How to cheat on your next eye test

Next time your at the Department of Motor Vehicles renewing your driver's license, don't be surprised if you see people in the lobby staring into spinning spirals just before they take their eye test.

Why? It turns out an old favorite illusion, referred to as the "expanding motion effect," can induce increased visual acuity. This illusion is demonstrated in the Exploratorium's "Depth Spinner" Science Snack. It's a perennial favorite among visitors to our ExploratoRio Open House event.

In any case, researchers at the Universities of Glasgow and York incorporated use of the illusion with eye chart tests.

The team discovered that visual acuity—the ability to see fine detail—can be enhanced by an illusion known as the ‘expanding motion aftereffect’. While under its spell, viewers can read letters that are too small for them to read normally.

When participants stare at the center of a spinning pattern that spirals inward for about 30 seconds, shifting their view to a stationary object will induce the illusion that the static object is expanding.

Participants who started with normal visual acuity and saw [inward spinning] spirals ... showed improved visual acuity.

It's as it they were looking through a camera and zooming in on the smallest letters in the eye chart.

It is important that the spiral is spinning inward. Staring at an outward spinning spiral induces a shrinking effect.

Those who saw [outward spinning] spirals ... actually performed worse after exposure to the spirals.

Anyone who's enjoyed this illusion knows the effect is temporary.

But don’t throw out your eyeglasses just yet: the researchers note that the overall boost to visual acuity is small and fleeting.

I would not have expected this outcome. Hat tip to Richard Wiseman's appearance on Skeptics' Guide to the Universe. The Sun ran an article with the obligatory animated spinner.

Illusions on Rainy Lake

I spent part of my vacation with my son and other family and friends fishing. We were staying on the shore of a very large body of water on the Minnesota/Canadian border called Rainy Lake. The weather, fishing, and companionship were all fantastic. One morning the winds were very light and  the sun was shining over the chilly lake water. I noticed something strange on the horizon. There appeared to be trees floating in the sky.

This did not look like the typical mirage. I recalled something about a type of mirage that is often seen over ice or cold bodies of water. I kept a watch on the horizon as we pulled one walleye after another into our boat. I had my Cannon HD video camera that can take pretty good 8 MB low-light stills. Over the next hour or so I took pictures of some other strange sights on the horizon.

Some small islands and parts of the shoreline joined the trees in the sky. We were witnessing the formation of superior mirages. These form when there is a layer of cold air below a layer of warm air. The cold lake water was keeping the air near it cooler than the air above, forming a temperature gradient known as an inversion layer. Light from distant objects was bending down as it encountered the less dense warmer air. The path of the light from the objects can follow the curvature of the Earth, allowing objects beyond the horizon to be seen. This effect can be demonstrated by partially dissolving sugar or corn syrup in an aquarium. If done carefully, the density gradient of the sugar mimics that of the inversion layer, causing the path of a laser beam to bend down.

Inversion layers are stable, allowing the mirages to be seen for long periods. They also lack the shimmering of inferior mirages often seen on the road on a sunny day. This makes superior mirages seem more real and provoked an eerie feeling. Some of the images I had a hard time explaining. This one shows a superior mirage forming in front of an island.

On returning from my trip I did some reading about mirages to learn more about what I had seen. Superior mirages have been reported throughout history and have sometimes altered it. Early explorers trying to find the Northwest Passage turned around when they saw a mountain range looming in the distance. Later explorers returning to the same place saw no mountains. They had probably been discouraged by a complex superior mirage known as a Fata Morgana. Another stranded group of arctic explorers saw the polar night end two weeks early when the sun formed a superior mirage over the ice. In fact, anytime you watch the sun rise or set its image is being refracted around the curve of the Earth by the density gradient always present in the atmosphere. This is technically not a superior mirage because the density gradient is pressure, not temperature-based but the effect is the same.

There are other fascinating stories of superior images and Fata Morgana sightings that are worth reading. I found the Wikipedia article about mirages and Fata Morgana useful, as well as this website and this one. I am now better prepared for the next time I observe this unusual phenomenon. Another illusion on Rainy Lake was self created. When posing with my 23-inch walleye, we found we could make it look a lot bigger with some creative posing. If anyone from the Fish and Wildlife service is reading this, we did throw it right back in the water.

Fibonacci zeotrope sculptures

Sorry for the sudden aggregation binge. I should be working on my genuflection to The College Board (AP Physics 1 and AP Physics 2 syllabi), but my motivation for that exercise is so. very. low.

In the meantime, let's enjoy this confluence of Fibonacci numbers, 3D printing, and stroboscopy, shall we?

This San Francisco Globe article introduces it nicely.

And, of course, video.

Fibonacci Zeotrope Sculptures


Fibonacci Zoetrope Sculptures from Pier 9 on Vimeo.

"These are 3-D printed sculptures designed to animate when spun under a strobe light. The placement of the appendages is determined by the same method nature uses in pinecones and sunflowers. The rotation speed is synchronized to the strobe so that one flash occurs every time the sculpture turns 137.5º—the golden angle. If you count the number of spirals on any of these sculptures you will find that they are always Fibonacci numbers.

For this video, rather than using a strobe, the camera was set to a very short shutter speed (1/4000 sec) in order to freeze the spinning sculpture."

Mould's Magic of Magenta

I don't know much about this Steve Mould character, but I feel like I should. He's responsible for showing off the bead chain curiosity posted below and now (via serendipitous clicking), I come across this.

This video relates color vision back to the optical biology involved. It compelled me to learn more about cones and rods than I knew.

For example, I didn't know there was a 20:1 between these two types of photoreceptors, but there is. I'll leave it to you to figure out which is preferred. (The population of the preferred one is 90 million, vs. 4.5 million of the other.) I didn't know about S, M, and L cone types, either. Why must I get dumber as I get older?

Anyway, check out this story of color vision as told by Steve Mould. At the risk of offending fans of My Little Pony, I'm going to say that friendship is simple; magenta is magic!

Colour Mixing: The Mystery of Magenta




But what about violet? It's a pure, unmixed color with a wavelength range all its own. If magenta is triggered by [spoiler alert] the red cones and blue cones getting tickled while the green cones are not, is violet the result of a weak tickling on the blue cones while the rods are reporting plenty of light?

My ignorance knows no bounds.

Anamorphic Illusions: Cube Tape Shoe Edition

Bogged down in grades and lab manual manuscript preparations. So enjoy this gem.

Camoulopods

This nifty vid keeps popping up in my Facebook feed, and I'm deep in lab book manuscript prep mode, so here you go. If you are either of the two people who haven't seen it, take a look. It's one of Lichtman's best, and it is worthy its "groovy" tag. NPR's Science Friday does it again!



The fact that I've got a big nerdcrush on Flora Lichtman is entirely beside the point. Still though, she is pretty dreamy!

Color illusion

Saw it. Liked it. Enough to post it.



(I recommend downloading before showing in class so as to avoid pop-up ad distraction. You definitely want to go full-screen.)

Having posted it, I now run the risk of being deluged with the comment, "I've seen that one a million times." If that statement captures your sentiment, felicitations! And you've been spared from the chore of commenting.

Due to some flaw in my character, I hadn't seen it before and was so struck that I was compelled to share. I tried recreating it with a photo of my own and it worked, but not as well.

I'm conversant in chromatic retinal fatigue, but there's a wee bit more going on here.

The classic chromatic retinal fatigue illusion is to stare at a color negative of a US flag, for example, then at a white surface. You see a ghostly Old Glory in its standard glory.

But look at the color negative here. Seems to be just orange and blue. The orange becomes the blue sky. But the blue? Curious.

Follow this link to see some illusions you've seen a billion times!

PTSOS2: Heat Waves in Sacramento

Despite the chilly tule fog, a group of physics teachers gathered to discuss the pedagogy of heat and waves at Rio Americano High School yesterday. It was PTSOS2: Give Physics a Whirl.

We ran through kinetic theory, temperature, specific heat, and heat transfer in the morning. Demonstrations were demonstrated, with presentation tips aplenty. Corresponding presos were presented (with my usual admonitions about how bad PowerPoints can be). Lab activities from the Conceptual Physics Lab Manual: Activities · Experiments · Demonstrations · Tech Labs were discussed and summarized.

Specifics included conductometers, radiometers, radiators, Miracle Thaws, and many others. We can never resist the Leidenfrost effect. (A full episode of Jearl Walker's Kinetic Karnival is devoted to this topic.) That led us to busting the paranormal explanation of firewalking.

One highlight was Steve Keith's Rubens' Tube.



During lunch, we were treated to a surprise visit from the Physics Go Girls (Morgan and Riley), who brought treats. With their chartreuse db-T's, they could have been seen from outer space.



Their customized carbohydrate comestibles were enjoyed by participants and workshop leaders alike.

After lunch, we launched into mechanical waves and sound. We discussed the connection of vibrations to waves (without getting bogged down into the robust details of simple harmonic motion). We delved into the Bell Labs wave machine, a Doppler rocket, PhET sims, WavePort, and others. I really like WavePort for creating and analyzing sounds.

A roommful of Talkie Tapes was too silly to not take a video of.



The fact that some users often mishear the word "fun" led us on a tangent of audio pareidolia. Our visit to Jeff Milner's Backmasking website resulted in laughter (wincing, cringing) of varying degrees of propriety.

Steve piped some heavy gas (the eco-friendly freon replacement) through a song flute (recorder) so we could hear the difference that makes. Much like the Mythbusters Fun with Gas clip.

We ended the day with the real make-n-take: Steve Keith's newest and improved-est version of the ever-popular String Thing. (Here's the Exploratorium's version.)

I couldn't resist slowing the finished product down with my compact FH-100.



It was a great day! More photos can be found at my Flickr site.

PTSOS is sponsored by the NCNAAPT and made possible by a grant from the Karl L. Brown Memorial Scholarship fund.

The World Spins Madly On

I was a fan of Mad Magazine in my youth. I'm a fan of the Weepies now. I'm a fan of the Exploratorium and their clever optical delusions. And Halloween is coming.

With all that in mind, click this link if you dare. (And be patient. It will need several seconds to load. Don't worry: your money back if you're not satisfied!)

Best. Color. Illusion. Ever?

There is no blue in the spiral pattern below. Truly.


The Bad Astronomer, Richard Wiseman, and Buzzhunt have all the details.

Go ahead and load it into Photoshop and check the values to see for yourself. The bright color in the blue spiral is identical to the bright color in the green spiral.

The Bad Astronomer (Phil Plait) and Richard Wiseman are regulars at TAM, by the way. They never fail to bring a heaping helping of groovy.