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PubMed1992

Spatial judgments with monoscopic and stereoscopic presentation of perspective displays.

Spatial judgments with monoscopic and stereoscopic presentation of perspective displays were investigated in the present study. The stimulus configuration emulated a visual scene consisting of a volume of airspace above a ground reference plane. Two target symbols were situated at various positions in the space, and observers were instructed to identify the relative depth or altitude of the two symbols. Three viewing orientations (15, 45, or 90 deg elevation angle) were implemented in the perspective projection. In the monoscopic view, depth cues in size, brightness, occlusion, and linear perspective were provided in the format. In the stereoscopic view, binocular disparity was added along the line of sight from the center of projection to reinforce the relative depth in the visual scene. Results revealed that spatial judgments were affected by manipulation of the relative spatial positions of the two target symbols and by the interaction between relative position and viewing orientation. The addition of binocular disparity improved judgments of three-dimensional spatial relationships, and the enhancement was greater when monocular depth cues were less effective and/or ambiguous in recovering the three-dimensional spatial characteristics.

Aircraft↗
PubMed1994

Positional disparity sensitivity of neurons in the cat accessory optic system.

There is considerable evidence supporting the view that the accessory optic system (AOS) and the closely associated nucleus of the optic tract (NOT) provide visual signals used in the control of optokinetic nystagmus (OKN). In frontal-eyed animals such as the cat and primate, the high degree of overlap in the visual fields of each eye, along with a substantial projection from the visual cortex, gives rise to an increased incidence of binocularly responsive neurons in the AOS. In previous studies, my collaborators and I have shown that visual cortical input to the AOS mediates ipsilateral eye responses and high speed tuning, and can function independently of the contralateral eye. However, beyond fairly gross assessments such as these, the binocular interactions of AOS cells have not been subject to detailed examination. The present study set out to determine whether the responses of binocular cells in the dorsal terminal nucleus (DTN) of the AOS are sensitive to horizontal retinal disparity. Single units were recorded from the DTN of anaesthetized, paralysed cats. A large random-dot pattern was moved under computer control at a constant velocity in the preferred and non-preferred direction. Convergent and divergent disparities were generated by deviating the visual axis of the contralateral (dominant) eye using wedge prisms. The responses of DTN units fell into three categories: (1) cells showing tuned excitatory responses (29% or 7 cells) consisting of a marked facilitation for a single or a limited range of disparities; (2) cells broadly tuned for inhibition (25% or 6 cells); and (3) cells relatively insensitive to disparity (46% or 11 cells), showing a relatively flat response profile across the entire range of disparity conditions, or cells without clear tuning. In summary, this study demonstrates that some AOS cells are sensitive to positional disparity and, therefore, this system may provide signals which specify the plane of motion for ocular stabilization. Some of these results have been presented in brief form [Grasse (1991a) Society of Neuroscience Abstracts, 17, 1380].

Animals↗
PubMed1990

Effects of direction and magnitude of horizontal disparities on binocular unmasking.

Conditions under which binocular unmasking (BU), as an analogue of binaural unmasking, occurs have been explored. Observers were to detect through a stereoscope a Gabor signal in patches of two-dimensional broadband gaussian noise surrounded by a frame of uniform noise. The right-eye gaussian field was displaced relative to the left eye so that it appeared either in front of or behind the frame. Performance when signal disparity was equal to that of the noise--a condition functionally equivalent to monocular processing--was compared to that obtained when signal disparity was zero--a case in which BU should occur. Enhanced signal detectability of up to 12 dB and of nearly constant magnitude was observed in the latter condition when uncrossed disparities of up to 67.60 min visual angle and display durations of 1 s were employed. Signal detectability declined appreciably with increasing disparity (both crossed and uncrossed) when display duration was reduced to 90 ms, thus preventing the occurrence of compensatory vergence eye movements. It is suggested that BU effects may result from a process of linear summation of monocular inputs.

Adult↗
PubMed1994

Binocular displacement of unpaired region.

Binocular displacement of binocularly unpaired parts of the stimulus was examined by means of the Poggendorff figure. The Poggendorff figure can be used to investigate displacement since lateral displacement of the transversal may cause bias in judgments of its collinearity. In experiment 1, the transversal had a disparity, and thus binocularly unpaired parts, relative to the rectangle. The magnitude of the Poggendorff illusion should not have changed by addition of binocular disparity if displacement occurred. There was no or slight change when the transversal was seen behind the rectangle, but there was significant decrease when the transversal was seen in front of the rectangle, suggesting absence of displacement in this case. There were two possible explanations. One was that displacement depended on the positional relation between the unpaired stimuli and the binocularly presented rectangle, ie the occlusion constraint, which the case with the transversal in front did not satisfy. The alternative was that the decrease was due to the perceived front depth of the transversal, and not related to binocular displacement at all. In order to discriminate between these two possibilities, the transversal was reduced to only the unpaired parts, resulting in dichoptic stimulation in experiment 2. In this stimulus, the positional relation between the unpaired and the paired stimuli was the same as in the previous experiment, yet no front depth could be perceived. The results showed similar asymmetry as in experiment 1. Thus we conclude that binocular displacement depends on the positional relation between the unpaired and the paired stimuli, regardless of their perceived depth. This may imply that binocular displacement is not symmetric about the sign of disparity, hence that it is not just averaging but is a reconstruction of the spatial layout of objects in the outside world to keep the visual direction of the unsuppressed unpaired region veridical by using explicit cues to depth discontinuity.

Cues↗
PubMed2001

Integration of perspective and disparity cues in surface-orientation-selective neurons of area CIP.

We investigated the effects of linear perspective and binocular disparity, as monocular and binocular depth cues, respectively, on the response of surface-orientation-selective (SOS) neurons in the caudal part of the lateral bank of the intraparietal sulcus (area CIP). During the single-unit recording, monkeys were required to perform the delayed-matching-to-sample (successive same/different discrimination) of discriminating surface orientation in stereoscopic computer graphics. Of 211 visually responsive neurons, 66 were intensively tested using the solid-figure stereogram (SFS) of a square plate with both disparity and perspective cues (D+P condition), and 62 of these were identified as SOS neurons for responding selectively to the orientation of stimuli. All these neurons were further tested using a solid figure with perspective cues alone (P-only condition), and 58% (36/62) of these showed selective response to the orientation of the stimuli. Of the 62 SOS neurons, 35 neurons were also tested using SFS with disparity cues alone (D-only condition) in addition to the D+P and P-only conditions. We classified these 35 neurons into four groups by comparing the response selectivity under the P-only and D-only conditions. More than one-half of these (19/35) were sensitive to both perspective and disparity cues (DP neurons), and nearly one-third (11/35) of these were sensitive to disparity cues alone (D neurons), but a few (2/35) were sensitive to perspective cues alone (P neurons). The remaining (3/35) neurons exhibited orientation selectivity only when both cues were present. In DP neurons, the preferred orientation under the D+P condition was correlated to those under the D-only and P-only conditions, and the response magnitude under the D+P condition was greater than those under the D-only and P-only conditions, suggesting the integration of both cues for the perception of surface orientation. However, in these neurons, the orientation tuning sharpness under the D+P and D-only conditions was higher than that under the P-only condition, suggesting the dominance of disparity cues. After the single-unit recording experiments, muscimol was microinjected into the recording site to temporarily inactivate its function. In all three effective cases out of six microinjection experiments, discrimination of a three-dimensional (3D) surface orientation was impaired when disparity cues alone were present. In only one effective case, when a relatively large amount of muscimol was microinjected, discrimination of a 3D surface orientation was impaired even when both disparity and perspective cues were present. These results suggest that linear perspective is an important cue for representations of a 3D surface of SOS neurons in area CIP, although it is less effective than binocular disparity, and that both of these depth cues may be integrated in area CIP for the perception of surface orientation in depth.

Algorithms↗
PubMed1991

Stereopsis from motion-defined contours.

Random-dot stereograms demonstrate that monocularly visible contours are not necessary for stereopsis, although in the absence of point-for-point correspondence, they are sufficient for stereoscopic combination. The quality of stereopsis from interocularly uncorrelated motion-defined forms was examined here. Results indicate that perceived magnitude of depth is not veridical, and that more depth is seen for crossed than uncrossed disparities. The difficulty in perceiving "behind" depth is due to a monocular depth cue which conflicts with binocular disparity in specifying depth only in the absence of interocular correlation. The overall reduction in depth is not the result of binocular rivalry from the lack of interocular correlation, and so appears to be a function of the type of feature being matched.

Depth Perception↗
PubMed1997

Perceived angular and linear size: the role of binocular disparity and visual surround.

An experiment was conducted to investigate the effects of perspective cue and binocular disparity on perceived angular and linear size. Following the 'angular' and 'linear' instructions, subjects matched the size of two squares, for which the binocular disparity between the centers of the squares and the configuration of the stimulus surrounding the squares were manipulated. Results showed that angular-size matches depended on the retinal-image size and the binocular disparity, and not on the visual-surround stimulus. Linear-size matches, on the other hand, depended on the visual-surround stimulus as well as on the image size and the binocular disparity. The visual-surround stimulus also affects the perceived depth between the test squares. These findings indicate that perceived angular and linear size depend on different processes that use different cues, and suggest that there is a causal relationship between perceived depth and perceived linear size.

Adult↗
PubMed2003

Paired and unpaired features can be equally effective in human depth perception.

The horizontal separation of the eyes results in the projection of slightly different images in each eye that are used to recover depth. One source of depth information is disparity, the relative position of paired features in the two eyes. Another source of depth information comes from features that are present in only one eye's view. These unpaired features arise from occlusion and by definition cannot generate a conventional disparity signal. Here we compare the depth signals generated by paired and unpaired features using stimuli that differ only in whether a given feature (a vertical gap) is paired or unpaired. Ecologically, both stimuli are consistent with two panels separated in depth at the gap, but only the paired gap provides a conventional disparity signal. We found strikingly that depth thresholds for the two gap conditions were the same and that there was perfect cross-adaptation of perceived depth from the unpaired to paired condition, strongly suggesting a common mechanism.

Contrast Sensitivity↗
PubMed2001

Perceiving slant about a horizontal axis from stereopsis.

Rotating a surface about a horizontal axis alters the retinal horizontal-shear disparities. Opposed torsional eye movements (cyclovergence) also change horizontal shear. If there were no compensation for the horizontal disparities created by cyclovergence, slant estimates would be erroneous. We asked whether compensation for cyclovergence occurs, and, if it does, whether it occurs by use of an extraretinal cyclovergence signal, by use of vertical-shear disparities, or by use of both signals. In four experiments, we found that compensation is nearly veridical when vertical-shear disparities are available and easily measured. When they are not available or easily measured, no compensation occurs. Thus, the visual system does not seem to use an extraretinal cyclovergence signal in stereoscopic slant estimation. We also looked for evidence of an extraretinal cyclovergence signal in a visual direction task and found none. We calculated the statistical reliabilities of slant-from-disparity and slant-from-texture estimates and found that the more reliable of the two means of estimation varies significantly with distance and slant. Finally, we examined how slant about a horizontal axis might be estimated when the eyes look eccentrically.

Convergence, Ocular↗
PubMed2005

Perception of depth and motion from ambiguous binocular information.

The visual system can determine motion and depth from ambiguous information contained in images projected onto both retinas over space and time. The key to the way the system overcomes such ambiguity lies in dependency among multiple cues--such as spatial displacement over time, binocular disparity, and interocular time delay--which might be established based on prior knowledge or experience, and stored in spatiotemporal response characteristics of neurons at an early cortical stage. We conducted a psychophysical investigation of whether a single ambiguous cue (specifically, interocular time delay) permits depth discrimination and motion perception. Data from this investigation are consistent with the predictions derived from the response profiles of V1 neurons, which show interdependency in their responses to each cue, indicating that spatial and temporal information is jointly encoded in early vision.

Cues↗
PubMed2001

Organisation of signals involved in binocular perception and vergence control.

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

Adult↗
PubMed1988

Stereoacuity testing: an illusion of tilt when viewing two parallel vertical rods or lines.

When stereoacuity was measured, some subjects (but not all) saw the two vertical rods of the test to be tilted. The perceived tilt indicated that the top of a rod was nearer to or farther from the observer than the bottom. Sometimes one rod appeared tilted and sometimes both. It was rare for both to appear tilted in the same direction. There are 9 possible tilt combinations including both rods vertical. All were observed but only 1 of the 3 subjects observed them all. In some instances, the frequency with which a particular tilt combination was seen was influenced by which rod was nearer and by the binocular disparity presented by the rods. During a stereoacuity test, tilt can confuse the identification of the nearer rod. Uncertainty is avoided by regarding the middle of the rods. Lines drawn on paper were also seen to tilt by some subjects.

Adult↗
PubMed2006

Fixation disparity analysis: sensory and motor approaches.

PURPOSE: Fixation disparity measurement as a tool for analyzing the binocular visual system has taken very different approaches in the United States and Central Europe. In the United States, testing has primarily followed a motor approach, and resulting management has followed parameters established by graphical analysis closely. In German-speaking countries, a strong sensory-based analysis has been popular for decades, utilizing equipment rarely seen in the United States. Management in these countries has been almost exclusively directed toward prismatic prescription. METHODS: This report examines the instrumentation, underlying strategies, and management used in both the motor and sensory approaches to fixation disparity analysis. Testing protocols and management options are detailed for each approach. CONCLUSION: Although both approaches agree that fixation disparity has the potential to reveal a more realistic view of binocular system functioning under normal viewing conditions than other systems of analysis, the approaches diverge in some very important ways, particularly in the understanding of the development of fixation disparity and its management. Whereas the philosophy underlying testing and management of the motor-based approach will be familiar to most clinicians in the United States, the sensory approach offers a very different perspective. It views the development of fixation disparity as a shift of correspondence within Panum's area. In effect, this may be thought of as the oxymoron "a normal, anomalous correspondence"; that is, a shift of correspondence occurring in nonstrabismic patients. Management in these cases is based on accurate prism prescription to re-establish bifoveal fusion.

Asthenopia↗
PubMed1997

Is stereopsis effective in breaking camouflage for moving targets?

It has been suggested that breaking camouflage is one of the major functions of stereopsis (Julesz, 1971). In this study, we found that stereopsis is less effective in breaking camouflage for moving targets than for static ones. Observers were asked to detect a single dot moving on a straight trajectory amidst identical noise dots in random motion. In the three-dimensional (3D) condition, the noise dots filled a cylindrical volume 5.7 cm in height and diameter; the trajectory signal dot moved on an oblique 3D trajectory through the center of the cylinder. In the two-dimensional (2D) control condition, observers viewed one half-image of the 3D cylinder binocularly. Surprisingly, trajectory detection in the 3D condition was only slightly better than in the 2D condition. Stereoscopic tuning for motion detection was also measured with a novel target configuration in which the random motion noise was presented in two depth planes that straddled the fixation plane where the trajectory target was presented. As the disparity between the noise planes and the fixation plane was increased, trajectory detection improved, reaching a peak between 6 and 12 arcmin, and then declining to the 2D level at larger disparities, where the noise became diplopic. Similar tuning measurements were made for detecting a static pattern, a string of five aligned dots presented in the fixation plane between two planes of static noise dots. Adding disparity to the noise planes produced a far greater improvement in static detection than in motion detection, for a comparable range of disparities (1.5-12 arcmin). We speculate that the temporal characteristics of the stereo system are not well suited for responding to moving targets, with the result that stereo does not greatly enhance motion detection in noise.

Depth Perception↗
PubMed2000

Disparity sensitivity of frontal eye field neurons.

Information about depth is necessary to generate saccades to visual stimuli located in three-dimensional space. To determine whether monkey frontal eye field (FEF) neurons play a role in the visuo-motor processes underlying this behavior, we studied their visual responses to stimuli at different disparities. Disparity sensitivity was tested from 3 degrees of crossed disparity (near) to 3 degrees degrees of uncrossed disparity (far). The responses of about two thirds of FEF visual and visuo-movement neurons were sensitive to disparity and showed a broad tuning in depth for near or far disparities. Early phasic and late tonic visual responses often displayed different disparity sensitivity. These findings provide evidence of depth-related signals in FEF and suggest a role for FEF in the control of disconjugate as well as conjugate eye movements.

Animals↗
PubMed1998

Modelling human depth perception in binocular vision: obtaining the horizontal disparity map.

The paper presents a computer application developed as a tool for implementing, developing, and testing computational models for stereopsis. Two models for solving the correspondence problem and computing the stereo disparity map have been implemented. One of them is biologically inspired (it models the behaviour of simple and complex cells from the striate cortex) and the paper details the results obtained on random-dot stereograms and on pairs of real images.

Algorithms↗
PubMed1989

Stereopsis and contrast.

We have measured threshold disparity as a function of the spatial frequency (0.25-20 c/deg) and contrast (0.02-0.75) of sine-wave gratings. In forced-choice trials, subjects indicated whether a target grating had crossed or uncrossed disparity relative to a reference grating. Thresholds were lowest near 3 c/deg and rose in proportion to spatial period at lower frequencies. Above 3 c/deg, there were marked individual differences. Across the range of spatial frequencies, disparity sensitivity and contrast sensitivity were correlated (r = 0.84). Threshold disparity was inversely proportional to the square root of contrast. When the contrast seen by one eye was reduced producing unequal monocular contrasts, threshold disparity rose more than when the contrast seen by the two eyes was reduced by the same amount. Our results have implications for stereo models that use zero crossings, peaks and troughs, or centroids as matching primitives. These models can account for the decline in disparity sensitivity at low sapatial frequencies but only the peak model satisfactorily accounts for the effect of contrast. If the limiting sources of noise in the two eyes are highly correlated, the effect of unequal monocular contrast can be accounted for using a differential-amplifier principle.

Contrast Sensitivity↗
PubMed2003

Integration of binocular disparity and monocular cues at near threshold level.

We examined the dependency of the integration of multiple depth cues upon the combined cues and upon the consistency of depth information from different cues. For each observer, depth thresholds were measured by the use of stimuli in which different depth cues (motion parallax, binocular disparity, and monocular configuration) specified the surface undulating sinusoidally with different spatial frequencies and different phases. Analysis of d(') showed that the performance was better than the prediction of probability summation only when parallax and disparity cues specified an undulation with the same spatial frequency and same phase. The probability summation model overestimated the performance for the other conditions of combination of disparity and parallax, and for all of the conditions of combination of disparity and monocular configuration. These results suggest that the improvement in depth perception caused by integration of multiple cues depends on the type of combined cues, and that the visual system possibly integrates the depth information from different cues at different stages of the visual processing.

Cues↗