seeing black

[gib65]

I'm wondering how it is that we see black when we look skyward at night? I mean, I know enough physics to understand that black is the lack of colored light and is therefore considered not to be a color, but why does the subjective experience of seeing black feel like a color? I'm guess it's because the neural centers for color perception work similarly for black as they do for other colors, but it's just, unlike other color centers that become active when actual colored light enters the eye, the black centers become active when no colored light enters they eye. That is, they are like the "default" neurons that become active when no other neurons are firing.

 

Has there ever been studies done to support/refute this?

[swansont]

Are there actually black color centers, or is that the sensation of no signal at all?

[scicop]

Are there actually black color centers, or is that the sensation of no signal at all?

 

There are no black color centers. It is the lack of signal. Also, the reception of light, at least at the light receptor (cell) level is inhibitory!

 

With respect to perception, well that's the brain! Color assignment is purely brain manifested response/assigntment to light stimulation at defined frequencies (i.e. 488nm for Green, 570nm for yellow, 600nm for red etc.

 

There are wavelength specific receptors (rhodopsins, member of the Family A superfamily of G-protein coupled-receptors) which depend on light energy for conformational change. Since black is not a color (in a physical sense..no wavelengths etc) then there is no way of activating any color selective rhodopsins. Hope I'm clear here.

[gib65]

Are there actually black color centers, or is that the sensation of no signal at all?

 

Well, my thinking is that if you can say that you're experiencing it, it's got to have a neurological counterpart. When I look at my keyboard (which is black) I can say "I'm experiencing the sight of black."

 

scicop,

 

Rhodopsins is the active chemical in cone cells, right? So that makes sense that no light would mean no stimulation. But at the level of the brain, could there not be neurons that are inhibited when signals from the eyes enter the brain, and then start firing only when no signals from the eyes enter the brain? I don't doubt your knowledge on the subject, but I'm sure I remember reading that research on how the brain perceives color is still not well understood. Couldn't it be possible that there are black color centers in theory - or do you know there aren't for fact?

[SkepticLance]

gib.

Your reasoning is excellent.

I don't know the answer, either, but suspect it is to do with further information processing in the brain, more than any receptors closer to the eye.

[ashennell]

Colour is coded through 2 opponency channels - red-green and yellow-blue. Often, descriptions of the visual system include a third channel coding black-white information. But this channel is not really the same as colour information because black and white are not coded in opponency to each other. i.e., we can perceive intermediates (greys) between black and white. I doubt if the colour sensitive 'blob' regions of the cortex code this black/white distinction.

 

It's late , I will try and give a clearer explanation when im not half asleep.

[smommer]

My keyboard is also black, but if asked when i look at it i would say the keys are black, if i look closely however, they are more a light grey colour because of the reflection of white light from my monitor. I know this doesnt apply for the sky but could the reflections off black surfaces contribute towards what gives 'black' a percieved sense of colour.

 

Another cool trick i have always liked is how Overhead projectors make the colour black, it is actually no signal with colour projected around it (e.g. black text on a white background), i always thought it was cool how you can get such a clear illusion of black on a whiteboard.

 

A colleague of mine wrote an article about whether or not white is a colour in a computing journal last year. it would probably be of interest to you.

 

http://www.comp.lancs.ac.uk/computing/users/dixa/papers/is-white-a-colour-2005/

 

smom

[gib65]

Colour is coded through 2 opponency channels - red-green and yellow-blue. Often' date=' descriptions of the visual system include a third channel coding black-white information. But this channel is not really the same as colour information because black and white are not coded in opponency to each other. i.e., we can perceive intermediates (greys) between black and white. I doubt if the colour sensitive 'blob' regions of the cortex code this black/white distinction.

 

It's late , I will try and give a clearer explanation when im not half asleep.[/quote']

 

But what you're saying then, is there is some neural activity going on when we see black. Am I interpreting you right?

[Nevermore]

Blind people don't see black, they just plain don't see. The whole world looks to them like the back of your head looks to you: You can't see it at all, there is an absance of stimulis/responce there, and the result is a total lack of vision.

 

So, since a total lack of stimuli doesn't result in black, but in nothingness, we can infer that there is a nerotransmiter for black.

 

Of course, that's just my two cents.

[ashennell]

What you have to remember is that most neurons in the early visual cortex respond most vigourously to specific changes in intensity; lines, edges, corners and other features. So a matt black object in the visual field wouldnt produce much activity because a lack of contrast. But the same could be said for a solid green object or blue object. What neurons respond to are changes across their receptive fields.

 

The short answer is that , if you are in a pitch black room then there is not a population of neurons coding 'this is black.' I expect that this is the situation in which there would be least activity in the visual cortex. Most black objects do reflect some light, highlights, etc that provide texture information or contours.

 

People who are blind from birth do not see black, as has been pointed out, but this is not because their black coding neurons dont work. These people have not had the experience to learn an internal representation of visual space. Therefore they don't really have a 'canvas' to paint black. If you have had enough visual experience to develop your internal model of the visual world then you do need a way of representing no input.

[Nevermore]

People who are blind from birth do not see black' date=' as has been pointed out, but this is not because their black coding neurons dont work. These people have not had the experience to learn an internal representation of visual space. Therefore they don't really have a 'canvas' to paint black. If you have had enough visual experience to develop your internal model of the visual world then you do need a way of representing no input.[/quote']

People who recently went blind don't see black either, and they have learned a nero response to black.

[ashennell]

People who recently went blind don't see black either, and they have[/i'] learned a nero response to black.

 

Some people who are blind still see patterns of colours in the visual field. Not caused by external stimuli but from nerual activity. So it is obviously not as clear cut as what you are suggesting.

 

What do you you mean by 'learned a neuro response to black?'

[gib65]

Blind people don't see black' date=' they just plain don't see. The whole world looks to them like the back of your head looks to you: You can't see it at all, there is an absance of stimulis/responce there, and the result is a total lack of vision.

 

So, since a total lack of stimuli doesn't result in black, but in nothingness, we can infer that there [i']is[/i] a nerotransmiter for black.

 

Of course, that's just my two cents.

 

Wow! Good argument.