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 ...
- 52.3k
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 ...
- 52.3k
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 "...
- 24.7k
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 ...
- 9,432
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 ...
- 35.2k
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 ...
- 52.3k
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 ...
- 52.3k
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 ...
- 52.3k
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 ...
- 52.3k
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 ...
- 43.9k
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 ...
- 439
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 ...
- 52.3k
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 ...
- 43.9k
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 ...
- 3,304
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 ...
- 52.3k
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 ...
- 51.5k
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 ...
- 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 ...
- 291
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 ...
- 68k
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 ...
- 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 ...
- 52.3k
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 ...
- 10.3k
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 ...
- 29.7k
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 ...
12
votes
Accepted
What is the function of the human eye white?
Short answer
The relative large surface area of the white sclera in humans has been linked to an enhanced ability to detect eye gaze.
Background
The white of the eye is caused by the sclera. Human ...
- 52.3k
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 ...
- 883
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 ...
- 1,364
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 ...
- 52.3k
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. ...
- 52.3k
Only top scored, non community-wiki answers of a minimum length are eligible