What does a scanner see? he asked himself. I mean, really see? Into the head? Down into the heart? Does a passive infrared scanner like they used to use or a cube-type holo-scanner like they use these days, the latest thing, see into me – into us – clearly or darkly? I hope it does, he thought, see clearly, because I can’t any longer these days see into myself. I see only murk. Murk outside; murk inside. I hope, for everyone’s sake, the scanners do better. Because, he thought, if the scanner sees only darkly, the way I myself do, then we are cursed, cursed again and like we have been continually, and we’ll wind up dead this way, knowing very little and getting that little fragment wrong too.
Philip K. Dick, A Scanner Darkly