Paranormal Misinterpretations of Vision Phenomena We Can Actually See Things That Aren’T Really There in Front of Our Eyes
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SI Nov. Dec 11_SI new design masters 9/27/11 12:44 PM Page 44 Paranormal Misinterpretations of Vision Phenomena We can actually see things that aren’t really there in front of our eyes. Simple activities can help us to understand the real causes of such phenomena and to reject paranormal interpretations. MICHAEL MAUSER re they auras or afterimages? Vitality globules or white corpuscles? Angels or phosphenes? What we believe often determines what we see and A experience. Some simple activities can help us understand vision phenomena that may be misinterpreted as evidence for the paranormal. Auras In a brief review on the aura, a “glowing the illusion as a series of silhouettes and skin against a dark background pro- field surrounding a human being,” Perez shows how an aura might be perceived. vides high contrast and good condi- In either case, the bands can be revealed tions for after-images. As the eyes and Hines (2011) mention perceptual move slightly but rapidly about (as illusions as among many possible rea- as truly uniform if you cover the borders they always do), an after-image builds sons the belief in auras persists. Dale et with your fingers. The illusion results up around the edge of the hand and al. (1978) suggest two vision phenom- from a process known as lateral inhibi- produces a light blur. ena that may be involved in a perception tion, wherein neurons associated with adjacent photoreceptors on the retina Most people are well acquainted with of an aura: border contrast effects and afterimages, so the only surprise here afterimages. can influence each other to emphasize a border. may be that our eyes are always moving When uniformly shaded fields are without our being aware of it. You can presented adjacent to one another, we With regard to afterimages, I cannot see this jitter by first staring for a minute perceive them as non-uniformly shaded say it better than Blackmore (1996, 37), at the circle where the grid lines cross in with enhanced contrast at the border. who wrote: figure 3, which will “print” the image of This visual illusion was first reported by the grid on your retina. If you then stare Ernst Mach (1865), and it is often pre- If you hold out your hand against a dark background and look at the space at the plus sign in the square, you should sented as “Mach bands” as shown in fig- just beside the skin, you will begin to notice that the afterimage jumps around ure 1 (Ratliff 1965). Figure 2 presents see a faint glow around it. ... Light as your eyes move. Figure 1. Mach bands Figure 2. A series of silhouettes Figure 3. Eye movement demonstration (see text for explanation) 44 Volume 35 Issue 6 | Skeptical Inquirer SI Nov. Dec 11_SI new design masters 9/27/11 12:44 PM Page 45 Vitality Globules William Flexner informs us in the capillaries as numerous short- Intro duction to Parapsychology that lived, seemingly erratic, rapidly any normal person can usually see moving dots of light with dark what are variously called prana, tails. vitality globules, or etheric glob- To see the larger blood vessels ules. By “focusing the gaze in- on the retina, close one eye and tently into the sky for a few mo- look straight ahead at a blank wall ments” (Flex ner 2004, 128) you with the other while flashing a will see that the “globule wells out beam of light across the pupil from an invisible source, appears from the periphery. This will cause and moves rapidly away, to give a spot of light to be focused on the place to more globules” (147). periphery of the retina. The spot Flexner writes that when we acts as an internal light source breathe in these globules of “raw casting shadows of the blood ves- energy” our bodies change them sels on the ret ina. These shadows into “personal vitality” (128), so he are not nor mally seen because the Figure 4: Shadows of parafoveal capillaries on the retina clearly regards them as an atmos- retina adjusts for any constant sen- (Horner 1834) Under ideal viewing conditions, you can retinal capillaries that surround the fovea see dozens of these white cells moving when staring at a bright surface, partic- ularly after physical exertion. The white at a time and recognize that they always blood cells are relatively large and must deform to fit in the capillaries, causing a trace out the same paths and move in space to open up ahead of them and the time with your pulse. much more numerous and smaller red cells to pile up behind. The red cells ab- sorb more light, so what we see are short, bright streaks with dark tails moving in the short, convoluted paths of the capil- laries. Under ideal viewing conditions, pheric phenomenon that is beneficial to sation. For other viewing techniques and you can see dozens of these white cells our health. more information, see Walker (1982). moving at a time and recognize that they We can never be sure exactly what To see the parafoveal cap illaries on always trace out the same paths and someone else is seeing, but what Flexner the retina, put a pinhole (~0.8 mm) in a move in time with your pulse. To im- describes seems a lot like the blue field business card and look at a bright, fea- prove your viewing, you can hold a piece entoptic phenomenon (also called tureless surface (or the sky) while hold- of cobalt glass or blue plastic up against Scheerer’s phenomenon or flying cor- ing the pinhole close to your eye. Rap- a blue sky. A science museum (see www. puscles). We sense light with the retina, idly move the card in small circles, and exploratorium.edu/xref/exhibits/blood_c which is at the back of the eye. Arteries, through the hole you should see a pat- ells_in_the_eye.html) or an ophthalmol- veins, and capillaries are present on top tern similar to that shown in figure 4. ogist may have a viewer (sometimes of the retina, and these plus the blood Note the capillary-free zone at the cen- called an entoptoscope), which is essen- flowing through the capillaries can be ter of vision marking the fovea, where tially just a bright, diffuse source of nar- seen under the right conditions. We see photo receptors are most tightly packed. row-band blue light. For more informa- the arteries, veins, and capillaries as net- Most people have occasionally seen tion, see Sinclair et al. (1989) and Walker works of shadows and the blood flow in the blood cells moving through these (1982). Skeptical Inquirer | November / December 2011 45 SI Nov. Dec 11_SI new design masters 9/27/11 12:44 PM Page 46 Angels Who knows what someone has ac- tually seen when he or she claims to have seen an angel or a ghost? But some of the descriptions I have read sound like the person was seeing floaters or other entoptic (within the eye) phenomena. If you are really looking for and expecting to see an angel or ghost, just about any blurry thing you can’t explain will probably do. There are plenty of entoptic phe- nomena that look like blurry things, but I think floaters, phosphenes, and Purkinje’s blue arcs are the most likely candidates for misinterpreta- Figure 5. Seeing floaters clearly tion. Floaters are cells and tissue sus- pended in front of the retina. They cast distinct shadows of things on and inside movement of the eye can also result in a shadows on the retina that can be very your eye as shown in figure 5. If you phosphene at the optic nerve because the conspicuous when looking at a bright, move the foil back and forth and up and retina is apparently stretched there featureless surface. If a floater is in your down while continuing to look straight (Friedman 1941). If you do this at night, peripheral vision, you may become ahead, you will be able to gauge the rel- it can be quite noticeable, but only for aware of it moving around but will not ative distance of various things from the the first one or two attempts—and you be able to get a clear view of it because retina as well as see more of the eye’s in- can’t see it very clearly because it is fif- it will move with your eye movement. terior. Moving your head relative to a teen degrees from your center of vision You can dramatically improve the horizontal plane may also result in some where visual activity is substantially less. visibility of floaters by holding a point of the floaters moving closer to the See Walker (1981) for more informa- source of diffuse light close to your eye. fovea where the shadows can be seen tion on phosphenes. Put a small piece of aluminum foil on a more clearly. See Walker (1982) for The photoreceptors can also activate hard surface and twirl a needle point on more information. spontaneously. This is why even in the it to make a tiny hole (~0.2 mm). Cover When you press on one corner of total absence of light you don’t see ab- the hole with matte-surface cellophane your eye, you can activate the photore- solute blackness but instead a mottled tape, and hold the foil close to your eye ceptors, causing you to see a spot of light gray called “dark noise” or “equivalent while looking at a bright light source on the opposite side of the eye.