Steve Gadd, says composer extraorinaire Paul Simon, has a particularity: while he improvises he can recall a pattern that he just played and play it again exactly the same. It sounds like an obvious thing to do, but when you have the technique that he has, it becomes a very complicated job for the brain to remember what 5 voices are doing (Bass drum, snare drum, right hand, left foot AND ghost notes).
Although I heard what Mr Paul Simon said, I can tell you that that is something I had noticed in Steve Gadd about 30 years ago. My calculation was this one: He strated with jazz, he has great improvisational skills, but he is a star of fun and groovy session, and he’s able to do all these very difficult patterns at will: what a memory he must have.
And I started working on that specific concept.
Here is an exercise to develop that: call and answers. You take a 4 beats pattern and you try to repeat it. Always start with only one sound source and with 1/4 notes, just to establish tempo. As you go, you can get more complicated patterns. Then add one more sound source, and one more, etc… Work on your weaknesses like remembering the dynamics or the syncopated patterns. You can mushroom that exercise to a cathedral of complexities with 4 bars repeated note for note and then improvising on 4 bars repeated exactly, and so on and so forth.