While it is becoming increasingly obvious that the fundamental architecture of a system has a profound Influence on the quality of its human factors, the vast majority of human factors studies concern the surface of hardware (keyboards, screens) or the very surface of the software (command names, menu formats).
L.M. Branscomb, J.C. Thomas (1984) "Ease of use: a system design challenge". in: IBM Systems Journal. Vol 23.3, Sept 1984. Pages 224-235