Biology subjects

Dumoulin, S. O.

Publications and source records attributed to Dumoulin, S. O..

11 recordsLinked to original sources

bioRxiv2025

Attraction of population receptive fields towards the attended locus is invariant to contrast

Attention enhances perception and spatial resolution. One mechanism by which attention achieves this is by attracting receptive fields towards the attended locus. The literature remains unclear on whether stimulus-driven parameters like contrast should alter this attraction. On one hand, Bayesian interpretation predicts changes in attraction due to contrast, whereas attention field models do not. Here we investigate whether stimulus contrast alters attention-driven attraction towards the attended locus. We used a demanding attentional task at fixation (0.1{degrees}) while mapping population receptive fields (pRFs) using either a low-contrast (5% Michelson contrast) or a high-contrast (80% Michelson contrast) checkerboard bar. Behavioral performance across conditions was matched. We show large and consistent differences in the amplitude of responses, but surprisingly, no difference in the amount of attraction towards the attended locus. The variance explained in this experiment was comparable to that of similar studies, which did observe pRF property changes, suggesting sufficient sensitivity to detect attraction towards the attended locus had it occurred at a similar magnitude. Our results cannot be explained by the Bayesian interpretation that predicts attention-based attraction effects varying with contrast. Instead, attention field models better account for our observations.

neuroscience↗

bioRxiv2025

The precision of attention controls attraction of population receptive fields

We alter our sampling of visual space not only by where we direct our gaze but also by where and how we direct our attention. Attention attracts receptive fields toward the attended position, but our understanding of this process is limited. Here we show that the degree of this attraction towards the attended locus is dictated not just by the attended position, but also by the precision of attention. We manipulated attentional precision while using 7T fMRI to measure population receptive field (pRF) properties. Participants performed the same color-proportion detection task either focused at fixation (0.1{degrees} radius) or distributed across the entire display (more than 5{degrees} radius). We observed BOLD response amplitude increases as a function of the task, with selective increases in foveal pRFs for the focused attention task and vice versa for the distributed attention task. Furthermore, cortical spatial tuning changed as a function of attentional precision. Specifically, focused attention more strongly attracted pRFs towards the attended locus compared to distributed attention. This attraction also depended on the degree of overlap between a pRF and the attention field. A Gaussian attention field model with an offset on the attention field explained our results. Together, our observations indicate the spatial distribution of attention dictates the degree of its resampling of visual space.

neuroscience↗

bioRxiv2025

Non-invasive mapping of the temporal processing hierarchy in the human visual cortex

Vision is not instantaneous but evolves over time. However, simultaneously capturing the fine spatial details and the rapid temporal dynamics of visual processing remains a major challenge, resulting in a gap in our understanding of spatiotemporal dynamics. Here, we introduce a forward modeling technique that bridges high-spatial resolution fMRI with high-temporal resolution MEG, enabling us to non-invasively measure different levels of the visual hierarchy in humans and their involvement in visual processing with millisecond precision. Using fMRI, levels of the visual hierarchy were identified by measuring individuals population receptive fields and determining visual field maps. We predicted how much the activity patterns in each visual field map would contribute to brain responses measured with MEG. By comparing these predicted responses with the measured MEG responses, we assessed how much a given visual field map contributed to the measured MEG response, and, most importantly, when. We combined information from all MEG sensors and revealed a cortical processing hierarchy across visual field maps. We validated the method using cross-validations and demonstrated that the model generalized across MEG sensor types, stimulus shapes, and was robust to the number of visual field maps included in the model. We found that the primary visual cortex captured most of the variance in the MEG sensors and did so earlier in time than extrastriate regions. We also report a processing hierarchy across extra-striate visual field maps and clusters. We effectively combined the advantages of two very different neuroimaging techniques, opening avenues for answering research questions that require recordings with high spatiotemporal detail. By bridging traditionally separate areas of research, our approach helps close longstanding gaps in our understanding of brain function. Author SummaryVision doesnt happen instantaneously, but unfolds over time. While we understand a lot about how the brain processes visual space, understanding how the brain processes information over both space and time is much more challenging. Vision happens incredibly fast, space and time are tightly linked, but current technology is limited in capturing these spatiotemporal dynamics. Here, we developed a method that combines two non-invasive human brain imaging techniques using computational models: fMRI, which provides high spatial detail, and MEG, which captures millisecond-level timing. We use fMRI to model the detailed layout of the visual system, and predict how this spatial layout responds to specific visual stimuli and compare these predictions with MEG recordings. This allows us to pinpoint not just where visual processing happens, but also when. Our results reveal a clear processing hierarchy: primary visual cortex responds first and explains most of the MEG signal, while higher-level visual areas activate later. We show that our method works across different stimuli, MEG sensor types, and brain areas, proving its robustness. This approach offers a new way to track how information flows through the living human brain, opening up new possibilities to study vision in both health and disease.

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bioRxiv2025

Psilocybin alters visual-contextual computations

Psilocybin alters perception and brain dynamics. Contextual computations are ubiquitous in the brain. Here, we investigate the effects of psilocybin using psychophysics, ultra-high field functional MRI, and computational modeling. We find that 1) psilocybin alters contextual perception in the Ebbinghaus illusion, 2) psilocybin alters contextual modulation in cortical responses to visual stimuli, and 3) we propose a computational model capable of capturing and linking these changes. Leveraging vision as a beachhead, our findings highlight the alteration of contextual computations as a potential general mechanism underlying psychedelic action. TeaserPsilocybin alters visual-contextual computations, a potential general computational mechanism for psychedelic effects in the human brain.

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bioRxiv2024

Numerosity adaptation suppresses early visual responses

Humans and many animals rapidly and accurately perceive numerosity, the number of objects, in a visual image. The numerosity of recently viewed images influences our perception of the current images numerosity: numerosity adaptation. How does numerosity adaptation affect responses to numerosity in the brain? Recent studies show both early visual responses that monotonically increase with numerosity, and later numerosity-tuned responses that peak at different (preferred) numerosities in different neural populations. We have recently shown that numerosity adaptation affects the preferred numerosity of numerosity-tuned neural populations. We have also shown that early visual monotonic responses reflect image contrast, which follows numerosity closely. Here we ask how monotonic responses in the early visual cortex are affected by adaptation to different numerosities, using ultra-high field (7T) fMRI and neural model-based analyses. FMRI response amplitudes increased monotonically with numerosity throughout the early visual field maps (V1-V3, hV4, LO1-LO2 & V3A/B). This increase in response amplitudes becomes less steep after adaptation to higher numerosities, with this effect becoming stronger through the early visual hierarchy. This suppression of responses to numerosity is consistent with perceptual effects where adaptation to high numerosities reduces the perceived numerosity. These results imply that numerosity adaptation effects in later numerosity-tuned neural populations may originate in early visual areas that respond to image contrast in the adapting image.

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bioRxiv2024

Bistable perception of symbolic numbers

Numerals, i.e., semantic expressions of numbers, enable us to have an exact representation of the amount of things. Visual processing of numerals plays an indispensable role in the recognition and interpretation of numbers. Here, we investigate how visual information from numerals is processed to achieve semantic understanding. We first found that partial occlusion of some digital numerals introduces bistable interpretations. Next, by using the visual adaptation method, we investigated the origin of this bistability in human participants. We showed that adaptation to digital and normal Arabic numerals, as well as homologous shapes, but not Chinese numerals, biases the interpretation of a partially occluded digital numeral. We suggest that this bistable interpretation is driven by intermediate shape processing stages of vision, i.e., by features more complex than local visual orientations but more basic than the abstract concepts of numerals.

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bioRxiv2021

The influence of objecthood on the representation of natural images in the visual cortex

Neurons in early visual cortex are not only sensitive to the image elements in their receptive field but also to the context determining whether the elements are part of an object or background. We here assessed the effect of objecthood in natural images on neuronal activity in early visual cortex, with fMRI in humans and electrophysiology in monkeys. We report that boundaries and interiors of objects elicit more activity than the background. Boundary effects occur remarkably early, implying that visual cortical neurons are tuned to features characterizing object boundaries in natural images. When a new image is presented the influence of the object interiors on neuronal activity occurs during a late phase of neuronal response and earlier when eye movements shift the image representation, implying that object representations are remapped across eye-movements. Our results reveal how object perception shapes the representation of natural images in early visual cortex.

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bioRxiv2021

Encoding of motion by spatial and temporal frequency in the human middle temporal cortex measured by 7T fMRI

Perception of dynamic scenes in our environment results from the evaluation of visual features such as the fundamental spatial and temporal frequency components of a moving object. The ratio between these two components represents the objects speed of motion. The human middle temporal cortex hMT+ has a crucial biological role in the direct encoding of object speed. However, the link between hMT+ speed encoding and the spatiotemporal frequency components of a moving object is still under explored. Here, we recorded high resolution 7T blood oxygen level-dependent BOLD responses to different visual motion stimuli as a function of their fundamental spatial and temporal frequency components. We fitted each hMT+ BOLD response with a 2D Gaussian model allowing for two different speed encoding mechanisms: 1) distinct and independent selectivity for the spatial and temporal frequencies of the visual motion stimuli 2) pure tuning for the speed of motion. We show that both mechanisms occur but in different neuronal groups within hMT+, with the largest subregion of the complex showing separable tuning for the spatial and temporal frequency of the visual stimuli. Both mechanisms were highly reproducible within participants, reconciling single cell recordings from MT in animals that have showed both encoding mechanisms. Our findings confirm that a more complex process is involved in the perception of speed than initially thought and suggest that hMT+ plays a primary role in the evaluation of the spatial features of the moving visual input.

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bioRxiv2020

A Population Receptive Field Model of the Magnetoencephalography Response

1Computational models which predict the neurophysiological response from experimental stimuli have played an important role in human neuroimaging. One type of computational model, the population receptive field (pRF), has been used to describe cortical responses at the millimeter scale using functional magnetic resonance imaging (fMRI) and electrocorticography (ECoG). However, pRF models are not widely used for non-invasive electromagnetic field measurements (EEG/MEG), because individual sensors pool responses originating from several centimeter of cortex, containing neural populations with widely varying spatial tuning. Here, we introduce a forward-modeling approach in which pRFs estimated from fMRI data are used to predict MEG sensor responses. Subjects viewed contrast-reversing bar stimuli sweeping across the visual field in separate fMRI and MEG sessions. Individual subjects pRFs were modeled on the cortical surface at the millimeter scale using the fMRI data. We then predicted cortical time series and projected these predictions to MEG sensors using a biophysical MEG forward model, accounting for the pooling across cortex. We compared the predicted MEG responses to observed visually evoked steady-state responses measured in the MEG session. We found that pRF parameters estimated by fMRI could explain a substantial fraction of the variance in steady-state MEG sensor responses (up to 60% in individual sensors). Control analyses in which we artificially perturbed either pRF size or pRF position reduced MEG prediction accuracy, indicating that MEG data are sensitive to pRF properties derived from fMRI. Our model provides a quantitative approach to link fMRI and MEG measurements, thereby enabling advances in our understanding of spatiotemporal dynamics in human visual field maps.

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bioRxiv2019

Triple visual hemifield maps in optic chiasm hypoplasia

In humans, each hemisphere comprises an overlay of two visuotopic maps of the contralateral visual field, one from each eye. Is the capacity of the visual cortex limited to these two maps or are plastic mechanisms available to host more maps? Using an integrative approach of submillimeter fMRI, diffusion-weighted imaging and population receptive field mapping, we found three hemiretinal inputs to converge onto the left hemisphere in a rare individual with chiasma hypoplasia. This generates extremely atypical responses in striate and extrastriate cortices, specifically an overlay of three hemifield representations. Unexpectedly, the effects of this large abnormality on visual function in daily life are not easily detected. We conclude that developmental plasticity including the re-wiring of local intra- and cortico-cortical connections is pivotal to support the coexistence and functioning of three hemifield maps within one hemisphere.

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bioRxiv2016

Slice-sampled Bayesian PRF mapping

Functional magnetic resonance imaging (FMRI) allows to non-invasively measure human brain activity at the millimeter scale. As such, it is widely used in computational neuroimaging studies that aim to build models to predict stimulus-induced neural responses in visual cortex. A popular method is population receptive field (PRF) mapping, which is able to characterize responses to a large range of stimuli. For each voxel, the PRF method estimates the best fitting receptive field properties (such as location and size in the visual field) using a coarse-to-fine approach which minimizes, but not eliminates, the risk of returning a local minimum. Here, we provide a Bayesian approach to the PRF method based on the slice sampler. Using this approach, we provide estimates of receptive field properties while at the same time being able to quantify their uncertainty. We test the performance of conventional and Bayesian approaches on simulated and empirical data.

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