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At least 19 recordsLinked to original sources
PubMed2001

Human cortical activity correlates with stereoscopic depth perception.

Stereoscopic depth perception is based on binocular disparities. Although neurons in primary visual cortex (V1) are selective for binocular disparity, their responses do not explicitly code perceived depth. The stereoscopic pathway must therefore include additional processing beyond V1. We used functional magnetic resonance imaging (fMRI) to examine stereo processing in V1 and other areas of visual cortex. We created stereoscopic stimuli that portrayed two planes of dots in depth, placed symmetrically about the plane of fixation, or else asymmetrically with both planes either nearer or farther than fixation. The interplane disparity was varied parametrically to determine the stereoacuity threshold (the smallest detectable disparity) and the upper depth limit (largest detectable disparity). fMRI was then used to quantify cortical activity across the entire range of detectable interplane disparities. Measured cortical activity covaried with psychophysical measures of stereoscopic depth perception. Activity increased as the interplane disparity increased above the stereoacuity threshold and dropped as interplane disparity approached the upper depth limit. From the fMRI data and an assumption that V1 encodes absolute retinal disparity, we predicted that the mean response of V1 neurons should be a bimodal function of disparity. A post hoc analysis of electrophysiological recordings of single neurons in macaques revealed that, although the average firing rate was a bimodal function of disparity (as predicted), the precise shape of the function cannot fully explain the fMRI data. Although there was widespread activity within the extrastriate cortex (consistent with electrophysiological recordings of single neurons), area V3A showed remarkable sensitivity to stereoscopic stimuli, suggesting that neurons in V3A may play a special role in the stereo pathway.

Attention↗
PubMed2002

Functional MRI of self-controlled stereoscopic depth perception.

Stereoscopic depth perception was studied in healthy young adults using fMRI imaging at 2.0 T. In a novel paradigm we compared the cortical activation elicited by single-image stereograms which create alternating 2D and 3D percepts (event-related analysis triggered on the self-controlled switches between the two percepts) with the activation caused by a more conventional approach contrasting pairs of stereoscopic images with pairs of identical images (block design). The data show a distributed network of cortical areas embedded within the visual pathways that included about one-quarter of the cortical surface activated by 2D visual stimulation and about one-half of the area activated by 3D percepts based on stereoscopic image pair. 3D perception recruited mostly neuronal populations in higher order visual areas: whereas about 40% of the visually activated locations along the intraparietal sulcus were also activated by 3D perception based on single-image stereograms (resp. 90% stereoscopic images), only 10% such overlap was found in striate cortex. The study revealed no sup-port for a right-hemispheric lateralization of depth perception.

Adult↗
PubMed1999

Abnormal depth perception from motion parallax in amblyopic observers.

Many similarities exist between the perception of depth from binocular stereopsis and that from motion parallax. Moreover, Rogers (1984, cited in, Howard, I. P., & Rogers, B. J. (1995). Binocular vision and stereopsis. Oxford Claridon, New York.) suggests a relationship between an observer's ability to use disparity information and motion parallax information in a depth perception task. To more closely investigate this relationship, depth perception was studied in normal observers and amblyopic observers with poor stereo vision. As expected, amblyopic observers performed much worse than normal observers on depth discriminations requiring use of binocular disparity. However, amblyopic observers also performed much worse than normal observers on depth discriminations based on motion parallax. This result provides supporting evidence for a psychoanatomical link between the perception of depth from motion and the perception of depth from binocular disparity.

Amblyopia↗
PubMed1998

Top-down influences on stereoscopic depth-perception.

The interaction between depth perception and object recognition has important implications for the nature of mental object representations and models of hierarchical organization of visual processing. It is often believed that the computation of depth influences subsequent high-level object recognition processes, and that depth processing is an early vision task that is largely immune to 'top-down' object-specific influences, such as object recognition. Here we present experimental evidence that challenges both these assumptions in the specific context of stereoscopic depth-perception. We have found that observers' recognition of familiar dynamic three-dimensional (3D) objects is unaffected even when the objects' depth structure is scrambled, as long as their two-dimensional (2D) projections are unchanged. Furthermore, the observers seem perceptually unaware of the depth anomalies introduced by scrambling. We attribute the latter result to a top-down recognition-based influence whereby expectations about a familiar object's 3D structure override the true stereoscopic information.

Brain↗
PubMed1996

Depth perception in Alzheimer's disease.

Abnormal depth perception contributes to visuospatial deficits in Alzheimer's disease. Disturbances in stereopsis, motion parallax, and the interpretation of static monocular depth cues may result from neuropathology in the visual cortex. We evaluated 15 patients with mild Alzheimer's disease and 15 controls matched for age, sex, and education on measures of local stereopsis (stereoscopic testing), global stereopsis (random dots), motion parallax (Howard-Dolman apparatus), and monocular depth perception by relative size, interposition, and perspective. Compared to controls, the patients were significantly impaired in over-all depth perception. This impairment was largely due to disturbances in local stereopsis and in the interpretation of depth from perspective, independent of other visuospatial functions. Patients with Alzheimer's disease have disturbed interpretation of monocular as well as binocular depth cues. This information could lead to optic interventions to improve their visual depth perception.

Aged↗
PubMed1993

Clinicopathological correlations of visual depth perception in patients with cerebrovascular disease.

Visual depth perception in 100 patients with cerebrovascular disease was evaluated using the Titumus stereotest. Twelve patients showed depth perception impairment. CT scans revealed that the lesion was located on the right hemisphere in 6 patients and on the left hemisphere in 3 patients, and that the remaining 3 patients had multiple infarctions. 123I SPECT was performed in 7 patients with moderate to severe depth perception impairment, of whom 6 patients showed a reduced blood flow in the posterior half of both the right and left cerebral hemispheres. Moderate to severe impairment of depth perception was more frequently observed in patients with a lesion in the right hemisphere or in the posterior half of either hemisphere.

Aged↗
PubMed1997

Responses of primary visual cortical neurons to binocular disparity without depth perception.

The identification of brain regions that are associated with the conscious perception of visual stimuli is a major goal in neuroscience. Here we present a test of whether the signals on neurons in cortical area V1 correspond directly to our conscious perception of binocular stereoscopic depth. Depth perception requires that image features on one retina are first matched with appropriate features on the other retina. The mechanisms that perform this matching can be examined by using random-dot stereograms, in which the left and right eyes view randomly positioned but binocularly correlated dots. We exploit the fact that anticorrelated random-dot stereograms (in which dots in one eye are matched geometrically to dots of the opposite contrast in the other eye) do not give rise to the perception of depth because the matching process does not find a consistent solution. Anti-correlated random-dot stereograms contain binocular features that could excite neurons that have not solved the correspondence problem. We demonstrate that disparity-selective neurons in V1 signal the disparity of anticorrelated random-dot stereograms, indicating that they do not unambiguously signal stereoscopic depth. Hence single V1 neurons cannot account for the conscious perception of stereopsis, although combining the outputs of many V1 neurons could solve the matching problem. The accompanying paper suggests an additional function for disparity signals from V1: they may be important for the rapid involuntary control of vergence eye movements (eye movements that bring the images on the two foveae into register).

Animals↗
PubMed2003

Stereoscopic depth perception from oblique phase disparities.

In order to understand the role of oblique retinal image disparities in the perception of stereoscopic depth, we measured the depth perceived from random dot stereograms in which phase disparities were introduced in a selected band of stimulus orientations. A band of orientation was defined by a center orientation that ranged from 7.5 (near vertical) to 82.5 o[rientation]deg and by a bandwidth that was defined as the difference between the highest and the lowest orientation in the band. The bandwidths tested were 15, 30 and 45 odeg. A constant phase disparity of 90 p[hase]deg was introduced in all of the oriented spatial frequency components within the orientation band and the perceived depth of each stimulus was matched using a small square binocular probe. For each bandwidth, perceived depth increased with an increase in the center orientation up to approximately 60 odeg. This suggests that the human stereovision system derives a large proportion of information about perceived stereoscopic depth from oblique phase disparities. Simulations using an energy model of stereoscopic depth perception indicate that oblique phase disparities are unlikely to be processed by neural mechanisms tuned to near-vertical orientations within the stimulus. Our results therefore suggest that oblique retinal disparities are initially detected as oblique phase disparities by binocular mechanisms tuned to oblique orientations. Because the perceived depth from oblique phase disparities is consistent with the trigonometrically determined equivalent horizontal disparities, we presume that the information from oblique phase disparities is included in the visual system's computation of the horizontal retinal disparity.

Analysis of Variance↗
PubMed2001

Depth perception in telemedical consultations.

This study aimed at quantifying diminished depth perception in telemedicine due to the two-dimensional image and to devise coping strategies for the problem. Two hundred and thirty-five patients in the telemedicine room of a Minor Accident and Treatment Service were studied. The magnitude of impaired depth perception was noted. Seven coping strategies were used and the resolution of the problem was measured. Depth perception was judged to be less than 90% of binocular vision in 235 cases. This improved to more than 90% of binocular vision in 99 of the 234 cases (42.13%) when using of all strategies. Improvement by rotation of the camera 30 degrees at a time in the axial plane was the most useful strategy and it occurred in all 235 (100%) cases. Light adjustment and angulation occurred in 206 of 235 cases (87.66%). Comparison with the opposite side helped in 179 of 235 cases (76.17%), skin color and texture in 139 of 235 cases (59.15%), shutting one eye in 103 of 235 cases (43.83%), enlarging the image in 85 of 235 cases (36.17%), and diminishing depth of field of lens in 77 of 235 cases (32.77%). Other visual cues occurred in 63 of 235 cases (26.81%). Impaired depth perception is a significant problem in telemedicine. It can be improved to make a confident diagnosis in most cases by adopting a variety of strategies that are described in this paper.

Adolescent↗
PubMed1996

[Effect of interpupillary distance on acuity of depth perception].

BACKGROUND: Until today it is not really known, what kind of influence the interpupillary distance (IPD) has on depth perception. Actual literature says that haploscopic separation of pictures is of disadvantage for subjects with small IPD. This study intended to verify the influence of IPD on stereopsis in order to get valid and comparable results when testing the depth perception of different subjects. SUBJECTS AND METHODS: We examined 58 normosensoric soldiers for their stereoscopic sensation while changing their individual IPD. By using flexible flat plates of glass, the subjects' IPD could be changed infinitely variable to fix depth perception in haploscopic stereotesting. RESULTS: The variety of the interpupillary distance (IPD) of different people has to be strictly differentiated from the intraindividual changes of interpupillary distance, which, by a change of convergence, lead to a change of depth perception. A decrease in intraindividual IPD reveals an increase of depth perception. This change of perception follows, in mathematical terms, the law of logarithm. In case of intraindividual change of IPD the size of objects is also influenced. CONCLUSIONS: Using conventional stereotests, the IPD of different subjects has negligible influence on the depth perception. Different results of depth perception obtained with the help of stereoscopic examination of normosensoric subjects probably correspond with an individual and egocentric dealing with the visual localization of distances (distance between objects, size of objects, depth of objects).

Adult↗
PubMed1983

Depth perception of surfaces in pictures: looking for conventions of depiction in Pandora's box.

The perception of depth in monocularly viewed pictures has been investigated with the use of a binocular rangefinder developed by Gregory. Two experiments are reported which focus upon stimulus conditions that were identified by Haber as conventions for rendering depth in pictures. Several conclusions, which concern assumptions that must be made in interpreting pictures according to such conventions, are supported by the results. There is a default or assumed layout of background space. The interpretation of a point in a depiction depends upon the interpretation of neighboring points, so that interpretations of local features influence the interpretations of nearby 'empty' areas. In photographs, the magnitude of apparent depth depends upon the degree of discrepancy between the position of the illuminating source and the observer's supposed light-source position. Also in photographs, apparent depth increases as the contrast between highlights and attached shadows increases.

Cues↗
PubMed1987

Role of extraocular muscle proprioception in the development of depth perception in cats.

1. The ophthalmic branch of the trigeminal nerve (V1), which carries extraocular proprioceptive afferents, was sectioned unilaterally or bilaterally in kittens and adult cats. Depth perception was measured behaviorally in these sectioned cats, as well as in control cats. 2. For kittens that underwent unilateral V1 sections at 6-11 wk of age, postsurgical values of binocular depth perception--measured 1.5-3 mo later--were 2-3 times worse than in normal control animals. Cats that underwent unilateral V1 sections as adults, however, showed no postsurgical deficits in binocular depth perception. 3. For kittens that underwent bilateral V1 sections at 6.5-7.5 wk of age, similar longterm impairments were found in binocular depth perception. No impairment was found in two kittens bilaterally sectioned at 11.5 wk of age. A cat that underwent bilateral sections as an adult also showed no binocular depth perception deficits. 4. Although these behavioral effects were observed only when unilateral and bilateral V1 sections were performed up to a certain age in development, they differed in two ways. 1) Imbalance of extraocular proprioceptive inflow produced by unilateral section had a deleterious effect at an age when the final adult level had been reached. At that stage, complete suppression of inflow produced by the bilateral section failed to impair the final level of binocular performance. 2) Short-term effects observed during the week following the section appeared in bilaterally operated animals as a transient freezing of the presurgical binocular performance whatever the age of the section during the sensitive period. In contrast, short-term effects produced by unilateral section were found to be age dependent: a progressive slowing down in the normal rate of improvement of binocular thresholds was observed following a section performed at 5 wk of age; an arrest in development was found when surgery was done at 6-7 wk of age. A significant impairment appeared within 2 days when the section was performed at 11 wk of age. 5. In all experimental kittens, monocular depth perception thresholds were unaffected or impaired only to a minor extent (less than 15% change) following the unilateral or bilateral section. In unilaterally operated kittens, there were no consistent differences associated with the side of the section. 6. A sham-operated kitten, in which the V1 was visualized but not cut, showed no impairments in binocular or monocular depth perception.(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent Pathways↗