Antizipative Anpassung von Griffkräften während des Hebens von Alltagsgegenständen bei Gesunden und nach unilateraler Hirnschädigung

The aim of this dissertation was to investigate anticipatory grip force scaling when lifting everyday objects. Previous studies were mostly restricted to lifting and grasping of neutral objects. In this study participants lifted everyday objects when grip force was registered. Our routine of everyday life is dominated by object manipulation. The ability to estimate objects properties and anticipate the grip force to grasp and lift the object promotes smooth and efficient object manipulation. We investigated anticipatory grip force scaling when lifting everyday objects in two different samples: healthy subjects (study 1) and patients with unilateral brain damage after stroke (study 2). While the first study reveals basic principles of grip force scaling in healthy Young adults, the second study evaluates the effects of brain damage. For this purpose, different objects of everyday life with a wide range of weight were handled. In study 1 eleven healthy subjects lifted 12 objects under two different conditions. In the first trial, the objects were wrapped with paper to obscure the identity of the objects. Grip force was measured by force sensors taped on the fingertips. In addition, load force was measured by the means of a scale. Data from the first lift under the unwrapped condition confirmed that participants anticipated an object’s weight and scaled their grip force correspondingly. The maximum grip force rate at the force increase phase was identified as the most reliable measure to verify that object weight was predicted. Other force measures like maximum load force rate were not as reliable, they were scaled to object weight also when object identity was not known. Variability and linearity of the relationship between grip force and weight improved during the lifting, assumably with the help of sensory information. A second and third trial with the same object in a separate block did not refine the accuracy of the grip force scaling. The aim of study 2 was to investigate whether left brain damage impairs anticipatory force scaling when lifting everyday objects. Therefore, we examined 26 patients with unilateral brain damage (16 with left brain damage, ten with right brain damage) and 21 healthy control subjects. Different tests, like pantomime of familiar tool-use and imitation of meaningless hand postures, assessed 27 limb apraxia. The objects were equal to the first study, once again grip force was measured with the help of sensors taped on the fingertips. Again, the maximum grip force rate thought to be the most reliable parameter for anticipatory grip force scaling was determined. Regression analysis showed a clear deficit of anticipatory grip force scaling for the group with left- hemisphere stroke. The group with stroke of the right hemisphere yielded non impaired force scaling compared with the control group. Lesion-analyses indicate that stroke in the left inferior frontal gyrus (IFG) and the premotor cortex (PMC) causes the described deficits. Interestingly, these are the same structures which are associated with object manipulation. Further, significant correlations of impaired anticipation with limb apraxia scores were found. However, also dissociations between the tests of limb apraxia und impaired grip force anticipation emerged, which implicates independent processes. Summarized, our findings implicate that the underlying neural substrate is not restricted to a single region; rather it may rely on the intact left hemisphere network. Overlapping is presumably explained as the left hemisphere dominantes tool use either

An embodied and grounded perspective on concepts

By the mainstream view in psychology and neuroscience, concepts are informational units, rather stable, and are represented in propositional format. In the view I will outline, instead, concepts correspond to patterns of activation of the perception, action and emotional systems which are typically activated when we interact with the entities they refer to. Starting from this embodied and grounded approach to concepts, I will focus on different research lines and present some experimental evidence concerning concepts of objects, concepts of actions, and abstract concepts. I will argue that, in order to account for abstract concepts, embodied and grounded theories should be extended

Material perception and action : The role of material properties in object handling

This dissertation is about visual perception of material properties and their role in preparation for object handling. Usually before an object is touched or picked-up we estimate its size and shape based on visual features to plan the grip size of our hand. After we have touched the object, the grip size is adjusted according to the provided haptic feedback and the object is handled safely. Similarly, we anticipate the required grip force to handle the object without slippage, based on its visual features and prior experience with similar objects. Previous studies on object handling have mostly examined object characteristics that are typical for object recognition, e.g., size, shape, weight, but in the recent years there has been a growing interest in object characteristics that are more typical to the type of material the object is made from. That said, in a series of studies we investigated the role of perceived material properties in decision-making and object handling, in which both digitally rendered materials and real objects made of different types of materials were presented to human subjects and a humanoid robot. Paper I is a reach-to-grasp study where human subjects were examined using motion capture technology. In this study, participants grasped and lifted paper cups that varied in appearance (i.e., matte vs. glossy) and weight. Here we were interested in both the temporal and spatial components of prehension to examine the role of material properties in grip preparation, and how visual features contribute to inferred hardness before haptic feedback has become available. We found the temporal and spatial components were not exclusively governed by the expected weight of the paper cups, instead glossiness and expected hardness has a significant role as well. In paper II, which is a follow-up on Paper I, we investigated the grip force component of prehension using the same experimental stimuli as used in paper I. In a similar experimental set up, using force sensors we examined the early grip force magnitudes applied by human subjects when grasping and lifting the same paper cups as used in Paper I. Here we found that early grip force scaling was not only guided by the object weight, but the visual characteristics of the material (i.e., matte vs. glossy) had a role as well. Moreover, the results suggest that grip force scaling during the initial object lifts is guided by expected hardness that is to some extend based on visual material properties. Paper III is a visual judgment task where psychophysical measurements were used to examine how the material properties, roughness and glossiness, influence perceived bounce height and consequently perceived hardness. In a paired-comparison task, human subjects observed a bouncing ball bounce on various surface planes and judged their bounce height. Here we investigated, what combination of surface properties, i.e., roughness or glossiness, makes a surface plane to be perceived bounceable. The results demonstrate that surface planes with rough properties are believed to afford higher bounce heights for the bouncing ball, compared to surface planes with smooth properties. Interestingly, adding shiny properties to the rough and smooth surface planes, reduced the judged difference, as if surface planes with gloss are believed to afford higher bounce heights irrespective of how smooth or rough the surface plane is beneath. This suggests that perceived bounce height involves not only the physical elements of the bounce height, but also the visual characteristics of the material properties of the surface planes the ball bounces on. In paper IV we investigated the development of material knowledge using a robotic system. A humanoid robot explored real objects made of different types of materials, using both camera and haptic systems. The objects varied in visual appearances (e.g., texture, color, shape, size), weight, and hardness, and in two experiments, the robot picked up and placed the experimental objects several times using its arm. Here we used the haptic signals from the servos controlling the arm and the shoulder of the robot, to obtain measurements of the weight and hardness of the objects, and the camera system to collect data on the visual features of the objects. After the robot had repeatedly explored the objects, an associative learning model was created based on the training data to demonstrate how the robotic system could produce multi-modal mapping between the visual and haptic features of the objects. In sum, in this thesis we show that visual material properties and prior knowledge of how materials look like and behave like has a significant role in action planning

Objekt-Manipulation und Steuerung der Greifkraft durch Verwendung von Taktilen Sensoren

This dissertation describes a new type of tactile sensor and an improved version of the dynamic tactile sensing approach that can provide a regularly updated and accurate estimate of minimum applied forces for use in the control of gripper manipulation. The pre-slip sensing algorithm is proposed and implemented into two-finger robot gripper. An algorithm that can discriminate between types of contact surface and recognize objects at the contact stage is also proposed. A technique for recognizing objects using tactile sensor arrays, and a method based on the quadric surface parameter for classifying grasped objects is described. Tactile arrays can recognize surface types on contact, making it possible for a tactile system to recognize translation, rotation, and scaling of an object independently.Diese Dissertation beschreibt eine neue Art von taktilen Sensoren und einen verbesserten Ansatz zur dynamischen Erfassung von taktilen daten, der in regelmäßigen Zeitabständen eine genaue Bewertung der minimalen Greifkraft liefert, die zur Steuerung des Greifers nötig ist. Ein Berechnungsverfahren zur Voraussage des Schlupfs, das in einen Zwei-Finger-Greifarm eines Roboters eingebaut wurde, wird vorgestellt. Auch ein Algorithmus zur Unterscheidung von verschiedenen Oberflächenarten und zur Erkennung von Objektformen bei der Berührung wird vorgestellt. Ein Verfahren zur Objekterkennung mit Hilfe einer Matrix aus taktilen Sensoren und eine Methode zur Klassifikation ergriffener Objekte, basierend auf den Daten einer rechteckigen Oberfläche, werden beschrieben. Mit Hilfe dieser Matrix können unter schiedliche Arten von Oberflächen bei Berührung erkannt werden, was es für das Tastsystem möglich macht, Verschiebung, Drehung und Größe eines Objektes unabhängig voneinander zu erkennen

Rate Effects on Timing, Key Velocity, and Finger Kinematics in Piano Performance

We examined the effect of rate on finger kinematics in goal-directed actions of pianists. In addition, we evaluated whether movement kinematics can be treated as an indicator of personal identity. Pianists' finger movements were recorded with a motion capture system while they performed melodies from memory at different rates. Pianists' peak finger heights above the keys preceding keystrokes increased as tempo increased, and were attained about one tone before keypress. These rate effects were not simply due to a strategy to increase key velocity (associated with tone intensity) of the corresponding keystroke. Greater finger heights may compensate via greater tactile feedback for a speed-accuracy tradeoff that underlies the tendency toward larger temporal variability at faster tempi. This would allow pianists to maintain high temporal accuracy when playing at fast rates. In addition, finger velocity and accelerations as pianists' fingers approached keys were sufficiently unique to allow pianists' identification with a neural-network classifier. Classification success was higher in pianists with more extensive musical training. Pianists' movement “signatures” may reflect unique goal-directed movement kinematic patterns, leading to individualistic sound

The Clever Body

In Western civilization, we have come to regard the body as an instrument or a machine that responds to external challenges but does not have a life or creativity of its own. Thanks to some of its inherent capabilities, however, the living body can act in a highly intelligent and creative manner. All of us have noticed from time to time that our body can move naturally, without any conscious effort; it can adapt to new situational demands and propose unexpected solutions. While skiing or rock climbing or sailing, we may have abandoned ourselves to our bodily timing and responsiveness, our acute feeling for new solutions. In The Clever Body, Gabor Csepregi describes in detail the nature and scope of these innate abilities sensibility, spontaneity, mimetic faculty, sense of rhythm, memory, and imagination and reflects on their significance in human life