Charpentier's illusion

   Also known as size-weight illusion and *Demoor's sign. The eponym Charpentier's illusion refers to the French ophthalmologist and physiologist Augustin Charpentier (18521916), who has been credited with being the first to describe the phenomenon, complete with appropriate experimental evidence, in 1891. The eponym Demoor's sign refers to the Belgian physician Jean Demoor (1867-1941), who employed the concomitant phenomenon as a diagnostic test in children with developmental disorders. The eponym Demoor's sign was coined in or shortly before 1903 by the Swiss neurologist and child psychologist Edouard Claparède (1873-1940). The three terms above are used interchangeably to denote the illusory difference in weight experienced when two containers of the same weight, but of different size, are lifted up simultaneously. In the ensuing illusion, the smaller container is experienced as heavier than the bigger one. Charpentier sought to explain the size-weight illusion by referring to a neu-rophysiological model of weight perception, and a psychological model pertaining to the "feeling of mental effort". Even today, the debate continues as to which of these two factors should be granted primacy. Charpentier's illusion tends to be classified as a *physiological illusion. Sometimes the eponym Charpentier's illusion is also used as a synonym for * autokinetic effect.

   References

   Charpentier, A. (1891). Analyse expérimentale de quelques éléments de la sensation de poids. Archive de Physiologie normale et pathologique, 3, 122-135.

   Claparède, E. (1903). L'illusion de poids chez les anormaux et le "signe de Demoor". Archives de Psychologie, 2, 22-32.

   Demoor, J. (1898). Notes médico-pédagogiques: à propos d'une illusion musculaire. Journal Médical de Bruxelles,18Jan.

   Murray, D.J., Ellis, R.R., Bandomir, C.A., Ross, H.E. (1999). Charpentier (1891) on the size-weight illusion. Perception & Psychophysics, 61, 1681-1685.