Tag Archives: illusion

Frank Force wins Best Illusion of 2019 award with a simple, but effective shape

What was the greatest illusion of 2019? Was it that you’ll finally ‘get in shape at the gym’? Was it true love? Both have their merits but, according to the Best Illusion of the Year contest, it was actually a moving shape that (frustratingly enough for my brain) seems to rotate in all directions at once, created by game developer and artist Frank Force.

Image credits Frank Force via Youtube.

The contest is a yearly event run by the Neural Correlate Society (NCS), a nonprofit that aims to promote scientific research into the neural correlates of perception and cognition.

Seeing is believing

“How we see the outside world — our perception — is generated indirectly by brain mechanisms, and so all perception is illusory to some extent. The study of illusions is critical to how we understand sensory perception, and many ophthalmic and neurological diseases,” the NCS explains.

The contest is ran “democratically”, according to the NCS, with the first, second, and third places being awarded by an online vote.

Force’s “Dual Axis Illusion” won this year’s first prize, and it’s easy to see why: the more you look at it, the weirder it gets. Force helps inch the illusion along through the use of colored lines that highlight how his creation works.

So, without further ado, here it is in action:

Like all optical illusions, Force’s creation hijacks our brain’s tendency to cut corners when interpreting sensory data — sight is especially well-suited to this task. Our brain’s interpretation of sight is built on a huge amount of individual bits of information that the brain tends to treat as a meaningful whole to simplify the process. Force expertly abuses that process by adding and removing contextual information, such as the colored lines that temporarily appear on the screen, or by anchoring your perception on key elements of the shape — in this case, where the lines overlap.

It’s surprising to see the sheer extent to which these cues shape my perception of what is fundamentally a two-dimensional black line on a white background. Practically speaking, there is no volume to this image and no real rotation happening — but Force can still make me perceive them, and then turn that perception on its head.

And I love it.

This illusion can hack your brain into feeling the space around you

Neuroscientists at the Karolinska Institute in Stockholm, Sweden have found that they can make people “feel” the space immediately around them. The participants describe the sensation like a “force field” surrounding them.

Image credits Amely/Pixabay

Our brains have developed to be aware not just of our body’s position in space, but also of the objects in our immediate vicinity known as the peripheral space. This ability allows us to effectively grasp or interact with the objects that surround us and serves to protect us from harm.

Imagine you’ve just finished lunch with a friend in a restaurant. As you’re getting up to leave, a waitress passes through your peripheral vision. You’ll instinctively move in such a way as not to collide with her; your sense of peripheral space has saved you from getting doused in scalding hot coffee.

The first evidence of this phenomenon appeared in the late 1990s. Researchers at Princeton University studied the brains of monkeys and found that neurons in the parietal and frontal lobes generate electric signals not only when an object touched their body, but also when it came close enough to any part of their bodies. When stimulating these neurons, the monkeys adopted defensive movements — reflexively moving their arms into a protective posture.

These experiments were never repeated on humans, but patients suffering from strokes in the right posterior parietal lobe report that they can’t sense peripheral stimuli on the left side of their bodies but “sense” things further away on that side.

“This suggests that there is a representation similar to those found in monkeys in the human brain,” says Arvid Guterstam of the Karolinska Institute in Stockholm, Sweden.

To test this theory, Guterstam and his colleagues employed the rubber hand illusion to trick humans into actually feeling our peripersonal space. This experiment involves hiding a volunteer’s hand from sight then stroking it with a paintbrush. The experimenter simultaneously strokes an adjacent, visible rubber hand during this time, at the same speed and in the same spot on the rubber and real hand. After a few minutes, the participants start feeling the touch on the rubber hand, as if it were their own. This only works as long as the two hands are close enough together.

For the new study, the team recruited 101 adults but instead of brushing the rubber hand directly, they moved the brush above it as they touched the real hand. The volunteers thus felt the stroke on their body but saw the brush move in mid-air, about 10 centimeters above the rubber hand.

For the most part, volunteers reported feeling a “magnetic force” or a “force field” between the paintbrush and the rubber hand. They describe it as the brush hitting an invisible barrier. They also reported feeling that the rubber hand belonged to them.

“We can elicit this bizarre sensation of there actually being something in mid-air between the brush and the rubber hand,” says Guterstam.

Here too, distance seems to be a factor. When the brush was held more than 30 or 40 centimeters above the rubber hand, the illusion disappeared. Placing an opaque metal barrier between the rubber hand and the brush also had this effect. Guterstam speculates that this happens because the barrier makes it impossible for the hand to reach up and grasp anything, or for anything to hit the hand; in essence, it limits the perceived peripersonal space of the limb.

“This is a wonderful study,” says Michael Graziano, who conducted the 1990s experiments. “For decades, the neuroscience of the parietal and frontal lobes has filled in our knowledge of the special margin of safety, or buffer zone, around the body. Now we have a clever way to get at the phenomenon through an illusion that is easy to implement in the lab.”

The full paper, titled “The magnetic touch illusion: A perceptual correlate of visuo-tactile integration in peripersonal space” has been published online in the journal Cognition and is available here.

This optical illusion will make you doubt your eyes

There’s no image manipulation or processing of any type going on… so what’s happening? Obviously the people can’t be changing sizes, so something’s going on. It’s called an Ames Room, and it was invented by American ophthalmologist Adelbert Ames, Jr. in 1934 to screw with your brain.

There are actually two illusions associated with the Ames Room. First of all, the room looks cubic when viewed from a specific viewing point, when in fact, it is a trapeze – as you can see below.

The room is viewed through a pinch hole such as to avoid any clues from stereopsis, and it is constructed so that from the front it appears to be an ordinary cubic-shaped room; it’s a trick of perception.

The second illusion is that within an Ames Room, people or objects can appear to grow or shrink when moving from one corner to the other. This trick is also related to the specific shape of the room. The roof is inclined, but to the viewer, it appears straight, so a person standing in one corner appears to the observer to be a giant, while a person standing in the other corner appears to be a dwarf. The illusion is so convincing that a person walking back and forth from the left corner to the right corner appears to grow or shrink. Oh, and the coolest thing about this illusion is that you can’t unsee it after you see it: if you do see people growing or shrinking in size, you’ll always see them like that.

Image credits: Silly Little Man.

Ames’ original design also contained a groove that was positioned such that a ball in it appears to roll uphill, against gravity. Richard Gregory, a British psychologist and Emeritus Professor of Neuropsychology at the University of Bristol, regards this apparent “anti-gravity” effect as more amazing than the apparent size changes, although today it is often not shown when an Ames room is exhibited. Still not convinced? Let’s look at it a bit closer.

Although the floor appears to be level, it is actually at an incline (the far left corner is much lower than the near right corner). The walls also appear perpendicular to the floor, although they are somewhat slanted. Your eyes and your brain is tricked because you’re used to seeing normal, rectangular rooms. Your brain creates a mental shortcut so that when you see a room that appears to be rectangular – it is, so it just assumes all rooms are rectangular and it’s easier to trick. If you’d show this illusion to someone that had never seen a room or a regular construction, he’d be less likely to be fooled.

In the media, Ames Rooms have been used extensively; most notably, they were used in the Lord of the Rings, to manipulate the size of the hobbits relative to Gandalf. An Ames room is also depicted in the 1971 film adaptation of the Roald Dahl novel Charlie and the Chocolate Factory

Scans reveal what happens in your brain during an out-of-body experience

Neuroscientists at the Karolinska Institute in Sweden have created an out-of-body illusion in participants placed inside a brain scanner to see what happens in the brain during this time and understand what are the brain parts responsible for our sense of position.

This is the visual perspective from one of the out-of-body positions. Illustration of study published in Current Biology April 2015. Credit: Arvid Guterstam


The idea of having a body placed somewhere in space is a sense we generally take for granted. However, to our brains, this is a monumental task which involves continuous analysis and integration of sensorial data. Studies in rats have shown that specific regions of the brain contain GPS-like ‘place cells’ that signal the body’s position – a finding which was rewarded with a Nobel Prize for Medicine in 2014.

But for the more complex human brain, this is still a mystery. In a new study, scientists created an out-of-body illusion in fifteen healthy participants placed inside a brain scanner. In the experiment, participants viewed themselves and the brain scanner from another part of the room. From the new visual perspective, the participant observes the body of a stranger in the foreground while their physical body is visible in the background. To further emphasize the illusion, a scientist touched the participant body with an object just as he was touching the stranger’s body, in full view of the participant – just like in another recent experiment, which made participants feel like they’re invisible.

“In a matter of seconds, the brain merges the sensation of touch and visual input from the new perspective, resulting in the illusion of owning the stranger’s body and being located in that body’s position in the room, outside the participant’s physical body,” says Arvid Guterstam, lead author of the present study.

The goal was to analyze the brain with scanners and see what’s happening as the illusion materializes. They then employed pattern recognition techniques to analyze the brain activity and managed to show a systematic connection between the information content in these patterns and the participants’ perceived vividness of the illusion. In other words, the participants’ brains dealt with the out-of-body experience the same way.

“The sense of being a body located somewhere in space is essential for our interactions with the outside world and constitutes a fundamental aspect of human self-consciousness,” says Arvid Guterstam. “Our results are important because they represent the first characterization of the brain areas that are involved in shaping the perceptual experience of the bodily self in space.”

The finding is important because it is a significant step forward in identifying what cells play the key role in our perceived self-location.

“This finding is particularly interesting because it indicates that place cells are not only involved in navigation and memory encoding, but are also important for generating the conscious experience of one’s body in space,” says principal investigator Henrik Ehrsson, professor at the Department of Neuroscience.

Experiment made people feel like they’re invisible

We’ve all had days when we’ve felt invisible metaphorically, but Swedish researchers have taken it to the next level – they’ve made a man actually feel like he’s invisible.

Image via KJN Genealogy.

The experiment, which was conducted on 125 participants, was a variation of the so-called rubber hand illusion – a popular trick which actually holds a lot of insight on how the human brain works. In the rubber hand illusion, you sit with your real hand under a table and out of sight, while a rubber hand sits in front of you. The experimenter strokes the fake hand in time with your real one, and you only get to see the fake one, so you sort of believe that one is yours – sort of like a phantom hand. Henrik Ehrsson from the Karolinska Institute is a master of this illusion, and he wanted to see how far the trick can be taken.

In this new setup, participants wore a virtual reality headset, linked to a nearby downward-pointed camera. A researcher stood at arm’s length from the subject, with a paintbrush in each hand. With one hand, he was actually stroking the participant, while with the other one, he made a similar motion onto what the participant perceived to be his or her invisible body. To make the entire thing more interesting, experimenters had an audience of “seriously looking strangers” assist the entire thing. When the brush motions weren’t synced up, the subjects maintained their sense of self. But when they were, subjects reportedly felt like they actually were the empty space – in other words, they felt invisible.

“Within less than a minute, the majority of the participants started to transfer the sensation of touch to the portion of empty space where they saw the paintbrush move and experienced an invisible body in that position,” explained Arvid Guterstam, lead author from the Karolinska Institutet in Sweden. “The present study demonstrates that the ‘invisible hand illusion’ can, surprisingly, be extended to an entire invisible body,” he noted.

To actually prove that participants felt like they were the invisible space next to them, experimenters made a stabbing motion with a knife, towards the empty space. When the illusion was up, participants were scared and exhibited increased sweat response (in some cases, even a visible reaction).

But this isn’t just a cool experiment to make people feel like they’re invisible, it may have significant implications in terms of understanding and dealing with anxiety. As scientists explain, when people felt invisible, it actually made them significantly less anxious.

“We found that their heart rate and self-reported stress level during the ‘performance’ was lower when they experienced the invisible body illusion,” Guterstam noted.

They’re also interested in studying what feeling invisible does to participants’ sense of morality. If the internet is some sort of indication, feeling invisible will make people bring out the worse in them, but that’s something that still remains to be seen.

“We are planning to expose participants to a number of moral dilemmas under the illusion that they are invisible,” says co-author Arvid Guterstam, “and compare their responses to a context in which they perceive having a normal physical body.”

Journal Reference: Arvid Guterstam, Zakaryah Abdulkarim & H. Henrik Ehrsson. Illusory ownership of an invisible body reduces autonomic and subjective social anxiety responses. Scientific Reports 5, Article number: 9831 doi:10.1038/srep09831