Semantic Level of Arousal achieves figure-ground discrimination with meaning.
This occurs when we apply the highest level of energy into the perceptual process. We would like to be operating at this level as much as possible, particularly in classroom situations.
I was a student for 15 years in graduate school (when one graduates with a BA in Tropical Agriculture, there is much to make up), and on many occasions I swore on my way to class that I would attend to everything that was said for the entire period.
I never once succeeded. I would stay fully aroused for a while, and then my mind would sink to a lower level (to the sub-liminal on more than one occasion), only to be brought back by an awareness of a lot of pencils writing.
I would return to the semantic level, just in time to hear the instructor saying, "...and that will be one of the major questions on the final exam. Don't miss it!"