Why did Donders, after describing pseudotorsion, deny the existence of ocular counterrolling together with Ruete, Volkmann, von Graefe and von Helmholtz, until Javal reconfirmed its existence?

After the rapid spread of strabismus surgery by total tenotomy, which had been proposed by the orthopedist Louis Stromeyer from Göttingen 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.

Assessing the benefits of "gaze-down" display location in complex tasks.

BACKGROUND: Location of the image display is one of several factors that influence perceptual processing and endoscopic manipulation in minimal access surgery. Previous studies have proved the benefits of the gaze-down stance, as compared with the conventional gaze-up stance. This study investigates the effect of the gaze-down stance on the performance of a task with varying manipulative and perceptual demands. METHODS: The participants in this study were 20 medical students. Each student performed endoscopic touching tasks under standard conditions using the Dundee Projection System (DPS) display, positioned to provide gaze-up and gaze-down stances. To increase task complexity, two kinds of manual coordination (unilateral vs bilateral) and three endoscope positions (different positions of misalignment) were used. The outcome measures were task execution time and number of errors. RESULTS: Overall, the gaze-down stance reduced time and errors, as compared with the gaze-up display. However, the benefit obtained from the gaze-down stance was more significant in the more difficult tasks (bilateral task and 90 degrees misalignments). CONCLUSIONS: The gaze-down stance reduces task time and errors, as compared with a gaze-up stance. The reduction in time and errors is more appreciable as task complexity increases.

The eye as an optical instrument: from camera obscura to Helmholtz's perspective.

The era of modern vision research can be thought of as beginning in the seventeenth century with Johannes Kepler's understanding of the optics of the camera obscura with a lens and its relation to the eye. During the nineteenth century, Helmholtz used "The eye as an optical instrument" as the title for one of his Popular Lectures, and such a conception of the eye is now accepted as a fundamental feature of visual science. In analysing the optics of the eye, Helmholtz constructed some novel optical instruments for studying the eye. The development of optometers, ophthalmometers, and ophthalmoscopes is presented historically, with emphasis on how these instruments and camera analogies helped scientists to understand the functions of the eye, especially the enigma of accommodation. "The laws of optics are so well understood, and the knowledge of the eye, when considered as an optical instrument, has been rendered so perfect, that I do not consider myself capable of making any addition to it; but still there is a power in the eye by which it can adapt itself to different distances far too extensive for the simple mechanism of the parts to effect." (John Hunter in a letter to Joseph Banks in 1793, published by Home 1794, page 24).

Perceptual aspects of two-dimensional and stereoscopic display techniques in endoscopic surgery: review and current problems.

The aim of this review is to analyze the perceptual aspects of endoscopic imaging systems. After discussing depth perception in natural settings, the problems of perceiving depth in 2-dimensional representations are investigated. We discuss the impact of stereoscopic video systems on the cerebral perceptual system, emphasising the fact that despite the addition of binocular disparity information, existing stereoscopic video systems are still different from normal 3-dimensional vision. Both 2-dimensional and stereoscopic video systems require a rescaling of visual information to guide motor behavior. A review of the growing number of papers comparing 2-dimensional and stereoscopic video systems shows that only about 50% of investigators found a significant benefit for stereoscopic systems. It is unlikely that image display technology for endoscopic surgery can ever progress to the stage where it is equivalent to normal vision. Within this limitation, progress will result from a multidisciplinary approach, involving technological advances in the quality of the displayed image together with psychovisuomotor and ergonomics research, which facilitates the cerebral rescaling and perception process by the endoscopic surgeon.

Surveying the seen: 100 years of British vision.

Perceptual phenomena and their interpretations have fashioned the course of psychology. This article surveys how theories of visual perception and methodologies have developed during the lifetime of the British Psychological Society. The experimental study of vision was instigated by British natural philosophers in the early nineteenth century but this impetus was not maintained thereafter. Not until the 1930s and 1940s did research on perception resume in earnest within British universities. The adoption of concepts (such as schema) potentially grounded in neural organization, particularly by Bartlett and Craik, accelerated experimental, theoretical and applied vision research. From mid-century the influence of information processing models of perception became increasingly dominant, and they were often integrated with the rapidly expanding understanding of neurophysiological underpinnings. The epitome of these developments was Marr's model of vision which, in our view, marked the start of the modern era of vision research. Computers have transformed the nature of stimulus control and response measurement in perceptual experiments. More naturalistic stimuli can be presented and manipulated, and complex behavioural responses, such as patterns of eye movements, fractionated. Non-invasive recording of brain activity to visual stimulation has similarly been transformed with a variety of methods for imaging brain activity. Neuroimaging has been applied to localizing perceptual and cognitive functions and in studying patients with known deficits in visual recognition. However, the eagerness with which the computer has been adopted by perceptual psychologists is likely to be tempered by a growing awareness of the differences between viewing scenes and simulations of them.

William Charles Wells (1757-1817) and vestibular research before Purkinje and Flourens.

Vestibular research before Flourens typically involved vertigo and eye movements. In 1820 Purkinje integrated these in studies of postrotary vertigo and he is linked with Flourens as a founder of vestibular research. In the late eighteenth century Erasmus Darwin described vertigo in detail, but he did not accept that it involved an oculomotor component. Darwin reached this conclusion despite detailed experiments by William Charles Wells (1757-1817), who described the pattern of postrotary nystagmus and its dependence on head orientation during rotation. Wells generated afterimages prior to rotation and subsequently compared their motions with those of real images. He was able to distinguish between the slow and fast phases of nystagmus, its reducing amplitude following cessation of rotation, its suppression with fixation, and its torsional dimension. In many ways, Wells's experiments were more sophisticated than those of Purkinje, and he should be recognised as a founder of vestibular research. Possible reasons for the neglect of Wells's work are discussed.

Jean Théophile Desaguliers (1683-1744) and eighteenth century vision research.

The emergence of psychology as an empirical discipline was influenced to a great extent by experimental investigations of visual phenomena, particularly in the nineteenth century. Less attention has been paid to experimental enquiries conducted in the eighteenth century, especially those of Jean Théophile Desagliers (1683-1744). He was an ardent advocate of Newtonian optics, on which he lectured and gave demonstrations. His research on colour and binocularity is outlined, together with those of other students of vision in that century. Experiments on visual vertigo conducted at the end of the century are also described. In 1716 Desaguliers reported a method of binocular combination that became widely employed in other studies of binocular vision, namely, placing an aperture in such a position that two more distant, adjacent objects were in the optical axes of each eye. Under these circumstances red and green patches of silk did not mix after the manner of combining prismatic lights, but engaged in rivalry. Desaguliers also investigated size perception and showed that apparent size was determined by apparent distance rather than physical distance. Moreover, he did not base his conclusions on his own observation but on those of 'any unprejudic'd Person'. Thus, both stimulus control and the use of the unbiased observer were employed in eighteenth century experimental studies of vision.

Porterfield and Wells on the motions of our eyes.

William Porterfield (ca 1969-1771) and William Charles Wells (1757-1817) conducted experimental investigations on eye movements related to accommodation, binocular vision, and vertigo. Porterfield gave a correct interpretation of Scheiner's experiment and invented an optometer to measure the near and far points of distinct vision. He also demonstrated the involvement of the crystalline lens in accommodation by examining vision in an aphakic person. Wells devised an alternative means of measuring the limits of vision and noted his own deterioration of sight with age; he studied the effects of belladonna on pupil size and accommodation. Their analyses of binocular visual direction contrasted Porterfield's view that perceived location was innately determined with Well's argument that visual direction was innate whereas visual distance was learned. Both Porterfield and Wells investigated the involvement of eye movements in binocular vision and in postrotary visual motion. Porterfield maintained that the eyes did not move following body rotation, whereas Wells, using an afterimage as stabilised retinal image, described the characteristics of postrotary nystagmus and their dependence on head orientation. Despite the neglect of Well's work, he should be considered as laying the foundations for the study of vestibular-visual interaction, even though the function of the vestibular system was not known at that time.

Fooling the eyes: trompe l'oeil and reverse perspective.

Trompe l'oeil pictures have been produced for hundreds of years. They attempt to create the impression of a surface that has different three-dimensional structure to the work; successful examples of trompe l'oeil typically constrain the observer's viewpoint and require use of a single eye. The works of Patrick Hughes are in relief but are painted to appear like conventional flat pictures; those parts that protrude from the picture plane are pictorially distant, or in reverse perspective. Movements of the observer result in fluid distortions of the pictorial image. These distortions occur with binocular observation and over a wide range of viewing distances.

Visual motion aftereffects: differential adaptation and test stimulation.

The local motion adaptation at the basis of the motion aftereffect (MAE) can be expressed in a variety of ways, depending upon the structure of the test display [Wade et al. (1996). Vision Research, 36, 2167-2175]. Three experiments are reported, which examined the characteristics of the test display and of the local adaptation process. In Experiment 1, MAEs were recorded in the central of three test gratings but their directions depended on the location of the centre relative to the adapting gratings. The effects of adapting motions in different directions were examined in Experiments 2 and 3, in which one or two adapting gratings were presented above or above and below a fixation cross. The upper grating always received the same (leftward) direction of motion during adaptation, and the lower grating was: moving in the opposite direction, stationary, moving in the same direction, or absent. The results indicate that no MAE is visible in the upper grating when a single test grating is observed experiment 2) and only occurs with two test gratings following differential adaptation between the upper and lower gratings (Experiment 3). Thus, the MAE occurs as a consequence of adapting restricted retinal regions to motion but it can only be expressed when differentially adapted regions are also tested.

Light and sight since antiquity.

Light and sight were not distinguished from one another until the dioptrics and the anatomy of the eye had been adequately described in the seventeenth century. A survey of early theories of light is presented, together with descriptions of developing knowledge of ocular anatomy. Once the analogy between the eye and a camera had been made, the problem of accommodation was exposed, and corrections for errors of refraction could be given theoretical support. Theories of accommodation in the seventeenth and eighteenth centuries are briefly reviewed, as is the early history of eye glasses.

Early studies of eye dominances.

Early accounts of eye dominances are considered. An index of sighting dominance (eye closure) was described by Aristotle, and Porta (1593) introduced an alignment test for it. Porta also described rivalry dominance, and asserted that it favoured the right eye. Acuity dominance, on the other hand, was assigned to the left eye by Borelli (1673). These views are placed in the context of prevailing theories of binocular vision.

Bain on neural networks.

In his book Mind and body (1873), Bain set out an account in which he related the processes of associative memory to the distribution of activity in neural groupings--or neural networks as they are now termed. In the course of this account, Bain anticipated certain aspects of connectionist ideas that are normally attributed to 20th-century authors--most notably Hebb (1949). In this paper we reproduce Bain's arguments relating neural activity to the workings of associative memory which include an early version of the principles enshrined in Hebb's neurophysiological postulate. Nonetheless, despite their prescience, these specific contributions to the connectionist case have been almost entirely ignored. Eventually, Bain came to doubt the practicality of his own arguments and, in so doing, he seems to have ensured that his ideas concerning neural groupings exerted little or no influence on the subsequent course of theorizing in this area.

Scopes of perception: the experimental manipulation of space and time.

Discussions of space and time have been grist to the philosophers' mill for centuries. We argue that the evolution of psychology as an independent discipline was in part a consequence of addressing philosophical questions concerning the perception of space and time by recourse to experiment rather than exposition. Two initially separate factors assisted in establishing this independence. On the one hand, it was driven by the invention of instruments for stimulus control so that the methods of physics could be applied to the study of perceptual phenomena. On the other hand and somewhat later, it was followed by the development of psychophysical methods, which opened the possibility of quantifying the responses to such controlled stimulation. The principal instruments were invented in the first half of the nineteenth century, and they consisted of simple contrivances that manipulated time and space in ways that had not previously been appreciated. This article examines the devices that were invented, like stroboscopes, anorthoscopes, stereoscopes, tachistoscopes, chronoscopes, and more recently oscilloscopes, and the ways in which they influenced the scope of perceptual psychology in the past as well as in the present. In contemporary experimental psychology all these instruments have been replaced by the computer. While it has extended the scope of experiments even further it has introduced a new set of limitations.

Visual motion aftereffects: critical adaptation and test conditions.

The visual motion aftereffect (MAE) typically occurs when stationary contours are presented to a retinal region that has previously been exposed to motion. It can also be generated following observation of a stationary grating when two gratings (above and below it) move laterally: the surrounding gratings induce motion in the opposite direction in the central one. Following adaptation, the centre appears to move in the direction opposite to the previously induced motion, but little or no MAE is visible in the surround gratings [Swanston & Wade (1992) Perception, 21, 569-582]. The stimulus conditions that generate the MAE from induced motion were examined in five experiments. It was found that: the central MAE occurs when tested with stationary centre and surround gratings following adaptation to surround motion alone (Expt 1); no MAEs in either the centre or surround can be measured when the test stimulus is the centre alone or the surround alone (Expt 2); the maximum MAE in the central grating occurs when the same surround region is adapted and tested (Expt 3); the duration of the MAE is dependent upon the spatial frequency of the surround but not the centre (Expt 4); MAEs can be observed in the surround gratings when they are themselves surrounded by stationary gratings during test (Expt 5). It is concluded that the linear MAE occurs as a consequence of adapting restricted retinal regions to motion but it can only be expressed when nonadapted regions are also tested.