Is trompe l’eoil an example of ‘humor art’ or ‘optical illusion’? Many use the term ‘illusion’ to encompass both. Some researchers say that trompe l'œil pictures and optical illusion designs are the same in the sense that they are both connected with the human mechanism of visual perception—but in academic terms trompe l'œil and optical illusions differ from one another. “In short, trompe l'œil does not make use of optical illusion.” The key difference is that with a trompe l'œil the inconsistency is exposed in its entirety just before the brain completes the process of seeing. In psychology this is termed “high-order perception.” In contrast, an optical illusion occurs at the point when the brain perceives shape or color, which is termed “low-order perception.” In other words, it occurs in the very first stage of the process of seeing.