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1. Perceiving ensemble statistics of novel image sets

   https://doi.org/10.3758/s13414-020-02174-0  

   Khayat, Noam; Fusi, Stefano; Hochstein, Shaul (April 2021, Attention, Perception, & Psychophysics)

   null (Ed.)

   Abstract Perception, representation, and memory of ensemble statistics has attracted growing interest. Studies found that, at different abstraction levels, the brain represents similar items as unified percepts. We found that global ensemble perception is automatic and unconscious, affecting later perceptual judgments regarding individual member items. Implicit effects of set mean and range for low-level feature ensembles (size, orientation, brightness) were replicated for high-level category objects. This similarity suggests that analogous mechanisms underlie these extreme levels of abstraction. Here, we bridge the span between visual features and semantic object categories using the identical implicit perception experimental paradigm for intermediate novel visual-shape categories, constructing ensemble exemplars by introducing systematic variations of a central category base or ancestor. In five experiments, with different item variability, we test automatic representation of ensemble category characteristics and its effect on a subsequent memory task. Results show that observer representation of ensembles includes the group’s central shape, category ancestor (progenitor), or group mean. Observers also easily reject memory of shapes belonging to different categories, i.e. originating from different ancestors. We conclude that complex categories, like simple visual form ensembles, are represented in terms of statistics including a central object, as well as category boundaries. We refer to the model proposed by Benna and Fusi ( bioRxiv 624239, 2019) that memory representation is compressed when related elements are represented by identifying their ancestor and each one’s difference from it. We suggest that ensemble mean perception, like category prototype extraction, might reflect employment at different representation levels of an essential, general representation mechanism. 

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2. Category Learning Selectively Enhances Representations of Boundary-Adjacent Exemplars in Early Visual Cortex

   https://doi.org/10.1523/JNEUROSCI.1039-23.2023  

   O’Bryan, Sean R.; Jung, Shinyoung; Mohan, Anto J.; Scolari, Miranda (November 2023, The Journal of Neuroscience)

   Category learning and visual perception are fundamentally interactive processes, such that successful categorization often depends on the ability to make fine visual discriminations between stimuli that vary on continuously valued dimensions. Research suggests that category learning can improve perceptual discrimination along the stimulus dimensions that predict category membership and that these perceptual enhancements are a byproduct of functional plasticity in the visual system. However, the precise mechanisms underlying learning-dependent sensory modulation in categorization are not well understood. We hypothesized that category learning leads to a representational sharpening of underlying sensory populations tuned to values at or near the category boundary. Furthermore, such sharpening should occur largely during active learning of new categories. These hypotheses were tested using fMRI and a theoretically constrained model of vision to quantify changes in the shape of orientation representations while human adult subjects learned to categorize physically identical stimuli based on either an orientation rule (N = 12) or an orthogonal spatial frequency rule (N = 13). Consistent with our predictions, modeling results revealed relatively enhanced reconstructed representations of stimulus orientation in visual cortex (V1–V3) only for orientation rule learners. Moreover, these reconstructed representations varied as a function of distance from the category boundary, such that representations for challenging stimuli near the boundary were significantly sharper than those for stimuli at the category centers. These results support an efficient model of plasticity wherein only the sensory populations tuned to the most behaviorally relevant regions of feature space are enhanced during category learning. 

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3. The representational glue for incidental category learning is alignment with task-relevant behavior

   Roark, C. L.; Lehet, M.; Dick, F.; Holt, L. L. (January 2021, Journal of experimental psychology)

   null (Ed.)

   Category learning is fundamental to cognition, but little is known about how it proceeds in real-world environments when learners do not have instructions to search for category-relevant information, do not make overt category decisions, and do not experience direct feedback. Prior research demonstrates that listeners can acquire task-irrelevant auditory categories incidentally as they engage in primarily visuomotor tasks. The current study examines the factors that support this incidental category learning. Three experiments systematically manipulated the relationship of four novel auditory categories with a consistent visual feature (color or location) that informed a simple behavioral keypress response regarding the visual feature. In both an in-person experiment and two online replications with extensions, incidental auditory category learning occurred reliably when category exemplars consistently aligned with visuomotor demands of the primary task, but not when they were misaligned. The presence of an additional irrelevant visual feature that was uncorrelated with the primary task demands neither enhanced nor harmed incidental learning. By contrast, incidental learning did not occur when auditory categories were aligned consistently with one visual feature, but the motor response in the primary task was aligned with another, category-unaligned visual feature. Moreover, category learning did not reliably occur across passive observation or when participants made a category-nonspecific, generic motor response. These findings show that incidental learning of categories is strongly mediated by the character of coincident behavior. 

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4. Memory for incidentally learned categories evolves in the post-learning interval

   https://doi.org/10.7554/eLife.81855  

   Gabay, Yafit; Karni, Avi; Holt, Lori L (March 2023, eLife)

   Humans generate categories from complex regularities evolving across even imperfect sensory input. Here, we examined the possibility that incidental experiences can generate lasting category knowledge. Adults practiced a simple visuomotor task not dependent on acoustic input. Novel categories of acoustically complex sounds were not necessary for task success but aligned incidentally with distinct visuomotor responses in the task. Incidental sound category learning emerged robustly when within-category sound exemplar variability was closely yoked to visuomotor task demands and was not apparent in the initial session when this coupling was less robust. Nonetheless, incidentally acquired sound category knowledge was evident in both cases one day later, indicative of offline learning gains and, nine days later, learning in both cases supported explicit category labeling of novel sounds. Thus, a relatively brief incidental experience with multi-dimensional sound patterns aligned with behaviorally relevant actions and events can generate new sound categories, immediately after the learning experience or a day later. These categories undergo consolidation into long-term memory to support robust generalization of learning, rather than simply reflecting recall of specific sound-pattern exemplars previously encountered. Humans thus forage for information to acquire and consolidate new knowledge that may incidentally support behavior, even when learning is not strictly necessary for performance. 

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5. Incidental Nonspeech Auditory Learning Scaffolds Phonetic, Category, and Word Learning in a Foreign Language Classroom

   https://doi.org/10.1111/lang.12700  

   Wiener, Seth; Murphy, Timothy K; Holt, Lori L (January 2025, Language Learning)

   Abstract There is considerable lab‐based evidence for successful incidental learning, in which a learner's attention is directed away from the to‐be‐learned stimulus and towards another stimulus. In this study, we extend incidental learning research into the language learning classroom. Three groups of adult second language (L2) learners (N= 52) engaged in structured classroom Mandarin learning took part in an 8‐week study. One group served as a classroom‐only control group. The second group underwent additional intentional auditory training involving Mandarin speech and explicit feedback. The third group underwent additional incidental learning combined with nonspeech “perceptual building block” categories—categories that share critical perceptual dimensions with target L2 speech categories but that are not perceived as speech. We demonstrate that when supplemented with structured classroom learning, incidental learning involving nonspeech analogs promotes phonetic, category, and word learning equivalent to learning from more traditional intentional auditory training. 

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