May 5, 2011 | David F. Coppedge

The Eyes Have It: Pro Software

You have a biological version of Photoshop in your eyes.  That’s what Richard Robinson, a freelance science writer from Massachusetts, said in PLoS Biology.1 

The eye is not a camera, and the retina is not a piece of film.  Indeed, the retina might be better likened to a computer running Photoshop, given the extent of image processing that it performs before passing visual information along to the brain.  A central aspect of that processing is called center-surround inhibition, in which illumination stimulates the firing of a small number of retinal cells, accompanied by inhibition of surrounding cells.  This phenomenon increases spatial contrast and sharpens perception of edges.

Robinson was discussing a new find from UC Berkeley that the retina employs both positive feedback and negative feedback systems to improve imaging, something that researchers had missed before in 50 years of study.  (See also Robinson’s article about cell zip codes last month: 04/20/2011).
    Medical Xpress has a graph showing how these two independent mechanisms work together.  “The human eye long ago solved a problem common to both digital and film cameras: how to get good contrast in an image while also capturing faint detail,” the article said, with the headline announcing that the eye does the better job.
    Speaking of vision, eyesight has been found where biologists might have least expected it – in sea urchins.  National Geographic News reported that work by European scientists publishing in PNAS2 shows that the spines transmit light to the animal, making these pincushion-critters like big eyeballs on the seafloor; “we suggest a model in which the entire sea urchin, deploying its skeleton as PRC [photoreceptor cell] screening device, functions as a huge compound eye,” the authors said.


1.  Richard Robinson, “After 40 Years, Retina Reveals It Uses Positive Feedback, as Well as Negative,” PLoS Biology, 9(5): e1001058. doi:10.1371/journal.pbio.1001058.
2.  Ullrich-Luter et al, “Unique system of photoreceptors in sea urchin tube feet,” Proceedings of the National Academy of Sciences, pprint May 2, 2011, doi: 10.1073/pnas.1018495108 PNAS May 2, 2011.

WYSIWYG-BWYGINWOT: What you see is what you get, but what you get is not what’s out there.  This bears on old philosophical questions about perception, sensation, and correspondence.  If what we get has been Photoshopped, what would it look like before the image processing?  It would probably render life impossible, because we would not be able to make sense of the world.  The Creator has given each creature what it needs to carry on its life.  For that we should remain thankful, and amazed.

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