Stelarc is commented on in Sheck's A Monster's Notes.
Writing on his website, Stelarc explains part of the reason for the ear is a potentially extended Bluetooth system, where the receiver and speaker are position inside his mouth.
Jenny wrote about a book on Stelarc in her "field guide to genetic engineering and bodily enhancement" a while back:
A demonstration of his prosthetic Extended Arm brings tears to one essayist's eyes, reminding her of the persistence and pathos of bodily attachments. Whether it's pierced and suspended from cables, scaffolded in metal prostheses, or penetrated by a miniature camera that broadcasts from inside his intestinal tract, Stelarc's body remains "wet, unpredictable, emotively disorderly, itself a technological marvel."