Claude Prablanc

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The exact role of posterior parietal cortex (PPC) in visually directed reaching is unknown. We propose that, by building an internal representation of instantaneous hand location, PPC computes a dynamic motor error used by motor centers to correct the ongoing trajectory. With unseen right hands, five subjects pointed to visual targets that either remained(More)
1. The aim of this study was to demonstrate that goal-directed pointing movements, executed at normal speed to a small visual target, but without vision of the movement, do not rely on preprogrammed commands (open-loop process); by contrast these responses are under the control of a feedback loop, which compares the ongoing response and the goal (or its(More)
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(More)
The spatial and temporal organization of hand and eye movements were studied in normal human subjects as they pointed toward small visual targets. The experiment was designed to assess the role of information about target position in correcting the trajectory of the hand when view of the hand was not available. To accomplish this, the duration of target(More)
The performance of subjects walking blindly to previously inspected visual targets (located at 5, 10 or 15 m from the subjects) was studied in 2 experiments. In Expt. 1, subjects selected as good visual imagers were instructed to build up a mental representation of the target. Then they had to either actually walk or imagine themselves walking to the(More)
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(More)
It is long known that the posterior parietal cortex (PPC) is critically involved in goal-directed movements. Nevertheless, there are still some controversies about its specific functions. Although most published studies have emphasised the role of PPC in sensorimotor planning processes, it has been recently suggested that PPC can also participate to on-line(More)
1. Subjects were asked to point toward visual targets without visual reafference from the moving hand in two conditions. In both conditions the pointing fingertip was viewed only before movement onset. 2. In one condition, the pointing fingertip was viewed through prisms that created a visual displacement without altering the view of the target. In another(More)
Reaching movements performed without vision of the moving limb are continuously monitored, during their execution, by feedback loops (designated nonvisual). In this study, we investigated the functional anatomy of these nonvisual loops using positron emission tomography (PET). Seven subjects had to "look at" (eye) or "look and point to" (eye-arm) visual(More)
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(More)