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Otmar Bock

Publications and source records attributed to Otmar Bock.

16 recordsLinked to original sources
PubMed2006

A method to reversibly degrade proprioceptive feedback in research on human motor control.

In research on human motor skills, it is often desirable to manipulate proprioceptive feedback in order to determine its contribution towards subjects' performance. Here we evaluate an easy-to-use, non-invasive method to temporarily reduce proprioceptive responsiveness. Two physiotherapy vibrators contacted the distal end of the subjects' forearm on the flexor and extensor side; they were either turned off, or they vibrated at 80 Hz with an amplitude of 1mm. We found that vibration substantially impaired subjects' ability to use their hand in an angle matching, a force production and a haptic shape perception task. We also found that vibration strongly attenuated the H-reflex of the ipsilateral M. flexor carpi radialis. These results suggest that agonist-antagonist vibration is a useful method to degrade proprioceptive responsiveness for research on higher motor functions.

Adaptation, Physiological↗
PubMed2006

The contribution of proprioceptive feedback to sensorimotor adaptation.

It is known that proprioceptive signals from muscles, joints, and skin are involved in the execution of aimed arm movements, but their role in the acquisition of new motor behaviour is largely unknown. Previous research using deafferented patients yielded inconsistent findings: sensorimotor adaptation was found to be less, equal, or even better than in controls. The present study uses a different approach: we degraded proprioceptive signals in healthy subjects by wrist vibration, while leaving them intact in a control group. In order to induce sensorimotor adaptation, both groups executed pointing movements under a visual (Exp. A) or a mechanical perturbation (Exp. B). We found that adaptation to the visual distortion was little affected by vibration, while adaptation to the mechanical distortion was substantially impaired. We conclude that proprioceptive signals which overtly disagree with visual ones (Exp. A) are not used for adaptation, while those which largely agree with visual ones (Exp. B) are used to enhance adaptive recalibration. These results indicate that intact proprioception is needed for mechanical but not for visual adaptation, which implies that the underlying mechanisms are at least partly distinct.

Adaptation, Physiological↗
PubMed2006

Practice ameliorates deficits of isometric force production in +3 Gz.

BACKGROUND: In our earlier work, we have shown that human subjects produce exaggerated isometric forces when exposed to three times terrestrial gravity (+3 Gz). In the present work, we investigated whether prolonged practice under +3 Gz reduces this deficit, and whether it affects the cognitive costs of force production. METHODS: There were 24 young male student volunteers who produced forces without visual feedback of prescribed directions and magnitudes with their dominant hand, and used their other hand for a four-choice reaction-time task. Both tasks were performed separately and concurrently, in normal terrestrial gravity (normal G), 30 s after the beginning of +3 Gz, and after practice in +3 Gz. RESULTS: During early +3 Gz responses, initial force (100 ms into the response) increased abruptly by about 140%, and peak-produced force by 30%. Both values decreased again after prolonged practice; this recovery was complete for peak force, but only partial for initial force. Dual-task interference was observed, which did not vary with G level or practice. DISCUSSION: The detrimental effects of +3 Gz on force production are compensated for by adaptive reprogramming (see initial force) and by additional feedback-based corrections (see difference between peak and initial force). Force production is cognitively demanding, but cognitive costs do not seem to vary with G level or practice.

Adult↗
PubMed2005

Relationship between sensorimotor adaptation and cognitive functions in younger and older subjects.

We investigated whether deficits of adaptive improvement in seniors are related to an age-dependent decay of the brain's executive functions. Younger and older subjects completed a battery of cognitive tests, and preformed aimed arm movements before and during exposure to rotated visual feedback. In accordance with previous work, we found that adaptive improvement during exposure was degraded in seniors, while the transfer of adaptation to a new motor task was not. This pattern of findings confirms that strategic control but not sensorimotor recalibration is affected by old age. Using multiple linear regression (MLR) to extract separate executive components from our test battery, we found that basic response speed and decision-making, but not the inhibition of prepotent responses or mental flexibility, were degraded in our older subjects. Again using MLR, we found that degraded adaptive improvement in our seniors was partly related to the decay of basic response speed and decision-making, and partly to age-dependent phenomena not addressed by our cognitive-test battery. Finally, we observed that interindividual variability of cognition and adaptive improvement was larger in old than in young subjects, which could explain why some previous studies found degraded adaptation in seniors while others did not.

Adaptation, Physiological↗
PubMed2005

Concurrent adaptations of left and right arms to opposite visual distortions.

Previous research has shown that subjects can adapt with either arm to an opposite visual distortion, and the two adaptive states can then be used in sequence to control the respective arm. To extend this finding, we exposed the left and right arms of our subjects to opposite-directed rotations of the visual field alternately for 20 s each, and determined the time-course of adaptation, as well as aftereffects without visual feedback under uni- and bimanual conditions. Our data confirm that two adaptive states can co-exist in the sensorimotor system, one for each arm. We further found that the time-course of adaptive improvement was similar for both arms, that the improvement was present as early as the first movement after a change of arm and discordance, and that the magnitude of adaptation was similar to control data yielded by a single arm and discordance. Taken together, these findings suggest that the two adaptive states were formed concurrently, and without mutual interference. We also observed significant aftereffects. They were smaller but still appreciable under bimanual conditions; the two arms moved at the same time in different directions even though they were aimed at a common visual target. This outcome indicates that the two adaptive states were not merely of a strategic nature, but rather changed the rules by which sensory information was transformed into motor outputs; it also suggests that the two states not only co-exist, but can also be engaged concurrently in movement control. The reduced aftereffects observed under bimanual conditions can be attributed to the well-known phenomenon of bimanual coupling, which is unrelated to adaptation.

Adaptation, Physiological↗
PubMed2005

The effect of rest breaks on human sensorimotor adaptation.

We have studied the effect of rest breaks on sensorimotor adaptation to rotated visual feedback in a pointing task. Adaptive improvement was significantly poorer after 1-s breaks than after 5-40-s breaks, with no significant difference among the latter break durations. The benefit of >1-s breaks emerged soon after the onset of adaptation, and then remained steady throughout the adaptation, retention (next day), and persistence (no feedback) phases. This pattern of findings indicates that break-induced facilitation is not a result of strategic adjustments, motivation, or recovery from fatigue, but rather to consolidation of previously acquired sensorimotor recalibration rules.

Adaptation, Physiological↗
PubMed2005

Isometric force production in high Gz: mechanical effects, proprioception, and central motor commands.

BACKGROUND: We have shown in the past that human subjects produce exaggerated isometric responses when exposed to high +Gz. The present study investigated the role played by different factors in this phenomenon. METHODS: There were 12 healthy non-pilot volunteers who were seated in the gondola of a centrifuge and were exposed to a +1, +1.5, and +3 Gz environment. During each exposure, they produced forces of prescribed magnitudes and directions in their frontal plane using an isometric joystick. From the registered data, we determined initial (100 ms after onset), peak, and end (70 ms before trial end) force. RESULTS: For a given target magnitude, initial, peak, and end force were each smallest in 1 G, higher in 1.5 G, and higher still in 3 G. This G-related exaggeration was most pronounced for initial, and less for peak and end force. We further found that responses in high G were biased downwards for end force, but not for initial and peak force. CONCLUSIONS: The G-related excesses of produced force are probably due to less appropriate central commands, since it manifests before proprioception becomes effective. The amelioration of this deficit for peak and end force is probably achieved by partial corrections based on proprioceptive feedback, or by direct mechanical effects. Our findings are relevant for the safe operation of high-performance aircraft during high-G maneuvers.

Adult↗
PubMed2005

Wrist vibration affects the production of finely graded forces.

INTRODUCTION: It is still unclear how central commands and afferent feedback interact to produce finely graded forces. To explore this question, we experimentally degraded afferent responsiveness using wrist vibration. METHODS: Subjects grasped an isometric joystick with their preferred hand and produced forces of different magnitudes and directions according to visually presented vectors. In one condition, the dorsal and palmar sides of the wrist were vibrated at 80 Hz to degrade proprioception; in another condition, the wrist was not vibrated. RESULTS: Response magnitude averaged 2.46 kg of force (kgf) without, and decreased to 1.90 kgf with vibration. The coefficient of magnitude variation was vibration-independent and averaged 0.30 kgf. The directional error of responses and its standard deviation were also vibration-independent, averaging -2.6 degrees and +/-17 degrees, respectively. Subjects' maximum voluntary force was 9.77 kgf without, and decreased to 8.83 kgf with vibration. CONCLUSION: Our findings clearly indicate that afferent feedback plays a role in the production of finely graded forces, probably by facilitating descending motor commands.

Adult↗
PubMed2004

Components of sensorimotor adaptation in young and elderly subjects.

Previous studies have found that sensorimotor adaptation to visual distortions is degraded in seniors compared with younger subjects, whereas after-effects on removal of the distortion are age-independent. The latter finding was interpreted as evidence that adaptive recalibration is not affected by old age, and that the observed degradation is therefore due to impairment of strategic control. However, after-effects are not a reliable measure of recalibration, because they can be artificially inflated by perseveration, a characteristic symptom in old age. The present work therefore introduces a test of recalibration which is insensitive to perseveration. Twelve young and twelve old subjects executed center-out pointing movements while visual feedback about their fingertip was either veridical (baseline), 60-deg rotated (adaptation), or absent (after-effect). They also executed tracking movements toward an unpredictably moving object before and after the pointing task. Seniors adapted less than younger subjects but their after-effects were not degraded. More importantly, transfer of adaptation from a pointing to a tracking task was not degraded in seniors. The latter outcome documents, in a more compelling fashion than previous work, that recalibration in the elderly is not impaired, and that the observed deficit of adaptation is therefore most probably because of impaired strategic control. This conclusion is supported by two additional findings: compared with young subjects our seniors performed less well on a cognitive screening test and acquired no explicit knowledge about the nature of the imposed visual distortion.

Adaptation, Physiological↗
PubMed2003

Human adaptation to rotated vision: interplay of a continuous and a discrete process.

The mechanisms for adaptation to visual rotation were investigated by exposing subjects to different rotation angles in a stepwise fashion. We found that response direction continuously changed to compensate for the imposed rotation, but this change was limited to 90 deg. Larger changes were accomplished by inverting both spatial axes (which is equivalent to a 180 deg rotation), and then gradually changing response direction "backwards" to the prescribed value. The angle of 0 deg had no such limiting value like 90 deg: Response direction could continuously change through 0 deg and beyond. Our data provided no evidence that adaptation to opposite-directed visual rotations results in interference, due to competition in working memory; instead subjects' performance under such conditions is fully explained by the said continuous changes of response direction. We conclude that adaptation is achieved by a coordinated interplay of continuous (gradual rotation between +/-90 deg) and discrete (sign reversal) processes.

Adaptation, Physiological↗
PubMed2003

Sensorimotor adaptation to visual distortions with different kinematic coupling.

We investigated the mechanisms of sensorimotor adaptation by sequentially exposing human subjects to different visual distortions. Subjects performed a manual tracking task, while the relationship between their actual finger movement and its visual feedback was manipulated either by a position-to-position (PP), or by a position-to-velocity (PV) transformation. The outcome confirmed previous findings, in that adaptation to PP facilitated the subsequent adaptation to a second, additional PP. More importantly, our present data documented that pre-exposure to PP interferes with the subsequent adaptation to PV, and vice versa. Thus, we observed anterograde interference between two transformations of common physical nature (i.e., visual), but different kinematic coupling. When previous work on sequential adaptation to visual and mechanical transformations is reconsidered in light of this finding, converging evidence is yielded in favor of a distributed adaptive mechanism, where the magnitude of interference between two successive adaptation sessions depends on the overlap of the involved neural structures.

Adaptation, Ocular↗
PubMed2003

Sensorimotor performance and computational demand during short-term exposure to microgravity.

INTRODUCTION: Previous research suggests that human sensorimotor performance depends both on task difficulty, and on the allocation of the brain's computational resources to the task. We employ this view to analyze the changes of sensorimotor performance during the microgravity episodes of parabolic flight. METHODS: There were seven subjects who participated before, during, and after exposure to the microgravity episodes of parabolic flight. They performed a tracking task with one hand, and a four-choice reaction time task with the other hand, either alone or concurrently. Overall performance scores across tasks were calculated. RESULTS: Overall single-task performance deteriorated by about 50% microgravity, with little sign of recovery during the flight. Overall dual-task interference was more than twice as great at the onset of microgravity than at the onset of the 1-G baseline, but converged toward that baseline within about 4.5 min. CONCLUSIONS: Our subjects accepted a consistently poor level of sensorimotor performance throughout exposure to microgravity. To maintain that level, they increased the allocation of computational resources to the tasks at the onset of microgravity, but an increase was no longer necessary after 4.5 min of microgravity exposure. We take the initial increase as evidence of a brief phase of sensorimotor adaptation.

Adult↗
PubMed2002

Transfer of sensorimotor adaptation between different movement categories.

It is well known that sensorimotor adaptation will transfer from the practiced to the unpracticed arm, which has been taken as evidence that adaptation is located in the brain before the divergence point for left and right arm control. We now explore whether adaptation will transfer between different movement categories as well. Subjects were exposed to a 60-deg visual rotation first in a tracking and then in a pointing task, or vice versa. We found a substantial transfer of adaptation between tasks, but its magnitude was larger from pointing to tracking than from tracking to pointing. This benefit of pointing persisted when the use of cognitive strategies was minimized by a concurrent, attention-demanding task, but it was lost when pointing amplitudes were very small. We conclude that adaptation is located in the brain before the divergence point for different movement categories, and that movements with a large ballistic component facilitate adaptation transfer.

Adaptation, Physiological↗
PubMed2002

Sensorimotor adaptation in young and elderly humans.

Our brain's capacity for adaptation allows us to interact meaningfully with an ever-changing environment. Experimental evidence suggests that the time course of sensorimotor adaptation is preserved or only moderately degraded in old age, and that seniors benefit from a previous adaptive experience even more than younger subjects. However, experimental evidence suggests that sensorimotor adaptation seems to be associated with a higher computational load in the elderly. We discuss two possible explanations for this pattern of findings: Older adults may take longer to consolidate newly gained information into long-term motor memory, or they may have problems to utilize supplementary (e.g. cognitive) strategies. In any case, the age-related deficits were relatively mild. If these deficits are related to an increased computational load, it should be possible to reduce them by extended practice on adaptation tasks.

Adaptation, Physiological↗
PubMed2002

Learning a new bimanual coordination pattern is influenced by existing attractors.

The present study investigates whether the acquisition of a rhythmical bimanual coordination pattern is influenced by existing intrinsic coordination tendencies. Participants were required to learn 1 of 5 new coordination patterns, whose relative phase phi was either 36, 60, or 90 degrees away from the 0 degree and 180 degree attractors, respectively. They performed 35 trials, each consisting of 2 conditions: In the augmented feedback condition, continuous visual guidance was provided, while in the normal feedback condition participants were required to rely on normal vision of their arms. We found that all to-be-learned patterns were performed with higher accuracy in the visually guided condition, whereas interference with pre-existing coordination tendencies was more pronounced in the normal vision condition. Comparing the learning progress of the 5 groups, we found for patterns close to anti-phase, a smaller improvement and significantly larger phase errors than for patterns close to in-phase. This indicates that the acquisition of a new phase relationship is influenced by existing attractors and that the 180 degree attractor interfered more strongly with the to-be-learned pattern than the 0 degree attractor.

Adult↗