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258 results on '"Jeka, John J."'

3. Using Perturbations to Probe the Neural Control of Rhythmic Movements

Author

Kiemel, Tim, Logan, David, and Jeka, John J.

Subjects
Quantitative Biology - Neurons and Cognition
Abstract

Small continuous sensory and mechanical perturbations have often been used to identify properties of the closed-loop neural control of posture and other systems that are approximately linear time invariant. Here we extend this approach to study the neural control of rhythmic behaviors such as walking. Our method is based on the theory of linear time periodic systems, with modifications to account for ability of perturbations to reset the phase of a rhythmic behavior. We characterize responses to perturbations in the frequency domain using harmonic transfer functions and then convert to the time domain to obtain phase-dependent impulse response functions (IRFs) that describe the response to a small brief perturbation at any phase of the rhythmic behavior. IRFs describing responses of kinematic variables and muscle activations (measured by EMG) to sensory and mechanical perturbations can be used to infer properties of the plant, the mapping from muscle activation to movement, and of neural feedback, the mapping from movement to muscle activation. We illustrate our method by applying it to simulated data from a model and experimental data of subjects walking on a treadmill perturbed by movement of the visual scene.

Published
2016

42. Manipulating symmetry in the coordination dynamics of human movement

Author

Jeka, John J. and Kelso, J.A.S.

Subjects
Symmetry -- Research, Human mechanics -- Research, Neurophysiology -- Research, Motor ability -- Research, Psychology and mental health
Abstract

J. A. S. Kelso and J. J. Jeka (1992) demonstrated that symmetry is a useful conceptual tool to distinguish the coordination between components with similar versus different anatomical properties. The present experiments studied human arm-leg patterns to test whether their coordinative asymmetry was changed by manipulating the inertial properties of a single limb. The results showed that (a) consistent with model predictions, adding weight to the arm or the leg minimized or enhanced coordinative asymmetry, respectively and (b) the response to a perturbation slowed as movement frequency increased but in a fashion that reflected the underlying coordinative asymmetry. The observed coordinative effects suggest the influence of neural phase relationships and emphasize that symmetry plays an important role in understanding coordination in systems in which control cannot be traced unequivocally to a single end-effector or a neurophysiological substrate.

Published
1995

43. Book reviews

Author

Jeka, John J., Kelso, J. A. S., Kapral, Raymond, Troy, William, and Sauer, Tim

Published
1991
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47. Light touch contact as a balance aid

Author

Jeka, John J.

Subjects
Staffs (Sticks, canes, etc.) -- Usage, Gait disorders -- Care and treatment
Abstract

Canes and crutches are commonly used mobility aids, and most studies of their use have focused on issues equating support with the resulting decrease in force required of the affected limb. Clinicians, however, often observe patients with poor balance control using light touch of surrounding objects and surfaces to stabilize themselves while standing and walking. A series of studies have shown that sensory input to the hand and arm through contact cues at the fingertip or through a cane can reduce postural sway in individuals who have no impairments and in patients without a functioning vestibular system, even when contact force levels are inadequate to provide physical support of the body. This article summarizes these results, which have implications for design considerations of rehabilitation aids. Mobility devices or rehabilitation aids that provide feedback about applied force or enhance existing resolution of applied force changes across the skin surface may lead to new rehabilitation techniques. [Jeka JJ. Light touch contact as a balance aid. Phys Ther. 1997;77:476-487.], Key Words: Cane, Fingertip, Mobility aid, Neural plasticity, Posture, Rehabilitation, Somatosensory, Vestibular. Mobility aids such as canes and crutches are commonly used for rehabilitation from musculoskeletal or neuromuscular injuries and [...]

Published
1997

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