Déjà Vu

I think we have all experienced Déjà Vu at least once. "Have I seen this before?" "Did the cat just walk by twice?" "Is there a glitch in the Matrix?" The science of Déjà Vu can be boiled down to some basic principles of sensation and perception. Although the exact cause of Déjà Vu is unknown, scientists have come up with three main theories about the likely cause of this phenomenon. Here is a lovely TED-Ed video to introduce the topic:

This week in class, we learned a lot about sensation and perception of sight. Sight is the main sense in which Déjà Vu is found because sensations for the other four main senses can be replicated. You can taste, touch, hear, and smell something more than once. Why is sight different? In life, people are never in the exact same place at the exact moment in time after that one moment. Additionally, the eyes have ways of improperly processing the information they receive.

Here are the basics of sensation of sight. Light waves enter the cornea (protective film over the eye), travel past the iris (muscle that controls the amount of light allowed into the eye) and into the pupil (black hole that leads directly to the inner eye). From there, the light goes to the lens. The lens then projects the light onto the retina, which turns the light waves into neural messages. The neural messages are processed in the rods and cones, which process color and black and white respectively. The messages then go through the horizontal, bipolar, and amacrine cells to the ganglion cells to the optic nerve to the thalamus and FINALLY to the visual cortex for perception. As others have already said, there are many many many steps occurring just so that we can see.

Another interesting point of note is that the first theory presented in the video has to do with dual processing. When so many messages are being sent throughout the brain at once, it is easy for one processing mechanism to run slower than others, causing you to feel like you have seen the thing you are seeing right now before. When the brain works properly, no one notices. People go through their entire lives without ever knowing that is actually happening in the brain. When something goes wrong with the brain, it causes curiosity. Since Déjà Vu is such a fleeting and sporadic experience, scientists can't actually pinpoint what causes it or how they can reproduce the sensation in the same way that the brain produces it.

Curiosity is an important part of science. By the time we are working adults, scientists may be closer to finding the causes of Déjà Vu. For now, it is all speculation. At the same time, I find it wonderful and fascinating that there are still things that people don't understand.