Every year, the nonprofit Neural Correlate Society, an organization "that promotes scientific research into the neural correlates of perception and cognition," holds a competition for the Best Illusion of the Year. This year's winner is the above "Dual Axis Illusion" created by Frank Force (USA).

"This spinning shape appears to defy logic by rotating around both the horizontal and vertical axis at the same time!" reads the description. "To make things even more confusing, the direction of rotation is also ambiguous. Some visual cues in the video will help viewers change their perception."

Below, second prize winner "Change the Color" by Haruaki Fukuda (Japan) and third prize winner "The Rotating Circles Illusion" by Ryan E.B. Mruczek and Gideon Paul Caplovitz (USA).

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The brilliant optical illusions of stop motion animator Kevin Parry. Read the rest

And I thought the people with six fingers on one hand were impressive! Watch below.

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"Impossible Somatosensation" is a paper written by Isabel Won, Steven Gross, and Chaz Firestone Johns of Hopkins University. From the abstract: "We show that, even in full-cue conditions with objects that can be freely inspected, subjects can be made to experience a single object alone as feeling heavier than a group of objects that includes the single object as a member — an impossible and phenomenologically striking experience of weight. Impossibility can not only be seen, but also felt."

Stimuli and Procedure

Subjects saw three opaque boxes in a stack, which we refer to here as Boxes A, B, and C. Subjects were instructed to perform two lifts, one immediately after the other: In one case, they lifted Boxes A, B, and C together; in another case, they lifted Box A alone. Here in Experiment 1, subjects lifted the boxes simply by grasping them with their hands, in whatever posture felt natural (though later experiments varied this grasp posture).

After the two lifts (whose order was counterbalanced across subjects), subjects were asked which lift felt heavier (or, for half of the subjects, which lift felt lighter), and the experimenter recorded the subject’s response.

Results

Subjects overwhelmingly reported that Box A alone felt heavier than Boxes A, B, and C together (90% of subjects reporting A heavier than A+B+C, binomial probability test, p<.001 against chance [50%] responding; Figure 3)1. However, this result should be “impossible”, because the sum of weights over a set of objects could never be less than the sum of weights over a subset of those objects: Unless the boxes somehow changed between lifts, Box A couldn’t weigh more than a group of weighted objects that includes Box A as a member.

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Reddit user BeardoGREG shared this unusual selfie of his family. I was mightily confused until one commenter explained it: "You were shot out of a cannon. The cannon is behind you and you are flying straight into the camera with that determined look on your face."

(r/confusing_perspective) Read the rest

When this curious contraption is switched on, an inner circle of white balls appears to be rolling inside the outer circle, but that's actually not the case at all. Below is a video explaining this circular motion illusion. Learn more about the mathematics behind it, specifically Copernicus’ Theorem, and the ingenious hypocycloid mechanical gear design by Girolamo Cardano (1501-1576) over at The Kid Should See This.

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And if shaking your head really fast is, er, problematic, you can also just look at an angle or move away from the screen until the image appears.

Here's an Instructable on how to make your own head-shaking illusions.

(via r/interestingasfuck)

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Science Alert claims this illusions mimics time travel in the brain. I think the illusion works, but I saw no dinosaurs. Read the rest

Caltech researchers developed the illusion above to illustrate postdiction, a sensory phenomenon "in which a stimulus that occurs later can retroactively affect our perceptions of an earlier event." From Caltech Matters:

"Illusions are a really interesting window into the brain," says first author Noelle Stiles (PhD '15), a visitor in biology and biological engineering and a postdoctoral scholar–research associate at USC. "By investigating illusions, we can study the brain's decision-making process. For example, how does the brain determine reality with information from multiple senses that is at times noisy and conflicting? The brain uses assumptions about the environment to solve this problem. When these assumptions happen to be wrong, illusions can occur as the brain tries to make the best sense of a confusing situation. We can use these illusions to unveil the underlying inferences that the brain makes...."

Postdictive processing has been demonstrated within individual senses, but this work focuses on how the phenomenon can bridge multiple senses. The key to both of the new illusions is that the audio and visual stimuli occur rapidly, in under 200 milliseconds (one-fifth of a second). The brain, trying to make sense of this barrage of information, synthesizes the stimuli from both senses to determine the experience, using postdiction to do so.

Read more in the researchers' scientific paper: "What you saw is what you will hear: Two new illusions with audiovisual postdictive effects" (PLoS ONE) Read the rest

Get your game on, go play. (AsapSCIENCE)

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Look at the above image. The higher the peaks, the more sensitive your eyes are to contrasts at those frequencies. Ian Goodfellow spotted the image in a scientific paper about spatial frequency analysis and brilliantly observed that "It's like a graph that is made by perceiving the graph itself." Over at Mind Hacks, Tom Stafford explains the science of spatial frequency, the same concept behind the classic "Marilyn Einstein" image below that was created by Aude Oliva in 2007. From Mind Hacks:

Spatial frequency means how often things change in space. High spatial frequency changes means lots of small detail. Spatial frequency is surprisingly important to our visual system – lots of basic features of the visual world, like orientation or motion, are processed first according to which spatial frequency the information is available at...

Spatial frequency is also why, when you’re flying over the ocean, you can see waves which appear not to move. Although your vision is sensitive enough to see the wave, the motion sensitive part of your visual system isn’t as good at the fine spatial frequencies – which creates a natural illusion of static waves.

See Einstein below? Now go a few steps back from your screen and look again:

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Vsauce3's Jake Roper reveals the wondrous perceptual paradoxes of "impossible objects" from Escher's cube to the Penrose triangle.

(via Laughing Squid)

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The folks at Snarkitecture collaborated with the Portuguese design firm UVA to create the "Slip Chair", which looks like it's tipping over, but is safe to sit in.

Or so they say! Me, I'd like to see a picture of someone actually sitting in one. But for now I'll take their word, as they write on the UVA site ....

Slip Chair is a wooden chair that appears to be sinking into the ground. As it may seem unusable at first, the wooden frame is even out with a tapered stone and a functional surface for sitting is provided. The apparently opposed elements of the chair are counterbalanced through the monolithic volume of the stone. The chair revolves upon two axes and the suggested unsteadiness of the sliding forms conceals the complete stability of Slip.

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What does this DeWalt knife, posted to the "midly interesting" subreddit by turltlecam_son, look like?

a) a chicken b) a unicorn c) a fish d) a knife Read the rest

Jonathan Harris shows you how to draw (and cut) your way to this floating cube illusion. His YouTube channel has many more drawing illusions like it.

Previously in floating cube illusions: cool floating cube illusion. Read the rest

I could watch this all day.

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Artist Geoffroy Amelot created this Lego-centric replica of Vincent Van Gogh’s famous self-portrait. Read the rest