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At least 181 records · Page 10Linked to original sources
PubMed1998

Compensatory arm-trunk coordination in pointing movements is preserved in the absence of visual feedback.

This study examined the influence of trunk recruitment on the kinematic characteristics of pointing movements. The distribution of final positions of the hand, the extent and direction of the hand trajectory was basically preserved when trunk movement was combined with arm pointing. These effects were observed during pointing not only with but also without vision. The results imply that two functionally independent units of coordination are used in pointing regardless of visual feedback-one producing arm movement to the target (the reaching synergy) and the other coordinating trunk and arm movements diminishing the influence of the trunk on the arm endpoint trajectory (the compensatory synergy).

Adaptation, Physiological↗
PubMed1998

Changes in the force-sharing pattern induced by modifications of visual feedback during force production by a set of fingers.

We investigated force-sharing among three fingers which acted in parallel and produced ramp profiles of total force from zero to the maximal voluntary force. The feedback to the subject was provided by a visual signal on the monitor and could correspond to the sum of forces of all the fingers or to the sum of forces of two fingers, while the force of the third finger was added with a coefficient 2 or 0.5. If the subjects did not know about the distorted feedback, they showed a template-sharing pattern within the whole range of total force values. This pattern did not depend on which finger force was multiplied and by which coefficient. If the subjects knew in advance how the feedback signal would be calculated, they tried to perform the task using either only the finger whose force was multiplied by 2 or two fingers when the force of the third one was multiplied by 0.5. Further into the trial, however, they were unable to track the ramp pattern using only one or two fingers and demonstrated a search activity that could continue until the end of the trial or lead eventually to a three-finger sharing pattern similar to the template pattern used in cases of undistorted feedback. We conclude that the limited number of preferred sharing pattern within the studied task reflects an organization of the fingers into a structural unit (involving one, two, or all three fingers) by the central nervous system. The availability of structural units defines the presence of stable solutions available for the system.

Adult↗
PubMed1997

Increased Sensitivity to Changes in Visual Feedback With Practice.

In recent work investigating motor learning, the focus has been on the effect of modifying feedback at different levels of learning. Results suggest that learning is specific to the practiced conditions and that this specificity increases with practice. In a replication and extension of this previous work, 3 groups (N = 30 subjects) practiced a sequential positioning movement: Controls performed 300 trials with visually presented on-line kinematic feedback, whereas the other 2 groups, low practice (LP) or high practice (HP), performed, respectively, 50 or 300 trials without feedback. Pretest and posttest sessions of 10 trials each were performed with the on-line feedback. All groups improved with practice. It was apparent that the HP group exhibited more of a performance decrement in the posttest than the LP group did, suggesting that motor learning is the process of forming an increasingly specific sensorimotor representation. These results have implications for motor learning paradigms, models of motor learning, and training.

humans↗
PubMed1993

Effects of noise on a delayed visual feedback system.

Experimentally it is known that some patients with Parkinson's disease are not able to use visual information in a normal manner in a simple motor tracking task involving a time delay. We considered the possibility that pathological tremor present in these individuals acts as noise and prevents them from performing normally. To test this hypothesis the effects of adding coloured noise was investigated experimentally and theoretically. Ten adult subjects with no known neurological disease were asked to track their own delayed finger position with different levels of coloured noise and delays introduced. Also, a model for the task utilizing first-order delay-differential equations was constructed and coloured noise was injected into simulations. The theoretical implications of the inclusion of a stochastic component are considered, and the prospect of the dynamics being driven by noise is discussed. Experimental and numerical results indicate that augmented noise tends to corrupt and curtail the oscillations normally induced by time delays. This augmented noise may explain why some patients with Parkinson's disease are not able to utilize visual information in a normal manner.

Adult↗
PubMed2000

The effect of practice on component submovements is dependent on the availability of visual feedback.

Participants (N = 16) were given extensive practice (1,500 trials) on a perceptual-motor aiming task. The full-vision (FV) group practiced with vision of their response cursor, whereas the no-vision (NV) group practiced in a condition without vision. Movements were made as quickly and accurately as possible, and knowledge of results (KR) was provided. The authors tested the importance of vision early and late in practice by transferring participants to the NV condition without KR. The effects of practice differed between the two conditions. The FV group increased the speed of initial impulse to get to the target quickly, then relied on vision to make discrete error corrections. Transfer tests revealed that reliance on vision remained after extensive practice. For the NV group, practice effects were associated with a reduction in the extent to which discrete error corrections were produced.

Feedback↗
PubMed2003

Adaptation to rotated visual feedback: a re-examination of motor interference.

We have tested human visuo-motor adaptation in rotated-feedback tasks in which subjects first learn to move a cursor to visual targets with a rotational perturbation between joystick and cursor, and are then challenged with the opposing rotation. We then retest the subjects in the original adaptation task, to measure retention of a short-term memory of its earlier learning. Others have used similar tasks and report retrograde interference between one task and the short-term motor memory of the preceding task, such that later performance is impaired. However, we show that in the short-term conditions tested here, these effects can be considered as anterograde interference effects between the two tasks and we find no evidence of retrograde interference.

Adaptation, Physiological↗