BY Dawn Foster on 03/12/2009

I noticed on Paranormal Shows that some investigators seem to "see a face" or "see a shape" more often than any of the other investigators. I knew there must be a reason for this other than they are faking or than they are a sensitive. I don't believe either of those things apply to many of them. Then I got to thinking there must be something that goes on in the eye that can cause the impression of "seeing" something. The reason I thought about this is because I get what is called optical migraines. Whether the migraine manifests in pain or not I get the blind spot or aura. It starts as a little tiny dot blocked out of my field of vision in both eyes sort of like when you have a flash go off in your face. Then the blind spot gets gradually bigger and bigger until it is quite large in my field of vision. It becomes crescent shaped and then within the crescent shape, a sparkling zigzag (like the AZ Diamond Backs Logo) begins to develop. And lastly it gradually moves across my field of vision to the side of my visual area. If I weren't familiar with this phenomenon I might think it was actually something floating about.

So I checked with my optometrist and, sure enough, I was right. The technical term for catching glimpses of "something" that isn't there is

Afterimage. And when we understand what this actually is we're all gonna go, "OH, well, DUH!" My optometrist explained to me that you can get a light in one eye and because of the imprinting on the optical nerve you can actually experience the afterimage in the other eye. He also said if pressure is applied to the side of your eye you can make yourself see lights in your field of vision. Crazy, huh?

When investigating partners are in the midst of an investigation they have equipment with them. Cameras with LCD screens, meters with screens & dials, Thermal cameras with lighted screens, small UV flashlights, etc. The partners are walking around looking into the darkness, looking down at the lighted screens on their equipment. And we have to admit they look at the screens for more than a few seconds. Or they look into the partner's face with the dim flashlight. Then they look back into the darkness. So, the investigator's eyes, being more sensitive (theory) gets a quicker and brighter afterimage than their partner and it appears to them that they are actually seeing, for a split second, an apparition.

Additionally this same type of think can cause the illusion of a darting figure or a figure from the corner of the eye. (See Motion Aftereffect, below)

So now I'm going to get all technical on you and show you what Wikipedia (don't groan) says about this.

Afterimage

From Wikipedia, the free encyclopedia

An afterimage or ghost image is an optical illusion that refers to an image continuing to appear in one's vision after the exposure to the original image has ceased. One of the most common afterimages is the bright glow that seems to float before one's eyes after staring at a light bulb or a headlight for a few seconds. The phenomenon of afterimages may be closely related to persistence of vision, which allows a rapid series of pictures to portray motion, which is the basis of animation and cinema.

If the viewer stares at this image for 20-60 seconds and stares at a white object a negative afterimage will appear (in this case being blue on maroon). This can also be achieved by the viewer closing his/her eyes and tilting their head up.

Afterimages come in two forms, negative (inverted) and positive (retaining original color). The process behind positive afterimages is unknown, though thought to be related to neural adaptation. On the other hand, negative afterimages are a retinal phenomenon and are well understood.

Negative afterimages

Negative afterimages are caused when the eye's photoreceptors, primarily those known as cone cells, adapt from the over stimulation and lose sensitivity.^[1] Normally the eye deals with this problem by rapidly moving the eye small amounts (see: microsaccade), the motion later being "filtered out" so it is not noticeable. However if the colour image is large enough that the small movements are not enough to change the color under one area of the retina, those cones will eventually tire or adapt and stop responding. The rod cells can also be affected by this.

When the eyes are then diverted to a blank space, the adapted photoreceptors send out a weak signal and those colors remain muted. However, the surrounding cones that were not being excited by that colour are still "fresh", and send out a strong signal. The signal is exactly the same as if looking at the opposite color, which is how the brain interprets it.

Ewald Hering explained how the brain sees afterimages, in terms of three pairs of primary colors. This opponent process theory states that the human visual system interprets color information by processing signals from cones and rods in an antagonistic manner. The opponent color theory suggests that there are three opponent channels: red versus green, blue versus yellow, and black versus white. Responses to one colour of an opponent channel are antagonistic to those to the other colour. Therefore, a green image will produce a red afterimage. The green color tires out the green photoreceptors, so they produce a weaker signal. Anything resulting in less green, is interpreted as its paired primary colour, which is purple.

Example movie which produces distortion illusion after one watches it and looks away. See Motion aftereffect.

This next part applies to those who are especially sensitive to this type of optical condition;

Medical conditions

In a visual disturbance called palinopsia, patients have an increased propensity for seeing afterimages, having both a reduced amount of time required to form an afterimage, and an increased duration of the afterimage. Positive afterimages are particularly noticeable, such that even routine eye movement is often accompanied by flickers of what the eye has scanned over (called "tracers"). However, increased negative afterimages are also experienced by palinopsia sufferers. It is unknown if the negative afterimages encountered in palinopsia are formed by the same process described above, although what little research that exists regarding the phenomena suggests that it is brain-related, and not eye-related. Palinopsia can be a persistent condition, but it is also experienced periodically by migraine sufferers.