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PubMedDate not supplied

[Study of binocular vision by the binary metric method].

The authors describe a method for binocular vision studies with the use of spatial visual effects emerging when double images are fused in physiologic diplopia. Various forms of binocular cooperation were detected and a clinical classification of these forms developed, based on the ability to obtain a binocular visual image. One of the distinctions of the suggested method is the detection of not only binocular fusion, but of the ability to in-depth perception. The authors analyze the status of binocular function in subjects with various forms of binocular sensor cooperation, basing on binary metric data and the findings of the color test and synaptophore studies. Binocular cooperation impairments, detected by binary-metry, appear less severe than if detected by the color test or synaptophore studies in the same patients.

Adolescent↗
PubMed1998

Cortical area MT and the perception of stereoscopic depth.

Stereopsis is the perception of depth based on small positional differences between images formed on the two retinae (known as binocular disparity). Neurons that respond selectively to binocular disparity were first described three decades ago, and have since been observed in many visual areas of the primate brain, including V1, V2, V3, MT and MST. Although disparity-selective neurons are thought to form the neural substrate for stereopsis, the mere existence of disparity-selective neurons does not guarantee that they contribute to stereoscopic depth perception. Some disparity-selective neurons may play other roles, such as guiding vergence eye movements. Thus, the roles of different visual areas in stereopsis remain poorly defined. Here we show that visual area MT is important in stereoscopic vision: electrical stimulation of clusters of disparity-selective MT neurons can bias perceptual judgements of depth, and the bias is predictable from the disparity preference of neurons at the stimulation site. These results show that behaviourally relevant signals concerning stereoscopic depth are present in MT.

Animals↗
PubMed2002

Experiments on the role of painted cues in Hughes's reverspectives.

The English artist Patrick Hughes has created an extraordinary class of painted artpieces, most commonly referred to as 'reverspectives'. They consist of truncated pyramids and prisms with their smaller faces closer to the viewer, in such a way as to allow a realistic scene to be painted on them. The works of art contain rich perspective and other painted cues that conspire to elicit an illusory depth percept that is the reverse of the physical depth arrangement. This reverse depth is obtained under a wide range of viewing conditions, and competes with the veridical depth percept in a classical bistable paradigm that was found to exhibit a high degree of hysteresis. Under the illusory depth percept, reverspectives appear to move vividly as the viewer moves in front of them. This paper reports two experiments that were designed to assess the effectiveness of the painted cues in eliciting the illusory depth percept by using three different measures for the strength of the illusion. As expected, the illusion was favored by monocular viewing and large viewing distances. The results from these two experiments are in close agreement with each other, and they indicate that the painted cues are powerful in influencing the ultimate percept.

Cues↗
PubMed1996

Can random-dot stereograms serve as a model for the perception of depth in relation to real three-dimensional objects?

The ability to perceive depth in a random-dot stereogram is a valuable test for the perception of retinal image disparities, whether they arise from the viewing of a stereogram or from the viewing of a real 3-D object. However, a stereogram cannot be regarded as a proper model for the perception of depth in the case of a real 3-D object. This conclusion comes out most clearly in relation to changes in viewing distance. Whereas the viewing of real objects and stereograms both obey the rules of size constancy, this is not the case with depth constancy. With changes in viewing distance, the viewing of real objects obeys the rules of depth constancy. By contrast, the magnitude of the depth intervals in a stereogram are not constant but appear to increase in direct proportion to the increase in viewing distance. In a stereogram these changes in the amplitude of the depth intervals are based on the same mechanisms as those responsible for size constancy.

Convergence, Ocular↗
PubMed1997

Blur and contrast as pictorial depth cues.

Studies have shown that blur can act as a pictorial cue to depth perception. But blurring a stimulus reduces its contrast, and studies have also shown that contrast can act as a pictorial cue to depth perception. To determine whether blur and contrast have separate influences on depth perception, each variable was independently manipulated in two experiments. Observers reported depth alternations in a simple reversible figure. Both contrast and blur were found to influence depth perception, but blur had its greatest effect at moderate contrasts. When blurred and sharp stimuli were equated on either Michelson or RMS contrast, blur continued to affect depth perception. Hence blur can act as a depth cue independently of contrast. It is speculated that blur is effective as a pictorial cue because of its usual association with other depth cues, particularly in pictures and photographs.

Adult↗
PubMedDate not supplied

Is monocular perception of depth through the rigid endoscope a disadvantage compared to binocular vision through the operating microscope in paranasal sinus surgery?

Vision through the endoscope is strictly monocular. Perception of depth (stereopsis) during ethmoid surgery through the operating microscope would be expected to be superior due to binocular view. To investigate whether monocularity of the endoscope is a disadvantage in paranasal sinus surgery, we compared stereoacuity in a model of the nasal cavity using a headlamp, an operating microscope, and a 0 degree-Hopkins-endoscope. Twenty volunteers were asked to touch defined points in a spatial model of the nasal cavity. Due to the configuration of the model, which allowed binocular vision of all contact points with headlamp, performance was significantly better than with optical instruments. Manipulations were performed faster with the endoscope than with the microscope. Under microscopic guidance more faults in point sequence were made than with the endoscope. Various monocular phenomena obviously allow sufficient spatial orientation through the endoscope, so that monocularity of the endoscope appears not to be a disadvantage for quick and safe manipulations during functional endoscopic sinus surgery.

Depth Perception↗
PubMed2000

Neither occlusion constraint nor binocular disparity accounts for the perceived depth in the 'sieve effect'.

Current notions of binocular depth perception include (1) neural computations that solve the correspondence problem and calculate retinal positional disparity, and (2) recovery of ecologically valid occlusion relationships. The former framework works well for stimuli with unambiguous interocular correspondence, but less so for stimuli without well-defined disparity cues. The latter framework has been proposed to account for the phenomenon of perceived depth in stimuli without interocular correspondence, but its mechanism remains unclear. In order to obtain more insight into the mechanism, we studied the depth percept elicited by a family of stereograms - 'sieve' stimuli, adapted from Howard (1995) [Perception, 24, 67-74] - with interocular differences but no well-defined positional disparity cue. The perceived depth was measured by comparison to references at various depths established by standard retinal disparity and was consistently found to lie behind the fixation plane. Moreover, the magnitude of the depth percept depended on both the horizontal and vertical spatial characteristics of the stimulus in ways that were at odds with constraints of occlusion geometry. In comparison to the depth percept elicited by stimuli with well-defined disparity cues, the precision of the percept from the sieve stimuli was 10-20 times worse, suggesting that a different underlying computation was involved. Thus, neither of the above frameworks accounts for the depth percept arising from these stimuli. We discuss implications of our results for physiologically based computations underlying binocular depth perception.

Convergence, Ocular↗
PubMed1994

Contrast as a depth cue.

One consequence of aerial perspective is that far objects have lower contrast than near objects. We tested the efficacy of contrast as a cue for depth perception by measuring the apparent, relative depth of two areas that differed in contrast with a background and in size. We tested monocularly and binocularly. Differences in contrast were achieved by making the areas different in luminance, than varying the luminance of the background. Subjects reported that the area having lower contrast with the background appeared farther than the area having higher contrast. Even when size opposed it, contrast continued to have a significant effect on depth perception. Monocular observation yielded larger apparent depth than binocular observation. Contrast is an effective depth cue in the absence of any other depth information. We suggest that contrast acts as a pictorial depth cue simulating the optical effects of aerial perspective.

Contrast Sensitivity↗
PubMed1998

Vergence eye movements elicited by stimuli without corresponding features.

We have observed quantitative depth perception with a dichoptic stimulus which possessed no contrast-defined binocular corresponding features (phantom stereogram). The depth perception can be the result of appreciation of a partial-occlusion situation depicted by the stimulus, or the result of activities of low-level disparity detectors which are capable of combining dissimilar local features in the stimulus. Although both mechanisms predict similar depth perception, they predict different vergence eye-movement outputs, especially in the vertical dimension. To identify the underlying mechanisms of the phantom stereopsis, we recorded vergence tracking eye movements to four types of dichoptic stimuli: (a) conventional stereogram with horizontal disparity (HD); (b) horizontal phantom stereogram (HP); (c) conventional stereogram with vertical disparity (VD); and (d) vertical phantom stereogram (VP). We found that HD, HP, and VD stimuli could elicit robust vergence tracking eye movements but VP stimulus could not. While the success of HP stimulus in eliciting vergence tracking may be explained by proximal vergence, the failure of VP stimulus in eliciting vergence tracking clearly indicates that phantom stereogram could not elicit coherent responses among low-level disparity detectors. Partial occlusion, therefore, has to play an important role in the depth perception from the phantom stereogram.

Data Interpretation, Statistical↗
PubMed1983

The perception of depth contours with yellow goggles.

The ability of subjects to discriminate the depth of depressions in the snow was conducted at a cross-country ski area. The percentage of correct judgments on an overcast day was significantly greater with yellow goggles than with luminance-matched neutral goggles. This experiment, suggested by the chromatic-achromatic theory of color vision, indicates why yellow goggles are popular despite many previous unsuccessful attempts to prove their effectiveness.

Color Perception↗
PubMed1990

Perceptual deficits and the activity of the color-opponent and broad-band pathways at isoluminance.

The deficits in texture, motion, and depth perception incurred in monkeys at isoluminance were compared with the responses of neurons of the color-opponent and broad-band systems in the lateral geniculate nucleus. Texture perception, assumed to be carried by the color-opponent system, and motion and depth perception, ascribed to the broad-band pathway, were all found to be compromised but not abolished at isoluminance. Correspondingly, both the color-opponent and the broad-band systems were affected at isoluminance, but the activity of the neurons in neither system was abolished. These results suggest that impairment of visual capacities at isoluminance cannot be uniquely attributed to either of these systems and that isoluminant stimuli are inappropriate for the psychophysical isolation of these pathways.

Animals↗
PubMed1988

Perceptions of depth elicited by occluded and shearing motions of random dots.

A computer-controlled display of random dots was used to study perceptions of depth. In this display, a field of stationary random dots surrounded a rectangular area in which random dots moved with uniform velocity in a single direction. The boundaries of this rectangle did not move. When dot motion was perpendicular to the longer boundary of the rectangle (occluded motion), the rectangle seemed to be behind the stationary background surround. Motion parallel to the longer boundary of the rectangle (shearing motion) made it appear in front of the surround. The relative lengths of the sides of the rectangle determined which effect predominated. Thus, for motion perpendicular to the long axis of the rectangle the occlusion predominated and naive subjects reported that the central area seemed farther away than the surround. For shearing motion parallel to the long axis, the subjects reported that the rectangle was closer than the surround and the strength of both effects also depended on the length-to-width ratio of the rectangle. If there was occluded motion along the long axis, as the length-to-width ratio increased so did the likelihood that subjects would report seeing the rectangle behind the surround. Conversely, with shearing motion along the long axis, increasing the length-to-width ratio increased the likelihood that the rectangle would appear unambiguously in front of the surround. Some subjects integrated the two cues with the resulting perception being a rotating cylinder. The occlusion effect was stronger than the shearing effect.(ABSTRACT TRUNCATED AT 250 WORDS)

Acceleration↗
PubMed2002

[Synthesis of binocular disparity with motion parallax in depth slant perception: statistical efficiency approach].

Statistical efficiency approach is used in order to investigate sampling properties of both binocular disparity and motion parallax processes in depth slant perception and to examine the independent decisions model (Mulligan & Shaw, 1980) consisting of these processes. We carried out two experiments in which each cue was displayed solely (i.e., single condition) and both cues were displayed simultaneously (i.e., multiple condition). A two-alternative forced-choice (2AFC) task was used under the situation where a Gaussian noise was added to the stimulus value of depth slant. Statistical efficiencies were calculated in each experiment. The results showed that sampling size from binocular disparity was at least comparable or larger by a factor of 2.5-3.5 with that from motion parallax and that efficiencies of the multiple condition considerably exceeded those of the single condition. This suggests invalidity of the independent decisions model.

Cues↗
PubMed1984

Stereopsis from disparity of complex grating patterns.

Vertical grating patterns containing more than one spatial frequency component were presented stereoscopically. The depth percepts resulting from differences in relative horizontal position (or phase) in left- and right-eye views were measured using a depth-matching procedure. When the frequency components were similar in contrast, the depth percept was mediated by the overall disparity of the compound. However, a relatively low contrast component could make no contribution to the depth percept while still remaining clearly visible in the grating pattern. When two frequency components were equal in contrast but carried different individual disparities derived from local edge and spatial frequency information, the resulting percept contained multiple depth planes.

Depth Perception↗
PubMed1996

Dentists' variability in restorative decisions, microscopic and radiographic caries depth.

Restorative and dental caries depth decisions were recorded for 5168 un restored approximal tooth surfaces by 17 dentists who worked in the school dental clinics of the North York (Ontario) Public Health Department. Each dentist examined 15 pairs of experimental bitewing radiographs for which true caries depth had previously been determined by microscopy of the sectioned teeth following production of the radiographs. The dentists independently recorded their restorative decisions and radiographic caries depth perceptions. The relationship between the variation in the dentists' restorative decisions and their perceptions of caries depth based on a re-reading of the bitewings on the one hand, and true caries depth on the other was also examined. The percentages of total variability in each dentist's restorative decisions attributable to radiographic and to microscopic caries depth were estimated using regression analyses. Large variations were found among the 17 dentists' distributions of overall restorative and depth decisions. The relationship between microscopic caries depth and the dentists' restorative decisions was, understandably, less strong than that of the dentists radiographic perceptions of caries depth and restorative decisions. Relative to true caries depth, high numbers of false positive and false negative restorative decisions were made. Overall, 50% of the variability in the dentists' restorative decisions was explained by the perceptions of radiographic caries depth; however, among individual dentists, the range was from 29% for one dentist to 69% for another. A much lower percentage of the overall restorative variation was explained by microscopic depth, 18%. Like the finding of the only two previous European studies that quantified the role of radiographs on clinical decisions, this study demonstrated that dentists' perceptions of dental caries depth using bitewing radiographs play a major but variable role in their restorative decisions for approximal tooth surfaces.

Clinical Competence↗
PubMed1978

Improvement of visual acuity in partially and fully sighted subjects as a function of practice, feedback, and instructional techniques.

Three experiments were conducted to examine improvement of partially (20/200 or 6/60) and normally (20/20 or 6/6) sighted adults. Measures of resolution and vernier acuity were examined in the first two experiments to determine whether practice, feedback, and instructions would have differential effects on the degree of visual improvement achieved in a 20-min. testing session. The results indicated extensive visual work to be the important factor in the improvement of impaired vision. The third experiment compared monocular and binocular depth perception of individuals with unilateral optic atrophy. The results yielded an unexpected finding where binocular depth perception was, in most cases, inferior to that of the strong eye alone. The first two experiments demonstrated the possibility of improving impaired visual functions and the third experiment suggests important implications for a theoretical model of depth perception with limited vision.

Depth Perception↗
PubMed1997

Differences in perceived shape from shading correlate with activity in early visual areas.

The perception of shape from shading depends on the orientation of the shading gradient [1] [2] [3] [4]. Displays composed of elements with vertically oriented shading gradients of opposite polarity produce a strong and stable percept of 'concave' and 'convex' elements. If the shading gradients are rotated 90 degrees , the depth percept is reduced and appears much more ambiguous. Results from psychophysical [1] [2] [3] [4] [5] [6], neuropsychological [7] and computational studies [8] [9] suggest that the perception of shape from shading engages specific mechanisms in early cortical visual areas. In a three-dimensional functional magnetic resonance imaging (fMRI) study at 1.5 Tesla using a three-dimensional, interleaved-echoplanar imaging technique and a surface radio frequency (RF) coil placed under the visual cortex, we investigated the activity in these early visual areas associated with viewing shape from shading displays at two different orientations. We found significantly greater activation in area V1 and neighbouring low-level visual areas of cortex when subjects viewed displays that led to weak and unstable depth percepts than when they viewed displays that led to strong and stable depth percepts.

Adult↗
PubMed1988

[Binocular functional exploration: fundamental aspects and analysis by the Fusio-Test].

After reviewing psychophysical and neurophysiological data concerning disparity processing and stereoscopic depth perception, as well as the limits of variation in perceived depth and fusion in function of binocular disparity, a new computer controlled apparatus named Fusio-Test is presented for functional binocular exploration. A battery of stereograms available in the test library made it possible to study in particular depth perception or stereoacuity, aniseikonia and fixation disparity, using the most suitable preprogrammed psychophysical procedure such as the limit method, constant stimuli, Cornsweet's psychophysical staircase, and one alternative forced choice method or multiple choice method. The test selected for each phase of the binocular examination was presented in polarized light on two Video Units. The required measurements were displayed on a small terminal and occasionally the data variations were recorded in real time. For the control of depth perception and the evaluation of stereoscopic acuity, two types of tests were programmed: line stereograms made of series of vertical lines varying in number and relative spacing or stylized shapes, random dot stereograms with different cyclopean shapes (circle, square, triangle or scaled pyramid), some of them with reduced binocular correlation according to Julesz. The originality of this apparatus for aniseikonia lies in its use of a battery of Ogle's spatial test stereograms, having incorporated vertical and horizontal magnifications ranging from 0 to 15% by 1% increments. The measurements were obtained by trying to find the pair of stereograms that must be presented to the right and the left eyes in order to eliminate the perceived distorsions (geometric or induced effect) and to recover the normal classical configuration of the spatial test. The test for fixation disparity was comprised of the Ogle arrangement with two polarized vertical lines forming a binocular nonius in the middle of a field surrounded with letters to stimulate fusion. Data for a sample of observers wearing glasses, contact lenses or implants, are presented and analyzed, bringing to light certain anomalies in binocular disparity processing. Differences in stereoacuity are noted: partial or total stereoblindness depending on the test selected (line stereograms or random dot stereograms, crossed or uncrossed disparities), on the spacing of the test elements; variations of threshold in time.(ABSTRACT TRUNCATED AT 400 WORDS)

Aniseikonia↗