Perceptual illusions are percepts that depart from veridicality. They are important, ubiquitous, and surprising. With the notable exception of James J. Gibson (1904-1979), most theorists hold that illusions play an important role in psychology. Being errors, illusions highlight the limitations of “finite individual minds” to evoke the classic definition of the object of psychological science offered by William James (1842-1910). Therefore, studying non-veridical as well as veridical instances of perception should enhance understanding of observer-environment interactions.
