Apple Motion 4 - Manual (Page 584)

To change the interpolation method for an entire parameter
µ
In the Keyframe Editor, click the Animation menu and choose a method from the
Interpolation submenu.
The selected interpolation method (Constant in this example) is applied to the green
curve.
To change the interpolation method for multiple parameters
1 In the parameter list of the Keyframe Editor, Shift-click to select the parameters you wish
to change.
2 Click the Animation menu (in the Keyframe Editor) and choose a method from the
Interpolation submenu.
584 Chapter 10 Keyframes and Curves