How to use individual differences to isolate functional organization, biology, and utility of visual functions; with illustrative proposals for stereopsis

Measuring object recognition ability: Reliability, validity, and the aggregate z-score approach

Measurement of domain-general object recognition ability (o) requires minimization of domain-specific variance. One approach is to model o as a latent variable explaining performance on a battery of tests which differ in task demands and stimuli; however, time and sample requirements may be prohibitive. Alternatively, an aggregate measure of o can be obtained by averaging z-scores across tests. Using data from Sunday et al., Journal of Experimental Psychology: General, 151, 676-694, (2022), we demonstrated that aggregate scores from just two such object recognition tests provide a good approximation (r = .79) of factor scores calculated from a model using a much larger set of tests. Some test combinations produced correlations of up to r = .87 with factor scores. We then revised these tests to reduce testing time, and developed an odd one out task, using a unique object category on nearly every trial, to increase task and stimuli diversity. To validate our measures, 163 participants completed the object recognition tests on two occasions, one month apart. Providing the first evidence that o is stable over time, our short aggregate o measure demonstrated good test-retest reliability (r = .77). The stability of o could not be completely accounted for by intelligence, perceptual speed, and early visual ability. Structural equation modeling suggested that our tests load significantly onto the same latent variable, and revealed that as a latent variable, o is highly stable (r = .93). Aggregation is an efficient method for estimating o, allowing investigation of individual differences in object recognition ability to be more accessible in future studies.

Face recognition's practical relevance: Social bonds, not social butterflies

Research on individual differences in face recognition has provided important foundational insights: their broad range, cognitive specificity, strong heritability, and resilience to change. Elusive, however, has been the key issue of practical relevance: do these individual differences correlate with aspects of life that go beyond the recognition of faces, per se? Though often assumed, especially in social realms, such correlates remain largely theoretical, without empirical support. Here, we investigate an array of potential social correlates of face recognition. We establish social relationship quality as a reproducible correlate. This link generalises across face recognition tasks and across independent samples. In contrast, we detect no robust association with the sheer quantity of social connections, whether measured directly via number of social contacts or indirectly via extraversion-related personality indices. These findings document the existence of a key social correlate of face recognition and provide some of the first evidence to support its practical relevance. At the same time, they challenge the naive assumption that face recognition relates equally to all social outcomes. In contrast, they suggest a focused link of face recognition to the quality, not quantity, of one's social connections.

Manipulating and measuring variation in deep neural network (DNN) representations of objects

We explore how DNNs can be used to develop a computational understanding of individual differences in high-level visual cognition given their ability to generate rich meaningful object representations informed by their architecture, experience, and training protocols. As a first step to quantifying individual differences in DNN representations, we systematically explored the robustness of a variety of representational similarity measures: Representational Similarity Analysis (RSA), Centered Kernel Alignment (CKA), and Projection-Weighted Canonical Correlation Analysis (PWCCA), with an eye to how these measures are used in cognitive science, cognitive neuroscience, and vision science. To manipulate object representations, we next created a large set of models varying in random initial weights and random training image order, training image frequencies, training category frequencies, and model size and architecture and measured the representational variation caused by each manipulation. We examined both small (All-CNN-C) and commonly-used large (VGG and ResNet) DNN architectures. To provide a comparison for the magnitude of representational differences, we established a baseline based on the representational variation caused by image-augmentation techniques used to train those DNNs. We found that variation in model randomization and model size never exceeded baseline. By contrast, differences in training image frequency and training category frequencies caused representational variation that exceeded baseline, with training category frequency manipulations exceeding baseline earlier in the networks. These findings provide insights into the magnitude of representational variations that can be expected with a range of manipulations and provide a springboard for further exploration of systematic model variations aimed at modeling individual differences in high-level visual cognition.

Temporal mechanisms in frontoparallel stereomotion revealed by individual differences analysis

Masking experiments, using vertical and horizontal sinusoidal depth corrugations, have suggested the existence of more than two spatial-frequency disparity mechanisms. This result was confirmed through an individual differences approach. Here, using factor analytic techniques, we want to investigate the existence of independent temporal mechanisms in frontoparallel stereoscopic (cyclopean) motion. To construct stereomotion, we used sinusoidal depth corrugations obtained with dynamic random-dot stereograms. Thus, no luminance motion was present monocularly. We measured disparity thresholds for drifting vertical (up-down) and horizontal (left-right) sinusoidal corrugations of 0.4 cyc/deg at 0.25, 0.5, 1, 2, 4, 6, and 8 Hz. In total, we tested 34 participants. Results showed a small orientation anisotropy with lower thresholds for horizontal corrugations. Disparity thresholds as a function of temporal frequency were almost constant from 0.25 up to 1 Hz, and then they increased monotonically. Principal component analysis uncovered two significant factors for vertical and two for horizontal corrugations. Varimax rotation showed that one factor loaded from 0.25 to 1-2 Hz and a second factor from 2 to 4 to 8 Hz. Direct Oblimin rotation indicated a moderate intercorrelation of both factors. Our results suggest the possible existence of two somewhat interdependent temporal mechanisms involved in frontoparallel stereomotion.

Large-scale citizen science reveals predictors of sensorimotor adaptation

Sensorimotor adaptation is essential for keeping our movements well calibrated in response to changes in the body and environment. For over a century, researchers have studied sensorimotor adaptation in laboratory settings that typically involve small sample sizes. While this approach has proved useful for characterizing different learning processes, laboratory studies are not well suited for exploring the myriad of factors that may modulate human performance. Here, using a citizen science website, we collected over 2,000 sessions of data on a visuomotor rotation task. This unique dataset has allowed us to replicate, reconcile and challenge classic findings in the learning and memory literature, as well as discover unappreciated demographic constraints associated with implicit and explicit processes that support sensorimotor adaptation. More generally, this study exemplifies how a large-scale exploratory approach can complement traditional hypothesis-driven laboratory research in advancing sensorimotor neuroscience.

Designing for sensory adaptation: what you see depends on what you've been looking at - Recommendations, guidelines and standards should reflect this

Sensory systems continuously recalibrate their responses according to the current stimulus environment. As a result, perception is strongly affected by the current and recent context. These adaptative changes affect both sensitivity (e.g., habituating to noise, seeing better in the dark) and appearance (e.g. how things look, what catches attention) and adjust to many perceptual properties (e.g. from light level to the characteristics of someone's face). They therefore have a profound effect on most perceptual experiences, and on how and how well the senses work in different settings. Characterizing the properties of adaptation, how it manifests, and when it influences perception in modern environments can provide insights into the diversity of human experience. Adaptation could also be leveraged both to optimize perceptual abilities (e.g. in visual inspection tasks like radiology) and to mitigate unwanted consequences (e.g. exposure to potentially unhealthy stimulus environments).

Distinct but related abilities for visual and haptic object recognition

People vary in their ability to recognize objects visually. Individual differences for matching and recognizing objects visually is supported by a domain-general ability capturing common variance across different tasks (e.g., Richler et al., Psychological Review, 126, 226-251, 2019). Behavioral (e.g., Cooke et al., Neuropsychologia, 45, 484-495, 2007) and neural evidence (e.g., Amedi, Cerebral Cortex, 12, 1202-1212, 2002) suggest overlapping mechanisms in the processing of visual and haptic information in the service of object recognition, but it is unclear whether such group-average results generalize to individual differences. Psychometrically validated measures are required, which have been lacking in the haptic modality. We investigate whether object recognition ability is specific to vision or extends to haptics using psychometric measures we have developed. We use multiple visual and haptic tests with different objects and different formats to measure domain-general visual and haptic abilities and to test for relations across them. We measured object recognition abilities using two visual tests and four haptic tests (two each for two kinds of haptic exploration) in 97 participants. Partial correlation and confirmatory factor analyses converge to support the existence of a domain-general haptic object recognition ability that is moderately correlated with domain-general visual object recognition ability. Visual and haptic abilities share about 25% of their variance, supporting the existence of a multisensory domain-general ability while leaving a substantial amount of residual variance for modality-specific abilities. These results extend our understanding of the structure of object recognition abilities; while there are mechanisms that may generalize across categories, tasks, and modalities, there are still other mechanisms that are distinct between modalities.

Evidence for an amodal domain-general object recognition ability

A general object recognition ability predicts performance across a variety of high-level visual tests, categories, and performance in haptic recognition. Does this ability extend to auditory recognition? Vision and haptics tap into similar representations of shape and texture. In contrast, features of auditory perception like pitch, timbre, or loudness do not readily translate into shape percepts related to edges, surfaces, or spatial arrangement of parts. We find that an auditory object recognition ability correlates highly with a visual object recognition ability after controlling for general intelligence, perceptual speed, low-level visual ability, and memory ability. Auditory object recognition was a stronger predictor of visual object recognition than all control measures across two experiments, even though those control variables were also tested visually. These results point towards a single high-level ability used in both vision and audition. Much work highlights how the integration of visual and auditory information is important in specific domains (e.g., speech, music), with evidence for some overlap of visual and auditory neural representations. Our results are the first to reveal a domain-general ability, o, that predicts object recognition performance in both visual and auditory tests. Because o is domain-general, it reveals mechanisms that apply across a wide range of situations, independent of experience and knowledge. As o is distinct from general intelligence, it is well positioned to potentially add predictive validity when explaining individual differences in a variety of tasks, above and beyond measures of common cognitive abilities like general intelligence and working memory.

Test-retest reliability of eye tracking measures in a computerized Trail Making Test

The Trail Making Test (TMT) is a frequently applied neuropsychological test that evaluates participants' executive functions based on their time to connect a sequence of numbers (TMT-A) or alternating numbers and letters (TMT-B). Test performance is associated with various cognitive functions ranging from visuomotor speed to working memory capabilities. However, although the test can screen for impaired executive functioning in a variety of neuropsychiatric disorders, it provides only little information about which specific cognitive impairments underlie performance detriments. To resolve this lack of specificity, recent cognitive research combined the TMT with eye tracking so that eye movements could help uncover reasons for performance impairments. However, using eye-tracking-based test scores to examine differences between persons, and ultimately apply the scores for diagnostics, presupposes that the reliability of the scores is established. Therefore, we investigated the test-retest reliabilities of scores in an eye-tracking version of the TMT recently introduced by Recker et al. (2022). We examined two healthy samples performing an initial test and then a retest 3 days (n = 31) or 10 to 30 days (n = 34) later. Results reveal that, although reliabilities of classic completion times were overall good, comparable with earlier versions, reliabilities of eye-tracking-based scores ranged from excellent (e.g., durations of fixations) to poor (e.g., number of fixations guiding manual responses). These findings indicate that some eye-tracking measures offer a strong basis for assessing interindividual differences beyond classic behavioral measures when examining processes related to information accumulation processes but are less suitable to diagnose differences in eye-hand coordination.

Calibrating Vision: Concepts and Questions

The idea that visual coding and perception are shaped by experience and adjust to changes in the environment or the observer is universally recognized as a cornerstone of visual processing, yet the functions and processes mediating these calibrations remain in many ways poorly understood. In this article we review a number of facets and issues surrounding the general notion of calibration, with a focus on plasticity within the encoding and representational stages of visual processing. These include how many types of calibrations there are - and how we decide; how plasticity for encoding is intertwined with other principles of sensory coding; how it is instantiated at the level of the dynamic networks mediating vision; how it varies with development or between individuals; and the factors that may limit the form or degree of the adjustments. Our goal is to give a small glimpse of an enormous and fundamental dimension of vision, and to point to some of the unresolved questions in our understanding of how and why ongoing calibrations are a pervasive and essential element of vision.

Emphasizing speed or accuracy in an eye-tracking version of the Trail-Making-Test: Towards experimental diagnostics for decomposing executive functions

The Trail-Making-Test (TMT) is one of the most widely used neuropsychological tests for assessing executive functions, the brain functions underlying cognitively controlled thought and action. Obtaining a number of test scores at once, the TMT allows to characterize an assortment of executive functions efficiently. Critically, however, as most test scores are derived from test completion times, the scores only provide a summary measure of various cognitive control processes. To address this problem, we extended the TMT in two ways. First, using a computerized eye-tracking version of the TMT, we added specific eye movement measures that deliver a richer set of data with a higher degree of cognitive process specificity. Second, we included an experimental manipulation of a fundamental executive function, namely participants’ ability to emphasize speed or accuracy in task performance. Our study of healthy participants showed that eye movement measures differed between TMT conditions that are usually compared to assess the cognitive control process of alternating between task sets for action control. This demonstrates that eye movement measures are indeed sensitive to executive functions implicated in the TMT. Crucially, comparing performance under cognitive control sets of speed vs. accuracy emphasis revealed which test scores primarily varied due to this manipulation (e.g., trial duration, number of fixations), and which were still more sensitive to other differences between individuals (e.g., fixation duration, saccade amplitude). This provided an experimental construct validation of the test scores by distinguishing scores primarily reflecting the executive function of emphasizing speed vs. accuracy and those independent from it. In sum, both the inclusion of eye movement measures and of the experimental manipulation of executive functions in the TMT enabled a more specific interpretation of the TMT in terms of cognitive functions and mechanisms, which offers more precise diagnoses in clinical applications and basic research.

Test-retest reliability for common tasks in vision science

Research in perception and attention has typically sought to evaluate cognitive mechanisms according to the average response to a manipulation. Recently, there has been a shift toward appreciating the value of individual differences and the insight gained by exploring the impacts of between-participant variation on human cognition. However, a recent study suggests that many robust, well-established cognitive control tasks suffer from surprisingly low levels of test-retest reliability (Hedge, Powell, & Sumner, 2018b). We tested a large sample of undergraduate students (n = 160) in two sessions (separated by 1-3 weeks) on four commonly used tasks in vision science. We implemented measures that spanned a range of perceptual and attentional processes, including motion coherence (MoCo), useful field of view (UFOV), multiple-object tracking (MOT), and visual working memory (VWM). Intraclass correlations ranged from good to poor, suggesting that some task measures are more suitable for assessing individual differences than others. VWM capacity (intraclass correlation coefficient [ICC] = 0.77), MoCo threshold (ICC = 0.60), UFOV middle accuracy (ICC = 0.60), and UFOV outer accuracy (ICC = 0.74) showed good-to-excellent reliability. Other measures, namely the maximum number of items tracked in MOT (ICC = 0.41) and UFOV number accuracy (ICC = 0.48), showed moderate reliability; the MOT threshold (ICC = 0.36) and UFOV inner accuracy (ICC = 0.30) showed poor reliability. In this paper, we present these results alongside a summary of reliabilities estimated previously for other vision science tasks. We then offer useful recommendations for evaluating test-retest reliability when considering a task for use in evaluating individual differences.

Do You See What I See? Diversity in Human Color Perception

In our tendency to discuss the objective properties of the external world, we may fail to notice that our subjective perceptions of those properties differ between individuals. Variability at all levels of the color vision system creates diversity in color perception, from discrimination to color matching, appearance, and subjective experience, such that each of us lives in a unique perceptual world. In this review, I discuss what is known about individual differences in color perception and its determinants, particularly considering genetically mediated variability in cone photopigments and the paradoxical effects of visual environments in both contributing to and counteracting individual differences. I make the case that, as well as being of interest in their own right and crucial for a complete account of color vision, individual differences can be used as a methodological tool in color science for the insights that they offer about the underlying mechanisms of perception. Expected final online publication date for the Annual Review of Vision Science, Volume 8 is September 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Two graphs walk into a bar: Readout-based measurement reveals the Bar-Tip Limit error, a common, categorical misinterpretation of mean bar graphs

How do viewers interpret graphs that abstract away from individual-level data to present only summaries of data such as means, intervals, distribution shapes, or effect sizes? Here, focusing on the mean bar graph as a prototypical example of such an abstracted presentation, we contribute three advances to the study of graph interpretation. First, we distill principles for Measurement of Abstract Graph Interpretation (MAGI principles) to guide the collection of valid interpretation data from viewers who may vary in expertise. Second, using these principles, we create the Draw Datapoints on Graphs (DDoG) measure, which collects drawn readouts (concrete, detailed, visuospatial records of thought) as a revealing window into each person's interpretation of a given graph. Third, using this new measure, we discover a common, categorical error in the interpretation of mean bar graphs: the Bar-Tip Limit (BTL) error. The BTL error is an apparent conflation of mean bar graphs with count bar graphs. It occurs when the raw data are assumed to be limited by the bar-tip, as in a count bar graph, rather than distributed across the bar-tip, as in a mean bar graph. In a large, demographically diverse sample, we observe the BTL error in about one in five persons; across educational levels, ages, and genders; and despite thoughtful responding and relevant foundational knowledge. The BTL error provides a case-in-point that simplification via abstraction in graph design can risk severe, high-prevalence misinterpretation. The ease with which our readout-based DDoG measure reveals the nature and likely cognitive mechanisms of the BTL error speaks to the value of both its readout-based approach and the MAGI principles that guided its creation. We conclude that mean bar graphs may be misinterpreted by a large portion of the population, and that enhanced measurement tools and strategies, like those introduced here, can fuel progress in the scientific study of graph interpretation.

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

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

Haptic object recognition based on shape relates to visual object recognition ability

Visual object recognition depends in large part on a domain-general ability (Richler et al. Psychol Rev 126(2): 226–251, 2019). Given evidence pointing towards shared mechanisms for object perception across vision and touch, we ask whether individual differences in haptic and visual object recognition are related. We use existing validated visual tests to estimate visual object recognition ability and relate it to performance on two novel tests of haptic object recognition ability (n = 66). One test includes complex objects that participants chose to explore with a hand grasp. The other test uses a simpler stimulus set that participants chose to explore with just their fingertips. Only performance on the haptic test with complex stimuli correlated with visual object recognition ability, suggesting a shared source of variance across task structures, stimuli, and modalities. A follow-up study using a visual version of the haptic test with simple stimuli shows a correlation with the original visual tests, suggesting that the limited complexity of the stimuli did not limit correlation with visual object recognition ability. Instead, we propose that the manner of exploration may be a critical factor in whether a haptic test relates to visual object recognition ability. Our results suggest a perceptual ability that spans at least across vision and touch, however, it may not be recruited during just fingertip exploration.

Measurement of individual differences in face-identity processing abilities in older adults

BACKGROUND

Face-identity processing declines with age. Few studies have examined whether face-identity processing abilities can be measured independently from general cognitive abilities in older adults (OA). This question has practical implications for the assessment of face-identity processing abilities in OA and theoretical implications for the notion of face processing as a specific ability. The present study examined the specificity of face memory and face matching abilities in OA aged 50 + .

METHODS

Performance of younger adults (YA) and OA was measured on face tasks: Cambridge Face Memory Task (CFMT), the Glasgow Face Matching Task (GFMT), holistic processing; and tasks of general cognition: fluid intelligence, selective attention, and mental rotation. Data were analyzed using multiple regression models encompassing (i) the CFMT/GFMT and measures of general cognition; and (ii) all face processing tasks.

RESULTS

Across the two age groups, models encompassing all face tasks were significant and accounted for more variance in the data than models encompassing the CFMT/GFMT and measures of general cognition. General cognitive abilities accounted for 17% of variance for the GFMT (p < 0.01) and 3% for the CFMT (p > 0.05).

DISCUSSION

Our results suggest that face memory can be measured independently from general cognition using the CFMT in OA. Implications for the notion of a general face processing factor across the adult lifespan are discussed.

Different measures of holistic face processing tap into distinct but partially overlapping mechanisms

Holistic processing, which includes the integration of facial features and analysis of their relations to one another, is a hallmark of what makes faces 'special'. Various experimental paradigms purport to measure holistic processing but these have often produced inconsistent results. This has led researchers to question the nature and structure of the mechanism(s) underlying holistic processing. Using an individual differences approach, researchers have examined relations between various measures of holistic processing in an attempt to resolve these questions. In keeping with this, we examined relationships between four commonly used measures of holistic face processing in a large group of participants (N = 223): (1) The Face Inversion Effect, (2) the Part Whole Effect (PWE), (3) the Composite Face Effect, and (4) the Configural Featural Detection Task (CFDT). Several novel methodological and analytical elements were introduced, including the use of factor analysis and the inclusion of control conditions to confirm the face specificity of all of the effects measured. The four indexes of holistic processing derived from each measure loaded onto two factors, one encompassing the PWE and the CFDT, and one encompassing the CE. The 16 conditions tested across the four tasks loaded onto four factors, each factor corresponding to a different measure. These results, together with those of other studies, suggest that holistic processing is a multifaceted construct and that different measures tap into distinct but partially overlapping elements of it.

Competition between perceptual grouping cues in an indirect objective task

The integration between Gestalt grouping cues has been a relatively unexplored issue in vision science. The present work introduces an objective indirect method based on the repetition discrimination task to determine the rules that govern the dominance dynamics of the competition between both intrinsic (Experiment 1: proximity vs luminance similarity) and extrinsic grouping cues (Experiment 2: common region vs connectedness) by means of objective measures of grouping (reaction times and accuracy). Prior to the main task, a novel objective equating task was introduced with the aim of equating the grouping strength of the cues for the visuomotor system. The main task included two single conditions with the grouping cues acting alone as well as two competing conditions displaying the grouping factors pitted against one another. Conventional aggregated analyses were combined with individual analysis and both revealed a consistent pattern of processing dominance of: (1) luminance similarity over proximity and (2) common region over connectedness. Interestingly, the individual analyses showed that, despite the heterogeneous responses to the single conditions, the pattern of dominance between cues was robustly homogeneous among the participants in the competing conditions.

Time-dependent discrimination advantages for harmonic sounds suggest efficient coding for memory

Perceptual systems have finite memory resources and must store incoming signals in compressed formats. To explore whether representations of a sound's pitch might derive from this need for compression, we compared discrimination of harmonic and inharmonic sounds across delays. In contrast to inharmonic spectra, harmonic spectra can be summarized, and thus compressed, using their fundamental frequency (f0). Participants heard two sounds and judged which was higher. Despite being comparable for sounds presented back-to-back, discrimination was better for harmonic than inharmonic stimuli when sounds were separated in time, implicating memory representations unique to harmonic sounds. Patterns of individual differences (correlations between thresholds in different conditions) indicated that listeners use different representations depending on the time delay between sounds, directly comparing the spectra of temporally adjacent sounds, but transitioning to comparing f0s across delays. The need to store sound in memory appears to determine reliance on f0-based pitch and may explain its importance in music, in which listeners must extract relationships between notes separated in time.

Feature-specificity in visual statistical summary processing

Visual statistical summary processing enables people to extract the average feature of a set of items rapidly and accurately. Previous studies have demonstrated independent mechanisms for summarizing low (e.g. color, orientation) and high-level (facial identity, emotion) visual information. However, no study to date has conclusively determined whether there are feature-specific summarization mechanisms for low-level features or whether there are low-level, feature agnostic summarization mechanisms. To address this issue, we asked participants to report either the average orientation or the average size from a set of lines where both features varied. Participants completed these tasks either in single-task or mixed-task conditions; in the latter, successful performance required extraction of both summaries concurrently. If there were feature-specific summarization mechanisms that could operate in parallel, then errors in mean size and mean orientation tasks should be independent, in both single and mixed task conditions. On the other hand, a central domain-general mechanism for low-level summarization would imply a correlation between errors for both features and greater error in the mixed than single task trials. In Experiment 1, we found that there was no correlation between the mean size and mean orientation errors and performance was similar across single and mixed-task conditions, suggesting that there may be independent summarization mechanisms for size and orientation features. To further test the feature-specificity account, in Experiment 2 and 3 (with mask), we manipulated the display duration to determine whether there were any differences in the summarization of earlier (orientation) vs. later (size) features. While these experiments replicated the pattern of results observed in Experiment 1, at shorter display durations, no differences emerged across features. We argue that our data is consistent with independent, multi-level feature-specific statistical summary mechanisms for low-level visual features.

Individual differences in processing orientation and proximity as emergent features

Numerous examples of meaningful inter-individual differences in visual processing have been documented in low- and high-level vision. For mid-level vision or perceptual organization, vision scientists have only recently started to study the inter-individual differences structure. In this study, we focus on orientation and proximity as emergent features and combine a quantitative information processing approach with an individual differences approach. We first replicated the results reported in Hawkins, Houpt, Eidels, and Townsend (2016) in a set of 52 observers. That is, observers showed higher processing capacity for detecting a change in a stimulus configuration when the emergent features orientation or proximity were changed. Next, we asked whether individual differences processing capacities were similar across emergent features. The capacity to detect any type of change correlated moderately across individuals, whereas the capacity to detect changes in either emergent feature alone was not strongly correlated. This indicates that there is no general sensitivity to emergent features and that observers can be good at detecting orientation changes whilst being poor at detecting proximity changes (and vice versa). An additional exploratory multivariate analysis of the data revealed that response times and accuracies correlated strongly within each emergent feature. Moreover, specific factors related to change detection and inward displacements were observed, revealing consistent individual differences in our data. We discuss the results in the context of the literature on individual differences in vision where both specific, fragmented factors as well as broad, general factors have been reported.

Independent and parallel visual processing of ensemble statistics: Evidence from dual tasks

The visual system can represent multiple objects in a compressed form of ensemble summary statistics (such as object numerosity, mean, and feature variance/range). Yet the relationships between the different types of visual statistics remain relatively unclear. Here, we tested whether two summaries (mean and numerosity, or mean and range) are calculated independently from each other and in parallel. Our participants performed dual tasks requiring a report about two summaries in each trial, and single tasks requiring a report about one of the summaries. We estimated trial-by-trial correlations between the precision of reports as well as correlations across observers. Both analyses showed the absence of correlations between different types of ensemble statistics, suggesting their independence. We also found no decrement (except that related to the order of report explained by memory retrieval) in performance in dual compared to single tasks, which suggests that two statistics of one ensemble can be processed in parallel.

Individual differences and their implications for color perception

Individual differences are a conspicuous feature of color vision and arise from many sources, in both the observer and the world. These differences have important practical implications for comparing and correcting perception and performance, and important theoretical implications for understanding the design principles underlying color coding. Color percepts within and between individuals often vary less than the variations in spectral sensitivity might predict. This stability is achieved by a variety of processes that compensate perception for the sensitivity limits of the eye and brain. Yet judgments of color between individuals can also vary widely, and in ways that are not readily explained by differences in sensitivity or the environment. These differences are uncorrelated across different color categories, and could reflect how these categories are learned or represented.

Cross-cultural analysis of attention disengagement times supports the dissociation of faces and patterns in the infant brain

Infants are slower to disengage from faces than non-face patterns when distracted by novel competing stimuli. While this perceptual predilection for faces is well documented, its universality and mechanisms in relation to other aspects of attention are poorly understood. We analysed attention disengagement times for faces and non-face patterns in a large sample of 6-to 9-month-old infants (N = 637), pooled from eye tracking studies in socioculturally diverse settings (Finland, Malawi, South Africa). Disengagement times were classified into distinct groups of quick and delayed/censored responses by unsupervised clustering. Delayed disengagement was frequent for faces (52.1% of trials), but almost negligible for patterns (3.9% of trials) in all populations. The magnitude of this attentional bias varied by individuals, whereas the impact of situational factors and facial expression was small. Individual variations in disengagement from faces were moderately stable within testing sessions and independent from variations in disengagement times for patterns. These results point to a fundamental dissociation of face and pattern processing in infants and demonstrate that the bias for faces can be robust against distractors and habituation. The results raise the possibility that attention to faces varies as an independent, early-emerging social trait in populations.

On Visually-Grounded Reference Production: Testing the Effects of Perceptual Grouping and 2D/3D Presentation Mode

When referring to a target object in a visual scene, speakers are assumed to consider certain distractor objects to be more relevant than others. The current research predicts that the way in which speakers come to a set of relevant distractors depends on how they perceive the distance between the objects in the scene. It reports on the results of two language production experiments, in which participants referred to target objects in photo-realistic visual scenes. Experiment 1 manipulated three factors that were expected to affect perceived distractor distance: two manipulations of perceptual grouping (region of space and type similarity), and one of presentation mode (2D vs. 3D). In line with most previous research on visually-grounded reference production, an offline measure of visual attention was taken here: the occurrence of overspecification with color. The results showed effects of region of space and type similarity on overspecification, suggesting that distractors that are perceived as being in the same group as the target are more often considered relevant distractors than distractors in a different group. Experiment 2 verified this suggestion with a direct measure of visual attention, eye tracking, and added a third manipulation of grouping: color similarity. For region of space in particular, the eye movements data indeed showed patterns in the expected direction: distractors within the same region as the target were fixated more often, and longer, than distractors in a different region. Color similarity was found to affect overspecification with color, but not gaze duration or the number of distractor fixations. Also the expected effects of presentation mode (2D vs. 3D) were not convincingly borne out by the data. Taken together, these results provide direct evidence for the close link between scene perception and language production, and indicate that perceptual grouping principles can guide speakers in determining the distractor set during reference production.

Spatial suppression promotes rapid figure-ground segmentation of moving objects

Segregation of objects from their backgrounds is a fundamental visual function and one that is particularly effective when objects are in motion. Theoretically, suppressive center-surround mechanisms are well suited for accomplishing motion segregation. This longstanding hypothesis, however, has received limited empirical support. We report converging correlational and causal evidence that spatial suppression of background motion signals is critical for rapid segmentation of moving objects. Motion segregation ability is strongly predicted by both individual and stimulus-driven variations in spatial suppression strength. Moreover, aging-related superiority in perceiving background motion is associated with profound impairments in motion segregation. This segregation deficit is alleviated via perceptual learning, but only when motion segregation training also causes decreased sensitivity to background motion. We argue that perceptual insensitivity to large moving stimuli effectively implements background subtraction, which, in turn, enhances the visibility of moving objects and accounts for the observed link between spatial suppression and motion segregation.

The visual system excels at segregating moving objects from their backgrounds, a key visual function hypothesized to be driven by suppressive centre-surround mechanisms. Here, the authors show that spatial suppression of background motion signals is critical for rapid segmentation of moving objects.

Global precedence effects account for individual differences in both face and object recognition performance

There has been an increase in studies adopting an individual difference approach to examine visual cognition and in particular in studies trying to relate face recognition performance with measures of holistic processing (the face composite effect and the part-whole effect). In the present study we examine whether global precedence effects, measured by means of non-face stimuli in Navon's paradigm, can also account for individual differences in face recognition and, if so, whether the effect is of similar magnitude for faces and objects. We find evidence that global precedence effects facilitate both face and object recognition, and to a similar extent. Our results suggest that both face and object recognition are characterized by a coarse-to-fine temporal dynamic, where global shape information is derived prior to local shape information, and that the efficiency of face and object recognition is related to the magnitude of the global precedence effect.

Individual differences in visual salience vary along semantic dimensions

What determines where we look? Theories of attentional guidance hold that image features and task demands govern fixation behavior, while differences between observers are interpreted as a "noise-ceiling" that strictly limits predictability of fixations. However, recent twin studies suggest a genetic basis of gaze-trace similarity for a given stimulus. This leads to the question of how individuals differ in their gaze behavior and what may explain these differences. Here, we investigated the fixations of >100 human adults freely viewing a large set of complex scenes containing thousands of semantically annotated objects. We found systematic individual differences in fixation frequencies along six semantic stimulus dimensions. These differences were large (>twofold) and highly stable across images and time. Surprisingly, they also held for first fixations directed toward each image, commonly interpreted as "bottom-up" visual salience. Their perceptual relevance was documented by a correlation between individual face salience and face recognition skills. The set of reliable individual salience dimensions and their covariance pattern replicated across samples from three different countries, suggesting they reflect fundamental biological mechanisms of attention. Our findings show stable individual differences in salience along a set of fundamental semantic dimensions and that these differences have meaningful perceptual implications. Visual salience reflects features of the observer as well as the image.

The prevalence and diagnosis of 'stereoblindness' in adults less than 60 years of age: a best evidence synthesis

PURPOSE

Stereoscopic vision (or stereopsis) is the ability to perceive depth from binocular disparity - the difference of viewpoints between the two eyes. Interestingly, there are large individual differences as to how well one can appreciate depth from such a cue. The total absence of stereoscopic vision, called 'stereoblindness', has been associated with negative behavioural outcomes such as poor distance estimation. Surprisingly, the prevalence of stereoblindness remains unclear, as it appears highly dependent on the way in which stereopsis is measured.

RECENT FINDINGS

This review highlights the fact that stereopsis is not a unitary construct, but rather implies different systems. The optimal conditions for measuring these varieties of stereoscopic information processing are discussed given the goal of detecting stereoblindness, using either psychophysical or clinical stereotests. In that light, we then discuss the estimates of stereoblindness prevalence of past studies.

SUMMARY

We identify four different approaches that all converge toward a prevalence of stereoblindness of 7% (median approach: 7%; unambiguous-stereoblindness-criteria approach: 7%; visual-defect-included approach: 7%; multiple-criteria approach: 7%). We note that these estimates were derived considering adults of age <60 years old. Older adults may have a higher prevalence. Finally, we make recommendations for a new ecological definition of stereoblindness and for efficient clinical methods for determining stereoblindness by adapting existing tools.

The uphill battle for action-specific perception

The action-specific account of perception states that a perceiver's ability to act influences the perception of the environment. For example, participants tend to perceive distances as farther when presented up hills than on the flat ground. This tendency is known as the distance-on-hill effect. However, there is debate as to whether these types of effects are truly perceptual. Critics of the action-specific account of perception claim that the effects could be due to participants guessing the hypothesis and trying to comply with the experimental demands. The present study aims to explore the distance-on-hill effect and determine whether it is truly perceptual or whether past results were due to response bias. Participants judged the relative distance to targets on a hill and the flat ground. We found the distance-on-hill effect in virtual reality using a visual matching task. The distance-on-hill effect persisted even when participants were given explicit feedback about their estimates. We also found that the effect went away, as predicted by a perceptual explanation, when participants had to match the distance between two cones that were both on hills. These results offer important steps toward the painstaking task of determining whether action's effect on perception is truly perceptual.

Early development of visual attention in infants in rural Malawi

Eye tracking research has shown that infants develop a repertoire of attentional capacities during the first year. The majority of studies examining the early development of attention comes from Western, high-resource countries. We examined visual attention in a heterogeneous sample of infants in rural Malawi (N = 312-376, depending on analysis). Infants were assessed with eye-tracking-based tests that targeted visual orienting, anticipatory looking, and attention to faces at 7 and 9 months. Consistent with prior research, infants exhibited active visual search for salient visual targets, anticipatory saccades to predictable events, and a robust attentional bias for happy and fearful faces. Individual variations in these processes had low to moderate odd-even split-half and test-retest reliability. There were no consistent associations between attention measures and gestational age, nutritional status, or characteristics of the rearing environment (i.e., maternal cognition, psychosocial well-being, socioeconomic status, and care practices). The results replicate infants' early attentional biases in a large, unique sample, and suggest that some of these biases (e.g., bias for faces) are pronounced in low-resource settings. The results provided no evidence that the initial manifestation of infants' attentional capacities is associated with risk factors that are common in low-resource environments.

How to Enhance the Power to Detect Brain-Behavior Correlations With Limited Resources

Neuroscience has been diagnosed with a pervasive lack of statistical power and, in turn, reliability. One remedy proposed is a massive increase of typical sample sizes. Parts of the neuroimaging community have embraced this recommendation and actively push for a reallocation of resources toward fewer but larger studies. This is especially true for neuroimaging studies focusing on individual differences to test brain-behavior correlations. Here, I argue for a more efficient solution. Ad hoc simulations show that statistical power crucially depends on the choice of behavioral and neural measures, as well as on sampling strategy. Specifically, behavioral prescreening and the selection of extreme groups can ascertain a high degree of robust in-sample variance. Due to the low cost of behavioral testing compared to neuroimaging, this is a more efficient way of increasing power. For example, prescreening can achieve the power boost afforded by an increase of sample sizes from n = 30 to n = 100 at ∼5% of the cost. This perspective article briefly presents simulations yielding these results, discusses the strengths and limitations of prescreening and addresses some potential counter-arguments. Researchers can use the accompanying online code to simulate the expected power boost of prescreening for their own studies.

Multidimensional internal dynamics underlying the perception of motion

When ambiguous visual stimuli are presented continuously, they often lead to oscillations between usually two perceptions. Because of these oscillations, it has been thought that the underlying neural dynamics also arises from a binary or two-state system. Contradicting the binary assumption, it has been shown recently that the perception of some ambiguous stimuli is governed by continuously varying internal states, measured as biases that differ considerably from one observer to the next and that can also evolve over time (Wexler, Duyck, & Mamassian, 2015). Here I study bias patterns in the motion quartet, an ambiguous apparent motion stimulus, as the quartet's orientation is varied. The bias patterns are robustly idiosyncratic, and are even more complex than those that have been described previously. There are two qualitatively different bias types: Some observers prefer a translation axis, while others show preference for a rotation direction. Each type also varies parametrically: the orientation of the preferred axis, and the direction of preferred rotation. There are also clear cases of combination of the two bias types. When measured repeatedly over 9 hr, the bias patterns usually remain stable, but also sometimes evolve both parametrically (e.g., change of preferred axis), as well as across bias type (change from axial to rotational bias). Control experiments revealed that the variety of bias patterns observed across subjects, and their changes over time, are not due to voluntary decisions. Overall, these results exhibit the multidimensional complexity of internal states underlying the perception of even simple stimuli.

Early development of attention to threat-related facial expressions

Infants from an early age have a bias to attend more to faces than non-faces and after 5 months are particularly attentive to fearful faces. We examined the specificity of this "fear bias" in 5-, 7-, and 12-month-old infants (N = 269) and 36-month-old children (N = 191) and whether its development is associated with features of the early rearing environment, specifically maternal anxiety and depression symptoms. Attention dwell times were assessed by measuring the latencies of gaze shifts from a stimulus at fixation to a new stimulus in the visual periphery. In infancy, dwell times were shorter for non-face control stimuli vs. happy faces at all ages, and happy vs. fearful, but not angry, faces at 7 and 12 months. At 36 months, dwell times were shorter for non-faces and happy faces compared to fearful and angry faces. Individual variations in attention dwell times were not associated with mothers' self-reported depression or anxiety symptoms at either age. The results suggest that sensitivity to fearful faces precedes a more general bias for threat-alerting stimuli in early development. We did not find evidence that the initial manifestation of these biases is related to moderate variations in maternal depression or anxiety symptoms.

Interpreting and Utilising Intersubject Variability in Brain Function

We consider between-subject variance in brain function as data rather than noise. We describe variability as a natural output of a noisy plastic system (the brain) where each subject embodies a particular parameterisation of that system. In this context, variability becomes an opportunity to: (i) better characterise typical versus atypical brain functions; (ii) reveal the different cognitive strategies and processing networks that can sustain similar tasks; and (iii) predict recovery capacity after brain damage by taking into account both damaged and spared processing pathways. This has many ramifications for understanding individual learning preferences and explaining the wide differences in human abilities and disabilities. Understanding variability boosts the translational potential of neuroimaging findings, in particular in clinical and educational neuroscience.

Determinants of neural responses to disparity in natural scenes

We studied disparity-evoked responses in natural scenes using high-density electroencephalography (EEG) in an event-related design. Thirty natural scenes that mainly included outdoor settings with trees and buildings were used. Twenty-four subjects viewed a series of trials composed of sequential two-alternative temporal forced-choice presentation of two different versions (two-dimensional [2D] vs. three-dimensional [3D]) of the same scene interleaved by a scrambled image with the same power spectrum. Scenes were viewed orthostereoscopically at 3 m through a pair of shutter glasses. After each trial, participants indicated with a key press which version of the scene was 3D. Performance on the discrimination was >90%. Participants who were more accurate also tended to respond faster; scenes that were reported more accurately as 3D also led to faster reaction times. We compared visual evoked potentials elicited by scrambled, 2D, and 3D scenes using reliable component analysis to reduce dimensionality. The disparity-evoked response to natural scene stimuli, measured from the difference potential between 2D and 3D scenes, comprised a sustained relative negativity in the dominant response component. The magnitude of the disparity-specific response was correlated with the observer's stereoacuity. Scenes with more homogeneous depth maps also tended to elicit large disparity-specific responses. Finally, the magnitude of the disparity-specific response was correlated with the magnitude of the differential response between scrambled and 2D scenes, suggesting that monocular higher-order scene statistics modulate disparity-specific responses.

Is There a Common Summary Statistical Process for Representing the Mean and Variance? A Study Using Illustrations of Familiar Items

A number of studies revealed that our visual system can extract different types of summary statistics, such as the mean and variance, from sets of items. Although the extraction of such summary statistics has been studied well in isolation, the relationship between these statistics remains unclear. In this study, we explored this issue using an individual differences approach. Observers viewed illustrations of strawberries and lollypops varying in size or orientation and performed four tasks in a within-subject design, namely mean and variance discrimination tasks with size and orientation domains. We found that the performances in the mean and variance discrimination tasks were not correlated with each other and demonstrated that extractions of the mean and variance are mediated by different representation mechanisms. In addition, we tested the relationship between performances in size and orientation domains for each summary statistic (i.e. mean and variance) and examined whether each summary statistic has distinct processes across perceptual domains. The results illustrated that statistical summary representations of size and orientation may share a common mechanism for representing the mean and possibly for representing variance. Introspections for each observer performing the tasks were also examined and discussed.

Individual differences in visual science: What can be learned and what is good experimental practice?

We all pass out our lives in private perceptual worlds. The differences in our sensory and perceptual experiences often go unnoticed until there emerges a variation (such as 'The Dress') that is large enough to generate different descriptions in the coarse coinage of our shared language. In this essay, we illustrate how individual differences contribute to a richer understanding of visual perception, but we also indicate some potential pitfalls that face the investigator who ventures into the field.

Thresholds for sine-wave corrugations defined by binocular disparity in random dot stereograms: Factor analysis of individual differences reveals two stereoscopic mechanisms tuned for spatial frequency

Threshold functions for sinusoidal depth corrugations typically reach their minimum (highest sensitivity) at spatial frequencies of 0.2-0.4 cycles/degree (cpd), with lower thresholds for horizontal than vertical corrugations at low spatial frequencies. To elucidate spatial frequency and orientation tuning of stereoscopic mechanisms, we measured the disparity sensitivity functions, and used factor analytic techniques to estimate the existence of independent underlying stereo channels. The data set (N = 30 individuals) was for horizontal and vertical corrugations of spatial frequencies ranging from 0.1 to 1.6 cpd. A principal component analysis of disparity sensitivities (log-arcsec) revealed that two significant factors accounted for 70% of the variability. Following Varimax rotation to approximate "simple structure", one factor clearly loaded onto low spatial frequencies (≤0.4 cpd), and a second was tuned to higher spatial frequencies (≥0.8 cpd). Each factor had nearly identical tuning (loadings) for horizontal and vertical patterns. The finding of separate factors for low and high spatial frequencies is consistent with previous studies. The failure to find separate factors for horizontal and vertical corrugations is somewhat surprising because the neuronal mechanisms are believed to be different. Following an oblique rotation (Direct Oblimin), the two factors correlated significantly, suggesting some interdependence rather than full independence between the two factors.

The Integration of Occlusion and Disparity Information for Judging Depth in Autism Spectrum Disorder

In autism spectrum disorder (ASD), atypical integration of visual depth cues may be due to flattened perceptual priors or selective fusion. The current study attempts to disentangle these explanations by psychophysically assessing within-modality integration of ordinal (occlusion) and metric (disparity) depth cues while accounting for sensitivity to stereoscopic information. Participants included 22 individuals with ASD and 23 typically developing matched controls. Although adults with ASD were found to have significantly poorer stereoacuity, they were still able to automatically integrate conflicting depth cues, lending support to the idea that priors are intact in ASD. However, dissimilarities in response speed variability between the ASD and TD groups suggests that there may be differences in the perceptual decision-making aspect of the task.

The numerosity and mean size of multiple objects are perceived independently and in parallel

It is well documented that people are good at the rapid representation of multiple objects in the form of ensemble summary statistics of different types (numerosity, the average feature, the variance of features, etc.). However, there is not enough clarity regarding the links between statistical domains. The relations between different-type summaries (numerosity and the mean) are of particular interest, since they can shed light on (1) a very general functional organization of ensemble processing and (2) mechanisms of statistical computations (whether averaging takes into account numerical information, as in regular statistics). Here, we show no correlation between the precision of estimated numerosity and that of the estimated mean. We also found that people are very good at dividing attention between numerosity and the mean size of a single set (Experiment 1); however, they show some cost of dividing attention between two same-type (two numerosities or two mean sizes, Experiment 2) and two different-type (one numerosity and one mean size, Experiment 3) summaries when each summary is ascribed to a different set. These results support the idea of domain specificity of numerosity and mean size perception, which also implies that, unlike regular statistics, computing the mean does not require numerosity information. We also conclude that computational capacity of ensemble statistics is more limited by encoding several ensembles than computing several summaries.