Joseph-Remi-Leopold Delboeuf

Born in Liège in 1831, Joseph Rémi Léopold Delboeuf was a Belgian philosopher, mathematician, and experimental psychologist. He studied at the University of Liège, earning doctorates in philosophy and in physical and mathematical sciences, and later continued his research in Bonn.

Delboeuf taught in Ghent and then at the University of Liège. He became widely known for his studies of sensation and visual perception, including the optical effect now called the Delboeuf illusion, and he also wrote on psychophysics, sleep, dreams, and hypnosis.

What makes his career especially interesting is how broad it was: he brought together careful scientific observation and big philosophical questions at a time when psychology was just beginning to emerge as its own field. He died in Bonn in 1896, but his name still appears in discussions of perception and the history of psychology.