Tag Info

Hot answers tagged

57

Good question. If you look at the spectral energy distribution in the accepted answer here, we see that photons with wavelengths less than ~300 nm are absorbed by species such as ozone. Much beyond 750 infrared radiation is largely absorbed by species such as water and carbon dioxide. Therefore the vast majority of solar photons reaching the surface have ...


22

Actually, the Army and Air Force (and I assume the Navy) teach their life support troops about this (as well as the aviators), since so many missions are conducted at night. It is actually some very interesting physiology involved in this. This Army Instructional manual should be of help (PDF File). On an average it takes 30 to 45 minutes for your rods ...


18

Like these questions :) Many of these illusions come from Prof. Akiyoshi Kitaoka, a japanese Psychologist and expert for Gestalt Psychology. On his website you'll find some more fascinating illusions and questions to ask here ;) The illusion above is named Cafe Wall illusion and the newest model to explain those illusions is the contrast-polarity model. ...


16

Short answer, your eyelids does not block all light. Since they are only a thin layer of skin, the light is able to pass through although not completely obviously. Since the eyes are still completely functional when you close them, only covered by the eyelids, you are able to see when light strikes your face.


14

Possible, yes but probable, no. (I assume that the history of the parental family as you mention is important) Let us first consider HERC2 (H=brown, h=blue) and OCA2 (O=brown, o=blue) as per the names mentioned in the reference you cite, to be completely unlinked, such that they are independently assorted. Since the father's lineage has no history of the ...


13

If you zoom in on the image, you can see that it is not just composed of black vertical lines, but also has pixels with different gray tones in the white areas. When you move your head sideways, you perceive the gray tones more. If you were to remove the black lines, you could see the face clearly. Initially I thought that by blurring the gray shapes when ...


13

Cats and dogs can both view tv screens & monitors ... though their viewing experience is a little different to ours thanks to differences in cone structure leaving them color blind and giving low acuity. Both species have lower levels of color vision than humans. Cats see slightly more color (in the blue green and yellow end of the spectrum) than dogs ...


12

Overview Laser eye surgery works by altering the shape of the cornea. The cornea works together with the lens to focus rays of light onto the retina. The cornea accounts for two-thirds of the optical power of the eye (1) (i.e. the eyes capability to focus light), however unlike the lens is of fixed power. It is the lens that changes is shape by the ...


11

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 Orthostatic Hypotension which, in term, results in a transitory reduction in the blood supply necessary for brain function. You experience a momentary loss of ...


10

I'll address the question in the title "At which time did sight evolve for the first time?" by assuming that by the evolution of vision, we mean the evolution of the eye. Molluscs are an excellent phylum to investigate this question because they exhibit a wide range of eye designs and levels of complexity. At the most basic level, limpets such as Patella ...


10

OK, I'll field this one. I'll ignore any of the tell-tale signs of hokum such as writing in ALL CAPS. Nevertheless, it's a lot of hokum. It's true that he goes into a lot of detail and I'm sure his math looks nice but the fact is that it's not grounded in reality. I would consider myself to be something of an expert (in training) in the field of ...


10

You will be interested in Aphakia, which is the lack of an eye lens usually through surgery but sometimes from birth. These individuals supposedly see UV as a whitish-blue or whitish-violet: This appears to be because the three types of colour receptor (red, green and blue) have similar sensitivity to ultraviolet, so it comes out as a mixture of all ...


9

The answer can be found in the excellent lecture from 1983 The Life History of Retinal Cells which also has gorgeous microscope fotos. The renewal time of rod outer membrane proteins is less than two weeks. Cells stay indefinitely, as I understand, but are periodically rebuilt in a logistical nightmare/wonder.


9

There are 2 reasons for light to appear red through the eyelids. 1) Eyelids get a rich supply of blood which contains iron (in hemoglobin). The iron in blood absorbs all colors of light but reflects red light (reference). 2) Our tissue transmits red wavelengths of light very well, but it doesn't transmit blue or wavelengths of light towards the blue end of ...


8

The selection you refer in multiple species could be due to a mutual advantage. If fruits absorb visible wavelengths, they can be spotted by other animals and eaten together with the seeds. Seeds can then mature inside the host and, once eliminated with the feces, grow up a new plant in a different place. This is not only valid for light absorption, but for ...


8

Both fruit flies (Drosophila) and mice (Mus) are classified under Bilateria. The presence of such a highly conserved sequence in both species suggests that they share a urbilaterian ancestor who also used a similar gene to turn on eye formation (not create the whole eye, just start the process). Even though the structure of insect and mammalian eyes ...


8

It's less a problem of speed and more of raw photon count. Assuming a brightly lit day, the bullet will move so fast that it doesn't reflect enough photons to register against the background. High speed images of bullets usually involve a very bright flash (and other controlled settings) for the camera to pick it up. (Also, a very short flash helps the ...


8

This is quite common. It is most likely dried rheum (also know by slang terms such as "sleep", "eye boogers", "eye crusties", etc.). Rheum is the result of dried mucus, tears (and the salt and minerals therein), as well as dead blood and skin cells. Essentially it is all the stuff that’s normally in your eye that eventually dries up making the contents ...


7

"To me, it also makes sense that the evolution of sight would have accompanied the evolution of advanced brain functions in almost every case." Not necessarily! For instance, think of phototropism: the plant detects the presence of light and uses it to grow towards the light, but that's very simple process regulated by auxins. Or the light-sensitivity ...


7

I found the explanation given below here (my emphasis). It may not be authoritative, but it makes sense to me. You can determine the approximate shape of your visual field by looking straight ahead, and holding a hand out to each side and noticing where you can no longer see them. Do the same for above and below, and you'll see that your peripheral ...


7

There are a couple of advantages and disadvantages of possessing the eyes of octopuses. The first advantage of the octopus eye is that it has no blind spot. This means that octopuses can see everything that is going on in their environment, and are more aware of predators and prey than some vertebrates. Also, they have many more photoreceptors than ...


7

The colour of human eyes is determined by the pigmentation present and the scattering of light. Variance in the colour and density of the pigments affects how light is absorbed and reflected causing the different iris colours we see. Wiki has a fairly comprehensive coverage on the topic so,I'll use a few of the wikipedia examples to explain how the ...


7

Never. Even if the country arrives at the unlikely day when there is no one alive in the United States with the blue eye phenotype, there are still plenty of people with the unexpressed recessive gene, and if two of them get together, those genes can combine to produce another blue-eyed child. If this happens twice, with one boy and one girl, and they ...


6

It's difficult to give an exact answer without actually observing the light and performing measurements. I have a theory, though. Your peripheral vision is hyper-sensitive to changes in light - an evolutionary trait that provided quicker reactions to predators sneaking up on you. As such, even the tiniest fluctuations in light can be registered with your ...


5

I've read somewhere that humans are most capable of distinguishing shades of green, that is a human can differentiate more shades of green than any other color. Is it true? I'd say it's plausible, depending on your definition of "Green." While your eyes do, indeed, have RGB receptors (cones) and Rods for grayscale - they don't perceive the Visible ...


5

This is an optical pinhole effect. If the amount of light passed through the lens decreases, the sharper the image is at the focal point. For a camera this is accomplished by increasing the f stop (f22 is a smaller aperture size than f6 — f-stop is an inverse number). For the eye the iris will dilate (get larger) or contract to be smaller. In very ...


5

I cannot obviously speak for the specific case you mention (and, anyway, I am not a medical doctor so I would not make a diagnosis in any case), but one thing that comes to mind is that eyes are part of the immunologically privileged sites of the body. This means that an inflammatory response is not elicited in case of the introduction of an antigen. I ...


5

It is not completely true. Babies develop the lacrimal system at 42 days, in utero. The canals and ducts for tears are formed at 60 days [2]. At birth, tear production by the lacrimal gland is minimal. Normal tearing develops several days to 2 weeks after birth.[1] Some 6% of newborns are born with a tear duct obstruction (in some online articles it ...


5

Circular pupils are always functionally superior to vertical pupils; a slit does not correctly focus light from all directions whereas a circular pupil does. If you observe cats when they're hunting at dawn and dusk*, they have big, circular pupils; it's only when they're in bright light that the pupil shrinks to a slit. So why have vertical pupils at all? ...



Only top voted, non community-wiki answers of a minimum length are eligible