Biology subjects

De Weerd, P.

Publications and source records attributed to De Weerd, P..

12 recordsLinked to original sources

bioRxiv2026

Stimulus dependent modulation of perceptual filling-in is predicted by the properties of early visual cortex

Filling-in occurs during the perceptual disappearance of a blank figure presented on a textured background. Current models of perceptual filling-in are based on a two-stage model where the figure boundary weakens after a period of adaptation, followed by the spreading of the background representation into the region representing the figure. This suggests a competition between figure boundary and background representations whereby filling-in is facilitated by a weaker boundary representation and a stronger background representation. Here, we test this interpretation, by using the oblique effect and surround-modulation suppression, which are functional properties of early visual cortex that modulate the expected strengths of the responses to the background texture and to the figure boundary. In a sample of N=58 participants, we found more filling-in with background textures of cardinal compared to oblique orientations (earlier onset time, with more and longer episodes of filling-in per trial), in line with a known, stronger neuronal response for cardinal than for oblique orientation in early visual cortex. We found more filling-in when the main axis of the rectangular figure was iso-oriented rather than cross-oriented with the background texture (more and longer episodes of filling-in per trial, but no change in onset time), in line with a lower response to oriented stimuli when surrounded by iso-oriented flankers compared to cross-oriented flankers. Overall, our results support the two-stage model and suggest the involvement of early visual cortical areas characterized by the oblique effect and orientation-tuned surround-suppression.

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bioRxiv2026

Feedback to deep layers in human V1 during perceptual filling-in

Visual surface perception is a fundamental aspect of vision, yet its neural implementation remains poorly understood. Troxlers perceptual filling-in paradigm provides a tractable illusion for studying surface perception, in which a peripheral figure becomes perceptually assimilated into the surrounding background after a period of sustained fixation. Although neural correlates of this phenomenon have been reported in early visual cortex, the underlying mechanisms, particularly the contribution of feedback signaling, remain unresolved. Here we use ultra-high-field (7T) layer-fMRI to investigate perceptual filling-in in the human visual cortex. While experimentally controlling perceptual filling-in, we measured GE-BOLD responses in ten participants. Analyses across cortical depth in the independently localized figure representation in primary visual cortex (V1) revealed neural correlates of filling-in in deep cortical layers, which are associated with feedback input. These findings provide evidence that perceptual filling-in and visual surface perception in general are supported by feedback signals to early visual cortex.

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bioRxiv2025

Neural correlates of implicit memory for reoccurring sound patterns

The human brain exhibits remarkable sensitivity to auditory patterns. Previous research has shown that beyond the detection of such patterns, humans form memories for them that are implicit, robust to interference, and persistent over time. Here, we examine the mechanisms underlying implicit memory formation for reoccurring regular tone patterns using UHF fMRI. Prior to scanning, implicit memory was induced through a standard behavioral task where participants detected regular patterns embedded in random tone sequences. Unbeknownst to participants, five regular patterns reoccurred sporadically (every 1.5 min) across trials. Consistent with previous reports, behavioral performance indicated a reaction time advantage to reoccurring patterns, confirming the formation of implicit memory traces. During passive listening in the scanner, regularity engaged the superior temporal gyrus, inferior frontal gyrus, insula, putamen, and hippocampus, a result we interpret as reflecting the higher perceptual precision of regular patterns. Reoccurrence interacted with regularity in the superior temporal gyrus and a frontal cluster, showing higher activity for reoccurring compared to novel regular patterns. The hippocampus showed sensitivity to reoccurrence in both regular and random patterns. Together, these results indicate that the neocortex may selectively amplify reoccurring inputs in line with their enhanced (memory driven) perceptual precision.

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bioRxiv2025

Unveiling early visual cortical mechanisms in perceptual filling-in: a parametric study of eccentricity and movement dependence

Surface perception relies on interactions between boundary encoding and surface filling-in. In a perceptual filling-in paradigm, a blank figure becomes perceptually replaced by a textured background after prolonged fixation of a point away from the figure. Filling-in begins when neurons representing the figures boundary adapt, allowing background-related activity to spread into the figures retinotopic representation. Adaptation proceeds faster the better the boundary is stabilized in a neurons receptive field (RF). We hypothesized that moving the figure boundary beyond a neurons RF would reduce adaptation and hinder filling-in, with larger movements permitting progressively less filling-in. As RF size increases with eccentricity, we further hypothesized that greater eccentricities would require larger movements to interfere with filling-in. Our results confirmed both predictions. The reduction in filling-in duration with increasing motion range permitted estimating RF size at each eccentricity. The slope of a linear function relating RF size to eccentricity matched values reported in human fMRI studies of V1/V2, suggesting that boundary adaptation involves early visual areas. We also explored whether microsaccade amplitude affects filling-in, but found no supporting evidence. Thus, external figure motion and microsaccades may disrupt adaptation through different mechanisms. These findings provide new insights into neural adaptation processes preceding perceptual filling-in.

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bioRxiv2024

Gamma Synchrony Mediates Figure-Ground Perception

Gamma synchrony is ubiquitous in visual cortex, but whether it contributes to perceptual grouping remains contentious based on observations that gamma frequency is not consistent across stimulus features and that gamma synchrony depends on distances between image elements. These stimulus dependencies have been argued to challenge the idea that the visual system groups image elements by synchronizing the neural assemblies that encode them. Here we argue instead that these dependencies may shape synchrony in perceptually meaningful ways. Indeed, according to the theory of weakly coupled oscillators (TWCO), synchrony-based grouping mechanisms require stimulus dependence. Synchronization among coupled oscillators depends on frequency dissimilarity and coupling strength, which in early visual cortex relate to local feature dissimilarity and physical distance, respectively. We manipulated these factors in a texture segregation experiment wherein human observers identified the orientation of a figure defined by reduced contrast heterogeneity compared to the background. Human performance followed TWCO predictions both qualitatively and quantitatively, as formalized in a computational model. Moreover, we found that when enriched with a Hebbian learning rule, our model also predicted human learning effects: Increases in model gamma synchrony due to perceptual learning predicted improvements in texture segregation across sessions. Taken together, our data suggest that the stimulus-dependence of gamma synchrony captures local image statistics and is linked to the stimulus-dependence of texture segregation, and that the effect of visual experience on gamma synchrony provides a viable perceptual learning mechanism for training-induced improvements in texture segregation. Our results suggest that gamma synchrony with its inherent stimulus dependencies can provide a plausible mechanistic basis for perceptual grouping and visual scene segmentation.

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bioRxiv2020

Frequency-specific transcranial neuromodulation of oscillatory alpha power alters and predicts human visuospatial attention performance

Unilateral transcranial alternating current stimulation (tACS) at alpha frequency modulates the locus of spatial attention. However, the neural mechanisms by which tACS influences spatial attention remain poorly understood. Here, we applied high-definition tACS at the individual alpha frequency (IAF), two control frequencies (IAF+/-2Hz) and sham to the left posterior parietal cortex and measured its effects on visuospatial attention performance as well as alpha power (using electroencephalography, EEG). Our results revealed a leftward lateralization of alpha power relative to sham. At a high value of leftward alpha lateralization, we also observed a leftward attention bias, which differed from sham. Moreover, the magnitude of the alpha lateralization effect predicted the attention bias. These effects occurred for tACS at IAF but not for the control frequencies. This suggests that tACS operates through oscillatory interactions with ongoing brain rhythms in line with the synchronization theory. Our results also highlight the importance of personalized stimulation protocols, especially in potential clinical settings.

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bioRxiv2019

Interfering with a memory without erasing its trace

Previous research has shown that performance of a novice skill can be easily interfered with by subsequent training of another skill. We address the open questions whether extensively trained skills show the same vulnerability to interference as novice skills and which memory mechanism regulates interference between expert skills. We developed a recurrent neural network model of V1 able to learn from feedback experienced over the course of a long-term orientation discrimination experiment. After first exposing the model to one discrimination task for 3480 consecutive trials, we assessed how its performance was affected by subsequent training in a second, similar task. Training the second task strongly interfered with the first (highly trained) discrimination skill. The magnitude of interference depended on the relative amounts of training devoted to the different tasks. We used these and other model outcomes as predictions for a perceptual learning experiment in which human participants underwent the same training protocol as our model. Specifically, over the course of three months participants underwent baseline training in one orientation discrimination task for 15 sessions before being trained for 15 sessions on a similar task and finally undergoing another 15 sessions of training on the first task (to assess interference). Across all conditions, the pattern of interference observed empirically closely matched model predictions. According to our model, behavioral interference can be explained by antagonistic changes in neuronal tuning induced by the two tasks. Remarkably, this did not stem from erasing connections due to earlier learning but rather from a reweighting of lateral inhibition.

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bioRxiv2019

Empirically Constrained Network Models for Contrast-dependent Modulation of Gamma Rhythm in V1

Here we present experimentally constrained computational models of gamma rhythm and use these to investigate gamma oscillation instability. To this end, we extracted empirical constraints for PING (Pyramidal Interneuron Network Gamma) models from monkey single-unit and LFP responses recorded during contrast variation. These constraints implied weak rather than strong PING, connectivity between excitatory (E) and inhibitory (I) cells within specific bounds, and input strength variations that modulated E but not I cells. Constrained models showed valid behaviours, including gamma frequency increases with contrast and power saturation or decay at high contrasts. The route to gamma instability involved increased heterogeneity of E cells with increasing input triggering a breakdown of I cell pacemaker function. We illustrate the models capacity to resolve disputes in the literature. Our work is relevant for the range of cognitive operations to which gamma oscillations contribute and could serve as a basis for future, more complex models.

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bioRxiv2019

Hippocampal-striatal functional connectivity supports processing of temporal expectations from associative memory

The hippocampus and dorsal striatum are both associated with temporal processing, but they are thought to play distinct roles. The hippocampus has been reported to contribute to storing temporal structure of events in memory, whereas the striatum contributes to temporal motor preparation and reward anticipation. Here, we asked whether the striatum cooperates with the hippocampus in processing the temporal context of memorized visual associations. In our task, participants were trained to implicitly form temporal expectations for one of two possible time intervals associated to specific cue-target associations, and subsequently were scanned using 7T functional magnetic resonance imaging. During scanning, learned temporal expectations could be violated when the pairs were presented at either the learned or not-learned time intervals. When temporal expectations were not met during testing trials, activity in hippocampal subfields CA3/CA2 and CA1 decreased while right putamen activity increased, compared to when temporal expectations were met. Further, psycho-physiological interactions showed that functional connectivity between left CA1 and caudate, as well as between putamen and caudate, decreased when temporal expectations were not met. Our results indicate that the hippocampus and striatum cooperate to process implicit temporal expectation from mnemonic associations, with different but complementary contributions from caudate and putamen. Our findings provide further support for a hippocampal-striatal network in temporal associative processing.

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bioRxiv2019

Depth-resolved ultra-high field fMRI reveals feedback contributions to surface motion perception

Human visual surface perception has neural correlates in early visual cortex, but the extent to which feedback contributes to this activity is not well known. Feedback projections preferentially enter superficial and deep anatomical layers, while avoiding the middle layer, which provides a hypothesis for the cortical depth distribution of fMRI activity related to feedback in early visual cortex. Here, we presented human participants uniform surfaces on a dark, textured background. The grey surface in the left hemifield was either perceived as static or moving based on a manipulation in the right hemifield. Physically, the surface was identical in the left visual hemifield, so any difference in percept likely was related to feedback. Using ultra-high field fMRI, we report the first evidence for a depth distribution of activation in line with feedback during the (illusory) perception of surface motion. Our results fit with a signal re-entering in superficial depths of V1, followed by a feedforward sweep of the re-entered information through V2 and V3, as suggested by activity centred in the middle-depth levels of the latter areas. This positive modulation of the BOLD signal due to illusory surface motion was on top of a strong negative BOLD response in the cortical representation of the surface stimuli, which depended on the presence of texture in the background. Hence, the magnitude and sign of the BOLD response to the surface strongly depended on background properties, and was additionally modulated by the presence or absence of illusory motion perception in a manner compatible with feedback. In summary, the present study demonstrates the potential of depth resolved fMRI in tackling biomechanical questions on perception that so far were only within reach of invasive animal experimentation.

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bioRxiv2019

Left parietal tACS at alpha frequency induces a shift of visuospatial attention

BackgroundVoluntary shifts of visuospatial attention are associated with a lateralization of occipitoparietal alpha power (7-13Hz), i.e. higher power in the hemisphere ipsilateral and lower power contralateral to the locus of attention. Recent noninvasive neuromodulation studies demonstrated that alpha power can be experimentally increased using transcranial alternating current stimulation (tACS).\n\nObjective/HypothesisWe hypothesized that tACS at alpha frequency over the left parietal cortex induces shifts of attention to the left hemifield. However, spatial attention shifts not only occur voluntarily (endogenous), but also stimulus-driven (exogenous). In order to study the task-specificity of the potential effects of tACS on attentional processes, we administered three conceptually different spatial attention tasks.\n\nMethods36 healthy volunteers were recruited from an academic environment. In two seperate sessions, we applied either high-density tACS at 10Hz, or sham tACS, for 35-40 minutes to their left parietal cortex. We systematically compared performance on endogenous attention, exogenous attention, and stimulus detection tasks.\n\nResultsIn the Endogenous attention task, we found a greater leftward bias in reaction times during left parietal 10Hz tACS as compared to sham. There were no stimulation effects in the exogenous attention or stimulus detection task.\n\nConclusionThe study shows that high-density tACS at 10Hz can be used to modulate visuospatial attention performance. The tACS effect is task-specific, indicating that not all forms of attention are equally susceptible to the stimulation.

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bioRxiv2019

Experience-related alterations in white matter structure and gene expression in adult rats

White matter (WM) plasticity during adulthood is a recently described phenomenon by which experience can shape brain structure. It has been observed in humans using diffusion tensor imaging (DTI). However, it remains unclear which mechanisms drive or underlie WM plasticity in adulthood. Here, we combined DTI and mRNA expression analysis and examined the effects of somatosensory experience in adult rats. Somatosensory experience resulted in differences in WM and grey matter structure. C-FOS mRNA expression, a marker of cortical activity, in the barrel cortex correlated with the structural WM measures, suggesting that WM plasticity is activity-dependent. Analysis of myelin-related genes revealed higher myelin basic protein expression in WM, while genome-wide RNA sequencing analysis identified 134 differentially-expressed genes regulating proteins involved in functions related to cell proliferation and differentiation, neuronal activity modulation and regulation of myelination. In conclusion, the macroscale measures of WM differences identified in response to somatosensory experience are supported by molecular evidence, which strongly suggest myelination as, at least, one of the underlying mechanisms.

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