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PubMed1964

BINOCULAR DEPTH PERCEPTION WITHOUT FAMILIARITY CUES.

The reported phenomena were obtained through the use of special techniques. (i) All monocular depth and familiarity cues were removed from the stimuli (through the use of randomdot stereo patterns). (ii) The statistical and topological properties of the stimuli were precisely known (since they were generated according to a specific computer program). (iii) Convergence motions of the eye and proprioceptive cues were eliminated (through the use of tachistoscopic illumination). (iv) The time of presentation was under control (through erasure of the persistent afterimages). Under these conditions stereopsis could be studied in its purest form. It was shown that depth can be perceived in the absence of monocular depth and familiarity cues and of all binocular depth cues except for disparity. These findings have important implications for some existing theories of stereopsis and open up areas for further research. Some phenomena based on stereo erasure are reported here for the first time. It has been demonstrated that the perception of ambiguous depth organizations can be influenced, even subliminally, by a preceding unambiguous stimulus. Perhaps the most interesting result is the finding that the correspondence of objects and patterns in the two retinal projections can be established without actual recognition of the objects and patterns. This pattern matching is based on some relatively simple processes of finding connected clusters formed by adjacent points of similar brightness, and the processes seem to be amenable to rigorous analysis.

Biomedical Research↗

PubMed2004

Slant from texture and disparity cues: optimal cue combination.

How does the visual system combine information from different depth cues to estimate three-dimensional scene parameters? We tested a maximum-likelihood estimation (MLE) model of cue combination for perspective (texture) and binocular disparity cues to surface slant. By factoring the reliability of each cue into the combination process, MLE provides more reliable estimates of slant than would be available from either cue alone. We measured the reliability of each cue in isolation across a range of slants and distances using a slant-discrimination task. The reliability of the texture cue increases as |slant| increases and does not change with distance. The reliability of the disparity cue decreases as distance increases and varies with slant in a way that also depends on viewing distance. The trends in the single-cue data can be understood in terms of the information available in the retinal images and issues related to solving the binocular correspondence problem. To test the MLE model, we measured perceived slant of two-cue stimuli when disparity and texture were in conflict and the reliability of slant estimation when both cues were available. Results from the two-cue study indicate, consistent with the MLE model, that observers weight each cue according to its relative reliability: Disparity weight decreased as distance and |slant| increased. We also observed the expected improvement in slant estimation when both cues were available. With few discrepancies, our data indicate that observers combine cues in a statistically optimal fashion and thereby reduce the variance of slant estimates below that which could be achieved from either cue alone. These results are consistent with other studies that quantitatively examined the MLE model of cue combination. Thus, there is a growing empirical consensus that MLE provides a good quantitative account of cue combination and that sensory information is used in a manner that maximizes the precision of perceptual estimates.

Cues↗

PubMed1990

Comparison of disparometer fixation disparity curves as measured with and without the phoropter.

Traditionally, Disparometer fixation disparity curve (FDC) measurement has been performed using a phoropter, although more recently some clinicians have suggested that the Disparometer be used outside the phoropter. Whereas vertical fixation disparity (FD) measurements have been found to correlate well when obtained with and without a phoropter, there is currently no evidence that horizontal FDC's are similar in the two testing situations. A FDC was plotted for 30 visually asymptomatic young adults both in and out of the phoropter. Statistical analysis revealed no significant differences between results on the basis of curve type, slope, y- or x-intercept; however, noteworthy individual variations did occur. Therefore, we conclude that consistency of testing method is important when serial curves are plotted for a given patient. Although each method has some advantages and disadvantages, neither is clearly superior based on this study.

Adult↗

PubMed2005

The role of (micro)saccades and blinks in perceptual bi-stability from slant rivalry.

We exposed the visual system to an ambiguous 3D slant rivalry stimulus consisting of a grid for which monocular (perspective) and binocular (disparity) cues independently specified a slant about a horizontal axis. When those cues specified similar slants, observers perceived a single slant. When the difference between the specified slants was large, observers alternatively perceived a perspective- or a disparity-dominated slant. Eye movement measurements revealed that there was no positive correlation between a perceptual flip and both saccades (microsaccades as well as larger saccades) and blinks that occurred prior to a perceptual flip. We also found that changes in horizontal vergence were not responsible for perceptual flips. Thus, eye movements were not essential to flip from one percept to the other. After the moment of a perceptual flip the occurrence probabilities of both saccades and blinks were reduced. The reduced probability of saccades mainly occurred for larger voluntary saccades, rather than for involuntary microsaccades. We suggest that the reduced probability of voluntary saccades reflects a reset of saccade planning.

Blinking↗

PubMed1995

Control of vertical eye alignment in three-dimensional space.

A target that is nearer to one eye than the other subtends a larger visual angle in the closer eye. Consequently, when making saccades between vertically separated targets that are closer to one eye, there is a vertical retinal disparity that must be overcome by a change in the relative alignment of the eyes. We recorded eye movements in three normal subjects and showed that in such viewing circumstances subjects made unequal vertical saccades that led to a rapid change (peak velocity up to 30 deg/sec) in vertical eye alignment. On average, 81% of the required change in alignment occurred within the saccade for downward movements and 47% for upward movements. Such unequal vertical saccades occurred independently of immediate disparity cues; saccades remained unequal when refixing to the remembered locations of the vertically-oriented targets, or even when the natural vertical disparity was nullified by a prism. On the other hand, when subjects wore the nullifying prism in front of the inferior visual field of the left eye for 8-20 hr, they showed a decrease in saccade disconjugacy (to 12-35% of the preadaptation value) to targets closer to the left eye in the inferior but not in the superior visual field. We suggest that the brain develops a three-dimensional map (horizontal, vertical, depth) for vertical saccade yoking, which is under adaptive control, and which is used to preprogram automatically the relative excursions of the eyes during vertical saccades as a function of the current and the desired point of regard.

Adaptation, Ocular↗

PubMed2005

Binocular depth perception from unpaired image points need not depend on scene organization.

Dichoptic stimuli containing unmatched features can produce depth perception despite the absence of binocular disparity, a phenomenon known as da Vinci stereopsis. Unmatched points can arise from depth discontinuities and partial occlusion in the real world. It has been hypothesized that spatial organization of unmatched image features as dictated by the ecological optics of occlusion might determine perceived depth in da Vinci stereopsis. We tested this hypothesis by creating dichoptic stimuli containing unmatched points in which local cues and overall organization could be dissociated. For these stimuli, observers' perception of depth did not depend on the organization of the scene, but only on the local cues. This finding shows the perceived depth of unpaired points need not depend on reconstructing the spatial organization of depth discontinuities in real-world scenes.

Depth Perception↗

PubMed1989

Neural and psychophysical correlates of induced interocular transmission disparities.

We investigated the influences of luminance and temporal asymmetries on the pattern visually evoked potential (pVEP) as a function of stimulus contrast. Monocular and binocular baseline steady-state (ss) and transient (t) pVEP's were recorded on 10 visually normal young adults using a reversing checkerboard pattern ranging in contrast from 4 to 65%. Neutral density (ND) filters were then placed before the right eye in 0.5 ND increments (maximum 3.5 ND), as monocular and binocular pVEP's were recorded. Visual acuity, brightness sense, and the Pulfrich effect were then measured to similar luminance and temporal asymmetries. Neural and psychophysical data were compared. Monocular visual acuity and pVEP results appeared to be luminance-dependent. Brightness sense, the Pulfrich effect, and binocular pVEP amplitudes appeared to be temporarlly dependent. The binocular pVEP amplitude seemed to be less sensitive to temporal asymmetries for lower contrast targets.

Adult↗

PubMedDate not supplied

Impaired binocular depth inversion in patients with alcohol withdrawal.

Binocular depth inversion represents an illusion of visual perception. Such inversion does not occur in all cases, especially when objects with a higher degree of familiarity (e.g. photographs of faces) are displayed. Cognitive factors are assumed to override the binocular disparity cues of stereopsis. We tested the hypothesis that during alcohol withdrawal the human CNS is unable to correct the implausible perceptual hypothesis. Measurements of binocular depth inversion in perception of 3D objects were performed in 10 patients with mild alcohol withdrawal and in 11 healthy volunteers. The binocular depth inversion scores were highly elevated in the patients group in comparison to the healthy volunteers. The data demonstrates a strong impairment of binocular depth inversion in alcohol withdrawal and support the view that alcohol withdrawal may be accompanied by a disorganization of the interaction between sensory input and generation of perceptual hypotheses.

Adult↗

PubMed1997

[Pro-psychotic change of binocular depth inversion by sleep deprivation].

Binocular depth inversion represents an illusion of visual perception. Such inversion does not occur in all cases, especially when objects with a higher degree of familiarity (e.g. photographs of faces) are displayed. Cognitive factors are assumed to override the binocular disparity cues of stereopsis. We tested the hypothesis that during sleep deprivation the human CNS is unable to correct the implausible perceptual information. Measurements of binocular depth inversion in perception of 3D objects were taken in sleep-deprived medical staff and healthy volunteers. The binocular depth inversion scores were highly elevated in the sleep-deprived group in comparison to the healthy volunteers. The data demonstrate a strong impairment of binocular depth inversion after sleep deprivation and support the view that sleep deprivation may be accompanied by a disorganisation of the interaction between sensory input and generation of perceptual hypotheses.

Adult↗

PubMed1991

[Behavior of the other eye in measuring fixation disparity].

In the subjective measurement of FD, the proband fuses contours presented in the peripheral macular areas of both eyes ('fusion lock'). The position of both eyes relative to each other is monitored by means of two haploscopically seen vertical lines presented in the central visual field, one above and one below a binocularly seen horizontal line. The subject is instructed to shift one of the vertical lines horizontally until the two are aligned, while fixating their intersection with the horizontal line. It has recently been questioned whether the foveolae really are pointed at the perceived intersection. To investigate this matter, we registered the position of one eye while intermittently covering the fellow eye, while the subject maintained fixation of the intersection. We found slight differences in monocular eye position depending on the presence or absence of fusion in the macular periphery, confirming earlier findings in part. These differences were more pronounced in the nondominant eye.

Adult↗

PubMed1995

Speed discrimination of motion-in-depth using binocular cues.

Although it is well known that motion-in-depth can be detected using binocular cues, it is not known whether those cues can be used to judge the speed of an object moving in depth. There are at least two possible binocular cues that could be used by the visual system to calculate three dimensional (3-D) speed: the rate of change of binocular disparity, or a comparison of the speeds of motion in the two eyes. We tested which of these cues is used to discriminate the speed of motion-in-depth. First, speed discrimination was measured for a dot moving away from the observer in depth (along the z-axis) and for a random dot stereogram in which a central square moved away from the observer in depth. These stimuli contained both disparity and monocular motion cues. Speed discrimination thresholds were as good for 3-D motion as for monocular sideways motion. Second, a dynamic random dot stereogram (in which the random dot pattern was replaced by a new dot pattern every frame) was used to remove consistent monocular cues. 3-D speed discrimination was now very poor, suggesting that the rate of change of disparity is not a good cue for 3-D speed. Finally, we tested whether observers were able to use the monocular motion cue from one eye to perform the speed discrimination task, or whether there had to be a comparison of the two eyes' monocular cues. By adding a small x-axis velocity component (with random direction) to the z-axis motion, it was possible to disrupt the monocular motion signals without altering the speed of the motion in 3-D. This manipulation did not disrupt the observers' performance, suggesting that monocular speed cues were not being used independently but that there was a comparison of monocular motion signals from the two eyes.

Cues↗

PubMed2001

Envelope size tuning for stereo-depth perception of small and large disparities.

Stereopsis is the sense of depth derived from binocular disparities that are formed between targets that are matched between the two retinal images. Binocular matches for sustained stereopsis are based on similarity of orientation, spatial frequency and contrast of the two retinal images whereas matches for transient stereopsis depend on these parameters to a very limited extent. In this investigation we have tested the possibility that transient stereopsis forms matches between objects of similar overall size. The tuning of sustained and transient stereopsis to contrast-envelope size was investigated by presenting narrow-band Gabor targets of unequal size to the two eyes. Bandwidth for envelope-size tuning was estimated from the range of dichoptic size-differences over which stereo performance remained above chance level. An equal bandwidth of 2 octaves was found for the sustained and transient stereo systems when stimulated with parallel orientation Gabors that subtended a small disparity. Sustained-stereo performance with orthogonal carriers was reduced with large envelope sizes. Bandwidth of the transient stereo system increased to 3 octaves when tested with a larger disparity stimulus and it was independent of carrier orientation. Reducing the contrast of the larger-size Gabor improved transient-stereo performance from near chance (48-58%) to 85-95%. Thus the bandwidth for envelope-size tuning is much broader than indicated with equal physical contrast stimuli. The observed tuning to envelope size, while broad, is tighter than that observed for carrier spatial-frequency [Vis. Res. 38 (1998) 3057], carrier orientation [Vis. Res. 39 (1999) 2717] and contrast polarity [Vis. Res. 39 (1999) 4010] of the stimulus. Thus it would appear that envelope size and, to a greater extent, temporal synchrony of the dichoptic stimuli [Perception 24 (1995) 33] are the primary means for selecting matched binocular inputs for transient stereopsis.

Contrast Sensitivity↗

PubMed1996

A clinical evaluation of stereopsis required to see 3-D images.

Some children with esotropia who have been diagnosed as 'stereoblind' on the basis of conventional stereotests (which principally use static images with small disparity) may nevertheless enjoy stereopsis for three-dimensional (3-D) animations that use dynamic images with large disparity. The purpose of this study was to develop a new stereotest equipped with dynamic random-dot stereogram (DRDS) which has larger disparity with movement and use it with esotropic children to see if they can attain stereopsis for such images. Subjects were 17 esotropic children between 5 and 10 years old (mean age 6.8 years) who had failed to demonstrate stereopsis with the Titmus fly test. Seven children had infantile esotropia and 10 had partially accommodative esotropia. The test images were DRDS that were presented on a fluorescent screen (12 x 9 cm) viewed through a lenticular lens. The dots were displayed in circle and triangle patterns that have counterphase front-rear movement with maximum disparity of 800 s. Patients were placed with eyes at a distance of 60 cm from the screen and were instructed to point out the pattern (circle or triangle) that was produced. The average angle of strabismus was 7.7 delta by alternating prism cover test (5 m). Seven patients passed and 10 failed the DRDS test. There was no significant difference in the mean angle of strabismus or the age of examination between the two groups; however, the age at onset of strabismus was significantly higher in those who passed the DRDS test. These results suggest that the DRDS test is useful in evaluating the potential stereopsis in children with esotropia who do not pass conventional stereotests.

Accommodation, Ocular↗

PubMed2001

Double fusion does not occur in Panum's limiting case: evidence from orientation disparity.

When two lines of different orientations are combined in regular stereograms, the orientation of the resulting line is different from those of the monocular lines. In this study we investigate the percept elicited by orientation disparity in Panum's limiting case. A variant of Panum's limiting case was designed to include orientation disparity. The single line in one half-image tilted leftwards. One of the double lines in the other half-image was parallel to the single line, while the other one tilted rightwards with obliquity one third that of the single line. In this stimulus configuration, if the single line in one half-image fuses with both lines in the other half-image at the same time, both of the two lines perceived after fusion should tilt leftwards. If double fusion does not happen, the two lines should tilt leftwards and rightwards respectively. The results of this study are in agreement with the latter prediction, which implies that double fusion does not occur in this variant of Panum's limiting case.

Depth Perception↗

PubMed1996

Is the site of non-linear filtering in stereopsis before or after binocular combination?

There is recent evidence that both linear and non-linear filtering operations subserve stereoscopic localization. For example, for spatially band-pass stimuli, the overall Gaussian envelope, which is not explicitly represented by the output of linear filters, can provide coarse disparity information. Here we ask three questions about the nature of this non-linear processing in stereopsis. First, is the site of the non-linearity before or after binocular combination? Second, is the stimulus envelope extracted by orientation or non-orientation selective spatial filters? Finally, we ask whether the envelope-based 3-D localization performance is similar to that for monocular 2-D localization as would be the case if the localization of the monocular contrast envelope was common to both operations. Our results suggest that envelope extraction occurs before binocular combination and that the filters involved are orientation selective. Finally, we provide preliminary evidence that is compatible with the proposal that 3-D and 2-D localization use the same envelope extraction operations.

Contrast Sensitivity↗

PubMed2002

A planar and a volumetric test for stereoanomaly.

Stereoanomaly is the failure to see differences in depth when the viewer is presented with stimuli having different magnitudes of stereoscopic disparity. In the absence of eye movements, everyone suffers from stereoanomaly for extremely large disparities. Typically, such disparities are seen at the same depth as monocular stimuli. However, about 30%, of the population exhibit some form of stereoanomaly even for very small disparities, provided eye movements are avoided. In some cases, the sign of the disparity will be confused, and the perceived depth will be incorrectly seen as 'behind' rather than 'in front of' the fixation point, for example. Because anomalies provide useful information about perceptual mechanisms, tests that measure and quantify the extent of a blindness are important investigative tools for research. Here we offer two easy-to-administer tests for stereoanomaly. The first test is based on depth judgments of two bars relative to a fixation point. The second test involves judgments of volumetric stimuli, seen stereoscopically. In each case, subjects indicate depth by setting a rectangle (with fixed base) to match the perceived depth. Although both tests are correlated, some differences in stereo processing are seen, depending upon whether or not the stimuli are presented near the point of fixation.

Depth Perception↗

PubMed1998

Extra-retinal and perspective cues cause the small range of the induced effect.

With a horizontal magnifier before one eye, a frontoparallel surface appears rotated about a vertical axis (geometric effect). With a vertical magnifier, apparent rotation is opposite in direction (induced effect); to restore appearance of frontoparallelism, the surface must be rotated away from the magnified eye. The induced effect is interesting because it was thought until recently that vertical disparities do not play an important role in surface perception. As with the geometric effect, the required rotation for the induced effect increases linearly to approximately equal to 4% magnification; unlike the geometric effect, it plateaus at approximately 8%. Current theory explains the linear portion: vertical size ratios (VSRs) are used to compensate for changes in horizontal size ratios (HSRs) that accompany eccentric gaze, so changes in VSR cause changes in perceived slant. The theory does not explain the plateau. We demonstrate that it results from differing slant estimates obtained by use of various retinal and extra-retinal signals. When perspective cues to slant are minimized or sensed eye position is consistent with VSR, the induced and geometric effects have similar magnitudes even at large magnifications.

Cues↗

PubMed2003

The influence of cyclovergence on unconstrained stereoscopic matching.

In order to perceive depth from binocular disparities the visual system has to identify matching features of the two retinal images. Normally, the assigned disparity is unambiguously determined by monocularly visible matching constraints. The assigned disparity is ambiguous when matching is unconstrained, such as when we view an isolated long oblique disparate line. Recently we found that in order to perceive a depth probe at the same depth as the oblique line, the probe needs to have the same horizontal disparity as the line (i.e. matching occurs along horizontal "search-zones" [Vis. Res. 40 (2000) 151]). Here we examined whether the depth probe disparity in unconstrained matching of long lines is influenced by cyclovergence, by cyclorotation between stereogram half-images, or by combinations of the two. We measured retinal rotation (>6 deg in cyclovergence conditions). We found that in those conditions in which the retinal images were the same (a condition with, say, both zero cyclovergence and zero cyclorotation between the half-images, creates the same retinal images as a condition with both 6 deg cyclovergence and 6 deg cyclorotation) assigned depth was the same too, i.e. independent of cyclovergence. Thus, the assigned depth of the test-line seems to be determined solely by the retinal test-line orientation, implying that the binocular matching algorithm does not seem to incorporate the eyes' cyclovergence when matching is unconstrained.

Depth Perception↗