The tricks our brains play on us…
[via Gizmodo] The Most Wicked Optical Illusion I’ve Seen So Far
This is sick. Sick because the spiral effect is making me sick and sick because it reminds me how flawed/awesome/trippy our color perception is. Believe it or not, the green and the blue in this spiral is the same color.
I couldn’t believe it either, but I just measured the value in Photoshop: Red 0, Green 255, Blue 150 on both. Crazy.
The reason why we are perceiving one color as different colors is because of the other colors surrounding the stripes. Each eye has six to seven million cones, which are concentrated in a central yellow spot known as the macula (I recently got mine lasered to fix some leaking blood vessels). These cones measure color in different wavelengths, overlapping in some of them. Our brain then compares those signals in an antagonistic manner, measuring differences in wavelengths between them. When some colors are combined, the brain can’t process the info from the cones correctly and we simply get confused. [gsu and Techi] [Read More]
Just never get old.
Thank goodness for it!
(PhysOrg.com) — Flies like watching computer screens as much as the next animal. Set them on a trackball in front of a monitor, and they’ll follow the action – if the images in front of them move in one direction, the flies will try to move the same way.
That’s because flies – like humans, monkeys, birds and a host of other animals – can perceive what researchers call “phi motion.” If a bright point appears at one position, and then reappears at a position shifted to the right, we tend to see a single object moving left to right. It’s a basic effect, and one that underlies the apparently fluid motions we see in movies and animations.
But all of these animals also perceive an odd “reverse-phi” illusion. If the second point we see is the opposite of the first – with a dark point becoming light, for example – we see motion away from the second point, rather than toward it.
For years, researchers thought this second illusion was an artifact of “normal” motion vision, and was not involved in real motion perception. The effect, it was argued, simply wouldn’t appear outside a laboratory setting.
Now, a group of Stanford biologists, physicists and computational scientists are turning this view on its head. In papers published last month in the journals Neuron and Proceedings of the National Academy of Sciences, researchers demonstrate that this and other illusions appear integral to how fly brains process motion. And in doing so, the scientists may have come up with a new understanding of how we see movement.
Dissecting the circuit
“Motion vision is one of the more basic things that our brains can do,” explained Thomas Clandinin, associate professor of neurobiology and a senior author of the two studies. “Nearly everything that has an eye uses it.”
But judging motion can be more difficult than it sounds. The problem is essentially one of correlation – the brain needs to associate changes in one part of the visual field with changes elsewhere.
How this is accomplished isn’t fully understood, even in simple animals like fruit flies. But we do know that a fly brain’s first step should be to distinguish between different types of contrast changes.
In fact, fly photoreceptors appear to send visual motion information to the brain down two separate neural pathways. One pathway responds to dark edges moving onto bright backgrounds, while the other reacts only to the opposite: bright edges moving onto dark backgrounds.
Researchers initially proposed this was a case of “on” and “off” pathways – the neurons in one pathway should respond to darkening, while neurons in the other pathway should respond to brightening. But Damon Clark, a postdoctoral scholar in neurobiology and primary author of the Neuron paper, found an alternative explanation.
“That model is a perfectly good way to be selective for dark and bright edges,” explained Clark, “but there’s another way that appears to actually be encoded in the circuits.”
Instead, what seem to distinguish the pathways are their responses to the reverse-phi illusion. One pathway is responsible for recognizing dark-to-bright changes, while the other responds to bright-to-dark shifts.
With computer modeling, the researchers showed that this kind of selectivity was enough to explain the flies’ ability to distinguish between edge types. Clark had noticed that reverse-phi motion wasn’t just a special type of motion – it takes place every time an edge moves across a background.
When a dark edge is moving to the right, a fly brain could look at it in the “phi motion” way: dark points on the left are followed by the appearance of dark points on the right. But by looking first at the bright background, the fly brain could also see a signal in the opposite direction – the bright points on the right are followed by dark points on the left.
What was thought to be a laboratory artifact was, in fact, happening in the real world. And, in context, this seemingly bizarre reversal of direction was perfectly reasonable.
As Clark put it, “If reverse phi, as unintuitive as it appears, is actually useful to extract motion from visual scenes, then what other structures could be used to help perceive motion?”
“Illusions in general may just be natural signatures of motion taken out of context,” said Fitzgerald.
This offers an explanation for a host of other questions about visual perception, including a long-debated class of motion illusions called “non-Fourier motion.” When humans look at these displays, they perceive movement – but traditional, two-point models of motion perception see them as motionless.
“This model is completely general,” said Clandinin. “It provides a framework to think about not just the reverse-phi illusion, but every motion illusion that’s been observed.”
Clark and Fitzgerald are now in collaboration, testing the model’s predictions for fly behavior. Their research is supported by a National Science Foundation Integrative Graduate Education and Research Traineeship from the Stanford Center for Mind, Brain and Computation. Mark Schnitzer, associate professor of biology and of applied physics, was also a senior author on both studies. [Read More]
Recent collaboration with incredible painter and artist Alivia George, this video revisits the concept of film as a poem, a first person viewing experience, a waking dream. The phi phenomenon, as it’s called in Gestalt psychology, is what allows us to perceive motion pictures through persistence of vision, the same thing that makes us see any optical illusion. Without us trying, without even realizing, our brains substitute what we don’t see with something else. The flicker between each frame of a film is imperceptible, but it’s there. We see uninterrupted movement, this series of pictures flashing before us becomes a world all our own. Consciousness becomes subconscious, truly we enter a state of mild hypnosis.
Indeed it was even Lucretius the roman poet who discovered persistence of vision, using it to explain the stories and journeys we all experience through the images of our dreams. Turn off the lights, put this on full screen and allow yourself the experience, the experiment of the next 6 minutes. Remember ‘movie’ is just short for moving picture, picture comes from ‘pingere’ Latin for paint or ‘pict’, ‘pik’, ‘pig’ – pigmentum. We’re all just monkeys anyways.
After all, I do not have to understand it HOW it is happening…
To appreciate it.