Defining types of déjà vu is a very slippery area. Those who have studied it have applied their own categories and differentiations -- each usually tied to a specific theory about what causes déjà vu. 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. He believes there is déjà vu caused by biological dysfunction (e.g., epilepsy), implicit familiarity and divided perception. In 1983, Dr. Vernon Neppe, Director of the Pacific Neuropsychiatric Institute in Seattle, proposed four subcategories of déjà vu, including epileptic, subjective paranormal, schizophrenic and associative.
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 vuThe most common type of déjà vu experienced by normal, healthy people is associative in nature. You see, hear, smell or otherwise experience something that stirs a feeling that you associate with something you've seen, heard, smelled or experienced before. Many researchers think that this type of déjà vu is a memory-based experience and assume that the memory centers of the brain are responsible for it.
- Biological déjà vu There are also high occurrences of déjà vu among people with temporal lobe epilepsy. Just before having a seizure they often experience a strong feeling of déjà vu. This has given researchers a slightly more reliable way of studying déjà vu, and they've been able to identify the areas of the brain where these types of déjà vu signals originate. However, some researchers say that this type of déjà vu is distinctly different from typical déjà vu. The person experiencing it may truly believe they've been through the exact situation before, rather than getting a feeling that quickly passes.
Next, we'll look at how researchers have studied this phenomenon.