one theory of the mind that was examined in these experiments was the "brain as serial computer" philosophical metaphor of the 1970s. psychologist zenon pylyshyn theorized that the human mind processes mental images by decomposing them into an underlying mathematical proposition. roger shepard and jacqueline metzler challenged that view by presenting subjects with 2d line drawings of groups of 3d block "objects" and asking them to determine whether that "object" is the same as a second figure, some of which rotations of the first "object". shepard and metzler proposed that if we decomposed and then mentally re-imaged the objects into basic mathematical propositions, as the then-dominant view of cognition "as a serial digital computer" assumed, then it would be expected that the time it took to determine whether the object is the same or not would be independent of how much the object had been rotated. shepard and metzler found the opposite: a linear relationship between the degree of rotation in the mental imagery task and the time it took participants to reach their answer.