The Duck-Rabbit: A bistable visual stimulus used by Thomas Kuhn in order to illustrate the concept of a paradigm-shift.
Thomas Kuhn used the duck-rabbit to illustrate the fundamental perceptual change that accompanies a scientific paradigm-shift. The concept of incommensurability is pertinent in this context, i.e., the impossibility of direct comparison of complementary theories. It is impossible to see both percepts simultaneously (it is either a rabbit or a duck – the ambiguous superposition of both cannot be perceived by the visual system). In the same way, it is impossible to entertain conflicting scientific paradigms simultaneously. The human cognitive system automatically reduces ambiguity and thrives for closure (Webster & Kruglanski, 1994).