Astrid M L Kappers

VU University Amsterdam, Amsterdamo, North Holland, Netherlands

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Publications (293)445.81 Total impact

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    ABSTRACT: The term ‘synergy’ – from the Greek synergia – means ‘working together’. The concept of multiple elements working together towards a common goal has been extensively used in neuroscience to develop theoretical frameworks, experimental approaches, and analytical techniques to understand neural control of movement, and for applications for neuro-rehabilitation. In the past decade, roboticists have successfully applied the framework of synergies to create novel design and control concepts for artificial hands, i.e., robotic hands and prostheses. At the same time, robotic research on the sensorimotor integration underlying the control and sensing of artificial hands has inspired new research approaches in neuroscience, and has provided useful instruments for novel experiments.
    Full-text · Article · Feb 2016 · Physics of Life Reviews
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    ABSTRACT: In a previous study, we found the perception of force magnitude to be anisotropic in the horizontal plane. In the current study, we investigated this anisotropy in three dimensional space. In addition, we tested our previous hypothesis that the perceptual anisotropy was directly related to anisotropies in arm dynamics. In experiment 1, static force magnitude perception was studied using a free magnitude estimation paradigm. This experiment revealed a significant and consistent anisotropy in force magnitude perception, with forces exerted perpendicular to the line between hand and shoulder being perceived as 50% larger than forces exerted along this line. In experiment 2, postural arm dynamics were measured using stochastic position perturbations exerted by a haptic device and quantified through system identification. By fitting a mass-damper-spring model to the data, the stiffness, damping and inertia parameters could be characterized in all the directions in which perception was also measured. These results show that none of the arm dynamics parameters were oriented either exactly perpendicular or parallel to the perceptual anisotropy. This means that endpoint stiffness, damping or inertia alone cannot explain the consistent anisotropy in force magnitude perception.
    Full-text · Article · Dec 2015 · Scientific Reports
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    Myrthe A Plaisier · Astrid M L Kappers

    Preview · Article · Nov 2015 · Perception

  • No preview · Conference Paper · Jun 2015
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    Sander E. M. Jansen · Wouter M. Bergmann Tiest · Astrid M. L. Kappers
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    ABSTRACT: In order to acquire information concerning the geometry and material of handheld objects, people tend to execute stereotypical hand movement patterns called haptic Exploratory Procedures (EPs). Manual annotation of haptic exploration trials with these EPs is a laborious task that is affected by subjectivity, attentional lapses, and viewing angle limitations. In this paper we propose an automatic EP annotation method based on position and orientation data from motion tracking sensors placed on both hands and inside a stimulus. A set of kinematic variables is computed from these data and compared to sets of predefined criteria for each of four EPs. Whenever all criteria for a specific EP are met, it is assumed that that particular hand movement pattern was performed. This method is applied to data from an experiment where blindfolded participants haptically discriminated between objects differing in hardness, roughness, volume, and weight. In order to validate the method, its output is compared to manual annotation based on video recordings of the same trials. Although mean pairwise agreement is less between human-automatic pairs than between human-human pairs (55.7% vs 74.5%), the proposed method performs much better than random annotation (2.4%). Furthermore, each EP is linked to a specific object property for which it is optimal (e.g., Lateral Motion for roughness). We found that the percentage of trials where the expected EP was found does not differ between manual and automatic annotation. For now, this method cannot yet completely replace a manual annotation procedure. However, it could be used as a starting point that can be supplemented by manual annotation.
    Full-text · Article · Feb 2015 · PLoS ONE
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    Vonne van Polanen · Wouter M. Bergmann Tiest · Astrid M L Kappers
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    ABSTRACT: In a haptic search task, one has to detect the presence of a target among distractors using the sense of touch. A salient target can be detected faster than a non-salient target. However, little is known about the exploration strategies that are used, especially in 3D search tasks where items are held in the hand. In this study, we investigated which parts of the hand were used to contact the target and which strategies were performed. Blindfolded participants performed search tasks in four conditions, where the targets differed in relevant property and saliency. The positions of the target and the hand were tracked during exploration. It was found that target saliency had a large effect on the use of the hand parts and the strategies. In the non-salient target conditions, the fingers, especially the thumb, contacted the target more often than in the salient target conditions. This could also be seen in the strategies, where the thumb was used to explore the items in a serial way by moving them in the hand or touching them individually. In the salient target conditions, more parallel strategies like grasping or shuffling of the items in the hand were used.
    Full-text · Article · Sep 2014 · Scientific Reports
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    Femke E van Beek · Wouter M. Bergmann Tiest · Astrid M L Kappers
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    ABSTRACT: While quite some research has focussed on the accuracy of haptic perception of distance, information on the precision of haptic perception of distance is still scarce, particularly regarding distances perceived by making arm movements. In this study, eight conditions were measured to answer four main questions, which are: what is the influence of reference distance, movement axis, perceptual mode (active or passive) and stimulus type on the precision of this kind of distance perception? A discrimination experiment was performed with twelve participants. The participants were presented with two distances, using either a haptic device or a real stimulus. Participants compared the distances by moving their hand from a start to an end position. They were then asked to judge which of the distances was the longer, from which the discrimination threshold was determined for each participant and condition. The precision was influenced by reference distance. No effect of movement axis was found. The precision was higher for active than for passive movements and it was a bit lower for real stimuli than for rendered stimuli, but it was not affected by adding cutaneous information. Overall, the Weber fraction for the active perception of a distance of 25 or 35 cm was about 11% for all cardinal axes. The recorded position data suggest that participants, in order to be able to judge which distance was the longer, tried to produce similar speed profiles in both movements. This knowledge could be useful in the design of haptic devices.
    Full-text · Article · Aug 2014 · PLoS ONE
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    Daisuke Shibata · Astrid M L Kappers · Marco Santello
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    ABSTRACT: Humans are able to modulate digit forces as a function of position despite changes in digit placement that might occur from trial to trial or when changing grip type for object manipulation. Although this phenomenon is likely to rely on sensing the position of the digits relative to each other and the object, the underlying mechanisms remain unclear. To address this question, we asked subjects (n = 30) to match perceived vertical distance between the center of pressure (CoP) of the thumb and index finger pads (dy ) of the right hand ("reference" hand) using the same hand ("test" hand). The digits of reference hand were passively placed collinearly (dy = 0 mm). Subjects were then asked to exert different combinations of normal and tangential digit forces (Fn and Ftan , respectively) using the reference hand and then match the memorized dy using the test hand. The reference hand exerted Ftan of thumb and index finger in either same or opposite direction. We hypothesized that, when the tangential forces of the digits are produced in opposite directions, matching error (1) would be biased toward the directions of the tangential forces; and (2) would be greater when the remembered relative contact points are matched with negligible digit force production. For the test hand, digit forces were either negligible (0.5-1 N, 0 ± 0.25 N; Experiment 1) or the same as those exerted by the reference hand (Experiment 2).Matching error was biased towards the direction of digit tangential forces: thumb CoP was placed higher than the index finger CoP when thumb and index finger Ftan were directed upward and downward, respectively, and vice versa (p < 0.001). However, matching error was not dependent on whether the reference and test hand exerted similar or different forces. We propose that the expected sensory consequence of motor commands for tangential forces in opposite directions overrides estimation of fingertip position through haptic sensory feedback.
    Full-text · Article · Aug 2014 · Frontiers in Human Neuroscience

  • No preview · Conference Paper · Jul 2014
  • Wouter M. Bergmann Tiest · Astrid M. L. Kappers
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    ABSTRACT: The object of this study was to see whether differences in texture influence grip force in the very early phase of grasping an object. Subjects were asked to pick up objects with different textures either blindfolded or sighted, while grip force was measured. Maximum force was found to be adjusted to suit the differences in coefficient of friction, confirming earlier results. Surprisingly, statistically significant differences in grip force were already present as short as 10 ms after touch onset in the blindfolded condition, despite the fact that only haptic information about the texture was available. This suggests that the haptic system is very fast in identifying a texture’s friction.
    No preview · Chapter · Jun 2014
  • Vonne van Polanen · Wouter M. Bergmann Tiest · Astrid M.L. Kappers
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    ABSTRACT: In a haptic search task, one has to determine the presence of a target among distractors. It has been shown that if the target differs from the distractors in two properties, shape and texture, performance is better than in both single-property conditions (Van Polanen, Bergmann Tiest, & Kappers, 2013). The search for a smooth sphere among rough cubical distractors was faster than both the searches for a rough sphere (shape information only) and for a smooth cube (texture information only). This effect was replicated in this study as a baseline. The main focus here was to further investigate the nature of this integration. It was shown that performance is better when the two properties are combined in a single target (smooth sphere), than when located in two separate targets (rough sphere and smooth cube) that are simultaneously present. A race model that assumes independent parallel processing of the two properties could explain the enhanced performance with two properties, but this could only take place effectively when the two properties were located in a single target.
    No preview · Article · May 2014 · Acta psychologica
  • Virjanand Panday · Wouter M. Bergmann Tiest · Astrid M L Kappers
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    ABSTRACT: From previous studies, it is unclear how bimanual length discrimination differs from unimanual length discrimination. To investigate the difference, we designed an experiment with four conditions. In the first two conditions, unimanual and bimanual discrimination thresholds are determined. In the third and fourth conditions, length is explored with the two index fingers like in the bimanual condition, but the reference is either internal, by clasping the hands together, or external, by grasping handles connected to the table. We find that thresholds for the unimanual condition (7.0 %) and the clasping condition (9.2 %) are both lower than for the bimanual condition (16 %) and the grasping handles condition (15 %). We conclude that when discriminating length unimanually and bimanually while clasping the hands together, the internal reference within the hand can be used and that explains the lower discrimination thresholds.
    No preview · Article · May 2014 · Experimental Brain Research
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    ABSTRACT: Haptic perception is bidirectionally related to exploratory movements, which means that exploration influences perception, but perception also influences exploration. We can optimize or change exploratory movements according to the perception and/or the task, consciously or unconsciously. This paper presents a psychophysical experiment on active roughness perception to investigate movement changes as the haptic task changes. Exerted normal force and scanning velocity are measured in different perceptual tasks (discrimination or identification) using rough and smooth stimuli. The results show that humans use a greater variation in contact force for the smooth stimuli than for the rough stimuli. Moreover, they use higher scanning velocities and shorter break times between stimuli in the discrimination task than in the identification task. Thus, in roughness perception humans spontaneously use different strategies that seem effective for the perceptual task and the stimuli. A control task, in which the participants just explore the stimuli without any perceptual objective, shows that humans use a smaller contact force and a lower scanning velocity for the rough stimuli than for the smooth stimuli. Possibly, these strategies are related to aversiveness while exploring stimuli.
    Preview · Article · Mar 2014 · PLoS ONE
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    Astrid M L Kappers · Wouter M. Bergmann Tiest
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    ABSTRACT: RECENTLY, WE SHOWED A STRONG HAPTIC SIZE AFTEREFFECT BY MEANS OF A SIZE BISECTION TASK: after adaptation to a large sphere, subsequently grasped smaller test spheres felt even smaller, and vice versa. In the current study, we questioned whether the strength of this aftereffect depends on shape. In four experimental conditions, we determined the aftereffect after adaptation to spheres and tetrahedra and subsequent testing also with spheres and tetrahedra. The results showed a clear influence of shape: the haptic aftereffect was much stronger if adaptation and test stimuli were identical in shape than if their shapes were different. Therefore, it would be more appropriate to term such aftereffects haptic shape-size aftereffects, as size alone could not be the determining factor. This influence of shape suggests that higher cortical areas are involved in this aftereffect and that it cannot be due to adaptation of peripheral receptors. An additional finding is that the geometric property or combination of properties participants use in the haptic size bisection task varies widely over participants, although participants themselves are quite consistent.
    Preview · Article · Feb 2014 · PLoS ONE
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    Virjanand Panday · Wouter M Bergmann Tiest · Astrid M L Kappers
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    ABSTRACT: We investigated if and how length and curvature information are integrated when an object is explored in one hand. Subjects were asked to explore four types of objects between thumb and index finger. Objects differed in either length, curvature, both length and curvature correlated as in a circle, or anti-correlated. We found that when both length and curvature are present, performance is significantly better than when only one of the two cues is available. Therefore, we conclude that there is integration of length and curvature. Moreover, if the two cues are correlated in a circular cross-section instead of in an anti-correlated way, performance is better than predicted by a combination of two independent cues. We conclude that integration of curvature and length is highly efficient when the cues in the object are combined as in a circle, which is the most common combination of curvature and length in daily life.
    Preview · Article · Jan 2014 · Scientific Reports
  • Vonne van Polanen · Wouter M. Bergmann Tiest · Astrid M.L. Kappers
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    ABSTRACT: In a haptic search task, one has to determine the presence of a target among distractors. It has been shown that if the target differs from the distractors in two properties, shape and texture, performance is better than in both single-property conditions (Van Polanen, Bergmann Tiest, & Kappers, 2013). The search for a smooth sphere among rough cubical distractors was faster than both the searches for a rough sphere (shape information only) and for a smooth cube (texture information only). This effect was replicated in this study as a baseline. The main focus here was to further investigate the nature of this integration. It was shown that performance is better when the two properties are combined in a single target (smooth sphere), than when located in two separate targets (rough sphere and smooth cube) that are simultaneously present. A race model that assumes independent parallel processing of the two properties could explain the enhanced performance with two properties, but this could only take place effectively when the two properties were located in a single target.
    No preview · Article · Jan 2014
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    Sander E M Jansen · Wouter M. Bergmann Tiest · Astrid M L Kappers
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    ABSTRACT: Haptic exploratory procedures (EPs) are prototypical hand movements that are linked to the acquisition of specific object properties. In studies of haptic perception, hand movements are often classified into these EPs. Here, we aim to investigate several EPs in a quantitative manner to understand how hand dynamics and contact forces differ between them. These dissimilarities are then used to construct an EP identification model capable of discriminating between EPs based on the index finger position and contact force. The extent to which the instructed EPs were distinct, repeatable, and similar across subjects was confirmed by showing that more than 95 percent of the analyzed trials were classified correctly. Finally, the method is employed to investigate haptic exploratory behavior during similarity judgments based on several object properties. It seems that discrimination based on material properties (hardness, roughness, and temperature) yields more consistent classification results compared to discrimination based on the acquisition of shape information.
    Full-text · Article · Oct 2013 · IEEE Transactions on Haptics
  • Femke E van Beek · Wouter M Bergmann Tiest · Astrid M.L. Kappers
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    ABSTRACT: Although force-feedback devices are already being used, the human ability to perceive forces has not been documented thoroughly. The haptic perception of force direction and magnitude has mostly been studied in discrimination tasks in the direction of gravity. In our study, the influence of physical force direction on haptic perception of force magnitude and direction was studied in the horizontal plane. Subjects estimated the direction and magnitude of a force exerted on their stationary hand. A significant anisotropy in perception of force magnitude and direction was found. Force direction data showed significant subject-dependent distortions at various physical directions. Normalized force magnitude data showed a consistent elliptical pattern, with its minor axis pointing roughly from the subject's hand to his/her shoulder. This pattern could be related to arm stiffness or manipulability patterns, which are also ellipse-shaped. These ellipses have an orientation consistent with the distortion measured in our study. So, forces in the direction of highest stiffness and lowest manipulability are perceived as being smaller. It therefore seems that humans possess a "sense of effort" rather than a "sense of force," which may be more useful in everyday life. These results could be useful in the design of haptic devices.
    No preview · Article · Oct 2013 · IEEE Transactions on Haptics
  • Astrid M L Kappers · Wouter M. Bergmann Tiest
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    ABSTRACT: Haptic matching of the orientation of bars separated by a horizontal distance leads to large systematic deviations. This finding leads to the following intriguing question which we investigated in this study: How will a bar moving from left to right in a fixed orientation be perceived by blindfolded observers? Interestingly, this previous finding predicts that the translating bar will cause the illusory perception of a rotation. In our experiment, we used psychophysical methods to determine the rotation needed to perceive the bar as non-rotating, for both rightward and leftward translations. From our results, it can be estimated that, on average, a bar translating in parallel over 60 cm is perceived as rotating 18°, so we established that the predicted illusory rotation indeed exists. This implies that static and dynamic signals are processed in a similar way.
    No preview · Article · Sep 2013 · Experimental Brain Research
  • Sander E. M. Jansen · Wouter M. Bergmann Tiest · Astrid M. L. Kappers
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    ABSTRACT: Active movement of the hand and fingers enables dynamic exploration of objects. Lederman and Klatzky [1987] have proposed a set of stereotyped movement patterns called Exploratory Procedures (EPs) that are linked to the acquisition of knowledge concerning specific object properties. For example, lateral motion is the optimal EP for acquiring roughness information and compliance is best estimated by employing pressure.
    No preview · Conference Paper · Aug 2013

Publication Stats

4k Citations
445.81 Total Impact Points

Institutions

  • 2013-2015
    • VU University Amsterdam
      • • MOVE Research Institute Amsterdam
      • • Faculty of Human Movement Sciences
      Amsterdamo, North Holland, Netherlands
  • 1995-2014
    • Utrecht University
      • • Helmholtz Institute
      • • Division of Physics of Man
      Utrecht, Utrecht, Netherlands
  • 1992-2008
    • Netherlands Institute for Space Research, Utrecht
      Utrecht, Utrecht, Netherlands
  • 1996-1997
    • The Ohio State University
      • Department of Psychology
      Columbus, OH, United States