Well there are really three stages of the spawning period:
Prespawn
Spawn
Postspawn

Bass are really active in the prespawn because they are fighing for prime bed space, mates, etc, and just starting to be a lot more active after all the cold water. The spawn is basically bass just sitting on beds. Thats why during this time period you just basically go sight fishing for them with polarized glasses. And the postspawn, well I'm not totally sure about that, but I believe that the bass go back out of the shallows and become a lot less active...