Wednesday Landscapes, 31 January 2018

[Leslie Reid]

I’m still contemplating contemplative landscapes from last week’s discussion, and this isn’t one of them, though I’ve spent a fair bit of time contemplating it. I can’t figure out why the sand ripples seem to shimmer when I look at the tracks.

 

[Gup]

Hello all. It's a bit blustery here this morning.

 

[michaellinder]

I’m still contemplating contemplative landscapes from last week’s discussion, and this isn’t one of them, though I’ve spent a fair bit of time contemplating it. I can’t figure out why the sand ripples seem to shimmer when I look at the tracks.

 

[ATTACH=full]1230496[/ATTACH]

 

Maybe because of the limited highlights within each of the tracks?

[michaellinder]

From Red Rock Canyon, Nevada . . .

[paul_hoyt]

Sort of an answer, if you Google Rotating Optical Illusions, you will se objects that appear to rotate, but they are not. It is the close juxtaposition of the light and dark ripples, very similar to the rotating gears, that trick the eye.

[Andrew Gosden]

[sjmurray]

Patterns and textures in nature certainly catch the eye. I'm sticking with the animal track theme with the only "landscape" type photo I have with animal (deer) tracks. Shot with medium format film along the Mississippi. There's also the textures of the sand ripples under the water.

[Bill Bowes]

Out of breath at 10,000 feet, a bit nippy for Hawaii (37f) but Wow ! Fuji XE-1 & Minolta MD 50. Aloha, Bill

[Deborah Vallette]

[Glenn McCreery]

Leslie - I find an explanation for your fine example of a "Venetian blind" or "McKay" illusion, where a series of high contrast lines induce the illusion of motion perpendicular to the the lines in, " Illusory motion in Enigma: A psychophysical investigation ". The authors explain that "...The perceived illusory activity is believed to be a consequence of neural signals emanating from high-contrast bars and edges in the image that emit randomly fluctuating signals, as expected from spiking cortical neurons. These fluctuations may induce illusory motion....". Note that the illusory motion is only in the high contrast regions of you sand ripples, and not in the low contrast regions.

 

There are other examples of the McKay illusion and similar illusions in the wonderful book, "Vision and Art, the Biology of Seeing", by Margaret Livingston, Harry N. Abrams, Inc., New York, 2014

[Glenn McCreery]

Here is my own example of the illusion using a rippling sand dune (with my dog running across it), although the illusion is not as intense as in your photo. Stare at the mid-distance footprints for a few seconds to see the effect.

[Bill Bowes]

Hope this one "warms" all you soul's in the frigid climes. Aloha, Bill XE-1 & 16-50mm

[western_isles]

I’m still contemplating contemplative landscapes from last week’s discussion, and this isn’t one of them, though I’ve spent a fair bit of time contemplating it. I can’t figure out why the sand ripples seem to shimmer when I look at the tracks.

 

[ATTACH=full]1230496[/ATTACH]

I think that this is a classic case of the wonder of natural light. Terrific image.

[Leslie Reid]

I find an explanation

Many thanks, Glenn! A really interesting paper--thanks very much for the link. And the Livingston book is one of my favorites. I had read up on the McKay illusion, but hadn't been able to figure out how it translated to the lateral oscillations I was seeing in the photo. After reading the paper, I suspect that what I'm perceiving as a lateral oscillation is actually a secondary illusion created by the McKay illusion of motion along the vertical lighter bands--as something dark appears to move vertically along the lighter band, my peripheral vision interprets the dark band as broadening slightly, then contracting, creating the oscillation. Now I'm wondering if vision is more sensitive to horizontal motion than to vertical motion (which would make evolutionary sense)...back to the Livingston book...and back to Lightroom to turn the image onto its side and stare at it some more...

[Glenn McCreery]

Leslie - I tried your suggestion of turning your photo on its side and staring at it. I still see the oscillations perpendicular to the bands, but perhaps a little bit less intense than in the original orientation? It is hard to tell, since if I stare at the bands themselves, rather than at the central footprints, the illusion disappears from my central (foveal) vision. The illusion, like Mona Lisa's smile, only appears in peripheral vision.

 

I don't see any motion along the vertical lighter bands, just perpendicular to the bands. I tried pasting a strip of uniform light color both parallel and perpendicular to the bands to see if I could induce a McKay illusion of motion along the strip, but was unsuccessful. Perhaps the illusion would depend on both the width of the strip and the luminosity? Something(s) to think about.