Deja vu means feeling of familiarity (already seen). This term is used when a person, upon perceiving something that he has never seen before, has the distinct feeling that he had had the experience sometime in the past. It is not uncommon among psychiatric patients, particularly those with hysteria and epilepsy. A patient , for example, while visiting a town for the first time in his life may feel certain that he has been there on some previous occation.
Jamais vu is a paramnestic phenomenon consisting of the erroneous feeling or conviction that one has never experienced or seen anything like that before. Such a denial produces a fragmentation or break in continuity of memory.