Joseph-Remi-Leopold Delboeuf

Born in Liège in 1831, Joseph-Rémy-Léopold Delboeuf studied philosophy and went on to teach at the University of Liège. His work moved between philosophy, mathematics, and the new science of psychology, reflecting a time when those fields were still closely connected.

Delboeuf is best remembered for research on visual perception and for describing the Delboeuf illusion, in which surrounding shapes change how large something appears. He also wrote about sleep, dreams, and the psychology of suggestion, and became known for thoughtful studies of hypnosis.

Across his career, he brought a curious, wide-ranging mind to questions about how people sense, think, and believe. He died in 1896, but his ideas still appear in the history of psychology and in discussions of perception today.