The Base and Treble Clefts are classic examples of Selective Focus.
The Base versus the Treble Cleft is a classic example of selective focus. The note value of the lines of a measure carry a different significance depending upon which one it is.
Music is treasure chest of alternating focus tasks. Notes are continually switching their count; changing their pitch (between, sharps and flats); switching their rhythm (eg. from 3/4 to 4/4 to 2/2 as in Carmen by Bizet.)
The piano is also a study in divided focus! Learning to do different activities with each hand simultaneously is the name of the game. Also one must learn to read the notes as they move their hands over the keyboard.
And of course one has to read the notes on the Treble and Base Cleft bars at the same time! Then some people even sing and/or talk while doing all this.