Dual Task Training in Parkinson's Disease

20 patients diagnosed with Parkinson's disease will be randomly assigned to either intervention or control group. And 10 healty subjects will be included to study in order to determine the reference values.The intervention group will be recieved cognitive and motor dual task training consisting of balance and walking activities 3 days a week for 8 weeks. Control group will be recieved same balance and walking activities in single task condition 3 days a week for 8 weeks. In order to evaluate the effects of the training, evaluations will be performed before and after the training period.