The "Mumford Effect" in psychology is the closing off of new theoretical ideas as a result of technologically inspired progress in psychological science. To adapt to advances in AI (Artificial Intelligence) technology, psychologists adopt a logic of vested belief in the metaphors of the computer making their prevailing paradigm difficult to change. I outline how methodological rationale affects paradigm change and analyze the AI model's effects on psychology. Lewis Mumford's mega-machine principle predicts that a technological model applied to human events ultimately reduces them to a mechanistic determinism. I propose that such reduction includes explanations of the cognitive processes of psychologists as observers. These reductions and the AI methodological rationale formulated in the Turing Test change the status of the default paradigm, putting a burden of proof on competing explanations: The falsity of alternate or competing paradigms has to be disproved before the default paradigm can be changed. This rationale is presented as an "attitude" and contrasted with R. A. Fisher's strategy of disproving null propositions and K. R. Popper's concept of the falsifiability of a theory.