Wikipedia:Reference desk/Archives/Science/2022 June 16

= June 16 =

Can optical illusions be used for medical purposes?
I stumbled upon this picture: https://twitter.com/SteveStuWill/status/1537102642345746435

And I did see curly green lines instead of the straight ones which they really are. For military duty we were asked to look at a picture filled with colored dots and asked if we could see a number. The color blind couldn't, the others said "that's obviously a 9". I think the test had no false negatives and no false positives.

Such tests are very simple and cheap while at the same time testing a full range of brain functions in a few seconds. Listening, understanding, looking, explaining, and let's not forget turning light into an image and minimizing the image to what is being asked, it's almost absurd what our brains can do. And it's not a vague Rorschach test, the answer to each picture is just Yes or No.

It might be possible that if you don't see curly lines, there's an 80% chance that you will be diagnosed with Alzheimer disease within 10 years. Or maybe people answering No to picture 3, 5 and 8 show a more than average shortage of vitamin X after a blood test. I have no medical background but I think such correlations are very well possible. I wonder if someone researched to see if optical illusions are not just funny on Twitter, but could actually be helpful in a doctor's office. Joepnl (talk) 01:29, 16 June 2022 (UTC)


 * The test you did in the military was likely some version of the Ishihara test. Without needing much specialized training from the examiner, it gives a >99% correct classification of the various color-blindness tests. It is very cheap, quick, and not very invasive for the patient.
 * Such a test is really an outlier within all diagnosis tests, both in ophtalmology and in all of medicine. The usual status is either that there is no test with really great stats of precision and recall (= many false positives and/or false negatives), or that the test is highly invasive. For instance, breast cancer screening can be done by three tests: self-examination by the patient, which is not very invasive but is not very reliable; mammography, which is more invasive but more reliable; and biopsy, which is super-invasive but super-reliable.
 * The Ishihara test works very well because the underlying condition has one single symptom, it is (almost) binary (most people with color vision deficiency are entirely color-blind, not kind-of-have-difficulty-to-separate-color-partially-blind), and the symptom is constantly present among affected individuals (so that no special conditions are required to do the test).
 * Without a medical background, I can understand why a visual test showing colored stuff detects color-blindness. But when it comes to detecting vitamin deficiency etc. it’s hard to see how that could be diagnosed with visual tests. I suppose that some medical problems that are not directly vision-related cause some vision changes and that a diagnosis test could be based on that; but I expect that the average such test would have abysmal precision and/or recall. Tigraan Click here for my talk page ("private" contact) 09:10, 16 June 2022 (UTC)
 * The trick image seen by the OP is an example of contradictory patterns that compete in the viewer's mind for recognition. That describes many "impossible" objects that can be drawn. The artist M. C. Escher was able to fill art galleries with such Trompe-l'œil illusions. These optical illusions work for the majority of normal people and are of no use to indicate ill health as the OP speculates. Please leave the design and use of images for medical tests to qualified medical practitioners. Such images are entirely different and include the Ishihara tests for colour vision, the Rorschach tests for examining pareidolia (seeing an object, pattern, or meaning where there is none), your opthalmologist's Snellen chart for visual acuity or an Amsler grid for macular degeneration. A claim to diagnose future Alzheimer's disease or some unspecified vitamin deficiency using only an image would be so extraordinary that without extraordinary evidence the notion must be rejected. Philvoids (talk) 11:07, 16 June 2022 (UTC)


 * The fact that an optical illusion is an extremely simple and quick test is why I'm asking. Posters in the waiting room of the GP, "if you don't see curly lines, please tell the doctor", something like that. Don't know which illusions to use, don't know which diseases to detect, but an extremely wild guess is that patients suffering from migraine or epilepsy have different answers than patients who don't. I'm sure blindness is one, but who knows what an illusion can also detect? Compare the story of a girl who got advertisements for diapers, just the words she typed in a search engine was enough to guess she was pregnant before she knew herself. I was hoping someone did the research and did find a huge correlation with a vitamin deficiency. Joepnl (talk) 12:02, 16 June 2022 (UTC)
 * who knows what an illusion can also detect? Nobody knows, but the most likely answer is "not much", and I would bet quite a large sum of money on "nothing that isn’t related to vision". The fact that it’s cheap/easy to set up might mean it’s cheaper to test, but that’s a "searching for keys under the lamppost" way of choosing one’s research goals.
 * Regarding the diaper advertisement etc., this has grown into some sort of an urban legend. The original source is this NYT article. The facts are that Target Corporation had a project to identify pregnant women based on consumption IDs; that they sent explicit advertisement based on that ("congratulations on your pregnancy!"); that the father of such a (teenage) woman received that advertisement, complained to the store, and the girl later admitted to pregnancy. So in that one instance, the women was not unaware of her pregnancy. The strong claim is that Target’s model "knows" some woman is pregnant before she does (for some statistical definition of "knowing"; I am sure I can get quite a good record by just guessing "yes" on every married women between 25 and 30). To my knowledge, there is no public evidence of that. (Yes, journalists have found women that received Target’s advertisement before they knew they were pregnant. The question is whether much more did than would be managed by demographic-based messaging.) Tigraan Click here for my talk page ("private" contact) 13:32, 16 June 2022 (UTC)
 * You might be interested in [//www.nytimes.com/2021/02/01/health/alzheimers-prediction-speech.html] and perhaps [//www.nature.com/articles/s41746-021-00470-z]. Note that it is clear from these that attempts to use big data analysis to provide or improve predictions of dementia or specifically Alzheimer's are still in a very early stage, while they may be considered simple, require significantly more from an individual than just viewing one image and no one particularly expects the prediction will be anything close to a yes or no. On the other side, there are attempts to develop blood tests using biomarkers for predictions [//www.lunduniversity.lu.se/article/app-predicts-risk-developing-alzheimers]+[//www.lunduniversity.lu.se/article/new-blood-test-shows-great-promise-diagnosis-alzheimers-diseasesince] in most of the developed world with decent medical systems blood tests are fairly low cost tests and also fairly non invasive for most patients. Nil Einne (talk) 01:23, 17 June 2022 (UTC)


 * See the Treatment section in Phantom limb. manya (talk) 06:45, 17 June 2022 (UTC)
 * Visual cliff is an interesting test of depth perception. DMacks (talk) 17:22, 17 June 2022 (UTC)

What do plants do to counter animal-waste?
Plants have been crapped on for as long as plants and animals have been around. We know for humans, we have chemicals and non-chemicals to fight bacteria and viruses. Non-chemicals such as macrophages, lysozymes, and white blood cells, and chemicals such as H2O2 and HOCl. What do plants have for chemicals and non-chemicals to fight that? Also, plants can sometimes be urinated on, but I think, mammalian urine does more good than bad. It has fertilizer properties, as well as cations and anions which can be for nutrition. So I imagine urinating on plants is not an issue. 67.165.185.178 (talk) 02:41, 16 June 2022 (UTC).
 * Plant cuticle resists penetration of foreign matter. The waxes are fairly inert. Though if a plant is buried under a cowpat, it won't get any light. It may grow a new shoot to get around the problem. Graeme Bartlett (talk) 04:07, 16 June 2022 (UTC)
 * Cattle urine patches talks on one of your topics. Graeme Bartlett (talk) 01:20, 18 June 2022 (UTC)

Could racism and cruelty be caused by infections from bacteria or viruses?
Could evil emotions be caused by infections that either affect our hormones or get in our brains? To be objective, I should ask,could good emotions like kindness, patience and honesty also be caused by infections? ..We often observe that a child's ethics or lack of can be learned from the example given by their parents, but how do we know that the child's ethics aren't passed on from a pathogen given to the child by a parent? Also, what about low average intelligence, could that be caused by infections?Rich (talk) 05:40, 16 June 2022 (UTC)
 * See Nature versus nurture. --←Baseball Bugs What's up, Doc? carrots→ 06:21, 16 June 2022 (UTC)


 * It is well known that some infections (meningitis!) can cause lasting neurological impairments that diminish the patient's intelligence. Some pathogenic microorganisms are known to affect the behaviour of infected animals. Spinochordodes tellinii and Paragordius tricuspidatus are extreme examples, inducing suicide by drowning in infected grasshoppers and crickets. Another well-studied example is Toxoplasma gondii, that makes infected mice lose their fear of cats. Dicrocoelium dendriticum makes an infected ant climb night after night to the top of a blade of grass and sit there till dawn, until it is eaten by a grazing animal. For humans, there is evidence that some gut bacteria, usually considered non-pathogenic, may contribute to autism, while others may relieve anxiety and depression. So, yes, at least in theory it is conceivable that some infectious agents have effects on the relative strengths of various emotions. --Lambiam 10:42, 16 June 2022 (UTC)
 * Toxoplasma gondii infection in mice lowers general anxiety, increases explorative behaviors and surprisingly increases a general loss of aversion to predators without selectivity toward cats. I mean to point out that it's beyond the scope of a virus, bacteria, or even an intracellular parasite, to select for the recognition of some complex entity like a cat, even in a mouse, never mind in humans with all our abstract and creative ideas. It's debatable whether there are any such things as grandmother cells (used for recognition of grandmothers), and even if there are, it would be extraordinary for a microorganism to be able to target them, since they probably have no predictable characteristics, and their locations probably vary from person to person, if they exist. Even then, the infection could only cause an unreasoning disgust about, say, Samoan people (which I mention since "racism" is in the post's title), which is not at all the same thing as interfering with the host's ethics. That is to say, a good person ought to be able to use reason to overcome any irrational visceral disgust. I might find myself having to carry a sick bag whenever hanging out with my Samoan best friend, and perhaps we'd tend to prefer to be online buddies, but this needn't affect my ethics or my politics. This kind of gut feeling can prompt racism or cruelty, but doesn't directly control it.  Card Zero (talk) 11:39, 16 June 2022 (UTC)
 * The more successful viruses cause a behaviour change which aids propagation, for example the rabies virus is present in saliva and rabid dogs bite anything they come into contact with. 2A00:23C5:C719:7201:1A:5EB9:69D5:D178 (talk) 17:20, 17 June 2022 (UTC)

Well, among the infections that are at least somewhat survivable, like the ones in ants and mice, can those infections be transmitted to offspring from parents, or, in the case of ants, to other ants?Rich (talk) 22:30, 17 June 2022 (UTC)
 * Children can catch an infection from their parents. --Lambiam 07:19, 19 June 2022 (UTC)
 * Erma Bombeck once said, "Insanity is inherited. You get it from your kids." --←Baseball Bugs What's up, Doc? carrots→ 11:40, 19 June 2022 (UTC)

Electric animals
I've just been playing Let's Go Pikachu on my Switch tonight. It got me thinking. We have loads and loads of aquatic animals that can use electrical discharges for attack and defense, right? Why is it that we don't have any terrestrial animals that can also do that (say, if a lion could emit an electric arc to paralyze and drop a zebra, or a bug where it's jaws were like the two terminals of a stun gun)? Or not any that I'm aware of. Maybe I'm wrong? Was there a little jungle bird somewhere a few years ago that could emit electricity if touched? I may have dreamed that. Is there a physical reason why that couldn't happen on land? --Iloveparrots (talk) 07:22, 16 June 2022 (UTC)


 * Actually, thinking about it further. We have stun guns, that require skin contact. We have tazers that rely on shooting out wires at a distance to deliver an electric attack. But I don't think we have a weapon (yet?) that can deliver a targeted electric discharge at a chosen target across a distance? Is that right? Which leads me to believe that this is is difficult, if not impossible? So, probably the same in nature? But less evolutionary complex than an organism that can emit two electrode terminals somehow? So one of my points upthread may be invalid. --Iloveparrots (talk) 07:33, 16 June 2022 (UTC)


 * Further research. Ignore the "little bird" claim above. I was thinking of the hooded pitohui, which emits a neurotoxin, not electricity in defense. But yeah, I'm still curious as to why electric animals don't exist on land. --Iloveparrots (talk) 07:46, 16 June 2022 (UTC)
 * Dammit, you got my hopes up that there was an electric oriole. Card Zero  (talk) 11:00, 16 June 2022 (UTC)


 * Electroreception and electrogenesis claims that The capabilities are found almost exclusively in aquatic or amphibious animals, since water is a much better conductor of electricity than air. That sentence is unsourced, and I kind of doubt it when it comes to shock-stunning prey, which requires physical contact anyway. Of course, it is tempting to believe that there is a simple physical reason of water vs. air, but it seems like physicist’s speculation to me. Tigraan Click here for my talk page ("private" contact) 08:37, 16 June 2022 (UTC)
 * Water (in particular seawater) is a decent electrical conductor, air is not. It's far worse than any land animal. So a land animal trying to send an electric discharge through air, will instead send it though its own body. Feathers and fur are decent insulators too, so the attacking land animal has to penetrate the victims skin with its teeth or claws before it can deliver an electric discharge. As it has to bite the victim already, the costly electric tissue has limited added value. PiusImpavidus (talk) 09:42, 16 June 2022 (UTC)
 * An electrical discharge through normal, non-ionized air takes the form of an electric spark, "created when the applied electric field exceeds the dielectric breakdown strength of the intervening medium. For air, the breakdown strength is about 30 kV/cm at sea level." 30 kV is about 35 times the voltage Electrophorus voltai, "the strongest bioelectricity generator in nature", is capable of generating. The advantage for the electric eel of delivering a shock is largely that it can stun its prey before engaging in physical contact. --Lambiam 10:03, 16 June 2022 (UTC)
 * But as Tigraan says above, electric eels (and electric catfish) don't have ranged weapons. I note that the article "Electroreception and electrogenesis" is talking about those two things as related. It has most to say about electroreception. This looks like a clue. Platypuses have electroreception (and sometimes wander about on land, particularly the big Tasmanian ones) so I can imagine them having evolved electric weapons, if they had undergone enough evolution. If only the world had been dominated by platypuses at any time, in greater variety. The connection to water might be due to the advantage water's conductivity confers on electroreception, which then provides an evolutionary pathway to weaponization. Card Zero  (talk) 11:13, 16 June 2022 (UTC)


 * As a not-entirely irrelevant sidetrack,, although it is of course (science-) fiction, you might be interested in reading Naomi Alderman's 2016 novel The Power, which utilises this idea. {The poster formerly known as 87.81.230.195} 90.201.73.162 (talk) 11:06, 16 June 2022 (UTC)
 * As a side-sidetrack, what about electric sheep? 2603:6081:1C00:1187:6181:9552:92F5:90C1 (talk) 17:06, 16 June 2022 (UTC)
 * "Eee!" said Tykebot 3. "When I were a lad, we used t' dream of havin' an electric sheep!" {The poster formerly known as 87.81.230.195} 90.201.73.64 (talk) 13:13, 18 June 2022 (UTC)