In a report, published in Current Directions in Psychological Science, Anne Cleary of Colorado State University says deja vu may occur when aspects of a current situation resemble aspects of previously occurring situations -- the more overlap between the elements of the new and old situations the stronger the feeling of familiarity
"Many parallels between explanations of deja vu and theories of human recognition memory exist," Cleary says in a statement. "Theories of familiarity-based recognition and the laboratory methods used to study it may be especially useful for elucidating the processes underlying deja vu experiences."
In experiments using celebrity names and photographs Cleary found even when the participants were unable to identify a celebrity by photo, they had a sense of which names they had mentioned earlier and which had not. The same thing happened in an experiment using famous places.
Cleary also ran experiments that found features or elements of situations can trigger feelings of familiarity. Simply hearing a word that sounds similar to another -- for example lady and eighty -- or seeing a geometric fragment of a scene seen before can trigger familiarity.