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February 25

Feynman Lectures. Lecture 49. Ch.49-4. [1]

...
There would be, if there were no spring, a certain natural frequency ω0 for this one alone. The equation of motion without a spring would be
$m\,{\tfrac {d^{2}x}{dt^{2}}}=-m\omega _{0}^{2}x.$

— Feynman • Leighton • Sands, The Feynman Lectures on Physics, Volume I

How have he derived that? If we have a coordinate system with upward Y and rightward X , then:
$m{\tfrac {d^{2}}{dt^{2}}}x=-{\tfrac {x}{L}}T$
$m{\tfrac {d^{2}}{dt^{2}}}y=-{\tfrac {y}{L}}T-mg$
$x^{2}+y^{2}=L^{2}$
$T+mg{\tfrac {y}{L}}-{\tfrac {mv^{2}}{L}}=0$
Putting the 4th eq. to 1st :

$m{\tfrac {d^{2}}{dt^{2}}}x=-{\tfrac {x}{L}}(-mg{\tfrac {y}{L}}+{\tfrac {mv^{2}}{L}})=-mx({\tfrac {-gy+v^{2}}{L^{2}}})$
But I can't see that $\omega _{0}^{2}=({\tfrac {-gy+v^{2}}{L^{2}}})$ . Moreover if initial conditions are $x(0)=L,y(0)=0,v_{x}(0)=0,v_{y}(0)=0$ , then $\omega _{0}=0$ and at the bottom point ( $y=-L$ ) $\omega _{0}>0$ . Username160611000000 (talk) 09:39, 25 February 2017 (UTC)[reply]

Since Feynman talks about a single equation of motion, this suggests we simplify the problem to a one dimensional one. If we work in polar co-ordinates then the distance from the pivot, r, is constant (it is always L) and we have just one equation of motion in θ, the angle of the pendulum from the vertical. This is derived in our article pendulum (mathematics). Note the approximation for small θ which makes the equation linear.:

{\frac {d^{2}\theta }{dt^{2}}}=-{\frac {g}{\ell }}\theta

which has the same form as Feynmann's equation with

\omega _{0}^{2}={\frac {g}{\ell }}

This is an example of simple harmonic motion. Gandalf61 (talk) 10:24, 25 February 2017 (UTC)[reply]

Hm. Thank you. In the small angle approximation

({\tfrac {-gy+v^{2}}{L^{2}}})={\tfrac {+gL+({\tfrac {dx}{dt}})^{2}}{L^{2}}}

. And so we must put

({\tfrac {dx}{dt}})^{2}=0

. But is it correct? If x is small there is no guarantee that

({\tfrac {dx}{dt}})^{2}

is small.Username160611000000 (talk) 11:57, 25 February 2017 (UTC)[reply]

Taste of VX

I heard a report of VX (nerve agent) being tasteless and wondered how we could know. The article itself has a [further explanation needed] tag. Could you explain? --Error (talk) 15:43, 25 February 2017 (UTC)[reply]

Since treatment is possible, it may well be possible to ask the victims if they tasted anything. A more inexplicable case is in the article on radon, where Rn is described to be tasteless; although this is stated in some actual reliable sources, it still sounds rather silly because if there was enough Rn around to taste, the alpha radiation from its decay would presumably be much more significant. Double sharp (talk) 16:01, 25 February 2017 (UTC)[reply]

Since it's tasteless, "if there was enough Rn around to taste" is an impossible condition. Henry ^Flower 16:35, 25 February 2017 (UTC)[reply]

Well, being an unreactive noble gas, it is almost certainly tasteless, but what would be interesting to see how this could have been verified experimentally. Double sharp (talk) 16:41, 25 February 2017 (UTC)[reply]

They might have asked the Radium Girls. - Nunh-huh 05:56, 1 March 2017 (UTC)[reply]

There are plenty of reliable sources to confirm that it is tasteless, but nobody says how they know that, as far as I can tell. Alansplodge (talk) 18:25, 25 February 2017 (UTC)[reply]

The taste and smell of chemical weapons is a matter of some importance, as even human noses are a pretty good early warning system. Also practically every agent, even the post-war nerve agents, isn't that toxic - you can smell these things and survive, especially if you use the warning to run.

The taste/smell is known from a few sources: someone tasted it by accident and their last words were "tastes like chicken" (there are a few of these) or simply that they didn't notice any distinctive smell, the structure is close enough to less toxic analogues with recognisable smells that it can be inferred, or if the material's physical properties aren't volatile enough at ambient temperatures, it can be assumed to have little or no practical smell (it might smell of something if heated, or in concentration).

Most nerve agents simply don't smell though - their function is to be hazardous at such low concentrations that they need not be odorous. Andy Dingley (talk) 19:51, 25 February 2017 (UTC)[reply]

Having fewer early-warning signs makes it a better weapon too. See for example Phosgene#Chemical warfare. Another article I remember mentioning that a certain chemical-weapons agent that had noticeable odor was doped with another easily-smelled chemical to mask the odor, leading to the opponent recognizing the innocuous odor as the sign of a chemical weapon attack, but I can't find the article at the moment. DMacks (talk) 21:47, 25 February 2017 (UTC)[reply]

The US Army's Edgewood Arsenal has infamously done several human volunteer trials on nerve agents. There are people who claim the UK's biological/chemical defense labs at Porton Down performed similar research in human volunteers. Smell and taste are phenomena which occur at chemical concentration levels much lower than lethal cholinesterase inhibition caused by nerve agents. For VX, the LCt₅₀ for inhalation is estimated to be 30–50 mg·min/m³.

So it's plausible, at least, that a human volunteer did indeed inhale a sub-milligram dose of VX and live to tell the tale. Or at least report his impressions before dying. loupgarous (talk) 01:48, 26 February 2017 (UTC)[reply]

Porton Down did do experiments on humans, see Ronald Maddison. Widneymanor (talk) 09:02, 26 February 2017 (UTC)[reply]

That was Sarin though, not the V agents. These are too toxic (V agents maybe 10× the G agents) for such skin exposure experiments and their development also post-dates the abandonment of such testing. Although remember that they were developed as insecticides: Amiton (it's good against mites) was sold as such in the early '50s.

The point here though is that even a skin drop exposure is considerably more exposure than a potential smell. Andy Dingley (talk) 11:29, 26 February 2017 (UTC)[reply]

Military development of nerve agents for Chemical warfare is concerned as much with lethality (typically gauged by Median lethal dose LD₅₀) as with measures for protecting and decontaminating friendly troops and non-combatants. Against VX exposure, antidotes Atropine, Pralidoxime (2-PAM) and injection of Diazapam are indicated, and a US Army source dead link? described a Nerve Agent Antidote Kit. Clearly such antidotes could have been tested only by trial exposure of human subjects who survived to report the experience. Incidentally, some forms of the Botulinum toxin that celebrities pay to have injected into their pretty faces have even lower LD₅₀ than VX. Blooteuth (talk) 14:21, 26 February 2017 (UTC)[reply]

The newly discovered 7 earth size planets II

I am beating a dead horse. It is about this Internet cnn article: [2].I want to describe my motivation. I don't believe there is another planet in the Galaxy with intelligent life. I think the development of such life here on Earth was a result of events with extremely low probabilities, like acquiring mitochondria by unicellular organisms, so I wonder why people are so optimistic about those 7 planets. I just posted here in this desk a couple of days ago [3] Now I have a different question though. Those planets are so close to the star they must experience significant tidal forces. The magnitude of them should affect the chance for any life to develop. Could they be calculated? Thanks, - --AboutFace 22 (talk) 16:42, 25 February 2017 (UTC)[reply]

Tidal forces may be able to be calculated, but we don't understand abiogenesis nearly well enough to calculate how any particular force would affect liklihood of it occurring. Also: I wouldn't say the scientists are "optimistic", I'd say they are excited about interesting new things to look at. Popular press coverage is often breathlessly excited hype with little grounding in science or reason. Blooteuth had a lot to say about that and some good refs in the previous post, look there for more on that. SemanticMantis (talk) 17:57, 25 February 2017 (UTC)[reply]

Why the assumption of rarity? Forgetting intelligent life (since we don't have a lot of examples to look at), endosymbiosis seems to have happened at least twice in Earth biological history. --OuroborosCobra (talk) 18:12, 25 February 2017 (UTC)[reply]

Indeed. According to endosymbiont, many times.--Wikimedes (talk) 19:49, 25 February 2017 (UTC)[reply]

Multiverse theories would suggest that we live in a universe where the probability of our existence is maximized. So, if creating life in the lab is hard then that's probably only because life arising in a too easy way would have interfered with the development of more complex life that could give rise to us. Count Iblis (talk) 19:25, 25 February 2017 (UTC)[reply]

I would like to know what the magnitude of the tidal forces on those planets are. It is all speculation on my part but most of the answers so far, e.g. about the multiverses, etc. are even more speculative. So, if the tidal forces are high then first, the planets may have a lot of internal heating occur. What's the surface temperature then? Suppose one of the planets has water oceans and some land mass. If the tidal waves are high, the oceans may easily roll over the land mass every other day or so. If this is true, if the tidal forces are problematic, a certain class of earth size planets could be ruled out of consideration.

I want to give a real life example for comparison, just to appreciate the "magnitude" of very, very low probability events. It concerns Sporadic Creutzfeldt-Jakob disease. It affects prions, the structural proteins in all living forms. Imagine how many cells are in a human body, and each cell has countless number of prion molecules. They are subject to dying and regeneration, plus during the earlier development billions of them are created. This process is flawless, ALMOST. Once in a billion billion replications a quantum tunneling occurs and bingo, a misformed prion is made. It has a terrible property to convert all neighboring similar prions into this misformed state and the individual dies. Different species apparently have different probability of such an occurrence but in humans it is very low. Now listen here. At the end of WWII when missioners penetrated inner parts of New Guinea they found a tribe where almost everyone had this disease but it was not sporadic. They infected each other. It was calculated that the first case happened in 1910 and it was sporadic. Those people lived there for thousands years and never had Creutzfeldt-Jakob. Each of them had billions of prions which for generations were normal. And all of a sudden in 1910 that incredibly low probability event occurred. My point is that acquiring the mitochondria could have been even a much lower probability event the true frequency of which we don't know.

Homo sapiens developed in Africa but not in the Americas. The Americas haven't even had apes. There is one ape species in Asia but not intelligent development beyond that. This is one more strange probability that may not happen elsewhere ever again. --AboutFace 22 (talk) 21:26, 25 February 2017 (UTC)[reply]

We can speak of tidal forces in the TRAPPIST-1 system but these may be only stresses in planetary rock material; ocean tides such as we see on Earth would only be possible if liquid water (possibly on any of the 3 planets in the "Goldilocks" zone) is confirmed. We have estimates of the individual planet masses and orbits but I do not see any solution of the 8-body system that would yield an orbital almanac or Ephemerides that would be the basis for calculating tidal forces. Individual orbital periods ("years") seem short at mostly under 20 days but if the orbits are not in a simple resonance, there may be much longer time between tidal maxima than the time we have been observing the system. Note that gravitational forces are inversely proportional to the square of the distance but tidal forces are inversely proportional to the cube of the distance; the significance is that if a TRAPPIST-1 system resident were observing Earth and wondering about our tides, (s)he/it would very likely miss our tiny Moon that due to its relative closeness exerts more than double the tidal force of our Sun. Actually the near equal inclination of all 7 TRAPPIST-1 orbits is consistent with the planets being the result of the breakup by tidal forces of a previous single body, and after such short observation we don't know whether we are looking at a stable orbital system. It is not possible to make statements about chances for life to arise without invoking one's own belief system. The scientific community favours a variety of Abiogenesis mechanisms followed by a hardly-to-be-questioned evolution of the species₁ that culminates in ourselves₂. That is the background of the sourced statement here "All seven planets are likely to be tidally synchronized (one day = one year) making the development of life there "much more challenging". To the implicitly assumed Western tenet that Abiogenesis precedes Consciousness I respond with the opposing view expressed in Tibetan Buddhism that conscious existence predates the existence of bodily life. To read further: Gentle Bridges - Conversations with the Dalai Lama on the Sciences of Mind 1992, Random House / Shambhala Publications. Quote: "Buddhists cannot accept (the scientist's view) that consciousness arises from a material cause." Blooteuth (talk) 21:50, 25 February 2017 (UTC)[reply]

Note that when the Moon formed it was ten times closer to Earth and the tidal forces were as a consequence a thousand times stronger than what they are today. Count Iblis (talk) 22:53, 25 February 2017 (UTC)[reply]

Tidal forces vary with the cube of the distance ? I would have expected the square. Do you have a source for that ? StuRat (talk) 04:32, 26 February 2017 (UTC)[reply]

Yes, tidal force is approximately inversely proportional to the cube of the distance, since it depends on the difference between the gravitational force between two points. See the last equation in our tidal force article.

It should be noted that some theories of abiogenesis suggest that tides were beneficial or even essential to the development of life on earth [4]. By these theories, "water rolling over the land every other day" is a good way to get life started, since the prebiotic chemicals get concentrated in the drying tide pools. CodeTalker (talk) 05:02, 26 February 2017 (UTC)[reply]

Thanks. Does that mean (water) tides would be 1000 times higher ? StuRat (talk) 05:09, 26 February 2017 (UTC)[reply]

Yes, but the initial distance between the Earth and the Moon is believed to have been more like 60% of the current distance, not 10% a good summary of the thinking here. So more like 4.6 times higher, rather than 1000 times higher. I'm pretty sure I'd have remembered something about kilometer high tides. Someguy1221 (talk) 09:29, 26 February 2017 (UTC)[reply]

I do actually remember hearing about mile-high tides shortly after the formation of the moon, but the source would have been Discover Magazine, most likely. Here, SciAm predicts the moon being twice as close, with 12-hr days. This forum says critically that the History Channel gave tides 1,000X today's height. μηδείς (talk) 03:28, 27 February 2017 (UTC)[reply]

See here: "It is not easy to estimate how far away from the Earth the Moon was when it formed, but simulations suggest is was about 3-5 times the radius of the Earth, or about 20 to 30 thousand kilometers. (The Moon is currently about 384,000 km or 60 Earth radii away from Earth, which is about fifteen times further away than it was when it first formed.) The Moon probably couldn't have formed closer than 3 Earth radii because tidal forces from the Earth would just pull it apart again, and it is unlikely that the impact could have ejected material further than 5 Earth radii. It's not a totally easy questions to answer though as it depends a lot on the (unknown) details of the impact and how the hot material behaved in space."

Also note that just after the Moon formed the enormous tides would have made the Moon recede from the Earth at a fast rate, thousands of times faster than the current rate. Oceans had not yet formed on Earth, the Earth's surface was much too hot. In fact, as pointed out here: "The moon, being much smaller than Earth cooled more quickly. Because the Earth and the moon were tidally locked from the beginning, the still hot Earth -- more than 2500 degrees Celsius -- radiated towards the near side of the moon. The far side, away from the boiling Earth, slowly cooled, while the Earth-facing side was kept molten creating a temperature gradient between the two halves." Count Iblis (talk) 05:33, 27 February 2017 (UTC)[reply]

There is unlikely any tidal force at all because the planets dont rotate around their own axis but are in Synchronous rotation aka Tidal locking to the sun, like our moon orbits earth, always showing the same side to us. In such narrow orbits this tidal locking is very likely. This is also assumed for the closest known exoplanet Proxima Centauri b. --Kharon (talk) 12:20, 26 February 2017 (UTC)[reply]

Io (moon) is in a locked orbit and it experiences significant tidal heating due to the excentricity of its orbit. To quote from the discovery paper: "The TRAPPIST-1 system ...represents a unique opportunity to thoroughly characterize temperate Earth-like planets that are orbiting a much cooler and smaller star than the Sun, and, notably, to study the impact of tidal locking, tidal heating, stellar activity and an extended pre-main-sequence phase on their atmospheric properties." Scientists are optimistic that all these things (including detection of signatures of life IF there is life) can be studied in the system, but the investigations have only begun. --Wrongfilter (talk) 12:47, 26 February 2017 (UTC)[reply]

@Kharon is correct that there are no tidal forces when only 2 bodies orbit circularly around their common center of mass, and each rotates once per orbit. That is a classic soluble Two-body problem. However each body (planet or sun) of the TRAPPIST-1 system is pulled by gravity to each of the other (known) 7 bodies. Nobody promises that Celestial mechanics is easy; Celestial mechanics#Perturbation theory suggests where the work is needed on this thorny n-body problem. The article Orbital mechanics gives specific mathematical solutions. You may however enjoy the beauty of some demonstrable multi-body orbital solutions of the choreographic kind, or sketch your own, on this Java page. Blooteuth (talk) 13:38, 26 February 2017 (UTC)[reply]

Extra visual colors via eye tracking?

As I understand it, some of the VR applications? or other equipment coming out do eye tracking where they have a good idea of where the user is looking. It just occurred to me that maybe this isn't entirely for spying on people after all...

Suppose a reader frequently looks at a high resolution computer screen (or, ideally, set of binocular computer screens) that displays video content. The reader is color blind. A camera very closely tracks where he is looking, and superimposes a fine-grained pattern that goes wherever he is looking. The fineness of the grains depends on how accurately it can follow his gaze, the resolution of the system, and whether it's binocular. In half the superimposed pattern, the screen content is changed to exclude the green channel - in the other half, to exclude the red. As a result, there are small fixed regions within his vision, so long as he uses the computer, which are "red-sensitive" and others which are "green-sensitive" - perhaps with some degree of channel mixing to help them appear as one image; after all the red-green receptors themselves have overlap.

Now I've read that people can get used to looking at the world rotated 180 degrees, so I'm thinking maybe in time, supposing he has a heavy computer job for example, or the system is made a standalone prosthesis, that is all it takes to perceive different green and red color values. The person's eyes might learn to process the colors differently and he might even see them as different colors subjectively.

Some time after the experiment, I'd expect these regions to return to normal; if the experiment were repeated with a different set of random regions, I wonder if the person could relearn to see the difference between green and red in those new areas. Would green and red seem like different colors subjectively than they did the preceding time?

Of course, there's nothing in principle to keep the same experiment from being done by people who have normal 3-color vision who want to get a taste of the tetrachromat life.

Is there anything to back up any of this, and is anyone working on such lunacy? I take the X-mosaicism tetrachromats to support the idea of learning to link regions to colors can be done by simple random differentiation - is that sound, at least? Wnt (talk) 21:43, 25 February 2017 (UTC)[reply]

There's certainly work being done on representing colours via other senses: see e.g. this abstract. (Note however the mention of "low spatial resolutions"). I can't see the whole paper, but e.g. this article covers some of the same research and does say that the input can be perceived as colours (caveat again: the systems can take a long time to learn to use). Henry ^Flower 22:32, 25 February 2017 (UTC)[reply]

Eye tracking describes techniques for a real-time experiment. False color images can render non-visible parts of the Visible spectrum or simulate the effect of Color blindness. Blooteuth (talk) 22:54, 25 February 2017 (UTC)[reply]

I believe that eye-tracking has been used experimentally to stabilize images to generate the perception of impossible colors such as bluish-yellow and reddish-green. See https://www.ncbi.nlm.nih.gov/pubmed/17736657 -- The Anome (talk) 14:15, 26 February 2017 (UTC)[reply]

But the OP's question (insofar as I track it accurately) would hinge on the degree and exact mechanism of the colour blindness. If the retina simply lacks sufficient cones receptive to the right wavelengths of light (particularly in the fovea), then it won't matter what colors the monitors preferentially exclude. Wnt seems to be inquiring as to whether the overstimulation of a colour will lead to it's "negative" for that cone type being slowly imposed over it, but that belief seems to be based on the assumption that the phenomena of an afterimage is a top-down process occurring in the brain; in reality it is an effect that results from overstimulation of the actual photo-receptive cells. So the effect on a person who lacks sensitivity to colour at the level of the retina would be unaffected by the suggested technology. So the notion of adaptive vision in this respect doesn't hold; the studies of the flipping of one's vision along the horizontal axis involve entirely different visual cognition systems, so what holds for them in terms of adaptability cannot be generalized to visual processes broadly. The ability of the brain to adjust to a flipped stream of visual input seems to be related to the fact that the brain already has separate module for this process, because it already has to flip the image "once" (the optics of the eye are such that visual stimuli is delivered upside-down to the retina). As a result, the phenomena has become very interesting to those intrigued by the complexities of qualia.

Now, if we were talking about someone who had impaired colour vision as the result of brain trauma, then you might inquire as to whether Wnt's technology might illicit a sensation of colour, and while I wouldn't stake a guess on the likelihood, I wouldn't say it's strictly speaking impossible. On that same line of open-mindedness and addressing Wnts last inquiry, experiments on genetically modified mice (naturally dichromats) given trichromatic eyes seem to impart them a somewhat increased ability to differentiate between certain colours they would otherwise lack, although that research has been somewhat debated. Regardless, there are a lot of known types of phenomena where the brain is able to adjust a the modality of a sense; some research seems to suggest that in blind people who use echolocation techniques, parts of the visual system usually used to coordinate spatial dimension and object position in neurotypical persons are co-opted for improving the acuity of this process. There are other examples. One caveat; these phenomena (to lesser or greater extents) generally have to be hardwired to some extent during early developmental stages; the adaptability to flipped vision is kind of an outlier in this regard. Snow ^{let's rap} 09:17, 1 March 2017 (UTC)[reply]

It's true that I was assuming a colorblindness like red-green where cones are present that can sense the light - just not tell which color it is. I suppose hypothetically a subject could conceivably learn to see color even with rods alone by this mechanism, but I'd think it would be less likely the eye could actually adapt to that. Wnt (talk) 14:23, 1 March 2017 (UTC)[reply]

The thing is, each cone is sensitive to a certain frequency range of light, and mostly fire only when triggered by accordant stimuli. So the notion of them them being able to "sense light but not know which colour it is" doesn't make much sense. That's the status quo for a cone. A photoreceptive cell never "knows" anything about colour; colour perception results when a large number of such cells are stimulated by light in the frequency they are sensitive to and (if that stimuli passes a certain threshold) are then triggered to report that status by firing messages (at various rates). That data is aggregated at several levels and then passed to the brain, where it is integrated, filtered and somehow results in qualia (though one of the big questions in cognitive science is how stimuli and its processing results in a subjective experience of colour itself, or any sensory experience--that is, an element of the hard problem of consciousness). But speaking strictly about physics and biomechanics, colour does not, in any empirical sense, exist at that level, so the cone is oblivious, if you will, to its existence as phenomena. It either receives the stimuli and is triggered to fire or it doesn't. It can't be triggered to the sense of "green" or any other colour. So no, your hypothetical would not result in any additional colour vision via rods alone, because rods play a much, much smaller role in color perception and even then, they are sensitive to a wavelength entirely different from those of the cones you are proposing they would compensate for. Snow ^{let's rap} 19:57, 1 March 2017 (UTC)[reply]

@Snow Rise: I've put a figure of cone cell sensitivities at top. As you see, there is a large region of M and L (green and red sensitive cones) that overlaps. So the eye learns to distinguish between the overlapping cones based on which ones have a bit higher reading - and if we create this situation artificially, we can carve out a new sensitivity profile (though no wider than the original) by giving the cones in a certain small area a higher signal when the color falls within parameters. Wnt (talk) 00:55, 2 March 2017 (UTC)[reply]

I'm not really understanding what you are proposing there, but I can assure you that the eye doesn't "learn to distinguish" anything and the hypothetical you proposed above just doesn't jive with the basic biomechanics (or neurology) of sight. You proposed above a situation in which the photoreceptive cell "senses" the light but "can't determine what colour it is." That suggests a breakdown of the stimulus into two discrete components, but that's just not physically how that system works. The photoneuron is either sensitive to the wavelength of light it absorbs, or it isn't, and thus fires or does not fire accordingly (actually its a lot more complicated than that of courses, because the way the number of incoming photons and their varying wavelengths is processed is very comlex, plus there are some specialized support nuerons that integrate the information received from the complex patterns of firing between the photoreceptive cells--but the basic mechanism by which the individual cone interacts with an individual photon is the situation I describe, not the one you postulate). If someone has a lack of sensitivity to a given wavelength because they simply lack functional cones, then the system you describe will do nothing to change their reception of that particular wavelength, because the disability is at the level of the individual cells. Further, while particular photoreceptors can be so heavily stimulated over the short term that when the composition of the stimulus is changed, there can be an afterimage, that is entirely a different mechanism from the one you are proposing; those cells are simply not adaptive in the way you would need them to be for your scenario to work (and if they were, they would be highly problematic for the rest of our vision system as it does work). Yes, there is some overlap in the wavelengths which contribute to stimulus response (but don't necessarily trigger the firing of the cell) in L and M cones, but that difference is not trivial, and the cells respond differentially, the closer the stimulus is to the wavelengths described in the peaks of those graphs. Otherwise, we would not be true trichromats. So you could use eye-tracking to try to increase the vibrancy of colors when the relevant part of the screen is being focused upon by the fovea, but I don't know why you would do that when you could just adjust the color of the entire image. Snow ^{let's rap} 03:23, 2 March 2017 (UTC)[reply]

We're definitely having trouble getting on the same page. It is my impression that:

a) As described at photoreceptor cell there is a so-called "principle of univariance" (they link W. A. H. Rushton) that photons of any color a cone cell absorbs will cause the same response in the cone cell, if absorbed. The probability of absorption varies by wavelength. So a green cone and a red cone both respond to yellow and orange - they just do so with slightly different efficiency, and the color depends on which responds more.

b) The existence of tetrachromat humans means that, amazingly, the eye is not hard-wired to only respond to the three pigments. If an extra type of cone cell expressing a fourth pigment in mosaic pattern is thrown into the mix, the system is actually capable of recognizing it as an additional source of information about what colors are present. I would think, but do not have proof, that if some cone cells of one of the three types in the retina start firing at different rates than the others of the same type, that this is conceptually similar to making a genetic change to the tetrachromat mosaic condition, and eventually will lead to perception of an additional color distinction.

c) Therefore, if we could track the eye motions during a large proportion of some days or weeks and always change the degree of light broadcast by the parts of the screen that are seen by one of those sets of small groups of cells and not by the other, I'd hypothesize it ought to mimic the effect of having a receptor with a different color sensitivity, creating a tetrachromat distinction. And I was wondering if anyone had tried anything along this line. Wnt (talk) 04:43, 2 March 2017 (UTC)[reply]

a) Roughly correct, though it's important to note the much higher rate at which the peak wavelengths trigger firing wavelengths and the fact that cells are usually clustered together with similarly constituted receptors and that their firing is integrated into intermediary specialist neurons which will themselves fire or not (at differing rates) depending on how their whole little network of cones is stimulated. That. combined with a high threshold of mostly just the right light for each individual cone, tends to limit the impact of light in the shared middle range, although there is some overlap in how much light in that range stimulates both varieties of cone. The last clause of that last sentence, I am unsure of how to interpret. Yes, the efficiency of the absorbing proteins relative to each wavelength do change which cells fire more regularly. But it's worth repeating that the "red" or "green" don't really come into play until all of this data gets dumped into our lovely noggin' meat.

b)The question of tetrachromacy in humans is extremely controversial, although there is some belief that a limited perception of ultraviolet light in circumstances where it reaches the retina may be possible, but it would probably be in the very near range of the ultra-violet spectrum to wavelengths we can already confirm we see. There is that anecdotal evidence of the mice purported to have been changed from dichromats to limited trichromats but there have been questions about the reproducibility of the original study. In any event, its kind of a stretch to assume that the ability of one brain to move from interpreting the dichromat color field to trichromat field to mean that another brain, from a different species no less, could accomplish the same feat to create a functional tetrachromat from a trichromat; the difference in the number of colors that the brain would have to be capable of processing is orders higher. But more to the point your theory is just not remotely a biological possibility. The cells will not start "adapting" themselves to firing differently, if we are talking about one actual retina of an actual person. They will continue to faithfully report the exact wavelengths that stimulate them at the level of stimuli they are experiencing. The system they are plugged into would eventually downgrade the overall impact they are contributing to the "final" gestalt perception (hence afterimage optical illusions), but only to a limited extent, and only temporarily.

c) And so, no. :) Snow ^{let's rap} 09:32, 2 March 2017 (UTC)[reply]