How is it possible for investment spending to increase even in a period in which the real interest rate rises? Is the relationship between changes in spending and changes in real GDP in the multiplier...

How is it possible for investment spending to increase even in a period in which the real interest rate rises? Is the relationship between changes in spending and changes in real GDP in the multiplier effect a direct (positive) relationship or is it an inverse (negative) relationship? How does the size of the multiplier relate to the size of the MPC? The MPS? What is the logic of the multiplier-MPC relationship?