Effect of the Visual Information Change in Functional Dystonia

Inclusion Criteria: Case * Presenting a cervical dystonia that occurs only during handwriting tasks, diagnosed by a neurologist specialised in movement disorders * Being treated or not by injection of Botulinum Neurotoxin (but last injection \> 3 months before the initial assessment) Control * No cervical dystonia * Same sex, age (± 5 years), socio-professional level and hand laterality as the cases Exclusion Criteria: Case * Cervical dystonia occuring in other circumstances than handwriting * Neurological disease other than cervical dystonia (e.g. Parkinson's syndrome) * Pain, trauma or pathology of the cervical spine of another cause than cervical dystonia and which have required medical or surgical treatment in the last 6 months preceding the initial assessment Control * Cervical disorders requiring medical or surgical treatment in the last 6 months prior to the tests * Neurological disease affecting the cervical region or the writing hand * Uncorrected visual disorders