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PubMed2003

Eye movements provide the extra-retinal signal required for the perception of depth from motion parallax.

It has been unclear whether the perception of depth from motion parallax is an entirely visual process or whether it requires extra-retinal information such as head movements, vestibular activation, or eye movements. Using a motion aftereffect and static test stimulus technique to eliminate visual cues to depth, this psychophysical study demonstrates that the visual system employs a slow eye movement signal, optokinetic response (OKR) in particular, for the unambiguous perception of depth from motion parallax. A vestibular signal, or vestibularly driven eye movement signal is insufficient for unambiguous depth from motion parallax. Removal of the OKR eye movement signal gives rise to ambiguous perceived depth in motion parallax conditions. Neurophysiological studies suggest a possible neural mechanism in medial temporal and medial superior temporal cortical neurons that are selective to depth, motion, and direction of eye movement.

Depth Perception↗
PubMed2000

Binocular disparity can explain the orientation of ocular dominance stripes in primate primary visual area (V1).

In the primate primary visual area (V1), the ocular dominance pattern consists of alternating monocular stripes. Stripe orientation follows systematic trends preserved across several species. I propose that these trends result from minimizing the length of intra-cortical wiring needed to recombine information from the two eyes in order to achieve the perception of depth. I argue that the stripe orientation at any point of V1 should follow the direction of binocular disparity in the corresponding point of the visual field. The optimal pattern of stripes determined from this argument agrees with the ocular dominance pattern of macaque and Cebus monkeys. This theory predicts that for any point in the visual field the limits of depth perception are greatest in the direction along the ocular dominance stripes at that point.

Animals↗
PubMed1998

The perception of depth and slant from texture in three-dimensional scenes.

The perception of depth and slant in three-dimensional scenes specified by texture was investigated in five experiments. Subjects were presented with computer-generated scenes of a ground and ceiling plane receding in depth. Compression, convergence, and grid textures were examined. The effect of the presence or absence of a gap in the center of the display was also assessed. Under some conditions perceived slant and depth from compression were greater than those found with convergence. The relative effectiveness of compression in specifying surface slant was greater for surfaces closer to ground planes (80 degrees slant) than for surfaces closer to frontal parallel planes (40 degrees slant). The usefulness of compression was also observed with single-plane displays and with displays with surfaces oriented to reduce information regarding the horizon.

Computer Graphics↗
PubMed1993

Vergence eye movements facilitated by saccades.

This study was carried out to determine whether the vergence velocity is influenced or not by the richness in visual cues for the perception of depth and by the association of saccade. Vergence eye movements associated with and without saccades were recorded in 4 normal subjects with two CCD cameras in both dark and illuminated rooms. Subjects fixated between the targets, which differed in direction and in depth. The peak vergence velocity was 50 degrees to 90 degrees per second for 10 degrees vergence change and 30 degrees to 70 degrees per second for 5 degrees vergence change. Transient vergence change was found during horizontal or vertical saccade. Even after deleting this transient vergence change, the peak velocity of vergence became faster when it was associated with vertical or horizontal saccade. Trajectories of fixation locus were calculated when the vergence and saccade were required simultaneously. Whether or not the room was rich in visual cues for depth perception seemed to have no effect on vergence velocity. Blinking also speeded up divergence. Most eye movements in daily life are the combination of vergence and saccade, and this vergence facilitation by saccade helps to attain prompt binocular fixation on the new target.

Adult↗
PubMed1999

Visual characteristics of clay target shooters.

A comprehensive battery of standardised visual tests was administered to 11 skilled and 12 novice clay target shooters in an attempt to determine the distinctive visual characteristics of expert performers in this sport. The static and dynamic visual acuity, ocular muscle balance, ocular dominance, depth perception and colour vision of each of the subjects was measured in addition to their performance on simple and choice reaction time, peripheral response time, rapid tachistoscopic detection, coincidence timing and eye movement skills tasks. Expert superiority was observed on the simple reaction time measure only, and the novices actually outperformed the skilled subjects on a number of the other visual measures (viz., static acuity at near distance, dynamic acuity, vertical ocular muscle balance, choice reaction time and rapid target detection discriminability). Scores on all measures for both groups were within the expected normal range indicating that normal and not necessarily above-average basic visual functioning is sufficient to support skilled clay target shooting. An important implication of the finding that skilled shooters are not characterised by supranormal levels of basic visual functioning is the recognition that any attempt to improve shooting performance through training of general attributes of vision to supranormal levels is likely to be unproductive.

Adolescent↗
PubMed1985

Learning arthroscopy.

Problems have been uncovered in learning arthroscopy at the resident level or for the beginner at any level of orthopedic practice. The problems are varied, and are not all present in the same individual. This study delineates problems involving vision impairments, depth perception, spatial recognition, speed of accommodation, and data confrontation requiring immediate action. Speed is an additional factor in relation to accomplishing a task within an acceptable time limit. Through testing mechanisms, surgeons can discover their own inadequacies and thus learn to perform well in this new field.

Arthroscopy↗
PubMed1992

Binocular chromatic rivalry and single vision.

Depth perception is known to be impaired for chromatic equiluminant patterns. To investigate this phenomenon I have compared the effects of binocularly presented stimuli in the form of stripes, which contain only luminance information with similarly presented stimuli which contain only chromatic information. Observations of the reported percepts for the two conditions demonstrate that mechanisms of colour vision can impede stereopsis based on binocular fusion when the chromatic stripes are at, or even near, equiluminance, provided that their saturation is high. This observation is consistent with inhibitory interactions within the chromatic-sensitive neuronal groupings in the visual cortex.

Color Perception↗
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↗