"Our senses can be trusted but they can be easily fooled"

- Aristotle

Way back in 350 BC, philosophy great Aristotle noticed that when watching a waterfall and then shifting your gaze over to static rocks, the rocks will begin to appear to move in the opposite direction.  It is what is now called the motion aftereffect or the waterfall illusion.  He felt that the brain's neurons could not keep up with the change of motion so when our gaze is shifted from the moving water to the still rocks, our neurons over-compensate which causes us to perceive the rocks as moving. Even earlier than that, still in Ancient Greece, people became fascinated with Greek temple rooftops and the illusion that they appeared to be curved when viewed from below when they were in fact slanted.  Greek philosopher Epicharmus tried to explain that our brains were not at fault and that we were perceiving the image correctly, it was our senses that were actually deceiving us.  Protagoras said our eyes had nothing to do with how we saw things and that the illusions were dependent on the environment in which they were viewed.  All of these are descriptions and theories of what we now refer to as optical illusions.  

People investigate the paranormal in the dark at night for a range of reasons.  For many, you can only gain access at night.  Some locations don't have running electricity to even turn a light on.  Others like to investigate in the dark as they feel it heightens their senses.  The obvious answer of course is also, it adds to the spooky atmosphere.  While spooky, it also means that our eyes can play tricks on us, especially when our eyes are adjusting to different levels of light.  One of these illusions is known as the Purkinje Effect

What is the Purkinje Effect?

Referred to as the Purkinje effect, phenomenon or shift, this optical illusion occurs as a part of the dark adaptation process. In short, it means we process and see colours differently in low levels of light. Reds will appear to be darker than they actually are as the level of light decreases. It means colour contrast looks different and the way we then perceive our surroundings is affected. 

In 1819, Jan Evangelista Purkyně observed during his morning meditations and long walks that his favourite flowers were bright and red on a sunny afternoon yet appeared much darker at dawn. It was still daylight, but the light levels were vastly different. Purkyně wrote of the experience

Objectively, the degree of illumination has a great influence on the intensity of color quality. In order to prove this most vividly, take some colors before daybreak, when it begins slowly to get lighter. Initially one sees only black and grey. Particularly the brightest colors, red and green, appear darkest. Yellow cannot be distinguished from a rosy red. Blue became noticeable to me first. Nuances of red, which otherwise burn brightest in daylight, namely carmine, cinnabar and orange, show themselves as darkest for quite a while, in contrast to their average brightness. Green appears more bluish to me, and its yellow tint develops with increasing daylight only.

Purkinje's Vision: The Dawning of Neuroscience (2001)

Image By Twinsday Public Domain

You may remember a while ago I wrote about the dark adaption process and how it affects us as paranormal investigators. It is also the reason you will see people using red lanterns and flashlights during an investigation. While it gives a spooky vibe, there is actually a solid reason behind it. You can read more about the dark adaptation process in my article Dark adaptation and red Light

Now back to the Purkinje Effect. If you are looking for the scientific explanation, here you go!

Purkinje Effect.—The relative sensibility of the retina varies for different colors with a change in brightness; or it may be better to state that the relative sensations for various colors alters as the brightness values are reduced to a low intensity. For example, if a reddish purple (consisting of red and blue or violet rays) be illuminated in such a manner that the intensity of illumination, and consequently its brightness, may be reduced from normal to a low value (approximating moonlight conditions), it will be seen to vary from reddish purple to violet. In doing this its appearance changes through the range of[Pg 140] purples from reddish to violet. This can be accomplished by orientation of the purple surface throughout various angles with respect to the direction of light or by reducing the illumination by means of screens.

In general the Purkinje effect may be described as an increasing sensibility of the retina for light of shorter wave-lengths (violet, blue, green) as the brightness decreases, or a corresponding decreasing sensibility for light of longer wave-lengths (yellow, orange, red). The effect may be seen on any colored surfaces at twilight illumination. A blue and a red flower, which appear of the same brightness before sunset will begin to appear unequal in this respect as twilight deepens. The red will become darker more rapidly than the blue if there are no appreciable changes in the color of the daylight. Finally all color disappears. It is better to perform this experiment under artificial light, in order that the spectral character of the illuminant may be certain to remain constant. In this case rheostats must not be used for dimming the light because of the attendant changes in color or quality of the light.

The Purkinje effect may be noticed by the careful observer and it is responsible for certain illusions. Apparently it cannot operate over one portion of the retina, while the remainder is stimulated by normal intensities of light.

Visual Illusions, their causes, characteristics and applications, by Matthew Luckiesh (2011)

This video may explain it better

Purkinje's Tree

You may have seen this on Tik Tok or YouTube, but there is a little trick called Purkinje's Tree which allows you to see the blood vessels in your eye when a light is shone into the retina at an angle.  Look it up if you want a video or you can follow these instructions:

Darken the room: Turn off all lights and dim any monitors for the best effect.

Cover one eye: Use your fingers to cover one eye completely.

Position the light

Turn on your phone's flashlight, close your eyes, and hold the light gently against your eyelid near the corner of your eye.

Move the light: Gently move the light across your eyelid or the edge of your pupil.

Look for the pattern: You'll see a branching, tree-like shadow of your own blood vessels on a dark background. 

Image By Brad Macario - Public domain

This is what is known as Entoptic phenomena which is a visual effect caused by the eye itself.

Obviously, use with caution.  (I get a migraine if I try anything like this!)

While a cool trick, it makes you wonder just what happens when someone accidentally shines a light right in your face in the middle of a paranormal investigation?  Or how about if they are taking a photo and the flash goes off and the light hits your eye at the right angle?  Could these create Purkinje's Spectre?

Purkinje's Spectre

In the world of paranormal investigation, we are often looking for things in low light, staring at grainy photos or just staring at surfaces for long periods of time.  It means we are prone to experiencing all sorts of optical illusions and potentially labelling them as something paranormal. This is where the Purkinje effect could really become Purkinje's Spectre!

Interestingly, I was actually inspired to write this from an old newspaper article I read, implying just that!

The following excerpt is from an article published 27 Feb 1949 in the Sunday Herald

HAVE you never seen a ghost? It's easy enough, and can be a most alarming experience. If you want to try it out hold a dim light, a candle, say, about the level of your chin and look along a dark hall or passageway. The dancing image which can then be seen is known as Purkinje's Spectre. ' It has a perfectly natural explanation; is caused by the shadow on the back of the eye of certain blood vessels, which shadow is seemingly projected ahead of and outside the eye. It must be angled for, as the "ghost" is seen only with the light in a certain position.

Purkinje's Spectre roams the universe and can be conjured from the realms of darkness whenever conditions are suitable and the occasion demands.It is very likely responsible for the legends surrounding a good half of the "haunted houses" of traditional repute, whether they are in Blackpool, Bilge-on-Bidewater, Bombay or Boggabilla.

Trove 

The Purkinje effect explains why "blue ghost" fireflies appear to us as bluish-white orbs in the dark, even though their true bioluminescence colour is a greenish-yellow. It is also linked to what is known as Bidwell's Ghost. This is caused by the Purkinje effect and occurs when a bright spot of light like the candle mentioned above, is moved rapidly across a dimly lit surface while the observer's gaze remains fixed. You will then see a trailing ghost, which is referred to as an afterimage. (A secondary image or light trailing a split second behind the actual light).

One of the biggest issues in paranormal investigation is how easily our perception can be altered by natural causes.  Light is obviously one of those.  Many investigators will investigate in the dark using a small bright light source like a flashlight.  We can see above already just how easily that can unknowingly cause us to see something differently to what it is.  It makes you wonder just how many visual anomalies are actually just the light playing tricks with our eyes. If you want specific examples, an easy one I can think of is a simple red object in a room.  If you are walking into a room where you are not familiar with the surroundings, a bright red hat or scarf hanging on a hook could suddenly appear to someone like a dark blue apparition or floating figure if their eyes are not properly adjusted.  Looking at a light source and seeing a secondary light trailing behind it can be interpreted by some people as something else.  

How can we avoid this?  Turn the lights on or use red light to help with the dark adaptation process.  You absolutely can investigate the paranormal with the lights on or even in the middle of the day if you have access and opportunity to do so.  Before any investigation, you should always be doing a sweep of a building to familiarise yourself with the surroundings.  I always recommend taking a photograph or video of every single room so that if you capture or experience an anomaly, you can go back to this photo or video later.  Many years ago now I was at Aradale asylum doing an investigation.  I was startled by what appeared to be a child-like figure standing in the room.  I had taken a photo of it with my phone without the flash.  It appeared as a dark shadow.  What I didn't know was that it was actually a bright red fire extinguisher.  I was able to debunk this low-light photo from the baseline photos I took at the beginning of the night.  There is absolutely no way I would have been able to debunk this without the photo.  We don't always absorb or take in our surroundings and it is really impossible for us to remember every single detail of every single room.  

While this one is not as obvious or prominent as some other optical illusions, it is a reminder that as humans one of the things we have to consider debunking is ourselves.

References

Visual Illusions, their causes, characteristics and applications, by Matthew Luckiesh (2011)

Trove 

https://www.lens.com/what-is/the-purkinje-tree/

Cover Image - Created by LLIFS & AI