For people who want a brief synopsis of this long-standing intellectual debate, please go to The Media Debate.
It seems like with any of these opposing viewpoints, there are constructs within each that have merit.
I am in the middle of studying this in some detail. Clark is absolutely right and has empirical evidence to support these views. His assertion has the ring of common sense. Yet as a technophile, it troubles me that media had no direct impact on learning outcomes.
Now I am reading Kozma and beginning to see Clark as having a macro view of media as it pertains to instructional design. If you take a broad approach, he is right. If all images, video audio and computer generated media are the same, applied the same and perceived in the same way, then it will never make any difference. But I think Kozma is saying that it is not the same. The two viewpoints are not so different in one way of thinking.
Just trying to make sense of what I have read and discussed here! 