77 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 ...
AliceD's user avatar
  • 52.4k
74 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 ...
AliceD's user avatar
  • 52.4k
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 "...
anongoodnurse's user avatar
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 ...
March Ho's user avatar
  • 9,452
40 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 ...
WYSIWYG's user avatar
  • 35.6k
35 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 ...
AliceD's user avatar
  • 52.4k
35 votes
Accepted

Did predators evolve eyes first?

Short answer Complex eyes may have evolved first in predator species, specifically in box jellyfish. Trilobites are another group of animals where complex eyes may have evolved first. The trilobites ...
AliceD's user avatar
  • 52.4k
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 ...
AliceD's user avatar
  • 52.4k
30 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 ...
AliceD's user avatar
  • 52.4k
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 ...
Bryan Krause's user avatar
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28 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 ...
llama's user avatar
  • 439
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 ...
Bryan Krause's user avatar
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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 ...
AliceD's user avatar
  • 52.4k
20 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 ...
Chris's user avatar
  • 51.6k
20 votes

Did predators evolve eyes first?

AliceD's answer is great but just to address your points 1 and 2. Eyes are expensive. From a study on fish loosing their vision in caves. The cost of vision was calculated to be 15% of resting ...
Sam Dean's user avatar
  • 301
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 ...
Eric Towers's user avatar
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 ...
Remi.b's user avatar
  • 68.1k
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 ...
gilhad's user avatar
  • 261
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 ...
AliceD's user avatar
  • 52.4k
14 votes
Accepted

Do colour-blind people see white?

It's definitely not white or grey generally, it's a mix of other colors, they often have low resolution of a particular color so that it's less visible rather than visible and grey. Here's a page ...
bandybabboon's user avatar
  • 10.4k
13 votes

Why do blood vessels in the eye not obstruct vision?

You CAN see your blood vessels! Following-up from Bryan Krause's answer: Bryan mentioned that the blood vessels are typically not visible partially because they are unchanging (i.e., static). In ...
theforestecologist's user avatar
13 votes

Did predators evolve eyes first?

Eyes evolved multiple independent times in convergent evolution. Almost all the vertebrates have eyes. Those few that doesn't lost their eyes through evolution and live in deep ocean of in caves where ...
Victor Stafusa - BozoNaCadeia's user avatar
12 votes

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

There's probably a theoretical capacity to do so. The brain is amazingly good at signal processing, and could probably pull off such a summation. However, there is a limit. You have to hold very ...
Cort Ammon's user avatar
  • 1,364
12 votes

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

This is an interesting phenomenon which I have been aware of for several years, but I haven't yet come across any official description of it or explanation for it. Nonetheless, the phenomenon is easy ...
Gwen's user avatar
  • 883
12 votes

Why do I still see a bright light after looking directly at it?

Short answer The effect you describe is called a negative after image. It can be explained by adaptation effects of the photoreceptors in the eye. Background source: Dresden University Steadily ...
AliceD's user avatar
  • 52.4k
10 votes
Accepted

Can "red" cone cells actually see much red light?

This is a good question. The first thing to note is that human colour vision is very complex and still poorly understood. If you visit the wikipedia page on RGB, you will find that this correctly ...
Anon's user avatar
  • 837
10 votes

Best colour for a dog to track an object against green background

Dogs are a dichromatic species, featuring only a long wavelength (L) and a short wavelength (S) cone (source: Smithsonian). As such, they are thought to perceive mainly blues and yellowish hues (Fig. ...
AliceD's user avatar
  • 52.4k
10 votes

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

From experiments it seems you should better use dark mode if you want to prevent myopia: Using optical coherence tomography (OCT) in young human subjects, we found that the choroid, the heavily ...
asmaier's user avatar
  • 201
9 votes

Do insects with compound eyes have depth perception?

Short Answer: Yes. Nityananda et al. (2018) confirmed a novel form of stereo vision by putting tiny colored glasses on praying mantises. (Newcastle University, England) [source] Long Answer ...
theforestecologist's user avatar

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