About

Justin Halberda is a professor in the Department of Psychological & Brain Sciences at Johns Hopkins University, where he also serves as Co-Director of Undergraduate Studies. His research interests include the interaction of vision, cognition, and language. He directs two laboratories that often collaborate: the Laboratory For Child Development, co-directed with Lisa Feigenson, which investigates language acquisition and the role of logical deductive inference in learning new words, working with infants, children, and adults. This lab trains students in eye-tracking and anticipatory-looking paradigms, focusing on the development of logical reasoning abilities and the interaction between quantifier terms and non-linguistic numerical systems. The second lab, the Vision And Cognition Lab, explores the organization of attention, working memory, and how the mind constructs representations of the world from sensory information, utilizing empirical methods and computational modeling. Students are encouraged to collaborate across labs and participate in research studies.

Research topics

• Computer Science
• Psychology
• Linguistics
• Cognitive psychology
• Artificial Intelligence
• Philosophy
• Natural Language Processing
• Mathematics
• Developmental psychology
• History
• Epistemology
• Cognitive science
• Arithmetic
• Biology
• Evolutionary biology
• Neuroscience
• Communication

Selected publications

• Guessing reveals internal models of perceptual precision

  bioRxiv (Cold Spring Harbor Laboratory) · 2026-01-16

  articleOpen accessSenior author

  Abstract When observers lack sufficient information to support a confident response, they often guess. Guessing plays a pervasive role in visual cognition and working memory, yet the mechanisms that govern how observers generate guesses remain poorly understood. Standard models traditionally assume that responses produced in the absence of information are either uniformly distributed over feature space or are perhaps weighted towards prevailing environmental statistics. In contrast, here we consider an intriguing alternative: that guesses incorporate observers’ knowledge of their own perceptual capacities. We empirically measured guessing by eliciting responses under extreme target uncertainty (Experiment 1) as well as a novel “0ms presentation” approach in which no stimulus appeared but subjects believed one had (Experiment 2). We evaluated three accounts of guesses under these conditions: unsystematic (lapse) responding, biases toward environmental statistics, and a self-representational account in which guesses reflect observers’ knowledge of their own feature-dependent precision (e.g., preferring to guess feature values they believe they would be likely to miss). Guess responses were non-uniform and systematically biased toward feature values typically encoded with the least precision (e.g., oblique orientations) — a counterintuitive bias away from high-frequency, high-fidelity feature values (e.g., cardinal orientations). This complementary relationship between guessing and perceptual fidelity held within individuals and across paradigms, and was recoverable via an empirical-guess mixture model that replaced the standard uniform assumption with empirically measured guess distributions. Our findings challenge prevailing views that guesses reflect random noise, and suggest instead that guessing behavior reflects metacognitive knowledge of internal precision. Rather than defaulting to environmental priors, observers appear to model their own sensory limitations and leverage these representations to inform decisions in the absence of evidence. These results reframe guessing as a theoretically informative behavior that expresses observers’ own beliefs about their perceptual capacities. Significance Guessing is commonly treated as random noise in models of perception and memory, assumed to reflect lapses or uninformed responses. Instead, we show that human guesses are systematically structured across feature space: observers preferentially guess values they typically encode with the least precision, revealing a consistent, strategic bias away from high-fidelity representations. By directly measuring guess behavior on stimulus-absent trials and integrating these empirical distributions into a mixture model, we find that guesses on stimulus-present trials can be systematically recovered, and that they too form the complement of perceptual precision. These findings challenge foundational psychophysical modeling assumptions and position guessing as a strategic, informative behavior that engages self-representation.

  PublisherOA PDFDOI

• Gradual inversion costs as a function of rotation for face recognition in a flicker paradigm

  Journal of Vision · 2025-07-15

  articleOpen accessSenior author

  Faces are harder to recognize when they appear upside down—an inversion cost. This classic result is explained by a shift from configural & component processing to only component processing. However, this shift in encoding is not well characterized in the face literature through intermediate rotations. Is a face also harder to recognize when it is nearly upside down, e.g. rotated by 135°? How hard is it, comparatively, when the rotation is 90° or 45°? Face recognition as a function of orientation—from upright to upside down—should reveal how and why face processing mechanisms absorb costs for inversion. We therefore investigated face recognition as a function of orientation using flicker change detection. In Experiment 1, participants searched for a changing face within an array of five (drawn from the Chicago Face Database) at orientations between 0° and 180° in 45° steps. When all the faces were upside down reaction times were significantly longer than when all were upright—an inversion cost. Reaction times increased through the intermediate rotations following a sigmoidal function, with an inflection at 90°. These results are consistent with a monotonic, non-linear loss of configural signal as faces rotate from upright to inverted rather than an immediate and complete loss at any non-upright orientation. In Experiment 2, we characterized the inversion cost for other objects (scenes, animals, and vehicles). If faces are special, they should be an outlier among our tested objects. However, all object classes contributed to the positive relationship between time to detect an item change and the inversion effect – i.e., the magnitude of the inversion effect scales with the overall difficulty of identification. That is, all categories show an inversion effect that is proportional to the difficulty of processing that item type, and faces are not special in this regard.

  PublisherDOI

• Number adaptation survives spatial displacement

  Current Biology · 2025-11-13 · 4 citations

  articleSenior author
  PublisherDOI

• Logical concepts of (im)possibility guide young children's decision-making

  2025-06-06

  preprintOpen accessSenior author

  The human capacity for rational decisions hinges on modal judgment: the discernment of what could, has to, or cannot happen. This ability was proposed to be a late outcome of human cognitive development, contingent on the mastery of linguistic structures. Here, we show that preschool-age children are capable of sophisticated forms of modal judgment. In two experiments, 96 children (aged 34-to-65 months) helped an agent attain a benefit or avoid harm. Consistent with logical distinctions, we found that children perform best when faced with choices that cross the logical categories of necessity, possibility, and impossibility, while they struggle with choices only differing in probability. Our results reveal that preschoolers spontaneously recruit logical concepts required for modal judgment, which likely predates modal language

  PublisherOA PDFDOI

• Conscious perception travels with early visual paths

  Journal of Vision · 2025-07-15

  articleOpen accessSenior author

  A staggering example of apparent motion is the Ternus illusion: when two discs are shown side by side, and then shifted horizontally, the temporal gap between the successive presentations determines whether observers perceive element-wise or group motion. At long (20ms) intervals, group motion is perceived; at brief (0ms) intervals, element-wise motion is perceived. Will an object-file travel with our conscious percept, or will assignment prioritize spatiotemporal proximity? To test these possibilities, we exploited a well-known paradigm – the object-specific preview benefit (OSPB) – in which “previewing” information presented on one object results in faster and more accurate retrieval if the information later reappears on the “same” object relative to another object. If moving objects are defined by spatiotemporal proximity, an OSPB should not follow an object that appears to “jump” when element-wise motion is perceived. However, if the object file system tracks conscious perception, we should expect to see benefits at the “perceived” final position of the object. Observers viewed an apparent motion display consisting of three horizontally adjacent discs containing letters. Following a variable blank inter-stimulus interval, (0ms or 20ms), the discs reappeared shifted one position rightward, with a probe letter reappearing on either the same or different discs. Observers reported whether the probe contained the same letter shown at the beginning of the trial. Strikingly, observers’ reaction times and accuracy reflected a characteristic OSPB in accordance with the induced percept: participants retrieved the feature faster and more accurately both when the probed object appeared to translate (20ms intervals), as well as when it appeared to jump (0ms intervals). These results suggest that object identity is mapped across the perceived object motion path induced by the inter-stimulus interval, even if the induced motion path is not the shortest. Thus, in the Ternus display, object files mirror our conscious percepts.

  PublisherDOI

• Popout and object re-identification

  Journal of Vision · 2025-07-15

  articleOpen access

  The phenomenon of pop-out is commonplace in everyday experience and fundamental to studying the interface between early and mid-level vision (e.g., object-based representation). One question concerns how the visual system prioritizes features following pop-out. Does the feature that caused the pop-out get represented with higher priority or fidelity compared to the object’s other features? For instance, one might perceive a colored rectangular object among colored disks and perceptually represent, “that rectangle (pop-out feature) over there just happens to be red (ancillary feature)” Furthermore, given its task of reidentifying objects over time, it makes sense that the visual system would prioritize pop-out features. For example, if an object’s color is distinctive but its shape is not, then it can be reidentified more accurately using color. To explore the perceptual priority of pop-out features, 20 adults participated in a visual search and memory task using a staircase procedure. In each trial, participants viewed 9 objects, one of which was unique (a singleton, differing in color, orientation, or size) for 500 ms. Participants were asked to detect the unique object and remember its features. Following a 500 ms mask, participants clicked on the pop-out target's location. Then a probe item appeared in the same location as the target. The probe either matched the original or had one altered feature, with the degree of difference in the altered cases adapting to the participant's performance on each feature dimension. Results revealed a significant memory advantage for pop-out features over non-pop-out features, demonstrating that pop-out features are prioritized in visual working memory, supporting their enhanced role in the visual processing and reidentification of objects.

  PublisherDOI

• Logical Concepts of (Im)possibility Guide Young Children's Decision‐Making

  Developmental Science · 2025-06-27 · 1 citations

  articleSenior authorCorresponding

  The human capacity for rational decisions hinges on modal judgment: the discernment of what could, has to, or cannot happen. This ability was proposed to be a late outcome of human cognitive development, contingent on the mastery of linguistic structures. Here, we show that preschool-age children are capable of sophisticated forms of modal judgment. In two experiments, 96 children (aged 34-65 months) helped an agent attain a benefit or avoid harm. Consistent with logical distinctions, we found that children perform best when faced with choices that cross the logical categories of necessity, possibility, and impossibility, while they struggle with choices only differing in probability. Our results reveal that preschoolers spontaneously recruit logical concepts required for modal judgment, which likely predates modal language. Summary Rational plans and decisions under uncertainty hinge on modal judgment: the discernment between goals that are attainable, unattainable, or guaranteed. It has been proposed that modal concepts are not available prior to the age of 4 years and the acquisition of modal words like "can" and "have to." In a novel paradigm, we found that preschoolers successfully make one-shot decisions between options that cross logical categories (i.e., necessity vs. possibility, possibility vs. impossibility). In contrast, 3-year-olds struggled when asked to compare probabilities within the same category (i.e., highly probable possibility vs. improbable possibility). Our findings reveal that young children have a logical understanding of modal categories that emerges spontaneously to guide their decisions and predates the mastery of modal language.

  PublisherDOI

• Non-numerical features fail to predict numerical performance in real-world stimuli

  Cognitive Development · 2024-01-01 · 7 citations

  articleOpen accessSenior author

  It has been proposed that humans use non-numerical features (such as convex hull and surface area) to estimate the number of objects in a scene. This would be an evolutionarily advantageous strategy if such features truly patterned with number in the world, but this has never been empirically tested. Here, we quantify the strength of the relationship between number and non-numerical features in two relevant image sets: the illustrations from children’s counting books, and real-world photographs. We find that non-numerical features are much less predictive of the number of objects in counting books than in photographs, despite the former being specifically designed for use in teaching children about numbers. Then, across three behavioral experiments, we ask whether the stronger relationship in photographs predicts better number estimation performance in adults (N = 120) and in children (N = 94; M age = 7;2 years). Our experiments reveal that number estimation is easier from the counting books than the photographs, even though non-numerical features are less predictive of number in books. This analysis uses real-world stimuli and draws into question the claim that non-numerical features are intrinsically involved in number extraction.

  PublisherDOI

• Number: Still a primary visual feature

  Journal of Vision · 2024-09-15 · 2 citations

  articleOpen accessSenior author

  Some of the strongest evidence that number is a primary visual feature (like color or contrast) comes from experiments demonstrating visual adaptation to number (e.g., Burr & Ross, 2008), wherein staring at a large number of dots decreases numerosity estimates of subsequent probe displays. Recently, these findings have been challenged by a deflationary account on which these effects reflect spatiotopic attenuation to unchanging information (Yousif et al., 2023). Here, we conduct a crucial comparison of these accounts by testing number adaptation for arrays whose spatial properties constantly change. Centrally fixating observers viewed two large discs subtending 9° that independently and randomly translated on either side (left or right) of the display. During the adaptation phase, varying numbers of dots appeared and faded at changing locations within each continuously-moving disc. After 12 seconds, the dots disappeared and the discs continued moving for an additional 1000ms. Following this delay, a tone signaled the appearance of a new number of probe dots, appearing for 500ms in new locations within each disc; observers judged which disc contained more dots. On critical trials, probe dots were equal in number at the time of the tone. If number is a primary visual feature that can be bound to an object, then subjects should show an adaptation effect (thereby judging the disc previously containing the smaller adapter number as greater). If number adaptation effects are really spatiotopic attenuation to unchanging information, then subjects should not show an adaptation effect. Subjects showed the predicted adaptation effect. This result suggests that number adaptation persists despite drastic changes to spatiotopic and retinotopic position, contra an explanation in which adaptation results from filtering out information that remains unchanged between adapter and probe displays. Our findings re-open the case for genuine number adaptation and numerosity as a primary visual feature more broadly.

  PublisherDOI

• Observers Efficiently Extract the Minimal and Maximal Element in Perceptual Magnitude Sets: Evidence for a Bipartite Format

  Psychological Science · 2024-01-18 · 2 citations

  articleOpen accessSenior author

  The mind represents abstract magnitude information, including time, space, and number, but in what format is this information stored? We show support for the bipartite format of perceptual magnitudes, in which the measured value on a dimension is scaled to the dynamic range of the input, leading to a privileged status for values at the lowest and highest end of the range. In six experiments with college undergraduates, we show that observers are faster and more accurate to find the endpoints (i.e., the minimum and maximum) than any of the inner values, even as the number of items increases beyond visual short-term memory limits. Our results show that length, size, and number are represented in a dynamic format that allows for comparison-free sorting, with endpoints represented with an immediately accessible status, consistent with the bipartite model of perceptual magnitudes. We discuss the implications for theories of visual search and ensemble perception.

  PublisherOA PDFDOI

Recent grants

• The Psychophysical Assessment of Number-Sense Acuity

  NSF · $293k · 2009–2012

• NIH Grant R01HD057258

  NIH · $1.6M · 2014

• Empirical Research - Collaborative Research - A Bayesian Approach to Number Reasoning

  NSF · $159k · 2011–2014

Frequent coauthors

• Lisa Feigenson

  Johns Hopkins University

  33 shared

• Darko Odic

  University of British Columbia

  30 shared

• Melissa E. Libertus

  University of Pittsburgh

  24 shared

• Jeffrey Lidz

  University of Maryland, College Park

  19 shared

• Paul M. Pietroski

  Rutgers Sexual and Reproductive Health and Rights

  17 shared

• Hrag Pailian

  Huawei Technologies (Canada)

  16 shared

• Hee Yeon Im

  University of British Columbia

  13 shared

• Tim B. Hunter

  12 shared

Labs

• Justin Halberda LaboratoryPI