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At least 541 records · Page 30Linked to original sources
PubMed1992

Occlusion as a depth cue in the Wheatstone-Panum limiting case.

We examined the hypothesis (Ono & Wade, 1985) that occlusion of far stimuli by a near one on the same visual line can operate as a depth cue in stereograms containing different numbers of targets in the two eyes. By controlling eye positions, we created conditions in which the visual system could interpret the retinal images as originating from stimuli on the visual axis of one eye and also created other conditions in which the origin of the retinal images was ambiguous. In Experiment 1, we presented two lines to one eye and a single line to the other eye. When the image of the line on the temporal side of the line pair on one retina fused with the image of the single line on the other retina, the nonfused line appeared farther away more often than it did when the image on the nasal side fused. In Experiment 2, we used two differently shaped stimuli. In the condition in which the nonfused stimulus represented an object being occluded, it appeared farther away more often than in the four conditions in which it did not. In Experiment 3, we extended the idea to three different objects. When the middle of the three images fused with the single image, the nonfused stimulus appeared farther when it could be interpreted as being occluded than when it could not. In the condition in which the most temporal image fused with the single image, the nonfused stimuli appeared farther than in the condition in which the most nasal one fused. The results supported the hypothesis that occlusion plays a role in depth perception in the Wheatstone-Panum limiting case.

Adult↗
PubMed1984

Binocular sensory fusion is limited by spatial resolution.

Binocular sensory fusion which was previously thought to have a maximum spatial extent at the fovea of 1 deg is at least 600% larger when stimulated by low spatial frequency (coarse) detail. This upper limit for sensory fusion has a constant phase disparity limit of 90 deg which corresponds to the monocular Rayleigh criterion for spatial resolution of two diffraction patterns. At low spatial frequencies the sensory fusion limit equals the upper disparity limit for stereoscopic depth perception which suggests that a common mechanism underlies these two phenomena.

Depth Perception↗
PubMed2001

Organisation of signals involved in binocular perception and vergence control.

A novel type of dynamic random-dot stereogram (DRS) was used to study vergence movements and depth detection in response to temporal modulations of interocular correlation. Each DRS consisted of the repeated presentation of a pair of correlated images alternated by the presentation of a pair of uncorrelated images. The intervals of high (T(c)) and low (T(u)) correlation varied from 14 to 224 ms in steps of 14 ms. Depth detection and vergence responses behaved very different from each other as functions of T(c) and T(u). The different behaviours suggest that depth and vergence most likely result from independent streams of disparity processing. It is speculated that magnocellular layers process disparities that drive vergence and that a parvocellular stream of disparity processing is involved in depth perception. This suggestion is discussed in relation to recent findings on binocularly perceived direction and depth. The discussion leads to suggesting a headcentric organisation of signals involved in binocular perception and a retinal organisation of signals involved in vergence control.

Adult↗
PubMed1996

Cues to illumination do not cause Coren and Komoda's illusion of lightness in an ambiguous tube.

The inside of a picture of a uniformly gray tube drawn with black circles appears lighter than the outside. Coren and Komoda, who first described this illusion, argued that observers take illumination into account to infer that the inside is lighter. That is, the inside of the tube should receive less illumination than the outside but reflects the same amount of light into the eyes. Observers, therefore, infer that it must be lighter. The inside of a gray tube drawn with white circles should appear lighter as well according to this account, but the experiments reported here show that the outside appears lighter in such a tube. We believe that depth perception is involved in this illusion but that lightness constancy is not.

Contrast Sensitivity↗
PubMed2005

Effect of interocular delay on disparity-selective v1 neurons: relationship to stereoacuity and the pulfrich effect.

The temporal properties of disparity-sensitive neurons place important temporal constraints on stereo matching. We examined these constraints by measuring the responses of disparity-selective neurons in striate cortex of awake behaving monkeys to random-dot stereograms that contained interocular delays. Disparity selectivity was gradually abolished by increasing interocular delay (when the delay exceeds the integration time, the inputs from the 2 eyes become uncorrelated). The amplitude of the disparity-selective response was a Gaussian function of interocular delay, with a mean of 16 ms (+/-5 ms, SD). Psychophysical measures of stereoacuity, in both monkey and human observers, showed a closely similar dependency on time, suggesting that temporal integration in V1 neurons is what determines psychophysical matching constraints over time. There was a slight but consistent asymmetry in the neuronal responses, as if the optimum stimulus is one in which the right stimulus leads by about 4 ms. Because all recordings were made in the left hemisphere, this probably reflects nasotemporal differences in conduction times; psychophysical data are compatible with this interpretation. In only a few neurons (5/72), interocular delay caused a change in the preferred disparity. Such tilted disparity/delay profiles have been invoked previously to explain depth perception in the stroboscopic version of the Pulfrich effect (and other variants). However, the great majority of the neurons did not show tilted disparity/delay profiles. This suggests that either the activity of these neurons is ignored when viewing Pulfrich stimuli, or that current theories relating neuronal properties to perception in the Pulfrich effect need to be reevaluated.

Action Potentials↗
PubMed1994

[VEPs induced by binocular disparity stimulus of the retinal nasotemporal overlap].

The human visual evoked potentials (VEPs) elicited by retinal disparity stimulation of the nasotemporal overlap area of the fundus, where ipsilaterally and contralaterally projecting retinal ganglion cells intermingle, were recorded bilaterally at the cortical hemispheres, and the contribution of the nasotemporal overlap to the mechanism of stereopsis was studied. The stimulus was a slit of a stereogram or correlogram applied to the center of the fovea of the right eye, or 3 degrees or 6 degrees nasal or temporal to the fovea. The negative waves of the VEPs evoked by the stereogram were located at O1 and O2. The VEP amplitudes evoked by the stereogram markedly exceeded those by the correlogram. In comparing the VEP amplitude of O1 with that of O2, when the slit of the stereogram hit the nasal side of the nasotemporal overlap O1 exceeded O2, and on the temporal side, this was reversed. The difference between the amplitudes at O1 and O2 was significant at 3 degrees from the fovea. These results showed electrophysiologically that the width of the nasotemporal overlap in the human retina is more or less 4 degrees and that the activity from the overlap area converges to disparity selective neurons in the visual cortex, suggesting that the overlap area is the region where cues to depth perception are obtained in the front-posterior plane of the fixation point.

Adolescent↗
PubMed1990

Behavioral effects of early postnatal lead exposure in herring gull (Larus argentatus) chicks.

Lead exposure early in life affects behavioral and intellectual development in humans. In this paper, I use the herring gull, Larus argentatus, as an animal model to examine effects of lead exposure on early development. Like humans, birds rely mainly on visual and vocal, rather than olfactory, modes of communication. Each of 24 one-day-old herring gull chicks was randomly assigned to one of three treatment groups to receive a lead nitrate solution at a concentration of 0.0, 0.1 and 0.2 mg/g. The control dose was an equal volume of sterile saline. The trios were not siblings, but were matched by weight. Behavioral tests were performed either daily, every two to five days, or at the end of the experiment (45 days posthatching), depending on the nature of the experiment. The behavioral tests examined locomotion, balance, righting response, begging, recognition, thermoregulation and visual cliff. Although on most days, begging behavior, balance and righting response did not differ significantly, over the 45 days of the experiment control birds performed better on more days than the lead-injected birds. Balance was disturbed by lead-injection for the first six days following injection. Individual recognition developed by day 5 in control birds, by day 10 for 0.1 Pb mg/g birds, and by day 14 for 0.2 Pb mg/g birds. Depth perception and thermoregulation behavior were also adversely affected by lead.

Animals↗
PubMed1980

On the depth of the cyclopean retina.

The maximum disparity which can elicit depth perception was measured in dynamic random-dot stereograms as a function of stimulus size and duration. Maximum disparity increased with size as a function of the square root of stimulus area, and depth could under optimal conditions be perceived up to several arc degrees of disparity, even for short (48 ms) durations of exposure. These data delineate the limiting disparity/depth characteristics of the cyclopean retina, and provide fresh evidence of the distinction between local and global disparity processing.

Animals↗
PubMed1995

Stereopsis due to luminance differences in the two eyes.

A local region in an image is seen as slanted when the two eyes are shown different luminance values in that region. The steepness of the slant depends upon the size of the region and the difference in the luminance values in the two eyes. Three examples where this phenomenon influences depth perception are given: (1) stereopsis without corresponding binocular luminance edges is shown to be a limiting case of the phenomenon; (2) edges less than 1 min arc apart can be seen in relative depth with respect to each other; and (3) regions that appear transparent or translucent can be seen in depth despite having all the luminance edges at zero disparity in simple stereo images.

Depth Perception↗
PubMed1982

Strabismus surgery and its effect upon infant development in congenital esotropia.

Parents of children with congenital esotropia have reported improvements in their child's fine motor development and visual functions after surgery. Eighteen patients with congenital esotropia were tested pre- and post-operatively with The Bayley Scales of Infant Development to determine if these observations were valid. A three-point increase in the Bayley raw score of strabismus patients was noted after operation that is significant at the 0.01 level, as compared to the performance of age-matched controls. An improvement in fine motor skills was observed in 35% of the children, and visually directed reaching and grasping increased in 41%. Item #87 on the Bayley, which requires the child to recognize depressions without monocular clues, appears to be related specifically to depth perception. On this item, the study population showed the greatest improvement.

Child Development↗
PubMed1997

Spatial scale in stereo and shape from shading: image input, mechanisms, and tasks.

The problem of spatial scale in depth perception can be considered at three stages: image input, mechanisms, and depth descriptors specific for certain tasks. A review is presented of a number of earlier experiments supporting the distinction between a coarse, correlation-based mechanism and a feature-matching mechanism of stereopsis in terms of their respective inputs and outputs. In order to measure the influence of the correlation mechanism on the perception of three-dimensional shape, a shape-probe experiment was designed. For smooth intensity profiles with constant disparity, the results show that perceived shape is largely independent of overall disparity but does make use of shape from shading as well as the assumption that brighter parts are in front (proximity-luminance covariance).

Depth Perception↗
PubMed1996

Perceiving the orientation-in-depth of triangular surfaces: static-monocular, moving-monocular, and static-binocular viewing.

Although data from simulations suggest that motion information and binocular information each elicit veridical depth perception, data from real stimuli, such as trapezoidal surfaces, are equivocal; the discrepancy might be explained by the complexity of nonveridical pictorial information in the latter. In the present study, observers judged the orientations-in-depth of triangular surfaces about a vertical axis: Pictorial information resided only in the visual lengths of surfaces, so it was predicted that motion and binocularity would be fully effective. Viewing conditions were static-monocular (SM), moving-monocular (MM), and static-binocular (SB). SM judgments were largely frontal, reflecting the equidistance tendency that applies in impoverished conditions. SB judgments were broadly veridical, as predicted. However, MM judgments were only partly influenced by motion information; the equidistance tendency and visual length also contributed--the latter in contrast to SM. It is concluded that motion information is only weakly effective, no matter what the complexity of pictorial information. Instead, motion may be valuable in enhancing pictorial information.

Adolescent↗
PubMed2001

The physiology of stereopsis.

Binocular disparity provides the visual system with information concerning the three-dimensional layout of the environment. Recent physiological studies in the primary visual cortex provide a successful account of the mechanisms by which single neurons are able to signal disparity. This work also reveals that additional processing is required to make explicit the types of signal required for depth perception (such as the ability to match features correctly between the two monocular images). Some of these signals, such as those encoding relative disparity, are found in extrastriate cortex. Several other lines of evidence also suggest that the link between perception and neuronal activity is stronger in extrastriate cortex (especially MT) than in the primary visual cortex.

Animals↗
PubMed1991

Stereoscopic display of MR angiograms.

Recent developments in magnetic resonance (MR) allow high resolution imaging of flowing blood. To overcome the tomographic nature of conventional MR acquisitions, projection angiograms can be produced. These angiograms are similar in their display of blood vessels to plain film or digital subtraction angiograms. However, the three-dimensional information inherent in them is partly lost when single projections are viewed. We describe a method of three-dimensional display consisting of stereo pairs of the MR angiograms. With these an examiner experienced in stereo viewing can recover depth perception.

Carotid Artery, Internal↗
PubMed2000

3-D vision improves performance in a pelvic trainer.

BACKGROUND AND STUDY AIMS: Experienced endoscopic surgeons have adapted to the absence of depth perception while using two-dimensional (2-D) visualization. However, three-dimensional (3-D) vision may prove useful at least at the beginning of the learning curve in celioscopic training. METHODS: In a pelvitrainer with a fixed camera, two skill tests were designed to assess the performance of three groups of operators: "non-surgeons", "non-celioscopist surgeons", and "trained celioscopists". In the first test, the candidate had to touch with a needle a sequence of dots distributed on a 7.1-cm2 area. In the second test, a 6-0 C-1 needle had to be passed consecutively through two 1-mm holes made in a thin vertical plastic wall. Each test was performed ten times, using either 2-D vision (five times) or 3-D vision (five times) interspersed in a random manner. RESULTS: In both tests and within each group, performance was related to the experience of the operator, with the trained celioscopists' group obtaining the best results and the non-surgeons the worst. In every situation, including the trained celioscopists' group, 3-D vision significantly improved performances. No significant difference was observed between the results of the non-celioscopist surgeons' group using 3-D vision and those of the trained celioscopists' group using 2-D vision. CONCLUSIONS: 3-D vision improves the performance and accuracy of endoscopic surgeons. It provides a visual perception "close to reality", and helps celioscopic beginners to accelerate their training.

Adult↗
PubMed1987

Interpolation and the detection of fine structure in stereoscopic matching.

Under some conditions, the perceived depth of a stereogram made of regularly-spaced points depends on the disparity of the edges of the stereogram rather than on discrete stereo matching of the points themselves. These depth percepts are seen only if the viewing time is brief, less than 2-3 sec, and the spacing between the points is small, less than 5-7 min of arc. In this paper, we examine the hypothesis that depth interpolation reflects a failure of the stereo matching apparatus to resolve the fine structure of the stereogram. We show that fine structure can be resolved during brief presentations (160 msec). It seems likely that interpolation represents an intermediate stage in the stereo matching process.

Convergence, Ocular↗
PubMed1973

Steroscopic vision: cortical limitations and a disparity scaling effect.

The spatial limitations of stereoscopic vision were studied by using vertical line stimuli containing sinusoidal disparity variations such that different parts of the line appeared at different depths. Stimuli with a finer grain than about 3 cycles per degree did not elicit depth perception, even though the sinusoidal curvature was clearly visible monocularly. At low spatial frequencies of curvature, stereoacuity was limited to the same extent as the monocular sensitivity. The limiting disparity for Panum's fusional region and the upper depth limit are subject to a scaling effect in proportion to stimulus dimensions. The disparity scaling can be characterized by a fixed maximum angular difference between the parts of the stereoscopic half-images.

Depth Perception↗
PubMed1989

The roles of convergence and apparent distance in depth constancy with motion parallax.

The question of whether motion parallax is calibrated by convergence or by apparent distance for depth perception was addressed in three experiments. In Experiment 1, a random dot parallactic display was viewed monocularly at a distance of 80 cm, and the convergence angles were set for distances of 40, 60, and 80 cm. Averaged apparent depth was not different across conditions. In Experiment 2, a display consisting of one surface showing dollar bills and one surface showing random dots was viewed monocularly at a distance of 80 cm. It was presented at two different apparent distances, which were manipulated by varying the size of the dollar bills. In one condition, normally sized dollar bills were presented, and in another condition, the size was reduced by 30%. The averaged apparent depth associated with the small-bill display was larger than the depth associated with the normally sized bill display. In Experiment 3, a random dot display was viewed monocularly at 120 cm. In the primary condition, the random dot display was viewed with an induction screen at 80 cm, and it was moved from side to side such that it appeared stationary and close to the plane of the induction screen. In a comparison condition, the display was viewed without the induction screen and was moving from side to side at 120 cm. In another comparison condition, the display was again viewed without the induction screen but was stationary at 120 cm. Observers adjusted the extent of motion parallax so that apparent depth was 1 cm. The mean extent of parallax was larger in the primary conditio.(ABSTRACT TRUNCATED AT 250 WORDS)

Accommodation, Ocular↗