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Biomedical subjects

C Prablanc

Publications and source records attributed to C Prablanc.

52 records · Page 3Linked to original sources
PubMed1984

The contribution of coordinated eye and head movements in hand pointing accuracy.

The accuracy of pointing movements of the hand, directed at visual targets 10 degrees to 40 degrees from the midline, was measured in normal human subjects. No visual feedback from the moving hand was available to the subjects. The head could be either maintained stationary (head-fixed condition) or free to move (head-free condition) during the pointing movements. It was found that the error in pointing was reduced for all targets in the head-free condition. This reduction was more important for the more eccentric target (40 degrees). Improvement in accuracy was observed without any significant change in either the latency or the duration of eye, head or hand movements. In the head-free condition, it was found that the head was displaced in the direction of the target by an amount representing no more than 2/3 of the target amplitude. The improvement in accuracy was not influenced by the amplitude of the head movement. A model is proposed which shows how coordinated eye and head movements could improve the encoding of target position.

Adaptation, Physiological↗
PubMed1984

The control of hand movements in a case of hemianaesthesia following a parietal lesion.

A 46-year-old patient with a lesion limited to the left retrorolandic area without involvement of the prerolandic motor strip was examined. Anaesthesia to tactile, warm, cold, and painful stimuli was complete for the right hand and wrist. Position sense was abolished for the right wrist and finger joints. Performance of the right hand in motor tasks was severely impaired. Simple visual and auditory reaction times were lengthened. Sustaining a constant level of force was impossible. In the absence of visual feedback, only simple, monoarticular movements could be correctly executed; more complex movements requiring coordination between several joints, such as prehension, were poorly, or not, performed. The role of somatosensory cortex in conveying kinaesthetic input to the motor areas and the importance of vision in substituting for kinaesthetic loss, are discussed.

Brain Neoplasms↗
PubMed1982

The coordination of eye, head, and arm movements during reaching at a single visual target.

The time of occurrence of eye, head, and arm movements directed at the same visual target was measured in five human subjects. The latency of activation of the corresponding neck and arm muscles was also measured. It appears that although the overt movements are sequentially ordered (starting with the eye movement, then the head and finally the arm) the EMG discharges are synchronous with respect to the eye movement onset. In addition, eye movement latency appears definitely (though weakly) correlated with either neck or arm EMG latencies. Neck and arm EMG latencies are also mutually correlated. These results indicate a clustering of segmental motor programs for target oriented actions.

Adult↗
PubMed1982

Saccadic responses evoked by presentation of visual and auditory targets.

Saccadic eye movements evoked by the presentation of visual and auditory targets were examined and compared. Differences were found either in the pattern of the saccadic response and in the characteristics of single saccades of the same amplitude. The longer latency and the higher percentage of multiple saccade responses in the auditory case were attributed to a more complex central processing, whereas the longer duration and the lower peak velocity of the saccades to auditory targets were attributed to reduced performances of the execution mechanism in the absence of vision.

Acoustic Stimulation↗
PubMed1981

An attempt at correlating visuomotor-induced tilt aftereffect and ocular cyclotorsion.

Subjects were exposed to an optical rotation of visual reafferences from hand movements. This is known to produce visuomotor adaptation. An experiment is reported where it also induced a perceptual aftereffect measured as a displacement of the apparent vertical and as an ocular cyclotorsion, both in the direction of the optical rotation. No correlation could be found between the two phenomena which can be considered as independent adaptive responses to the visuomotor conflict.

Adaptation, Ocular↗
PubMed1979

Optimal response of eye and hand motor systems in pointing at a visual target. I. Spatio-temporal characteristics of eye and hand movements and their relationships when varying the amount of visual information.

In a task requiring an optimal hand pointing (with regards to both time and accuracy) at a peripheral target, there is first a saccade of the eye within 250 ms, followed 100 ms later by the hand movement. However the latency of the hand movement is poorly correlated with that of the eye movement. When the peripheral target is cut off at the onset of the saccade, there is no correlation between the error of the gaze position and the error of the hand pointing. This suggests an early parallel processing of the two motor outputs. The duration of hand movement does not change significantly when subjects either see or not see their hand (closed or open loop). In the open loop situation, the undershoot of the hand pointing increases with target eccentricity, whatever the subjects are allowed or not to do a saccade toward the target. It suggests that the encoding of eye position by itself is a poor index for an accurately guided movement of the hand.

Adult↗
PubMed1979

Optimal response of eye and hand motor systems in pointing at a visual target. II. Static and dynamic visual cues in the control of hand movement.

The closed loop situation of hand pointing at a target has been experimentally divided into its static and dynamic components. When the subjects see their hand at first (closed loop) until the start of the hand movement cuts off the vision of the hand (open loop), the pointing is significantly more accurate than when it is performed without any vision of the hand before and throughout the movement (fully open loop). This suggests that initial cues as regards hand and target position, improve the motor program by a better identification of initial and final states. As poor as it is, the extra retinal signal (encoding of eye position) improves performance when the foveation is done under closed loop; it allows a better redefinition of target position, and thus modulates the hand motor program through a direct central pathway, which is quicker than the processing of the visual feedback of the hand movement error.

Eye Movements↗
PubMed1977

Spatial localization with paralyzed eye muscles.

Four subjects suffering from a unilateral peripheral paralysis of the 3rd or the 6th nerves have been studied in spatial localization tasks, with their normal eye occluded. When peripheral targets were presented in the hemifield corresponding to the paralysis, the saccadic eye movements (recorded from the normal occluded eye) were of an exaggerated amplitude. 'Staircase' oculomotor patterns, closely similar to those occurring in 'open-loop' visual stimulation, could also be observed. Our patients also presented the classical hypermetric misreaching when attempting to point by hand at visual targets in an otherwise dark room. This effect (past-pointing) was likely to be due to a monitoring of the exaggerated oculomotor signal: in one subject past-pointing disappeared when reaching at the targets on the basis of the sole retinal cues. Finally, the classically described illusory visual effects of ocular paralysis were limited to a feeling of instability during self-motion.

Abducens Nerve↗
PubMedDate not supplied

Large adjustments in visually guided reaching do not depend on vision of the hand or perception of target displacement.

When we reach towards an object that suddenly appears in our peripheral visual field, not only does our arm extend towards the object, but our eyes, head and body also move in such a way that the image of the object falls on the fovea. Popular models of how reaching movements are programmed have argued that while the first part of the limb movement is ballistic, subsequent corrections to the trajectory are made on the basis of dynamic feedback about the relative positions of the hand and the target provided by central vision. These models have assumed that the adjustments are dependent on seeing the hand moving with respect to the target. Here we present evidence that a change in the position of a visual target during a reaching movement can modify the trajectory even when vision of the hand is prevented. Moreover, these dynamic corrections to the trajectory of the moving limb occur without the subject perceiving the change in target location. These findings demonstrate that visual feedback about the relative position of the hand and target is not necessary for visually driven corrections in reaching to occur, and the mechanisms that maintain the apparent stability of a target in space are dissociable from those that mediate the visuomotor output directed at that target.

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