Swim enjoys psychedelics. One day Swim was describing to me the effects that psychedelics have on color perception, and it got me curious about the visual system, and how it encodes what we see as colors. I've been trying to understand how our visual system works, and it inspired me to type this out. I've done my best to offer an accurate account of whats going on, but as I'm not formally educated on the subject just yet, there might be some minor misconceptions. If you notice any, I ask that you please point them out...I encourage polite criticism! Please let me know what you think, add any related information, and/or your own perspective on the topic. I'm really interested in learning all that I can about this fascinating subject. :thumbsup:
(anything that adds to this subject, please post in the thread I started...simple discussion is fine, but I don't want to distract people from the actual thread I made...I just like to add my favorite posts to my blog )
So if you haven't guessed by the title, I'm rather intrigued by the nature of color. I often find myself asking questions that most people laugh at me for even pondering. What is color? How do we go from a wave frequency of photons, to our perception of color? How do we communicate our experience of color? At first glance these questions might seem easy to answer, or even obvious. However, upon further meditation we encounter very real problems when it comes to our subjective experiences, that begs the question, "Do we even see the same colors as one another?"
When we look at something, we aren't seeing the actual object being observed. We are seeing photons that have reflected off of the object. If an object is blue, it absorbs all frequencies of light, except those needed to make the color qualia blue (qualia is a term used to define the subjective experience of a quality). These electro-magnetic wave/particles of light then make contact with the receptors in our eyes. The photons make contact with cone photoreceptor cells, which depending on what color the pigment is in the cone cell, will absorb the light (essentially it's red, green, and blue pigment...but more specifically they are ranges of frequency that cover slightly more than just those colors, referred to as short (S), medium (M), and long (L)). By the activation of these three photoreceptors at varying levels, our brains are able to create the range of color qualias that we perceive.
Once the photoreceptors are activated by the absorbed light, the signal is translated, via bipolar cells, into an action-potential that can be interpreted by the brain. The bipolar cells activate the retinal ganglion cells where the signal then cascades down the optic nerve, to the optic chiasm where the two optic nerves meet and signals from the contralateral visual field cross, and becomes the optic tracts. The optic tracts then project to the Lateral Geniculate Nucleus (LGN) of the Thalmus (with a few branches to other nuclei). The pathway to the LGN that carries most of the information of the stimulus' wavelength is the parvocellular pathway (P-pathway). Along this pathway photon frequencies are deciphered by differencing through center-surround antagonization with red vs. green wave-lengths and blue vs. green/red wavelengths.
From the LGN the signal branches off into what's known as the optic radiation, or geniculostriate pathway, that projects primarily to the primary visual cortex (V1) in the back of the brain, but also to some extrastriate areas. Once in V1, color encoding becomes far more complex and still isn't completely understood, but it involves determining hues. This is where our subjective experience of color seems to be encoded...though further color processing takes place in extrastriate areas, such as V4, as well.
But what's really interesting is that all of our brains are networked a little differently. Not only are our brains networked differently, but different gene variations cause neurons to behave differently, which causes the structures and outputs of neurons to vary from person to person.
So how is it that we can subjectively experience the same color qualias as one another if our subjective experience of those colors is dependent on how the stimuli is encoded in the brain, and each person's brain is different?
Well, the only real argument as of yet, that I'm aware of, is our ability to communicate the experience of color. When I say I see the color blue and point to a blue object, you too would respond that it's blue. This is because we as humans have evolved to communicate most effectively. In reality, all this tells us is that the same photoreceptors are being activated in the eye, and the parvocellular pathway is calculating the ratios of receptors that are activated. If you remember correctly, it's not until the signal reaches the complex network of the occipital lobe that the information is more accurately analyzed and encoded. The only thing that the P-pathway does is determine what frequency of light hit the retina by differencing what color cones were activated in the area corresponding to the location of that object, which also allows us to distinguish between warm (red, yellow, orange) and cold (blue, green, violet) colors. This doesn't have anything to do with our subjective experience...only with our ability to effectively communicate those experiences.
If someone were to receive damage to an area encoding color, they would only be able to see the world in black, white, and shades of grey. This person would still be able to distinguish between colors, because the photoreceptors in the retina, as well as the neurons in the LGN, are still intact, but they wouldn't be able to identify hues. This type of agnosia is called cerebral achromatopsia. What's truely remarkable is that patients with this type of brain damage not only can't see color, but also cannot remember or imagine what color would look like. Patients with cerebral achromatopsia describe the world as being dull, dreary, or depressing, but don't generally understand why.
Oliver Sacks and Robert Wasserman published a case study titled, "The Case of the Colorblind Painter," where they described this agnosia in the patient Jonathon I.. The authors wrote:
So, upon further meditation, it would seem that we have no grounds to reasonably assert that the color qualia that I perceive as, lets say green, is the same qualia that any other person would perceive. We simply evolved to effectively communicate our experiences of photon frequency with one another. I'm not saying that this is scientific fact, but it is a major problem when it comes to philosophy of mind, and has yet to be resolved, despite the exponential growth in our understanding of the brain.
Originally posted here: http://www.drugs-forum.com/forum/showthread.php?p=837772#post837772