SEARCH · Search PubMed
Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
2-year-old children's pointing responses to the closer or farther of 2 pictured houses were consistently accurate when the depth information included either interposition or relative height in the picture plane. Picture-plane size was not an effective source of depth information. These results place the emergences of pictorial depth perception prior to 20 months of age for children with previous exposure to pictures.
OBJECTIVE: To review the clinical classification of strabismus, to describe the timing and method of strabismus screening examinations, and to discuss the principles of treatment. QUALITY OF EVIDENCE: Current literature (1983 to 1995) was searched via MEDLINE using the MeSH headings strabismus, ocular motility disorders, and amblyopia. Articles were selected based on their date of publication, clinical relevance, and availability. Preference was given to more recent articles, articles with large numbers of subjects, and well-designed cohort studies. Official recommendations from academic groups were analyzed. Descriptions of clinical tests and their illustrations are based on classic texts. MAIN FINDINGS: Primary care physicians should screen all low-risk children. High-risk children (low birth weight, family history of strabismus, congenital ocular abnormality, or systemic conditions with vision-threatening ocular manifestations) should be referred to an ophthalmologist for screening. Screening should be performed in the neonatal period, at 6 months, and at 3 years (Grade A recommendation), as well as at 5 to 6 years (Grade B recommendation). Screening examination includes inspection, examining visual acuity, determining pupillary reactions, checking ocular alignment, testing eye movements, and ophthalmoscopy. CONCLUSIONS: Primary care physicians are essential to early detection of strabismus and amblyopia. Early detection can help minimize visual dysfunction, allow for normal development of binocular vision and depth perception, and prevent psychosocial dysfunction.
In the present study some specific properties of the learning effects reported for random-dot stereograms are examined. In experiment 1 the retinal position-specific learning effect was reproduced and in a follow-up experiment it was shown that the position specificity of learning can be accounted for by selective visual attention. In experiments 2 and 3 evidence was obtained that suggests that observers can learn, to a certain degree, monocular random-dot patterns and that this learning facilitates the depth percept. This result indicates that the traditional belief that random-dot stereograms are devoid of monocularly recognizable or useful forms should be reconsidered. In the second set of experiments the learning of two binocular surface properties of random-dot stereograms, depth edges and internal depth regions, was investigated. It was shown in experiment 4 that the depth edges of random-dot stereograms are not learned, whereas the results of experiment 5 indicate that the internal depth regions are learned. Finally, in experiment 6 it was shown that depth edges are learned when the internal depth regions of the stereogram are ambiguous. The results are discussed in terms of the importance of the particular type of stimulus used in the learning process and in terms of perceptual learning and attention.
The ability of observers to extract depth from opposite luminance-contrast-polarity stimuli was investigated. The stimuli consisted of two dichoptic-pairs of Gaussians, with one of the Gaussians in each pair having a positive contrast-polarity and the other a negative contrast-polarity. Stimulus durations ranging from 0.2 to 4 s were used. This range of durations was employed to reveal stereo mechanisms that were preferentially sensitive to transient or sustained stimuli. Stimuli were presented in a raised-cosine temporal envelope. Performance with stimuli of the same contrast-polarity was also tested. Observers could easily perceive depth with the same-polarity stimuli, at both long and short durations. Depth could be perceived with low-contrast opposite-polarity stimuli only at short durations. However, depth could be perceived with long-duration stimuli presented within a raised cosine temporal-envelope if a high contrast was used. Depth could also be perceived with low-contrast long-duration stimuli if they were presented within a rectangular temporal-envelope. These findings suggest there are separate sustained and transient mechanisms for stereopsis and that the transient-stereoscopic system can extract depth from opposite-contrast stereograms while the sustained system cannot. Further, it is likely that depth perception with opposite-contrast stereograms found in many previous studies was mediated by the transient-stereopsis system.
A goal in visual neuroscience is to reveal how the visual system reconstructs the three-dimensional (3D) representation of the world from two-dimensional retinal images. Although the importance of texture gradient cues in the process of 3D vision has been pointed out, most studies concentrate on the neural process based on binocular disparity. We report the neural correlates of depth perception from texture gradient in the cortex. In the caudal part of the lateral bank of intraparietal sulcus, many neurons were selective to 3D surface orientation defined by texture gradient, and their response was invariant over different types of texture pattern. Most of these neurons were also sensitive to a disparity gradient, suggesting that they integrate texture and disparity gradient signals to construct a generalized representation of 3D surface orientation.
BACKGROUND: Head-mounted display (HM) units are used in various industries, but they have been tried only recently in surgery. In this study, we evaluated whether a commercially available HMD would improve or impede a laparoscopic task-in this case, suturing. METHODS: Six participants performed a total of 120 laparoscopic suture knots in an experimental model. The Olympus FMD011 model with a two-dimensional image was used. The order of each task with or without the head display unit was random. The time to complete each knot was recorded, and the results were analyzed. RESULTS: The display unit prolonged the suturing times of the subjects by 10% (p < 0.04). CONCLUSIONS: In this experimental model, the HMD we utilized did not appear to improve laparoscopic suturing. More developments, such as improved depth perception and better resolution, may increase its usefulness for laparoscopic tasks.
A parallel algorithm operating on the units ('neurons') of an artificial retina is proposed to recover depth information in a visual scene from radial flow fields induced by ego motion along a given axis. The system consists of up to 600 radii with fewer than 65 radially arranged neurons on each radius. Neurons are connected only to their nearest neighbors, and they are excited as soon as a sufficiently strong gray-level change occurs. The time difference of two subsequently activated neurons is then used by the last-excited neuron to compute the depth information. All algorithmic calculations remain strictly local, and information is exchanged only between adjacent active neurons (except for the final read-out). This, in principle, permits parallel implementation. Furthermore, it is demonstrated that the calculation of the object coordinates requires only a single multiplication with a constant, which is dependent on only the retinal position of the active neuron. The initial restriction to local operations makes the algorithm very noise sensitive. In order to solve this problem, a predication mechanism is introduced. After an object coordinate has been determined, the active neuron computes the time when the next neuronal excitation should take place. This estimated time is transferred to the respective next neuron, which will wait for this excitation only within a certain time window. If the excitation fails to arrive within this window, the previously computed object coordinate is regarded as noisy and discarded. We will show that this predictive mechanism relies also on only a (second) single multiplication with another neuron-dependent constant. Thus, computational complexity remains low, and noisy depth coordinates are efficiently eliminated. Thus, the algorithm is very fast and operates in real time on 128 x 128 images even in a serial implementation on a relatively slow computer. The algorithm is tested on scenes of growing complexity, and a detailed error analysis is provided showing that the depth error remains very low in most cases. A comparison to standard flow-field analysis shows that our algorithm outperforms the older method by far. The analysis of the algorithm also shows that it is generally applicable despite its restrictions, because it is fast and accurate enough such that a complete depth percept can be composed from radial flow field segments. Finally, we suggest how to generalize the algorithm, waiving the restriction of radial flow.
This project extends previous work on stereographic projection of 2D x-ray images and aims to overcome a number of problems, namely: confusing stereo cues; distortion between stereo pairs; and increased radiation exposure from additional x-ray images. Images are distortion corrected and a polygonal representation of a bone fitted to the x-ray image, to approximate the bone surface. The polygonal representation is rendered and blended with the x-ray image to add surface detail, without obscuring salient features within the original x-ray. A reduction in x-ray exposure by using a stereo pair of computer-generated polygonal bone images blended with a mono x-ray image is investigated. An experiment provides evidence that depth perception is increased with the inclusion of bone surface rendering, and is achievable with a mono x-ray image.
It is argued that (1) the work of Burt and Julesz does not challenge the classical notion of Panum's fusional area; (2) their disparity gradient concept is contradicted by some of their own findings as well as by those of Krol and van de Grind; (3) their results can be accounted for by the classical concept of Panum's fusional area if eye vergence is taken into account; (4) the explanations suggested by Burt and Julesz for the depth perception aspects of Panum's limiting case and the double-nail illusion are based on unwarranted generalisation of results concerning binocular direction vision.
Vision science is a truly interdisciplinary field of research, lying at the interface between psychology, computer science and neurobiology. It spans a broad range of research questions, from what visual neurons in the brain do, to the design and use of virtual reality technology. Here, I will take one well-researched area of human vision binocular depth perception, as an exemplar of the various ways in which the processes of human perception can be studied: from basic questions about the sensitivity of binocular vision to understanding how having two eyes helps us function in the natural environment.
In 11 normal healthy human subjects an evoked potential was elicited by moving dynamic random dot stereograms. The random dots were generated by a minicomputer. An average of each of 8 EEG channels of the subjects tested was made. The maximum of the cerebral evoked potentials thus found was localized in the central and parietal region. No response earlier than 130--150 msec after the stimulus could be proved. The influence of fixation, the number of dots provided, an interocular interstimulus interval in the presentation of the dots, and lense accommodation movements on the evoked stereoptic potentials was investigated and discussed. An interocular interstimulus interval (left eye leading) in the presentation of the dots caused an increase in latency of the response much longer than the imposed interstimulus interval itself. It was shown that no accommodation was needed to perceive the depth impression, and to evoke the cerebral response with random dot stereograms. There are indications of an asymmetry between the two hemispheres in the handling of depth perception after 250 msec. The potential distribution of the evoked potentials strongly suggests that they are not generated in the occipital region.
Functional MRI studies have identified a cortical region designated as KO between retinotopic areas V3A/B and motion area V5 in human cortex as particularly responsive to motion-defined or kinetic borders. To determine the response of the KO region to more general aspects of structure, we used stereoscopic depth borders and disparate planes with no borders, together with three stimulus types that evoked no depth percept: luminance borders, line contours and illusory phase borders. Responses to these stimuli in the KO region were compared with the responses in retinotopically defined areas that have been variously associated with disparity processing in neurophysiological and fMRI studies. The strongest responses in the KO region were to stimuli evoking perceived depth structure from either disparity or motion cues, but it showed negligible responses either to luminance-based contour stimuli or to edgeless disparity stimuli. We conclude that the region designated as KO is best regarded as a primary center for the generic representation of depth structure rather than any kind of contour specificity.
All major retinal pathways in the Siamese cat are abnormal, with almost total crossing of the projections to the pretectum and superior colliculus. These projections represent a marked disruption in the customary neural substrate for binocular vision, which implies a consequent impairment in stereoscopic depth perception. Crossed eyes, commonly seen in the Siamese cat, may therefore arise from a neuroanatomical defect in the primary visual pathways.
Natural stereopsis is better with a large interpupillary distance (IPD). With haploscopic devices, depth perception is better with a small IPD. This apparently unknown fact has been trigonometrically calculated and experimentally shown by enlarging and diminishing the IPD in 20 subjects.
We measure the performance of five subjects in a two-alternative-forced-choice slant-discrimination task for differently textured planes. As textures we used uniform lattices, randomly displaced lattices, circles (polka dots), Voronoi tessellations, plaids, 1/f noise, "coherent" noise and a leopard skin-like texture. Our results show: (1) Improving performance with larger slants for all textures, (2) and some cases of "non-symmetrical" performance around a particular orientation. (3) For orientations sufficiently slanted, the different textures do not elicit major differences in performance, (4) while for orientations closer to the vertical plane there are marked differences among them. (5) These differences allow a rank-order of textures to be formed according to their "helpfulness"--that is, how easy the discrimination task is when a particular texture is mapped on the plane. Polka dots tend to allow the best slant discrimination performance, noise patterns the worst. Two additional experiments were conducted to test the generality of the obtained rank-order. First, the tilt of the planes was rotated by 90 degrees. Second, the task was changed to a slant report task via probe adjustment. The results of both control experiments confirmed the texture rank-order previously obtained. We then test a number of spatial-frequency-based slant-from-texture models and discuss their shortcomings in explaining our rank-order. Finally, we comment on the importance of these results for depth-perception research in general, and in particular the implications our results have for studies of cue combination (sensor fusion) using texture as one of the cues involved.
We investigated the influence of temporal frequency on binocular depth perception in dynamic random-dot stereograms (DRS). We used (i) temporally correlated DRS in which a single pair of images alternated between two disparity values, and (ii) temporally uncorrelated DRS consisting of the repeated alternation of two uncorrelated image pairs each having one of two disparity values. Our results show that disparity-defined depth is judged differently in temporally correlated and temporally uncorrelated DRS above a temporal frequency of about 3 Hz. The results and simulations indicate that (i) above about 20 Hz, the complete absence of stereomotion is caused by temporal integration of luminance, (ii) the difference in perceived depth in temporally correlated and temporally uncorrelated DRS for temporal frequencies between 20 and 3 Hz, is caused by temporal integration of disparity.
This paper reviews much of the basic literature on stereopsis for the purpose of providing information about the ability of humans to utilize stereoscopic information under operational conditions. This review is organized around five functional topics that may be important for the design of many stereoscopic display systems: geometry of stereoscopic depth perception, visual persistence, perceptual interaction among stereoscopic stimuli, neurophysiology of stereopsis, and theoretical considerations. The paper concludes with the presentation of several basic ideas related to the design of stereoscopic displays.
This research develops design recommendations for surface textures (patterns of color on object surfaces) rendered with stereoscopic displays. In 3 method-of-adjustment procedure experiments, 8 participants matched the disparity of a circular probe and a planar stimulus rendered using a single visible edge. The experiments varied stimulus orientation and surface texture. Participants more accurately matched the depth of vertical stimuli than that of horizontal stimuli, consistent with previous studies and existing theory. Participants matched the depth of surfaces with large pixel-to-pixel luminance variations more accurately than they did surfaces with a small pixel-to-pixel luminance variation. Finally, they matched the depth of surfaces with vertical line patterns more accurately than they did surfaces with horizontal-striped texture patterns. These results suggest that designers can enhance depth perception in stereoscopic displays, and also reduce undesirable sensitivity to orientation, by rendering objects with surface textures using large pixel-to-pixel luminance variations.