hypnotic crystal, he began to research the phenomenon and its medical applications. Dissatisfied with the unscientific nature of the field, Hull sought to bring greater academic rigor through measuring behavior instead of relying on self-reports. While teaching, he encouraged his students to do their research with hypnosis, teaching them the techniques involved. His work Hypnosis and Suggestibility (1933) was a rigorous study of the phenomenon, using statistical and experimental analysis. Hull's studies demonstrated emphatically once and for all that hypnosis is not related to 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"). His research even goes as far as to say that hypnosis is the opposite of sleep, because he found that hypnosis gave responses linked to alertness rather than lethargy. In Hull's research, some of his subjects even felt that hypnotism made their sensitivity and alertness better. In fact, many of Hull's subjects in hypnotic states did believe that their senses had increased. They genuinely thought their senses were better, but this was never proven to be a significant result. The main question of Hull's study was to examine the veracity of the apparently extravagant claims of hypnotists, especially regarding extraordinary improvements of cognition or the senses by hypnosis. Hull's research indicated that hypnotic states and waking states are the same, besides a few simple differences. One of these differences is that subjects in hypnotic states respond to suggestions more readily than those in a waking state. The only other notable difference is that Hull believed that those in hypnotic states were better able to remember events that had happened far in the subject's past. Other than those two differences, not much differentiated between waking and hypnotic states, according to Hull's controlled studies. Hull's experiments showed the reality of some classical phenomena such as mentally induced pain reduction and apparent inhibition of memory recall. However, Hull's work indicated that these effects could be achieved without hypnosis being considered as a distinct state, but rather as a result of suggestion and motivation, which was a forerunner of the behavioral study of hypnosis. Similarly, moderate increases of certain physical capacities and changes to the threshold of sensory stimulation could be induced psychologically; attenuation effects could be especially dramatic. After moving to Yale, his work in hypnosis quickly encountered resistance. The medical school's concern