Biomedical subjects

Marc H E de Lussanet

Publications and source records attributed to Marc H E de Lussanet.

4 recordsLinked to original sources

PubMed2004

The quantitative use of velocity information in fast interception.

We ask whether a target's velocity is considered when planning a fast interceptive action. Human volunteers hit targets that could move at different velocities from across a tilted screen (the hand starting 40 cm away from the screen). We examined how the direction in which the hand initially moved depended on the target's velocity, using various analyses. For slow targets, the initial movement direction was appropriate for the target's velocity. This is evidence that velocity information was used quantitatively in directing the hand. A model analysis showed though that velocity information is probably not used to predict the future target position. For targets moving at a velocity above average, or above 12 cm/s, the initial movement direction did not depend on the target's velocity. Similar behaviour is also known from pursuit eye movements.

Adult↗

PubMed2002

The relation between task history and movement strategy.

In the present study, we examine whether subjects hit identical moving targets differently when the task history is different. Twelve subjects each took part in four experimental sessions. Each session consisted of recurring targets that were the same in all sessions, randomly interleaved with context targets that differed per session. We compared the movements that subjects made towards the recurring targets. There were clear influences of the preceding target on the hitting movements within a session, and clear differences between movements towards the same targets between sessions, but the latter differences were not consistently related to the kind of sessions involved. This indicates that influences of task history are limited to the use of information from preceding trials rather than to changes in how information is used (movement strategy).

Humans↗

PubMed2002

Relative damping improves linear mass-spring models of goal-directed movements.

A limitation of a simple linear mass-spring model in describing goal directed movements is that it generates rather slow movements when the parameters are kept within a realistic range. Does this imply that the control of fast movements cannot be approximated by a linear system? In servo-control theory, it has been proposed that an optimal controller should control movement velocity in addition to position. Instead of explicitly controlling the velocity, we propose to modify a simple linear mass-spring model. We replaced the damping relative to the environment (absolute damping) with damping with respect to the velocity of the equilibrium point (relative damping). This gives the limb a tendency to move as fast as the equilibrium point. We show that such extremely simple models can generate rapid single-joint movements. The resulting maximal movement velocities were almost equal to those of the equilibrium point, which provides a simple mechanism for the control of movement speed. We further show that peculiar experimental results, such as an 'N-shaped' equilibrium trajectory and the difficulties to measure damping in dynamic conditions, may result from fitting a model with absolute damping where one with relative damping would be more appropriate. Finally, we show that the model with relative damping can be used to model subtle differences between multi-joint interceptions. The model with relative damping fits the data much better than a version of the model with absolute damping.

Attention↗

PubMed2002

Independent control of acceleration and direction of the hand when hitting moving targets.

Human subjects were asked to hit moving targets as quickly as they could. Nevertheless the speed with which the subjects moved toward identical stimuli differed between trials. We examined whether the subjects compensated for a lower initial acceleration by aiming further ahead of the target. We found that the initial acceleration of the hand and its initial direction were hardly correlated. Thus subjects did not aim further ahead when they hit more slowly. This supports our earlier suggestion that the acceleration of the hand and the direction in which it moves are controlled separately.

Acceleration↗