Cees van Leeuwen

Cees van Leeuwen
KU Leuven | ku leuven · Brain and Cognition Research Unit

Ph.D.
As Emeritus Professor, I keep working on a small scale with Ph.D. Students, Visiting Researchers, and collaborators.

About

351
Publications
58,484
Reads
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5,428
Citations
Citations since 2017
61 Research Items
2399 Citations
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Introduction
The Laboratory for Perceptual Dynamics studies visual awareness from a 'complex systems' perspective. In this view, ongoing internal processes in the brain prepare it for the experience of objects, textures, and shapes. To become awareness, they need to function in a wider context, ultimately including the evolution of our species. The laboratory is achieving its aims through a combination of perceptual psychophysics, psychophysiology, and computational modeling.
Additional affiliations
May 2013 - present
Technische Universität Kaiserslautern
Position
  • Professor
October 2011 - present
KU Leuven
Position
  • Research Chair
Description
  • The Laboratory for Perceptual Dynamics (PDL) was first established in 2001 at RIKEN Brain Science Institute, Japan. With support from the Odysseus program of the Flemish Science Foundation (FWO) PDL was transferred in 2012 to the KU Leuven.
April 2000 - October 2011
RIKEN
Position
  • Group Leader
Education
August 1975 - February 1989
University of Nijmegen
Field of study
  • Psychology

Publications

Publications (351)
Article
The visual appearance of an object is a function of stimulus properties as well as perceptual biases imposed by the observer. The context-specific trade-off between both can be measured accurately in a perceptual judgment task, involving grouping by proximity in ambiguous dot lattices. Such grouping depends lawfully on a stimulus parameter of the d...
Article
We compared problem‐solving in four sets of classical insight and analytic problems in the verbal and spatial domains, and examined the impact of externalization (verbalization or sketching). In a within‐participants factorial design, we presented 24 classical insight and analytic problems, half verbal and half spatial. Participants solved these pr...
Article
Full-text available
Computer-aided design (CAD) systems have advanced to become a critical tool in product design. Nevertheless, they still primarily rely on the traditional mouse and keyboard interface. This limits the naturalness and intuitiveness of the 3D modeling process. Recently, a multimodal human–computer interface (HCI) has been proposed as the next-generati...
Article
Full-text available
In the cognitive neuroscience of consciousness, participants have commonly been instructed to report their conscious content. This, it was claimed, risks confounding the neural correlates of consciousness (NCC) with their preconditions, i.e., allocation of attention, and consequences, i.e., metacognitive reflection. Recently, the field has therefor...
Poster
Full-text available
This is an R markdown document representing our poster for TEAP 2022 in Köln. To study the time courses of the global precedence, global-to-local interference, and local-to-global interference effects in a global/local matching task, we analyzed the RT and accuracy distributions using discrete-time event history analysis and conditional accuracy an...
Article
Brain networks are continually rewired adaptively, adjusting their topology to bring about functionality and efficiency in sensory, motor, and cognitive tasks. In model neural network architectures, adaptive rewiring generates complex, brain-like topologies. Present models, however, cannot account for the emergence of complex directed connectivity...
Article
Full-text available
Structural plasticity of the brain can be represented in a highly simplified form as adaptive rewiring, the relay of connections according to the spontaneous dynamic synchronization in network activity. Adaptive rewiring, over time, leads from initial random networks to brain-like complex networks, i.e., networks with modular small-world structures...
Preprint
Full-text available
Mind wandering occurs when spontaneous thought generation is increased while cognitive control is decreased, presumably in response to antagonistic effects of default mode- (DMN) and goal-directed network (GDN) activity. Previous studies assumed that DMN or GDN activity manifests in behavior with minimal delays and has rigid effects, i.e., DMN alwa...
Preprint
Full-text available
Brain networks are adaptively rewired continually, adjusting their topology to bring about functionality and efficiency in sensory, motor and cognitive tasks. In model neural network architectures, adaptive rewiring generates complex, brain-like topologies. Present models, however, cannot account for the emergence of complex directed connectivity s...
Preprint
Full-text available
Self-organization through adaptive rewiring of random neural networks generates brain-like topologies comprising modular small-world structures with rich club effects, merely as the product of optimizing the network topology. In the nervous system, spatial organization is optimized no less by rewiring, through minimizing wiring distance and maximiz...
Article
Full-text available
Brain network connections rewire adaptively in response to neural activity. Adaptive rewiring may be understood as a process which, at its every step, is aimed at optimizing the efficiency of signal diffusion. In evolving model networks, this amounts to creating shortcut connections in regions with high diffusion and pruning where diffusion is low....
Article
Gestalt psychology has traditionally ignored the role of attention in perception, leading to the view that autonomous processes create perceptual configurations that are then attended. More recent research, however, has shown that spatial attention influences a form of Gestalt perception: the coherence of random-dot kinematograms (RDKs). Using ERPs...
Article
Full-text available
Eye movement research has shown that attention shifts from the currently fixated location to the next before a saccade is executed. We investigated whether the cost of the attention shift depends on higher-order processing at the time of fixation, in particular on visual working memory load differences between fixations and refixations on task-rele...
Article
Full-text available
Activity-dependent plasticity refers to a range of mechanisms for adaptively reshaping neuronal connections. We model their common principle in terms of adaptive rewiring of network connectivity, while representing neural activity by diffusion on the network: Where diffusion is intensive, shortcut connections are established, while underused connec...
Preprint
Structural plasticity of the brain can be represented in highly simplified form as adaptive rewiring; the relay of connections according to the spontaneous dynamic synchronization in network activity. Adaptive rewiring, over time, leads from initial random networks to complex networks, i.e. networks with modular small-world structures and a rich cl...
Article
Full-text available
Predicting future brain signal is highly sought-after, yet difficult to achieve. To predict the future phase of cortical activity at localized ECoG and MEG recording sites, we exploit its predominant, large-scale, spatiotemporal dynamics. The dynamics are extracted from the brain signal through Fourier analysis and principal components analysis (PC...
Preprint
Full-text available
Background: In electrical brain signals such as Local Field Potential (LFP) and Electroencephalogram (EEG), oscillations emerge as a result of neural network activity. The oscillations extend over several frequency bands. Between their dominant components, various couplings can be observed. Of these, Phase-Amplitude Coupling (PAC) is intensively st...
Article
Spatial constituents of adult symbolic number representation produce effects of size-value congruity, Spatial Numerical Association of Response Codes (SNARC), and numerical distance. According to behavioral experiments, these effects belong to distinct processing stages. Yet, these effects evoke overlapping responses in both early and late Event Re...
Article
Full-text available
The brain can be considered as a system that dynamically optimizes the structure of anatomical connections based on the efficiency requirements of functional connectivity. To illustrate the power of this principle in organizing the complexity of brain architecture, we portray the functional connectivity as diffusion on the current network structure...
Preprint
Full-text available
Information uptake during scene viewing under free viewing conditions is crucially determined by the scanning plan. This plan is determined both by top-down and bottom-up factors. To capture top-down factors affecting saccade planning, we compared EEG between first fixations and refixations on items varying in task-relevance. First fixations and re...
Preprint
Full-text available
Spontaneously emerging cortical maps related to the functional architecture of visual cortex have been observed initially in anesthetized cats and, subsequently, in monkey, albeit only under certain anesthetic regimes, and not in the awake state. Here we propose a network model that can accommodate these diverse findings. The model identifies two c...
Preprint
Full-text available
Activity dependent plasticity is the brain’s mechanism for reshaping neural connections. Representing activity by graph diffusion, we model plasticity as adaptive rewiring. The rewiring involves adding shortcut connections where diffusion on the graph is intensive while pruning underused ones. This process robustly steers initially random networks...
Article
Full-text available
Using the method of experience sampling, we studied the fluctuations in thought generation and cognitive control strength during the wakeful hours of the day, centered around episodes of mind wandering. Thought generation, measured in terms of the number of thoughts that concurrently occupy the mind at sampling time, goes through regular 4-6 h cycl...
Preprint
Full-text available
Withdrawal statement The authors have withdrawn this manuscript because of the issue in the data analysis, which was found during revision. Specifically, not all eye movement characteristics were matched between experimental conditions of interest, and these characteristics were confounded with the main EEG findings. When the issue was corrected th...
Article
Full-text available
We investigated visual working memory encoding across saccadic eye movements, focusing our analysis on refixation behavior. Over 10-s periods, participants performed a visual search for three, four, or five targets and remembered their orientations for a subsequent change-detection task. In 50% of the trials, one of the targets had its orientation...
Article
Full-text available
We studied the global precedence effect in primary school children with and without developmental dyslexia, using a compound figures task with familiar (Latin) or unfamiliar (Hebrew) letters. The two components of the global precedence effect were considered separately: global advantage (faster processing of global than local letters) and asymmetri...
Article
Full-text available
When we synchronize finger tapping with a visual metronome, we experience a strikingly robust phenomenon of extended agency known as Spizzo’s effect. This effect is the compelling sense that we are controlling the metronome. The effect arises even though the agent knows that the metronome operates autonomously. We propose that the extended agency h...
Article
Full-text available
Human connectome studies suggest that the brain has a modular small world network structure with rich-club effect. Such structure emerges spontaneously in simple model neural networks, (e.g. coupled maps), through adaptive rewiring according to the dynamic functional connectivity. The utility of adaptive rewiring has so far exclusively been demonst...
Article
Full-text available
An unresolved problem in eye movement research is how a representation is constructed on-line from several consecutive fixations of a scene. Such a scene representation is generally understood to be sparse; yet, for meeting behavioral goals a certain level of detail is needed. We propose that this is achieved through the buildup of latent represent...
Article
Full-text available
The size congruity effect involves interference between numerical magnitude and physical size of visually presented numbers: congruent numbers (either both small or both large in numerical magnitude and physical size) are responded to faster than incongruent ones (small numerical magnitude/large physical size or vice versa). Besides, numerical magn...
Article
In free viewing, the eyes return to previously visited locations rather frequently, even though the attentional and memory-related processes controlling eye-movement show a strong antirefixation bias. To overcome this bias, a special refixation triggering mechanism may have to be recruited. We probed the neural evidence for such a mechanism by comb...
Article
While viewing a scene, the eyes are attracted to salient stimuli. We set out to identify the brain signals controlling this process. In a contour integration task, in which participants searched for a collinear contour in a field of randomly oriented Gabor elements, a previously established model was applied to calculate a visual saliency value for...
Article
Critical dynamics are thought to play an important role in neuronal information-processing: near critical networks exhibit neuronal avalanches, cascades of spatiotemporal activity that are scale-free, and are considered to enhance information capacity and transfer. However, the exact relationship between criticality, awareness, and information inte...
Preprint
Full-text available
A prominent feature of brain activity with relevance to cognitive processes is Phase-Amplitude Coupling (PAC) between slow and fast oscillatory signals. A newly developed neural mass model of cross-frequency coupling [1] predicts, counter-intuitively, that PAC shows sustained increases after repetitive Transcranial Magnetic Stimulation (rTMS). This...
Preprint
Full-text available
Spontaneous thought and lapses in executive control are key processes leading to mind wandering. We used real-life experience sampling to observe how these processes vary over the wakeful hours of the day. Long term regularities were found: loosely coupled with executive control, the number of thoughts that concurrently occupy the mind goes through...
Article
Full-text available
In spontaneous, stimulus-evoked, and eye-movement evoked EEG, the oscillatory signal shows large scale, dynamically organized patterns of phase. We investigated eye-movement evoked patterns in free-viewing conditions. Participants viewed photographs of natural scenes in anticipation of a memory test. From 200 ms intervals following saccades, we est...
Article
Full-text available
Transcranial alternating-current stimulation (tACS) for entraining alpha activity holds potential for influencing mental function, both in laboratory and clinical settings. While initial results of alpha entrainment are promising, questions remain regarding its translational potential—namely if tACS alpha entrainment is sufficiently robust to conte...
Article
Full-text available
A recently proposed model of sensory processing suggests that perceptual experience is updated in discrete steps. We show that the data advanced to support discrete perception are in fact compatible with a continuous account of perception. Physiological and psychophysical constraints, moreover, as well as our awake-primate imaging data, imply that...
Article
Full-text available
Sense of agency can be defined as the self-awareness of bodily movement, whereas extended agency as the self-awareness of affecting, through movement, events concomitant with movement. As a distinctive manifestation of agency, we review Spizzo's effect. This effect arises when agents coordinate their rhythmic movements with visual pulses. Once coor...
Article
Full-text available
Complex networks emerging in natural and human-made systems tend to assume small-world structure. Is there a common mechanism underlying their self-organisation? Our computational simulations show that network diffusion (traffic flow or information transfer) steers network evolution towards emergence of complex network structures. The emergence is...
Conference Paper
Full-text available
We investigate the connectivity within different incre-mental sets of Japanese Kanji characters. Individual characters constitute the vertices in the network, components shared between them provide their edges. We find the resulting networks to have a high clustering coefficient and a low average path length, characterizing them as small worlds. We...
Article
In free visual exploration, eye-movement is immediately followed by dynamic reconfiguration of brain functional connectivity. We studied the task-dependency of this process in a combined visual search-change detection experiment. Participants viewed two (nearly) same displays in succession. First time they had to find and remember multiple targets...
Chapter
Our actions are continuously shaped by what we perceive. When a hammer is picked up, this is done in one smooth movement, the hand adjusting in anticipation to the scale and position of the target. But the opposite is also true: what we perceive is determined by our actions. We tend to see those properties of the world which are meaningful for our...
Presentation
Full-text available
Using graph diffusion to explain the emergence of modular and centralised structures in complex networks as well as feedforward motifs in directed networks
Preprint
Full-text available
A prominent feature of brain activity with relevance to cognitive processes is Phase-Amplitude Coupling (PAC) between slow and fast oscillatory signals. A newly developed neural mass model of cross-frequency coupling [1] predicts, counter-intuitively, that PAC shows sustained increases after repetitive Transcranial Magnetic Stimulation (rTMS). This...
Article
In compound, hierarchical stimuli (also known as Navon figures), a Global Precedence Effect (GPE) can reliably be observed for both letters and non-letters. However, when presentation conditions sufficiently resemble those of reading, the GPE for letters has occasionally been found to disappear. We corroborate this effect in a study with a large gr...
Article
In the course of perceptual organization, incomplete optical stimulation can evoke the experience of complete objects with distinct perceptual identities. According to a well-known principle of perceptual organization, stimulus parts separated by shorter spatial distances are more likely to appear as parts of the same perceptual identity. Whereas t...
Article
Full-text available
In cat early visual cortex, neural activity patterns resembling evoked orientation maps emerge spontaneously under anesthesia. To test if such patterns are synchronized between hemispheres, we performed bilateral imaging in anesthetized cats using a new improved voltage-sensitive dye. We observed map-like activity patterns spanning early visual cor...
Article
Full-text available
Electrophysiological signals of cortical activity show a range of possible frequency and amplitude modulations, both within and across regions, collectively known as cross-frequency coupling. To investigate whether these modulations could be considered as manifestations of the same underlying mechanism, we developed a neural mass model. The model p...
Article
Culture-related differences in visual creativity were investigated, comparing Italian and Japanese participants in terms of divergent (figural completion task) and product-oriented thinking (figural combination task). Visual restructuring ability was measured as the ability to reinterpret ambiguous figures and was included as a covariate. Results s...
Article
Full-text available
Signals with multiple oscillatory components may exhibit cross frequency coupling (CFC): a slow component modulating the amplitude and/or frequency of a fast one. CFC is ubiquitous in oscillatory brain signals but how it arises has remained unclear. We recently proposed a systematic approach to simulate CFC, in which all common modulations are gene...
Article
We discuss the dynamics of modular networks of coupled nonlinear systems. Networks of this class can be viewed as locally connected clusters or modules of nodes with directed links from one cluster to another. Let these connections form an oriented cycle. Here we show that if connectivity within isolated clusters is diffusive with relatively strong...
Article
Full-text available
Perceptual learning improves visual performance. Among the plausible mechanisms of learning, reduction of perceptual bias has been studied the least. Perceptual bias may compensate for lack of stimulus information, but excessive reliance on bias diminishes visual discriminability.We investigated the time course of bias in a perceptual grouping task...
Article
We propose a novel framework for processing a continuous speech stream that contains a varying number of words, as well as non-speech periods. Speech samples are segmented into word-tokens and non-speech periods. An augmented version of an earlier-proposed, cascaded neuro-computational model is used for recognising individual words within the strea...
Article
Co-registration of EEG and eye movement has promise for investigating perceptual processes in free viewing conditions, provided certain methodological challenges can be addressed. Most of these arise from the self-paced character of eye movements in free viewing conditions. Successive eye movements occur within short time intervals. Their evoked ac...
Article
Full-text available
A computational theory of consciousness should include a quantitative measure of consciousness, or MoC, that (i) would reveal to what extent a given system is conscious, (ii) would make it possible to compare not only different systems, but also the same system at different times, and (iii) would be graded, because so is consciousness. However, unl...
Article
Full-text available
Brain activity shows phase–amplitude coupling between its slow and fast oscillatory components. We study phase–amplitude coupling as recorded at individual sites, using a modified version of the well-known Wendling neural mass model. To the population of fast inhibitory interneurons of this model, we added external modulatory input and dynamic self...
Article
Full-text available
Threshold theory predicts a positive correlation between IQ and creativity scores up to an IQ level of 120 and no correlation above this threshold. Primary school children were tested at beginning (N = 98) and ending (N = 70) of the school year. Participants performed the standard progressive matrices (SPM) and the Test of Creative Thinking—Drawing...
Article
Full-text available
Globally coherent patterns of phase can be obscured by analysis techniques that aggregate brain activity measures across-trials, whether prior to source localization or for estimating inter-areal coherence. We analyzed, at single-trial level, whole head MEG recorded during an observer-triggered apparent motion task. Episodes of globally coherent ac...
Data
Example traveling wave and quantification of its properties. A travelling wave moves in the superior to inferior direction. Its dominant direction of flow over the scalp is quantified and shown as an arrow. The wave has a temporal frequency of 7Hz, and its behavior is shown over a time-window centered on 176ms, the time of the visual dipole. Left a...
Data
Task-dependent biases in the direction of cortical waves. At 176ms, 7Hz, there is a preponderance of left to right, superior to inferior traveling waves. At other times the distribution is more uniform. The movie shows the model wave vectors for a single subject (O9), condition predictable right, across all trials (arrows) and changing over the cou...
Data
Single trial comparison of methods. A single trial is analyzed using either the phase-unwrapping procedure and scalar regression (upper row), or complex-valued phase and multi-grid search (middle row). The trajectory and speed components show the same qualitative pattern, not dependent on the method used. Fits greater than 0.7 are shown within the...