Ta·chis·to·scope
(greek “táxistos”, superlative of “tachýs” = engl. “swift”, “rapid” + “scope”, “range of view”)
A tachistoscope is a device that displays an image for a short time. It can be used to increase recognition speed, to show something too fast to be consciously recognized, or to test which elements of an image are memorable. Which is what we want to do here.