Wikipedia:Reference desk/Archives/Science/2009 February 8

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February 8

Where can I find information about NLP?

Especially about using NLP to make me invisible! I heard there's a British guy who perfected this.TinyTonyyy (talk) 01:35, 8 February 2009 (UTC)

Which NLP are you talking about? I don't think any of them offer a useful method of invisibility. Algebraist 01:57, 8 February 2009 (UTC)

I believe TinyTonyyy is referring to neuro-linguistic programming, which British magician Derren Brown claims (or, apparently, is generally thought to claim) can make someone think Brown is invisible. But Brown is a magician and showman by trade, and if you believe that you can do this kind of stuff in real life, you're probably really missing the point of performing magic on stage: it's all skilled about misdirection, illusions and entertainment, not a display of actual supernatural powers. -- Captain Disdain (talk) 03:46, 8 February 2009 (UTC)

TinyTonyyy, (and that could be your problem right there...) if you think you can stroll unobserved around the girls' dressing sheds at the beach, forget it. The ambient steam around your body gives your presence away. I know. Myles325a (talk) 01:19, 16 February 2009 (UTC)

effect of pulse polio programme on scheduled vaccinations!

hey. can anyone help me out with this one?

recently according to some research in india it has come to light that because of pulse polio pragramme people from villages are not taking their kids for getting the scheduled vaccines! i wanted to do a project on this topic. can anyone give me any information about this topic? i would be really grateful to anyone who helps! thanks. —Preceding unsigned comment added by 59.92.242.169 (talk) 16:05, 8 February 2009 (UTC)

I'm not sure what you mean. You seem to be saying that the Pulse Polio program is causing people to not be vaccinated, which seems unlikely, seeing that the whole purpose of the program is to do just that. --Milkbreath (talk) 16:53, 8 February 2009 (UTC)

Just a guess, but maybe the OP is saying that some people are skipping standardized ("scheduled") polio vaccinations, perhaps at their own cost, because they expect to get vaccination through the pulse programs. It stands to reason that the scheduled vaccine would be optimized to the child's age, whereas the pulse program would not be individualized. The population effect of the pulse program would be beneficial (catching many who would not otherwise get vaccine) but might have the unintended effect of delaying vaccination of those who would have gotten it anyway. Seems like a good thing to study, and I have a sense other vaccination programs have seen the same thing. --Scray (talk) 17:08, 8 February 2009 (UTC)

Possible. What I first thought was that a determined program to vaccinate against one disease might have the paradoxical effect of reducing overall childhood immunization compliance in uneducated mothers who would suppose that a little bit of vaccination is good enough, not differentiating between the different vaccines and forming wrong ideas around the existence of multiple vaccines like MMR. Word of mouth is a poor disseminator of scientific ideas, I'll bet. But I'd like 59.92 to give us a little more to go on, like what study he's referring to. --Milkbreath (talk) 17:25, 8 February 2009 (UTC)

Colour of the Sun

Having done an Astronomy qualification, one thing still puzzles me - why the Sun appears yellow. It seems several sources diagree slightly on this: whether it is because the scattering of blue light in Earth's atmosphere leaves yellow (i.e. white minus blue = yellow) or whether it was because the atmosphere of the Sun - white light came directly from the Sun, but yellow could also be emitted in other directions, absorbed by Hydrogen (or Helium) and re-emitted in the direction of Earth. Are they both factors, and, if so, which is more important? - Jarry1250 ^{(t, c)} 16:08, 8 February 2009 (UTC)

As far as I know, it's just scattering in our atmosphere. The light coming from the sun is thermal radiation from the photosphere. It is effectively a black body at 5800K, which corresponds to "white hot". --Tango (talk) 16:17, 8 February 2009 (UTC)

this is responding to an answer the poster had already deleted, not to Tango. Sorry, I was not paying attention. SpinningSpark

Sorry to be contrary, but the peak wavelength is actually well in to the green band, very nearly cyan, and nowhere near yellow. File:Solar Spectrum.png. Some astronomy books quite perversely insist on calling G2 stars "green stars". The particular mixture of colours we get from the sun is white by definition (a piece of paper reflecting all wavelengths appears white in sunlight). The yellow appearance is indeed due to Rayleigh diffraction scattering but is amplified in the brain through a visual processing of "integrate to white". That is the brain's visual processing is attempting to remove any colour bias of the light source from the scene. The blue sky requires yellow somewhere in order to integrate the whole scene to white. Rooms lit by tungsten fil. lighting look distinctly yellow, but should look a lot more yellow if it where not for this process. There is also the matter of refraction as the sun gets low in the sky causing the loss of blue. The sun low in the sky is easier to look at than at midday and at these times it really is orange or even red. SpinningSpark 16:58, 8 February 2009 (UTC)

Hello spinningspark. Yeah that was me. I remembered reading in an astronomy textbook that "our sun is a yellow star", but I did some look up immidiately and found that was not exactly true. Thanks for your explanationn, cheers! -- ReluctantPhilosopher (talk) 18:51, 9 February 2009 (UTC)

Spinningpsark alluded to this, but it bears saying by itself: We perceive the Sun as yellow because, when we can look at it, it's low in the sky and the higher frequencies are scattered away. When the Sun is directly overhead, it's white. In fact that's probably pretty much the definition of white. --Trovatore (talk) 21:47, 9 February 2009 (UTC)

Call me an idiot if you will, but when the Sun's overhead, the sky is still blue; therefore some blue light must be scattered. Does this mean the Sun is still yellow? And is my factor about difraction in the outer layers of the Sun wrong (which is fine) or does it not have a noticable effect? - Jarry1250 ^{(t, c)} 22:05, 9 February 2009 (UTC)

Yes, the sun will still be slightly yellow, just not as much. I didn't really understand what you were saying about the outer layers of the sun... the light we see comes from the photosphere (one of the outer layers) and is emitted because it is hot (the core is hotter, but the light from that is absorbed by the outer layers, which are pretty opaque). --Tango (talk) 22:17, 9 February 2009 (UTC)

Our eyes and brains have evolved to treat sunlight as "white" - regardless of what energies are emitted at what frequencies - the totality of sunlight MUST be "white" because it is the very definition of the word. Since the sky is blue - we know that some of the blue that comes directly from the sun must be being scattered across the sky - ergo the direct path of light from the sun must be white minus blue - which is yellow. SteveBaker (talk) 03:10, 10 February 2009 (UTC)

The sun looks white when it falls on a surface on a clear day. But when you look (briefly!) at it it is surrounded by a blue sky, and color contrast may make it look yellow. Edison (talk) 21:03, 10 February 2009 (UTC)

Sleep

This question has been removed. Per the reference desk guidelines, the reference desk is not an appropriate place to request medical, legal or other professional advice, including any kind of medical diagnosis, prognosis, or treatment recommendations. For such advice, please see a qualified professional. If you don't believe this is such a request, please explain what you meant to ask, either here or on the Reference Desk's talk page.

This question has been removed. Per the reference desk guidelines, the reference desk is not an appropriate place to request medical, legal or other professional advice, including any kind of medical diagnosis or prognosis, or treatment recommendations. For such advice, please see a qualified professional. If you don't believe this is such a request, please explain what you meant to ask, either here or on the Reference Desk's talk page. --~~~~

--Scray (talk) 17:00, 8 February 2009 (UTC)

Whether this is or isn't a request for medical advice is being discussed here: [1]. StuRat (talk) 22:28, 9 February 2009 (UTC)

I won't answer any questions about whether you personally will suffer from having your sleep schedule split in two, but will make some general observations on sleep patterns:

1) The most important thing is to get enough total sleep.

2) The amount of sleep each adult requires varies quite a bit, but the 7-8 hour range is typical.

3) There is a certain minimum amount of time required for each sleep session to get to the deepest stages of sleep. Our sleep article seems to mention 90-110 minutes for each stage, and 5 stages of sleep (some repeated), which would give me 450-550 contiguous minutes of sleep needed to get all the stages. That's 7.5-9 hours. So, if those calcs can be trusted, split sleep cycles wouldn't work. However, there are cases of people with odd sleep patters, such as Thomas Edison, who would take many short naps in his office instead of going home for a full night's sleep, without any apparent ill effects. This suggests that the early sleep stages can be shortened, as needed, by some people, to make up for a deficit in the later stages. So, I'd say whether an individual can cope with a split sleep schedule depends on their own biology.

4) There are some cultures where a split sleep schedule was traditional. A siesta, for example, was often taken at the hottest part of the day in tropical climates, as anything more ambitious would be likely to result in overheating. Presumably, these people needed less sleep at night, so can take advantage of cool mornings and evenings to get work done. This pattern of sleep may be less common now that air conditioning is common. StuRat (talk) 18:31, 8 February 2009 (UTC)

Splitting one's sleep schedule deliberately can be known as polyphasia, and is the subject of self-research. BrainyBabe (talk) 21:32, 8 February 2009 (UTC)

A Spaniard I knew in the UK said that in Spain people typically went to bed much later than in the UK and got up early; so they got less sleep at night. However, she also said that she found she felt extremely refreshed after being in the UK a few weeks and shifting to getting more sleep at night, and found it shattering to go home and function on the little sleep typical there. One person's experience in one area... 79.66.57.25 (talk) 23:34, 8 February 2009 (UTC)

The British navy managed somehow to win the Napoleanic wars using crews (officers and men) who stood four-hour watches (four hours on, four hours off) for years at a time. I thihk the practice continues to the present day in most navies. See Watch system. -Arch dude (talk) 21:35, 8 February 2009 (UTC)

There used to be an old saying: Nature requires five hours, convention says eight; sloth takes eleven and wickedness fourteen. People who claim to survive on less than five hours' sleep tend to take mini-naps during their day, and people who stay in bed more than eight hours tend to be awake for some of that time. I agree with StuRat that the amount of sleep required does seem to vary between individuals, with some apparently needing less, but it is also a matter of habit. Lack of total sleep is normally easy to detect because eyes will close involuntarily whenever adrenalin levels drop. The body also seems to need more sleep when it is engaged in repair work, after infection or injury. Dbfirs 21:43, 8 February 2009 (UTC)

The way I read it (not sure where) was:

Nature takes five

Custom grants seven

Laziness takes nine

And Michaelmas eleven

No one I know actually observes Michaelmas (I couldn't even tell you what time of year it is without looking it up) so this is perhaps not as meaningful as it could be to me. --Trovatore (talk) 00:11, 10 February 2009 (UTC)

what is a time that is CERTAINLY too short for a person to displacce their hand by 1 meter ?

so, to give you an idea of why I'm asking, I'm thinking about what notes are a physical impossibility to play in immediate succession on the piano (where "immediate sucession" would be a 64th note, or 128th or 256th, 512th, 1024th or whatever), even for someone who was playing the piano since birth + was the world's record fastest piano player + did this particular test on performance enhancing drugs... so I'm really asking about physics possibility!

what might be a good way to come up with a time in which it is CERTAIN no one can move their hand by, say, 1 meter, even once. I have some ideas for upper bounds: you can figure out the "jerk" that would be required (change in accelleration) and figure out what the time interval would be for which such a jerk would be sufficient to sever a hand. I mean, if you think about it, there MUST be a certain jerk that would sever a person's hand completely! But this is a way way way way way too high upper bounds! I'm looking for a more reasonable one... Any ideas?

One approach could be like, taking the power required for the displacement in the given amount of time, and making it larger than the maximum power human muscles can produce for any lenght of time. But it's hard because there are SO many muscles, the maximum instantaneous power oculd be huge -- I don't see why it coulnd't a gigawatt, if we're only talking about a SINGLE microsecond.

So any way to estimate physical impossibility?

p.s. I have another upper bounds: the time it takes to move 1 meter at the speed of light. but 1 m / c is 3.33 nanoseconds.

A boxer is certainly snapping a jab as fast as he can. The British Journal of Sports Medicine has an article on the biomechanics of punches that gives a speed figure of about 9 m/s, which would be 111 ms for one meter, a little more than a tenth of a second. If you halve that to account for mutants like Roy Jones I think you have a reasonable limit. --Milkbreath (talk) 18:47, 8 February 2009 (UTC)

9 m/s sounds low. That's only about 20 mph! A major-league pitcher can deliver a baseball at up to 100 mph, occasionally higher. Granted he wouldn't be able to do that if he threw it by extending his arm straight from his shoulder, but still, five to one? Really? --Trovatore (talk) 09:19, 10 February 2009 (UTC)

Is that with or without roller skates on their elbows? It was Robert Rankin's idea, not mine. ៛ BL ៛ (talk) 19:03, 8 February 2009 (UTC)

I thinks it's a silly question, but let's play anyway. For a single pair of notes, the player does not need to stop his hand over the first or last note. His hand can already be moving in the correct direction. -Arch dude (talk) 21:30, 8 February 2009 (UTC)

The question doesn't say whether the player is bouncing one finger on one key, or can use multiple fingers and/or hit different keys. I initially read the question as one&one (since asked about short individual notes, not speed to accomplish a range or maximum range in a time)--Arch dude's "running start and over-run the base" don't help:( However, then it continues with ideas about moving one's whole hand and motions on the order of a meter, so now I'm not sure we're just on one key. Interesting question about maximum acceleration before joint dislocation though! DMacks (talk) 07:24, 9 February 2009 (UTC)

I don't understand the need to move your hand by a meter - that's an awful long way on a keyboard instrument! Surely the shortest note is the time between depressing the key far enough to launch the piano's hammer toward the string to releasing it far enough to actuate the damper. I play keyboard instruments - but I'm used to electronic keyboards. On occasions I've played a real piano, the force you have to apply to the key and the relative lack of control you have over the note duration seems like a much bigger limitation than how fast my fingers can move. So I think we should be considering:

• The shortest duration of a single note on an electronic instrument (from "Note-On" to "Note-Off" in MIDI terms).
• The shortest time to move finger/hand from one key to another over a 'reasonable' span.

We do have numbers for typists...that's gotta be comparable. A good typist can reach 120 words per minute - and (I believe) the metric assumes an average of four characters per word plus a space - so that's 600 keystrokes per minute - ten per second. Stenographers can manage 250 words per minute - but they never have to move their fingers from one key to another - and most words are a single "chord"...so again, we're probably around 10 keystrokes per second. The world record for a stenography machine is 375 words per minute - so the best that people can do is only maybe 50% better than a normal but experienced person.

So on that basis - I'd guess that the answer is something like 15 notes per second per finger. But not on a piano - and not if hands have to move large distances between notes.

SteveBaker (talk) 16:39, 9 February 2009 (UTC)

tips to enthuse proto-computer scientists

I have to encourage a group of moderately disaffected youngsters to take seriously the need to express themselves clearly in written English. If all goes well, they will be accepted into Year One of university computer science programs. Their maths and CS abilities are in need of a little attention, hence this Year Zero program. Their English is in need of a lot of attention, hence this remedial class. As a generalisation, the group as a whole was "never good at English" at school, which is why they have opted for CS degrees. Some of them see little point in attempting to improve their written English, as they do not expect to have to use it in the careers they hope for.

My question to you: many of you, I take it, have or have had jobs to do with computers. Many of you enjoy the art of written expression (attested to by your voluntary participation here). How would you suggest I awaken the interest of these students? Or, if that is too blatantly an opinion question, what sources can you point me towards that demonstrate the value of clear written expression in the obtaining of desirable CS jobs? How does good English help in a good career? Many thanks! BusinessAsUnusual (talk) 21:56, 8 February 2009 (UTC)

You can always divide them into groups of three or four and make a competition which group writes a better l33t <=> English interpreter code :) --Dr Dima (talk) 22:34, 8 February 2009 (UTC)

If their English, Maths and CS skills all need extra help, are they really cut out for a Uni CompSci course? Or university at all? There are plenty of jobs out there that don't require degrees, perhaps you should be concentrating on giving them the skills they need for them... </rant!> Anyway, if you insist, you could show them some computer manuals - technical writing is a very important skill, you can't be a good programmer (I'm assuming if they aren't good at maths that they equate computer science with programming) if you can't write decent documentation. The Computer reference desk may have better answers. --Tango (talk) 23:41, 8 February 2009 (UTC)

Documentation is a good point about the need for clear writing! How about having them write some simple program (whatever is at their level) and user-doc for it. Then put them and "some users" (could be you, could be some real-world people:) in two different rooms and let them field customer-support calls for users following the docs. DMacks (talk) 00:09, 9 February 2009 (UTC)

You can be bluntly honest with them. They are not special. Nobody cares about them. If they want a job, it is up to them to convince a group of people, likely much older than they are, that they are willing to conform to the university or work environment. If proper English is used, the chance of being accepted increases drastically. If, instead, they treat the situation like an instant chat and blow it off, they themselves will be blown off. This is seen here on the RD every week. People who ask questions with clear English tend to get good answers. People who use poor English do not receive good answers. -- kainaw™ 02:05, 9 February 2009 (UTC)

You could split that even further (based on two flavors of this type of student attitude). Type 1 is that they're (at least in their mind) really really good but just cooler, nonconformist, "not an uptight suit" and so they don't need no formal book-learnin' English. It's fine to be casual, but unless you can express yourself clearly and precisely and at least neaten up when the situation calls for it, nobody will recognize (i.e., "hire") how good you might be. Type 2 is the fact that the economy sucks and there's always competition and others who are at least as smart and experienced vying for the same job. Even if your CS skill can be recognized, someone who is technicalls skilled and also more polished and able to dress up and become clear and formal when the situation dictates will get the job every time. DMacks (talk) 07:09, 9 February 2009 (UTC)

A large portion of my time as a computer programmer was spent trying to get the customers to define the specs. This involved many e-mails which needed to ask very specific questions in order to get good enough answers. StuRat (talk) 07:56, 9 February 2009 (UTC)

Assuming they ever make it into the world of employment, they will also need some administrative skills, because it seems to be the policy of larger corporations to make people with no training in administration do their own administration. Admin skills don't just involve the ability to type fast! They will need to fill in forms - which involves reading them in the first place, deciphering what is required in each space of the form, composing entries for each space in the form which are legible and make sense - and also to speak to other people clearly and in a language the other person can understand, which doesn't involve grunts! Finally, their willingness to learn is crucial to making a success in IT based provision. They will always be asked to work in a language they've never used, with software and hardware they've never used, and systems they are not familiar with. How do they learn them? Well, these days, it's FOFO - so back to books usually! BTW I love the help desk scenario as given above - most geeks seem to think that end users are irrelevant, whereas without end users there's no point to any computer system. --TammyMoet (talk) 09:48, 9 February 2009 (UTC)

I've been a computer programmer for 35 years - and I'm very certain that I've written more English than C++ code (or any other kind of code) in the course of my job in all of those years. Documentation, comments inside code, messages to users from within your code...all of those things require good English skills. It's certainly a fact that you need good English skills. It's also a fact that many programmers are just like your kids and hate being made to write documentation and copious code comments...sadly. It's going to be hard to convince them that this is true though. I have a hard enough time making people write decent documentation who have the requisite skills. Math skills MAY be less important - it depends on what you're doing. You can write accountancy software knowing nothing but how to add and subtract...but if you want to write video games - your math skills had better be razor sharp or you won't even make it to interview. When the companies I have worked for are thinking of interviewing a job candidate, we first subject them to a half hour to an hour of 'phone interview' which probes math skills in great detail. Fail that and you'll never get as far as the front door. One of the things beginning programmers don't understand is that programming is a team activity. It's very rare indeed for someone to be able to write something by themselves. Yet schools and colleges (and people playing around with computers at home) pretty much treat it as a solo activity. When you have 10, 20, 50 people writing a piece of software containing several MILLION lines of software - the ability to communicate effectively is paramount. A lot of that is in email - Wiki's and (rarely) paper documentation...but it's English. If you think you can write emails in 'leet-speak'...you've got to be kidding! You'd be laughed off the team in the game programming teams I've worked on.

Sadly - I can't think of any way to enthuse them. I suppose you could get a real, live game programmer to come and talk to them (most companies are receptive to the idea of having their staff take a couple of hours out to go talk to local school/college kids once in a while). Unfortunately, your kids will cynically see this as another "Stay In School! Study Hard!" lecture and they'll likely just tune it out.

I applaud your efforts though. SteveBaker (talk) 16:20, 9 February 2009 (UTC)

I've known schools and universities do group programming assignments, but they rarely work very well. It usually ends up testing whether or not you can reach the end of the assignment without killing the rest of your group. The problem is that all the students are expected to work as equals, and that rarely works (unless you have significant maturity, experience and motivation, 3 things students are frequently lacking). In the real work there are hierarchies, they may be very loose most of the time, but they are there when they're needed, that is never replicated in the academic environment. Group assignments are also usually very badly graded - everyone gets pretty much the same grade regardless of how much they did (which harms the motivation element). --Tango (talk) 16:48, 9 February 2009 (UTC)

Yeah - I agree, this is hard to score and hard to motivate. But that's how the real world is. You WILL have poor team members - you WILL have the odd super-programmer who can write code (literally) a hundred times faster than the weakest member. This can get very difficult. Particularly with modern agile development methodologies (eg Scrum (development)) where it's impossible for the weaker members to hide their lack of ability. But team development is where it's at - and communication is everything once your team is more than three or four people. Documentation is vital - I even document my own solo projects because the "me" in the future is not the "me" now - he'll have different memories and a different perspective on the project - and a handy memory jogger as to why the "me" of today did what he did is often invaluable. SteveBaker (talk) 03:05, 10 February 2009 (UTC)

TV Noise

My girlfriend hears a high pitched noise when the tv set is on. She can tell when it's on even if she's not in the room.

what is she hearing?192.136.22.5 (talk) 23:51, 8 February 2009 (UTC)

Is it an old CRT TV? If so it will be the 15kHz line scan frequency. SpinningSpark 00:02, 9 February 2009 (UTC)

Specifically, from the flyback transformer or associated components. --Anonymous, 04:27 UTC, February 9, 2009.

... although obviously we can't be certain, and if your girlfriend has any concerns she should consult a professional and get her hearing tested. Gandalf61 (talk) 07:13, 9 February 2009 (UTC)

I have a suggestion. Since high frequency hearing decreases with age, give that TV to someone old enough not to be bothered and get a new one (or one in trade for this one) that won't drive your g/f crazy. After all, that's your job. StuRat (talk) 07:49, 9 February 2009 (UTC)

It's his job to get rid of the things that drive her crazy or is it his job to drive her crazy? Does being ambiguous drive your wife/girlfriend crazy, Stu?  :-) Dismas|^(talk) 08:45, 9 February 2009 (UTC)

It was intentionally ambiguous. It wouldn't have been funny if I'd said "it's your job to drive your g/f crazy" (although that still has an ambiguity to it) any more than if Bush'd said "it's our job to destroy this country". However, when he said "There are terrorists who want to destroy this country, but we won't let them, that's our job" (paraphrased), that was funny. StuRat (talk) 20:00, 9 February 2009 (UTC)

I hear high pitched noise from a great many common electronic devices like TVs (including a new flat screen one), ethernet hubs (wireless or not), palm pilot type devices, digital clocks, etc. Often the noise is very quiet. Certainly these sounds are generally overwhelmed by the relentless household noise of the furnace, refrigerator, misc computers, etc. Sometimes I try to turn it all off. Inevitably I end up still hearing some electronic noise after turning the obvious things off and search around until I discover that there is a little hiss coming from the egg timer, or something. But it is always very striking how quiet it is when all the electrical things are off, making me realize how a myriad of ordinary household noises add up to a constant din. I guess most people are just used to it, or don't hear it as well? Anyway, it makes me wonder what is it about electronics that makes so much noise--hisses and hums and such... usually fairly quiet for a given device. Sometimes I've noticed solid state devices, like musical synths, get noisers over the years. Could it have to do with power supplies? Do Operational amplifiers tend to produce a bit of noise? Curious. Pfly (talk) 08:50, 9 February 2009 (UTC)

So others do hear it! I grew up being able to know whether or not a household had their television on, even if the volume was turned all the way down, and I could determine this from the street in front of their house, with all of the house's doors and windows shut tight. That's how sensitive I was to that high pitched tone that others claimed they couldn't hear. As Pfly noted, it is much easier to hear those noises when other sound sources are at a minimum, but a television in the same room with me has an undeniable high pitched whine underlying every minute of usage. I used to hear a similar high pitched noise from computer monitors but either technology has rid monitors of that excess noise or maybe my hearing isn't what it used to be. 152.16.16.75 (talk) 11:26, 9 February 2009 (UTC)

Additional WP:OR and anecdotal evidence... Some friends of mine live off-grid. When house-sitting for them, I've noticed that their house is just quieter than any other house. When I lay in bed at night there, it's quieter than my own on-grid house at the same hour. We both live far away from any neighbors. Dismas|^(talk) 11:31, 9 February 2009 (UTC)

Yes, others certain can hear it. I can't, but I know at least 2 people that can tell if a room contains a TV on standby from outside the room (with the door shut). --Tango (talk) 11:36, 9 February 2009 (UTC)

I, too, hear TVs and such, provided that there are no other substantial noises. From what I learned in the past, I will probably lose this ability within a few years, since as humans age our ears lose sensitivity to sounds in the ultra-high frequency range. See Presbycusis and The Mosquito.-RunningOnBrains 18:45, 9 February 2009 (UTC)

Don't get your hopes up too soon. I've developed a gap in the higher reaches between inaudible to others and high pitched, but can still hear whether the bug chaser or the TV is on while it's muted. And the sound does stop when I unplug it so it's not tinnitus. 76.97.245.5 (talk) 21:56, 9 February 2009 (UTC)

Many people could hear the 15 khz TV noise when young.Audiograms taken over the decades may show that 15000 Hz is clearly audible in the young, but exposure to noise can cause severe hearing loss above 4000 Hz, Then when they are old, they may hear similar high pitched noise all the time, in the form of Tinnitus, although that is likely to be pulsating rather than steady. Exposure to loud noise like music, aircraft, traffic noise, shooting, mechanical or construction equipment, screaming babies over the years can eliminate the ability to hear high frequencies by causing Hearing impairment. This has led to Noise regulation laws. Edison (talk) 20:54, 10 February 2009 (UTC)