Disclaimer: I love spooky things and I also love science – I’m not trying to ruin one with the other.


In my work in microscopy and image analysis, I’ve spent a lot of time reading about vision and visual perception. As a species, humans depend heavily on their vision and we put great stock into having “seen it with my own eyes”. The problem though, is that our eyes and brain can be prone to exaggeration.

Perception is defined as the way in which something is understood and interpreted. Every one of us has a different understanding, knowledge, and experience of the world, and therefore each one of us will have a slightly different sense of perception. Simple things, such as not wearing your glasses, or looking at something too quickly, can impact our perception of what we are seeing – like thinking a bag under a table is a sleeping dog (below). This is known as pareiodolia, seeing random patterns as familar objects.



Camera vision

Take out your phone, open the camera, and watch the screen as you pan around the room. The image blurs as the camera moves. Our eyes do not move like a video camera, in smooth sweeps. Instead, they move in short, sharp movements called saccades (below).

Our vision functions much like an old-style cartoon – a series of still images that, when flicked through quickly, give the appearance of smooth movement. The eye is like a camera rapidly capturing still images, which are run together by the brain to create the appearance of smooth movement. This is why our vision doesn’t blur as our eyes move, the way it blurred for the video camera. The eye is sending these photographs to the brain, where they are being processed for object recognition and new information.



The brain loves new information, which is why we are prone to staring at things we find interesting or unusual – we are information gathering. If, however, the photographs are the same old photographs you see every day (such as on your daily commute) the brain mostly ignores what is in them. This is one of the reasons it can feel like being on autopilot while on your way to work, or taking a route that you have taken a thousand times before.


The Troxler effect

First described in 1804 by the philosopher and physician Paul Vital Troxler, the Troxler effect is a great example of how our brain picks and chooses what information is important, and also how our brain influences our perception.

Below is a classic example of the Troxler effect, known as the Lilac Chaser. Stare at the black cross in the centre, and within a few seconds, the purple dots around the edge will start to disappear. Because you are not focusing on the purple dots, your brain decides they are not important. It blends them into background, a process called ‘filling-in’ and you perceive them to vanish.

You will continue to perceive a moving green dot – it is of some interest to your brain because it is a moving object. There actually isn’t a green dot by the way. Your cone cells that are sensitive to purple are just getting tired, and the green appears as a result of that.

In essence, what is happening, is that the eye is sending the same photograph again and again and again to the brain. As nothing new or significant is showing up, the brain starts to ignore the unimportant parts of the image, i.e what is in the periphery. It will keep showing you the object that you are focused on, as this is of some apparent interest to you. Once you take your focus off the black cross, the purple dots reappear. By moving your eyes, you are capturing and sending a new photo, which is now slightly different to the repetitive one that you were sending.

You can find out more about the biology of the Troxler Effect here.


Fine! I’ll entertain myself…

When it comes to stimulation, the brain is greedy. The brain is constantly being fed a stream of information from the sensory organs (eyes, ears, skin, nose, mouth etc.), which it is assessing, cross-referencing, filing and re-filing. Much of this is done without us noticing, and your conscious mind only receives portions of information that your brain deems immediately necessary. Think of a ticking clock that goes silent after a few minutes. The clock hasn’t stopped ticking, your brain has just decided that you don’t need to know about that right now.

In response to lack of stimuli, the brain is known to hallucinate. During the Troxler effect experiment, the brain is not receiving any new input, so it starts to make substitutions. The hallucinations associated with the Troxler effect have been compared to taking LSD by some scientists. In Troxler experiments, people have reported seeing their face become distorted to the point of being demonic. They have also claimed to see objects, people, and animals in the mirror.


The experiment

  1. Sit in front of a mirror, in a dimly lit room. Try to find a time where there won’t be any distractions. I did this when I was alone in the house. In my bedroom we have mirrored wardrobes, and I sat against a plain wall to ensure there was the minimum of distractions.
  2. Set a timer for ten minutes. Use a timer instead of checking the time. Looking away to see what time it is will undo the experiment.
  3. Pick a point of concentration. I chose to focus on the pupil of my right eye.


The result

The Troxler Effect kicked in quite quickly. Within about ten seconds, features of my face started to blur and disappear. My right eye (the point I was focusing on) stayed visible but in slightly soft focus. It started with my other eye become darkened, enlarging, and vanishing. Then my nose and last my mouth. I could always see my nostrils, but that is because nostrils are high contrast compared to skin. After another minute or two my hair and upper body also started to fade into the background. At one point it was like I was turning into a line drawing – I could almost see an outline of myself, and lines around my features.


Some of the weird things that happened…

  • Blinking slightly resets the effect, and after a minute or two I started to blink in negative (i.e. anything white appears black, and anything black appears white).
  • At one point it seemed like my face shape had changed – my jaw appeared shortened and my cheeks a bit rounder, the best way I can describe it is that I started to look like a Cabbage Patch kid.
  • I also started to home in on micro-expressions. My eye appeared to be expressing different emotions that I wasn’t feeling or trying to express, so that was really interesting.

…and some of the creepy things that happened.

  • First, was the way that my iris appeared to turn black, making it appear like I had giant pupils. This would likely be from (a) the lower light levels in the room making my pupil larger, and (b) my focus softening, so the boundary line between pupil and iris blurred into one.
  • I started to see a rippling blue light on my face, as if I were underwater. I’m putting down to my S-cone cells (which are sensitive to blue light) firing in the low light levels, but I’m open to anyone else’s opinion on that.
  • At one point it looked like something black slithered across the floor behind me (I can’t explain that one).
  • The creepiest moment however, was when my eye (and I swear this happened), looked away and then looked back at me.


What I learned

It’s oddly difficult to keep your eyes still and my brain really did not appreciate the lack of stimuli – it was a real effort to not look away. It wasn’t psychologically uncomfortable, but I enjoy the weird and spooky anyway. It was physically uncomfortable because my eyes got tired and a bit watery. It was really interesting to see how the brain starts doing away with what it considers to be unnecessary information, and how a bored brain starts to entertain itself.

For me, the most interesting part was how easily the brain can stray from what we consider ‘reality’. Also, I wonder how the effect changes for different people. As the adage goes, “perception is reality”. The experiment was disturbing in parts because you are watching your face become distorted. I never had the metal to try the Bloody Mary experiment when I was younger, but I can fully understand how a young and influenceable mind could get a damn good fright from doing something like this.


Give it a try! Who knows what you might see?