How does our brain differentiate between a source of light and a painted circle?

[Trying2Learn]

TL;DR

How does my brain perceive light?

I approach a traffic light. It is red.

I know it is a light.

What is happening in my brain to inform me that I am looking at a red light, and not a brightly colored red circle on the canvas of my perceptions of the physical world?

If my eyes are moist and I squint, I see radiating red lines and that sort of informs me it light, since even a brightly colored red dot will not emit such rays. But that is based on prior experience with such objects. If I did not squint, how would I know it is light.

One could say that nearby objects are slightly tinted with red light and that is how I know it. But I could paint a similar scene and tint the nearby colors slightly red.

Here is a painting by La Tour. I ALMOST see the candle as a source of electromagnetic radiation (almost); so there is definitely a skill of artistic replication involved.

In any case, how do I know I am looking at a source of electromagnetic waves at a stop light, and not a white-specular red painted circle? How does my brain inform me that the candle below is not emitting electromagnetic waves (and I am ONLY seeing reflected white light from the area of the candle in the dark canvas. What is happening in my brain to inform me that I am looking at a source of light?

 

[Hill]

TL;DR Summary: How does my brain perceive light?

I approach a traffic light. It is red.

I know it is a light.

What is happening in my brain to inform me that I am looking at a red light, and not a brightly colored red circle on the canvas of my perceptions of the physical world?

If my eyes are moist and I squint, I see radiating red lines and that sort of informs me it light, since even a brightly colored red dot will not emit such rays. But that is based on prior experience with such objects. If I did not squint, how would I know it is light.

One could say that nearby objects are slightly tinted with red light and that is how I know it. But I could paint a similar scene and tint the nearby colors slightly red.

Here is a painting by La Tour. I ALMOST see the candle as a source of electromagnetic radiation (almost); so there is definitely a skill of artistic replication involved.

In any case, how do I know I am looking at a source of electromagnetic waves at a stop light, and not a white-specular red painted circle? How does my brain inform me that the candle below is not emitting electromagnetic waves (and I am ONLY seeing reflected white light from the area of the candle in the dark canvas. What is happening in my brain to inform me that I am looking at a source of light?
View attachment 336128

A prior knowledge. When you look at the Moon, for example, your brain does not have a way to know if the Moon is the source of the light or it reflects light from another source, other than through prior knowledge.

 

[Baluncore]

When you learn to drive, you learn that the traffic light at the top is red. After a while it is not the colour, but the position of the light in the assembly, that you notice. If you look, you will see it is red.
Red/green colour-blind drivers learn the red light position more quickly.

It does not need to be a light. If it was a red painted disc that could be covered by a black disc, then you would not be concerned, except at night when you could not see it so well, but the brighter green or amber disc would preclude red.

 

[phyzguy]

Everything you see is light. You see objects because light from the object enters your eyes. So I'm not really sure what your question is

 

[Dale]

TL;DR Summary: How does my brain perceive light?

But that is based on prior experience with such objects.

Pretty much all of your visual perception is based on prior experience. You have to learn to interpret what you see as indicating various facts about the world around you.

In fact, your brain sees many things that are not correct. These are called optical illusions. It uses lots of clues, like shadows to help us infer things that might not be real but that we have experience seeing.

 

[Ibix]

There are plenty of ways you can trick your visual system, which is fun. If you're ever in the Lake District in England, this museum of illusions is worth a visit. There are a few pictures on their website, mostly of forced perspective illusions which make ordinary people look like giants or dwarves. (Edit: this room is fun if you have a Spiderman obsessed child - mine was very proud of his "climbing the wall" picture.)

As others have said, you know it's a light source rather than a specular reflection because you've seen it before, including at night and other times when there's no obvious intense light source that could cause enough of a reflection. It would probably be possible to build something that looks like a traffic light but was solely a reflective surface illuminated by a very tight beam source, and you would probably be fooled. I wouldn't recommend doing that on public land, though...

 

[kuruman]

To what others have said, I should add that light waves (or photons if you prefer) enter your retina and the energy they carry stimulates the photoreceptors on your retina (see here for a simple description) that generate and send signals to your brain. Your brain interprets these signals into what we understand as "seeing."

The logical conclusion of this is that truly invisible persons must necessarily be blind because the light would have to pass through their eyes and not be converted into neural signals.

$\dots~$ mostly of forced perspective illusions which $\dots$

Yes, perspective illusions can be baffling. I was playing frisbee and couldn't understand why it was getting larger and then it hit me.

 

[gmax137]

Yes, prior experience. This is why infants lie in their cradle with a puzzled curious look on their face, saying "goo-goo." They don't have much prior experience.

 

[nasu]

The fact that you can tell it is the painting of a candle (versus a real candle) is just a small thing compared with what your brain had to learn in order to actualy "see" what you think that you see in that image. Even to be able to tell that there is a painting and that in the painting there is a candle and a mirror and a frame around the mirror. Even the fact that we see contours around objects (which does not actually physically exist) has to be learned. The eye produces just a patch of spots with various brigtness and colour. To make out indvidual objects out of this requires learning and combining the eye input with touch. Maybe even taste. After all, the babies like not just to touch things but also to put them in their mouths. And they "like" (do they?) these "books" with samples of various textures which they can touch.

An interesting series of studies were published in the 2010-2011 based on the research done on people who gained sight late in life after surgery to treat congenital blindness. I cannot find the exact one I saw at that time (in Science) but it was like this one, at the bottom. It seems that there was the belief that if you don't learn "to see" until 5-6 years of age you won't be able to do it in later years even if your eyes start to work. The study seem to show that there is more than that simple yes/no based on age and some functions may be pre-existent in the brain. But it seem to be clear that after surgery they have to learn to see objects, to make sense of the patterns of light sent by the eye to their brain.

https://www.science.org/content/art...lind-people-sight-illuminates-brain-s-secrets

 

[nightvidcole]

It isn't purely perception, it's also background knowledge. Someone could, in theory, place a nonluminous disk there and shine a spotlight on it. If the spotlight beam were incredibly precise and aimed correctly, and/or the disk embedded with a retroreflector, you could be "fooled" into thinking it was a light.

A "real life" example is when the Moon and planets appear to be luminous in the night sky, but are actually just illuminated by sunlight.