New research is shedding light onto déjà vu, a phenomena in which people believe they have previously experienced a situation. Roughly 2/3 of the population perceives a déjà vu in their lifetime. Studies show that these occurrences are more likely to occur with age, education, and wealth; especially amongst the population that remembers dreams, travels, are liberal and religious (paywall).

Scientists have narrowed déjà vu almost exclusively to cases involving sight. It is now believed that déjà vu is the result of 'processing lag' in the brain. Experiments show the brain must process separate sensory events (binocular vision) within 25 milliseconds to perceive them as the same. A fault in the processing of one optical signal may result in the same image, albeit a parallax shifted image, being processed twice which leads the brain to conclude a prior experience took place. The problem may lie with the passage of the sensory signals along the optic nerves or even within the visual cortex.