Visual spatial aftereffect from prolonged head-tilt.

Subjects with head upright were required to adjust a lighted bar in a dark room until the bar appeared vertical; the task was performed before and after 2 and 3 minutes of lateral head-tilt with their eyes closed. A visual spatial aftereffect was observed which varied as a function of the angle of head-tilt and which was opposite in direction to head-tilt.

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.

A balanced view of otolithic function: comment on Stoffregen and Riccio (1988)

Stoffregen and Riccio (1988) have presented a theory of orientation that dismisses the role of otolithic information in the perception of the direction of the gravitoinertial force (GIF). Their dismissal of otolithic involvement in GIF perception is not warranted because (a) the logic associated with their analysis is flawed. (b) the underwater experiments they analyzed do not reflect the isolated operation of otolithic function, and (c) they do not cite a large body of relevant evidence on otolithic function.

The effect of orientation and motion of enclosed texture on induced movement.

Optical expansion or contraction of a vertical grating induces rotation of an oblique line or bar superimposed upon it. Three experiments are reported in which the oblique (45 deg clockwise) bar was defined by parallel line segments that were varied in orientation and motion. In Experiment 1 subjects estimated the degrees through which the boundaries of the bar appeared to rotate during 2 sec expansion of the vertical grating background. The induced rotation declined with increasing relative orientation between the texture elements and the background; virtually no effect was reported when they were orthogonal. The texture elements were stationary in Experiment 1 whereas they expanded or contracted in Experiment 2: when their motion was in-phase with the background induced rotation of the boundary occurred irrespective of relative orientation. Expansion or contraction of the texture elements alone did not result in induced bar rotation (Experiment 3). It was concluded that induced movement at the boundaries between two patterns is reduced when they differ in static orientation and in the directions of motion due to zooming.

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.

Compound binocular rivalry.

Binocular rivalry was examined with random dot patterns consisting of three colours: red, green and grey. The microstructure of the patterns was defined by the individual dots, and the correspondence between the microstructures in the two eyes was manipulated. The macrostructures were defined by the distributions of red, green and grey dots over the displays, so that they consisted of orthogonally striped patterns. The degree of correspondence between the microstructures was varied in Expt 1, together with the spatial frequency of the microstructure. Rivalry periods of the macrostructures were briefer when the microstructures were in correspondence, In Expt 2 the spatial frequencies of the macrostructures were varied. The lower spatial frequency predominated for longer than the higher. The results are discussed in terms of independent pathways for corresponding and rivalry stimulation. In addition a stimulus pairing that produces clear dichoptic colour mixtures is presented.

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.

Cancelling of pattern motion: dichoptic and monoptic observations.

Patterns consisting of concentric rings, moving inwards and outwards are superimposed dichoptically and optically. In both conditions opponent patterns motions lead to apparent standstills for considerable periods. In a tentative model both the apparent standstills and the remaining pattern motions are described as by-products, resulting from pattern combinations rather than as direct products of component motions.

Induced rotary motion and ocular torsion.

When a large patterned annulus rotates around a stationary sectored disc the latter appears to rotate in the opposite direction. Such induced rotary motion was examined with central discs subtending 5, 20 and 40 deg at the eye, with the surround filling the remainder of the visual field. The annular surround or the central disc could be oscillated sinusoidally around the fixation point through 20 deg at 0.2 Hz. In each case, subjects estimated the angles through which the moving and stationary parts of the display appeared to rotate on one half-cycle. Subjects also estimated the angle of rotation of an oscillating display that filled the visual field. Induced rotation of the centre was around 100% of the inducing amplitude for all disc sizes, but there was no induced motion of the surround when the centre rotated. Ocular torsion was measured under the same conditions, using the scleral search-coil technique. The amplitude of ocular torsion was a function of the size of the stationary or rotating field. Thus, variations in stimulus conditions affected induced rotary motion and ocular torsion in different ways. The implications of the results for theories of induced motion in terms of underregistered eye movements are discussed.

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.

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.