One phrase that I often hear during my ghost tours, as well from fellow paranormal investigators; “I saw it out of the corner of my eye, and when I turned to look, it disappeared.” There is a reason for this, and it’s due to an evolutionary throwback in humans. It stems from when humans were more prey than predator. In a very simplistic explanation, our eyes are constructed with two different types of receptor cells, rods, and cones. Cones cells are concentrated in the center of the retina where most of the light that enters the eye is focused. Cone cells allow us to see color and are responsible for spatial acuity. Cones cells work best in bright light and are responsible for your forward vision. Rod cells are concentrated more on the edge of the retina. They are more sensitive to movement and work best in dim light. Rod cells are responsible for your peripheral vision.
Most ghost tours and paranormal investigations are conducted in the dark or in dim light, which are the ideal conditions for rod cells to function. When you see movement out of the corner of your eye, your natural instinct is to look towards it. Turning your head simply transfers sight of the object from your rod cells best suited for dim light, to your cone cells best suited for bright light. Your cone cells can’t focus in the dim light, therefore causing you to lose sight of the object.
Going against our natural instincts is hard. It is even harder when you’re scared. When something is detected in your peripheral vision, we are hardwired to look towards it. Humans do have a natural night vision, but it takes about thirty minutes for our eyes to adjust. This is almost impossible when your fellow investigators are turning on their flashlights and using their camera flash to take pictures. Every burst of light resets our natural night vision.
So take this into account when you see something out of the corner of your eye. You may very well be having a paranormal experience, but an evolutionary throwback in your vision may be preventing you from seeing it.