 In his concrete research in psychology Stevens focused on psychophysics, starting with his Ph.D. dissertation on the perceived attributes of tones, written under Boring’s supervision. Another notable operationist in psychology was Edward Chace Tolman (1886–1959), also a Harvard Ph.D., who taught for most of his life at the University of California at Berkeley. Starting with his research on problem-solving behavior in rats, Tolman gave an operational treatment of desire, for example operationalizing hunger in terms of “time since last feeding”. Tolman did not deny that hunger was a subjective feeling, nor was it the main object of his research, but insisted that controlling for degrees of hunger in his experiments required tractable operations that would allow scientists to get a hold on something related to that subjective experience (see Feest 2005, 136–138). In Gustav Bergmann’s assessment, operationism helped behaviorism to move from its initial metaphysical Watsonian variety to its modern version (Bergmann in Frank 1956, 53).