3. EEG testing procedure: A 64 channel ActiveTwo Biosemi EEG system (Biosemi Instrumentations, Amsterdam, Netherlands) will be used to record task-related evoked potentials over the entire scalp. Sampling rate at 1024 Hz. ActiveTwo Biosemi EEG system allows calibration changes which are not required for clinical treatment and is used for research purposes only. The ActiveTwo Biosemi EEG system is not used for outpatient or inpatient clinical use in Israel. In this study we will use the ActiveTwo Biosemi EEG system from the Weizmann institute at Sheba medical center. Subjects will be seated comfortably in a chair and the Biosemi cap put on their head. The 64-scalp electrodes are positioned according to the international 10-20 system. To place the cap, we will measure the distance between the nasion and inion and the distance between the two ears and situated the cap so that electrode Cz was exactly half way between the two ears and between nasion (intersection of the frontal bone and two nasal bones) and inion (external occipital protuberance).