TimPenner.ca

I first encountered this term in Scot Gardiner's A History of Media (2002). This is as opposed to the basic concept of making ourselves smarter as Donald Norman explains in his Things That Make Us Smart (1993). Gardiner sees how human intelligence has evolved through identifiable phases because of the amplification process enabled by our innate ability to adopt and adapt to various media.

The point is then that all media extend our minds meaningfully; and that social extension has the most potent prospect.

For more, see Gardiner's book, especially after I've done a proper job of reviewing Gardiner's book. (Minor note: I did actually do that, but lost it when my database at BlueFur tanked.)