Naomi Miyake, in her paper "Making Internal Process External for Constructive Collaboration" explains in which way how human cognitive processes not only rely on internal knowledge but also on a physical externalization of the interaction of those processes with the nvironments, made up of people and artifacts. The first and simplest example is the affordance of an object : the shape 'affords' some action. Another easy-to-get understand is the journal/log that could be seen as a way to store, sort and share information. I also like this example :

The mere location of a tool recently used can be interpreted for instance as a sign of the progress of the work

This paper would also be interesting : Miyake, N. (1986) Constructive interaction and the iterative process of understanding. Cognitive Science, 10, 151-177.