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PubMed1992

The history of stereoscopy.

Ptolemy (127-148 AD) studied physiological diplopia, correspondence and the horopter. He had all the data to build a theory of depth perception through disparity detection, but left that undone. Alhazen (1000 AD) associated depth perception with the sensation of binocular convergence, just as Kepler (1611) and Descartes (1637). With the development of the concept of retinal correspondence and the fusion of the retinal images in the brain (Huygens 1667, Newton 1704) a cerebral mechanism of disparity detection became thinkable. The rise of Empiricism (Molyneux' Premise, the case of Cheselden) postponed the solution of the problem, finally reached by Wheatstone (1838). Physiological proof of Wheatstone's theory came from the experiments of Barlow et al. (1967).

Depth Perception↗
PubMed2001

Ernst Mach and the episode of the monocular depth sensations.

Although Ernst Mach is widely recognized in psychology for his discovery of the effects of lateral inhibition in the retina ("Mach Bands"), his contributions to the theory of depth perception are not as well known. Mach proposed that steady luminance gradients triggered sensations of depth. He also expanded on Ewald Hering's hypothesis of "monocular depth sensations," arguing that they were subject to the same principle of lateral inhibition as light sensations were. Even after Hermann von Helmholtz's attack on Hering in 1866, Mach continued to develop theories involving the monocular depth sensations, proposing an explanation of perspective drawings in which the mutually inhibiting depth sensations scaled to a mean depth. Mach also contemplated a theory of stereopsis in which monocular depth perception played the primary role.

Austria↗
PubMed2002

Visual depth encoding in populations of neurons with localized receptive fields.

Stereopsis is the ability to perceive three-dimensional structure from disparities between the two-dimensional retinal images. Although disparity-sensitive neurons have been proposed as a neural representation of this ability many years ago, it is still difficult to link all qualities of stereopsis to properties of the neural correlate of binocular disparities. The present study wants to support efforts directed at closing the gap between electrophysiology and psychophysics. Populations of disparity-sensitive neurons in V1 were simulated using the energy-neuron model. Responses to different types of stimuli were evaluated with an efficient statistical estimator and related to psychophysical findings. The representation of disparity in simulated population responses appeared to be very robust. Small populations allowed good depth discrimination. Two types of energy neurons (phase- and position-type models) that are discussed as possible neural implementations of disparity-selectivity could be compared to each other. Phase-type coding was more robust and could explain a tendency towards zero disparity in degenerated stimuli and, for high-pass stimuli, exhibited the breakdown of disparity discrimination at a maximum disparity value. Contrast-inverted stereograms led to high variances in disparity representation, which is a possible explanation of the absence of depth percepts in large contrast-inverted stimuli. Our study suggests that nonlocal interactions destroy depth percepts in large contrast-inverted stereograms, although these percepts occur for smaller stimuli of the same class.

Action Potentials↗
PubMed1995

Disabled stereopsis may be the norm among well-educated people.

Most well-educated people, where the author lives, have lost the ability to perceive the third dimension in space during everyday life. This has passed unnoticed because poor depth perception is not a serious handicap in an urban environment and because clinical depth perception tests have not been designed to detect this deficit. The author's hypothesis is that disabled stereopsis is a global phenomenon. A simple way of testing for disabled stereopsis is presented, in the hope that investigators in other parts of the world will test a sample of their local population and send the results to the author.

Depth Perception↗
PubMed1980

The vision of submariners and National Guardsmen: A longitudinal study.

This study was designed to differentiate among possible causes of an increased incidence of myopia and related symptoms among submariners by making a longitudinal comparison of the visual functions of two groups of subjects, submariners and National Guardsmen. Refractive error, visual acuity, phorias, accommodation, and depth perception were measured. Submariners showed statistically significantly greater losses in visual acuity, accommodation, and depth perception over a 3.5-year period than did the guardsmen, but the differences were very small. Comparison with data in the literature gives evidence of large shifts in refractive error for young men, both submariners and guardsmen, born in recent years. it is suggested that whatever factors are responsible for the increase in myopia in the general population are operating even more effectively among submariners.

Accommodation, Ocular↗
PubMed1996

Image blur as a pictorial depth cue.

A range of cues are already known to mediate depth perception in pictures and have been exploited by artists in drawings and paintings. Modern images are commonly generated by photographic or video equipment, and these images contain a depth cue that cannot be found in artistic depictions of natural scenes: different image regions are often blurred by different amounts, because of depth of focus limitations. Demonstrations presented here show that this selective image blur also acts as a pictorial depth cue, even when other pictorial cues are removed. Experimental data indicate that the degree of blur at borders between blurred and sharp image regions is used by the visual system to establish the depth ordering of different regions. Selective image blur is thus a potentially useful addition to computer-generated and cartoon images to enhance the impression of depth they convey. It may well also contribute to depth perception in natural retinal images, because the depth of focus of the human eye is limited.

Computer Graphics↗
PubMed1994

Infants' perception of kinetic depth and stereokinetic displays.

Studies examined infants' perceptions of 3-dimensional form, using a kinetic depth effect (KDE) display and displays containing subsets of the motion present in the KDE display. One subset consisted of "between-contour" motion, and the second consisted of "within-contour" motion. Research with adults has suggested that only between-contour motion leads to a compelling depth percept. In Experiments 1 and 2, infants generalized habituation from a KDE display to the between-contour but not the within-contour changes. In Experiments 3 and 4, infants generalized habituation from a KDE display to the between-contour display viewed from a novel orientation but not to the within-contour display viewed from the original orientation. Results indicate sensitivity to between-contour but not within-contour information, suggesting that infants perceive the 3-dimensional form of these displays.

Depth Perception↗
PubMed1993

Pairwise comparison technique: a simple solution for depth reconstruction.

A new technique dramatically simplifies the analysis of matching and depth reconstruction by extracting three-dimensional rigid depth interpretation from pairwise comparisons of weak perspective projections. This method provides a simple linear criterion for testing the correctness of correspondence for a pair of images; the method also provides a description of a one-parameter family of interpretations for each pair of images that satisfies this criterion. We show that if at least three projections of a volumetric object are known, then a three-dimensional (3D) rigid interpretation can be inferred from pairwise comparisons between any one of these images and other images in the set. The 3D interpretation is derived from the intersection of corresponding one-parameter families. The method provides a common computational basis for different processes of depth perception, for example, depth-from-stereo and depth-from-motion. Thus, a single mechanism for these processes in the human visual system would be sufficient. The proposed method does not require information about relative positions of eye(s) or camera(s) for different projections, but this information can be easily incorporated. The method can be applied for pairwise comparison within a single image. If any nontrivial correspondence is found, then several views of the same object are present in the same image. This happens, for example, in views of volumetrically symmetric objects. Symmetry facilitates depth reconstruction; if an object possesses two or more symmetries, its depth can be reconstructed from a single image.

Algorithms↗
PubMed1998

Two-dimensional matches from one-dimensional stimulus components in human stereopsis.

Three-dimensional visual scenes project onto the retina of the eye as two-dimensional images. The third dimension, depth, is projected as subtle differences between left and right retinal images. As early as the 1830s, stereoscopic depth perception was shown to depend on horizontal disparities between these images. To detect disparity, the visual system must match corresponding parts of the two retinal images. To identify the stimulus elements used in stereo matching, I applied a disparity-adaptation technique to visual patterns whose one-dimensional components and two-dimensional features have very different disparities. Surprisingly, the adaptors that are effective in altering depth perception appear widely separated in depth from the patterns they adapt. I conclude that stereo matching occurs in all directions of two-dimensional space and that one-dimensional components are the stimulus primitives, the fundamental elements of stereo matching. This is a reversal of the classical view of stereo correspondence as a one-dimensional (horizontal) matching of monocular two-dimensional features.

Depth Perception↗
PubMed1986

Suprathreshold stereo-depth matches as a function of contrast and spatial frequency.

Thresholds for stereoscopic-depth perception increase with decreasing spatial frequency below 2.5 cycles deg-1. Despite this variation of stereo threshold, suprathreshold stereoscopic-depth perception is independent of spatial frequency down to 0.5 cycle deg-1. Below this frequency the perceived depth of crossed disparities is less than that stimulated by higher spatial frequencies which subtend the same disparities. We have investigated the effects of contrast fading upon this breakdown of stereo-depth invariance at low spatial frequencies. Suprathreshold stereopsis was investigated with spatially filtered vertical bars (difference of Gaussian luminance distribution, or DOG functions) tuned narrowly over a broad range of spatial frequencies (0.15-9.6 cycles deg-1). Disparity subtended by variable width DOGs whose physical contrast ranged from 10-100% was adjusted to match the perceived depth of a standard suprathreshold disparity (5 min visual angle) subtended by a thin black line. Greater amounts of crossed disparity were required to match broad than narrow DOGs to the apparent depth of the standard black line. The matched disparity was greater at low than at high contrast levels. When perceived contrast of all the DOGs was matched to standard contrasts ranging from 5-72%, disparity for depth matches became similar for narrow and broad DOGs. 200 ms pulsed presentations of DOGs with equal perceived contrast further reduced the disparity of low-contrast broad DOGs needed to match the standard depth. A perceived-depth bias in the uncrossed direction at low spatial frequencies was noted in these experiments. This was most pronounced for low-contrast low-spatial-frequency targets, which actually needed crossed disparities to make a depth match to an uncrossed standard. This bias was investigated further by making depth matches to a zero-disparity standard (ie the apparent fronto-parallel plane). Broad DOGs, which are composed of low spatial frequencies, were perceived behind the fixation plane when they actually subtended zero disparity. The magnitude of this low-frequency depth bias increased as contrast was reduced. The distal depth bias was also perceived monocularly, however, it was always greater when viewed binocularly. This investigation indicates that contrast fading of low-spatial-frequency stimuli changes their perceived depth and enhances a depth bias in the uncrossed direction. The depth bias has both a monocular and a binocular component.

Depth Perception↗
PubMed2003

Contribution of middle temporal area to coarse depth discrimination: comparison of neuronal and psychophysical sensitivity.

Recent work suggests that the middle temporal (MT) area contributes to depth perception in addition to its well established roles in motion perception. To determine whether single MT neurons carry disparity signals with sufficient fidelity to account for depth perception, we have compared neuronal and psychophysical sensitivity to disparity while monkeys discriminated between two coarse disparities (near vs far) in the presence of noise. The strength of the visual stimulus was titrated around psychophysical threshold by varying the percentage of binocularly correlated dots in a random dot stereogram. We find that the average MT neuron has sensitivity equal to that of the monkey, as was reported previously for direction discrimination in MT. We further address some important factors that could bias the neuronal/psychophysical sensitivity comparison, including the possibility that monkeys reach a decision before the end of the stimulus presentation. Unlike the predictions of a simple model that uses Poisson spiking statistics, the sensitivity of many MT neurons has little dependence on the time interval over which spikes are counted to compute a neuronal threshold. Thus the response properties of many MT neurons appear to be adapted for rapid discrimination of depth, and we describe how temporal variations in both signal and noise contribute to this effect. We therefore predicted that psychophysical thresholds should exhibit little dependence on viewing duration in our task, and this was confirmed by additional behavioral experiments. Overall, our findings show that MT is well suited to provide sensory signals that form the basis for perceptual judgments of depth.

Action Potentials↗
PubMed2001

A threshold explains modulation of neural responses to opposite-contrast stereograms.

Disparity-sensitive neurons respond to contrast-inverted stereograms (aRDS) that do not evoke depth percepts. This is in conflict with the idea that such neurons are the direct correlate of depth perception. However, the output of neurons responding to aRDS may be further processed: neurons at later processing stages show weaker responses to aRDS than early stage neurons. Here, we show that such a response hierarchy emerges in a three-layered neural network. A numerical analysis demonstrates that threshold operations can largely explain the network's behavior as well as the electrophysiological data. An extension of the energy neuron model for disparity-sensitive neurons predicts increased responses to aRDS for an identifiable sub-class of cells and can thus be tested in electrophysiological experiments.

Action Potentials↗
PubMed1983

Lateral differences in the detection of stereoscopic depth.

The experiment investigated the hemifield differences in stereoscopic depth perception. Random dot stereograms (Julesz figures) producing the experience of a square appearing in front or behind the fixation plane were used as stimuli. The patterns in depth were exposed either in the left or in the right side of the stereograms for 30 msec. Three different magnitudes of depth were used. The results showed a higher amount of correct detections of depth in the left visual field than in the right visual field. The effects of direction and magnitude of depth were also significant. The hypothesis referring the observed results to the right hemisphere superiority in stereoscopic depth perception is discussed.

Adolescent↗
PubMedDate not supplied

Using movement parallax for 3D laparoscopy.

The lack of depth perception hampers the surgeon during laparoscopic operation. Laparoscopes usually are monocular, but binocular ones are currently available. Depth perception, however, does not exclusively rely on binocular disparity. An observer, with only one eye, who is able to move that eye, obtains the same information as an observer who has two eyes. This principle of movement parallax can be applied to laparoscopy by coupling the head movements of the surgeon to the motions of the tip of the laparoscope. In an experiment we investigated if this principle is applicable to laparoscopy. Two groups of testees with no background in surgery were used. The first group was assisted by movement parallax, the second group was viewing a static image. Both groups of testees had to perform an exploration and a manipulation task. Since the amount of space for camera motion within the laparoscope is limited, implementation potential depends on the amount of movements that will be made by the observer. Therefore the movements of the observer performing the exploration task were registered and analysed. Results of the experiment indicate the advantage of movement parallax for the exploration task (performance increases by factor 2 while using only 30% more time) but not for the manipulation task. The analysis of the movements indicates that small movements are sufficient for implementation. Based on these results we concluded that movement parallax is applicable to laparoscopy.

Depth Perception↗
PubMed1991

A new training device for laparoscopic cholecystectomy.

Laparoscopic cholecystectomy provides a new approach for gallbladder removal with which most general surgeons are not familiar. Requisites for the safe performance of this procedure are good hand-eye coordination, depth perception, and team cooperation. To aid with problems in depth perception and in the opposing movements caused by the lever principle, a training model was designed in which surgeons may execute a variety of exercises to enhance their motor skills and learn to work cooperatively with two other surgeons before operating on an experimental animal.

Cholecystectomy↗
PubMed1988

Subjective effects of displacement errors in electronically processed stereo-television pictures.

Several aspects of the roles of object contours and of rivalry and suppression in binocular vision are considered in a TV engineering context. Three experiments, using 3D b/w stills, were conducted to explore subjective effects of irregular horizontal shifts at object contours (displacement errors), which are expected to be a typical picture impairment problem of future 3D TV multi-viewpoint systems. Performance and rating tasks on a wide range of impairment magnitudes and various picture parameters served to give a quantitative estimate of the influence of displacement errors on: (1) correctness of binocular depth perception; and (2) picture quality. Two experiments (constant vs. variable location of impairments over time) with vertical grating stimuli showed binocular depth perception to withstand levels of up to 90% misplaced contour elements in one part of the stereo pair. Quality assessments were much more critical. They depended both on the proportion of impaired pixels and on the maximum horizontal width of individual impairments. A corresponding stimulus model was found to be valid for pictures with natural content, too. Impairments were less annoying when visible by only one eye instead of both. A specific formulation is given of the influence of contrast and spatial frequency features on performance.

Adult↗