1. Signal Processing: This is the most basic level, where the brain simply processes the sounds as physical signals. You're not really paying attention to the meaning of the sounds, just that they exist.
2. Literal: At this level, you're processing the meaning of the words, but not necessarily understanding the deeper meaning or implications. You're focused on the facts and information being conveyed.
3. Critical: This is the highest level of listening, where you're not only processing the information, but also evaluating it, analyzing it, and drawing conclusions from it. You're actively engaging with the message and considering its implications.
So, the missing level is critical.