Flickering Curiosity?

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?"

Comments

Not just 60 Hz

[Alternate Interior]

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.

Everybody's different

[jgardn]

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.

I didn't read TFA, but...

[xami]

..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

the sound is unbearable

[St. Arbirix]

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.

Re:the sound is unbearable

[dpbsmith]

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.

variable refresh rate

[Froze]

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...

[tRenn]

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?

Re:Audio corollary

[cniebla]

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

[Flying Purple Wombat]

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.