This video from Johns Hopkins University feels like your basic memory game. Viewers are first asked to look at a series of moving images; later in the exercise, they must select the pictures they were shown from the ones they haven’t seen. If some images feel easier to memorize than others, that’s the point: The test demonstrates how motion can impact memory.

As Slate reports, objects that emerge twice from one side of the frame are more likely to stick in our heads than those that appear from opposite sides. That’s because our brain treats a single image that swaps sides as two items, while an image that stays in one half of the screen feels more like a single object. This fits into our understanding of the world: If we saw someone duck into a doorway on the left side of a room and come back the same way, we’d assume they were one person. But if we saw someone walk through that same door and re-enter the room from the right side, we’d be confused. See if you can conquer Johns Hopkins’s mind-bending motion trick below.

[h/t Slate]