At the time he wrote this, de Maupassant often saw a double himself, an autoscopic image. As he remarked to a friend, “Almost every time when I return home I see my double. I open the door and see myself sitting in the armchair. I know it’s a hallucination the moment I see it. But isn’t it remarkable? If you had not a cool head, wouldn’t you be afraid?”
De Maupassant had neurosyphilis at this point, and when the disease grew more advanced, he became unable to recognize himself in a mirror and, it is reported, would greet his image in a mirror, bow, and try to shake hands with it.
The persecuting yet invisible Horla, while perhaps inspired by such autoscopic experiences, is a different thing altogether; it belongs, like William Wilson and Golyadkin’s double in Dostoevsky’s novella, to the essentially literary, Gothic genre of the doppelgänger, a genre which had its heyday from the late eighteenth century to the turn of the twentieth.
In real life—despite the extreme cases reported by Brugger and others—heautoscopic doubles may be less malign; they may even be good-natured or constructive moral figures. One of Orrin Devinsky’s patients, who had heautoscopy in association with his temporal lobe seizures, described this episode: “It was like a dream, but I was awake. Suddenly, I saw myself about five feet in front of me. My double was mowing the lawn, which is what I should have been doing.” This man subsequently had more than a dozen such episodes just before seizures, and many others that were apparently unrelated to seizure activity. In a 1989 paper, Devinsky et al. wrote:
His double is always a transparent, full figure that is slightly smaller than life size. It often wears different clothing than the patient and does not share the patient’s thoughts or emotions. The double is usually engaged in an activity that the patient feels he should be doing, and he says, “that guy is my guilty conscience.”
Embodiment seems to be the surest thing in the world, the one irrefutable fact. We think of ourselves as being in our bodies, and of our bodies as belonging to us, and us alone: thus we look out on the world with our own eyes, walk with our own legs, shake hands with our own hands. We have a sense, too, that consciousness is in our own head. It has long been assumed that the body image or body schema is a fixed and stable part of one’s awareness, perhaps in part hardwired, and largely sustained and affirmed by the continuing proprioceptive feedback from joint and muscle receptors regarding the position and movement of one’s limbs.
There was general astonishment, therefore, when Matthew Botvinick and Jonathan Cohen showed in 1998 that a rubber hand, under the right circumstances, could be mistaken for one’s own. If a subject’s real hand is hidden under a table while the rubber hand is visible before him, and both are stroked in synchrony, then the subject has the convincing illusion, even though he knows better, that the rubber hand is his—and that the sensation of being stroked is located in this inanimate though lifelike object. As I found when I looked through the “eyes” of a robot, knowledge in such a situation does nothing to dispel the illusion. The brain does its best to correlate all the senses, but the visual input here trumps the tactile.
Henrik Ehrsson, in Sweden, has developed a great range of such illusions, using the simplest equipment—video goggles, mannequins, and rubber arms. By disrupting the usual unity of touch, vision, and proprioception, he has induced uncanny experiences in some people, convincing them that their bodies have shrunk or grown enormous, even that they have swapped bodies with someone else. I experienced this for myself when I visited his laboratory in Stockholm for a number of experiments. In one, I was convinced that I possessed a third arm; in another, I felt embodied in a two-foot-high doll, and as I looked through “its” eyes via video goggles, normal objects in the room appeared enormous.
It is evident, from all of this work, that the brain’s representation of the body can often be fooled simply by scrambling the inputs from different senses. If sight and touch say one thing, however absurd, even a lifetime of proprioception and a stable body image cannot always resist this. (Individuals may be more or less susceptible to such illusions, and one might imagine that dancers or athletes, who have an exceptionally vivid sense of where their bodies are in space, may be harder to fool in this way.)
