their collective affect. Are ensemble mechanisms sensitive to these dynamic properties of groups? Here, observers estimated the average emotion of a crowd of dynamic faces. The members of some crowds changed their expressions synchronously, whereas individuals in other crowds acted asynchronously. Observers perceived the emotion of a synchronous group more precisely than the emotion of an asynchronous crowd or even a single dynamic face. These results demonstrate that ensemble representation is particularly sensitive to coordinated behavior, and they suggest that shared behavior is critical for understanding emotion in groups.

Ensemble perception of size in 4-5-year-old children.

Groups of objects are nearly everywhere we look. Adults can perceive and understand the 'gist' of multiple objects at once, engaging ensemble-coding mechanisms that summarize a group's overall appearance. Are these group-perception mechanisms in place early in childhood? Here, we provide the first evidence that 4-5-year-old children use ensemble coding to perceive the average size of a group of objects. Children viewed a pair of trees, with each containing a group of differently sized oranges. We found that, in order to determine which tree had the larger oranges overall, children integrated the sizes of multiple oranges into ensemble representations. This pooling occurred rapidly, and it occurred despite conflicting information from numerosity, continuous extent, density, and contrast. An ideal observer analysis showed that although children's integration mechanisms are sensitive, they are not yet as efficient as adults'. Overall, our results provide a new insight into the way children see and understand the environment, and they illustrate the fundamental nature of ensemble coding in visual perception.

Perceiving crowd attention: ensemble perception of a crowd's gaze.

In nearly every interpersonal encounter, people readily gather socio-visual cues to guide their behavior. Intriguingly, social information is most effective in directing behavior when it is perceived in crowds. For example, the shared gaze of a crowd is more likely to direct attention than is a single person's gaze. Are people equipped with mechanisms to perceive a crowd's gaze as an ensemble? Here, we provide the first evidence that the visual system extracts a summary representation of a crowd's attention; observers rapidly pooled information from multiple crowd members to perceive the direction of a group's collective gaze. This pooling occurred in high-level stages of visual processing, with gaze perceived as a global-level combination of information from head and pupil rotation. These findings reveal an important and efficient mechanism for assessing crowd gaze, which could underlie the ability to perceive group intentions, orchestrate joint attention, and guide behavior.

Humans use summary statistics to perceive auditory sequences.

In vision, humans use summary statistics (e.g., the average facial expression of a crowd) to efficiently perceive the gist of groups of features. Here, we present direct evidence that ensemble coding is also important for auditory processing. We found that listeners could accurately estimate the mean frequency of a set of logarithmically spaced pure tones presented in a temporal sequence (Experiment 1). Their performance was severely reduced when only a subset of tones from a given sequence was presented (Experiment 2), which demonstrates that ensemble coding is based on a substantial number of the tones in a sequence. This precise ensemble coding occurred despite very limited representation of individual tones from the sequence: Listeners were poor at identifying specific individual member tones (Experiment 3) and at determining their positions in the sequence (Experiment 4). Together, these results indicate that summary statistical coding is not limited to visual processing and is an important auditory mechanism for extracting ensemble frequency information from sequences of sounds.