The various methods manufacturers use to improve response time are called "overdrive". Overdrive causes a pixel to go beyond the intended value, only to fall back to the end result. This will use more energy in theory, which is why many brands disable the overdrive feature by default, even if it's just to get approval for European markets. In our tests we noticed very little difference with overdrive enabled or disabled.
Overdrive does have a potentially even more important disadvantage, as it can negatively influence the image quality of moving images. A sort of digital noise-effect can appear, and this is particularly visible in even colour areas. You can also see dark or light lines around moving objects. These types of effects are difficult to capture and don't bother everyone as much, but it's something to be mindful of. It seems that monitors with VA or IPS panels suffer more from these problems than TN screens, perhaps because they require more aggressive overdrive techniques to get close to the response time of TN screens.
Where possible, we tested each monitor with overdrive enabled and disabled. Not all monitors have this option. We noticed that for some monitors it had no influence on response time, while it made a huge on others. Overdrive had very little effect on the other parameters. It should also be noted that all measurements were performed on static images, while the problems we just mentioned occur with moving images but are difficult to capture.
Most consumers leave their monitors on the factory settings, so we tested each monitor with its out-of-the-box settings. Only for testing the response times did we enable and disable the overdrive feature.
Many gamers value the smooth gaming experience on 120 Hz monitors, that arrived thanks to active 3D. It's difficult to measure the responsivity. On paper a 120 Hz monitor requires a refresh rate of at least 8.3 ms in order to display 120 frames per second. For a good 3D experience a much faster refresh rate is desirable. Several of the 60 Hz screens in this test are almost twice as fast as that 8.3 ms. The two actual 120 Hz screens in this round-up do indeed have exceptionally low response times, provided overdrive is enabled.