Complex sentence: The participant's interactions therefore become integral to the work to the extent that the (v) user takes up that responsibility, chooses the amount of time and involvement each cares to give, and is rewarded accordingly.
Split into simpler sentences: The participant's interactions become integral to the work to the extent that the (v) user takes up that responsibility. He or she chooses the amount of time and involvement that each cares to give, and is rewarded accordingly.