MK Dons have signed Simon Church, Cody Cropper and Dale Jennings on a busy day of transfer business for boss Karl Robinson.
Sheffield Wednesday skipper Glenn Loovens has signed a new one-year contract with the club.
The 34-year-old former Swansea, Wigan and Ipswich forward was handed a short-term deal until the end of this season when he joined Barnsley on a free transfer in late January.
"Jason has enthusiasm, energy and desire," manager David Flitcroft told the club's official website.
"He's a fantastic person who wants to help support the younger players in the squad and pass on his superb knowledge about the game.
"Everyone who watches Jason knows about his goalscoring abilities, but it's also the other side of him that really excites me because this is a player who has tremendous experience, know-how and drive that will benefit everyone.
"It's great to have Jason signed and I'm hopeful we can follow this up with others in the coming weeks."
Trinidad & Tobago international Scotland, who began his career in the UK with Dundee United and then St Johnstone, commanded a fee of £2million when he signed for Wigan from Swansea in 2009.
He arrived at Oakwell on a free transfer from Ipswich at the turn of the year and scored with his first touch for the club when making his debut as a substitute in a 2-0 win over Millwall. He scored six goals in 20 appearances for the Tykes this season.