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Ross Henry Day was an Australian experimental psychologist well known for his research on visual illusions and for his critical role in the establishment of experimental psychology in Australia. This role began with his creation of Australia’s first department of experimental psychology at Monash University in 1965. He also played a leading role in the formation of the Australian Psychological Society in 1966, and in the introduction to Australia of the study of human factors in engineering and ergonomics. He was the first psychologist to be elected Fellow of the Australian Academy of Science.

In the early 19

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.

Vision had long been investigated by Italian artists and scientists such as Brunelleschi, Alberti, Leonardo, and Galileo, and all of them had been concerned with illusions. The pace of experimental studies of a subset of illusions quickened in the second half of the 19th century, but the investigation of such geometrical optical illusions started rather late in Turin. It was stimulated by the arrival of Kiesow from Wundt’s laboratory in Leipzig. Botti initiated experiments on spatial illusions, followed by Ponzo, who wrote two articles in 1912 that indelibly linked his name to a simple configuration of equal circles or lines contained with converging lines—the Ponzo illusion. This happened despite the publication of essentially the same figures over a decade earlier by Thiéry and Sanford.

Nagel's book on vision with two eyes was published in 1861, during a period in which German visual scientists were struggling to rescue the doctrine of identical retinal points from the evidence of stereoscopic depth. The long observational history of binocular vision has been dominated by the appearance of a single world with two eyes and its breakdown when the eyes are distorted abnormally. Early in the nineteenth century the flat horopter of Aguilonius (proposed two centuries earlier) assumed curvature in the form of the Vieth-Müller circle which was linked to identical retinal points: there were only two possible states of binocular perception - singleness with images on the Vieth-Müller circle and doubleness otherwise. This elegant edifice was undermined when Wheatstone demonstrated singleness and depth from images with slight retinal disparities. Nagel responded by providing observations on combining simple line stimuli in the two eyes. In the last part of chapter 3 of his book, Nagel describes experiments with lines varying in orientation or curvature with respect to the two eyes; it is in this section that Nagel draws attention to cyclofusion and the involvement of the extraocular muscles in it. Ocular torsion was an issue of considerable contention in nineteenth century visual science. The possibility of torsion in opposite directions seemed fanciful and yet this is what Nagel proposed in order to maintain cyclofusion for lines inclined in opposite directions relative to the horizontal. Similar rotations about the vertical resulted in a depth effect with no cyclovergence. The involvement of cyclovergence remained hotly debated until photographic recording of eye movements verified it.

Wheatstone's demonstration of binocular single vision and depth with stimulation of non-corresponding points reverberated throughout mid-nineteenth century German visual science. It challenged the received view that single vision was a consequence of retinal correspondence otherwise objects were seen double. Wheatstone also argued that stimulation of corresponding points could yield double vision. He interpreted his experimental observations in psychological rather than physiological terms, as did Helmholtz later. Volkmann addressed both of these challenges in a long article on stereoscopic vision published in 1859. While he accepted the first of the questions Wheatstone posed Volkmann was more cautious with regard to the second. Volkmann was an experimentalist who applied psychophysical methods to determine thresholds for stereoscopic depth perception. In line with many of his colleagues in Germany, he took issue implicitly with Wheatstone's approach: how can the detailed quantitative experiments supporting Vieth and Müller's interpretation of binocular single vision be derailed by simple observations with a stereoscope? Unlike most of his colleagues, Volkmann was swayed in Wheatstone's favor through his own experiments: both physiological and psychological processes are involved in stereoscopic depth perception.

Experiences following stimulation of the senses have been recorded for millennia, and they could be related to the gross anatomy of the sense organs. Examination of their microanatomy was to await the development of achromatic microscopes in the early nineteenth century. Among the microscopic structures that were isolated and described were specialized sensory cells, called receptors, and they could be related to the stimuli that excited them. Those located in well-defined sense organs (like the eyes, ears, nose, and tongue) were named on the basis of their morphology, whereas the receptors in or beneath the surface of the skin were generally named after those who first described them. Illustrations of early representations of sensory receptors are combined with "perceptual portraits" of the microanatomists who described them.

After the rapid spread of strabismus surgery by total tenotomy, which had been proposed by the orthopedist Louis Stromeyer from Gottingen in 1838 and performed by the plastic surgeon Johann Friedrich Dieffenbach on October 26th and by the ophthalmologist Florent Cunier on October 29th, 1839, brilliant researchers studied the physiology of eye movements, resulting in the laws by Franciscus Cornelis Donders on pseudotorsion in tertiary positions of gaze and by Johann Benedict Listing that each eye position can be reached by rotation about an axis perpendicular to the primary and the new position of gaze. John Hunter had first described ocular counterrolling (OCR) with head tilt in 1786. The anatomist Alexander Friedrich von Hueck inferred from anatomical studies, however, that up to 28.6° OCR would be possible onhead-tilt to right or left shoulder in 1838, and estimated his own OCR seen in a mirror at approximately 25°. Donders, Christian Georg Theodor Ruete, Alfred Wilhelm Volkmann, Albrecht von Graefe and Hermann von Helmholtz subsequently denied the existence of OCR for many years and thought that only pseudotorsion existed. Louis Emile Javal had myopia and astigmatism, and he re-established the existence of OCR in 1867 when he noticed that, on head tilt to either shoulder, the axis of astigmatism of his eyes no longer coincided with the axis of astigmatism of his glasses.

In 1935 Guy Buswell, an educational psychologist at Chicago University, published How People Look at Pictures. In it he recorded photographically the eye movements of 200 observers when looking at a wide variety of pictures. He analysed the overall distribution of fixations on pictures, compared the first few fixations on a picture to the last few, measured the durations of fixations made early in viewing and those made near the end of viewing, examined how fixation duration changed with viewing time, recorded the consistency between different observers when viewing the same picture and he looked at the influence of instructions given to observers upon their eye movements when viewing a picture. He commented on the substantial differences between individuals and noted that instructions had a dramatic effect on the pattern of eye movements. Buswell’s analysis was graphical rather than statistical. In this article Buswell’s figures are recombined and his research is placed in the context of earlier investigations of eye movements with pictures by Stratton and Judd and later ones by Yarbus.

Vision with two eyes has been commented upon for many centuries, and the principal concern has been with binocular single vision. The terminology we apply to binocular vision developed rapidly after the invention of the stereoscope in the early 19th century. The origins of terms such as anaglyph, binocular lustre, chromatic stereoscope, cyclopean eye, dichoptic, horopter, pseudoscope, rivalry, stereoscope, stereograph, and stereopsis are described together with portraits of those who introduced them.

In 1866, Holmgren published an account of the physiological action of light on the retina. The article is taken as the origin of research on the electroretinogram, although the term was not introduced until much later. We present a translation of the article into English and provide a commentary on its reception and significance.

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.

Visual representations of biological states have traditionally faced two problems: they lacked motion and depth. Attempts were made to supply these wants over many centuries, but the major advances were made in the early-nineteenth century. Motion was synthesized by sequences of slightly different images presented in rapid succession and depth was added by presenting slightly different images to each eye. Apparent motion and depth were combined some years later, but they tended to be applied separately. The major figures in this early period were Wheatstone, Plateau, Horner, Duboscq, Claudet, and Purkinje. Others later in the century, like Marey and Muybridge, were stimulated to extend the uses to which apparent motion and photography could be applied to examining body movements. These developments occurred before the birth of cinematography, and significant insights were derived from attempts to combine motion and depth.

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.

Monocular rivalry was named by Breese in 1899. He made prolonged observation of superimposed orthogonal gratings; they fluctuated in clarity with either one or the other grating occasionally being visible alone. A year earlier, Tscherning observed similar fluctuations with a grid of vertical and horizontal lines and with other stimuli; we draw attention to his prior account. Monocular rivalry has since been shown to occur with a wide variety of superimposed patterns with several independent rediscoveries of it. We also argue that Helmholtz described some phenomenon other than monocular rivalry in 1867.

Vision and hearing are dependent on disparities of spatial patterns received by two eyes and on time and intensity differences to two ears. However, the experiences of a single world have masked attention to these disparities. While eyes and ears are paired, there has not been parity in the attention directed to their functioning. Phenomena involving binocular vision were commented upon since antiquity whereas those about binaural hearing are much more recent. This history is compared with respect to the experimental manipulations of dichoptic and dichotic stimuli and the instruments used to stimulate the paired organs. Binocular color mixing led to studies of binaural hearing and direction and distance in visual localization were analyzed before those for auditory localization. Experimental investigations began in the nineteenth century with the invention of instruments like the stereoscope and pseudoscope, soon to be followed by their binaural equivalents, the stethophone and pseudophone.

The term geometrical–optical illusions was coined by Johann Joseph Oppel (1815–1894) in 1855 in order to distinguish spatial distortions of size and orientation from the broader illusions of the senses. We present a translation of Oppel’s article and a commentary on the material described in it. Oppel did much more than give a name to a class of visual spatial distortions. He examined a variety of figures and phenomena that were precursors of later, named illusions, and attempted to quantify and interpret them.

Gottfried Wilhelm Osann (1796-1866) was a German scientist most renowned for his work in chemistry and physics. However, inspired by Goethe's work on color, he published a paper on simultaneous color contrast in 1833 using a method that is similar to that of later authors: reflection of an achromatic spot from an angled piece of glass. He wrote at least four more papers on color contrasts, in 1836 using essentially the same method as credited to others. We provide a description and translation of Osann's 1833 paper and the relevant part of his 1836 paper, say why these papers are interesting and important, give some biographical information about Osann, comment on the fate of Osann's papers, and describe Osann's other papers on color.

It is relatively easy to hide pictorial images, but this is of little value if they remain hidden. Presenting hidden images for visual purposes is a modern preoccupation, and some of the perceptual processes involved in them are described in this chapter. Pictorial images can be concealed in terms of detection or recognition. In both cases there is interplay between the global features of the concealed image and the local elements that carry it. Gestalt grouping principles can hinder as well as help recognition. Examples of images (mostly faces) hidden in geometrical designs and text as well as orientation are shown. Rather than being pictorial puzzles alone, hidden images can reveal aspects of visual processing. This chapter explores these concepts and related ideas such as perceptual portraits and pictorial puzzles.

Illusions are considered in the context of the history of vision rather than the history of psychology. For much of its long history, the study of vision has been confined to naturalistic observation, and many motion illusions were observed in the natural world. With the move to the laboratory, the oddities of visual perception multiplied, and they received ever more detailed scrutiny. This survey examines the origins of research on visual illusions in both the natural world and the laboratory. It commences with celestial illusions and pictorial representation then proceeds to subjective visual phenomena and spatial illusions like ambiguous figures and geometrical optical illusions. However, most attention is paid to motion illusions; these include visual persistence and stroboscopic motion, induced motion, motion aftereffects, visual vertigo, and autokinetic sensations. The basis for the explosion of research on visual illusions in the nineteenth century is speculated upon.

A brief tribute to Bela Julesz (1928−2003) is made in words and images. In addition to a conventional stereophotographic portrait, his major contributions to vision research are commemorated by two ‘perceptual portraits’, which try to capture the spirit of his main accomplishments in stereopsis and the perception of texture.