Sensitivity Threshold: What is the Hz Limit of Human Eye?

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Sensitivity Threshold: What is the Hz Limit of Human Eye?

Post by Chief Blur Buster » 02 Jan 2022, 15:51

Many people misunderstand the different sensitivity thresholds, such as "Humans can't see above 75Hz" -- but that is only a flicker threshold. The purpose of this post is to show that there are extremely different orders of magnitude that refresh rate upgrades do address.

Even in a non-gaming context, one thing many people forget is that there’s many thresholds of detectable frequencies.

These are approximate thresholds (varies by human), rounded off to nearest order of magnitude for reader simplicity of how display imperfection scale.

Threshold where slideshows become motion: 10
This is a really low threshold such as 10 frames per second. Several research papers indicate 7 to 13 frames per second, such as this one. This doesn't mean stutter disappears (yet), it just means it now feel like motion rather than a slideshow playback.
Example order of magnitude: 10

Threshold where things stop flickering: 100
A common threshold is 85 Hz (for CRTs). Also known as the “flicker fusion threshold”. Variables such as duty cycle (pulse width) and whether there’s fade (e.g. phosphor fade) can shift this threshold. This also happens to be the rough threshold where stutter completely disappears on a perfect sample-and-hold display.
Example order of magnitude: 100

Thresholds where things stop motion blurring: 1000
Flicker free displays (sample and hold) means there is always a guaranteed minimum display motion blur, even for instant 0ms GtG displays, due to eye tracking blur (animation demo). The higher the resolution and the larger FOV the display, the easier it is to see display motion blur as a difference in sharpness between static imagery and moving imagery, blurry motion despite blur free frames (e.g. rendered frames or fast-shutter frames).
Example order of magnitude: 1000

Threshold for detectable stroboscopic effects: 10,000
Where mouse pointer becomes a continuous motion instead of gapped. This is where higher display Hz helps (reduce distance between gaps) and higher mouse Hz (reduce variance in the gaps). Mouse Hz needs to be massively oversample the display Hz to avoid mouse jitter (aliasing effects). If you move a mouse pointer 4000 pixels per second, you need 4000Hz to turn the mouse pointer into a smooth blur (without adding unwanted GPU blur effect).
Example order of magnitude 10,000

An example:
Image
(From lighting industry paper but has also been shown to be true for stroboscopics on large displays, including VR displays intended to mimic the real world)

More information can be found in Research Section of Blur Busters.
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Re: Sensitivity Threshold: What is the Hz Limit of Human Eye?

Post by Chief Blur Buster » 14 Feb 2022, 21:19

Relevant Counter-Crosspost (Reverse):
New researcher best practices for Hz tests!
Chief Blur Buster wrote:
14 Feb 2022, 21:54
Best Practices: Hz versus Hz Testing and Research
For new readers who's been arriving to Blur Busters and just reading recent peer-reviewed scientific papers... (I'm cited in more than 20 now!)

High Hz No Longer Just for Gamers Only
Smooth scrolling benefits from higher Hz, such as scrolling web pages! Obviously, experienced people, experienced computer optimizers (eliminate mouse microstutter with 2000Hz+ mice, etc), and experienced esports athletes will more easily see apart smaller Hz differences. But for the average iPad users only barely noticing 60Hz-vs-120Hz iPad scrolling, 60Hz-vs-240Hz web scrolling (1/4th the motion blur) is much more visible.

High Hz Becomes Cheaper/Free Over Long Term
Price differentials of entry level high Hz will disappear (e.g. 60Hz vs 120Hz will be minor like 720p vs 1080p vs 4K). Color screens were rare in phones once. Now they're all retina resolution and more frequently 90Hz-120Hz in many new phones. Even the latest PlayStation and XBOX consoles now supports 120Hz too, and larger numbers of model 2022 televisions are now including native 120Hz for free. So it becomes more of a free feature. Over the coming years, decades and century, the dominoes will fall (240Hz mainstream, 480Hz mainstream, etc), as there is visible humankind benefit.

GPUs Will Catch Up With New Frame Rate Amplification Technologies
GPUs are an obvious weak link, but inexpensive 1000fps+ will eventually be made possible with future Frame Rate Amplification Technologies -- NVIDIA is already working on it.

Retina Refresh Rate Depends on Display Resolution/Size/FOV, but Can Be >10,000Hz
The weak link for "retina refresh rate" (where human visible differences of refresh rates increases disappear) will be the highest number of all the above, aka 10,000Hz+. The limitations of refresh rates below 10,000fps 10,000Hz is only human visible in the extreme cases, like a Holodeck -- essentially a retina resolution VR headset -- e.g. wide-FOV 8K display such as a VR headset -- because of Vicious Cycle Effect (where higher resolutions and wider FOV amplifies refresh rate limitations), a chapter in the article, Blur Busters Law: Amazing Journey To Future 1000Hz Displays.

Geometric Upgrades in Hz is Mandatory for Human Visible Differences
Sensitivity of refresh rate difference diminishes rapidly, geometric upgrades of ~2x to 4x are needed for human visible differences (e.g. 360Hz-vs-1000Hz) for average non-gamer humans. Much like how resolutions needed to be geometrically upgraded to be really visible to the "I can't see VHS vs DVD" or "I can't see DVD vs HDTV" Average Joe User crowds. So you need GtG=0ms (or tiny fraction of a refresh cycle) AND increasing refresh rate ~2x-to-4x to be really blatantly human-visible (assuming no source material limitations, as explained in the Ultra HFR article).

Once you reach stroboscopic and motion blur weak links, larger Hz differences are required to see difference during highest resolutions (4K 240Hz is much more visible than 1080p 240Hz at same size/FOV). While you might not see 144Hz-vs-165Hz well, you'll see 240Hz-vs-1000Hz much more easily on a relative basis (assuming framerate=Hz) -- a far bigger refresh rate difference ratio.
  • ~2.0x Upgrades: 60 ➜ 120 ➜ 240 ➜ 480 ➜ 1000 Hz
  • ~2.5x Upgrades: 60 ➜ 144 ➜ 360 ➜ 1000 Hz
  • ~4.0x Upgrades: 60 ➜ 240 ➜ 1000 Hz
Variables for Maximizing Human Visible Hz Differences

Many weak links exist to diminish differences between refresh rates, including causes such as framerates not matching refresh rate, as well as microstutter. To maximize visible differences between refresh rates, these are required:
  • Framerate = Hz (very critical)
    (frame rates below Hz will add more persistence blur and/or stroboscopic effects and/or stutter. frame rates above Hz will add jitter effects or tearing effects due to motion-aliasing effects between frame rate and Hz. Even high-frequency judder can blend to extra motion blur -- akin to a fast-vibrating string turning into blur. 3:2 pulldown judder at 1000fps will generally have ~50% more motion blur than 1:1 pulldown. So always have precise framerate=Hz perfectly, to eliminate this extra-blur error margin from the stutter-to-blur continuum)
  • GtG = 0ms
    (eliminate GtG blur from affecting Hz differences. However, as long as GtG is less than a half a refresh cycle, GtG will usually have a negligibly visible effect. This is not the case for older 33ms 60Hz LCDs or 5ms 360Hz LCDs, though -- the higher the Hz, the harder it is for GtG to be fast enough to avoid diminishing Hz differences. Often this is mis-blamed in human inability to see high Hz, as a false scientific misunderstanding/misinterpretation. We can't tell you how often Blur Busters has to re-educate some longtime researchers to avoid incorrect untested assumptions that are tested elsewhere (Remember.. Yesterdays' CRT couldn't do 8K color, so it wasn't possible to test certain weak links). So don't make the mistake and create a flawed paper that gets called out for not acknowledging error margins -- refusal to acknowledge error margins is a big researcher no-no.)
  • MPRT = frametime
    (This assumes MPRT 0%->100%, rather than the standard MPRT 10%->90% explained in Pixel Response FAQ: GtG vs MPRT)
  • Source-based-blur = none
    (camera blur obscures Hz differences. If you're using camera material, please follow the important UltraHFR guidelines)
  • Compression-artifacts = none
    (compression artifacts obscures Hz differences)
  • FOV = as wide as comfortable
    (not a keyhole FOV like holding a tiny smartphone at full arm-length extension)
  • Stutter = none
    (including game stutter, and mouse micro stutters from using older gaming mouse running at only 1000Hz or less. There is a new scientific paper that shows jitter between framerate, refresh rate and Hz can be an issue)
  • Motion-speed = significantly faster in pixels per second than the Hz number
    (Framerate=Hz motion going 240 pixels/sec is human-visible 60Hz-vs-240Hz but very invisible 240Hz-vs-1000Hz, for both motionblur and for stroboscopic effect. This is because 240 pixels/sec is less than 1 pixels/frame at 1000fps 1000Hz, which will frequently be below human resolving capability. Also, the pixels per frame needs to be higher than human angular resolving resolution. Obviously, this is much easier with a 4K VR headset than with a 4K phone, due to much wider FOV -- since the pixels are much more spread apart and easier to resolve. This is the Vicious Cycle Effect in action: You need test higher resolutions to push retina Hz upwards. This is why it is a huge researcher assumption-mistake and incorrectly try to claim "Humans Can't See Over 200fps" if you're only testing yesterday's low-resolution VGA CRT or blurry-slow LCDs)
    Eye Behavior = must always be acknowledged in your paper
    (Stationary eyes versus moving eyes have very different behaviors on displays. Just see www.testufo.com/eyetracking and www.testufo.com/persistence animations, where displays look different for stationary eyes versus moving eyes. Hz differences for certain material may only become visible, and your test subjects might behave differently; one person may eye-track and the other person may not eyetrack. Designing your test to force eye-tracking or force stationary-eye, can improve consistency of test results. Alternatively, this is a definite proven error margin that must be acknowledged in your research paper.[/b]
Excellent Example of Researcher Error Margin Surprise:
Hz-vs-Hz Can Look Different For Stationary Eyes Versus Eye Tracking On Displays


If you don't believe displays look different for stationary eyes versus moving eyes, just look at this below animation below on a sample-and-hold LCD/OLED display. Look at the first UFO, then look at the second UFO. There. I've proven a frequently not-acknowledged error margin in Hz-vs-Hz human visibility test.

1. Look only at the stationary UFO for 10 seconds.
2. Look only at the moving UFO for 10 seconds
3. Observe how the background behaves differently at different speeds and different frame rates!



Some games force you to eyetrack (e.g. Rocket League with the flying soccer ball). Other games force you to stationary-gaze (e.g. staring at CS:GO crosshairs). Remember different games create different eye-movement behavior. You need to acknowledge as such, as Hz differences are more visible in some games than others, or in certain activities than others (e.g. web page scrolling -- some people habitually track eyes on scrolling, and other people stationary-gaze while scrolling -- some hate eye-tracking motion blur and automatically have a habit of stationary-gaze while scrolling on LCDs (to avoid being bothered by scrolling blur). So, remember.... this is an error margin that can affects whether Hz-vs-Hz becomes visible or not for a certain person for a certain screen activity.

We have relevant Blur Busters textbook reading on this topic matter at The Stroboscopic Effect of Finite Frame Rate Displays, a portion of the Research Area on Main Blur Busters Website

Acknowledging Displays & Other Related Equipment Is Imperfect

You will not always be able to maximize Hz differences because no perfect GtG=0ms LCDs exist, as an example. But you must, therefore, properly acknowledge your error margins in your Hz-vs-Hz research paper, and your known confirmed (non-assumed) efforts to control it.

Remember...Do not assume! Even 1000Hz gaming mouse can have microstutter even on 144Hz gaming displays. You want to get a ultrahigh-Hz mouse like Razer Viper 8KHz to avoid motion-aliasing between mouse Hz, framerate, and display Hz. If you're including mouse usage in your Hz detection threshold research, this is an important error margin -- mouse jitter has a diminish/distract effect for human ability to see refresh rate differences.

Image

Image

Image

But if you have major mouse jitter, it will make it harder to see 60Hz-vs-120Hz-vs-240Hz, if the gap size is randomized rather than regular. So, REMEMBER, the mouse is ALSO an error margin in Hz-vs-Hz tests (e.g. mouseturns in FPS games).

Suffice to say, this is a researcher wake-up call on how many researchers have made massively incorrect assumptions over the years, on Hz-vs-Hz weak links. Not just mouse -- but dozens of weak links that diminish Hz-vs-Hz differences, that are disappearing because better and better displays are becoming available. Blur Busters is far ahead on our ability to point out Hz weak-link knowledge -- So if you want us to vet your research plan/outline -- we'd be happy to do so (and we do sometimes. Feel free to contact me. Happy to help make your research more perfect / more peer-criticism-proofed at no charge.

Human Tests in Comparing Hz Differences Must Acknowledge Limitations Diminishing Hz Differences

Many scientists, media article writers and YouTubers test for Hz detection ability. Even standards organizations! Even people at Dolby, VESA, and other organizations consistently underestimate human's ability to detect Hz differences, especially by not maximizing the necessary variables above to consistently properly test Hz differences.

When scientifically setting up blind-test experiments, please acknowledge the limitations of your test equipment that often aberrate away from these ideal variables. Blindly loading up a random game with a random 1000Hz gaming computer mouse, is a scientifically-unknowledgable way to test Hz differences. If you want to test a Hz-differences trial in university, in media, in YouTube, or other scientific institution, please allow Blur Busters to vet the flaws and weak links of your test apparatus -- some simple changes (often done by the most professional esports athletes that know Blur Busters stuff properly) can often make major differences . We'd be happy to look things over -- usually for free.
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Re: Sensitivity Threshold: What is the Hz Limit of Human Eye?

Post by Chief Blur Buster » 02 Mar 2022, 18:40

I am bumping this thread up again to prove my point that existing tests are often lacking.

For example, latency testing is not the same as motion blur testing.

And, testing flicker for human limits doesn't acknowledge other effects (motion blur, phantom arrays, etc). You flicker test someone, and they can't see beyond specific Hz, and you falsely conclude that humans can't benefit from a display above "X Hz".

Our forums are full of users who post "probably placebos, but potentially legit" posts that we sometimes try to invent new tests for, to figure out whether it's placebo/legit. Many researchers did this -- the mouse 2000 Hz guy created that paper because of a Twitter debate between me and a Korean researcher, Sunjun Kim, who tested 1000Hz vs 2000Hz vs 4000Hz vs 8000Hz pollrates. He initally said "I doubt" but after doing the scientific research paper from my prodding, he now agrees going over 1000Hz with mice has benefit -- and the screenshot of the red/white/green squares from mouse jitter, is a direct copy and paste from that paper. I *saw* a difference with my eyes but was too busy to do tests myself, so I convinced another researcher.

Even though I was not cited in the paper, it was very clear that it was my Twitter thread and egging-on that convinced this Korean researcher to invent tests to try to prove himself wrong. He was unable to, and acknowledged that I was right. This has happened dozens of times already.

There are over a hundred papers that are clearly incubated indirectly from a Blur Busters forum idea, while others are more directly cited (20+ of them).

I don't have time to be involved in all of them, but we love to incubate areas that needs tests by egging other researchers to invent tests for things that too narrow-scope to push confirmed limits.

That is what Blur Busters does -- we incubate new tests (directly and indirectly) to cover what was seen with human-visible observations & we convince others to invent new tests.

I see things with my eyes, and instantly recognize the current tests are often flawed (doesn't correctly test for what I saw) to the disbelief of many disbelieving researchers, and then I either invent new tests for them -- or they invent new test for it. And then, we're invariably proven correct.

It is true that for every 100 "assumed placebo" effects, researchers later find out 10 of them are actually not placebos. But that's the nature of our forums as a crowdsourced incubator of future research ideas. This is the birth of many "Better Than 60Hz" research. So we're a Great Defender of posts about placebos around here, so we can dissect and rip them apart.

Forum users can reply "Did you do test X" but we delete those "Haha, that's a placebo" posts here -- we're very serious about bleeding edge of temporal display sciences around here.

Importantly, if you are researcher-minded or a high school / university graduate eager to school people around here, whoa there buddy. Big mistake around this area. Before replying to posts that you think are placebo effects, it is best to do homework at www.blurbusters.com/area51 as well as forums.blurbusters.com/area51 (both places). Nobody shall do instant evidence-free dismissals of what only the human eye saw. This is a forum. Yes, we need research. Yes, we need papers. Yes, we need tests. But we need people telling about human observed effects. This is why too many researchers said "Humans do not benefit from a display above X Hz" (85Hz, 120Hz, 255Hz) because they didn't test all the effects of a finite frame rate but instead only tested flicker or momentary brief-flash object-identification (like an old fighter pilot test), or other narrow-scope effects. This was frequently spun over the years as a Hz limit of the human eye.

____

We've grown great reputation because of this enforced open-discussion about "potential placebos, potential legitimate" effects that we need to invent new tests for.

Sometimes we are directly cited (examples on Google Scholar where researchers cite me, my articles, my papers, or one of my www.blurbusters.com/area51 articles, etc) and sometimes I'm egging on other researchers to invent tests to cover things that are untestable using the tests they did.

TL;DR1: Tests often miss many things that the human eye/brain legitimately saw, and was only proven when additional tests were invented to cover things overlooked in earlier too-limited-scope tests.

TL;DR2: This is why we allow discussion about things that might be "unconfirmed placebos, unconfirmed legitimate". Lots of such stuff were laughed at until it became part of the Blur Busters textbook. We are an incubator (ourselves or other researchers) of inventing new tests for hard-to-test stuff. We are the site that convinced many people that >60Hz monitors were worthwhile too. (and technologies such as VRR or strobe backlights)
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