Questions tagged [vision]

Questions regarding how the brain interprets information from the eyes. Consider using the "eyes" tag for discussion of eye anatomy, physiology and evolution.

Filter by
Sorted by
Tagged with
120
votes
4answers
5k views

Is there a reason why human eyesight and plants make use of the same wavelength of light?

The accepted range for the wavelengths of light that the human eye can detect is roughly between 400nm and 700nm. Is it a co-incidence that these wavelengths are identical to those in the ...
81
votes
3answers
14k views

Is there an RGB equivalent for smells?

Millions of colors in the visible spectrum can be generated by mixing red, green and blue - the RGB color system. Is there a basic set of smells that, when mixed, can yield all, or nearly all ...
64
votes
2answers
21k views

What is the evolutionary advantage of red-green color blindness?

Red-green colorblindness seems to make it harder for a hunter-gatherer to see whether a fruit is ripe and thus worth picking. Is there a reason why selection hasn't completely removed red-green ...
40
votes
5answers
5k views

Why did life not evolve to use radio?

We use electromagnetic communication everywhere these days. Cell phones, wifi, old-school radio transmissions, television, deep space communication, etc. I'm curious about some of the possible ...
36
votes
7answers
51k views

Does red light preserve your night vision?

A number of companies have started marketing LED lamps that can be switched to a red mode. The claim is that red light is less harmful to one's night vision. Given that our eyes are less sensitive to ...
34
votes
1answer
20k views

What do you see when your eyes are closed?

If you are in pitch black and you close your eyes, you sometimes can see strange shapes of various colors. A lot of the time these shapes and colors change as you observe them. This phenomenon still ...
30
votes
3answers
7k views

Can one see flickering of a light bulb at 50 Hz?

Yesterday I had a BBQ with some friends. The sun had already set and the only light source left (besides some ambient light from the world around) was a low energy light bulb. After a while I started ...
29
votes
3answers
8k views

Can humans ever directly see a few photons at a time? Can a human see a single photon?

I am not asking the following question: Can humans ever see a photon in the same way we see a chair? My question is: Can a human retina respond to a single photon? If so, how does this happen and why ...
29
votes
2answers
8k views

Is it possible that by mutation a human could see infrared or other 'colours'?

Incoming light reacts with the several types of cone cells in the eye. In humans, there are three types of cones sensitive to three different spectra, resulting in trichromatic color vision. Each ...
25
votes
7answers
7k views

Why can't we see in low light if staring long enough?

For me it seems reasonable that if I kept my gaze on a fixed point in a room with low light, a progressively brighter and better picture would appear before my eyes, just like a camera can see in the ...
25
votes
1answer
10k views

Why do stars disappear when I look at them?

I've noticed that when I'm out at night stars seem to vanish when I focus on them. I assume the reason is physiological and not astronomic. Why does this happen? I would expect that things would be ...
24
votes
1answer
16k views

Why does my room suddenly look 'reddish'? My eyes seem to adapt to color

To get the context of this question clear, I would like you to walk through some parts of my house. We'll start with one of my rooms as it appears normally - As evident, this part of my house has a ...
22
votes
3answers
1k views

When did vision evolve for the first time?

Today I wondered what the first organism to evolve vision would have been. I assume that it would have been kind of primitive and basic, but of course extremely innovative and eventually useful to a ...
22
votes
1answer
2k views

Why can't I read everything in my field of view?

When I look at a piece of text, I can see all the text on the paper, no matter where I look, because my field of view covers it all. However, if I stare at a specific word, I cannot read the text a ...
22
votes
3answers
51k views

Why do I see different hues of colors between each of my eyes?

Frequently, I see colors with a slightly different hue when looking through my eyes individually. The right eye is more red-tinted ('warmer' hued) and the left is typically more blue-tinted ('cooler' ...
18
votes
6answers
20k views

Why is human vision restricted to 400-700 nm?

Across the electromagnetic spectrum, 400-700 nm is a narrow spectrum of frequencies and focused in the region of short wavelengths. For example, radio waves cover a large range of frequencies ...
18
votes
1answer
335 views

Haidinger's brush: Is this a by-product of the eye's physics, or are there any evolutionary grounds for it?

The human eye is, very subtly, sensitive to the polarization of light. This is an effect known as Haidinger's brush (see Wikipedia article of this name). What, if anything, is known or at least ...
17
votes
3answers
3k views

Superhuman eyesight

My ten year old son was reading car number plates that were too fast, too far away and at the wrong angle for any of us to read or even believe that it was possible for him to read. We thought he was ...
16
votes
5answers
6k views

What is the difference between a circular and a cat's-eye (slit) pupil?

I've been to local zoo the other day and one lizard caught my attention: its pupils are circular, which, I thought, is not usual for reptiles. Turns out it is, but now I can't find any explanation on ...
16
votes
1answer
9k views

What portion of the electromagnetic spectrum do cats see?

I have seen numerous articles and various information about how cats and dogs see into the ultraviolet spectrum with interesting artistic renderings such as this: http://www.livescience.com/40459-...
15
votes
2answers
11k views

If human eyes watch an area, what's the shape of its capturing shape? Rectangular? Half spherical?

A normal camera can capture a rectangular image. If human eyes watch an area, what's the shape of the captured region? Rectangular? Half-spherical?
15
votes
2answers
747 views

Are some animals, like dogs and cats, color-blind and how do we know that?

I have heard that some animals, including dogs, cats and donkeys, are color-blind. They cannot recognize any color. Is that true? And how can humans verify that animals are color-blind, or not? During ...
15
votes
4answers
3k views

Do insects with compound eyes have depth perception?

Do insects with compound eyes have depth perception? They fly as if they do, but their eyes are so close together it seems like the image would be 2 dimensional.
15
votes
1answer
6k views

Why do we go blind for a few seconds after switching off the light?

At night, when I switch off the lights, I always seem to go blind for a while. The room becomes pitch black and I am unable to see anything. After a while, however, my vision slowly recovers and I ...
15
votes
1answer
2k views

Telling distance with one eye

Basic mathematical/logical reasoning makes it clear that you need two eyes to have depth of vision. By seeing an object from two perspectives, our brain can calculate the distance of the object based ...
15
votes
1answer
5k views

How does this illusion work?

I found this image on Google+ If you shake your head you can see a portrait of a person. Can anyone explain how the image is constructed in the brain?
15
votes
1answer
1k views

Is it a limitation of the eyes, or the brain, that we can't see a moving bullet?

Are the photoreceptors in our eyes not fast enough to register the fast moving bullet, or is the brain not powerful enough to make sense of something happening that fast?
15
votes
2answers
322 views

Can a color-deficient person be made to visualize the missing colors?

Hope this is within the scope of this site. Color-deficient persons lack the cells in their retina needed for differentiating some (or all) colors. However, the part of the brain that actually ...
15
votes
1answer
566 views

Effect of pupil responses on the electroretinogram

The electroretinogram (ERG) is a measure of electrical activity of the retina. It is typically recorded from the cornea with a wire electrode or gold-foil electrode. Generally, the the ERG is ...
14
votes
5answers
11k views

Why can cones detect color but rods can't?

I don't know if this question applies to only humans but why can cones see much greater detail than rods? Is it possible to have a rod that can detect light intensity and color?
14
votes
3answers
2k views

How do we know the brain flips images projected on the retina back around?

Why do we turn images upside down again rather than dealing with them directly, still vertically rotated after passing through our lens? I don't see how that would cause any problems, and how we'd ...
14
votes
2answers
625 views

Seeing strange things in light

I have noticed that if you look directly at tubelight (I have only white ones in my home) and close your eyes little, you see little random shaped colourless things sometimes with slow speed and ...
14
votes
2answers
523 views

Is our color vision calibrated to sky, vegetation, and blood?

Our color vision is based on three types of receptors (cones) which are sensitive to three distinct locations on the spectrum: 420–440 nm, 534–555 nm, and 564–580 nm. We label them "red", "green", ...
14
votes
4answers
33k views

Why can't the human eye focus blue light?

I recently noticed that it is hard to focus on blue light sources, especially at night. When observing a blue light source, e.g. a neon sign, it looks somewhat blurry. A sign with a different colour ...
14
votes
1answer
246 views

Are there specific conditions that allow humans to see ultraviolet wavelengths

It is fairly common knowledge that the lens in its normal state absorbs ultraviolet (UV) radiation. An interesting notion has come up from time to time in my reading that suggests there are a small ...
12
votes
1answer
948 views

Why does this illusion work?

This is another image I found on Google+ All lines are absolutely straight, parallel and perpendicular but why does it appear to have a curvature? Related: How does this illusion work?
12
votes
2answers
556 views

Is mammalian vision processed as a sequence of frames?

I often read that people believe that human vision has an inherent frames-per-second rate (FPS) that causes stroboscopic effects - such as seeing the spokes of a rotating wheel apparently rotating at ...
12
votes
1answer
312 views

What really is color and how do we perceive it?

How do our brains actually transform the information that the cones in our eyes receive into the different colors that we can see and imagine?
11
votes
1answer
7k views

Why can I see a light flicker when it's in my peripheral vision?

When I'm looking at an old CRT monitor or a worn fluorescent lamp, but not directly in the center of my gaze, the light from it seems to flicker. When I focus my gaze onto the monitor or lamp, the ...
11
votes
1answer
4k views

Do colour blind people see white?

I know that white colour is perceived on excitation of red, blue and green cones simultaneously. It is also said that a colour blind person doesn't see a particular colour and just perceives it as a ...
11
votes
1answer
2k views

Can “red” cone cells actually see much red light?

In electronics, the most common color scheme is the "red-green-blue" (RGB) scheme. This choice is often justified by claiming that the long- (L), medium- (M), and short- (S) type cones in the human ...
11
votes
1answer
436 views

What are the “stars” we see after a bump on the head?

Sorry if this might appear funny. When I close my eyes for a longer time, and suddenly open it, I see some twinkling white small circles, and when i concentrate on anyone of them it disappears, as ...
11
votes
1answer
493 views

Dogs bark at familiar person in Santa costume. Why? Don't dogs trust smell over vision?

Last night 10 humans and 2 dogs spent Christmas together. At some point, one human dissappears for a few minutes and comes back wearing a full Santa outfit. Upon respawning, the dogs start barking ...
11
votes
3answers
11k views

Why does closing one eye in bright light allow me to open the other?

I often find it physically painful to open my eyes past a squint after stepping out into the full summer sun. However, if I close one eye entirely, I can keep the other open without pain. This seems ...
10
votes
6answers
3k views

What is the use of eye banks, if eyeball transplants do not exist at present?

Corneas are donated and transplanted, but not the eyeball. I don't understand. What is the purpose of donating a cornea without an eyeball to a blind person?
10
votes
1answer
30k views

What is the field of view for the human eyes?

I'd like to know how much a person can see regarding the angles. If it is a rectangle, I'd like to know it's height and width. But if is another shape, I'd like to know which kind of shape and the ...
10
votes
2answers
46k views

Is it safe to look at infrared LEDs?

What happens if one looks directly at infrared LEDs? Sometimes I see this kind of LED at night as red dots and I'm also courious about it. I was wondering what would happen if one looks directly to ...
10
votes
2answers
5k views

Why can't our eyes smoothly transition from side to side without focusing on a moving object?

Why are we not able to slowly and smoothly look from side to side, or up and down in a single and smooth transition, given that we are able to do this if our eyes are focused on a moving object?
10
votes
1answer
1k views

Are 2 eyes necessary for 3D vision?

To start off: I'm not a biology student, but a computer science major It has always been my understanding that humans have 2 eyes so that we can have 3D vision: the left eye see more of the left side ...
9
votes
1answer
5k views

Why does a light object appear lighter in your peripheral vision when it's dark?

So, I am not sure I can reproduce it via images, but the steps are: 1) At night, open a window and have a look at the surface of the earth 2) Suppose there's an object that reflects a tiny amount of ...

1
2 3 4 5 6