An object-centred reference frame for control of grasping: effects of grasping a distractor object on visuomotor control.

Previous evidence based on perceptual integration and arbitrary responses suggests extensive cross-modal links in attention across the various modalities. Attention typically shifts to a common location across the modalities, despite the vast differences in their initial coding of space. An issue that remains unclear is whether or not these effects of multisensory coding occur during more natural tasks, such as grasping and manipulating three-dimensional objects.

A cross-modal interference effect in grasping objects.

The aim of the present paper was to investigate how the kinematics of a hand reaching toward a visual target would be influenced by haptic and proprioceptive input from an unseen distractor actively grasped in the other, nonreaching hand. The main results were that the amplitude of maximum grip aperture was smaller and the time to maximum grip aperture was earlier when the distractor was smaller than the target. The interference effect from the distractor was similar for both hands as they reached.

Effect of asymmetrical limb loading on early postural adjustments associated with gait initiation in young healthy adults.

The aim of this work was to show how postural adjustments are modified in healthy subjects when gait initiation is made more difficult by an increase of the supported body weight under the starting limb. We show that the impulse due to the push of the foot against the ground is enhanced by an increase of the amplitude and duration of the initial vertical force variation. The corresponding lateral excursion of the global center of pressure (CPg) is determined mainly by this force variation, but also by lateral displacements of the centers of pressure under each foot.

Early postural adjustments associated with gait initiation and age-related walking difficulties.

To better understand the functional role of early postural adjustments associated with gait initiation, we studied ground reaction forces before the first step in a group of 10 young and 18 elderly normal subjects as well as in a group of 11 patients with marche à petits pas, an age-related gait disorder in which difficulties in executing the first step are encountered. Kinematic data and ground reaction forces were recorded synchronously and processed by an ELITE motion analysis system. Start difficulties in the patients might be explained by impaired amplitudes and directions of anteroposterior forces as well as smaller values of vertical forces than in the controls walking with comparable step lengths.