Simulating the corners of my eyes.
October 1, 2007 9:14 AM   Subscribe

Possible-Neuroscience-filter: How can I simulate the way things look through our fovea vs. through our peripheral? Using Photoshop.

I'm really interested in how 95% of the "pixels" of our eyes are in the center. I'm constantly trying to "look" at the corners of my eyes to see how I actually see things that I'm not looking at.

Would anybody be able to give me a rundown on the qualities our peripheral has that our fovea doesn't so I could whip up a Photoshop simulation? I feel it would be a great tool for understanding what people may experience when looking at any artwork I create.

My best possible answer would be like: "The peripheral doesn't have as many rods so detail would be blurry, however it has just as many cones so color would not be blurry." The more specific you can be, the better (but I'm not a neuroscientist, just a designer).
posted by Brainy to Science & Nature (4 answers total) 5 users marked this as a favorite
Alrighty. The difference comes down to rods and cones. Rods have a lot of convergence in the neural system (aka. they sum the input from a lot of areas on the retina/visual field) so they have greater sensitivity, so that in dimmer lighting situations, they can see more. However this convergence decreases the spatial resolution/acuity that can be seen, so things look blurrier or even individual points of light may be summed to look like 1 light source, not 2 (etc.). The cones are the opposite, they have very little to no convergence (especially in the fovea) and so they have great acutiy and can see fine detail, which makes the pictures look very sharp and clear. However, they have low sensitivity, so in the dark, you can't see much with your fovea.

In addition, you have the role of color. There are 3 types of cones in normal color vision people's eyes, most color blind people have 3 as well, but some have 2 and monochromats have only 1. There is only 1 type of rod, this is why it is said your cones do your color vision. However, the rods respond best to the blue/green area of vision, which is why at night, when you are mostly using the rods, the world seems much bluer/greener.

Your fovea only has cones, your periphery has mostly rods, with a few cones. In addition, as you go out in the periphery, you tend to have fewer receptors of any types, making vision "blurrier" out there. So apply all the above to this and use that to make your simulation.

How to do that in Photoshop, I don't know, I just teach Perception to college students : )

(obviously this is the simplified version of vision, which is all I think you are looking for).
posted by JonahBlack at 9:25 AM on October 1, 2007

These eye disease simulations may be of interest. Age related macular degeneration is close to what you are looking for.
posted by roofus at 2:07 PM on October 1, 2007

Desaturate the edges using the sponge tool (not too much -- it shouldn't be grey). Add a blue/green hint to it, and a slight bit of fuzziness (blur tool).
posted by flibbertigibbet at 6:42 PM on October 1, 2007 [1 favorite]

What other people said, especially JonahBlack's excellent answer. So, I'll just address this one point.

I'm constantly trying to "look" at the corners of my eyes to see how I actually see things that I'm not looking at.

While an interesting exercise, I don't believe that seeing out of the corner of your eyes is actually a good simulation of what it is like to see out of rods. What you're describing is a case of attending to the peripheral visual field while fixating your gaze on the centre of your visual field -- rather different from seeing out of your rods.

In fact, even what you see right in front of you isn't as stable as you think. At any given moment, what you perceive in your visual field is, roughly speaking, actually a mental construction of many tiny images resulting from your eyes constantly moving around (saccades). Even when you think you're stably fixating on a point, your eyes are actually moving very, very fast! In fact, it's actually impossible to see anything unless your eyes are saccading.

A closer approximation of seeing with your rods would be night-time vision. Cones are not as sensitive to light as rods are -- that is to say, cones need more light to be activated than rods. So, in low-light conditions, such as at night, you are really seeing out of your rods than your cones. Since rods have lower resolution, things look blurrier at night. Since rods are more sensitive to the blue end of the visible spectrum, things tend to have a bluish tint (you've probably noticed that shading night scenes with a deep blue tends to look better than shading them with black). This is pretty much what JonahBlack has said already.

roofus's link to the image simulating macular degeneration would probably work for you, too, since it is a condition that damages the foveal region, but not the periphery.

In my opinion, for the purposes of your art, it might be more interesting to consider other mechanisms involved in the visual process rather than limiting yourself to rods versus cones. Most people don't really see the world like the picture for macular degeneration, and your artworks are not really perceived like that, either -- the fact that, as you say, 95% of the pixels are located in the fovea is easily compensated by the rest of your visual system! I feel that, if you really want to go after how people consciously perceive your art, you need to look into attention; rods and cones are only a small part of a very long story.

But that's just me. :-)
posted by tickingclock at 2:42 AM on October 2, 2007

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