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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 ...

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 ...

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. ...

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 ...

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 ...

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 ...

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.

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 ...

"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 ...

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 ...

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 ...

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 ...

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 ...

At a fundamental level, no, we're fine with LED lighting. The absorption spectra of our cones are quite broad, and RGB LEDs are chosen to match our color sensitivity reasonably well. That red+green looks the same to us as light that is actually yellow is because our eyes can't tell the difference since we don't have good enough spectral resolution in our ...

To increase long range focus, the ciliary muscle is relaxed so that the zonular fibres flatten the lens. This flattening increases the focal distance and far away objects appear sharp. The process is reversed when increasing short range focus. In your example you are watching out of the window into distance. To see the mountains sharp you need to increase ...

In the situation you describe, the eye would be focused on the distant mountain. This would mean that the lens would be stretched and thin in order to minimize the focussing power of the eye. Therefore the ciliary muscles would be contracted rather than relaxed. When you are looking out of the window, it is possible to make a conscious decision to ...

There are two types of eye movement: smooth pursuit and saccadic. As the name suggests the latter movement involves quick and discontinuous movements of the eyes. Saccadic movement is used most of the time as the eyes move around analysing the current scene. According to Wikipedia, these saccades are the fastest movements produced by the human body: peak ...

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 ...

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 bright ...

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? ...

In rods, the pigment Rhodopsin can be thought of as a receptor protein with a pre-bound chemical agonist. The receptor protein is called Opsin, and the pre-bound agonist is called retinal. The absorption of light causes a change in the conformation of retinal so that it activates the opsin, causing bleaching (changing the wavelengths absorbed by rhodopsin). ...

Light is either monochromatic, or a combination of different wavelength in different proportions. In the eye, there're 4 types of sensor cells: one is greyscale-only, another 3 is for color vision. See the graph here with the spectral sensitivity of the 3 color vision cells. So, for any giver hue, you have very wide possibility of the light spectrum that ...

Your mention of cats hinted that vertical pupils have to do with night vision, and indeed they do. The retinas of cats and other nocturnal animals are very sensitive to even the tiniest amount of light. This can make their eyes hurt when exposed to bright sunlight. So their pupils have to shrink as much as possible in the sunlight, and, as you pointed out, ...

As you've already mentioned, cells near the primate macula tend to make one to one connections. Due to this lack of convergence they can be somewhat smaller than normal cells (particularly in the size of their dendritic arbors) earning them the moniker "midget" ganglion and bipolar cells (also P cells). By reducing the magnitude of photoreceptor ...

Any particular glial cell you're noticing this with? I know that Astrocytes modify Calcium concentrations in the synaptic cleft. Perhaps at places where there are more synapses, more Astrocytes must exist to regulate such thing? Here's an interesting paper on a possible role of Astrocytes on associative networks: http://www.antanitus.com/

I would guess that the eye muscle relaxes when the eye is closed. After having the eyes closed, just in the moment after opening them, it seems that the focus is in the distance. It takes a fraction of a second before you can read some text on your computer screen for example . This focusing-duration seems to be shorter when looking into the distance after ...

Bats distinguish day and night the same way that other animals do, with an internal circadian clock and by environmental cues (dawn and dusk). Most bats (over 1000 different species total) are nocturnal, meaning that they are out of their roost and foraging at night. This includes that vast majority of bats, which also echolocate. Some bats, notably ...

While there is no such thing as perfect vision, growing evidence from Asia shows that looking often at distant objects (which one does naturally when being outside) can stop myopia progression. Vice versa, progression appears to increase when myopic children mainly live indoors. D. J. Park, N. G. Congdon: Evidence for an "epidemic" of myopia. In: Annals of ...

Yes, this is most certainly possible and already being done. As long as the visual cortex of the brain (in the occipital lobe, i.e. at the back of your head) is functional, the correct stimulation will produce visual perception. In cases of blindness caused by malfunction of the retina, meaning that the rest of the visual pathway is functional, this is the ...