When I perform I can't say I really think about anything other than the the note that's being played at that exact moment. Each note is an eternal moment unto itself. To think ahead would be to lose that moment; to think of the notes I had just played would derail the flow of consciousness.

Composing is similar. However, there is some reflection of the past, and some anticipation of the future. But ultimately each note is a manifestation of the present. It cannot be otherwise.