Stereotypically, content experts focus on organization and flow. Visual and industrial designers focus on the presentation of the product.
Cognitive psychologists focus on the participant's process and problems over time.
And engineers focus on the implementation of software mechanisms. Not only do these multiple foci overlap, but they are intimately interrelated and ultimately inseparable. Information design regards the content's architecture. Interface design regards the sensory aspects of usability. Interaction design regards the ways we invite people to act.