Visuomotor control of leaping over a raised obstacle is sensitive to small baseline displacements

Katherine A. J. Daniels; J. F. Burn

doi:10.1098/rsos.201877

Visuomotor control of leaping over a raised obstacle is sensitive to small baseline displacements

Royal Society Open Science ◽

10.1098/rsos.201877 ◽

2021 ◽

Vol 8 (3) ◽

Author(s):

Katherine A. J. Daniels ◽

J. F. Burn

Keyword(s):

Continuous Mapping ◽

Ground Level ◽

Visuomotor Control ◽

Visual Sensing ◽

Mechanical Constraints ◽

Increase Risk ◽

Limb Kinematics ◽

Small Baseline ◽

Human Participants ◽

Obstacle Geometry

The limb kinematics used for stepping or leaping over an obstacle are determined primarily by visual sensing of obstacle position and geometry. In this study, we demonstrate that changes are induced in limb kinematics even when obstacle geometry is manipulated in a way that does not introduce a mechanical requirement for a change of limb trajectory nor increase risk of collision. Human participants performed a running leap over a single raised obstacle bar. Kinematic changes were measured when an identical second bar was introduced at a ground level underneath the obstacle and displaced by a functionally insignificant distance along the axis of travel. The presence or absence of a baseline directly beneath the highest extremity had no significant effect on limb kinematics. However, displacing the baseline horizontally induced a horizontal translation of limb trajectory in the direction of the displacement. These results show that systematic changes to limb trajectories can occur in the absence of a change in sensed mechanical constraints or optimization. The nature of visuomotor control of human leaping may involve a continuous mapping of sensory input to kinematic output rather than one responsive only to information perceived to be mechanically relevant.

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Forward Models in Visuomotor Control

Journal of Neurophysiology ◽

10.1152/jn.2002.88.2.942 ◽

2002 ◽

Vol 88 (2) ◽

pp. 942-953 ◽

Cited By ~ 180

Author(s):

Biren Mehta ◽

Stefan Schaal

Keyword(s):

Visual Information ◽

Motor Behavior ◽

Visuomotor Control ◽

Behavioral Experiments ◽

Forward Models ◽

Model Based ◽

Inverse Models ◽

Control Schemes ◽

The Central Nervous System ◽

Human Participants

In recent years, an increasing number of research projects investigated whether the central nervous system employs internal models in motor control. While inverse models in the control loop can be identified more readily in both motor behavior and the firing of single neurons, providing direct evidence for the existence of forward models is more complicated. In this paper, we will discuss such an identification of forward models in the context of the visuomotor control of an unstable dynamic system, the balancing of a pole on a finger. Pole balancing imposes stringent constraints on the biological controller, as it needs to cope with the large delays of visual information processing while keeping the pole at an unstable equilibrium. We hypothesize various model-based and non-model-based control schemes of how visuomotor control can be accomplished in this task, including Smith Predictors, predictors with Kalman filters, tapped-delay line control, and delay-uncompensated control. Behavioral experiments with human participants allow exclusion of most of the hypothesized control schemes. In the end, our data support the existence of a forward model in the sensory preprocessing loop of control. As an important part of our research, we will provide a discussion of when and how forward models can be identified and also the possible pitfalls in the search for forward models in control.

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Effects of Vibration on the Preparation of Ultrathin Sections

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s042482010007223x ◽

1973 ◽

Vol 31 ◽

pp. 358-359

Author(s):

Joseph M. Blum ◽

Edward P. Gargiulo ◽

J. R. Sawers

Keyword(s):

Cutting Speed ◽

Ground Level ◽

Environmental Vibration ◽

Block Face ◽

Ultrathin Sections ◽

Embedding Medium ◽

Thickness Variations ◽

Building Walls ◽

Cutting Direction ◽

Diamond Knife

It is now well-known that chatter (Figure 1) is caused by vibration between the microtome arm and the diamond knife. It is usually observed as a cyclical variation in “optical” density of an electron micrograph due to sample thickness variations perpendicular to the cutting direction. This vibration might be induced by using too large a block face, too large a clearance angle, excessive cutting speed, non-uniform embedding medium or microtome vibration. Another prominent cause is environmental vibration caused by inadequate building construction. Microtomes should be installed on firm, solid floors. The best floors are thick, ground-level concrete pads poured over a sand bed and isolated from the building walls. Even when these precautions are followed, we recommend an additional isolation pad placed on the top of a sturdy table.

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