The most common type of déjà vu experienced by normal, healthy people is associative in nature. Taking a very broad look at the research and resources available, we can put déjà vu experiences into two categories and then see the more subtle distinctions that researchers have placed on it: Associative déjà vu and Biological déjà vu. Vernon Neppe, Director of the Pacific Neuropsychiatric Institute in Seattle, proposed four subcategories of déjà vu, including epileptic, subjective paranormal, schizophrenic and associative. He believes there is déjà vu caused by biological dysfunction (e.g., epilepsy), implicit familiarity and divided perception. Alan Brown, a professor of psychology at South Methodist University and author of “The Déjà Vu Experience: Essays in Cognitive Psychology,” has three categories for déjà vu. Those who have studied it have applied their own categories and differentiations - each usually tied to a specific theory about what causes déjà vu. Defining types of déjà vu is a very slippery area. Unlike true déjà vu, which typically lasts from 10 to 30 seconds, these false memories or hallucinations can last much longer. False memories that are brought on by schizophrenia can be confused with déjà vu as well. Hallucinations that are brought on by illness or drugs sometimes bring a heightened awareness and are confused with déjà vu. See the Déjà Vu and Precognitive Dreams section.) (However, one theory about déjà vu deals with precognitive dreams that give us a “déjà vu feeling” afterwards. Precognitive experiences - if they are real - show things that will happen in the future, not things that you’ve already experienced. An important distinction is that déjà vu is experienced during an event, not before. The most common misuse of the term déjà vu seems to be with precognitive experiences - experiences where someone gets a feeling that they know exactly what’s going to happen next, and it does. Researchers have their own definitions, but generally déjà vu is described as the feeling that you’ve seen or experienced something before when you know you haven’t. There are often references to déjà vu that aren’t true déjà vu. French scientist Emile Boirac, one of the first to study this strange phenomenon, gave the subject its name in 1876. Déjà vu is a French term that literally means “already seen” and has several variations, including déjà vécu, already experienced déjà senti, already thought and déjà visité, already visited. In this article, we’ll explore a few of those theories to shed some light on this little understood phenomenon. There are more than 40 theories as to what déjà vu is and what causes it, and they range from reincarnation to glitches in our memory processes. The sight, sound, taste or even smell of something makes us think that we’ve experienced it before, although we know that we couldn’t have. Sixty to 70 percent of us admit to getting this feeling at least once in our lives. If you’ve ever found yourself in either of these situations, you’ve experienced déjà vu. Have you ever visited a store for the first time and had it feel eerily familiar? Or maybe you’re deep in conversation with a friend and you suddenly get the feeling that you’ve had the exact conversation before, even though you know that you haven’t.