Stereoscopic Depth Perception Research Articles

Depth Perception, Binocular Integration and Hand-Eye Coordination in Intact and Stereo Impaired Human Subjects

A series of tests was devised to assess stereoscopic depth processing, motion parallax depth processing, binocular integration and hand-eye coordination in normal, stereoblind, and stereo deficient subjects. Using a random- dot stereoscopic display viewed through a stereoscope we established that of the 262 subjects tested, 177 were categorized as having normal stereoscopic depth perception, 28 as being stereo deficient and 57 as being stereoblind. These three groups of subjects processed motion parallax information for depth equally well, but the stereoblind and stereo deficient subjects had significantly longer reaction times. On the hand-eye coordination tests the stereoblind subjects performed significantly less well than did normal and stereo deficient subjects, whose performance on these tests was similar. Our binocular integration tests revealed significantly less integration in stereoblind subjects than in normal and stereo deficient subjects. The tests we have devised will be useful for the accurate assessment of various forms of treatment for amblyopia and strabismus for the reinstatement of depth perception, hand-eye coordination and binocular integration.

Inferotemporal Cortex Subserves Three-Dimensional Structure Categorization

We perceive real-world objects as three-dimensional (3D), yet it is unknown which brain area underlies our ability to perceive objects in this way. The macaque inferotemporal (IT) cortex contains neurons that respond selectively to 3D structures defined by binocular disparity. To examine the causal role of IT in the categorization of 3D structures, we electrically stimulated clusters of IT neurons with a similar 3D-structure preference while monkeys performed a 3D-structure categorization task. Microstimulation of 3D-structure-selective IT clusters caused monkeys to choose the preferred structure of the 3D-structure-selective neurons considerably more often. Microstimulation in IT also accelerated the monkeys' choice for the preferred structure, while delaying choices corresponding to the nonpreferred structure of a given site. These findings reveal that 3D-structure-selective neurons in IT contribute to the categorization of 3D objects.

Vergence eye movements signifying 3D depth perception from 2D movies

A sensation of depth can arise from two-dimensional (2D) movies without any stereoscopic depth cue. Depth perception in three-dimensional (3D) space depends on the stability of stereoscopic gaze by vergence – coordinated movement of the two eyes in opposite directions – compensating the misalignment of the retinal images from the two eyes (i.e. binocular disparity) [1]. On the other hand, the oculomotor mechanisms that stabilize stereoscopic gaze and depth perception in 2D movie space remain unclear [2]. Here, we propose a hypothesis that vergence eye movements signifying 3D depth perception persist during prolonged 2D movie presentation without binocular disparity cues. By measuring eye positions while the subject viewed moving random-dot video stimuli, we show that sustained vergence is induced during 30-s exposure to radially expanding 2D optic flow. Moreover, a 2D video movie showing a passenger’s view of a roller coaster induces continuously changing vergence. In the absence of binocular disparity cues, the pictorial depth information within a 5°×5° gaze window and optic flow in the movie simultaneously and independently influence vergence. The pictorial gaze-area depth information affects vergence mainly in the virtual far space, whereas optic flow robustly affects vergence irrespective of the nearness. These findings demonstrate that vergence serves as a reliable marker signifying 3D depth perception from 2D movies, imposing critical constraints on creation of an effective and safe virtual reality.

Coding of Stereoscopic Depth Information in Visual Areas V3 and V3A

The process of stereoscopic depth perception is thought to begin with the analysis of absolute binocular disparity, the difference in position of corresponding features in the left and right eye images with respect to the points of fixation. Our sensitivity to depth, however, is greater when depth judgments are based on relative disparity, the difference between two absolute disparities, compared to when they are based on absolute disparity. Therefore, the visual system is thought to compute relative disparities for fine depth discrimination. Functional magnetic resonance imaging studies in humans and monkeys have suggested that visual areas V3 and V3A may be specialized for stereoscopic depth processing based on relative disparities. In this study, we measured absolute and relative disparity-tuning of neurons in V3 and V3A of alert fixating monkeys, and we compared their basic tuning properties with those published previously for other visual areas. We found that neurons in V3 and V3A predominantly encode absolute, not relative, disparities. We also found that basic parameters of disparity-tuning in V3 and V3A are similar to those from other extrastriate visual areas. Finally, by comparing single-unit activity with multi-unit activity measured at the same recording site, we demonstrate that neurons with similar disparity selectivity are clustered in both V3 and V3A. We conclude that areas V3 and V3A are not particularly specialized for processing stereoscopic depth information compared to other early visual areas, at least with respect to the tuning properties that we have examined.

Altered depth perception is associated with presence of schizotypal personality traits

Introduction. Impaired depth perception, a fundamental aspect of early visual processing, has been shown in patients with schizophrenia suggesting a disturbance to magnocellular and possibly parvocellular pathways. Despite some evidence showing visual-perceptive deficits in people with schizotypal personality traits (SPT), depth perception has not been evaluated in these subjects. Methods. 12 clinically healthy schizotypy and 17 control participants were examined using a novel stereoscopic depth perception task. A mixed ANOVA design considered the Group (SPT/control) as independent factor, and trial Block (BD/BD + /BD–) and target Condition (SDSS/SDDS/DDSS/DDDS) were considered as repeated measures. Results. Schizotypal participants were not significantly different to controls on simple judgements of depth but demonstrated a subtle impairment in perceiving binocular depth when performing high difficulty judgements. Conclusions. The presence of subtle depth perception problems in schizotypal subjects, similar but less marked than those of schizophrenia patients, may suggest a less pervasive disturbance of early information processing. If so, such deficits could be considered as innate neurological changes that may occur in people vulnerable for schizophrenia, thus with the potential to be a novel intermediate phenotype.

Matching and correlation computations in stereoscopic depth perception

A fundamental task of the visual system is to infer depth by using binocular disparity. To encode binocular disparity, the visual cortex performs two distinct computations: one detects matched patterns in paired images (matching computation); the other constructs the cross-correlation between the images (correlation computation). How the two computations are used in stereoscopic perception is unclear. We dissociated their contributions in near/far discrimination by varying the magnitude of the disparity across separate sessions. For small disparity (0.03°), subjects performed at chance level to a binocularly opposite-contrast (anti-correlated) random-dot stereogram (RDS) but improved their performance with the proportion of contrast-matched (correlated) dots. For large disparity (0.48°), the direction of perceived depth reversed with an anti-correlated RDS relative to that for a correlated one. Neither reversed nor normal depth was perceived when anti-correlation was applied to half of the dots. We explain the decision process as a weighted average of the two computations, with the relative weight of the correlation computation increasing with the disparity magnitude. We conclude that matching computation dominates fine depth perception, while both computations contribute to coarser depth perception. Thus, stereoscopic depth perception recruits different computations depending on the disparity magnitude.

Stereoscopic Depth Perception during Binocular Rivalry.

When we view nearby objects, we generate appreciably different retinal images in each eye. Despite this, the visual system can combine these different images to generate a unified view that is distinct from the perception generated from either eye alone (stereopsis). However, there are occasions when the images in the two eyes are too disparate to fuse. Instead, they alternate in perceptual dominance, with the image from one eye being completely excluded from awareness (binocular rivalry). It has been thought that binocular rivalry is the default outcome when binocular fusion is not possible. However, other studies have reported that stereopsis and binocular rivalry can coexist. The aim of this study was to address whether a monocular stimulus that is reported to be suppressed from awareness can continue to contribute to the perception of stereoscopic depth. Our results showed that stereoscopic depth perception was still evident when incompatible monocular images differing in spatial frequency, orientation, spatial phase, or direction of motion engage in binocular rivalry. These results demonstrate a range of conditions in which binocular rivalry and stereopsis can coexist.

Effects of age and optical blur on real depth stereoacuity

Stereoscopic depth perception utilizes the disparity cues between the images that fall on the retinae of the two eyes. The purpose of this study was to determine what role aging and optical blur play in stereoscopic disparity sensitivity for real depth stimuli. Forty-six volunteers were tested ranging in age from 15 to 60 years. Crossed and uncrossed disparity thresholds were measured using white light under conditions of best optical correction. The uncrossed disparity thresholds were also measured with optical blur (from +1.0D to +5.0D added to the best correction). Stereothresholds were measured using the Frisby Stereo Test, which utilizes a four-alternative forced-choice staircase procedure. The threshold disparities measured for young adults were frequently lower than 10 arcsec, a value considerably lower than the clinical estimates commonly obtained using Random Dot Stereograms (20 arcsec) or Titmus Fly Test (40 arcsec) tests. Contrary to previous reports, disparity thresholds increased between the ages of 31 and 45 years. This finding should be taken into account in clinical evaluation of visual function of older patients. Optical blur degrades visual acuity and stereoacuity similarly under white-light conditions, indicating that both functions are affected proportionally by optical defocus.

Analysis of disparity distortions in omnistereoscopic displays

An omnistereoscopic image is a pair of panoramic images that enables stereoscopic depth perception all around an observer. An omnistereo projection on a cylindrical display does not require tracking of the observer's viewing direction. However, such a display introduces stereo distortions. In this article, we investigate two projection models for rendering 3D scenes in omnistereo. The first is designed to give zero disparity errors at the center of the visual field. The second is the well-known slit-camera model. For both models, disparity errors are shown to increase gradually in the periphery, as visual stereo acuity decreases. We use available data on human stereoscopic acuity limits to argue that depth distortions caused by these models are so small that they cannot be perceived.

Stereoscopic perception of real depths at large distances

There has been no direct examination of stereoscopic depth perception at very large observation distances and depths. We measured perceptions of depth magnitude at distances where it is frequently reported without evidence that stereopsis is non-functional. We adapted methods pioneered at distances up to 9 m by R. S. Allison, B. J. Gillam, and E. Vecellio (2009) for use in a 381-m-long railway tunnel. Pairs of Light Emitting Diode (LED) targets were presented either in complete darkness or with the environment lit as far as the nearest LED (the observation distance). We found that binocular, but not monocular, estimates of the depth between pairs of LEDs increased with their physical depths up to the maximum depth separation tested (248 m). Binocular estimates of depth were much larger with a lit foreground than in darkness and increased as the observation distance increased from 20 to 40 m, indicating that binocular disparity can be scaled for much larger distances than previously realized. Since these observation distances were well beyond the range of vertical disparity and oculomotor cues, this scaling must rely on perspective cues. We also ran control experiments at smaller distances, which showed that estimates of depth and distance correlate poorly and that our metric estimation method gives similar results to a comparison method under the same conditions.

Monocular occlusions determine the perceived shape and depth of occluding surfaces

Recent experiments have established that monocular areas arising due to occlusion of one object by another contribute to stereoscopic depth perception. It has been suggested that the primary role of monocular occlusions is to define depth discontinuities and object boundaries in depth. Here we use a carefully designed stimulus to demonstrate empirically that monocular occlusions play an important role in localizing depth edges and defining the shape of the occluding surfaces in depth. We show that the depth perceived via occlusion in our stimuli is not due to the presence of binocular disparity at the boundary and discuss the quantitative nature of depth perception in our stimuli. Our data suggest that the visual system can use monocular information to estimate not only the sign of the depth of the occluding surface but also its magnitude. We also provide preliminary evidence that perceived depth of illusory occluders derived from monocular information can be biased by binocular features.

Opposite directions of motion enhance the perception of stereoscopic depth

Opposite directions of motion enhance the perception of stereoscopic depth

Drastic differences in binocular disparity tuning of V4 cells for random dots and solid figures: Quantitative analysis and mechanisms

A random-dot stereogram (RDS) contains many identical dots that give rise to numerous false matches for binocular correspondence. Thus, the determination of stereo matching is much more difficult when viewing an RDS than when viewing a solid-figure stereogram (SFS). Psychophysically, adaptation to left-right reversing spectacles differentially affects stereoscopic depth perception for figural stereograms than RDSs (Shimojo and Nakajima, 1981). In order to characterize the cortical processing required for stereoscopic depth perception when viewing RDSs and SFSs, we studied the responses of single neurons in area V4 to dynamic RDSs and SFSs (bars) in an alert, fixating monkey. Consistent with a previous study (Hegde and Van Essen, 2004), the binocular disparity tuning obtained with RDSs and SFSs differed markedly. Quantitative analysis revealed that the modulation amplitude, the tuning sharpness, and the preferred disparity of tuning curves tested with RDSs did not correlate with those of the SFSs, and the disparity tuning was sharper for RDSs than for SFSs. A possible cause of these differences may be the positional shift of monocular images that inevitably occurs with disparity changes in SFSs, but not in RDSs. We examined whether neuronal sensitivity for the positional shift of monocular images of SFSs could explain the differences in disparity tuning. In order to compensate for the response modulation caused by the monocular features of SFSs, we subtracted the linear sum of responses to the left and right monocular images from the binocular responses at each corresponding disparity. Despite this compensation, however, the differences between tuning curves obtained with the RDSs and SFSs remained essentially unaffected. A single read-out mechanism for V4 responses to the two types of stereograms would produce significantly different stereoscopic depth judgments. Our results suggest that stereo processing for RDSs and SFSs is not based on a single mechanism.

Time course of perceptual grouping by color

Does perceptual grouping operate early or late in visual processing? One position is that the elements in perceptual layouts are grouped early in vision, by properties of the retinal image, before perceptual constancies have been determined. A second position is that perceptual grouping operates on a postconstancy representation, one that is available only after stereoscopic depth perception, light- ness constancy, and amodal completion have occurred. The present experiments indicate that grouping can operate on both a precon- stancy representation and a postconstancy representation. Perceptual grouping was based on retinal color similarity at short exposure dura- tions and based on surface color similarity at long durations. These results permit an integration of the preconstancy and postconstancy positions with regard to grouping by color.

A Mathematical Expression for Stereoscopic Depth Perception

The metric nature of stereoscopic depth perception has remained an enigma. Several mathematical formulations proposed for measuring the stereoscopic effect have not shown to be reliable. This may be due to the lack of a conceptual distinction between the 3D model geometrically obtained by intersection of visual rays (geometric model), and the 3D model perceived in the observer's mind (perceptual model). Based on the assumption that retinal parallax is the only source of information on depth available to the brain, we developed an equation that shows real and perceptual space to be connected by a logarithmic function. This relationship has allowed us to formulate the vertical exaggeration for all sorts of stereoscopic conditions, including natural stereo-vision. The obtained formulations might involve possibilities of technological applications, such as the artificial recreation of a natural stereo-vision effect, and the design of stereoscopic instruments with a desired degree of vertical exaggeration.

Retinal-image quality and maximum disparity

The aim of this paper is to evaluate the role of interocular differences in retinal-image quality in stereoscopic depth perception. To characterize retinal-image quality, we took the Strehl ratio from a double-pass device. Stereopsis was quantified through maximum disparity using random-dot stereograms (RDS). Data were taken for 25 observers with ages ranging from 21 to 61 years. The results show a significant correlation between maximum disparity and interocular differences in the Strehl ratio: the lower interocular differences, the higher maximum disparity. No significant dependence with age was found.

Septa and processes: convergent evolution of the orbit in haplorhine primates and strigiform birds

According to the “nocturnal visual predation hypothesis” (NVPH), the convergent eyes and orbits of primates result from selection for improved stereoscopic depth perception to facilitate manual capture of prey at night. Within primates, haplorhines share additional derived orbital morphologies, including a postorbital septum and greater orbital convergence than any other mammalian clade. While the homology and function of the haplorhine septum remain controversial, experimental data suggest that septa evolved to inhibit mechanical disturbance of the orbital contents by the anterior temporalis muscle during mastication. According to this “insulation hypothesis,” haplorhines are particularly susceptible to disruption of the orbital contents because they have large and highly convergent eyes and orbits. However, comparative tests of the insulation hypothesis have been hindered by the morphological uniqueness of the haplorhine septum among mammals. Among birds, owls (Strigiformes) exhibit an expanded postorbital process that may be functionally analogous to the haplorhine septum. Here we present a comparative analysis of orbital morphology in 103 avian species that tests two hypotheses: (1) large, convergent orbits are associated with nocturnal visual predation, and (2) the strigiform postorbital process and haplorhine postorbital septum similarly function to insulate the eyes from contractions of mandibular adductors. Strigiforms, as nocturnal visual predators, possess relatively large orbits and exhibit the highest degree of orbital convergence in our sample. Notably, orbital convergence does not scale with orbit size in birds as in mammals. Owls are also unique among the birds examined in possessing extensive, plate-like postorbital processes that largely isolate the orbits from the temporal fossae. Furthermore, dissections of four owl species demonstrate that the expanded strigiform postorbital process deflects the path of mandibular adductors around the eye's inferolateral margin. These findings provide further comparative support for both the NVPH and the insulation hypothesis.

Neuromuscular Plasticity and Rehabilitation of the Ocular Near Response

The near response is composed of cross-coupled interactions between convergence and other distance-related oculomotor responses including accommodation, vertical vergence, and cyclovergence. The cross-coupling interactions are analogous to the body postural reflexes that maintain balance. Near-response couplings guide involuntary motor responses during voluntary shifts of distance and direction of gaze without feedback from defocus or retinal-image disparity. They optimize the disparity stimulus for stereoscopic depth perception and can be modified by optically induced sensory demands placed on binocular vision. In natural viewing conditions, the near response is determined by passive orbital mechanics and active-adaptable tonic components. For example, the normal coupling of vertical vergence with convergence in tertiary gaze is partly a byproduct of passive orbital mechanics. Both, adapted changes of vertical vergence in response to anisophoria, produced by unequal ocular magnification (aniseikonia), and adapted changes in the orientation of Listing's plane in response to torsional disparities can be achieved by a combination of passive orbital mechanics and neural adjustments for the control of the vertical vergence and cyclovergence. Adaptive adjustments are coupled with gaze direction, convergence angle, and head tilt. Several adaptation studies suggest that it is possible to achieve non-linear changes in the coupling of both vertical vergence and cyclovergence with gaze direction. This coupling can be achieved with changes in neural control signals of ocular elevator muscles that are cross-coupled with both convergence and direction of tertiary gaze. These linear and non-linear coupling interactions can be adapted to compensate for (1) anisophoria induced by spectacle corrections for anisometropia, (2) accommodative esotropia, (3) convergence excess and insufficiency, and (4) non-concomitant deviations with ocular torticollis associated with trochlear palsy. The adaptable near-response couplings form the basis of an area of orthoptics that optimizes visual performance by facilitating our natural ability to calibrate neural pathways underlying binocular postural reflexes.

54.4: Stereoscopic Depth Perception and Interocular Luminance Differences

AbstractWe investigated the effects of interocular luminance differences on stereoscopic depth perception. The stimuli were stereoscopic square‐shaped targets created from disparity embedded in a dynamic random‐dot stereogram, which eliminated other cues to depth perception. The results revealed that stereoscopic depth perception survived significant interocular differences in luminance levels, even up to differences of 60%, provided that display luminance was approximately 0.63 cd/m2 or higher. In terms of design criteria, developers of stereo displays can use a fairly large range of interocular luminance levels and still induce good stereo depth perception.

Stereoscopic depth perception survives significant interocular luminance differences

Abstract— The effects of interocular luminance differences on stereoscopic depth perception has been investigated. The stimuli were stereoscopic square‐shaped targets created from disparity embedded in a dynamic random‐dot stereogram, which eliminated other cues to depth perception. The results revealed that stereoscopic depth perception survived significant interocular differences in luminance levels, even up to differences of 60%, provided that display luminance was approximately 0.63 cd/m2 or higher. In terms of design criteria, developers of stereo displays can use a fairly large range of interocular luminance levels and still induce good stereo depth perception.