ULMB (Ultra Low Motion Blur) is Nvidia’s proprietary Blur Reduction Technology. It’s the successor to Nvidia’s older Lightboost technology. ULMB is designed to reduce eye tracking motion blur, however it should be noted that it can only be used by itself, so you cannot use it in tandem with G-Sync. It can also only be used at certain fixed refesh rates, such as 100Hz, 120Hz, …
Modern displays, due to the way their technology works, suffer from ‘sample-and-hold’, meaning that frames are displayed until the frame refreshes again, i.e. the image is always ‘on’. Each pixel (which is what the image on the screen is made out of) takes a while to change in brightness and color though, even on monitors with the fastest response times possible. When fast moving objects move around the screen this can cause eye tracking motion blur, since the display cannot respond fast enough to accurately display the objects’ travel line.
Our eyes are tracking the fast moving object so fast that our eyes will be at a different position at the start of a frame vs. at the end of a frame. This causes what we know to be ‘eye tracking motion blur’.
The only way to combat eye tracking motion blur is by shortening the amount of time each frame is on screen. That’s done by (for example) producing higher refresh rate monitors, but also by what we call ‘backlight strobing’, i.e. turning the backlight off in between frame refreshes, thus shortening the amount of time that a frame is displayed even more.
ULMB drastically reduces motion blur and makes for a much smoother and more natural image on your screen, given your system is capable of pushing high refresh rates consistently. With its predecessor Lightboost, people used to complain about it noticeably lowering the display’s brightness and image quality, along with some rare complaints about people being able to ‘notice’ the flickering.
ULMB drastically improved upon the existing Lightboost technology and is superior in every way, making it a very good option for reducing eye tracking motion blur to the absolute minimum. ULMB is nowadays completely ‘invisible’ to the naked eye (in the sense that you do not notice the backlight turning off and on) and is of course optional and can as such be turned off completely, in caser users do not want to use the technology.