A lot of delta blues has a thumping bass accompanying the picking on the higher strings. This short video shows you how to play that bass, and how to practice playing the higher notes along with it. Be sure to start slowly until you feel comfortable with where the bass notes intermingle with the high ones. Once you have it down slowly, speed it up in small increments. Eventually it will become second nature. Remember, you are not only developing mental memory; you are also developing muscle memory, and that is best done by starting slowly.
Below is Lightnin’ Hopkins using his thumb, with a thumb pick, to play the bass while also playing high notes on top of it. Note that sometimes he stops the bass thumping and just plays high notes. The blues is not always a steady pattern. Pulling the bass in and out creates drama and dynamics.