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Neurons of the visual system that exhibit depth specificity are prevalent in the medial temporal region of the cerebral cortex. Electrical activation of these cells can bias an observer's depth estimates, indicating that they play an important role in depth perception.
Our two eyes obtain slightly different views of the world. The resulting differences in the two retinal images, called binocular disparities, provide us with a stereoscopic sense of depth. The primary visual cortex (V1) contains neurons that are selective for the disparity of individual elements in an image, but this information must be further analysed to complete the stereoscopic process. Here we apply the psychophysical technique of reverse correlation to investigate disparity processing in human vision. Observers viewed binocular random-dot patterns, with 'signal' dots in a specific depth plane plus 'noise' dots with randomly assigned disparities. By examining the correlation between the observers' ability to detect the plane and the particular sample of 'noise' disparities presented on each trial, we revealed detection 'filters', whose disparity selectivity was remarkably similar to that of individual neurons in monkey V1. Moreover, if the noise dots were of opposite contrast in the two eyes, the tuning inverted, just like the response patterns of V1 neurons. Reverse correlation appears to probe disparity processing at the earliest stages of binocular combination, prior to the generation of a full stereoscopic depth percept.
In four experiments, observers attempted to align two sets of oblique edges to parallel. The contexts for these alignments included lines in isolation (2-D control), lines embedded in orthogonal drawings of same-oriented and different-oriented boxes (3-D objects), and each of these viewed against backgrounds depicting strong linear perspective (3-D backgrounds). A consistent distortion was observed in the alignments of different-oriented boxes relative to control lines, indicating that the parallel lines in these stimuli appeared to diverge toward the top of the picture. Furthermore, this box alignment illusion decreased with interstimulus distance, whereas alignment distortions in control lines and same-oriented boxes increased with distance. Viewing the stimuli against 3-D backgrounds produced a dramatic reversal of the illusion, with control lines now appearing to converge more than the boxes. These results suggest that the illusion reflects basic processes involved in pictorial depth perception.
An empirically based, conceptual model of human blur perception is presented. It incorporates the concepts of blur detection and blur discrimination in depth, and across the central and peripheral retina, in two- and three-dimensional visual space. Key aspects of the model are its dynamic nature, predictability regarding the blur-based depth-ordering of objects, patterns of retinal defocus with far and near viewing, and interactions related to retinal defocus between the central and peripheral retina. Furthermore, a two-dimensional schematic representation of the blur-free region during near viewing is depicted in dioptric space. This model has implications with respect to accommodative control, depth perception, and refractive error development and progression.
Non-architects answered multiple-choice questions about depth, size, shape, texture, and conformation in exterior building scenes presented by manual rendering or video-computer techniques including a single viewpoint, multiple viewpoints, and animation. They also rated (a) confidence in their answers, (b) overall judgments of clarity, and (c) overall impressions of realism. The viewing time needed for judgments was also measured. Presentation technique did not affect the viewing time, but it did affect perceptual accuracy and ratings of confidence, clarity, and realism. Animation yielded higher ratings in all categories. It also produced the highest accuracy for depth perception, but the lowest accuracy for size and texture perception. The low accuracy for size and texture was exacerbated by high confidence in the wrong answers. Multiple viewpoints caused neither false confidence nor reduced accuracy in any category, and yielded the highest accuracy in two categories: size and texture. The combined effects on perception and metaperception (knowledge about one's own perceptual processes) suggest that animation creates the best overall impression and is the best for conveying depth information. However, multiple viewpoints are better than animation for conveying size and texture information. These results are discussed with respect to theories of perceptual representation.
BACKGROUND: Strabism usually impairs central stereopsis irreversibly after a short time duration,however, the retinal periphery is more resistant to deterioration by binocular impairment. METHODS: In this prospective study 46 strabismic patients (9-56 years old) were tested for dynamic stereopsis in the peripheral visual field up to 20 degrees eccentricity. The effect of realignment of the visual axes by surgery on dynamic stereopsis was tested before and after surgery in 40 out of these patients. Patients were tested qualitatively for dynamically stereoactive fields of vision and quantitatively for the threshold value needed to create a three-dimensional impression. RESULT: We found residual dynamic stereopsis in 30% of patients without central static stereopsis: 56% of the patients improved after surgery, either through a significant (p<0.01) gain of stereoactive fields or through a decrease of threshold values. CONCLUSION: Strabismus surgery has benefits for the patients outside classical tests and seems to be independent of the static depth perception.
Previous research indicates that, when shown a collision between a moving and a stationary object, 11-month-old infants believe that the size of the moving object affects how far the stationary object is displaced. The present experiments examined whether 6.5- and 5.5-month-old infants hold the same belief. The infants sat in front of a horizontal track; to the left of the track was an inclined ramp. A wheeled toy bug rested on the track at the bottom of the ramp. The infants were habituated to an event in which a medium-size cylinder rolled down the ramp and hit the bug, propelling it to the middle of the track. Next, the infants saw two test events in which novel cylinders propelled the bug to the end of the track. The two novel cylinders were identical to the habituation cylinder in material but not in size: one was larger (large-cylinder event) and one was smaller (small-cylinder event) than the habituation cylinder. The 6.5-month-old infants, and the 5.5-month-old female infants, looked reliably longer at the small- than at the large-cylinder event. These and control results indicated that the infants (a) believed that the size of the cylinder affected the length of the bug's trajectory and (b) used the habituation event to calibrate their predictions about the test events. Unlike the other infants, the 5.5-month-old male infants tended to look equally at the small- and large-cylinder events. Further results indicated that this negative finding was not due to the infants' (a) failure to remember how far the bug rolled in the habituation event or (b) inability to use the habituation event to calibrate predictions about novel test events. Together, the present results suggest the following conclusions. First, when shown a collision between a moving and a stationary object, infants aged 5.5-6.5 months (a) believe that there is a proportional relation between the size of the moving object and the distance traveled by the stationary object and (b) can engage in calibration-based reasoning about this size/distance relation. Second, female infants precede males by a few weeks in this development, for reasons that may be related to sex differences in the maturation of depth perception.
The chromatic and achromatic channels of psychophysical models do not map simply onto the parvocellular and magnocellular channels of electrophysiology because the parvo channel carries both chromatic and achromatic signals. If vision of stabilized images be mediated by the parvo channel, then this channel mediates form and depth percepts.
In the laboratory, thresholds for stereoscopic depth perception are usually determined by asking observers to discriminate between a stimulus with a given depth offset and its mirror image. Threshold is most often defined as the disparity difference that yields 75% or 83% correct responses. Disparities used for clinical tests of stereopsis are much higher. Here it is argued that, among other factors, this is because of the fact that clinical tests usually require the detection of a depth difference (offset versus no offset), rather than the discrimination between two directions of depth difference (in front versus behind). From a formal comparison of the two tasks, the data show that discrimination, or classification is easier by at least a factor of 2 than detection. The contribution of variations of the threshold criterion and learning to the differences between stereoacuity as measured in laboratory and clinic is also discussed. These differences are relevant to the design of tests for clinical use.
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.
We present a computational model based on the heat conduction equation, which can well explain human performance of depth interpolation. The model assumes that the depth information is locally represented and spatial integration is made by iterative processing of mutual interaction of neighbors. It reconstructs a dynamically transforming surface which is in good agreement with the results of psychophysical experiments on depth perception of untextured (uniform-colored) surface moving in depth. The model can also explain a temporal-frequency property of human percept. We conclude that the local ambiguity, which is quite common in everyday visual scenes, is solved by an interpolation mechanism based on iterative local interaction of locally represented visual information.
The basis for training visual abilities to enhance sports performance is explored. Optometric intervention in sports assumes the following statements to be true: 1. Athletes have better visual abilities than non-athletes and better athletes have better visual abilities than the poorer athletes, 2. Visual abilities are trainable, and 3. Visual training is transferable to the performance of the athlete. The literature demonstrates that athletes have better visual abilities than non-athletes. Studies have shown this to be true in the following areas of vision: Larger extent of visual fields, larger fields of recognition (peripheral acuity), larger motion perception fields, lower amounts of heterophoria at near and far, more consistent simultaneous vision, more accurate depth perception, better dynamic visual acuity, and better ocular motilities. The literature also shows that all of the above skills are trainable. Two studies are cited that support the belief that visual training is transferable to athletic performance but they suffer from inadequate experimental design.
Due to the separation of the eyes, temporal retinal disparities are created during binocular stimulation and they have been proposed to be the basis of several stereo-visual effects. This paper studies the sensitivity of cortical neurons from area V1 to interocular temporal delay in the awake monkey (Macaca mulatta). Forty-four cells were included in this study. Temporal delay sensitivity was observed in 59% of them. About half of these temporal-delay-sensitive cells were also sensitive to the stimulation sequence of the eyes. The cells that preferred one eye to be stimulated first were termed asymmetrical (46%); those which were not sensitive to the eye sequence of stimulation were termed symmetrical (54%). No clear differences were observed in the distribution of delay-sensitive cells according to their eye dominance. Fifty-six percent of balanced cells and 65% of unbalanced cells were sensitive to interocular delay. These data underline the importance of temporal cues for depth perception.
Four experiments were conducted to examine the integration of depth information from binocular stereopsis and structure from motion (SFM), using stereograms simulating transparent cylindrical objects. We found that the judged depth increased when either rotational or translational motion was added to a display, but the increase was greater for rotating (SFM) displays. Judged depth decreased as texture element density increased for static and translating stereo displays, but it stayed relatively constant for rotating displays. This result indicates that SFM may facilitate stereo processing by helping to resolve the stereo correspondence problem. Overall, the results from these experiments provide evidence for a cooperative relationship between SFM and binocular disparity in the recovery of 3-D relationships from 2-D images. These findings indicate that the processing of depth information from SFM and binocular disparity is not strictly modular, and thus theories of combining visual information that assume strong modularity or independence cannot accurately characterize all instances of depth perception from multiple sources.
Motion information contributes weakly to veridical depth perception of real stimuli. To test whether background pattern might enhance veridicality, observers judged the orientations in depth of pictorially matched trapezoidal and rectangular surfaces, with and without a rectangular grid of vertical stripes in a frontal plane behind surfaces; viewing was monocular with lateral head motions of 15 cm extent. The grid did not enhance veridicality; instead, surfaces actually or pictorially slanted to the frontal plane were judged more slanted with the grid present. In a second experiment, observers were static or moved through 30 cm; the grid had little effect during stasis, but again elicited judgments of greater slant during motion, despite broadly veridical responses without the grid. Results from actual slant are interpreted in terms of motion contrast and suggest that motion information may be important in conveying differences in orientation. Results from pictorial slant suggest that the influence of pictorial information increases as its complexity increases.
Previously, the authors proposed a model of neural network extracting binocular parallax (Hirai and Fukushima, 1975). It is a multilayered network whose final layers consist of neural elements corresponding to "binocular depth neurons" found in monkey's visual cortex. The binocular depth neuron is selectively sensitive to a binocular stimulus with a specific amount of binocular parallax and does not respond to a monocular one. As described in the last chapter of the previous article (Hirai and Fukushima, 1975), when a binocular pair of input patterns consist of, for example, many vertical bars placed very closely to each other, the binocular depth neurons might respond not only to correct binocular pairs, but also to incorrect ones. Our present study is concentrated upon how the visual system finds correct binocular pairs or binocular correspondence. It is assumed that some neural network is cascaded after the binocular depth neurons and finds out correct binocular correspondence by eliminating the incorrect binocular pairs. In this article a model of such neural network is proposed. The performance of the model has been simulated on a digital computer. The results of the computer simulation show that this model finds binocular correspondence satisfactorily. It has been demonstrated by the computer simulation that this model also explains the mechanism of the hysteresis in the binocular depth perception reported by Fender and Julesz (1967).
Here, we show a new illusion of depth induced by psychophysical adaptation to dynamic random-dot stereograms (RDS) that are interocularly anticorrelated (i.e., in which the images for the two eyes have reversed contrast polarity with each other). After prolonged viewing of anticorrelated RDS, the presentation of uncorrelated RDS (i.e., in which two images are mutually independent random-dot patterns) produces the sensation of depth, although both anticorrelated and uncorrelated RDSs are perceptually rivalrous with no consistent depth by themselves. Contrary to other aftereffects demonstrated in a number of visual dimensions, including motion, orientation, and disparity, this illusion results from unconscious adaptation; observers are not aware of what they are being adapted to during the process of adaptation. We further demonstrate that this illusion can be predicted from the simulated responses of disparity-selective neurons based on a local filtering model. Model simulations indicate that the inspection of anticorrelated RDS causes the adaptation of all disparity detectors except one sensitive to its disparity; therefore, those selectively unadapted detectors show relatively strong activation in response to the subsequent presentation of uncorrelated RDS and produce depth perception.
Undergraduate students (N = 48) served as subjects in a test of Gregory's theory of illusions. Twenty-four students made judgments about the subjective depth of three reversible illusions--Necker cube, Book, and Pyramid--under the conditions of complete versus incomplete illusions and illusions without depth cues versus with depth cues. An additional 24 subjects recorded the three illusion reversal rates under slightly altered conditions. Differences were found among the various illusions with respect to complete versus incomplete illusions, reversal rate, subjective judgments of depth, and certain correlation values. Support for Gregory's theory of illusion as displaced or misleading depth perception is offered by these results.