of the concept of repression published by the psychoanalyst Ernest Jones in the American Journal of Psychology in 1911. Like other psychologists who attempted to submit the claims of psychoanalysis to experimental test, they did not immediately try to develop new techniques for that purpose, instead conducting surveys of the psychological literature to see whether "experiments undertaken to test other theoretical assertions" had produced results relevant to assessing psychoanalysis. In 1930, H. Meltzer published a survey of experimental literature on "the relationships between feeling and memory" in an attempt to determine the relevance of laboratory findings to "that aspect of the theory of repression which posits a relationship between hedonic tone and conscious memory." However, according to MacKinnon and Dukes, because Meltzer had an inadequate grasp of psychoanalytic writing he misinterpreted Freud's view that the purpose of repression is to avoid "unpleasure", taking the term to mean simply something unpleasant, whereas for Freud it actually meant deep-rooted anxiety. Nevertheless, Meltzer pointed out shortcomings in the studies he reviewed, and in MacKinnon and Dukes's view he also "recognized that most of the investigations which he reviewed had not been designed specifically to test the Freudian theory of repression." In 1934, the psychologist Saul Rosenzweig and his co-author G. Mason criticized Meltzer, concluding that the studies he reviewed suffered from two basic problems: that the studies "worked with hedonic tone associated with sensory stimuli unrelated to the theory of repression rather than with conative hedonic tone associated with frustrated striving, which is the only kind of 'unpleasantnesss' which, according to the Freudian theory, leads to repression" and that they "failed to develop under laboratory control the experiences which are subsequently to be tested for recall". In MacKinnon and Dukes's view, psychologists who wanted to study repression in the laboratory "faced the necessity of becoming clear about the details of the psychoanalytic formulation of repression if their researches were to be adequate tests of the theory" but soon discovered that "to grasp clearly even a single psychoanalytic concept was an almost insurmountable task." MacKinnon and Dukes attribute this situation to the way in which Freud repeatedly modified his theory "without ever stating clearly just which of his earlier formulations were to be completely discarded, or if not discarded, how they were to be understood in the light of his more recent assertions." MacKinnon and Dukes write that, while psychoanalysts were at first only