Impossible experiences are intuitively compelling, but they are also theoretically significant: They go beyond ordinary visual illusions (e.g., when stimuli appear larger, faster, or darker than they really are) in revealing how some principles of mental processing can be so entrenched and inflexible as to produce absurd and even self-contradictory outcomes that could not occur in reality. For example, when an image carefully exploits patterns of shading and layout, we may see it as a triangle with three 90° angles, or as a closed staircase that descends in every direction ( Figure 1), even though such objects could never actually exist. One of the most striking and puzzling aspects of our minds is that they permit “impossible” experiences: perceptions of the world that are physically, geometrically, or even conceptually incoherent.

Moreover, we suggest that this phenomenon-a special case of the size-weight illusion-reflects a kind of “anti-Bayesian” perceptual updating that amplifies a challenge to rational models of perception and cognition. We show that, even under full-cue conditions with objects that can be freely inspected, subjects can be made to experience a single object alone as feeling heavier than a group of objects that includes the single object as a member-an impossible and phenomenologically striking experience of weight. However, impossible experiences of this sort are mostly limited to visual perception are there “impossible figures” for other sensory modalities? Here, we import a known magic trick into the laboratory to report and investigate an impossible experience for somatosensation-one that can be physically felt. Escher to any popular perception textbook, such experiences show how some principles of mental processing can be so entrenched and inflexible as to produce absurd and even incoherent outcomes that could not occur in reality. Impossible figures represent the world in ways it cannot be.

Line abc box optical illusion