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PubMed1995

Human stereovision without localized image features.

Many theories of human stereovision are based on feature matching and the related correspondence problem. In this paper, we present psychophysical experiments indicating that localized image features such as Laplacian zerocrossings, intensity extrema, or centroids are not necessary for binocular depth perception. Smooth one-dimensional intensity profiles were combined into stereograms with mirror-symmetric half-images such that these localized image features were either absent or did not carry stereo information. In a discrimination task, subjects were asked to distinguish between stereograms differing only by an exchange of these half-images (ortho- vs. pseudoscopic stereograms). In a depth ordering task, subjects had to judge which of the two versions appeared in front. Subjects are able to solve both tasks even in the absence of the mentioned image features. The performance is compared to various possible stereo mechanisms. We conclude that localized image features and the correspondences between them are not necessary to perceive stereoscopic depth. One mechanism accounting for our data is correlation or mean square difference.

Contrast Sensitivity↗
PubMed1991

Stereopsis in the cat: behavioral demonstration and underlying mechanisms.

The neural substrates subserving stereopsis were investigated behaviorally and electrophysiologically in the cat. In one set of studies, we examined behaviorally the ability of normal cats to perceive depth on the sole basis of spatial disparity using random-dot stereograms. Results showed that the animals were able to carry out this discrimination. We then evaluated the contribution of the optic chiasm, the corpus callosum and the primary visual cortex to this function. Results indicated that: (1) chiasma transection drastically reduced the ability of the animals to solve the random-dot problem; (2) a callosal split had little or no effect on their ability to relearn the same discrimination; (3) a section of both the corpus callosum and optic chiasm abolished this ability; and (4) bilateral lesions of areas 17-18 also abolished it. In another set of studies, we examined electrophysiologically the properties of neurons in the various visual cortical areas where disparity-based depth discrimination processes are presumed to take place. We recorded from areas 17, 18 and 19 of normal and split-chiasm cats. Results showed that: (1) the primary visual cortex of the normal cat contained cells sensitive to stimulus disparity; (2) these disparity sensitive neurons were also present in area 19 although in a much lower proportion and were more widely tuned than those in areas 17-18; and (3) following the section of the optic chiasm, there was a significant decrease in the number of disparity sensitive cells in areas 17-18, whereas in area 19 they were nearly completely absent. The results obtained from the lesion studies and from the single unit recording experiments indicate that stereoscopic depth perception is highly dependent in the cat upon the integrity of the through-the-chiasm geniculo-striate pathway and its target primary visual cortex.

Animals↗
PubMed1998

The interaction of binocular disparity and motion parallax in determining perceived depth and perceived size.

Although binocular disparity and motion parallax are powerful cues for depth, neither, in isolation, can specify information about both object size and depth. It has been shown that information from both cues can be combined to specify the size, depth, and distance of an object in a scene (Richards, 1985 Journal of the Optical Society of America A 2 343-349). Experiments are reported in which natural viewing and physical stimuli have been used to investigate the nature of size and depth perception on the basis of disparity and parallax presented separately and together at a range of viewing distances. Observers adjusted the relative position of three bright LEDs, which were constrained to form a triangle in plan view with the apex pointing toward the observer, so its dimensions matched that of a standard held by the subject. With static monocular viewing, depth settings were inaccurate and erratic. When both cues were present together accuracy increased and the perceptual outcome was consistent with an averaging of the information provided by both cues. When an apparent bias evident in the observers' responses (the tendency to under-estimate the size of the standard) was taken into account, accuracy was high and size and depth constancy were close to 100%. In addition, given this assumption, the same estimate of viewing distance was used to scale size and depth estimates.

Depth Perception↗
PubMed1991

A definitive case of paradoxical stereopsis.

Author JF had perfect stereoacuity but was unaware that he did not make much use of stereopsis under everyday conditions of seeing, i.e., his stereopsis was paradoxical. We describe how this condition was diagnosed and everyday depth perception restored. The objective of this report is to demonstrate convincingly that paradoxical stereopsis exists as a clinical entity. A combination of signs and symptoms is presented as a syndrome for the diagnosis of paradoxical stereopsis.

Depth Perception↗
PubMed1977

Experience and latency to achieve stereopsis: a replication.

This study replicated and extended the findings of MacCracken and Hayes (1976). 10 students were presented the same complex stereogram for 5 trials daily over 2 nonconsecutive days, and latencies to achieve depth perception were recorded. Latencies decreased across 5 trials in the first session but were somewhat longer at the beginning of the second session than at the end of the first session.

Adolescent↗
PubMed1978

[Unilateral aphakia and pseudophakia].

Aniseikonia as well as binocular vision and depth perception are measured in 114 patients with unilateral pseudophakos. 86% of the cases exhibit a small degree of aniseikonia (3% or less). However, binocular vision and stereopsis remain subnormal or approximatively normal.

Adolescent↗
PubMed1986

Aberrant parenting and delayed offspring development in rats exposed to lithium.

Natural lithium (Li) salts, including those used routinely in manic depressive illness, consist of two stable nonradioactive isotopes: lithium-7 (Li-7) (92.6%) and lithium-6 (Li-6) (7.4%). Female rats (3 months old) were treated with either Li-7 chloride or Li-6 chloride or were untreated prior to and during gestation and lactation. Birth weights were lower for Li-treated animals than for normal pups. Maternal behavior of all Li-treated mothers was altered. Li-7 mothers ignored their pups and nursed them infrequently. Li-6 mothers groomed and nursed their pups more often than normal mothers. All pups showed delays in development, especially in the maturation of depth perception. Although Li-6-treated dams were over-protective mothers, their offspring showed longer developmental delays than those of Li-7-treated offspring.

Animals↗
PubMed1999

Perceptual depth synthesis in the visual system as revealed by selective adaptation.

Selective adaptations was used to determine the degree of interactions between channels processing relative depth from stereopsis, motion parallax, and texture. Monocular adaptations with motion parallax or binocular stationary adaptation caused test surfaces, viewed either stationary binocularly or monocularly with motion parallax, to appear to slant in the opposite direction compared with the slant initially adapted to. Monocular adaptations on frontoparallel surfaces covered with a pattern of texture gradients caused a subsequently viewed test surface, viewed either monocularly with motion parallax or stationary binocularly, to appear to slant in the opposite direction as the slant indicated by the texture in the adaptation condition. No aftereffect emerged in the monocular stationary test condition. A mechanism of independent channels for relative depth perception is dismissed in favor of a view of an asymmetrical interactive processing of different information sources. The results suggest asymmetrical inhibitory interactions among habituating slant detector units receiving inputs from static disparity, dynamic disparity, and texture gradients.

Adaptation, Physiological↗
PubMed1988

The observer-relative velocity field as the basis for effective motion parallax.

Earlier studies of motion parallax found unambiguous relative depth perception when random dot patterns were systematically translated in accordance with either motion of the observer's head or motion of the display scope. The need for such relative motion between an observer and a flow field was examined by placing a flow field in a limited area (window) in a large scope and translating the window relative to the observer. Accuracy in judging surface orientation and quantitative depth estimates were determined by the velocity field relative to the observer and were not measurably affected by whether this field was produced with a stationary or a moving window. Accuracy was consistently higher for smaller ratios of maximum to minimum projected velocities, reaching 100% in one experiment with a 1.12:1 ratio. We conclude that fully effective motion parallax does not require relative motion between the observer's head and the contours of a flow field.

Depth Perception↗
PubMed1987

[Why two eyes?].

Having two eyes instead of just one is advantageous in at least six respects: the danger of blindness is decreased, the visual field is enlarged, stereoscopic depth perception is possible on the basis of binocular disparities, the position of the eyes relative to the head can be computed from the images of both eyes, visual obstacles in front of the horopter perceptually shrink, and the signal-to-noise ratio is increased.

Blindness↗
PubMed1996

Interobserver variance in perceptual performance and learning.

PURPOSE: Normal observers and patients with apparent disease usually are tacitly expected to yield homogeneous thresholds in clinical tests of visual perception. The authors tested this assumption. METHODS: Through training of 70 observers, performance and improvement of performance were tested for different hyperacuity tasks using psychophysical tests. RESULTS: Although the assumption of homogeneous results might be true for many tasks limited by the physical properties of the eye, such as two-point resolution, the authors find a relatively wide variation of performance, especially in untrained observers, for tasks that require more elaborate processing in the visual cortex. Observers vary widely both in their baseline performance and in the extent and speed of learning for tasks such as vernier discrimination and stereoscopic depth perception. On average, speed of learning is inversely correlated to baseline performance, that is better initial performance usually is associated with slower improvement. CONCLUSIONS: This finding indicates that retesting of unusually high (pathologic) thresholds in clinical tests of visual perception might improve discrimination between patients whose performance is poor because of lack of familiarity with the task and who improve with training and patients who improve far less if their poor performance results from pathologic conditions.

Adult↗
PubMedDate not supplied

Interpolation in stereoscopic matching.

Anyone who has stared at a repeating wallpaper pattern, or a periodic pattern of tiles, has probably experienced the phenomenon of a false stereoscopic depth percept. This arises because of a mismatching in the two eyes of repeating elements in the pattern. The phenomenon is less likely to occur if an edge of the textured region is in view; the edge seems to fix the registration of elements. We describe here a stereogram which exemplifies this principle; it has a central, periodic region bounded on either side by edges with pre-assigned disparities. We find that the perceived depth of the central region is controlled by the edges. In certain conditions (when the period is spatially large), the edges simply impose one of the expected discrete matchings. In other conditions, however, we observe a striking phenomenon: interpolation in depth occurs between the edges, violating any possible feature-by-feature matching.

Depth Perception↗
PubMed1996

[Correspondence of depth sensitivity and visually evoked potential amplitude in retinal eccentricity].

It is believed that an enhancement of visual evoked potential (VEP) amplitude in response to stereograms is due to the activity of disparity-sensitive neurons in the visual center. However, it is unclear whether the enhancement works only on retinal disparity cues or on other depth cues as well, which are derived from the mental process of recognizing a depth. The aim of this study is to analyze this relationship by comparing the degree of amplitude increase in the VEP with that of the magnitude in depth perception by viewing a stereopair with a stereoscope. The reduction of the retinal disparity sensitivity in increasing retinal eccentricity was confirmed by psychophysical measurement tests and visual evoked potential measurement. However, the reduction rate of the sensitivity curve was greater in the VEP than in the psychophysiological curve. This means that changes in the VEP, when responding to a sterogram, are mainly due to factors in the disparity sensitive neurons rather than in the mental process of recognizing a depth.

Adult↗
PubMed2002

Quantitative evaluation of three advanced laparoscopic viewing technologies: a stereo endoscope, an image projection display, and a TFT display.

BACKGROUND: Compared to open surgery, minimally invasive surgery (MIS) relies heavily on advanced technology, such as endoscopic viewing systems and innovative instruments. The aim of the study was to objectively compare three technologically advanced laparoscopic viewing systems with the standard viewing system currently used in most Dutch hospitals. METHODS: We evaluated the following advanced laparoscopic viewing systems: a Thin Film Transistor (TFT) display, a stereo endoscope, and an image projection display. The standard viewing system was comprised of a monocular endoscope and a high-resolution monitor. Task completion time served as the measure of performance. Eight surgeons with laparoscopic experience participated in the experiment. RESULTS: The average task time was significantly greater (p <0.05) with the stereo viewing system than with the standard viewing system. The average task times with the TFT display and the image projection display did not differ significantly from the standard viewing system. CONCLUSION: Although the stereo viewing system promises improved depth perception and the TFT and image projection displays are supposed to improve hand-eye coordination, none of these systems provided better task performance than the standard viewing system in this pelvi-trainer experiment.

Analysis of Variance↗
PubMedDate not supplied

A neural model of the cortical representation of egocentric distance.

Neurons in the visual cortex of monkeys respond selectively to the disparity between the images in the two eyes. Recent recordings have shown that some of the disparity-selective neurons in the primary visual cortex and the posterior parietal cortex are modulated by the distance of fixation. A population of such gain-modulated, disparity-selective neurons forms a set of basis functions of horizontal disparity and distance of fixation that can be used as an intermediate representation for computing egocentric distance. This distributed representation is consistent with psychophysical studies of human depth perception; in contrast, neurons explicitly tuned to distance are not consistent with how we perceive distance. In a population model that includes noise in the firing rates of neurons, the perceived distance is shown to be the estimate of geometrical distance that minimizes the variance of the estimation.

Animals↗
PubMed1999

Stereo augmented reality in the surgical microscope.

We present an augmented reality system that allows surgeons to view features from preoperative radiological images accurately overlaid in stereo in the optical path of a surgical microscope. The purpose of the system is to show the surgeon structures beneath the viewed surface in the correct 3-D position. The technical challenges are registration, tracking, calibration and visualisation. For patient registration, or alignment to preoperative images, we use bone-implanted markers and a dental splint is used for patient tracking. Both microscope and patient are tracked by an optical localiser. Calibration uses an accurately manufactured object with high contrast circular markers which are identified automatically. All ten camera parameters are modelled as a bivariate polynomial function of zoom and focus. The overall system has a theoretical overlay accuracy of better than 1 mm. Implementations of the system have been tested on seven patients. Recent measurements in the operating room conformed to our accuracy predictions. For visualisation the system has been implemented on a graphics workstation to enable high frame rates with a variety of rendering schemes. Several issues of 3-D depth perception remain unsolved, but early results suggest that perception of structures in the correct 3-D position beneath the viewed surface is possible.

Depth Perception↗
PubMed1988

Task performance with base-in and base-out prism.

The effects of base-in (BI) and base-out (BO) prism upon performance of four occupational-like tasks were measured on a group of 10 subjects who had normal binocular vision. Performance on tasks which required depth perception was significantly poorer when subjects wore prism glasses with 8 and 12 delta BI and BO, whereas 4 delta BI and BO did not significantly affect performance. The performance decrements with prism (3.0 to 6.7%) were considerably less than those induced by denial of binocularity (20 to 30%) as measured in a previous study. Thus, vergence-inducing prism does impair task performance but not as much as does the denial of binocularity. The reading and counting tasks did not require critical depth judgement and were much less affected by the prism than the needle-threading and pointers-and-straws tasks.

Adult↗
PubMed1977

Stereopsis in the falcon.

Stereoscopic depth perception is demonstrated in the falcon, a non-mammalian with binocular vision. This result complements recent physiological evidence for binocular interaction in the bird visual system, and suggests that stereopsis may be a general attribute of vertebrate vision and not an exclusive product of mammalian evolution.

Animals↗