Under normal conditions, the tape recorder's record (encoding) or play (retrieval) functions may all be enabled. In 1979, De Nayer used a tape recorder as a metaphor for the déjà vu experience, likening the record and play buttons to the encoding and retrieving cognitive functions, respectively. However, if they were both activated at the same time – new information being encoded while old information was retrieved – the resultant impression may be that the new experience/information was being retrieved directly from memory. They maintain a strict synchronized relationship in which they are aware of each other's activation but are unable to activate simultaneously. Two dual processing theories will be presented below, one based on familiarity and retrieving and the other on encoding and retrieving.Įncoding and retrieval are both distinct cognitive processes that operate independently of one another, as input and output. encoding and retrieving, are combined together. familiarity and memory, or the opposite, when two similar but different functions, e.g. It could manifest as a random activation of one function in the absence of another, when they should be activated in tandem, e.g.

As a result of the interruption of normal cognitive operations, déjà vu occurs. The fundamental concept behind dual-processing theories is that déjà vu is caused by two otherwise parallel and synchronized cognitive processes being out of sync for a brief moment. While some theories consider functions and processes to fall into more than one of these categories and are therefore difficult to categorize, this division is made to highlight the shared characteristics of the theories and link them for a better overview.

Based on the functions and processes in question, the theories are grouped into four categories: dual-processing theories, neural theories, memory theories, and attentional theories. The following is a condensed list of hypotheses on déjà vu that have been found in scientific literature. Dual-processing, psychological, memory, and attentional theories make up the majority of scientific theories. Several hundreds of parapsychological, pseudoscientific, and scientific hypotheses have been suggested to explain the déjà vu phenomenon since the mid-nineteenth century, ranging from 'messages from God' to 'delayed neural transmission speed'. The word 'déjà vu' was coined in the 1890s to distinguish the syndrome from other paramnesias, but it was not until the mid-twentieth century that a strong agreement on its meaning was achieved.

The deja vu theory