Déjà Vu, Again and Again

Déjà Vu, Again and Again - New York Times: "Memory, like most systems we depend on continually, tends to fade into the background when it's working properly. Only when it fails or misleads us do we begin to ponder its mechanisms. The structure of memory has for centuries been one of psychology's most intractable mysteries. To the extent that science claimed to understand it at all, memory was seen as a kind of filing cabinet in which recollections were neatly stored, retrieved on demand and occasionally misplaced.

The research of the last three decades, however, has shattered that metaphor. The Canadian cognitive psychologist Endel Tulving struck a significant blow in the 1970's, when he postulated a distinction between episodic memories — our recollections about our own experiences — and semantic ones, involving facts and concepts. Knowing the capital of France is a semantic memory, for example; recalling your trip to Paris, an episodic one. When we access episodic memories, Tulving further observed, we don't just call up raw information. We actually re-experience the events themselves, and that feeling of recollection is part of what tells us that the memory is real. "Remembering," Tulving summarized in 1983, "is mental time travel, a sort of reliving of something that happened in the past."