Despite popular media portrayals, people cannot be hypnotized against their will. People differ in their susceptibility to hypnosis. People who tend to "space out" while daydreaming or who experience vivid fantasies are easier to hypnotize. Hypnotizability may also depend on which variant of the oxytocin receptor gene people have. Oxytocin is a neurotransmitter that promotes social cooperation and trust. People who are easily hypnotized can be led to create false memories under hypnotic suggestion. They may also experience posthypnotic amnesia—the failure to retrieve memories following hypnotic suggestions to forget.
According to dissociation theory, hypnosis represents an altered state in which consciousness is split into two components: a hypnotized component (the hypnotized self) and a nonhypnotized component (the hidden observer). The hidden observer maintains accurate perceptions of the world, while the hypnotized self is highly suggestible. Dissociation theory applies to age regression in hypnosis, which can occur when an adult is hypnotized and instructed to recall an event from the past. Even as the hypnotized self recalls an event from childhood, the hidden observer remains aware of actually being an adult. This phenomenon applies to the Poggendorff illusion, which involves the misperception of one part of a line running through an intersecting shape. Adults are more susceptible to the illusion than children. However, an adult experiencing age regression during hypnosis still perceives the illusion as an adult, not a child.
The hidden observer can also intervene to limit the hypnotized person's actions. In contrast, sociocognitive theory holds that hypnosis is a social role in which people hand over responsibility for their actions to the hypnotist. They maintain a highly focused state of attention in which they are only dimly aware of what is happening around them.