Quick exposure tests
During quick exposure testing, participants see a screen only for a very brief moment. When the screen disappears, they're asked a list of questions to reveal if they understand the content. The test is perfect for measuring comprehension as it mimics the real-life environment when users scan a page in a short span of time.
Since participants can see an interface only for a couple of seconds, the test allows revealing the honest first impression of a page and shows what sticks to users' memory and what goes unnoticed. The downside of this method is that human memory can be too unreliable a source of truth in a stressful environment. However, it's a quick and cheap way to gain some interesting insights.
The online Five second test allows you to discover how users perceive your designs after a short exposure (literally, 5 seconds!).