Abstract

Mariotte's discovery of the blind spot is often quoted, but his contribution to the physiology of vision is generally underestimated. Surprised by the result of his fundamental experiment, Mariotte abandoned his starting hypothesis on the physiological role of the retina and came to the conclusion that the site of vision is the 'choroid'. This was the name not only for the choroid layer in the modern sense but also for the pigmentated part of the retina, where Mariotte localized the seat of vision. Mariotte's 'heretical' assertion provoked an important public controversy with the anatomists Pecquet and Perrault. This debate is often misrepresented by historians, who, considering Mariotte's opinion basically mistaken, failed to enter into the details. Mariotte was the very first to measure the size of the unseen area in the visual field and to determine the corresponding optic disk on the fundus oculi. He proved that the central scotoma is not due to the vascular trunk, discovered the peripheric angioscotomas, explained the imperceptibility of the blind spot under ordinary conditions of binocular and monocular vision, posed the problem of filling-in, observed the phenomenon later known as staring-blindness and advanced a dioptric explanation of the luminous eye in some animals. The debate between Mariotte, Pecquet and Perrault is particularly instructive for the philosophy of science as an example of the intertwining of experimental reasoning and scholastic argumentation