hypnosis is not sleep, …

Clark Leonard Hull (1884 - 1952) was an influential American psychologist who sought to explain learning and motivation by scientific laws of behavior.
Hull conducted research demonstrating that his theories could predict and control behavior. His most significant works were the Mathematico-Deductive Theory of Rote Learning (1940), and Principles of Behavior (1943), which established his analysis of animal learning and conditioning as the dominant learning theory of its time. Hull is known for his debates with Edward C. Tolman.
He is also known for his work in Drive Theory. Hull’s model is couched in biological terms: Organisms suffer deprivation. Deprivation creates needs. Needs activate drives. Drives activate behavior. Behavior is goal directed. Achieving the goal has survival value. {It took 14 years to discover some of his theories in these areas were wrong.}

In experimental psychologist, his work Hypnosis and Suggestibility (1933) was a rigorous study of the phenomenon, using statistical and experimental analysis. Hull's studies emphatically demonstrated once and for all that hypnosis had no connection with sleep ("hypnosis is not sleep, … it has no special relationship to sleep, and the whole concept of sleep when applied to hypnosis obscures the situation").

The main result of Hull's study was to rein in the extravagant claims of hypnotists, especially regarding extraordinary improvements in cognition or the senses under hypnosis. Hull's experiments showed the reality of some classical phenomena such as mentally induced pain reduction and apparent inhibition of memory recall. However, Clark's work made clear that these effects could be achieved without hypnosis being seen as a distinct state, but rather as a result of suggestion and motivation, which was a forerunner of the behavioural approach to hypnosis. Similarly, moderate increases in certain physical capacities and changes to the threshold of sensory stimulation could be induced psychologically; attenuation effects could be especially dramatic.