Most people who stare at the image below will believe the dark oval in the middle is growing larger. But, believe it or not, it is just an illusion – a static image.
According to a study published in the journal Frontiers in Human Neuroscience, this illusion has something to teach us about how our brains and eyes collaborate to see the world. Researchers tested the illusion on 50 men and women with normal vision and found that those participants who had eyes with the strongest pupil dilation response had the greatest response to the illusion; while those with poor dilation response could not see it.
The pupils in the human eye are designed to automatically adjust to the surrounding light, dilating when it is dark so they can capture more light, and constricting when it is bright to prevent overexposure. Even though the hole in this illusion is not darkening, the perception or expectation in our mind that it should be darkening is enough to make our pupils respond.
Bruno Laeng, a psychology professor at the University of Oslo and an author of the study, says: “There is no reason that the pupil should change [while looking at this image], because nothing is changing in the viewers world, but something clearly has changed inside the mind.”
The researchers hypothesize that the illusion is deceiving because the gradient on the central hole makes it look to the viewer as if they are entering a dark hole or tunnel, which prompts the participants’ pupils to dilate. Our brains are making assumptions about what it sees based on past experience and is trying to predict and prepare our senses for what it thinks will happen next.
It takes time for light to reach our sensory organs and send the image to our brain. The brain then takes more time to process the image, make sense of it, and decide what actions to take based on the collected information. By the time our brain catches up with the present, time has already moved forward, and the user’s environment has most likely changed.
To minimize this image collection and processing delay, the brain may be constantly trying to predict a little bit into the future so that it can better perceive the present. Being fooled by this expanding hole illusion is not a flaw of the human species, but a feature. It is most likely built up from evolutionary history to help humanity survive.
The information we get from our senses is spotty and incomplete, so the brain has evolved over time to try to guess what is happening in the uncertain and ever-changing world – and to make decisions based on what is most likely to happen next.
People who possessed brains with the best ability to adapt and predict what is happening at any given moment most likely had an advantage over those that lacked the capacity to adapt. When the illusion image is communicated to the brain, it anticipates that the body will soon be entering a dark place and it responds by telling the pupils to begin dilating (so the body will be able to react sooner in case there is danger lurking inside that black hole).
Researchers tell us that everything we perceive is inconsistent with the physical reality of the world. It is not just that the information taken in by our senses can be misunderstood, it is also that there is a universe of information available in the physical world that is imperceptible to the human senses.
Consider light itself. The light our human eyes can detect is only a sliver of the total amount of light that’s out there. The 0.0035% of the electromagnetic spectrum we can see is referred to as visible light, but the other 99.9% percent of the spectrum consisting of radio waves, microwaves, infrared radiation, ultraviolet rays, X-rays and gamma rays are all undetectable by our eyes.
Humans have cone-shaped cells in our eyes that act as receivers specifically tuned to the wavelengths in the narrow visible light band of the spectrum. Other portions of the spectrum have wavelengths too large or too small and energetic for the biological limitations of our perception.
Evolution has not endowed us with the ability to see beyond the visible region of the electromagnetic spectrum; although it is possible to feel infrared radiation as heat and employ other parts of the electromagnetic spectrum for practical uses, such as X-Ray medical imaging.
But we carry on with our lives, oblivious to the huge spectrum of electromagnetic waves present all around us. Humans have managed to survive and reproduce despite our limited view. It’s a good thing that visible light was adequate to help our ancestors detect predators that would do them harm.
But imagine if our eyes were able to detect other parts of the electromagnetic spectrum — our universe would be unrecognizable. We could glean so much more visual information if we were able to see in the radio, infrared or even X-ray regions of the electromagnetic spectrum.
Bees and butterflies are examples of organisms that can detect Ultraviolet radiation. Some flowers have special markings that can only be seen in UV light. Bee and Butterfly eyes are able to view this electromagnetic radiation like lights on an airport runway, to find their way to the flower’s nectar. Snakes have special sensory organs on the front of their heads that let them ‘see’ infrared waves, which they put to use with particular effectiveness when hunting for warm-blooded prey.
Consider our sense of sound. Humans can detect sounds in a frequency range from about 20 Hz to 20 kHz, though the upper limit in average adults is closer to 15–17 kHz (because humans lose some high-frequency sensitivity as they mature).
That range of sounds allows humans to hear many of the sounds produced in nature, but not all. Any frequency that is below the human range is known as infrasound. It is so low that it may be detected only by a creature with big ears, such as an Elephant or by specialized instruments designed by scientists to detect the low frequency sounds that precede avalanches and earthquakes. Any frequency that is above the human frequency range is known as ultrasound. Bats and Dolphins use ultrasound frequencies as high as 200,000 Hz to help them navigate via echolocation.
Most dogs can hear sound frequencies as high as 47,000 to 65,000 Hz which is far too high-pitched for humans to hear. That is why dogs can be trained to detect when their owner is about to experience a seizure. Dogs ears are also much more sensitive to loud sounds than ours, which is probably why fireworks, thunderstorms and vacuum cleaners send them scurrying for cover.
Consider our sense of smell. Humans have 396 olfactory receptors which are employed to help us pick up scents. Almost all animals, however, have a larger number of olfactory receptors than humans (rabbits have 768 olfactory receptors) which provides them with an excellent ability to smell.
Among the animals with the greatest sense of smell are bears whose sense of smell is 300 times better than humans and is capable of detecting a deceased animal from up to 20 miles away; elephants who can smell water sources from up to 12 miles away; sharks who can smell the presence of a drop of blood in almost 100 liters of water; and bloodhounds whose sense of smell is 2,100 times better than that of a human’s and can detect trace amounts of drugs and explosives inside packages.
When you consider all these blind spots in our senses, it is obvious that humans live in a world in which many sights, sounds and smells exist that are beyond the ability of our limited senses to detect; and those that we can detect can be compromised by our overactive minds. It’s enough to make you think that all human perception is, fundamentally, just an illusion; or as Bob Dylan keenly observed “All the truth in the world adds up to one big lie“.
It could well be that we are each living in our own virtual reality world, bound by the limitations of our physical senses and the tricks employed by our minds. Dr Laeng believes we each do live in a virtual reality world. Much of what we see is an illusion, but we are not really being tricked – he believes the visual illusions help to reveal the mismatches between what our eyes see and what our mind’s eye thinks is happening.
So what lessons can we take away about how to live our lives knowing the limits of our senses and the tendency of our brains to trick us into seeing what it wants us to see.
One lesson is that we should remind ourselves that things are not always what they appear. It is possible for two people to witness the same event but still give contradictory descriptions of what they saw; even though they are certain their description of events are true. Knowing that our eyes are susceptible to being tricked should make the criminal justice system wary of judging guilt based solely on the testimony of eye-witnesses.
Another lesson is to be careful of letting our minds be swayed by our pre-conceived biases and political opinions. If we each live in our own virtual worlds then we need to be careful of falling into the trap of accepting information that matches our biases and opinions while discarding facts that don’t. If more people were careful to seek out an objective, agreed-upon, reality then maybe there would be less disagreement and discord in today’s society.
Finally, we should all be humbled and filled with wonder knowing that what our senses reveal to us is only a small portion of the great wide-world we live in. There is a whole universe out there beyond our human senses – a twilight zone if you will, a dimension not only of sight and sound but of the mind, one where there is so much more for us to discover.
Words to Live By... 