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 ...
- 51.8k
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 ...
- 51.8k
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 "...
- 24.5k
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 ...
- 9,424
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 ...
- 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 ...
- 51.8k
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 ...
- 51.8k
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 ...
- 51.8k
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 ...
- 39.9k
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 ...
- 51.8k
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 ...
- 429
23
votes
Accepted
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 ...
- 51.8k
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 ...
- 39.9k
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 ...
- 51.8k
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 (...
- 51.8k
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 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 ...
- 51.1k
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 ...
- 67.8k
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 ...
- 51.8k
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 ...
- 51.8k
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 ...
- 51.8k
14
votes
Accepted
Why can I see a light flicker when it's in my peripheral vision?
Your retina contains both rods and cones. Cones are color sensitive, slow, and concentrated near the center of your field of vision. Rods are "light" sensitive, fast, and concentrated near the ...
- 490
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 ...
- 9,123
13
votes
Accepted
Why don't myopic people see the world upside-down?
You have misinterpreted the nature of the light rays shown in the diagram in the question. The two rays are representing light coming from the same (distant) point in the environment, that is, some ...
- 8,799
13
votes
Accepted
What is the field of view for the human eyes?
The general shape of the field of view has been answered in the related question "If human eyes watch an area, what's the shape of its capturing shape? Rectangular? Half spherical?"
Regarding the ...
- 51.8k
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 ...
- 28.5k
12
votes
Accepted
Do animals exist which have good vision, but see only grayscale?
Preamble & Overview.
This is a rather unsatisfying answer I'm afraid. I can't seem to find any animal that has exceptional eyesight and sees in monochrome.
Baring in mind the context of humans vs ...
- 11.3k
Only top scored, non community-wiki answers of a minimum length are eligible