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Displays Science

Flickering Curiosity? 251

Posted by Cliff from the refresh-detection dept.
N8F8 writes "Why do some people see monitor flicker more readily than others? I happen to be one of the lucky folks who can spot a 60Hz monitor from across the room. Most people seem oblivious to this flicker. Other people can only see it in their peripheral vision. I tried researching an answer and I stumbled on plenty of information about something called 'Critical Fusion Frequency'. There even appears to be quite a bit of research into this phenomena but I couldn't find much information on why flicker perception varies so greatly. Can anyone shed some (flicker-free) light on this?"
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Flickering Curiosity? More

Flickering Curiosity?

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  • I see Flicker at other refresh rates.... (Score:3, Interesting)

    by haplo21112 ( 184264 ) <haplo AT epithna DOT com> on Tuesday March 15, 2005 @02:19PM (#11945692) Homepage
    ...it seems to depend on the day and the lighting, my level of awakeness...and seemingly even mood...

    Often if I change from using my laptop on LCD, or Projector back to monitor, I will be bothered by flicker no matter what refresh I set for a while.

  • flicker sucks. (Score:2, Interesting)

    by grub ( 11606 )

    I can walk into an office at work and spot a 60Hz monitor flickering instantly. Usually I'll ask if the person's eyes get tired, etc. and fix it for them. More often than not they report the eye irritations are reduced.

    • Re:flicker sucks. (Score:2, Interesting)

      by SilverspurG ( 844751 ) *
      Usually I'll ask if the person's eyes get tired, etc. and fix it for them.

      Wrong spin. The person's eyes have adjusted to by in sync with the 60 Hz refresh and they are not bothered by it. Your eyes, for some reason, never figured out how to sync.

      My eyes sync at whatever refresh is available.

      • Re:flicker sucks. (Score:2, Informative)

        by Anonymous Coward
        Nah, some people will complain that their eyes are tired after hours on a computer. A refresh fix eliminates that in many cases.
  • I bet this is also related to the differing perceptions of LCD response times?

    I happily play FPS games on my LCD, without any noticeable blurring, but I know many people still view it as a problem on LCD's.
  • Thank you! People always think I'm strange because I don't like crt monitors. I always see flickering, especially when I move my eyes from one position on the screen to another. Flickering is one reason I love my laptop, and rarely go around desktops anymore(excepting desktops with lcds).

  • also (Score:2, Interesting)

    by same_old_story ( 833424 )
    distance plays a big role on this. from a distance (6 feet +) you can usually spot flickering monitors very easily.

    • Re:also (Score:3, Informative)

      by museumpeace ( 735109 )
      SPATIAL DOMAIN:
      Yes. Distance is critical. Because of interleaving, you have neighboring rasters 180 out of phase...and that is intended to reduce percieved flicker. If you happen to view a monitor from such a distance that the space between even numbered [or harmonics ] rasters approximately projects to the retina at the spacing be individual receptors [rods? cones? idunno] you might undo some of the interleaving effect. This won't be a strong phenomenon because receptor cells are not layed out in a grid

      • Re:also (Score:2, Insightful)

        by Mr. Slippery ( 47854 )
        ever noticed flicker [ in periperal vision in my case] if you are looking off to one side of a monitor across the lab WHILE SOMETHING BUMPS YOUR HEAD?

        No need to smack yourself in the head - put the end of a plastic fork between your teeth and pluck it. Vibration goes into your skull, and you can see all kinds of cool flicker on a CRT.

  • Not just 60 Hz (Score:4, Interesting)

    by Alternate Interior ( 725192 ) * <slashdotNO@SPAMalternateinterior.com> on Tuesday March 15, 2005 @02:27PM (#11945777) Homepage
    There are a number of refresh rates that I notice.
    • 60 Hz is painful
    • 72 and 75 are usable, but I notice
    • 85 looks natural
    • 90 is similar to 75
    • 100 and 120 looks similar to 85
    It doesn't make sense that 90 is worse than anything else at 85+, so perhaps it's just the particular monitor. And I won't claim I can identify everything. I can't differentiate 85/100/120, or 72/75/90. But amongst the three groups of refresh rates, I can identify the group.

    • Beats (Score:2, Informative)

      by Anonymous Coward
      The issue at hand is constructive interference.

      90 Hz will interact very strongly with all the things around you that do pulse at 60 Hz. Fluorescent lights are the main culprit here, but almost anything may, since the A/C is being provided at 60 Hz.

      Two out of every three refreshes on the 90 Hz monitor will not coincide with the lighting flickering, but one will. That results in a weaker 30 Hz flicker on top of the 90 Hz.

      • Re:Beats (Score:2, Interesting)

        by Fascist ( 80604 )
        A/C is being provided at 60 Hz.

        Most countries privide AC at 50Hz. Only a handful of countries use 60Hz, even though it is the most effective for delivery of AC over long distances. Nikola Tesla recommended 240V at 60Hz after experiments with AC.
    • I'm fine with 60 on some displays, but I prefer 85. The fun part is when you start dealing with multiple monitors, and those monitors are different size and different manufacturer CRTs. Two different model trinitrons at 85hz, you might see some lines through one or the other or both - frequently going one way up one monitor and the other way down the other.

      To combat this, I run my work system at 85hz and 100hz (2x21") and my home system at 70hz/60hz/75hz (15"/20"/15")- oddly enough, I have no problems wi
      • So when you used to take LSD, all it did to you was make monitor flicker more obvious? I think you might have did it wrong.

      • Re:Not just 60 Hz (Score:2, Funny)

        by Zoyd ( 13778 )
        I have no problems with 60hz on my 20"... though on everything else I can simulate an LSD flashback just by crunching an ice cube.

        Ice cubes should not be chewed. The coldness cracks tooth enamel.

  • Annoyed by flickr (Score:5, Funny)

    by geoffspear ( 692508 ) * on Tuesday March 15, 2005 @02:29PM (#11945794) Homepage
    God, please make the endless stream of bad cameraphone pictures go away!

    Wait, what's this about refresh rates?

  • Fluorescent Lighting? (Score:3, Interesting)

    by Sparr0 ( 451780 ) <sparr0@gmail.com> on Tuesday March 15, 2005 @02:30PM (#11945804) Homepage Journal
    Sometimes I can see it when it coincides with the frequency of the lighting in the room, or is off by some small amount.

  • Everybody's different (Score:5, Interesting)

    by jgardn ( 539054 ) <jgardn@alumni.washington.edu> on Tuesday March 15, 2005 @02:31PM (#11945817) Homepage Journal
    I'd like to think that I have the same ability because I have spent so much time in front of monitors. But I know a lot of people who have spent many many more years and who still can't see it.

    I've marked this one up long ago to one of those weird attributes we're born with or we learn or that is a combination of both. I know that a lot of people thank me for raising their refresh rate, but there are some who can only work at about 60-65Hz and can't stand 75Hz or 80Hz, which is where I am comfortable.

    I've also fallen in love with LCD screens. I can finally work without getting tired! Now if only my mind could keep up with my eyes.

    I still use a CRT at work and that's led to the pile of notes and graphs and charts I've draqwn up and strewn about my office. I have to take a break from time to time or I can't look at the screen.
  • You will tend to notice it more out of the corner of your eye then head on. (Go ahead try it now), that is because the rods are more sensetive to motion.

    Also some people don't notice it because it is all they have ever really used. A lot of people just assume their monitor sucks. They notice it but have no idea what causes it.
  • Different people can percieve different things. Some people have an extra type of receptor in their eyes. Some people can hear the high pitched noise that various components in an average CRT make when they are poorly tuned. Some people cant tell the difference in Hershey and Milka :)
    • Simple. Hershey tastes like vomit.
    • Wait, everybody can't hear that high-pitched hum that TVs and monitors make? Jeez, I always wondered why I was the only person I knew who was really annoyed by it.

      Monitor flicker is one of the biggest annoyances to me... I can spot a 60Hz without any difficulty whatsoever, and I can see a 72Hz or 75Hz refresh rate out of the periphery. I personally can't deal with anything less than 85Hz unless I absolutely have to. It's one of the reasons that I often have my monitor's resolution lower than I'd like.

  • Lucky? (Score:3, Interesting)

    by Tom7 ( 102298 ) on Tuesday March 15, 2005 @02:40PM (#11945899) Homepage Journal
    Why do you consider that lucky?
    I'm often annoyed by effects that other people don't perceive, and I personally find it, well, annoying.

    • Re:Lucky? (Score:5, Funny)

      by Neil Blender ( 555885 ) <neilblender@gmail.com> on Tuesday March 15, 2005 @02:48PM (#11945995)
      I think he means it in the way that someone might say, "I'm one of those lucky people who have explosive bouts of diarrhea eight times a day."
      • I think he means it in the way that someone might say, "I'm one of those lucky people who have explosive bouts of diarrhea eight times a day."

        Compared to those people who have explosive bouts of diarrhea ten times or more per day, those who have it just eight times a day are pretty lucky.

  • I didn't read TFA, but... (Score:4, Interesting)

    by xami ( 740208 ) on Tuesday March 15, 2005 @02:47PM (#11945969)
    ..Toshiba, I think, made some tests in cinemas with 30fps and 70fps movies to see howmany people could distinguish between single frames.
    Surprisingly, a lot of them couldn't even notice the difference but there was a significant number (15% afaik) who could even notice single frames in 70fps

  • Audio corollary (Score:3, Interesting)

    by MrScience ( 126570 ) on Tuesday March 15, 2005 @02:47PM (#11945986) Homepage
    I can pick of the horizontal frequency of almost any television from more than 10 feet away. I can tell when the TV is on before I even enter the room... but everyone else in my family doesn't seem to pick up that frequency (15750hz?).
    • I can always tell when the TV is on but the cable box is off. Even though my housemates routinely push the off button but don't give the tv time to respond. They walk right by the TV a dozen times, yet I walk within 15 feet, and I pick up the audio whine which annoys the heck out of me. A quick look and I can see the TV is on by the shade of black on the screen.

    • I can pick of the horizontal frequency of almost any television from more than 10 feet away. I can tell when the TV is on before I even enter the room... but everyone else in my family doesn't seem to pick up that frequency (15750hz?).

      You mean that most other people can't hear that noise? I thought that most everyone could, and I was the only one who was really annoyed by it.

      • Re:Audio corollary (Score:5, Interesting)

        by Flying Purple Wombat ( 787087 ) on Tuesday March 15, 2005 @03:33PM (#11946441)
        You mean that most other people can't hear that noise? I thought that most everyone could, and I was the only one who was really annoyed by it.

        Most people can't hear it. It used to drive me crazy, I could hear CRTs, ultrasonic motion detectors, and other things that most people can't. As with many things, this is an individual variation. My son inherited this ability, but my daughter did not.

        Now that I'm 0x29 years old, I can't hear a CRT unless my left ear is within 6 inches of it (my right ear can't hear it at all). High frequency hearing loss is common as age increases. In my case, loud music and pyrotechnics accelerated the process.

    • Re:Audio corollary (Score:4, Interesting)

      by cniebla ( 158677 ) on Tuesday March 15, 2005 @03:32PM (#11946436) Homepage
      I can pick that noise too, but with an interesting twist: I actually can use it like some kind of sonar, really. Sometimes I'm on my laptop, giving my back to the door in the room, and to avoid a "comming-from-the-back-making-no-noise" joke, I just turn on the TV, with the sound mutted. It can give to me the actual position / movement from even a cat coming by, so no more jokes ;). By the way, where you found that freq.? (15750hz)

      • Re:Audio corollary (Score:3, Informative)

        by narcc ( 412956 )
        This link will explain it all [audiovideo101.com]
        • Well, most of it at least. The actual noise is created by the flyback transformer and is damn annoying. High pitched sounds are interesting because the short wavelength creates all sorts of interference when you move around your head. Turn your head slowly from one side to the other and you can almost visualize an interference pattern similar to a single slit and a light.

    • I used to work in an Apple service workshop, and we used to occasionally get CRTs in which the customer complained had a 'high pitched squeal'. Sometimes we could hear it, sometimes one or two of us could hear it and the rest couldn't, sometimes we would just have to take the customer at their word. Generally it is caused by a faulty high-voltage transformer.

  • the sound is unbearable (Score:5, Interesting)

    by St. Arbirix ( 218306 ) <matthew.townsendNO@SPAMgmail.com> on Tuesday March 15, 2005 @02:50PM (#11946016) Homepage Journal
    Who else can hear the sound a television or monitor makes? I can tell from another room when a TV has been turned off because the high-pitched squeal goes away. Those electronic mosquito repellers are equally annoying.

    I've read in various places that women can hear higher pitches than men but I've yet to meet anybody male or female who could hear some of the crap I put up with. Walking into a computer lab is the same to my ears as diving to the bottom of a pool.
    • I have the same problem. The only relief I get is at home where my wife's nagging covers the sound.

    • Re:the sound is unbearable (Score:5, Informative)

      by bill_mcgonigle ( 4333 ) * on Tuesday March 15, 2005 @03:37PM (#11946490) Homepage Journal
      Some department stores have security systems that cause the same effect. For me, anyway, the sound of a blank TV sounds different than a typical high-pitched sound. Does it for you?

      One source of very-high-pitched sound perception (~26-28KHz) is sympathetic vibrations of the ear bones. Normally the sound waves vibrate the tympanic membrane and the ear bones pick it up and transmit it to the cochlea which fires the nerve. But sometimes the bones can be vibrated directly which results in the perception of a high-pitched sound, higher than the tympanic membrane can respond to. This is one of the chief complaints of the 44.1KHz limit on CD's - they can't represent frequencies over 22050Hz, and people can perceive higher pitches even if they can't 'hear' them with the eardrum.

      Perhaps that's somehow involved here. Just a guess.
    • I can do this too. It is especially bad when my wife turns the video source off (dvd, game system, etc) but accidentally leaves the tv on. I can hear it a floor away.

      Also those sensormatic dealies in retail stores are rather annoying. A brief high buzzing noise, whee.

      Especially bad is that I have tinnitus [wikipedia.org] (constant high pitched noise that is usually masked by "surface" noise but not always, very loud in quiet rooms).

      The worst is electronic dog whistles. They are excruciating! Like a thin needle of noise

    • Re:the sound is unbearable (Score:5, Interesting)

      by dpbsmith ( 263124 ) on Tuesday March 15, 2005 @04:25PM (#11946997) Homepage
      Hee, hee... when I was a kid I could hear the 17,750-cycle horizontal scanning frequency (as it was then... it became 17,734 at about the same time it became "Hz") clearly. I'd ask adults about it. And none of them knew what I was talking about. When I was about ten I finally insisted that someone turn a TV off and on, with the volume all the way down, in an adjacent room, so that I could _prove_ that I could tell whether the TV was on or off and wasn't just imagining things.

      When I was in my twenties, I went to a dentist who used an "ultrasonic" cleaning device that was audible--and painfully loud--to me. I complained. They insisted that I couldn't possibly be hearing it because it was "ultrasonic." I said, "Oh? How do kids react to it?" They said, "Oh, we don't use it on kids, they jump out of the chair when we do." But they still didn't believe that it was because I, and the kids, heard it.

      Also in my twenties, I visited the mineral and gem room of the American Museum of Natural History, which I had visited many times with pleasure, and this time I confronted with the loudest "ultrasonic" sound I've ever heard the displeasure of hearing. I'm pretty sure it was higher than 15,750 Hz. Heaven only knows how many DB it was. It didn't even sound like a high-pitched done; it sounded like someone was clamping my head in a vise. It gave me a splitting headache within about five minutes. There was obviously some kind of standing-wave effect because if I moved my head or walked around it would fluctuate; I probably could have determined the wavelength if I'd thought about it, but I didn't.

      It got louder whenever I got near some little boxes mounted on the wall about ten feet. They were inconspicuous and painted black but in plain sight.

      I went to the guard, and said that it was daytime and he was on duty, would he mind turning off the ultrasonic burglar alarm because it was giving me a headache. He sort of freaked out. He said that they didn't have any ultrasonic burglar alarm and what was I talking about? I said I was talking about the extremely high-pitched, extremely loud sound that was coming from those boxes on the wall, and pointed to them. He insisted that they were not part of a burglar alarm system and were not making any noise.

      I don't know if he a) thought I was delusional, or b) was upset because the system was supposed to be top-secret, or whether c) I _was_ delusional... you figure it out.

      Well time took its toll on the old hair cells, and I got the twentieth-anniversary special CD of Sergeant Pepper's Lonely Hearts Club Band in 2000 and listened to the band that supposedly has an ultrasonic tone at the end of it... on my headphones... with the volume turned pretty high... and you know what? I couldn't hear a thing.

      Maybe I can visit the American Museum's gem room in comfort now.
      • Also in my twenties, I visited the mineral and gem room of the American Museum of Natural History, which I had visited many times with pleasure, and this time I confronted with the loudest "ultrasonic" sound I've ever heard the displeasure of hearing. I'm pretty sure it was higher than 15,750 Hz

        That's like going to get a TV where all of them are on one huge wall. Very annoying.

        Now if you want loud HF sound, you need to check out some of the 1200+L/min turbo molecular pumps. Some are *extremely* loud, ye

      • Well time took its toll on the old hair cells, and I got the twentieth-anniversary special CD of Sergeant Pepper's Lonely Hearts Club Band in 2000 and listened to the band that supposedly has an ultrasonic tone at the end of it... on my headphones... with the volume turned pretty high... and you know what? I couldn't hear a thing.

        CDs, with a 44kHz sample-rate, can only play sounds up to 22kHz. I'd bet anything that the ultrasonic tones can be heard on the LP version of that album. I'd also bet that that s
    • Typical TV sets whine at 15kHz. That's not a very high frequency; most of us _should_ be able to hear that. CRT monitors are a different beast; the >60kHz line refresh should be unhearable, were it not for subharmonics. Try filling your screen with 5 lines of white alternated with 5 lines of black. Chances are you'll hear something. (for the clueless: don't bother to try that on your LCD).

      Some other loosely related stuff:

      - More than twenty years ago remote controls used ultrasound. I could hear them fr
    • I'll second this one as well. I've had a few instances where someone turning on a TV or monitor has caused me to flee from the room because of the sound, which they, to my surprise, were oblivious to. It doesn't seem as bad as perhaps yours might be, but I've definitely noticed the same effect.

      What gets me is that I know it's not 'better hearing' - I have worse hearing and eyesight than most people, and yet I can still pick up on flicker (including some fluorescants) and monitor squeal (from lousy TVs).
    • Why the adjective "western" there? Chinese chess is not noticably more complex than western (the cannon makes it a bit more strategic, but not so much), and if you're trying to make an east-vs-west comparison other games are more representative of what's played in the far east.
      • That comment was shamelessly ripped from here [xmp.net].

        Go is to Western chess what philosophy is to double entry accounting.
        - From Shibumi, bestseller by Trevanian
    • Me too, although I'm not as sensitive as you are. Sometimes I ask other people if they hear the same sound and they look at me like I'm crazy.

      Also hear high pitched sounds from cable and dsl modems... but the CRT monitor sounds are much worse.
    • Yo! Right here. Worst things; A TV with no sync and the mozzy repellent at the entrance to David Jones in the city.

      Thankfully I can't see most monitor flicker, but early 100Hz TVs looked crap.

    • I've never noticed the sound from monitors much, but it's probably just because it vanishes in the other sounds you get inside of a building. I can hear the sound from AC power when I'm inside, as well as flourescent lights. You notice those sounds a lot more when they're not there. When the power goes out, it's almost eerily quiet. It's the only time I'm glad I had a bad ear infection as an infant and now have a faint but constant low-pitched ringing in my ears. I still have something to listen to when the
    • Strangely enough, I have issues with other sounds (low sounds in a crowded room), but I'm still doing fine with high pitches. I can hear those annoying squeeky monitors, TV sets, and various other electronic phenomenoa that are caused by crappy capacitors, etc.

  • Here's something... (Score:5, Informative)

    by Otter ( 3800 ) on Tuesday March 15, 2005 @02:54PM (#11946058) Journal
    I don't have time to research this thoroughly but figured I owed you something in return for your informing me of the existence of Google Scholar...

    From Shane Sidebottom's Masters thesis [vt.edu]:

    One factor that is not often examined in the flicker research conducted in psychophysics is individual variability. Some people are more sensitive to flicker than others (Rogowitz 1986). To develop an accurate flicker standard for the general population, the nature of the distribution of flicker sensitivity in the population must be considered. Individual differences may be attributable to many factors, such as gender, age, or personality. Young people are more sensitive to flicker than older people (Kim and Mayer, 1994). Women are more sensitive to flicker than men are (Maxwell, 1992). Personality has been cited by psychologists as affecting flicker perception (Amir and Ali, 1989). The factors that lead to individual variation in flicker sensitivity may be of little real use to those designing displays for the average user; however, knowledge of the extent of individual variability is useful.

    There's more (plus a graph!), and the references should keep you occupied for a while. As to *why* -- well, *why* is a question that can keep researchers busy for quite a while.

  • Monitor Whisperer (Score:4, Funny)

    by Neck_of_the_Woods ( 305788 ) on Tuesday March 15, 2005 @02:54PM (#11946065) Journal


    I can tell you anything you need to know about your monitor. They speak to me, in a very high pitched form of basic.

    Let me hold your monitor cord, press my forhead to your screen, or if possible....mount your monitor. I will gleem everything I need to fr..errr everything you need to know from your montior.

    I am not a frequency biggot, I like'm fast, slow, flickering, fleckering, high pitched, low pitch...I don't give a damn...just let me have go.

  • Big shocker! (Score:4, Insightful)

    by Cuthalion ( 65550 ) on Tuesday March 15, 2005 @02:55PM (#11946077) Homepage
    Surprise! It's a natural phenomenon that fits a normal distribution!

  • New LED tail lights... (Score:4, Interesting)

    by Drunken_Jackass ( 325938 ) on Tuesday March 15, 2005 @02:57PM (#11946097) Homepage
    are annoying to me. I can see them flicker in my peripheral vision and it's damned annoying. I figured that they musts oscillate around 60Hz or so, but does anyone have any more information about them?
    • I had one drive past me the other day at night- it destroyed my vision for a good full second. I was left with a streak of red LEDs running up and down the side of my view.

      If I turned my head- there followed another streak.

      I've written the manufacturer and BEGGED them to do anything to crank the refresh up to 120hz.... because it's honestly a hazard.

      I'm considering writing the appropriate government agency... but we'll see.... (or in the case of those lights, not see)

  • variable refresh rate (Score:5, Interesting)

    by Froze ( 398171 ) on Tuesday March 15, 2005 @02:58PM (#11946106)
    Others have mentioned that they only get bothered when switching from one display to another. I think this is because your brain (optic whatever) can vary the uptake rate of information from your eye.

    Test it out, try laying on the floor beneath a ceiling fan on low or medium. If you watch fan long enough you can stabilize the apparent interference rotation rate of the blades.

    When you can vary the rotation rate at will, you have less chance of being annoyed by flicker since you adjust rapidly. If you can't see the rate change then your eyes can't compensate for the flicker. Hence they get tired more easily.

    • Nerves and the brain... (Score:4, Interesting)

      by tRenn ( 867978 ) on Tuesday March 15, 2005 @03:13PM (#11946253)
      Ok, I'd like to know if there's a fundamental frequency that the average human's optic nerve/brain refreshes that make us comfortable with viewing CRTs at various refresh rates?
      • There isn't really a fixed frequency at which nerve cells operate/communicate at. The first thing to understand is that the rate at which nerves fire generally varies according to the intensity of the stimulus.

        Furthermore, there are many different types of nerve cells and receptors in your eyes. Some only respond to certain features based on the shape of the cell. Some only are activated with a certain intensity of stimulus. Some are only activated when a stimulus changes. Some are only activated when
    • ... but it CAN see ME, and it's stabby.

      Or rather, I can see it, but I don't really process the fact that I can until the headache sits in. I'm fine with a fixed rez and frequency monitor (typically 1280x1024x85hx), but going through a protracted period of switching, like you'd do with finding optimal video card settings for a video game, gives me one hell of a headache.

      Middle of last week I thought I was getting a migraine from the Splenda-laced drink I was enjoying, but it turned out to be Halo- 60hz on
  • I don't know much about the research, but my own experience is that I'm very bothered by low refresh rates. Looking at a 60Hz screen gives me a headache in less than 60 seconds. 75Hz is unpleasant after a few minutes. I can work at 85Hz, but I can tell the difference between 85 and 100Hz. I can't tell the difference between any frequencies over 100Hz. I've worked with people who literally can't tell. I'd switch back and forth between 60Hz and 100Hz, asking them to evaluate each, and they could see no

  • A simple answer.. (Score:3, Funny)

    by stefanlasiewski ( 63134 ) * <slashdot AT stefanco DOT com> on Tuesday March 15, 2005 @03:06PM (#11946184) Homepage Journal
    Can anyone shed some (flicker-free) light on this?"

    Simple-- YOU are a robot, THEY are not.

  • I'm wondering if there is any correlation between the people who notice 60Hz flicker and the 'lucky' 5% who are disturbed by the 'rainbow effect' caused by single-chip DLP systems (and slow and/or 3-4 segment color wheels).

    Anecdotally, I am afflitced with the ability to see both.

  • I happen to be one of the lucky folks who can spot a 60Hz monitor from across the room.

    Don't you perhaps mean unlucky? Most public terminals (Win) are set at the lowest rate of 60 Hz, regardless of the capability of the monitor. Makes it hard to concentrate at the library, etc., with crazy flicker in your peripheral vision.
  • I can see Flicker. It's the reason why I've cycled through four different monitors in the last year, before finally settling down on a Sony SDM-HS94P (flatscreen). Any refresh rate less than 72 is intolerable for me, and even faster refresh rates are noticeable when I move my eyes or look at it in my perhipheral vision.

    What's worst is eating crunchy food. The jarring motion of biting down on someting crunchy apparently jolts my head at the same speed the screen is refreshing, so the image breaks up for a s
  • It might have something to do with interference of the monitor with the light coming from TL-tubes. Then again, I get raving mad from a monitor flickering at 60Hz in a room that is lit by sunlight.

  • Human Perception (Score:3, Interesting)

    by Anna Merikin ( 529843 ) on Tuesday March 15, 2005 @04:10PM (#11946833) Journal
    Human perception varies widely. In the season he hit .406, Ted Williams, in answer to the question, "How do you hit so well?" replied, "I wait till the ball is as big as a watermelon and I can see the stitches and the printing on the hide and then I smack it."

    To explain how he alone avoided a terrible accident around a blind curve during a Grand Prix roadrace, Juan Manuel Fangio explained that as he drifted around the turn at about 120 mph, he became aware that the crowd along the side of the track was not watching him, but had turned their faces ahead and that gave him the clue to slow down as there must have been big trouble in the curve.

    Human perception varies greatly, or did I already say that?

    I do not usually see flicker, but some CRTs are better or worse than others. I cannot tell the difference between smoothed fonts and others. But I can sure hear a tiny bit of distortion above 10kHz! Even so small an amount that others cannot detect it drives me into the pain zone, so I have to choose my audio components very carefully.

    Human perception varies greatly.
  • i will say i use 1024x768@70 on my (low end) monitor instead of 1280x1024@60 because the latter is annoying.

  • My 2 cents... (Score:5, Informative)

    by MrIcee ( 550834 ) on Tuesday March 15, 2005 @04:26PM (#11947005) Homepage
    While I am not a vision researcher I have spent countless years in digital imaging and understand some of the basics of what is going on.

    The 60 hz frame rate (or actually, 2 fields at 30 hz) and the vertical retrace period can be viewed by just about any person - regardless of gifts....

    Think you know someone who can't see the flicker? Have them stand about 15 feet away from a monitor and chew a stick of gum - they will be amazed to see the jitter (or just pretend to chew a stick of gum or bob or weave VERY slightly on your toes).

    Not everyone is wired exactly the same and some of us have eye sensitivity - what we can actually consider a 'sample rate' that is higher, or lower, than the norm. In effect, what you are seeing when you see the jitter can be likened to aliasing effects - every now and then your sample rate syncs up (or desyncs slightly) and you catch the vertical blanking interval and/or scan itself.

    It is well known that dogs and cats in general don't see TV like we do - because their vision system is at a faster rate than ours - to them the screen looks like a lot of weird angled lines. However, everyone knows about that ONE cat or ONE dog that DOES watch TV - most people think they are gifted but instead, they are 'slower' in their vision system.

    Consider as well, car tires. As you go down the road they spin but you are very familiar with the effect of them 'apparently' spinning backwards - again, the sample rate of your eyes is just slightly out of sync with the rotation speed (or harmonic of) causing the hubcap to appear to turn backwords. And if your right in sync with the speed (or harmonic of) then the hubcap appears to be standing still (e.g., in it's rotational axis).

    If you were to consider two people, looking at the same tire rotation, they would undoubtedly report slight differences in what they see. The same effect is happening on the screen - the refresh rate is similar to the rotating hubcap and you are just slightly faster or slower than it is.

    (btw, yes, I've been able to see it for years and years and year)

    • Re:My 2 cents... (Score:3, Informative)

      by NereusRen ( 811533 )
      "As you go down the road they spin but you are very familiar with the effect of them 'apparently' spinning backwards - again, the sample rate of your eyes is just slightly out of sync with the rotation speed (or harmonic of) causing the hubcap to appear to turn backwords."

      The optical illusion of rapidly spinning objects "freezing" or starting to spin backwards when they hit a precise speed has nothing to do with the "sampling rate of your eyes," since there is no such thing.

      Rather, it depends on the ob

    • Car wheels don't do it (Score:3, Informative)

      by gr8_phk ( 621180 )
      Vehicle wheels only appear to be going backwards in 2 cases: 1) they're on film/tv where aliasing happens due to the "sampling" with each frame. 2) for it to happen live you need a strobe light - i.e. driving at night under bright non-incandecent lights (quite common). There is no "frame rate" for the eye, so this normally doesn't happen with real observed objects. You may also notice some intereting things when parts of the wheel shadow other parts - the large lugnuts on big trucks sometimes do this in the

  • obviously (Score:4, Funny)

    by jago25_98 ( 566531 ) <slashdot@@@phonic...pw> on Tuesday March 15, 2005 @04:29PM (#11947025) Homepage Journal
    Seeing as I can detect 60hz easily it must clearly be a sign of superior intellect

    come on, you thought it

  • Flicker seems more perceptible after I've gone running.

    Think it's the exercise?
  • brainwave frequencies:
    http://www.google.com/search?hl=en& l r=&safe=off&q= brainwave+frequencies+hz&btnG=Search

    eye:
    http://www.google.com/search?hl=en&lr=&saf e=off&q= %22specifications%22+%22human+eye%22+fps&btnG=Sear ch

    also consider optic nerve, and eye interface. It could be only USB1 and that could be presenting a problem - I suggest firewire iuntil manufacterors stop changing sensors without telling us.
  • While I can detect the 60Hz monitors, the real headache generators for me was interlacing, even at high refresh rates. Most people around me had no idea what I was talking about but it was clear as day when a monitor was set to interlacing. I would mention it, they would turn that off, and magically, they would have less eye strain, but still not be aware of the difference. Now I just use LCD monitors, and have since 99.

    And yes, I'm also one of those people that can hear electronic devices when they are
  • Even though my screen is running at 60 Hz. Oh... wait, it's a laptop screen. I can notice anything at 75 Hz or less from a great distance. I don't know why this is, but I can tell that for me it's an evolving thing. I wasn't able to spot 60 Hz, but now I can't watch TV without being a humongus distance away. I think the more you're in front of a screen, the more likely you are to notice, because your eyes become more picky... Or it could just be because I'm a teenager and my eyes are still getting a little
  • You might also want to look up "Critical Flicker Frequency" I am fairly sure this is either the same thing or a related thing. It describes the effect that allows for movies and other moving images based on rapidly shifting images.
  • A lot of studies were done in the NRC's anachoic chamber in Ottawa and eventually they decided to gather up a group of "golden ears" who had demonstrated in past studies superior discrimination. What they found was that time and frequency are a trade-off. The best in frequency were worse in time, etc. Someone determined could dig up the study. I last saw it on the internet about three years ago.

    I can sometimes tell the difference (staring normally) between 85 and 90Hz, but no higher. Wag a finger in f
  • I can't see flicker, my monitors are usually at a resolution that makes normal humans claw their eyes out if they look over my shoulder... I should patent that as a security technique ;-)
    • Oh, it's just occured to me, could it be my Goatse wallpaper that's making them claw their eyes out?

      (I know, I know, but I thought it was for the best that I make that "joke" before anyones else did)
  • I can spot the one-frame bits of brown blobs that are supposed to be used for tracing down where someone handi-cam'd a movie. What I don't understand is why no-one else can see them.

    Bah.
  • A fun trick with CRT monitors is to hold one of those massage vibrators on your head while you look at the screen. The screen starts looking really wavy.

    You can test your manliness (probably only works for men) by letting out as low a rumble as you can. If your voice is sufficiently deep you'll see the screen start to flicker or wave severely.
  • i find its usually easier to spot 60hz from across the room. as my eyes move, the 60hz becomes very apparent.

    if i'm sitting square in front of a monitor sometimes it'll be 5 minutes before i realize its at 60hz.

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