The Long and the Short of It: Comments on Multiple Timescale Studies of Human Activity.

It is a particular pleasure to comment on the four stimulating articles in this special issue of the Journal of the Learning Sciences (JLS). Each addresses critical issues of theory and method that have preoccupied me; all seek to analyze human activity across multiple time scales. Multiple time-scale analysis frames the right questions, however difficult answering them may be both conceptually and in practice. All four articles have a great deal in common with one another and with a more general model I have been developing. [ABSTRACT FROM AUTHOR]