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

Kensuke Koike demonstrates a cool visual trick involving an evenly-punched hard copy of an image turned into a regognizable avatar. 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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While the typical answer is 33 beats per minute, musician Adam Neely's answer morphs into a great primer on the "perceptual present," a concept widely discussed in both the philosophy of music and of consciousness. Read the rest

The five traditional senses are tied to visible sense organs, but depending on the definition, humans possess dozens of senses, including thermoception (temperature), proprioception (bodily spatial relations), nociception (pain), equilibrioception (balance), and mechanoreception (vibration). Read the rest

M.C. Escher: Adventures in Perception (1971) is a 20-minute Dutch documentary about the artist and includes scenes of him working in his studio. From Open Culture:

Obsessed with perspective, geometry, and pattern (Escher described tessellation as “a real mania to which I have become addicted”), his images have, by the count of mathematician and Escher scholar Doris Schattschneider, led so far to eleven separate strands of mathematical and scientific research.

The twenty-minute Adventures in Perception, originally commissioned by the Netherlands’ Ministry of Foreign Affairs, offers in its first half a meditation on the mesmerizing, often impossible world Escher had created with his art to date. Its second half captures Escher in the last years of his life, still at work in his Laren, North Holland studio. It even shows him printing one of the three titular serpents, threaded through a set of elaborately interlocking circles, of his very last print Snakes. He never actually finished Snakes, whose patterns would have continued on to the effect of infinity, and even says here of his officially complete works that none succeed, “because it’s the dream I tried for that can’t be realized.”

(via Neatorama)

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Water is viscous. With heat, the viscosity drops. And you can hear the difference in its splash.

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Induced dissociative states are the best dissociative states, and one cheap and easy way to get there is to stare into someone's eyes for about ten minutes. More researchers are looking into the phenomenon. Read the rest

Since Cory posted about the Deep Dream image recognition algorithm last month (and Rob earlier today) it's inspired an explosion of iterations like Roelof Pieters' DeepDreamed Fear & Loathing in Las Vegas. Read the rest

This unscientific but fun timed eye test asks viewers to guess which square is a slightly different shade than the others. Prepare for a minute or so of eye-melting challenge! Read the rest

This video explains the weirdness of the McGurk effect, a perceptual illusion demonstrating that understanding speech is not just about what we hear, but also what we see. You can learn more about the McGurk effect at Yale's Haskins Laboratories dedicated to the science of the spoken and written wordl. (via Imaginary Foundation) Read the rest

I really love the research that they're doing over at Yale's Haskins Laboratories: instead of studying speech perception and production in terms of faithfully replicating alllll of the sounds we make with our mouths, (like the minute clicks, pops, and hisses of consonants), the team is proposing that all we need to understand speech is to track and re-create a few select resonances of the vocal tract. I like to think of speech production in this context as a series of bottles with varying levels of water in them--the mouth is one bottle that changes pitch resonance when you move it to open it or close it, the nasal cavity another, and so on throughout the vocal tract. It ends up sounding like a bunch of complicated melodies that are then combined into a complex micro-tonal harmony, a.k.a., we're all better at perceiving and making music than we think we are!

The examples below break it down into isolated sine-wave patterns that you can combine yourself to build a sentence. What do you think? How easily can you hear words emerge?

Tone combinations

Play Tone 1 alone | Play Tone 2 alone | Play Tone 3 alone | Play Tones 1 and 2 together

Play Tones 1 and 3 together | Play Tones 2 and 3 together

If you like this, you can go here for more interactive demonstrations, or check out this great sine-wave-synthesized Robert Frost poem.

Thanks to Robert E. Remez, as well as Phillip Rubin and Jennifer Pardo at Haskins Labs for allowing me to embed their work here. Read the rest

BB guestblogger Andrea James on Wendy Carlos' experiments in color perception.