The American international joined the Blues ranks at the start of August 2011, having left West Ham earlier in the summer.
He made his debut later that same month in Blues' Europa League 0-0 draw away at Nacional.
During his time at St. Andrew's, Spector has played in a variety of positions across both defence and in midfield. He has a solitary Blues goal to his name, which came back in August 2012 in the Capital One Cup 3-2 defeat away at Coventry City.
To date this season he has made 22 appearances for Blues.
Born in the US state of Illinois, Spector began his footballing career in England with Manchester United in 2003, after being spotted playing for the United States U17 team as a striker.
During his three-year spell at Old Trafford he made a total of eight first team appearances for the Red Devils. In order to get regular first team football he then spent a season out on loan at South London side Charlton Athletic during the 2005/06 campaign, where he turned out 24 times for the Addicks.
In 2006, he left United to link up with West Ham, where he spent five years and played 111 times and scored four goals. He has represented his country 34 times at senior level and will be hoping to travel to Brazil in June with the US squad for the World Cup.
The 28-year-old signed a two-year deal with Blues in the summer of 2013.