Wikipedia:Reference desk/Archives/Science/2013 February 6
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February 6
editLaw of excluded middle, null hypothesis redux
editI have to ask this question again because it wasn't answered and was actually side tracked by a discussion I didn't intend. Long story short, can something be true, without it being proven? ScienceApe (talk) 01:34, 6 February 2013 (UTC)
- How would you prove that it hurt if I kicked you? Can you prove that existence exists without referring to anything which exists? There are axioms, and perceptions, neither of which can be proven true, but both of which are assumed veridical. The law of the excluded middle is also axiomatic--it is the basis for any proof, but cannot itself be proven without assuming its own truth. μηδείς (talk) 01:43, 6 February 2013 (UTC)
- (ec) :If you believe in philosophical realism, you pretty much have to believe that the answer is yes. --Trovatore (talk) 01:44, 6 February 2013 (UTC)
- You might also look at foundationalism and coherentism, both of which are true. Whereas skepticism is a self-refuting idea. μηδείς (talk) 01:48, 6 February 2013 (UTC)
- Additional concepts to consider: [David] Hume's Law (a.k.a.: Is–ought problem derived from: Fact–value distinction. For an in-depth exploration of proof vs. truth as it relates to logical constructs and string theory, (etc.) - look into Gödel's In/Completeness theorem. ~Eric the Read 74.60.29.141 (talk) 02:01, 6 February 2013 (UTC)
- Should we treat Hume's theory as true? μηδείς (talk) 02:07, 6 February 2013 (UTC)
- Maybe you ought to. ~E:74.60.29.141 (talk) 02:35, 6 February 2013 (UTC)
- :) ---- nonsense ferret 03:03, 6 February 2013 (UTC)
- (edit conflict) I believe the bottom line of this discussion will depend on the definition of "truth", and the answer will be "yes/no". Can truth apply to itself? 74.60.29.141 (talk) 03:14, 6 February 2013 (UTC)
- :) ---- nonsense ferret 03:03, 6 February 2013 (UTC)
- Maybe you ought to. ~E:74.60.29.141 (talk) 02:35, 6 February 2013 (UTC)
- Should we treat Hume's theory as true? μηδείς (talk) 02:07, 6 February 2013 (UTC)
- Additional concepts to consider: [David] Hume's Law (a.k.a.: Is–ought problem derived from: Fact–value distinction. For an in-depth exploration of proof vs. truth as it relates to logical constructs and string theory, (etc.) - look into Gödel's In/Completeness theorem. ~Eric the Read 74.60.29.141 (talk) 02:01, 6 February 2013 (UTC)
- Define "prove". ←Baseball Bugs What's up, Doc? carrots→ 03:28, 6 February 2013 (UTC)
- The question is nonsense as are the "answers". If there's no such thing as truth, it isn't true there's no such thing as truth. If there's no such thing as proof, there's no proof there's no such thing as proof. This thread is ready to destroy itself. μηδείς (talk) 03:35, 6 February 2013 (UTC)
- Such is the nature of Existence theorem: An existence theorem may be called pure if the proof given of it doesn't also indicate a construction of whatever kind of object the existence of which is asserted. (see also: Existential instantiation) >poof!< 74.60.29.141 (talk) 03:48, 6 February 2013 (UTC)
- If you say "I'm thinking of ___", and if you're really thinking of that, it's true, but there's no way to prove it. Quite obviously the answer is yes. Nyttend (talk) 04:05, 6 February 2013 (UTC)
- Such is the nature of Existence theorem: An existence theorem may be called pure if the proof given of it doesn't also indicate a construction of whatever kind of object the existence of which is asserted. (see also: Existential instantiation) >poof!< 74.60.29.141 (talk) 03:48, 6 February 2013 (UTC)
- The question is nonsense as are the "answers". If there's no such thing as truth, it isn't true there's no such thing as truth. If there's no such thing as proof, there's no proof there's no such thing as proof. This thread is ready to destroy itself. μηδείς (talk) 03:35, 6 February 2013 (UTC)
Unfortunately, that's not a very defensible example, because once the question is asked, you are thinking of "thinking of ____" - and you can immediately see the problem of recursive self-reference. -Thus the answer is both "yes" and "no" simultaneously. 74.60.29.141 (talk) 04:26, 6 February 2013 (UTC)
- Very well to be pedantic about it; what about "I was thinking about __ two minutes ago", or what if you're in out in the woods by yourself (no cameras around) and see a leaf fall; you can't prove that you saw it fall, but it still fell. Nyttend (talk) 04:35, 6 February 2013 (UTC)
- By the definition of "that which conforms to reality", it would indeed be true that the leaf fell (assuming that it actually did, which it didn't, since you just made-up that example). ;) ~:74.60.29.141 (talk) 05:06, 6 February 2013 (UTC):~
- I said that the hypothetical you is claiming to have seen it fall; since I live in the woods by myself, I'm frequently able to see things happen, and it's easy to prove that they happened, but impossible to prove that I was watching when they happened. It's simply common sense, just like denying the paradoxical nature of the first two of Zeno's paradoxes that we list; we need not make an answer more complicated that the one given (according to the paradoxes article) by Diogenes the Cynic. Nyttend (talk) 05:26, 6 February 2013 (UTC)
- (edit conflict) ~ If you define truth on a case-by-case basis such that there are an infinite number of definitions and an infinite number of proofs (e.g.: the leaf proved to you that it fell) - then the answer is "yes". ~:74.60.29.141 (talk) 05:31, 6 February 2013 (UTC):~
- I said that the hypothetical you is claiming to have seen it fall; since I live in the woods by myself, I'm frequently able to see things happen, and it's easy to prove that they happened, but impossible to prove that I was watching when they happened. It's simply common sense, just like denying the paradoxical nature of the first two of Zeno's paradoxes that we list; we need not make an answer more complicated that the one given (according to the paradoxes article) by Diogenes the Cynic. Nyttend (talk) 05:26, 6 February 2013 (UTC)
- By the definition of "that which conforms to reality", it would indeed be true that the leaf fell (assuming that it actually did, which it didn't, since you just made-up that example). ;) ~:74.60.29.141 (talk) 05:06, 6 February 2013 (UTC):~
(edit conflict) ←again ~:74.60.29.141 (talk) 06:07, 6 February 2013 (UTC):~ ~ Before I wrap my brain around a cup of hot chocolate with peppermint schnaps and head off to the realm of dreams where nothing and everything is true...
- "Believe those who are seeking the truth. Doubt those who find it." ~André Gide[1]
- Now that one I like. It's going into my list of quotes and anti-quotes. -- Jack of Oz [Talk] 06:51, 6 February 2013 (UTC)
- "Believe those who are seeking the truth. Doubt those who find it." ~André Gide[1]
Suppose we constrain the question to only axiom-based formal logic systems, such as mathematics, where "truth" and "prove" can be concretely defined using the structure of the system. Then according to Godel's incompleteness theorem, it is generally the case that one can write true statements using the logic of the system that nonetheless can never be proven to be true using the axioms and methods provided by the logic system. In this sense, in most logical systems (including mathematics) there exists statements which are true or false, and yet can not be proven to be true or false. The truth of such statements is essentially unknowable. So, if you model your worldview after formal logic, then it is generally the case that there will be things that are true (or false) and yet which can never be proven to be true or false. I think this comes as close to answering the original question as possible without going off and fretting about poorly defined subjective philosophies. Dragons flight (talk) 06:17, 6 February 2013 (UTC)
- The incompleteness theorems certainly make it more difficult to sustain the notion of truth-equals-provability in mathematics specifically. There are those who make the effort; intuitionists, for example, identify truth with provability, but they do so by disidentifying provability with provability in any specific formal system.
- I would be cautious, though, about generalizing that observation to more quotidian sorts of truth and provability. The Goedel theorems are specific to a particular sort of proof, namely proof in first-order logic from a computably enumerable collection of axioms strong enough to interpret Robinson arithmetic there are extensions to other sorts of deductive system, but that would take us rather far afield. So while I agree that a statement doesn't have to be proved in order to be true, I don't think the Goedel theorems are the best argument to make in non-mathematical situations. --Trovatore (talk) 08:43, 6 February 2013 (UTC)
- There are problems like the Halting problem which says that you cannot (in general) produce a procedure that will reliably prove whether a particular computer program will or will not eventually finish running. Whether a particular program will eventually halt is a simply boolean fact - it's true or false - but no algorithm that a Turing machine (a computer, in other words) can execute will tell us which it is. This is similar to Godel's incompleteness theorem - where there are theorems in mathematics that mathematical thinking can neither prove nor disprove.
- Now...the critical question is whether a computational engine that's (logically) more sophisticated than a Turing machine could (perhaps) solve the halting problem - or whether some form of logical thinking that's outside the realms of the mathematics that Godel's theorem addresses could resolve the truth or falsehood of all mathematical theorems. As far as we know, there are no such ways of thinking. It appears that human brains are turing machines - and the "Church-Turing" theorem says that all turing engines are logically equivalent. So we're doomed to being unable to resolve the halting problem - and (in all likelyhood) unable to escape Godel's incompleteness trap.
- Is it possible that some higher realms of logic/computation might exist? Maybe - but Godel and the Turing engine argument says that humans can never possibly find or comprehend it.
- So the answer to ScienceApe's original question is "Yes!"
- SteveBaker (talk) 13:49, 6 February 2013 (UTC)
- I guess the opposite is true too, some things can be proved and yet not be true, or at least lots of people think they have proved them but I of course know they are untrue. ;-) Dmcq (talk) 14:41, 6 February 2013 (UTC)
- That's just a matter of error though. The thing can obviously be untrue even though there is an erroneous proof out there that (incorrectly) said it was true. But for a correct proof with all of the i's dotted and t's crossed, then there obviously can't be something that's proven to be true that really isn't because that belies the very definition of the word "proof" - meaning "absolute certainty". SteveBaker (talk) 17:56, 6 February 2013 (UTC)
- You can certainly have a valid proof of a false statement, if you start with false axioms. (And yes, axioms can certainly be false. For example the axiom of determinacy is false, though useful.)
- The halting problem has a somewhat different set of issues from the Goedel theorems (which I discussed above; did you read it?) as a reason to accept that truth is different from provability. What the undecidability of the halting problem says is that there is no fixed algorithm that can correctly decide the halting or non-halting of all Turing machines. It doesn't say assert, for any specific Turing machine, that there is no way of knowing whether it halts. --Trovatore (talk) 20:09, 6 February 2013 (UTC)
- That's just a matter of error though. The thing can obviously be untrue even though there is an erroneous proof out there that (incorrectly) said it was true. But for a correct proof with all of the i's dotted and t's crossed, then there obviously can't be something that's proven to be true that really isn't because that belies the very definition of the word "proof" - meaning "absolute certainty". SteveBaker (talk) 17:56, 6 February 2013 (UTC)
- I guess the opposite is true too, some things can be proved and yet not be true, or at least lots of people think they have proved them but I of course know they are untrue. ;-) Dmcq (talk) 14:41, 6 February 2013 (UTC)
Touch one part of your body, feel it elsewhere
editI was going through the Allochiria article and it made me wonder if this is similar to touching one part of your body and then feeling it elsewhere. I've seen this discussed elsewhere, like on this forum. Ok, so two questions: is there an actual word for that phenomenon (touch/scratch/whatever one area of the body and feel it elsewhere)? There is a reverse phenomenon that someone mentions at the bottom of that forum, which is, you feel an itch in one area, but scratching it doesn't relieve it because the itch is actually elsewhere.
Okay, second question is, is this the same thing used in the children's trick where Person A closes their eyes and holds their arm out. Person B slowly tickles their arm from the wrist up toward the elbow (the inside bendy part — cubital fossa). Person A is supposed to point out when Person B's reached the center of their elbow, but Person B won't have... sort of like an "optical illusion" for touch. Hopefully that makes sense. Reflectionsinglass (talk) 05:53, 6 February 2013 (UTC)
- I'm not sure if there's a term for general touch, but there is a concept known as Referred pain which is very similar to your first question. --Jayron32 05:59, 6 February 2013 (UTC)
- Somewhat related is when somebody has a phantom limb. That is, they still feel pain or itchiness or other sensations coming from a limb which is no longer present. The nerves continue to fire even though they no longer extend all the way to their original locations. StuRat (talk) 06:01, 6 February 2013 (UTC)
- Hmmm... I would add to the examples a sore gum by the second molar that creates a pain along the rim of the ear, and an unpleasant sensation from the navel that can affect the tip of the penis. These match the Straight Dope examples in terms of target, but seem outside or at least poorly specified by the classic dermatomes --- I wonder if someone has totted up enough anecdotes to tell whether there are certain specific regions of the brain that "attract stray nerves" or something...? Wnt (talk) 15:17, 6 February 2013 (UTC)
- Only slightly related but I've noticed that occasionally, based on factors I can't figure out, the actual and perceived place a mosquito pierces my skin are not quite the same place. They can be several centimetres apart. No idea what is going on there but it struck me that it would be a useful risk reduction technique for a mosquito to have evolved. Sean.hoyland - talk 17:26, 6 February 2013 (UTC)
- I think that's just due to having few nerves in those areas (as opposed to fingertips, your tongue, etc.). With larger objects, which trigger multiple nerves, it's not a problem. However, a small object that triggers a single nerve could be anywhere in the area that nerve covers. StuRat (talk) 17:37, 6 February 2013 (UTC)
- The problem there is that I've only observed it for mosquitoes. None of the many other small biting and stinging insects, some of which are tiny, seem to produce the same effect, although admittedly they don't have the precision of the mosquito. Sean.hoyland - talk 18:06, 6 February 2013 (UTC)
- There's an experiment where you close your eyes, and have a friend poke you with either one or two pins, and you tell them if it's one or two. They try at different locations and with different distances between the two. It turns out that the distance at which you can't tell two pins from one is much greater in areas like the arms, where there are fewer nerve endings. StuRat (talk) 21:10, 6 February 2013 (UTC)
- ghost limb. μηδείς (talk) 21:06, 6 February 2013 (UTC)
- A Henny Youngman classic: "Guy goes to a doctor. Says, 'Everywhere I touch it hurts!' Doctor says, 'Your finger's broken!'" ←Baseball Bugs What's up, Doc? carrots→ 22:48, 6 February 2013 (UTC)
Thanks all for the replies! I'm not thinking of phantom/ghost limbs for sure. My own experience with this (hopefully without turning this into a medical issue) is that if I tickle the inside of my right elbow, the back of the inside of my right tongue tickles like you wouldn't believe (have to trill my tongue forever to get it to itch). I have other examples too. Someone once told me that's how acupuncture works (and incidentally that's mentioned in the forum I linked to above). That article doesn't go into it, unfortunately (because it's unknown?). Jayron32's "referred pain" may be the closest relevant answer so far: and its "the mechanism of referred pain is unknown" quote leaves me to think that may be the same thing here. I'll keep checking back for any other replies! Reflectionsinglass (talk) 09:08, 7 February 2013 (UTC)
single slit - interference in a slit
editIf you hold your index finger and ring finger close together and look through the little slit between them at some light, you see dark lines parallel, you can see dark lines parallel to the sides of your fingers. Undoubtedly this has something to do with the wave nature of light, interfering with itself. But this is a single slit - not a double slit. Why do you see the dark lines? Bubba73 You talkin' to me? 06:19, 6 February 2013 (UTC)
- Diffraction#Single-slit diffraction. --Jayron32 06:20, 6 February 2013 (UTC)
- I'm skeptical that diffraction comes into play here -- but I don't really understand the description of the phenomenon. Where are those dark lines? Looie496 (talk) 06:36, 6 February 2013 (UTC)
- I agree; diffraction/interference is not a very plausible explanation, as the patterns would be on the order of thousands of wavelengths, and the light source is neither spatially nor chromatically coherent. But so then what *is* the explanation? I'm curious too. --Trovatore (talk) 06:51, 6 February 2013 (UTC)
- I'm skeptical that diffraction comes into play here -- but I don't really understand the description of the phenomenon. Where are those dark lines? Looie496 (talk) 06:36, 6 February 2013 (UTC)
It sounds like you are describing the Black drop effect.
Here is a paper with a far better picture of it our article has: http://metaresearch.org/home/viewpoint/blackdrop.asp
Here is a video demonstrating it with fingers: http://www.youtube.com/watch?v=wylnvUor4Z0
Here is another paper on it: http://www.rasc.ca/sites/default/files/DuvalBlackDrop.pdf
Here is a 1922 paper that shows the parallel lines that you describe (figures 14 through 18): http://www.bo.astro.it/~biblio/Horn/Blackdrop.htm
If you look at the above links and the links in Black drop effect, you will not only see an explanation, you will see several mutually contradictory explanations! Who could ask for more?
--Guy Macon (talk) 07:32, 6 February 2013 (UTC)
- Nicely sourced explanation, @Guy Macon. Related question: how many Wikipedia editors monocularly occluded their own vision today reproducing this two-fingered effect? — Preceding unsigned comment added by Senra (talk • contribs) 14:35, 6 February 2013 (UTC)
- Also interesting; do the same thing against a dark background with a bright light illuminating your fingers. --Guy Macon (talk) 18:56, 6 February 2013 (UTC)
- I estimate that the width of the slit between my fingers is less than 0.001 meter and there are several of the lines visible. So I estimate that the lines are about 10-4 meters apart - on the order of 200 times the wavelength of visible light. I'm not sire about the Black Drop explanation since it connects things and these lines are discrete. Bubba73 You talkin' to me? 18:18, 6 February 2013 (UTC)
- Did you look at figures 14 through 18 of the 1922 paper? --Guy Macon (talk) 18:56, 6 February 2013 (UTC)
- Yes, I did, but there is only one line in there whereas there multiple lines (ten or so) in the finger slit. In the figures it looks like that line is in the process of making the black drop. I can see the black drop effect in the finger slip, and these lines don't seem to have anything to do with it. Bubba73 You talkin' to me?
- More like 20 or so lines. Bubba73 You talkin' to me? 02:34, 7 February 2013 (UTC)
- Let me describe what I see: When I hold two fingers in parallel, try to make the slit as thin as possible, and look at a lamp shade (bright but not blinding), I see many fine parallel dark lines in the opening, parallel to the slit. As I move the fingers apart, the lines seem to get thinner until they fade away. As I move my fingers closer together, the lines get thicker, until at some point there is no transparent lines between them and the block the light. Because my fingers are not perfectly straight, some part of the slit gets blocked first in what looks to me exactly like the black drop effect. When I do the same with the tips of my thumb and index finger I see one "line" that looks like the figures in the 1922 paper.
- All of the above are through the top of my bifocal glasses, meaning that the fingers are out of focus. When I look through the lower lenses, the many-lines effect vanishes and I can get the fingers much closer before I see a classic black drop with no lines. If I move my fingers far enough away that the lower lenses can't focus, I think I see lines, but it s hard to make out -- I need longer arms.
- It looks like an interference pattern to me. Given the fact that I am using a "camera" made out of jelly, I'm surprised that it works as well as it does. --Guy Macon (talk) 03:31, 7 February 2013 (UTC)
- I agree with your description (including the thumb and index finger) and it is the same with different types of indoor lighting. If it is interference, what causes it - perhaps reflections off both of the two fingers? The black drop article says that the effect is due to the atmosphere and optics, but that doesn't seem to be what is going on here. Bubba73 You talkin' to me? 04:55, 7 February 2013 (UTC)
- My best guess is that I am seeing a combination of black drop effect, which isn't very well understood, and an interference pattern. My theory about the interference pattern is that the slightly out-of-focus fingers have a region where the blurry edges of the fingers overlap, thus allowing an interference pattern. A good experiment for investigating this would be to use a high-quality digital camera to take a picture of the finger slit, with the fingers in sharp focus and out of focus. --Guy Macon (talk) 06:08, 7 February 2013 (UTC)
- It might take some work to photograph it. When I hold my hand at arm's length, the fingers are in focus but I can still see some lines. Bubba73 You talkin' to me? 06:13, 7 February 2013 (UTC)
POM application for ethanol
editIs POM compatible to 30% ethanol mixed Fuels. — Preceding unsigned comment added by 115.254.23.116 (talk) 07:10, 6 February 2013 (UTC)
- What's POM? 24.23.196.85 (talk) 07:13, 6 February 2013 (UTC)
- From POM and a quick search, I'm guessing Polyoxymethylene [2] Nil Einne (talk) 07:51, 6 February 2013 (UTC)
- In that case, it should be compatible with ethanol at any concentration. 24.23.196.85 (talk) 08:54, 6 February 2013 (UTC)
pKa-value in the medicine substance articles?
editHi,
what do you think about putting systematically pKa-values in the articles of medicine substances?
For example into the table that contains all the basic information (formula, mol. mass...)
194.100.75.169 (talk) 12:58, 6 February 2013 (UTC)
- This is an article editing question that should be proposed somewhere else - you might start with the talk page of the specific compound that you have in mind, and the WP:navigational template that it uses. Of course, many medical compounds are acids and have pKa values, but there could be other components of the pill (inert excipients); they may not be pure chemicals. If they are pure chemicals, likely the article has a Template:Chembox or the like that can be filled in. Wnt (talk) 14:59, 6 February 2013 (UTC)
- It should be noted that every compound with a hydrogen has a putative pKa value... --Jayron32 17:00, 6 February 2013 (UTC)
- Hmmm, what's the pKa of lithium hydride? :) Wnt (talk) 19:50, 6 February 2013 (UTC)
- Fair enough, but only because there are no known "lithides" to compare to. There are known examples of other Alkalides, so one could calculate the putative pKa of any other alkali-hydride compound. That doesn't mean that lithium hydride doesn't have a pKa, if lithides were known we could get numbers to calculate the putative pKa from that; the methods exist to do so, we just lack the numbers yet. The other alkalides have only been known for 40 years or so. --Jayron32 20:03, 6 February 2013 (UTC)
- Ab initio prediction of pKa is reasonable for some types of structures. There's less data about alkalides to use for validation, but LiH is such a simple molecule that one could do quite advanced calculations for it in reasonable time. DMacks (talk) 20:12, 6 February 2013 (UTC)
- Hmmm, what's the pKa of lithium hydride? :) Wnt (talk) 19:50, 6 February 2013 (UTC)
- It should be noted that every compound with a hydrogen has a putative pKa value... --Jayron32 17:00, 6 February 2013 (UTC)
Tests on a newborn baby
editWhen a baby is born (in the United States), I assume that the hospital staff does a battery of tests on the baby to assess his health. Do they test if the baby is blind and/or deaf? (I assume that they do.) If so, how exactly would they test for those conditions in a newborn? Thanks. Joseph A. Spadaro (talk) 20:17, 6 February 2013 (UTC)
- We have a fairly detailed article about the various newborn screening tests, which includes a section on hearing but does not appear to mention vision. DMacks (talk)
- For blindness, I expect that such a test is sufficiently elementary that it doesn't necessarily rate a mention -- specifically, does the baby react to bright light? Contrast this with the hearing screening described above, or any of the other disorders noted, which require specialized procedures and equipment. — Lomn 20:34, 6 February 2013 (UTC)
- Newborns can't focus, so sight tests would be unhelpful. A search on sight in newborns here gets you to the article on the disgusting, perverse, and evil movie, human centipede. But not to sight in newborns. μηδείς (talk) 21:05, 6 February 2013 (UTC)
- "Newborns can't focus, so sight tests would be unhelpful" -- the former does not imply the latter. Response to stimulus is a basic means of testing that does not necessarily require comprehension or cooperation on the part of the patient. Now, that said, any sort of infant vision screening will necessarily have limitations, as the results aren't much more detailed than "nothing" or "something" until the child is old enough to provide more detailed feedback. — Lomn 21:28, 6 February 2013 (UTC)
- Newborns can't focus, so sight tests would be unhelpful. A search on sight in newborns here gets you to the article on the disgusting, perverse, and evil movie, human centipede. But not to sight in newborns. μηδείς (talk) 21:05, 6 February 2013 (UTC)
- For blindness, I expect that such a test is sufficiently elementary that it doesn't necessarily rate a mention -- specifically, does the baby react to bright light? Contrast this with the hearing screening described above, or any of the other disorders noted, which require specialized procedures and equipment. — Lomn 20:34, 6 February 2013 (UTC)
- In the UK, "Newborn babies are usually screened for any potential hearing problems using two quick and painless tests. They are the: Automated Otoacoustic Emissions test (AOE), and Automated Auditory Brainstem Response test (AABR)." The AOE test consists of "A tiny earpiece is placed in the baby's ear and quiet clicking sounds will be played through it. If the baby's ear is working normally, reaction sounds (echoes) should be produced in the cochlea. A computer is used to record and analyse the reaction sounds." In the AABR test; "three small sensors will be placed on the baby's head and neck. Soft headphones will be put over the baby’s ears and quiet clicking sounds will be played through them. A computer will then be used to analyse how well the baby’s ears respond to the sound."
- A newborn baby's eyes are "checked for any obvious physical defects, including squints (where the eyes look in different directions), cloudiness (a possible sign of childhood cataracts) and redness." There are other tests including; "The pupil reflex test" (shining a light in the eyes to see if the pupil constricts), "The red reflex test" (using an ophthalmoscope to look for a red reflection from the retina, a lack of which could be an indication of a cataract) and "Attention to visual objects" (whether a newborn baby pays attention to visual objects). See National Health Service: Hearing and vision tests for children - How they are performed. I suspect that there is similar screening in other developed countries. Alansplodge (talk)
There is no routine screening for vision other than the discharging doctor assessing eye contact, which is an imperfect method. If eye contact is obviously poor, eyes are visibly abnormal, or moving abnormally (nystagmus)the child is likely to be referred to a pediatric ophthalmologist to examine the optic nerve. Many congenital defects of vision are only detected as parents begin to realize the eye contact is poor in the first months of life. One of the reasons vision screening is not done routinely is that there are no conditions which are treatable at birth but not at a few months of age, so there is little benefit from detection at 2 days as opposed to 2 months. Does this cover your concerns? alteripse (talk) 22:41, 6 February 2013 (UTC)
- Yes, once again, babies don't track or focus at birth, and they may react to light even if they are blind, but it is good to know that doctors slaving for the civilized national health get credit for performing non-diagnostic tests on newborns. Good for them. μηδείς (talk) 23:01, 6 February 2013 (UTC)
- It's not non-diagnostic, and pupillary response has nothing to do with the ability to focus the eyes. Blindness caused by damage to the optic nerve will result in no change in the pupil upon exposure to light, so confirming pupillary response in newborns at least rules out some (most?) types of blindness. I don't know much about the signs of nystagmus mentioned above, but I seriously doubt they would be in common use if they were not effective in establising vision problems. Evanh2008 (talk|contribs) 23:29, 6 February 2013 (UTC)
- Medeis stated that "babies don't track or focus at birth." In fact, my own newborn was given the Brazelton test series at the hospital (US) shortly after birth, and was quite able to track a face. Edison (talk) 16:59, 8 February 2013 (UTC)
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- We can't forget the bilirubin test, which results in babies occasionally named Billy Rueben. StuRat (talk) 07:03, 7 February 2013 (UTC)
- In that case, presumably test would be positive. Gzuckier (talk) 14:51, 7 February 2013 (UTC)