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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↗
PubMed1994

Stereo vision by self-organization.

We propose a new algorithm for stereoscopic depth perception, where the depth map is the momentary state of a dynamic process. To each image point we assign a set of possible disparity values. In a dynamic process with competition and cooperation, the correct disparity value is selected for each image point. Therefore, we solve the correspondence problem by a dynamic, self-organizing process, the structure of which shows analogies to the human visual system. The algorithm can be implemented in a massive parallel manner and yields good results for either artificial or natural images.

Algorithms↗
PubMed2001

[The Goldmann Memorial Lecture--historical and current aspects of stereopsis].

According to Goldmann stereopsis is the highest performance of binocular recognition. A historical review shows that binocular stereopsis was explained only in 1838 by Wheatstone, whereas the monocular clues for stereopsis e.g. size, position and covering of the objects, light and shadow, perspective of the air, parallax and linear perspective were known long ago. The denomination depth perception is ambiguous: "depth" is the opposite of "height". Stereopsis means natural recognition of distance and objects in space, stereoscopy means recognition by the aide of an instrument. Natural and dichoptic stereopsis and the influences of vertical structures, of pupillary distance and of astigmatism are discussed. Examination of stereopsis is discussed, among others the two pencil test, the stereo-modification Bagolini-glasses, the combination of the plano-cylinders of W. R. Hess with random dots without glasses, the disk stereopsis etc. Goldmann's theory of binocular vision helps to understand different forms of strabismus, e.g. the statistical interplay of fixation and fusion for microtropia, the fixation mechanism for the congenital strabismus syndrome, the use of binocular stereopsis only for near explains intermittent divergence.

Depth Perception↗
PubMed1990

Performance consequences of two types of stereo picture compression.

Two algorithms for stereo picture compression were evaluated. According to one algorithm, consistent with the fusion theory of depth perception, the reduction of information in the two pictures was about equal. The other algorithm, consistent with the suppression theory of depth perception, was based on very deep compression of one picture and minimal reduction of information in the second picture. Subjects performed depth decisions and object decisions on the compressed picture. They were able to perform both tasks on the compressed pictures, though performance generally was worse than in the un-compressed control conditions. In both tasks performance was better for an uneven division of information between the two pictures. These results are consistent with the suppression theory of depth perception.

Adult↗
PubMed2000

Stereoscopic vision: what's the first step?

Neurons in primary visual cortex respond to binocular disparity, the raw material of stereoscopic depth perception. Although these neurons are probably essential to depth perception, a recent study has shown that they are unable to compute depth itself.

Animals↗
PubMed1995

Mechanisms of stereoscopic processing: stereoattention and surface perception in depth reconstruction.

Consideration of the range of phenomena from studies of human stereopsis suggests that a five-stage model is required to provide a complete account of the processes involved, within which any stereoattention mechanism must operate. The information from the disparity field of the optical projections to the two eyes (stage 1) goes to a set of parallel Keplerian arrays of disparity detectors, each array selective for a different spatiotemporal property of the visual images (stage 2). Global interactions produce a cyclopean depth image that is cleaned of the spurious ghost images in the Keplerian arrays (stage 3) and that may then be processed for its (hypercyclopean) from elements (stage 4). Finally, there must be a stage of integration of the stereoscopic depth cues with monocular and kinesthetic depth cues to form the overall map of perceived distance (stage 5). The fact that multiple cyclopean surfaces may be perceived as transparent implies that the stereoscopic system is not limited by a singular-surface constraint. However, it is unclear whether multiple surfaces can be seen simultaneously or whether only one surface is seen at a time by a selective-attention process, with the others perceived as a purely inchoate (qualitative) depth impression. New experiments on cueing of ambiguous stereocorrugations by singular flat planes suggest that selective stereoattention is a powerful mechanism. In fact, the results show that attention can be focused not just in horopteral planes but in a variety of depth configurations. Moreover, this attention focus may act as a tracking mechanism to allow perception of smooth cyclopean stereomotion, which has a frequency response up to approximately 5 Hz (in contrast to the approximately 15 Hz limit for detecting planar disparity shifts as jerky appearance and disappearance effects). Finally, the spatial limits of stereosurface reconstruction are explored with cyclopean targets to show some interesting asymmetries of the surface-wrapping process that may represent object-oriented constraints on depth reconstruction.

Attention↗
PubMed1996

Non-syncopal falls in the elderly in relation to home environments.

Methods of prevention of falls in the home may differ for healthy and frail individuals. We therefore sought to determine whether measures of health and functioning in older persons are more useful in predicting falls at home not involving home hazards (non-environmental falls) than falls at home related to home hazards (environmental falls), and whether these relationships differ among those who fell once and those who fell multiple times during follow-up. Data for this analysis are from a 1-year prospective cohort study of 325 community-dwelling volunteers aged 60-93 years who had fallen during the year before baseline. In general, associations were stronger between poor functional ability and non-environmental falls than between poor functional ability and environmental falls. Independent predictors of non-environmental first falls during follow-up included Parkinson's disease (adjusted odds ratio (AOR) 7.66, 95% confidence interval (95% CI) 1.15-51.1) and being home alone 10 or more hours per day (AOR 2.36, 95% CI 1.20-4.61); independent predictors of environmental first falls during follow-up included arthritis (AOR 2.60, 95% CI 1.32-5.09) and poor depth perception (AOR 0.73, 95% CI 0.59-0.89, for each unit increase in depth perception score). Also, associations between poor function and falls were generally stronger among participants who fell repeatedly than among individuals who fell only once during the follow-up year. In conclusion, poor function predisposes to non-environmental falls at home in older persons and, to a lesser extent, environmental falls in those who fall repeatedly. Certain functional characteristics such as poor depth perception may predispose to environmental falls to a greater extent than do other disabilities.

Accidental Falls↗
PubMed1982

Simultaneous and successive contrast effects in the perception of depth from motion-parallax and stereoscopic information.

Prolonged inspection of a three-dimensional corrugated surface resulted in a successive contrast effect, or aftereffect, of depth, whereby a subsequently-viewed physically-flat test surface appeared to be corrugated in depth with the opposite phase to the adapting surface. The aftereffect occurred both when the depth was specified by motion parallax, in the absence of all other sources of depth information, and when it was specified solely by stereoscopic information. The depth aftereffect was measured by 'nulling' the apparent depth in the test surface with physical relative motion or binocular disparity until the test surface appeared flat. Up to 70% of the depth in the adapting surface was necessary to null the aftereffect. Simultaneous contrast effects in the perception of three-dimensional surfaces were used to investigate the spatial interactions that exist in the processing of motion-parallax and stereoscopic information. A physically vertical surface appeared to slope in depth in the opposite direction to the slope of a surrounding surface. In this case up to 50% of the slope of the inducing surface was necessary to null the contrast effect. Similar results were again obtained for motion-parallax and stereoscopic depth.

Adaptation, Ocular↗