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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
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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
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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
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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
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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 ...
AliceD's user avatar
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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
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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 ...
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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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

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
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17 votes
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Does the Ogre-Faced Spider regenerate part of its eyes daily?

A. D. Blest seems to be the primary researcher responsible for that wild (truly!) information on Ogre-faced Spider eyes, first publishing this finding in 1978, wherein he described this "...
anongoodnurse's user avatar
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
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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's user avatar
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
  • 52.6k
11 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
  • 211
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
  • 52.6k
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
9 votes
Accepted

Can a color-blind person see color with filter glasses?

Short answer Optical filters can optimize color contrast, but never restore color blindness. Filters remove colors, they can never add something. However, glasses like this can prove helpful for ...
AliceD's user avatar
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9 votes
Accepted

Is brain plasticity such that we can train ourself to see with our ears?

Short answer Yes, we can see with our ears. Background Bach-y-Rita famously stated "We see with our brains, not our eyes". Bach-y-Rita worked for decades on sensory substitution. Sensory substitution ...
AliceD's user avatar
  • 52.6k
9 votes

Is there an RGB equivalent for smells?

There are many, many more parameters than 200! As an example, look at the nomenclature system for olfactory receptors (ORnXm). "OR" is the root name (Olfactory Receptor superfamily) n = an integer ...
Drunken Code Monkey's user avatar
9 votes

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

Technically, we can sense the individual photons. Here is an quote from a cellular biology textbook: "Absorption of a single photon of light induces a conformational change in the rhodopsin molecule, ...
F16Falcon's user avatar
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9 votes
Accepted

Why did we lose our fourth type of cone cell (in the eye)?

Let's be clear: most mammals, including basal primates, had only 2 cone cell types. Primates evolved a new cone cell becasue frugivores have a distinct advantage being able to distinguish reds and ...
John's user avatar
  • 14.9k
9 votes

How is the extraordinary eyesight of some deep-sea creatures explained?

You will find quite a lengthy and nice discussion and review of current hypotheses (all with some support) in Porter et al. 2020,PNAS. To add even more intrigue, parts of the vision system (e.g.: ...
tsttst's user avatar
  • 1,597
8 votes
Accepted

Why can myopic eyes focus on nearby objects, but not on distant ones?

There are four common refractive errors, namely nearsightedness (myopia), farsightedness (hyperopia), astigmatism (Fig. 1) and presbyopia. Fig. 1. Refractive errors. source: Excimer Ophthalmologic ...
AliceD's user avatar
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8 votes
Accepted

How are colors outside the standard RGB color scheme perceived?

This question is both biology and physics I think (I guess it's biophysics! :) so I feel it's worth answering here. First, we must recognize the difference between wavelength, which is just a ...
Roland's user avatar
  • 5,725
8 votes
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What is the biological potential for vision of wavelengths outside the human visual range?

There are some limits on what light can be detected biologically based on physics and chemistry. Although there are animals that can sense more UV or more infrared than humans, they are still subject ...
Bryan Krause's user avatar
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