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

Here's something...

[Otter]

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:

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.

Re:the sound is unbearable

[bill_mcgonigle]

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.

My 2 cents...

[MrIcee]

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:LCD Response?

[PornMaster]

LCD pixels don't go dark between refreshes of what's on the screen. CRTs only light up a pixel when the electrons hit the phosphor, then dim until hit again. The LCD pixel stays lit between changes.