You should learn:
Overt behavior is publicly observable; it is what a person does openly or says out loud. In contrast, covert behavior is private; only the behaving person is consciously aware of what s/he is thinking. For example, a person may show manifest signs of paying attention to a lecture, such as sitting up and looking at the speaker, but as you know, attending is really a covert act. We have all learned how to fake doing one thing while thinking about something else. You have probably had the experience of starting to turn a page only to realize that you don't remember anything that you just read. The Principle of Active Participation says that you will only learn from verbal material if you notice it, think about it, actively attend to it.
The Principle of Active Participation is more complicated than it appears at first reading. One complication is that there are two different processes controlling one's attention. (There are also two kinds of rehearsal, which are discussed in a later chapter.) One process is called automatic attention. As the name implies, automatic attention is not voluntary or deliberate. Any strong, unusual, or unexpected event tends automatically to command attention. This is the attention process that Mark Twain used, but people don't (usually) need to be hit with a two-by-four. You tend automatically to attend to the loudest sound in music, to the most vivid color in a picture, or to an insect that is biting you. Events in the external world act to control attention automatically.
The other process is called selective attention. It might better be called "intentional attention" because the process is voluntary and deliberate. For example, if I now ask you whether you are breathing by expanding your chest or your abdomen, you can quickly shift your attention from my words to your body and find out how you are breathing. The important point is that cues from your body are there all along but they are normally in the background rather than at the center of your attention. But you can voluntarily turn your attention to them on command.
In sum, you can only focus your attention on one thing at a time. Salient events in the environment tend automatically to attract attention, but you can selectively attend to less salient stimuli.