Some thinkers have claimed that expert performance with technology is characterized by a kind of disappearance of that technology from conscious experience, that is, by the transparency of the tools and equipment through which we sense and manipulate the world. This is a claim that may be traced to phenomenological philosophers such as Heidegger and Merleau-Ponty, but it has been influential in user interface design where the transparency of technology has often been adopted as a mark of good design. Moreover, in the philosophy of cognitive science, such transparency has been advanced as necessary for extended cognition (the situation in which the technology with which we couple genuinely counts as a constitutive part of our cognitive machi...