Ocular Equivocation:The Rivalry Between Wheatstone and Brewster

Ocular equivocation was the term given by Brewster in 1844 to binocular contour rivalry seen with Wheatstone’s stereoscope. The rivalries between Wheatstone and Brewster were personal as well as perceptual. In the 1830s, both Wheatstone and Brewster came to stereoscopic vision armed with their individual histories of research on vision. Brewster was an authority on physical optics and had devised the kaleidoscope; Wheatstone extended his research on audition to render acoustic patterns visible with his kaleidophone or phonic kaleidoscope. Both had written on subjective visual phenomena, a topic upon which they first clashed at the inaugural meeting of the British Association for the Advancement of Science in 1832 (the year Wheatstone made the first stereoscopes). Wheatstone published his account of the mirror stereoscope in 1838; Brewster’s initial reception of it was glowing but he later questioned Wheatstone’s priority. They both described investigations of binocular contour rivalry but their interpretations diverged. As was the case for stereoscopic vision, Wheatstone argued for central processing whereas Brewster’s analysis was peripheral and based on visible direction. Brewster’s lenticular stereoscope and binocular camera were described in 1849. They later clashed over Brewster’s claim that the Chimenti drawings were made for a 16th-century stereoscope. The rivalry between Wheatstone and Brewster is illustrated with anaglyphs that can be viewed with red/cyan glasses and in Universal Freeview format; they include rivalling ‘perceptual portraits’ as well as examples of the stimuli used to study ocular equivocation

Receptor Visionaries

Sensory receptors were described and illustrated after they had been observed with the aid of microscopes. Most descriptions were made in the 19th century after the introduction of achromatic lenses in microscopes. In some senses (like vision), receptors were named according to their morphology whereas in others (like touch), they are known by the names of those who initially described them. Illustrations of the receptors from original sources are here combined with portraits of their originators. </jats:p

Faces and Photography in 19th-Century Visual Science

Reading faces for identity, character, and expression is as old as humanity but representing these states is relatively recent. From the 16th century, physiognomists classified character in terms of both facial form and represented the types graphically. Darwin distinguished between physiognomy (which concerned static features reflecting character) and expression (which was dynamic and reflected emotions). Artists represented personality, pleasure, and pain in their paintings and drawings, but the scientific study of faces was revolutionized by photography in the 19th century. Rather than relying on artistic abstractions of fleeting facial expressions, scientists photographed what the eye could not discriminate. Photography was applied first to stereoscopic portraiture (by Wheatstone) then to the study of facial expressions (by Duchenne) and to identity (by Galton and Bertillon). Photography opened new methods for investigating face perception, most markedly with Galton’s composites derived from combining aligned photographs of many sitters. In the same decade (1870s), Kühne took the process of photography as a model for the chemical action of light in the retina. These developments and their developers are described and fixed in time, but the ideas they initiated have proved impossible to stop.</jats:p

The vision of Helmholtz

Hermann Ludwig Ferdinand von Helmholtz (1821–1894) began investigating vision at a time when its study was undergoing a revolution. Laboratory experiments were augmenting the long history of naturalistic observations. Instruments of stimulus control enabled the manipulation of time and space in ways that had not been possible previously, and Helmholtz added to their tally. Vision was a central issue in his early years as an academic, and the bicentenary of his birth is here celebrated visually. Much of his research on vision was described in his Handbuch der physiologischen Optik, which was translated into English to mark the centenary of his birth. The history of his Handbuch is examined, together with illustrating highlights from it. Helmholtz’s contributions to understanding the eye as an optical instrument, the sensations of vision, and perception were expressed in the three parts of the Handbuch, which became the three volumes of his Treatise on Physiological Optics

Helmholtz at 200

Hermann von Helmholtz was born 200 years ago, but his influence on vision research is enduring. His legacy in vision is celebrated visually with anaglyphs that combine portraits of him with illustrations from his publications. Emphasis is directed principally to his Treatise on Physiological Optics . Among the optical instruments Helmholtz invented were the ophthalmoscope, ophthalmometer, and telestereoscope. Mention is made of his investigations into accommodation, colour vision, eye movements, stereoscopic vision, binocular rivalry, and lustre. Helmholtz also presented his analyses of vision and art in several of his Popular Lectures