[quoting Duchastel, 14 Sep 98.a] The idea I am championing is that motivation is a central function of ID...
I couldn't agree more. We (instructional designers) often tend to focus and measure short term human performance outcomes without considering or measuring long term learning outcomes directly related to motivation that may be more important.
I would highly recommend Dr. John Keller's (Florida State) work on motivation in instructional design.