Now, we have all seen the commercials about "Baby Mozart," babies who learn at an exponential rate because of listening to classical music. It appears ridiculous. But alas, I had hope in this theory, so I did a little self test (no, I am not a baby), involving being able to focus whilst doing simple cognitive work.
This was around the time I was doing summer school at 0530 'til 1200. One day, I would listen to my classical music compilation; the next day, simple lyrical music. I had then noticed that the lyrical music affected my focus, thereon affecting my test scores. Classical music, on the other hand, improved my focus and test scores. I'm not saying that the classical music on it's own helped my scores, I'm saying non-lyrical music helped my scores.
Now, to segway into what I'm getting at. Have you ever wondered why, when you pay no attention around you that you can still hear your name in a crowd? Or when you walk down the street, that your eyes fix on all the faces? Well, that is the subconscious' job, to do minor focusing. The subconscious, pre-installed with facial recognition, with voice recognition, and with word recognition, allows us to do everyday stuff without fully paying attention. What does this have to do with lyrical music? When focusing on one thing (i.e., school, books, art), the subconscious still focuses on outside stuff. When you listen to lyrical music while focusing on this task, the word and/or voice recognition is listening to your music and reminding you, "Hey, the guitar solo is coming up," or "Hey, I really think Lance Bass sounds gay in this song." So, as you are focusing on this task, your subconscious is nagging at you to listen to the music. Now back to the classical music. When listening to the non-lyrical/classical music, my subconscious had nothing to hone onto, improving my focus and concentration. Therefore non-lyrical/classical is today's "Ritalin."