Hot answers tagged

78 votes
Accepted

Is there an RGB equivalent for smells?

There are about 100 (Purves, 2001) to 400 (Zozulya et al., 2001) functional olfactory receptors in man. While the total tally of olfactory receptor genes exceeds 1000, more than half of them are ...
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73 votes
Accepted

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

Short answer Color-blind subjects are better at detecting color-camouflaged objects. This may give color blinds an advantage in terms of spotting hidden dangers (predators) or finding camouflaged ...
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46 votes
Accepted

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

For simplicity's sake, let's really reduce this to something like photography. A camera's aperture can stay open indefinitely, allowing the plate (or whatever is receiving and recording light) to "...
40 votes

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

Yes. Far-red vision (>700nm) The ability for retinal-binding proteins to absorb far-red (between 700nm-850nm) light has been experimentally confirmed in this paper. While the authors did not attempt ...
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38 votes
Accepted

What do you see when your eyes are closed?

This is called a phosphene — the experience of perceiving light in the visual cortex without light actually entering the eye. This commonly happens due to stimulation of the retinal ganglion ...
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38 votes

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

A single molecule of rhodopsin (actually the cis-retinal bound to it) can and actually does react to one photon (Purves et al. Chapter: Phototransduction in Neuroscience). It has been estimated ...
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36 votes
Accepted

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

Short answer The phenomenon you describe can be explained by the negative afterimage effect, which indeed is elicited by adaptive processes in the retinae. Background In the retina there are three ...
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33 votes
Accepted

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

Short answer Yes, the flickering of a light bulb may be noticeable, and yes, that's directly related to the mains frequency. However, since the flickering of a bulb is about two times higher than the ...
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30 votes

Why do blood vessels in the eye not obstruct vision?

Avoid the fovea Figure 2 from the same paper shows the distribution relative to the fovea: As you can see, it's pretty much devoid of this superficial vasculature, so anything you are directly ...
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29 votes
Accepted

Are humans more adapted to "light mode" or "dark mode"?

A question that requires quite a lot of guts to ask on this site :) Nonetheless, and risking sparking a debate, there are a few arguments that spring to (my!) mind that can support the notion that we ...
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27 votes
Accepted

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

The field of view is determined by the light-receptive parts of the eye: the retinae (Kolb, 2012). The fovea is the region with the highest resolution. It is located in the central part of the retina ...
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27 votes

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

A recent study published in Nature by Tinsley et al. Direct detection of a single photon by humans found that it is possible for dark-adapted humans to respond to a single-photon stimulus, but only ...
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25 votes
Accepted

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

The capture area of the eye is a bit fuzzier and harder to define than that of a camera. A camera captures consistent, fully detailed data right up to the edge of its sensor, and no data at all ...
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23 votes
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Why is human vision restricted to 400-700 nm?

Short answer The visible spectrum has the highest energy in sunlight at the earth's surface, explaining the gross location of the visible spectrum in life on earth. The specific frequency range varies ...
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22 votes

Telling distance with one eye

Depth perception consists of what are called monocular cues and binocular cues. As you mention, binocular vision has a lot of advantages for depth perception, but it is not completely necessary. Many ...
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21 votes

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

TL;DR: We have a good physiological understanding of how eyes work, so by examination of other species' eyes, we can tell a lot about what colours they are capable of seeing. First, a little bit ...
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21 votes
Accepted

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

Short answer The eyes need to adapt to the low lighting condition after you switch off the lights, a process called dark adaptation. Background The process behind the reduced visual function when ...
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19 votes
Accepted

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

Short answer Peripheral vision is more light-sensitive than central vision. Background When you look directly at an object the image is projected onto the fovea. The fovea has maximal visual acuity (...
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19 votes

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

March Ho's answer is quite good. A few extra tidbits: The population of humans contains DNA encoding for two substantially different M receptors. (differing by more than normal variation) See ...
19 votes

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

There seems to be some evolutionary advantages to red-green colorblindness. The paper in reference 1 (a summary can be found in reference 2) shows that people with red-green color blindness can ...
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19 votes

What are the floating translucent little objects called in the field of view?

I think you are talking about floaters (a.k.a. eye floaters or flying flies). You may want to have a look at this english.SE post in case you were not talking about floaters. Floaters are deposits ...
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17 votes

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

You are asking two questions that you think are connected but are actually not. Question 1 - What is the use of eye banks? Answer: It's to store corneas for transplant for people with cornea ...
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17 votes

Superhuman eyesight

Short answer Visual acuity decreases with age. Your son's age is within the age range that visual acuities are best. Acuity starts to decrease from about age 45. Background Visual acuity (visual ...
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16 votes
Accepted

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

Short answer Color vision is not based on a calibration to the sky, vegetation and blood. The current leading theory of the development of trichromatic vision in humans is based on the foraging of ...
  • 51.5k
16 votes

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

The simple answer is, that eye is not constructed such way. The eye have much more "pixels" than "links" to the brain and sends in "preprocessed" image. Moreover the the eye is constantly moving and ...
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16 votes

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

The differences at the photoreceptor level have been addressed by others. The mechanical restrictions of the visual system were shortly hinted at by @gilhad et al., but deserve more attention in my ...
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15 votes

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

I used to work at an eye bank so I have a bit of knowledge about this, though some of it may be out of date. There are several aspects to an eye bank. The corneas are one of the primary things that ...
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15 votes
Accepted

What portion of the electromagnetic spectrum do cats see?

Short answer Spectral sensitivity of cats indeed ventures into the UV, but not beyond ~320 nm. Their maximum is likely similar to ours, i.e., ~750 nm. Background The spectral sensitivity of blue ...
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14 votes
Accepted

Dark veil when getting up too fast

It's caused by a sudden shift in the pressure needed to circulate blood to your brain which your body fails to respond to sufficiently quickly. This results in a sudden loss of blood pressure termed ...
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