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This project aims at understanding better the role of the frontal lobe of the brain in our capacity to perceive visual information consciously, and also, in our capacity to perceive others' actions. It includes a test where we ask subjects to detect visual information in front of a computer screen, and another test where we ask them to imitate finger movements.

This project is a twofold exploration of the functions of the premotor cortex, concerning, on the one hand, its role in conscious visual perception, and on the other hand, the part it may play in the perception and imitation of other people's movements. Healthy subjects will be compared with subjects suffering from focal lesions within the premotor cortex, on two tasks: in the first task, the subjects will have to make a decision concerning the absence or presence of a visual item in their field of vision. They will make (virtual) bets based on the subjective certainty of their perceptions - they will be told that these bets are purely virtual, and will not result in any financial gain or loss. This study will help us understand the contribution of the prefrontal cortex to subjective weighing of perceptual certainty. In the second task, the subjects will imitate a finger movement, based either on a fixed picture, or on a short motion picture. Previous studies have shown that whether the movement is copied from a fixed picture or a moving picture changes reaction times and types of mistakes. Neuroimaging studies have shown that a premotor area is involved in this effect. The comparison of brain-damaged and healthy subjects will tell us what exactly the contribution of the prefrontal consists in.

Inclusion Criteria:

• Healthy subjects chosen from a pool of adult subjects, recruited through ads.
• In the second group, the subjects are recruited from a pool of brain-damaged patients treated at the hospital de la Pitié-Salpétrière. They must suffer from a focal lesion in the prefrontal cortex.

Exclusion Criteria:

• For the healthy group: any previous brain-related medical history.
• Widespread brain-damage, extending beyond the prefrontal cortex, that is to say, lesions that are not really focal.

The visual pereption of subjects willl be studied, but no attempt will be made at modifying it, or treating any problem that they might have.