Understanding How Our Brain Sees When you open your eyes or encounter something new, your brain quickly creates a picture of what you are seeing. In about 100 milliseconds (ms), your brain has already formed a basic image of your surroundings. This image isn't complete, but it gives you a clear outline of what is there. Here is what actually happened in that brief moment: 0-10 ms: Light hits the retina. At the back of the eye is the retina, which contains photoreceptors. Pho