Bernard Marius 't HartYork University · Centre for Vision Research
Bernard Marius 't Hart
Dr. rer. nat. (PhD)
About
68
Publications
8,890
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1,093
Citations
Introduction
Additional affiliations
October 2014 - present
January 2014 - April 2014
March 2013 - December 2013
Education
May 2008 - September 2011
September 1996 - May 2004
Publications
Publications (68)
People correct for movement errors when acquiring new motor skills (de novo learning) or adapting well-known movements (motor adaptation). These two motor learning types should be distinct, as de novo learning establishes new control policies while adaptation modifies existing ones. Here, we distinguish between these two motor learning types, and a...
People continuously adapt their movements to ever-changing circumstances, and particularly in skills training and rehabilitation, it is crucial that we understand how to optimize implicit adaptation in order for these processes to require as little conscious effort as possible. Although it is generally assumed that the way to do this is by introduc...
Human motor adaptation relies on both explicit conscious strategies and implicit unconscious updating of internal models to correct motor errors. Implicit adaptation is powerful, requiring less preparation time before executing adapted movements, but recent work suggests it is limited to some absolute magnitude regardless of the size of a visuomoto...
People continuously adapt their movements to ever-changing circumstances, and particularly in skills training and rehabilitation, it is crucial that we understand how to optimize implicit adaptation in order for these processes to require as little conscious effort as possible. Although it is generally assumed that the way to do this is by introduc...
Introducing altered visual feedback of the hand produces quick adaptation of reaching movements. Our lab has shown that the associated shifts in estimates of the felt position of the hand saturate within a few training trials. The current study investigates whether the rapid changes in felt hand position that occur during classic visuomotor adaptat...
Probes flashed within a moving frame are dramatically displaced (Özkan, Anstis, 't Hart, Wexler, & Cavanagh, 2021; Wong & Mack, 1981). The effect is much larger than that seen on static or moving probes (induced motion, Duncker, 1929; Wallach, Bacon, & Schulman, 1978). These flashed probes are often perceived with the separation they have in frame...
In response to unexpected perturbations during a motor task, we modify subsequent movements to compensate for errors and improve performance. Motor adaptation to a visuomotor rotation is characterized by reduced errors over time and aftereffects (errors in the opposite direction) following removal of the perturbation. In dual adaptation, participan...
Human motor adaptation relies on both explicit conscious strategies and implicit unconscious updating of internal models to correct motor errors. Implicit adaptation is powerful, requiring less preparation time before executing adapted movements, but recent work suggests it is limited to some absolute magnitude regardless of the size of a visuomoto...
Both implicit (unconscious, automatic) and explicit (effortful, strategic) processes contribute to various kinds of learning ¹ , including visuomotor adaptation 2–4 . Implicit adaptation may be capped at some level ⁵ , regardless of the level of explicit adaptation, or implicit and explicit adaptation could be linearly added in total adaptation 6,7...
The human motor system can adapt to unexpected perturbations during ongoing movements. Except for target jump studies, most of the research focused on adaptation to perturbations applied to the hand, such as force field or visuomotor rotation. But less is known about how we adapt to perturbations affecting objects that we interact with. For instanc...
Neuromatch Academy (https://academy.neuromatch.io; (van Viegen et al., 2021)) was
designed as an online summer school to cover the basics of computational neuroscience
in three weeks. The materials cover dominant and emerging computational neuroscience
tools, how they complement one another, and specifically focus on how they can help us
to better...
If a Gabor pattern drifts in one direction while its internal texture drifts in the orthogonal direction, its perceived position deviates further and further away from its true path. We first evaluated the illusion using manual tracking. Participants followed the Gabor with a stylus on a drawing tablet that coincided optically with the horizontal m...
Motor adaptation describes the ability of the motor system to counteract repeated perturbations in order to reduce movement errors. Most research in the field investigated adaptation in response to perturbations affecting the moving hand. Fewer studies looked at the effect of a perturbation applied to the movement target, however they used simplist...
Probes flashed within a moving frame are dramatically displaced (Ozkan et al, 2021; Wong & Mack, 1981). The effect is much larger than that seen on static or moving probes (induced motion, Duncker, 1929; Wallach et al, 1978). These flashed probes are often perceived with the separation they have in frame coordinates -- a 100% effect. Here we explor...
If a gabor pattern drifts in one direction while its internal texture drifts in the orthogonal direction, its perceived position deviates further and further away from its true path. We first evaluated the illusion using manual tracking. Participants followed the gabor with a stylus on a drawing tablet that coincided optically with the horizontal m...
Introducing altered visual feedback of the hand results in quick adaptation of reaching movements. And while this may be partly due to explicit strategies, our lab has shown that implicit changes like reach aftereffects and shift in estimates of the unseen hand, can also emerge and even saturate within a few training trials. The goal of the current...
Purpose
To explore the effect of joint hypermobility on acuity, and precision, of hand proprioception.
Materials and methods
We compared proprioceptive acuity, and precision, between EDS patients and controls. We then measured any changes in their estimates of hand position after participants adapted their reaches in response to altered visual fee...
Significance
Every eye movement drags the visual scene over our retinas and yet nothing appears to move. We now report a small-scale version of this visual stability with a square frame moving on a monitor in a well-lit room. Probes flashed before and after the frame’s motion are also stabilized in the frame’s coordinates—as if the frame were stati...
An amendment to this paper has been published and can be accessed via a link at the top of the paper.
Purpose
To explore the effect of joint hypermobility on acuity, and plasticity, of hand proprioception.
Materials and Methods
We compared proprioceptive acuity between EDS patients and controls. We then measured any changes in their estimate of hand position after participants adapted their reaches in response to altered visual feedback of their h...
Neuromatch Academy (https://neuromatch.io/academy) was designed as an online summer school to cover the basics of computational neuroscience in three weeks. The materials cover dominant and emerging computational neuroscience tools, how they complement one another, and specifically focus on how they can help us to better understand how the brain fu...
To capture where things are and what they are doing, the visual system may extract the position and motion of each object relative to its surrounding frame of reference (e.g., Johansson, 1950; Duncker, 1929). Here we report a particularly powerful example where a paradoxical stabilization is produced by a moving frame. We first take a frame that mo...
In motor learning, the slow development of implicit learning is traditionally taken for granted. While much is known about training performance during adaptation to a perturbation in reaches, saccades and locomotion, little is known about the time course of the underlying implicit processes during normal motor adaptation. Implicit learning is chara...
In learning and adapting movements in changing conditions, people attribute the errors they experience to a combined weighting of internal or external sources. As such, error attribution that places more weight on external sources should lead to decreased updates in our internal models for movement of the limb or estimating the position of the effe...
Knowing where our limbs are in space is essential for moving and for adapting movements to various changes in our environments and bodies. The ability to adapt movements declines with age, and age-related cognitive decline can explain a decreased ability to adopt and deploy explicit, cognitive strategies in motor learning. Age-related sensory decli...
In motor learning, the slow development of implicit learning, following explicit components of learning is well established. While much is known about behaviour during adaptation to a perturbation in reaches, saccades and locomotion, little is known about implicit processes during adaptation. Implicit learning is characterized by both changes in in...
Motor learning and adaptation are guided by the attribution of errors to internal or external sources. When errors are clearly external, we should not update our internal models for movement or state estimation, i.e. there should be no implicit learning. However, measures of implicit learning are the same whether or not we induce explicit adaptatio...
An accurate estimate of limb position is necessary for movement planning, before and after motor learning. Where we localize our unseen hand after a reach depends on felt hand position, or proprioception, but in studies and theories on motor adaptation this is quite often neglected in favour of predicted sensory consequences based on efference copi...
Awareness of task demands is often used during rehabilitation and sports training by providing instructions which appears to accelerate learning and improve performance through explicit motor learning. However, the effects of awareness of perturbations on the changes in estimates of hand position resulting from motor learning are not well understoo...
In this project we test if age has an effect on hand localization and if this can be altered by explicit instructions.
An accurate estimate of limb position is necessary for movement. Where we localize our unseen hand after a reach depends on felt hand position, or proprioception, but often only predicted sensory consequences based on efference copies of motor commands are considered. Both signals should contribute, so here we use passive training with rotated visu...
Awareness of task demands is often used during rehabilitation and sports training by providing instructions which appears to accelerate learning and improve performance through explicit motor learning. However, the effects of awareness of perturbations on the changes in estimates of hand position resulting from motor learning are not well understoo...
Explicit awareness of a task is often evoked during rehabilitation and sports training with the intention of accelerating learning and improving performance. However, the effects of awareness of perturbations on the resulting sensory and motor changes produced during motor learning are not well understood. Here, we use explicit instructions as well...
An accurate estimate of limb position is necessary for movement planning. Where we localize our unseen hand after a reach depends on felt hand position, or proprioception, but this is usually neglected in favour of predicted sensory consequences based on efference copies of motor commands. Both sources of information should contribute, so here we s...
Adapting reaches to altered visual feedback not only leads to motor changes, but also to shifts in perceived hand location; “proprioceptive recalibration”. These changes are robust to many task variations and can occur quite rapidly. For instance, our previous study found both motor and sensory shifts arise in as few as 6 rotated-cursor training tr...
[This corrects the article DOI: 10.1371/journal.pone.0163556.].
Training to reach with rotated visual feedback results in adaptation of hand movements, which persist when the perturbation is removed (reach aftereffects). Training also leads to changes in felt hand position, which we refer to as proprioceptive recalibration. The rate at which motor and proprioceptive changes develop throughout training is unknow...
During motor adaptation the discrepancy between predicted and actually perceived sensory feedback is thought to be minimized, but it can be difficult to measure predictions of the sensory consequences of actions. Studies attempting to do so have found that self-directed, unseen hand position is mislocalized in the direction of altered visual feedba...
Visual search can be accelerated when properties of the target are known. Such knowledge allows the searcher to direct attention to items sharing these properties. Recent work indicates that information about properties of non-targets (i.e., negative cues) can also guide search. In the present study, we examine whether negative cues lead to differe...
Background:
People with color vision deficiencies report numerous limitations in daily life, restricting, for example, their access to some professions. However, they use basic color terms systematically and in a similar manner as people with normal color vision. We hypothesize that a possible explanation for this discrepancy between color percept...
Recorded gaze-aligned video during search for targets of any color. The video frames have been analyzed by an object-detection algorithm. All detected objects have been marked in the video. The circle represents the region of the frames corresponding to the fovea. Note: The participant is fixating candies repeatedly, as can be seen when following t...
Participant during search in lawn.
Combined recording of head-fixed scene shot and gaze-directed camera. The black circle in the head-fixed shot shows the current direction of gaze. Note: Candies in head-fixed short are too small to be evaluated, while the gaze-camera delivers magnified shots that can be evaluated by an object-detection algorithm.
When reaching towards objects, the human central nervous system (CNS) can actively compensate for two different perturbations simultaneously (dual adaptation), though this does not simply occur upon presentation. Dual adaptation is made more difficult when the desired trajectories and targets are identical and hence do not cue the impending perturb...
Gaze is widely considered a good proxy for spatial attention. We address whether such "overt attention" is related to other attention measures in natural scenes, and to what extent laboratory results on eye movements transfer to real-world gaze orienting. We find that the probability of a target to be detected in a rapid-serial-visual-presentation...
For natural scenes, attention is frequently quantified either by performance during rapid presentation or by gaze allocation during prolonged viewing. Both paradigms operate on different time scales, and tap into covert and overt attention, respectively. To compare these, we ask some observers to detect targets (animals/vehicles) in rapid sequences...
The relation of selective attention to understanding of natural scenes has been subject to intense behavioral research and computational modeling, and gaze is often used as a proxy for such attention. The probability of an image region to be fixated typically correlates with its contrast. However, this relation does not imply a causal role of contr...
Gaze in real-world scenarios is controlled by a huge variety of parameters, such as stimulus features, instructions or context, all of which have been studied systematically in laboratory studies. It is, however, unclear how these results transfer to real-world situations, when participants are largely unconstrained in their behavior. Here we measu...
Background / Purpose:
Rapid serial visual presentation (RSVP) and prolonged viewing are both used to investigate object perception. Here we ask the question if the same low-level features are used for object perception in both paradigms. The luminance contrast within object and background are manipulated in one set of images which is used in both...
Visualization of the average illusory face. To visualize how averaging illusory faces quickly leads to the impression of a face even during prolonged viewing, we sequentially averaged 2,3,…50 illusory face stimuli, once ordered by performance, once ordered randomly. Top row: 50 illusory faces sorted by the probability of being selected as face in e...
Mooney faces. To test the holistic aspects of face processing against the use of individual features, face images are frequently reduced to half-tone (binary) images, consisting only of black and white areas, so-called Mooney faces [Mooney CM (1957) Canad J Psychol 11(4): 219–226]. Since human observers proficiently process these faces and detectio...
The human visual system seems to be particularly efficient at detecting faces. This efficiency sometimes comes at the cost of wrongfully seeing faces in arbitrary patterns, including famous examples such as a rock configuration on Mars or a toast's roast patterns. In machine vision, face detection has made considerable progress and has become a sta...
Our decisions are guided by the rewards we expect. These expectations are often based on incomplete knowledge and are thus subject to uncertainty. While the neurophysiology of expected rewards is well understood, less is known about the physiology of uncertainty. We hypothesize that uncertainty, or more specifically errors in judging uncertainty, a...
Humans typically direct their gaze and attention at locations important for the tasks they are engaged in. By measuring the direction of gaze, the relative importance of each location can be estimated which can reveal how cognitive processes choose where gaze is to be directed. For decades, this has been done in laboratory setups, which have the ad...
Discomfort glare, among different aspects of visual discomfort is a phenomenon which is little understood and hard to quantify. As this phenomenon is dependent on the building occupant's view direction and on the relative position of the glare source, a deeper knowledge of one's visual behavior within a space could provide pertinent insights into b...
Humans typically direct their gaze and attention at locations important for the tasks they are engaged in. By measuring the direction of gaze, the relative importance of each location can be estimated which can reveal how cognitive processes choose where gaze is to be directed. For decades, this has been done in laboratory setups, which have the ad...
Perception self-evidently affects action, but under which conditions does action in turn influence perception? To answer this question we ask observers to view an ambiguous stimulus that is alternatingly perceived as rotating clockwise or counterclockwise. When observers report the perceived direction by rotating a manipulandum, opposing directions...
In natural vision, shifts in spatial attention are associated with shifts of gaze. Computational models of such overt attention typically use the concept of a saliency map: Normalized maps of center-surround differences are computed for individual stimulus features and added linearly to obtain the saliency map. Although the predictions of such mode...
‘‘Natural’’ gaze is typically measured by tracking eye positions during scene presentation in laboratory settings. How informative are such investigations for real-world conditions? Using a mobile eyetracking setup (‘‘EyeSeeCam’’), we measure gaze during free exploration of various in- and outdoor environments, while simultaneously recording head-c...
Different aspects of preparation, especially processes related to knowing what to prepare versus applying that foreknowledge effectively, may be reflected in different types of brain activity, e.g., the lateralized readiness potential (LRP), beta-band event-related desynchronization and phase locking. In a previous study in which subjects had to sw...
Lateralized readiness potential (LRP) and time-frequency domain LRP-type measures, called motor-related amplitude asymmetries (MRAA), in the mu band (9-13 Hz; mu-MRAA) and the beta band (18-26 Hz; beta-MRAA) were used to study the time course of preparation in a task-switching task and a response precuing task. Several dissociations between LRP and...
Questions
Questions (2)
I'm thinking of doing an experiment that would be executed on a multitude of screens. Since I can't do a proper characterization with a colorimeter of all screens, it would be nice to have a robust way to estimate the gamma of screens perceptually. It's not absolutely necessary either, but if anybody has a recommendation, that would be great!
I want to do an experiment where participants have to judge the depth of stimuli, using shutter glasses. To make this harder, people usually generate a cloud of dots, each with a slightly different retinal disparity (disparity noise) so that the overall cloud is supposed to have an uncertain location, depth-wise. However, I've tested this on myself with discs of dots, and it doesn't really seem to make any difference. The perception of such a disc of dots stimulus is not a disc with an uncertain location, but rather a flattened globe with a pretty certain location. So I'd like to try to create stimuli that actually work, but have little idea where to start.
