Suggestion is the psychological process by which one person guides the thoughts, feelings, or behaviour of another. Nineteenth century writers on psychology such as William James used the words "suggest" and "suggestion" in senses close to those they have in common speech—one idea was said to suggest another when it brought that other idea to mind. Early scientific studies of hypnosis by Clark Leonard Hull and others extended the meaning of these words in a special and technical sense (Hull, 1933). The original neuro-psychological theory of hypnotic suggestion was based upon the ideo-motor reflex response of William B. Carpenter and James Braid.