Here's a potential outside reference to prior literature relevant to feature focusing instruction: I believe this Biederman and Shiffrar study indicates that instruction that draws attention to critical features enhances learning. (And, also, that idealizing/abstracting these features may be beneficial.)
Biederman, I., & Shiffrar, M. M. (1987). Sexing day-old chicks: A case study and expert systems analysis of a difficult perceptual learning task. Journal of Experimental Psychology: Learning, Memory, and Cognition, 13(4). pp. 640-645.
--Koedinger 22:35, 11 January 2009 (EST)