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Papers by Karl-theodor Kalveram

Informatik aktuell, 2007

In legged systems, springy legs facilitate gaits with subsequent contact and flight phases. Here,... more In legged systems, springy legs facilitate gaits with subsequent contact and flight phases. Here, we test whether electrical motors can generate leg behaviors suitable for stable hopping. We built a vertically operating sledge actuated by a motor-driven leg. The motor torque simulates either a linear leg spring or a muscle-reflex system. For stable hopping significant energy supply was required after midstance. This was achieved by enhancing leg stiffness or by continuously applying positive force feedback to the simulated muscle. The muscle properties combined with positive force feedback result in spring-like behavior which enables stable hopping with adjustable hopping height.

Motor control, 2005

The question addressed in the present study is whether children and adults are able to combine an... more The question addressed in the present study is whether children and adults are able to combine and decompose separate kinematic (visual-feedback-shift) and dynamic (velocity-dependent force) transformations in goal-directed arm movements. A total of 64 participants (32 adults and 32 children) performed horizontal forearm movements using a single-joint arm manipulandum. When participants first learned kinematic and dynamic transformations separately, target error decreased in a subsequent combined transformation task. This effect was based on previous learning of the kinematic transformation. When they first learned the combined transformation, target error was smaller in the following kinematic-but not in the dynamic-transformation. No difference was found in adaptation performance between children and adults. The results suggest that there are two separate models for the kinematic and dynamic transformation and that a possible differentiation of kinematic and dynamic features of th...

Physiology & behavior

The long-term observation of ingestive and excretory behaviors in freely ambulating and non socia... more The long-term observation of ingestive and excretory behaviors in freely ambulating and non socially isolated pigs is an important tool in the investigation of the physiological determinants of these behaviors. A computer-controlled laboratory setup for the recording of feeding, drinking, and defecation behavior in minipigs was developed, allowing for the observation of two pigs at a time for weeks. Four minipigs (29-52 kg) were conditioned to operate feeders with a precise food release per response and were then fed ad lib. The animals had up to 50% of their daily energy intake during the night. Meal size and time spent eating was highly correlated, meal size and the preprandial intermeal interval was moderately correlated, whereas meal size and the postprandial intermeal interval was not. Feeding facilitated defecation, supporting the assumption that the gastrocolonic response is present in the pig. The system has been shown to be highly reliable and valid, and thus provides an ex...

Psychological Research Psychologische Forschung, 2004

When humans are exposed to external forces while performing arm movements, they adapt by compensa... more When humans are exposed to external forces while performing arm movements, they adapt by compensating for these novel forces. The basis of this learning process is thought to be a neural representation that models the relation between all forces acting upon the system and the kinematic effects they produce, called inverse dynamic model (IDM). The present study investigated whether and how the predictability of a given external force affects the selection of an appropriate motor response to compensate for such force. Adult human subjects (N=32) held a handle that could rotate around the elbow joint and learned to perform goal-directed forearm flexion movements, while an external velocity-dependent negative damping force was applied that assisted forearm movement. Subjects were randomly assigned to two groups. In the associative group, the applied damping force was always associated with a specific initial position. Thus, after initial learning, the force application became predictable. In the nonassociative group, where the same movements were performed, the applied force was independent of the initial position, so that no association between force and location could be formed. We found that only the associative group significantly reduced target error when damping was present. That is, the location cue aided these subjects in generating dynamic responses in the appropriate limb. Our results indicate that motor adaptation to different dynamic environments can be facilitated by indicative stimuli.

Physiology & Behavior, 1994

To determine the effect of nutrient ingestion on rectal perception thresholds (first sensation, c... more To determine the effect of nutrient ingestion on rectal perception thresholds (first sensation, consistent urge to defecate, pain), rectosigmoid balloon distentions were performed with a computerized automated pump in eight healthy volunteers (four males, four females, 31.6 +/- 6.02 years). Two measurements of rectal balloon distention were performed on 2 separate days. Day 1 served as a control condition with no meal. On day 2 the subjects received a 600 kcal liquid meal. On the control day, determination of perception thresholds was performed two times with a 10-min break between measurements. On the experimental day, threshold determinations were made before and after the ingestion of the liquid standard meal. The order of the experimental days was counterbalanced. Distention volumes at the urge to defecate and the pain threshold (maximum tolerable volume) were significantly reduced following the meal. The average change from pre- to postprandial measurements of the threshold for urge to defecate was -20.55 +/- 4.22% and for the maximum tolerable volume it was -16.09 +/- 4.4%. These results extend data previously reported from animal studies using similar experimental methods.

Experimental Brain Research, 2002

When humans perform goal-directed arm movements under the influence of an external damping force,... more When humans perform goal-directed arm movements under the influence of an external damping force, they learn to adapt to these external dynamics. After removal of the external force field, they reveal kinematic aftereffects that are indicative of a neural controller that still compensates the no longer existing force. Such behavior suggests that the adult human nervous system uses a neural representation of inverse arm dynamics to control upper-extremity motion. Central to the notion of an inverse dynamic model (IDM) is that learning generalizes. Consequently, aftereffects should be observable even in untrained workspace regions. Adults have shown such behavior, but the ontogenetic development of this process remains unclear. This study examines the adaptive behavior of children and investigates whether learning a force field in one hemifield of the right arm workspace has an effect on force adaptation in the other hemifield. Thirty children (aged 6-10 years) and ten adults performed 30°elbow flexion movements under two conditions of external damping (negative and null). We found that learning to compensate an external damping force transferred to the opposite hemifield, which indicates that a model of the limb dynamics rather than an association of visited space and experienced force was acquired. Aftereffects were more pronounced in the younger children and readaptation to a null-force condition was prolonged. This finding is consistent with the view that IDMs in children are imprecise neural representations of the actual arm dynamics. It indicates that the acquisition of IDMs is a developmental achievement and that the human motor system is inherently flexible enough to adapt to any novel force within the limits of the organism's biomechanics.

Biological Cybernetics, 2005

A solution is proposed of the hitherto unsolved problem as to how neural feedforward through inve... more A solution is proposed of the hitherto unsolved problem as to how neural feedforward through inverse modelling and negative feedback realised by a mechanical spring can be combined to achieve a highly effective control of limb movement. The revised spring approach that we suggest does not require forward modelling and produces simulated data which are as close as possible to experimental human data. Control models based on peripheral sensing with forward modelling, which are favoured in the current literature, fail to create such data. Our approach suggests that current views on motor control and learning should be revisited.

Biological Cybernetics, 1991

It is demonstrated, that a two-joiried arm performing goal directed movements is controllable (a)... more It is demonstrated, that a two-joiried arm performing goal directed movements is controllable (a) by two central pattern generators (CPG) representing sampled data control, each referring to one joint, initiated for exactly one period, and producing the angular movement width about this joint, and (b) bV reflex-like processes operating continuously with respect to time. The latter eliminate the effects of dynamic coupling, gravity, inertia, and mechanical impedance on the movement by 'proprioceptive feedforward' of position, velocity and acceleration signals, thus enabling the CPGs to handle the arm segments as if they were independent and free from forces. Higher ordered centers (with respect to the CPGs) therefore only need to control the kinematics. not dynamics, of the arm.

Journal of Motor Behavior, 2004

The authors investigated adaptation of goal-directed forearm movements to an unknown external vis... more The authors investigated adaptation of goal-directed forearm movements to an unknown external viscous force assisting forearm flexion in 6 patients with cerebellar dysfunction and in 6 control participants. Motor performance was generally degraded in cerebellar patients and was markedly reduced under the force condition in both groups. However, patients and controls were able to adapt to the novel force within 8 trials. Only the healthy controls were able to improve motor performance when readapting to a null-force condition. The results indicate that cerebellar patients' motor control system has imprecise estimations of actual limb dynamics at its disposal. Force adaptation may have been preserved because single-joint movements were performed, whereas the negative viscous force alone and no interaction forces had to be compensated.

2003 by Karl-theodor Kalveram

When humans are exposed to external forceswhile performing arm movements, they adapt by compensat... more When humans are exposed to external forceswhile performing arm movements, they adapt by compensating for these novel forces. The basis of this learning process is thought to be a neural representation that models the relation between all forces acting upon the system and the kinematic eﬀects they produce, called inverse dynamic model (IDM). The present study investigated whether and how the predictability of a given external force aﬀects the selection of an appropriate motor response to compensate for such force.Adult human subjects (N =32) held a handle that could rotate around the elbow joint and learned to perform goal-directed forearm ﬂexion movements, while an external velocity-dependent negative damping force was applied that assisted forearm movement. Subjects were randomly assigned to two groups. In the associative group, the applied damping force was always associated with a speciﬁc initial position. Thus, after initial learn-ing, the force application became predictable. In the non-associative group, where the same movements were performed, the applied force was independent of the initial position, so that no association between force and location could be formed. We found that only the associative group signiﬁcantly reduced target error when damping was present. That is, the location cue aidedthese subjects in generating dynamic responses in theappropriate limb. Our results indicate that motor adaptation to diﬀerent dynamic environments can be facilitated by indicative stimuli.

2000 by Karl-theodor Kalveram

Objectives—To examine changes in predictive control of early antagonist responses to limb perturb... more Objectives—To examine changes in predictive control of early antagonist responses to limb perturbations in patients with defined lesions of the cerebellum. Methods—Eight cerebellar patients and eight sex and age matched control subjects participated. Subjects held a handle that was rotated around the elbow joint. They were instructed to hold the forearm at 90° flexion against a mechanical perturbation. Extensor torque (5 Nm) was applied for 140 ms (pulse), or for 1400 ms (step) through an external motor. Motor responses were tested under two divergent conditions of anticipatory information. In the expected condition, subjects anticipated and received a pulse. Under the unexpected condition, subjects expected steps, but received unexpected pulses. Biceps and triceps EMG as well as angular kinematics were compared between expected and unexpected pulse perturbations to quantify possible effects of prediction. Results—In all healthy subjects, the degree of overshoot in the return flexion movement was significantly less in expected pulse perturbations compared with unexpected trials. The degree of amplitude reduction was significantly smaller in the patient group than in the control group (22.8% v 40.0%). During the expected trials, latency of peak triceps activity was on average 20% shorter in the control group, but 4% larger in the cerebellar patients. Conclusions—In the expected condition, controls achieved a significant reduction in angular amplitude by generating triceps activity earlier, whereas the ability to use prediction for adjusting early antagonist responses after limb perturbation was impaired in cerebellar patients.