I've never heard of 'decisional' regeneration.
Decisional Regeneration = The process by which a person, through an act of the will, can make themselves born again.
An alternate definition:
Decisional Regeneration = The process by which a man or woman can cooperate with God in gaining the gift of eternal life, by contributing the one thing God "requires" to be born again...belief in His Son.
Simply put, the act of belief in Christ as Saviour, triggers the process of making one born again;
God is obliged to grant a person eternal life or eternal damnation, based on their choice of His Son.
IMO, it's very popular today, and was widely preached during a certain man's "crusades" all through the 50's, 60's, 70's, 80's and 90's.
It's also found all over television, radio and the internet, and varies slightly depending on who is preaching it.
But it always makes man the "weak link" by insisting that he contribute some piece or pieces to God's plan of salvation.
Essentially, it is distilled down to one equation:
God does His part, and man does his part.