Illusion Hole

[Gualberto Estrada]

Youreyes work in pairs. Your brain takes the right eye's image and the left eye's image and blends them together to present you with a full image. How does it do this? Simply put, there are some nerve cells in the occipital cortex (the part of the brain that processes most of our visual input) that receive signals from both eyes. It is those cells that allow us to process the visual input from both eyes simultaneously and thus have depth perception and 3D vision. Therefore, when one of your eyes sees a hole and the other sees a hand, your brain merges the two images together to create a hand with a hole in it!

INTERESTING POINT: If you found the effect stronger on one side than the other, it indicates that one eye is likely dominant. What's that mean? It means your brain has a slight preference for visual information from that eye over the other. It's a similar idea to having a dominant hand or foot. However, your dominant eye may not be the same as your dominant hand or foot.

Bring this into your classroom (which is most likely in your home right now during this pandemic), and explore the science and biology behind it. Test out different options and different illusions! The eyes are an awesome scientific wonder!

Most of the supplies will depend on the size of the box you're planning to make.

I used some really nice B/BB plywood, this is such a great material and so different from the 'normal' plywood you get from the big box stores. Very few (if any) voids and with the B grade face it's pretty much blemish free. It's a little heavier and quite a bit more expensive, I would say it's worth it for any 'public' facing project.

The size of the box I made was determined by the mirror that my wife was throwing out, this was used as the bottom mirror.

You'll need enough wood (ply) to make the four side of the box to a height of about 325 mm (13 inches).

I decided to go for a bulkhead light for the inside of the box as I thought this was in keeping with a mine shaft. You'll also need a length of mains cable.

The bottom mirror is a standard mirror but the top is where the 'magic' happens.

To reinforce the bottom mirror I mounted it to a piece of 4 mm plywood using some double-sided carpet tape.

This gave a total thickness of 8 mm, you'll need to remember this measurement for later as this is the size of the router bit you'll need for the rabbet.

Using a couple of 70 x 50 mm pine offcuts and an old broom handle I knocked up a little single rung ladder.

I distressed the pine by knocking it about with a hammer and painted it black to add to the mine shaft authenticity.

The height of you ladder will be determined by the space between your two mirrors, you want to make sure the ladder is tight up against the top mirror as any large gap will ruin the illusion. You also want to make sure the rung is in the middle for the same reason.

For added strength I decided to join the sides using super sized finger joints, to do this I made a quick jig, this allowed me to make multiple blade passes on my table saw, these were also at an exact 90.

I started by measuring the end of the long sides and dividing it by 5 to get the size of the fingers. These were then marked out on both ends of the two longer sides. Once I had made the cuts to make the fingers I then used the cutouts to mark up the corresponding fingers on the short side pieces.

Using an 8 mm router bit mounted into my router table I routed a slot for the bottom mirror around the bottom of each of the four sides. In the shorter sides this slot was stopped before the edge, so I was not visible from the outside.

I then routed a slot all around the top edge of each side, this slot was 4.5 mm deep as I was planning to use a 4 mm top mirror. The slot was cut to half the width of the sides, this gives the top mirror enough area to rest on.

All the top slots were stopped to line up with the corresponding slot on the joined piece.

I went to my local glass / mirror centre, having given them the measurements and told them what it was for, they strongly recommended I got toughened glass. This is a service they offer but there was a week delay.

Unfortunately I didn't get any pictures / video of me making the actual top mirror.

It took two attempts as I completely messed up the first one, I hadn't cleaned the glass well enough and managed to stick the mirror film to itself and crease it. I decided not to film my second attempt as I really needed to concentrate.

I used Titebond 2 wood glue but any PVA wood glue would work fine. Make sure you cover all the mating surfaces, if like me you're using plywood, make sure you use enough glue as the ply is thirst and you don't want a dry joint.

The 'magic' of this is how a 'one way' mirror works... As it was explained to me by the guy in the mirror shop is that the refection is always on the side of the mirror with the most light. This is why the police turn off the light when they are observing the interview from outside.

On the table when the light inside is off it just looks like a mirrored top, when the light is on you get the internal reflections, this is even more effective when the external light in the room is off too.

Do you see a hole in your hand? When you look through the tube and see a hole in your hand, you are seeing an optical illusion. The tube allows you to look into the distance with your left eye and to see your hand with your right eye. Your brain took what your left eye saw and put it together with what the right eye saw, forming one image. That image makes it seem like there's a hole in your hand.

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A brand new optical illusion tricks the majority of people into thinking that a dark "black hole" region at the center of a stationary image is rapidly expanding, as if the observer were moving toward it. Researchers now suspect that the image literally tricks the brain into thinking that the observer is moving into a darkened space, like a cave or tunnel.

The illusion consists of a large black ellipse surrounded by a dark halo on a white background filled with smaller black ellipses. Typically, as a person stares at the image, the dark elliptical region will appear to expand outward for a couple of seconds, which is why the design has been nicknamed the "expanding hole."

In a new study, researchers found that 86% of the 50 participants who looked at the optical illusion reported seeing the expanding darkness. The team suspects that the illusion plays on the brain's perception of changing light levels.

"The expanding hole is a highly dynamic illusion," lead researcher Bruno Laeng, a psychologist at the University of Oslo in Norway, said in a statement. The illusion tricks the mind into seeing a change in brightness that isn't really there, "as if the observer were heading forward into a hole or tunnel," Laeng added.

The illusion hijacks a natural reaction in the brain that predicts when light is about to change, the researchers said. The dark region at the center of the image mimics the entrance to a cave or tunnel, and the surrounding pattern gives the observer the impression that they are moving toward that cave or tunnel. When the brain registers a potential change in light intensity, such as walking into a cave, it can trigger the pupils to contract or dilate to prepare you for the upcoming disruption in advance.

The illusion is so good at tricking the brain that it also causes people's pupils to dilate as if they were actually moving into a darker space. The researchers used special cameras to track observers' eye movements as they looked at the illusion, and the scientists found that their subjects' pupils were expanding just like the dark region of the illusion appeared to expand in their minds. Those who saw a bigger dark hole showed more dilation than those who saw a less-stark "black hole," the researchers said.

"The illusion of the expanding hole prompts a corresponding dilation of the pupil, as it would happen if darkness really increased," Laeng said. This shows that "the pupil reacts to how we perceive light, even if this light is imaginary."

The researchers also exposed observers to versions of the illusions where the color of the ellipses had been changed. When this happened, the illusion's expanding effect was reduced and the observer's pupil dilations were less noticeable. And when the colors were inverted (placing white ellipses on a black background), the observers' pupils contracted, instead of expanding, as if they were moving toward a bright light.

The researchers have no idea why some people who look at the expanding hole are unable to see the dark region moving. The team hopes to test the illusion on other animals and see if they can learn more about how those visual systems differ from that in humans, to solve this mystery.

Harry is a U.K.-based senior staff writer at Live Science. He studied marine biology at the University of Exeter before training to become a journalist. He covers a wide range of topics including space exploration, planetary science, space weather, climate change, animal behavior, evolution and paleontology. His feature on the upcoming solar maximum was shortlisted in the \"top scoop\" category at the National Council for the Training of Journalists (NCTJ) Awards for Excellence in 2023. "}), " -0-10/js/authorBio.js"); } else console.error('%c FTE ','background: #9306F9; color: #ffffff','no lazy slice hydration function available'); Harry BakerSocial Links NavigationSenior Staff WriterHarry is a U.K.-based senior staff writer at Live Science. He studied marine biology at the University of Exeter before training to become a journalist. He covers a wide range of topics including space exploration, planetary science, space weather, climate change, animal behavior, evolution and paleontology. His feature on the upcoming solar maximum was shortlisted in the "top scoop" category at the National Council for the Training of Journalists (NCTJ) Awards for Excellence in 2023.

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