What framerates can we really see?
“Certainly 60 Hz is better than 30 Hz, demonstrably better,” Busey says. So that’s one internet claim quashed. And since we can perceive motion at a higher rate than we can a 60 Hz flickering light source, the level should be higher than that, but he won’t stand by a number. “Whether that plateaus at 120 Hz or whether you get an additional boost up to 180 Hz, I just don’t know.”
“I think typically, once you get up above 200 fps it just looks like regular, real-life motion,” DeLong says. But in more regular terms he feels that the drop-off in people being able to detect changes in smoothness in a screen lies at around 90Hz. “Sure, aficionados might be able to tell teeny tiny differences, but for the rest of us it’s like red wine is red wine.”
Chopin looks at the subject very differently. “It’s clear from the literature that you cannot see anything more than 20 Hz,” he tells me. And while I admit I initially snorted into my coffee, his argument soon began to make a lot more sense.
Certainly 60 Hz is better than 30 Hz, demonstrably better.
Professor Thomas Busey
He explains to me that when we’re searching for and categorising elements as targets in a first person shooter, we’re tracking multiple targets, and detecting motion of small objects. “For example, if you take the motion detection of small object, what is the optimal temporal frequency of an object that you can detect?”
And studies have found that the answer is between 7 and 13 Hz. After that, our sensitivity to movement drops significantly. “When you want to do visual search, or multiple visual tracking or just interpret motion direction, your brain will take only 13 images out of a second of continuous flow, so you will average the other images that are in between into one image.”
Discovered by researcher Rufin vanRullen in 2010,
this literally happens in our brains: you can see a steady 13 Hz pulse of activity in an EEG, and it’s further supported by the observation that we can also experience the ‘
wagon wheel effect’ you get when you photograph footage of a spinning spoked object. Played back, footage can appear to show the object rotating in the opposite direction. “The brain does the same thing,” says Chopin. “You can see this without a camera. Given all the studies, we’re seeing no difference between 20hz and above. Let’s go to 24hz, which is movie industry standard. But I don’t see any point going above that.”
Perception and reaction
This article is about what framerates the human eye can perceive. The elephant in the room: how fast can we
react to what we see? It's an important distinction between games and film worthy of another whole article.
So why can games
feel distinctly different at 30 and 60 fps? There's more going on than framerate.
Input lag is the amount of time that elapses between inputting a command, that command being interpreted by the game and transmitted to the monitor, and the monitor processing and rendering the image. Too much input lag will make any game feel sluggish, regardless of the LCD's refresh rate.
But a game programmed to run at 60 fps can potentially display your inputs more quickly, because the frames are narrower slices of time (16.6 ms) compared to 30 fps (33.3 ms). Human response time definitely isn't that fast, but our ability to learn and
predict can make our responses seem much faster.
The important thing here is that Chopin is talking about the brain acquiring visual information which it can process and on which it can act. He’s not saying that we can’t notice a difference between 20 Hz and 60 Hz footage. “
Just because you can see the difference, it doesn’t mean you can be better in the game,” he says. “After 24 Hz you won’t get better, but you may have some phenomenological experience that is different.” There’s a difference, therefore, between effectiveness and experience.
And while Busey and DeLong acknowledged the aesthetic appeal of a smooth framerate, none of them felt that framerate is quite the be-all and end-all of gaming technology that we perhaps do. For Chopin, resolution is far more important. “We are very limited in interpreting difference in time, but we have almost no limits in interpreting difference in space,” he says.
For DeLong, resolution is also important, but only to the small, central region of the eye that cares about it, which comprises only a couple of degrees of your field of view. “Some of the most compelling stuff I’ve seen has been with eye-tracking. Why don’t we do full resolution only for the areas of the eye where we actually need it?” But his real focus is on contrast ratios. “When we see really true blacks and bright whites it’s really compelling,” he says.
What we really know
After all of that, what do we really know? That the brain is complicated, and that there's truly no universal answer that applies to everyone.
- Some people can perceive the flicker in a 50 or 60 Hz light source. Higher refresh rates reduce perceptible flicker.
- We detect motion better at the periphery of our vision.
- The way we perceive the flash of an image is different than how we perceive constant motion.
- Gamers are more likely to have some of the most sensitive, trained eyes when it comes to perceiving changes in imagery.
- Just because we can perceive the difference between framerates doesn't necessarily mean that perception impacts our reaction time.
So it’s not a tidy subject, and on top of all of this, we have to also consider whether our monitors are actually capable of outputting images at these high framerates. Many don’t go above 60 Hz, and Busey questions whether monitors advertised at 120 Hz really display that fast (according to
some seriously in-depth testing at TFTCentral, they certainly do). And as someone who has also enjoyed games at the 30 frames per second (and often rather less) rendered by my consoles, I can relate to them suggesting that other aspects of visual displays might connect better with my visual perception.
On the other hand, I would love to hear from pro teams about their objective experiences with framerate and how it affects player performance. Perhaps they’ll corroborate or contradict science’s current thinking in this field. If gamers are so special when it comes to vision, perhaps we should be the ones to spearhead a new understanding of it.
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