In this project, investigators aim to investigate the effects of action observation therapy on pain, fear of movement, functional level and brain hemodynamics in patients with knee osteoarthritis. The study is unique in that this method, which has already been used for post-surgical or motor healing, aims at long-term administration for the first time with chronic pain and objective visualization of the results. This study will create a new perspective to understand the physiology of pain, which has attracted much interest in the literature in recent years, and will shed light on the studies that can be done in this regard. Participants' joint range of motion in the initial assessments will be measured by electro-goniometer, muscle strength assessment by JTech hand dynamometer at appropriate evaluation positions. In assessing pain, pain levels at rest and during activity will be questioned using Visual Analog Scale. Fear of movement of individuals will be assessed via Tampa Kinesiophobia Scale and functional levels will be assessed via Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) and the Timed Up and Go Test. Functional near infrared spectroscopy (fNIRS) will be used for evaluation of brain hemodynamics. The first group, will receive exercises with action observation therapy; and the second group will receive only exercises. The exercise programme will be administered under physiotherapist supervision for three days a week for six weeks. The evaluations will be repeated at the beginning of the study and at the end of the sixth week. Data obtained from the study will be analyzed using appropriate statistical methods.