Biology subjects

Walther, D. B.

Publications and source records attributed to Walther, D. B..

7 recordsLinked to original sources

bioRxiv2026

Shared symmetry detection with divergent temporal dynamics in marmosets and humans

Symmetry is a fundamental organizing principle of mid-level vision, yet which aspects of human symmetry processing are shared across primates remains unclear. Using steady-state visual evoked potentials during passive viewing, we compared responses to two well-matched wallpaper groups, double reflection (PMM) and four-fold rotation (P4), in common marmosets and humans, using identical stimuli. Marmosets showed robust reflection-symmetry responses comparable in relative magnitude, temporal dynamics and scalp distribution to those of humans. Rotation responses were also reliable but transient, lacking the sustained late component prominent in humans. This dissociation suggests that feedforward computations underlying symmetry detection are conserved across primates, whereas sustained processing that elaborates symmetry representations (likely recurrent or feedback in origin) is reduced in marmosets, particularly for rotation. These findings establish marmosets as a tractable model for symmetry processing and open a path to intracortical recording in accessible extrastriate cortex.

neuroscience↗

bioRxiv2023

Organization of pRF size along the AP axis of the hippocampus is related to specialization for scenes

The hippocampus is largely recognized for its integral contributions to memory processing. By contrast, its role in perceptual processing remains less clear. Hippocampal properties differ along the anterior-posterior (AP) axis. Based on past research suggesting a gradient in the scale of features processed along the anterior-posterior extent of the hippocampus, the representations have been proposed to differ as a function of granularity along this axis. One way to quantify such granularity is with population receptive field (pRF) size measured during visual processing, which has so far received little attention. In this study, we compare the pRF sizes within the hippocampus to its activation for images of scenes versus faces. We also measure these functional properties in surrounding medial temporal lobe (MTL) structures. Consistent with past research, we find pRFs to be larger in anterior than in the posterior hippocampus. Critically, our analysis of surrounding MTL regions, such as the perirhinal cortex, entorhinal cortex and parahippocampal cortex, shows a similar relationship between scene sensitivity and larger pRF size. These findings provide conclusive evidence for a tight relationship between pRF size and the sensitivity to image content in the hippocampus.

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bioRxiv2022

Multimodal Object Representations Rely on Integrative Coding

Combining information from multiple senses is essential to object recognition. Yet how the mind combines sensory input into coherent multimodal representations - the multimodal binding problem - remains poorly understood. Here, we applied multi-echo fMRI across a four-day paradigm, in which participants learned 3-dimensional multimodal object representations created from well-characterized visual shape and sound features. Our novel paradigm decoupled the learned multimodal object representations from their baseline unimodal shape and sound features, thus tracking the emergence of multimodal concepts as they were learned by healthy adults. Critically, the representation for the whole object was different from the combined representation of its individual parts, with evidence of an integrative object code in anterior temporal lobe structures. Intriguingly, the perirhinal cortex - an anterior temporal lobe structure - was by default biased towards visual shape, but this initial shape bias was attenuated with learning. Pattern similarity analyses suggest that after learning the perirhinal cortex orthogonalized combinations of visual shape and sound features, transforming overlapping feature input into distinct multimodal object representations. These results provide evidence of integrative coding in the anterior temporal lobes that is distinct from the distributed sensory features, advancing the age-old question of how the mind constructs multimodal objects from their component features.

neuroscience↗

bioRxiv2022

Neither sharpened or lost -- the unique role of attention in children's neural representations

One critical feature of childrens cognition is their relatively immature attention. Decades of research have shown that childrens attentional abilities mature slowly over the course of development, including the ability to filter out distracting information. Despite such rich behavioral literature, little is known about how developing attentional abilities modulate neural representations in children. This information is critical to understanding exactly how attentional development shapes the way children process information. One intriguing possibility is that attention might be less likely to impact neural representations in children as compared with adults. In particular, representations of attended items may be less likely to be sharpened relative to unattended items in children as compared to adults. To investigate this possibility, we measured brain activity using fMRI while adults (21-31 years) and children (7-9 years) performed a one-back working memory task in which they were directed to attend to either motion direction or an object in a complex display where both were present. We used multivoxel pattern analysis and compared decoding accuracy of attended and unattended information. Consistent with attentional sharpening, we found higher decoding accuracy for task-relevant information (i.e., objects in the object-attended condition) than for task-irrelevant information (i.e., motion in the object-attended condition) in adults visual cortices. However, in childrens visual cortices, both task-relevant and task-irrelevant information were decoded equally well. Whats more, exploratory whole-brain analysis showed that the children represent task-irrelevant information more than adults in multiple regions across the brain, including the prefrontal cortex. These findings show that 1) attention does not sharpen neural representations in the child visual cortex, and further 2) that the developing brain can represent more information than the adult brain.

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bioRxiv2020

Task dependence of neural representations of global scene properties but not scene categories in the prefrontal cortex

Natural scenes deliver rich sensory information about the world. Decades of research has shown that the scene-selective network in the visual cortex represents various aspects of scenes. However, less is known about how such complex scene information is processed beyond the visual cortex, such as in the prefrontal cortex. It is also unknown how task context impacts the process of scene perception, modulating which scene content is represented in the brain. In this study, we investigate these questions using scene images from four natural scene categories, which also depict two types of scene attributes, temperature (warm or cold), and sound level (noisy or quiet). A group of healthy human subjects from both sexes participated in the present study using fMRI. In the study, participants viewed scene images under two different task conditions; temperature judgment and sound-level judgment. We analyzed how these scene attributes and categories are represented across the brain under these task conditions. Our findings show that scene attributes (temperature and sound-level) are only represented in the brain when they are task-relevant. However, scene categories are represented in the brain, in both the parahippocampal place area and the prefrontal cortex, regardless of task context. These findings suggest that the prefrontal cortex selectively represents scene content according to task demands, but this task selectivity depends on the types of scene content; task modulates neural representations of scene attributes but not of scene categories. Significance statementResearch has shown that visual scene information is processed in scene-selective regions in the occipital and temporal cortices. Here, we ask how scene content is processed and represented beyond the visual brain, in the prefrontal cortex (PFC). We show that both scene categories and scene attributes are represented in PFC, with interesting differences in task dependency: Scene attributes are only represented in PFC when they are task-relevant, but scene categories are represented in PFC regardless of the task context. Taken together, our work shows that scene information is processed beyond the visual cortex, and scene representation in PFC reflects how adaptively our minds extract relevant information from a scene.

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bioRxiv2020

Scene wheels: Measuring perception and memory of real-world scenes with a continuous stimulus space

Precisely characterizing mental representations of visual experiences requires careful control of experimental stimuli. Recent work leveraging such stimulus control has led to important insights; however, these findings are constrained to simple visual properties like colour and line orientation. There remains a critical methodological barrier to characterizing perceptual and mnemonic representations of realistic visual experiences. Here, we introduce a novel method to systematically control visual properties of natural scene stimuli. Using generative adversarial networks (GAN), a state-of-art deep learning technique for creating highly realistic synthetic images, we generated scene wheels in which continuously changing visual properties smoothly transition between meaningful realistic scenes. To validate the efficacy of scene wheels, we conducted two behavioral experiments that assess perceptual and mnemonic representations attained from the scene wheels. In the perceptual validation experiment, we tested whether the continuous transition of scene images along the wheel is reflected in human perceptual similarity judgment. The perceived similarity of the scene images correspondingly decreased as distances between the images increase on the wheel. In the memory experiment, participants reconstructed to-be-remembered scenes from the scene wheels. Reconstruction errors for these scenes resemble error distributions observed in prior studies using simple stimulus properties. Importantly, perceptual similarity judgment and memory precision varied systematically with scene wheel radius. These findings suggest our novel approach offers a window into the mental representations of naturalistic visual experiences.

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bioRxiv2017

Modality-Independent Coding Of Concepts In Prefrontal Cortex

Natural environments convey information through multiple sensory modalities, all of which contribute to peoples percepts. Although it has been shown that visual or auditory content of scene categories can be decoded from brain activity, it remains unclear where and how humans integrate different sensory inputs and represent scene information beyond a specific sensory modality domain. To address this question, we investigated how categories of scene images and sounds are represented in several brain regions. A mixed gender group of healthy human subjects participated the present study, where their brain activity was measured with fMRI while viewing images or listening to sounds of different places. We found that both visual and auditory scene categories can be decoded not only from modality-specific areas, but also from several brain regions in the temporal, parietal, and prefrontal cortex. Intriguingly, only in the prefrontal cortex, but not in any other regions, categories of scene images and sounds appear to be represented in similar activation patterns, suggesting that scene representations in the prefrontal cortex are modality-independent. Furthermore, the error patterns of neural decoders indicate that category-specific neural activity patterns in the middle and superior frontal gyri are tightly linked to categorization behavior. Our findings demonstrate that complex scene information is represented at an abstract level in the prefrontal cortex, regardless of the sensory modality of the stimulus.\n\nStatement of SignificanceOur experience in daily life requires the integration of multiple sensory inputs such as images, sounds, or scents from the environment. Here, for the first time, we investigated where and how in the brain information about the natural environment from multiple senses is merged to form modality-independent representations of scene categories. We show direct decoding of scene categories across sensory modalities from patterns of neural activity in the prefrontal cortex. We also conclusively tie these neural representations to human categorization behavior based on the errors from the neural decoder and behavior. Our findings suggest that the prefrontal cortex is a central hub for integrating sensory information and computing modality-independent representations of scene categories.

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