Why do we see things?

Reply Sun 9 Aug, 2015 10:24 am
Taking a nap in a college darkroom once, even after a couple hours my presumedly fully dilated eyes couldn't see a thing. With no self-correcting cues I found it very difficult just getting out of the room without wobbling and steadying myself. It raised a question in my head though: what is it about light that enables us to see things illuminated by it?

Light propagates out from its' source as a wave and a particle (we'll skip the qm lecture.) Smile So it's illuminating things by smashing its' photons onto or against things being illuminated (like if we shine a flashlight onto something, photons are emitted striking the object.) But then what happens that we can see the object? Are the photons bouncing off and into our eyes? Why would that enable us to see the thing being lit? Wouldn't a photon be a photon regardless? Or is some information from the object being copied onto the photon so when the photon enters our eye we see that one photon's worth of the object like a single pixel?

Or is it that the molecules of what's being illuminated are being charged or having their energy state increased making them visible? The photons are being absorbed as well as reflected, but the thing being lit is becomming 'glow in the dark' like?
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Banana Breath
Reply Sat 3 Oct, 2015 05:40 pm
Yes, the photons bounce from objects into your eyes, striking the retina of the eye. The retina is basically a part of your brain with cone and rod cells specialized to react to different wavelengths and intensities of light. The activation of these cells passes into the occipital/visual cortex at the rear of the brain; the information is retinotopically mapped, meaning it maintains the same X-Y relationships in that region of the brain that it did in the visual field, thus preserving adjacencies of information. The visual cortex is then "read" in parallel by various regions of the brain. Some regions are basically doing pattern matching, trying to identify familiar shapes (the "what") while other parts, particularly in the parietal lobes, are concerned more with the location of items (the "where"), sorting things as to near and far, left and right, approaching or moving away, while other parts are looking for associations ("that looks like a dog, dogs have been mean to me in the past").
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