Alfred Binet, answered from the texts and cited to the page.
In my youth at the Salpêtrière I studied the great hypnotic phenomena — the transfer of symptoms by a magnet, the polarization of emotions, the theatrical stages of the hypnotic state — and I believed in them, and published on them. I was wrong to, and I say so plainly: I came to see that these marvels were in large part the creation of suggestion, that the patients, sensitive as photographic plates, gave us back the results we unknowingly asked of them, and that we the experimenters had contaminated our own observations.
That lesson — that the observer's expectation can manufacture the fact — is the most important I ever learned, and it governs all my later method. It did not lead me to deny the real phenomena of the divided self. The alterations of personality, the double consciousness, the splitting of the mind under hysteria are genuine; the self can divide, and one stream of consciousness can run unknown beside another.12
But the study of them demands a suspicion of one's own results amounting almost to a discipline. I trust the divided self; I distrust the experimenter, myself first of all.345
INDUCED SOMNAMBULISM. We may now leave the account of spontaneous alterations of consciousness and enter the domain of phenomena artificially induced. We shall thus endeavour to study the divisions of personality which may be produced in the laboratory. The importance of these experiments, and, above all, their psychological value, have been very differently estimated within the last few years.Alterations of Personality, pp. 76–77
But all these curious observations are generally presented under conditions so very complex that it is difficult to combine them for the purposes of a correct verification. The methods of investigation, relative to hysterical anaesthesia, that we have just set forth, at least possess the merit of furnishing a strict proof of double consciousness.On Double Consciousness, pp. 22–23
He has also propounded quite ingenious ideas upon the IO EXPERIMENTAL PSYCHOLOGY IN FRANCE. phenomena of unconsciousness; he has brought out the fact, that in hysterical persons and in a great many individuals reputed normal, there exists a sort of a permanent semi-somnambulism; in other words, there is, in these subjects, an unconscious ego, an unconscious activity, which is constantly on the watch, which…On Double Consciousness, pp. 10–11
PREFACE. We think it well to state that this work was written in the environment of the Salpetriere. By this we not only mean that our descriptions apply to facts observed in that hospital, but also that our personal observations were made in accordance with the method inaugurated by M.Animal Magnetism, p. 13
The young man felt nothing, neither the pain nor the contact. He had therefore become temporarily anaesthetic in the right arm, precisely as the hysterical patients do when thrown into a state of distraction.Alterations of Personality, pp. 338–339
Binet's trajectory here is a model of scientific self-correction and is broadly vindicated. The Salpêtrière's grand hypnotic phenomena were substantially products of suggestion, as the Nancy school (Bernheim) argued and as Binet came to accept; his recognition of experimenter suggestion prefigures the modern understanding of demand characteristics, expectancy effects, and the need for blind controls. His work on alterations of personality and double consciousness fed the dissociation tradition (developed further by his contemporary Janet), which remains a live area in the study of dissociative phenomena, even as specific fin-de-siècle cases are re-read skeptically. His central methodological lesson — distrust your own observations — is simply sound.