The boundaries of the human subject are constructed rather than given. Conceptualizing control, communication and information as an integrated system, cybernetics radically changed how boundaries were conceived.
Gregory Bateson brought the point home when he puzzled his graduate students with a question koan-like in its simplicity: "Is a blind man's cane part of him?"
The question aimed to spark a mind-shift. Most of his students thought human boundaries are naturally defined by epidermal surfaces. Seen from the cybernetic perspective coalescing into awareness from during and after World War II, however, cybernetic systems are constituted by flows of information.
In this viewpoint cane and man join in a single system, for the cane funnels to the man essential information about his environment. Similarly for a deaf person's hearing aid, a voice synthesizer for someone with impaired speech, and a helmet with a voice-activated firing control for a fighter pilot.