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I know that frame-rates above 60fps all look the same to the human eye. Is that true? Why? If so, why do graphics cards boast anything higher than that?

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While this is an interesting question, it really isn't within the scope of this site. There are no dubious claims here. Basically the fps numbers that they show are with a certain load, giving you an indication of how it might perform at a higher load. That said, vote to close for off-topic. –  Ustice May 18 '11 at 15:12
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Yes, there is claim, even when perhaps not expressed correctly: is there any perceivable difference when a computer game is running 60 Hz or more (say 120 Hz?). –  Suma May 18 '11 at 20:21
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The eye doesn't do full refreshes, so asking "what FPS does the eye see at" is missing the point. A static scene at 1fps looks just as smooth as one at 60fps, and a very fast moving object at 60fps looks jerky. The eye sees movement, not digital frames, it's all about how much any two frames change, not how often those frames come along. The '24fps' rule is, again, missing the point, there's quite heavy motion blur on those (And, indeed, TV and Movies are filmed at significantly higher framerates). A comment because I don't have any references to hand. –  Phoshi May 19 '11 at 12:23
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@jwenting If you say it looks good...lol Personally I and most gamers (read ANY gaming forum) can't stand anything below 50 preferably 60+ and I spend alot of money to get these frame rates with games on max settings. But I guess if you like choppiness that's your prerogative... Everybody is different. –  Kyle May 20 '11 at 1:40
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120Hz monitors exist for stereoscopic viewing at 60Hz per eye. –  vartec Aug 9 '11 at 13:29

5 Answers 5

up vote 25 down vote accepted

Eyes? No. Humans? Yes.

You'd be hard pressed to get 60fps out of the human eye.

In laboratory conditions, it takes around 150 ms for neurons in the visual system to begin to recognize and categorize a newly appearing visual input.

However, this little factoid is not the frame rate specification for human vision.

If real-world perception were to follow this same pattern, then for a considerable time after each saccade we would still be perceiving the old retinal input, rather than the information currently on the retina. In fact, we should have to wait around 150 ms to ‘see’ what is in front of our eyes after each saccade, by which time the oculomotor system has already begun to choose the next saccadic target.

That would suck.

Fortunately, the human eye is more than a camera* with fat pipe connection to the brain.

While holding a pen, for example, the sensory input is limited to the receptors of a few fingers, leaving the majority of the surface of the pen outside of our direct sensory range. Nonetheless, we perceive a complete object, not a pen with holes where our fingers do not touch. Similarly, our visual system actively perceives the world by pointing the fovea, the area of the retina where resolution is best, towards a single part of the scene at a time.

Human vision does not have properties like frame rate, latency, resolution, et al.

Visual constancy can also be viewed as a temporal phenomenon: objects appear to be continuously present over time. Yet the duration of external events are typically longer than that of a single sensory ‘sample’ such as a fixation. Although movements of the eyes, head and body disrupt our steady access to these objects and events, the stream of consciousness continues smoothly across these sensory disruptions. This is an amazing feat, given that each saccadic eye movement creates a temporal disruption in the flow of information from the retina to higher perceptual areas. The motor smear on the retina during the saccade is suppressed, making us largely unaware of the retinal stimulation during this time period. In addition, each saccade requires the visual system to ‘re-perceive’ the information from a new fixation.

Time is relative...

...perceived time seems to shift forward, towards the beginning of the new fixation, essentially compressing the time immediately before and during the saccadic eye movement. One possible interpretation is that space and time are inextricably linked in the brain, with the pattern of strange perceptual effects reported for stimuli flashed around the time of saccades reflecting a spatio-temporal transformation between fixations.


The Bottom Line...

Human vision is not bound by frame rate.


Source of all quotes: Visual stability, References

More...
Looking ahead: The perceived direction of gaze shifts before the eyes move
How Human Vision Perceives Rapid Changes
From eye movements to actions: how batsmen hit the ball
Vision and the representation of the surroundings in spatial memory

*Actually comparing the human eye to a camera is like comparing a thermonuclear weapon to a pen-knife.

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Removed chatty thread –  Sklivvz Nov 24 '12 at 11:15
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As to the human eye to a camera comparison, in many ways cameras are vastly superior to our eyes. Objectively, our eyes are pretty mediocre. However, the visual processing systems in our brains are absolutely fantastic. Another good "bottom line" is that we don't really see with our eyes, we see with our brains. –  whatsisname Nov 27 '12 at 4:04
    
@whatsisname Agreed. It is an awesome thing. –  Rusty Nov 28 '12 at 22:28

Yes, the eye can distinguish frame rates above 60 Hz. So can the brain. We are just not normally aware of it.

Conscious perception of flicker is measured in laboratories using the critical flicker frequency (CFF) threshold, which is the lowest frequency of flickering light (Hz) that produces the appearance of steady light in an individual. It's a probabilistic statistic that is estimated by testing an individual -- it depends on the individual and the testing methods. And the same person will have a different CFF depending on factors including fatigue.

Here is a pretty typical CFF plot (from Hartmann, E., B. Lachenmayr, and H. Brettel. "The peripheral critical flicker frequency." Vision research 19.9 (1979): 1019-1023.) showing how one person's CFF (the y-axis) varies at different visual eccentricities (the x-axis, greater eccentricities meaning looking at it less and less directly) and lighting levels (the different points and lines.)

enter image description here

As you can see, this person is around 60 Hz CFF in bright illumination when the flicker is around 15 visual degrees away from the center of their vision. This suggests that many people should be able to see the flicker of CRT monitors with 60 Hz refresh rates. They can. (As others have noted here, this is not possible with LCD monitors because LCD monitors do not flicker.)

Why isn't CFF even higher at these peak conditions? Good question. The bottleneck in consciously seeing flicker is not necessarily the human eye or even the thalamus or the cortex. The eye can transmit flicker well above 60 Hz to the thalamus and cortex. Lots of neurons can fire well above 100 Hz. And we can even measure neural response to high frequency flicker. Here are a few papers doing this:

Herrmann, Christoph S. "Human EEG responses to 1–100 Hz flicker: resonance phenomena in visual cortex and their potential correlation to cognitive phenomena." Experimental brain research 137.3 (2001): 346-353.:

It is also known that neurons in visual cortex respond to flickering stimuli at the frequency of the flickering light. .... We performed an experiment, where ten human subjects were presented flickering light at frequencies from 1 to 100 Hz in 1-Hz steps. The event-related potentials exhibited steady-state oscillations at all frequencies up to at least 90 Hz.

Williams, Patrick E., et al. "Entrainment to video displays in primary visual cortex of macaque and humans." The Journal of neuroscience 24.38 (2004): 8278-8288:

Macaque monkeys: Of 92 cells in the primary visual cortex exposed to a 100 Hz refresh, 21 (23%) significantly phase locked to high-contrast stimuli.

Humans: Responses measured using scalp EEG were seen at 72 Hz in some, but not all, observers.

Krolak‐Salmon, Pierre, et al. "Human lateral geniculate nucleus and visual cortex respond to screen flicker." Annals of neurology 53.1 (2003): 73-80.:

The first electrophysiological study of the human lateral geniculate nucleus (LGN), optic radiation, striate, and extrastriate visual areas is presented in the context of presurgical evaluation of three epileptic patients (Patients 1, 2, and 3). ... A periodic sinusoidal activity was recorded in Patient 1 at contacts lying in the LGN and optic radiation vicinity (G2 and G3) in the checkerboard reversal paradigm... Its frequency was 70Hz, identical to videodisplay refresh rate... In the same checkerboard paradigm, a similar periodic sinusoidal activity was recorded in Patients 2 and 3 at occipital electrode contacts (O1 to O6) exploring the calcarine area. It was not present in the other explored structures, especially not in the fusiform gyrus (contacts F1 to F6 in Patients 1, 2, and 3

So if the information is in the brain, why can't we perceive it? We don't really know. The simplest theory might be that these signals are just too weak. But it seems unlikely that we could record something with electrodes on the scalp that isn't strong in the brain.

It is also worth noting that our ability to perceive flicker is a side effect of our ability to perceive motion. Most motion perception takes place in situations where we have other information about the moving objects. Flicker perception as measured with CFF threshold or as noticed with monitor refresh rates is a strange edge case. It likely made little evolutionary sense to optimize this ability when we could already, for example, see most fast moving natural objects well enough to catch them. So you might invert the argument and ask why should we humans have bothered to see fast flicker?

Perhaps the most interesting possibility is that this may be a limitation of consciousness itself. An initial intuition is that conscious perception will likely be slower than the low-level processes it relies on. Because different types of perceptual processes have different computational demands, they take different durations to compute. Thus, combining perceptual processing in consciousness may be slowed by rate limiting steps. Alex Holcombe wrote a nice paper a few years ago summarizing the literature on temporal limits on visual perception of different kinds of stimuli. Moreover, Rufin VanRullen and Christof Koch have argued that conscious perception occurs in discrete batches. They don't think it is perfectly regular, but rather quasi-periodic and determined by the task at hand. Still, they are essentially arguing that consciousness itself has a refresh rate.

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The human eye is not able to distinguish between 60 Hz and 100 Hz when only watching (even less could suffice provided the image is prepared correctly, as evidenced by movies projected at 24 Hz in the theather), but there is a distinction when interacting - you can notice the response is faster even beyond 60 Hz. This is augmented by the fact response time (latency between the input and the displayed image) is often several frames because of pipelined nature of the rendering technology, therefore the latency of 60 Hz game is typically over 60 ms, as evidenced by Gamasutra Measuring Responsiveness in Video Games.

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I understand this should be referenced and I hope to find some sources, but I am afraid there is little reliable research done in this area and I have little time available now. I am marking this answer as community wiki in case anyone else would like to help improving it. –  Suma May 18 '11 at 20:19
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While projected film is typically shot at 24 frames per second, the projector opens the shutter twice on each frame for a flicker rate on screen of 48 fps. This exceeds the accepted measurement of 40 Hz for flicker fusion, and so the image appears continuous. Actually flashing at 24 Hz produces a distinctly non-continuous image. –  RBerteig May 18 '11 at 21:32
    
@RBerteig: Agreed, but the flashing in non-issue with current typical LCD/TFT screens, which are only changing pixels, not going dark in between like CRTs did. With LCD screen you do not see any flicker even with lowest framerates, only discontinuity in motion. –  Suma May 19 '11 at 6:55
    
right. The LCD is a new kind of animal in this game. Old, slow LCDs could blur so badly that you could loose the mouse pointer. (That is why the mouse trails feature was in Win3.1.) Modern LCDs are so fast that the actual pixel updates are nearly imperceptible and animation frame rate only affects uniformity of motion. –  RBerteig May 19 '11 at 7:13
    
FWIW, I hate 24fps in theaters. It jitters horribly, especially on large panning sequences. –  Macke May 19 '11 at 14:20

The Wikipedia article on Frame Rate suggests, IMO, that 60 Hz is not really the far end of the spectrum.

Major institutions such as Snell have demonstrated 720p72 pictures as a result of earlier analogue experiments, where 768 line television at 75 FPS looked subjectively better than 1150 line 50 FPS progressive pictures with higher shutter speeds available (and a corresponding lower data rate).

However the link to the cited article is broken.

Also, from same article, and more relevant:

Higher frame rates, including 300 FPS, have been tested by BBC Research over concerns with sports and other broadcasts where fast motion with large HD displays could have a disorientating effect on viewers. Whitepaper link

A higher FPS will also yield a natural motion blur, something that is usually computationally expensive to render, even at a lower FPS.

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I once pressed a gamer about why he tried to boost his framerates into hundreds (severely sacrificing picture quality, of course). In the end it turned out it was because some games couldn't properly handle extreme framerates and exploits started appearing (such as enemies not hearing your footsteps and the like).

Of course, this does not apply to all games or all people, but it is one reason for trying to squeeze as much as possible out of your VGA.


To make this less anecdotal I did some Googling. Here's an analysis of Quake 3's 125fps jumping bug. Apparently similar bugs are carried over to other games which use an engine derived from Quake's. Here's another analysis both for Quake3 and Call of Duty, which focuses on jumping and running sounds. The magical 333fps count stands out.

While googling I came upon many forum threads, and I gather from those that official tournaments have FPS limits to prevent players from using these exploits. However many threads mentioned that "everybody is doing this" which suggests that for simple game servers this is a widespread practice. This is quite understandable, because if one person does this, then others get an unfair disadvantage.

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Welcome to Skeptics! Please don't post anectdotal answers. Maybe you meant this as a comment? –  Sklivvz May 19 '11 at 12:31
    
@Sklivvz - how is this anecdotal? Is it not a valid reason why people (and for certain games I suspect the majority of players) boost their framerates? Should I provide a link to a bugreport for such a game? –  Vilx- May 19 '11 at 12:53
    
@Sklivvz - there, better? –  Vilx- May 19 '11 at 13:11
    
Thank you very much. –  Sklivvz May 19 '11 at 15:25
    
similarly they think (whether this is true or not I can't tell) that having higher framerates than "the enemy" will allow them to kill that enemy without the enemy ever knowing what hit them. Essentially to kill them in the frame the enemy never sees because his fps is lower. –  jwenting May 23 '11 at 11:28

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