Nicholas J. Wade

Yarbus, eye movements, and vision.

The impact of Yarbuss research on eye movements was enormous following the translation of his book Eye Movements and Vision into English in 1967. In stark contrast, the published material in English concerning his life is scant. We provide a brief biography of Yarbus and assess his impact on contemporary approaches to research on eye movements. While early interest in his work focused on his study of stabilised retinal images, more recently this has been replaced with interest in his work on the cognitive influences on scanning patterns. We extended his experiment on the effect of instructions on viewing a picture using a portrait of Yarbus rather than a painting. The results obtained broadly supported those found by Yarbus.

The influence of colour and contour rivalry on the magnitude of the tilt after-effect.

Abstract Tilt after-effects were generated by inspection of gratings inclined 10 or 15° from the vertical in six experiments. The results indicated that the magnitude of the tilt after-effect: was not influenced by the colour of the inspection and test gratings (Experiments I–IV); was not affected by binocular rivalry suppression (Experiment V); and was the same under various conditions of monocular and binocular inspection and testing (Experiment VI).

A Selective History of the Study of Visual Motion Aftereffects

The visual motion aftereffect (MAE) was initially described after observation of movements in the natural environment, like those seen in rivers and waterfalls: stationary objects appeared to move briefly in the opposite direction. In the second half of the nineteenth century the MAE was displaced into the laboratory for experimental enquiry with the aid of Plateaus spiral. Such was the interest in the phenomenon that a major review of empirical and theoretical research was written in 1911. In the latter half of the present century novel stimuli (like drifting gratings, isoluminance patterns, spatial and luminance ramps, random-dot kinematograms, and first-order and second-order motions), introduced to study space and motion perception generally, have been applied to examine MAEs. Developing theories of cortical visual processing have drawn upon MAEs to provide a link between psychophysics and physiology; this has been most pronounced in the context of monocular and binocular channels in the visual system, the combination of colour and contour information, and in the cortical sites most associated with motion processing. The relatively unchanging characteristic of the study of MAEs has been the mode of measurement: duration continues to be used as an index of its strength, although measures of threshold elevation and nulling with computer-generated motions are becoming more prevalent. The MAE is a part of the armoury of motion phenomena employed to uncover the mysteries of vision. Over the last 150 years it has proved itself immensely adaptable to the shifts of fashion in visual science, and it is likely to continue in this vein.

Motion over the retina and the motion aftereffect

The motion aftereffect (MAE) was measured with retinally moving vertical gratings positioned above and below (flanking) a retinally stationary central grating (experiments 1 and 2). Motion over the retina was produced by leftward motion of the flanking gratings relative to the stationary eyes, and by rightward eye or head movements tracking the moving (but retinally stationary) central grating relative to the stationary (but retinally moving) surround gratings. In experiment 1 the motion occurred within a fixed boundary on the screen, and oppositely directed MAEs were produced in the central and flanking gratings with static fixation; but with eye or head tracking MAEs were reported only in the central grating. In experiment 2 motion over the retina was equated for the static and tracking conditions by moving blocks of grating without any dynamic occlusion and disclosure at the boundaries. Both conditions yielded equivalent leftward MAEs of the central grating in the same direction as the prior flanking motion, ie an MAE was consistently produced in the region that had remained retinally stationary. No MAE was recorded in the flanking gratings, even though they moved over the retina during adaptation. When just two gratings were presented, MAEs were produced in both, but in opposite directions (experiments 3 and 4). It is concluded that the MAE is a consequence of adapting signals for the relative motion between elements of a display.

The perception of visual motion during movements of the eyes and of the head.

If physical movements are to be seen veridically, it is necessary to distinguish between displacements over the retina due to self-motion and those due to object motion. When target motion is in a different direction from that of a pursuit eye movement, the perceived motion of the target is known to be shifted in direction toward the retinal path, indicating a partial failure of compensation for eye movements (Becklen, Wallach, & Nitzberg, 1984). The experiments reported here compared the perception of target motion when the head and/or eyes were moving in a direction different from that of the target. In three experiments, target motion was varied in direction, phase, and extent with respect to pursuit movements. In all cases, the compensation was less effective for head than for eye movements, although this difference was least when the extent of the tracked and target motions was the same. Compensation for pursuit eye movements was better than that reported in previous studies.

The Representation of Uniform Motion in Vision

For veridical detection of object motion any moving detecting system must allocate motion appropriately between itself and objects in space. A model for such allocation is developed for simplified situations (points of light in uniform motion in a frontoparallel plane). It is proposed that motion of objects is registered and represented successively at four levels within frames of reference that are defined by the detectors themselves or by their movements. The four levels are referred to as retinocentric, orbitocentric, egocentric, and geocentric. Thus the retinocentric signal is combined with that for eye rotation to give an orbitocentric signal, and the left and right orbitocentric signals are combined to give an egocentric representation. Up to the egocentric level, motion representation is angular rather than three-dimensional. The egocentric signal is combined with signals for head and body movement and for egocentric distance to give a geocentric representation. It is argued that although motion perception is always geocentric, relevant registrations also occur at the three earlier levels. The model is applied to various veridical and nonveridical motion phenomena.

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. Copyright

On Interocular Transfer of the Movement Aftereffect in Individuals with and without Normal Binocular Vision

The duration of the movement aftereffect was measured in twenty-four normally binocular subjects and in eighteen subjects who lacked stereopsis as a consequence of childhood strabismus. Aftereffects were generated monocularly and binocularly, and compared to those which occurred after adaptation of one eye and testing with the other. Normal subjects were categorized on two indices of eye dominance, which involved sighting and rivalry tests. The monocular-aftereffect durations were slightly longer when the dominant eye was used, and interocular transfer from the dominant eye to the nondominant eye was greater than the transfer in the reverse direction; however, these differences were not statistically significant. The results from the strabismic subjects suggested that they fell into two distinct groups: one group (seven of the eighteen subjects) experienced no interocular transfer in either direction; the other group did yield some interocular transfer, and it was generally greater after adaptation of the dominant eye and testing the nondominant eye than in the reverse direction. Six of the seven subjects who failed to show any transfer still had misalignment of the visual axes, but this was not the case in any of the subjects exhibiting transfer.

Monocular and Binocular Rivalry between Contours

The temporal characteristics of binocular and monocular rivalry between orthogonal gratings of the same or complementary colours were investigated. Rivalry was measured in terms of the dominance of either grating or the visibility of composites comprised of parts of both gratings. The total duration for which either grating was dominant was significantly longer in binocular rivalry between gratings of complementary colours. A comparison of binocular and monocular rivalry indicated considerable phenomenal differences between them. Dominance in binocular rivalry corresponds to the visibility of one grating alone; this occurs rarely in monocular rivalry, which is characterized by fluctuations in the distinctiveness of the gratings. The changes in distinctiveness are influenced by colour in a similar manner to that in binocular rivalry, and the frequencies of fluctuations are higher for gratings of complementary colours.

Binocular rivalry with moving patterns

Binocular rivalry between a horizontal and a vertical grating was examined in six experiments. The gratings could be presented in a static form or dynamically so that either one or both gratings moved. The motion consisted of a symmetrical transformation of the gratings about their centers, so that the lines moved outwards or inwards. During rivalry, a moving pattern was visible for about 50% longer than an equivalently oriented static pattern (Experiments 1, 2, and 4). When both gratings were in motion (Experiments 3 and 5), the course of rivalry was similar to that found for two static gratings. The duration of dominance of the moving grating was influenced by its velocity (Experiment 6). The results are interpreted in terms of the stimulus strengths of the static and dynamic patterns.