light perception

[Pizzabeak]

why are we able to see in a dark room? after our eyes adjust to the darkness via rods/cones you can still see stuff like the dresser or a pair of shoes on the ground. i'm guessing there's still some minute source of visible band radiation in the area. this is different from being in pitch black darkness in which no light is present, i'm guessing: a casket, a forest with the sky covered by thick trees otherwise starlight may be noticeable unless said forest is located in a particular location which prevents clear weather(etc), or deep within the ocean where light apparently has a tough time penetrating.
in a dark room, while objects can be made out, if one had infrared thermometers then more detail of the objects could be made out (any other implications?)... apparently room temperature objects emit radiation in the infrared. however, it is still possible to make out the objects due to rods and cones. i would have to guess that there is still some source of visible light available, perhaps the light is on in the kitchen or some light is getting in through somewhere.

if the sun emits mostly visible light, what is the process of seeing stuff? the waves or photons hit an object, bounce off/reflect/get absorbed & emitted which then enter our eyes due to the sheer amount and we have this ability to process it and make out the overall idea of the object that is reflecting the radiation into our eyes? any discussion might be helpful, and appreciated.

 

[Whizzer666]

Actually, Sol emits far more energy along the electromagnetic spectrum than we could ever see....

 

[Pizzabeak]

explain yourself
i'm not exactly sure what that statement does. i'm sure our sun emits more than just visible... so collectively there's an assortment of light being put out? ultraviolet, x-rays, gamma rays, you're saying? either way, there's still visible light which we rely on by default. it's not like we're walking around looking at clouds of plasma in space with our x-ray vision.

so suppose as humans we used x-ray or gamma radiation to see... would that mean a source would be pumping that out and it would enter our eyes and begin the process, allowing us to see whatever it was previously reflected off of? the source could also emit in the visible band but since we use x-ray or gamma (take your pick) to see, i guess we would just mostly feel the visible light as heat?

i was wondering, in relation to blackbody radiation. people and objects generally emit (?) in the infrared mostly due to temperature. in a dark room with night vision goggles you can see a lot better than relying on the available visible light based off the infrared radiation the stuff is emitting. i'm sure you can start to feel infrared as it nears the visible band. raise the temp enough and you can actually see the radiation since that's what we are adapted to. in a dark area, if someone makes a fire, that would be our source of light. it'd be small yes, but that's because the log fire isn't as big as a star. i'm guessing the fire illuminates near objects via the particles being absorbed and re-emitted and then entering our peripherals. similarly if you raise the temp even more the fire goes from orange to blue to violet, then ultra violet... which some people can apparently see due to having some extra stuff in their eyes supposedly.
so if some mutant ended up having a system most sensitive to x-ray radiation, would he be blind if he was living on earth? would he just not be able to use visible light? would he have to walk around with an x-ray lamp and shine it on stuff he wants to see, and even then if he shone it on a person would he just see the body outline and mostly skeleton? i'm sure there a few intricacies that need to be brought up.

 

[Montresor]

why are we able to see in a dark room? after our eyes adjust to the darkness via rods/cones you can still see stuff like the dresser or a pair of shoes on the ground. Rods are the photoreceptors in your eyes that are used for night vision ... while cones respond to hue/wavelength, rods react to intensity. Cones offer you acuity as well; something the rods do not provide. So the effects are two-fold at least: you lose the ability to discern color/"hue" and your visual acuity plummets.....

i'm guessing there's still some minute source of visible band radiation in the area. this is different from being in pitch black darkness in which no light is present, which, in turn, is different from true darkness where no light in the visible spectrum is present.....

i'm guessing: a casket, a forest with the sky covered by thick trees otherwise starlight may be noticeable unless said forest is located in a particular location which prevents clear weather(etc), or deep within the ocean where light apparently has a tough time penetrating.

in a dark room, while objects can be made out, if one had infrared thermometers then more detail of the objects could be made out (any other implications?)... improved detail insofar as there exist temperature gradients in said blackbody apparently room temperature objects emit radiation in the infrared. Read: blackbody radiation. however, it is still possible to make out the objects due to rods and cones. Not possible for cones to function in low light. i would have to guess that there is still some source of visible light available, perhaps the light is on in the kitchen or some light is getting in through somewhere.

if the sun emits mostly visible light, what is the process of seeing stuff? the waves or photons hit an object, bounce off/reflect/get absorbed & emitted which then enter our eyes due to the sheer amount and we have this ability to process it and make out the overall idea of the object that is reflecting the radiation into our eyes? any discussion might be helpful, and appreciated.

Haven't done a color coded reply in a while so I hope you liked it.


I expect that scorpiomover will join this thread at some point and will provide four or five long deep paragraphs that answer all of your questions, however, I just want to point out a few things to steer you in the right direction; "big picture" explanations are not my forte but I'll give it a shot for the sake of self-improvement.


Key concepts for further study: retinotopic organization, thalamus, "dorsal stream", "ventral stream"


Perception, in general, follows a fairly linear process.

1. External stimulus (light) enters the body through the pupil and is focused (projected) on the retina by the lens.

2. Sensory receptors (rods and cones) are excited by the stimulus

3. A nerve impulse is generated through the action of the receptors (advanced topic - university level - very easy to forget over time ((i.e. further reading)))

4. The signals enter the brain through the thalamus (primary processing center) - bilaterally located deep in the middle of the brain, the thalamus receives input from the sensory system (i.e. via the optic or other cranial nerves, such as auditory), and begins to organize the raw data into a meaningful representation.

The thalamus is a collection of nuclei (typical usage of the word), which has nuclei for nearly every sensory system. The nucleus we are specifically concerned with is the lateral geniculate nucleus (LGN).

5. As the thalamus generates meaningful clusters of data it sends them to the primary visual cortex (VI - striate cortex) where the first levels of visual processing occur (initially, contrast between two areas of the visual field).

*I am being vague with the true functional role of the thalamus for the sake of simplicity. When I say "meaningful representation" and "clusters of data" I really mean to say that the LGN is basically bombarded with retinal information and it organizes and sorts different components of the visual picture (some data from rods, some data from cones), then sends it off to their respective regions of the brain (or pathways if you will) ... it's all sorted here, before it reaches the cortex.

This is like, first degree integration... ordering like terms , or whatever other form of simplification you prefer


Now is when any semblance of linearity goes flying out the window .....

6a. The striate cortex also sends a fair amount of visual information backto the thalamus so it can be relayed again to other areas of the perception system (namely the superior colliculus, which mediates the reflexive "turn and look response") ((this is actually a two way street))

Generally (perception = integration) and (sensation = differentiation) if you want to take a more conceptual stance.

The cortex is basically layer upon layer of cell bodies, and each layer sort of has a very specific and complicated "job" when it comes to processing the visual field. Effectively, though, just remember it simply fires an action potential when its time has come, whatever its purpose may be. Quite often it is when its (el neuron) respective visual field (see: retinotopic organization of cortex) is stimulated.

^This "layers of cell bodies" concept is crucial to the next step, in that we are setting up two distinct "pathways" of information to be processed through the "higher" regions of the cortex (i.e. further integrated into a whole) (((read: gestaltism)))

6b. Pathway 1 - dorsal stream "where and how" pathway

6c. Pathway 2 - ventral stream "what" pathway

[bimgx=250]http://www.rrnursingschool.info/nervous-system/images/8160_269_713-dorsal-ventral-visual-stream.jpg[/bimgx]

 

[Pizzabeak]

Thanks, I did like it.

Could we briefly discuss the color of normal everyday objects, including manufactured items. Sky is blue, grass is green... Some aspect of the perhaps 'chemical' composition of the item is responsible for the hue. Grass absorbs the visible light and emits/reflects mostly within the greenish-yellowish range (corresponding to whatever length nm the waves are). Perhaps this is getting a bit philosophical, but as far as blackbody radiation goes is a grass still green in a dark room or vacuum? No visible light present to make us see a green piece of grass, although, perhaps it is still "green" based off the stuff that it is comprised of which make us see green when there is light.
Furthermore, since objects are emitting infrared radiation based off their room temperature (not as hot as fire so they aren't glowing or burn when touched) what accounts for the different hues they display? Temperature gradients... Since they are all emitting infrared and if you add visible light into the mix you see different things.
There's a green bag and a purple bag. While they are both emitting infrared and are likely around the same temp we clearly see that they are different colors. Whoever made the purple one must have used a material that "absorbs and reflects purple wavelengths most efficiently." A piece of wood/cardboard must be brownish based off the atoms it is comprised of...
What about an object that is black, such as a hat or an electronic piece of equipment. If you begin to burn a piece of wood the area you applied heat to will turn black and be hotter than the rest of the material... That's also the same area that will glow red-orange when hot enough, and blue-violet when hottest... If the wood were sturdy enough we wouldn't see any glow, I guess, when hot enough via the ultraviolet band, although we would feel the heat (unless you were one of those that could see some ultraviolet, then you might be able to see some glow for a bit until the temp were raised enough to the point where you couldn't perceive wavelengths any tinier).

Are the individual hues of items we see related to blackbody radiation, or is it just due to the atoms involved - a relatively separate phenomena? Well, some items have multiple hues on them..
I think what I was trying to ascertain is whether the color of something depends on the temperature of it. In some cases apparently - red & blue stars, but a red piece of paper and a blue piece of paper is clearly a different case.
So a brown paper bag... Only starts being interesting once we light it on fire? Beforehand, blackbody radiation exists via the infrared being emitted and we can see that it is brown because all the available visible light thanks to the sun.. It must be easy for them to take advantage of this nowadays, what with all the product. Hair dye, sharpies, paint; etc. L.E.D. lights & lasers?

 

[Wolf18]

2 ideas from no expert:

1. Entropy of the object itself.
2. Element colour. (iron is red, copper is green, cobalt is blue, etc)

SW

 

[Pizzabeak]

Just kinda wanted to be more sure about some things so as to prevent false information from being spread, which isn't always a 'bad' thing I suppose.

 

[Kuu]

if the sun emits mostly visible light, what is the process of seeing stuff? the waves or photons hit an object, bounce off/reflect/get absorbed & emitted which then enter our eyes due to the sheer amount and we have this ability to process it and make out the overall idea of the object that is reflecting the radiation into our eyes?

Uh, that's basically the gist of it, yes.

so suppose as humans we used x-ray or gamma radiation to see... would that mean a source would be pumping that out and it would enter our eyes and begin the process, allowing us to see whatever it was previously reflected off of? the source could also emit in the visible band but since we use x-ray or gamma (take your pick) to see, i guess we would just mostly feel the visible light as heat?

That's a bingo!

i was wondering, in relation to blackbody radiation. people and objects generally emit (?) in the infrared mostly due to temperature

What do you mean "mostly due to temperature"? It makes no sense. All light is radiated, the energy of which, when it hits/traverses another material and is absorbed, becomes heat.

ultra violet... which some people can apparently see due to having some extra stuff in their eyes supposedly.

On the contrary, the lens in the human eye is opaque to some UV wavelengths the rods/cones are actually capable of sensing, effectively filtering those out. So, having a faulty lens, or having it surgically removed, can then let you perceive a slight part of the UV spectrum.

so if some mutant ended up having a system most sensitive to x-ray radiation, would he be blind if he was living on earth? would he just not be able to use visible light?

Q1: Depends on the specific details of how the perception system works; if it would be damaged by wavelengths other than x-rays, then yes, he could go blind. But since X-rays are generally higher energy, it's unlikely that a system that is specialised to perceive those would be damaged by lower-energy wavelengths. (I could be wrong on this).
Q2: This depends on how much of the light spectrum his perception system covers.

would he have to walk around with an x-ray lamp and shine it on stuff he wants to see, and even then if he shone it on a person would he just see the body outline and mostly skeleton?

If he's confined to that particular part of the spectrum then yes, probably. Not certain of the skeleton, since that depends on many variables, but he'd certainly not see the same as us.

Could we briefly discuss the color of normal everyday objects, including manufactured items. Sky is blue, grass is green... Some aspect of the perhaps 'chemical' composition of the item is responsible for the hue. Grass absorbs the visible light and emits/reflects mostly within the greenish-yellowish range (corresponding to whatever length nm the waves are). Perhaps this is getting a bit philosophical, but as far as blackbody radiation goes is a grass still green in a dark room or vacuum? No visible light present to make us see a green piece of grass, although, perhaps it is still "green" based off the stuff that it is comprised of which make us see green when there is light.

Our daily life usage of color labels is utterly unscientific, since color perception is a highly subject-dependent phenomenon. The wavelengths reflected or absorbed by a given object depends on the properties of the specific material(s) and their structural arrangement, and from those we can only perceive a fraction of, so it would be technically proper to say no material has "color" but merely absorbs wavelengths xxx and reflects wavelengths xxx.

I think what I was trying to ascertain is whether the color of something depends on the temperature of it. In some cases apparently - red & blue stars, but a red piece of paper and a blue piece of paper is clearly a different case.

You are confusing yourself because of the issue raised above regarding the subjectivity of "color". As long as you cannot perceive all light wavelengths, you cannot make a straightforward relation between temperature and "color".

2 ideas from no expert:

1. Entropy of the object itself.
2. Element colour. (iron is red, copper is green, cobalt is blue, etc)

SW

That made sense.


PS. For the love of great Cthulhu, learn to capitalize and stop making run-on sentences, Pizzabeak. Punctuation is your friend.

 

[Wolf18]

That made sense.

Sarcasm? As I said, I'm no expert. BTW, I was answering Pizzabreak's first question, not his latest post.

And you're able to see more in a dark room over time because your pupils open to let in more light.

SW