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PubMed1995

Rotation of Listing's plane by horizontal, vertical and oblique prism-induced vergence.

We examined the changes in Listing's plane resulting from prismatically induced vergence. The three-dimensional angular positions of the two eyes were compared in normal subjects wearing search coils and gazing at targets 1.9 m away with and without prisms. For horizontal base-out prisms each degree of convergence in one eye yielded 0.72 deg of temporal rotation of Listing's plane in that eye. The results from vertical prisms were not what was expected from the horizontal results. A base-up prism on the right eye induced a downward and temporal rotation of Listing's plane. A base-down prism on the right eye induced an upward and nasal rotation of Listing's plane. The effects of oblique prisms were those expected from combining the effects of horizontal and vertical prisms. Thus in addition to producing a horizontal or vertical misalignment of the gaze line, prisms induce an unexpected position-dependent torsional disparity.

Convergence, Ocular↗
PubMed1998

Spatial disparity coding in the superior colliculus of the cat.

Cells in the superficial layers of the superior colliculus of the cat have mainly binocular receptive fields. The aim of the present experiment was to investigate the sensitivity of these cells to horizontal spatial disparity. Unit recordings were carried out in the superficial layers of the superior colliculus of paralyzed and anesthetized cats. Centrally located receptive fields were mapped, separated using prisms, and then stimulated simultaneously using two luminous bars optimally adjusted to the size of the excitatory region of the receptive fields. Only binocular cells were tested, and 65% of these units were found to be sensitive to spatial disparities. Some cells (20%) were clearly insensitive to spatial disparity and the remaining 15% showed complex, unclassifiable interactions. The sensitive cells could be divided into four classes based on their disparity-sensitivity profiles: 38% showed excitatory interactions, whereas 9% showed inhibitory interactions. Moreover, 11% and 7% of the cells responded, respectively, to crossed or uncrossed disparities, and were classified as near cells and far cells. Whereas the general shapes of the sensitivity profiles were similar to those of cells in areas 17-18, selectivity in the superior colliculus was significantly coarser. The superficial layers of the superior colliculus project topographically to the deep layers of the superior colliculus, which are known to contain circuits involved in the control of ocular movements. The results thus suggest that disparity-sensitive cells of the superior colliculus could feed information to these oculomotor neurons, allowing for the localization and fixation of objects on the appropriate plane of vision.

Animals↗
PubMed1992

Depth capture and transparency of regions bounded by illusory and chromatic contours.

Spillmann and Redies noted that when a transparent textured pattern is held above the Ehrenstein figure, the subjective surfaces appear to lie not in the plane of the figures but in the plane of the overlying texture. In Experiment 1, we tested this phenomenon with chromatic squares and found that the perceived depth of regions bounded by the chromatic contours was captured by overlying texture planes when the square was equiluminous with the background. We then tested this phenomenon with a variety of illusory contour stimuli and found that it only occurs with figures involving fine line terminators, and not, for example, with the solid Kanizsa triangle. These results suggest that chromatic contours and the illusory contours induced by line terminators provide only weak binocular disparity signals and that these signals are easily overwhelmed by the disparity signals from the overlying luminance texture.

Color Perception↗
PubMed1993

Anisotropies in the perception of stereoscopic surfaces: the role of orientation disparity.

We measured stereoscopic slant detection thresholds for surfaces slanting about a horizontal or a vertical axis. For random-dot covered surfaces, 1.25 deg of slant was required to detect slant about a horizontal axis, whereas 2.1 deg of slant was required to detect slant about a vertical axis. This anisotropy could be due to the fact that orientation disparities, which contain information about surface slant, are generally smaller for surfaces slanting about a vertical axis. To test this possibility, slant thresholds were measured for surfaces whose orientation disparity content was manipulated independently of the other slant information present. When the magnitude of orientation disparity was the same for surfaces slanting about a horizontal and a vertical axis, both surface orientations required about 1.5 deg of slant to be detected; thus the anisotropy became negligible. In contrast, when the orientation disparity content of a surface slanting about a vertical axis was zero, 3-4 deg of slant was required for detection; thus the anisotropy became larger. Under the conditions of these experiments, it appears that the visual system utilizes orientation disparities.

Depth Perception↗
PubMed1991

Orientation disparity, deformation, and stereoscopic slant perception.

Koenderink and van Doorn's theory, that the basis of stereoscopic slant perception is the deformation component of the disparity, field, was tested for slant around a horizontal axis, which produces images with a vertical ramp of horizontal disparity (horizontal shear) characterised by a global orientation disparity at the vertical meridian. The disparity field in this case can be parsed into two components, deformation and curl, which each contribute half of the orientation disparity. This case was compared with similar random-dot stimuli in which the deformation component was doubled and the curl component eliminated or vice versa. All three types of stimuli had identical orientation disparity at the vertical meridian. A condition in which there was no such orientation disparity, but deformation was present, was also included. It was found that perceived slant was not related to the deformation present, as Koenderink and van Doorn's theory would predict, but was predictable from the orientation disparity at the vertical meridian per se.

Depth Perception↗
PubMed1995

Pictorial depth cues: a new slant.

Pictorial depth cues such as perspective projection, aspect ratio, and texture gradients can specify mathematically the slant of a planar surface. We performed experiments to measure the accuracy of human perception of surface slant from these cues. We calculated the perceived slant from judgments of the relative lengths of a pair of orthogonal lines embedded in the surface. Our results indicate that slant judgments are accurate to within 3 deg. This level of accuracy was achieved whether the cues were luminance differences or equiluminous color differences. We found no evidence of the recession to the frontal plane that has been reported by Gibson [J.J. Gibson, The Perception of the Visual World (Houghton Mifflin, Boston, Mass., 1950]) and others. We did find evidence suggesting that subjects do not make accurate depth estimates of disconnected surfaces. This may be the source of the discrepancy between our measures and those of Gibson and others. This research, combined with previous findings, supports a model of perception that involves at least two and possibly more representations of space: one local veridical representation of surface orientation derived primarily from pictorial cues and another global representation of observer-centered distance derived primarily from binocular disparity and motion parallax.

Depth Perception↗
PubMed1992

[Apparent depth by the stereograms without binocular retinal disparity: is Lau effect artifact?].

We examined the idea that, when the Zöllner figure in one eye and the principal lines in the figure in the other eye were presented, the perceived depth is due to "phenomenal" disparity. The phenomenal disparity is defined as apparent displacement between two illusory "oblique" principal lines in one eye and two "parallel" principal lines in the other. Observes were asked whether depth was seen or not at upper or lower part of the two perceived lines and, if seen, which line was closer. Seventeen observers showed that only 9% of their responses was consistent with the idea, although they reported depths for disparity stimuli. This suggests that the dichoptic presentation of such figures should not be considered as that requires the processing of binocular disparity.

Adult↗
PubMed1998

Self-organization of binocular disparity tuning by reciprocal corticogeniculate interactions.

This article develops a neural model of how sharp disparity tuning can arise through experience-dependent development of cortical complex cells. This learning process clarifies how complex cells can binocularly match left and right eye image features with the same contrast polarity, yet also pool signals with opposite contrast polarities. Antagonistic rebounds between LGN ON and OFF cells and cortical simple cells sensitive to opposite contrast polarities enable anticorrelated simple cells to learn to activate a shared set of complex cells. Feedback from binocularly tuned cortical cells to monocular LGN cells is proposed to carry out a matching process that dynamically stabilizes the learning process. This feedback represents a type of matching process that is elaborated at higher visual processing areas into a volitionally controllable type of attention. We show stable learning when both of these properties hold. Learning adjusts the initially coarsely tuned disparity preference to match the disparities present in the environment, and the tuning width decreases to yield high disparity selectivity, which enables the model to quickly detect image disparities. Learning is impaired in the absence of either antagonistic rebounds or corticogeniculate feedback. The model also helps to explain psychophysical and neurobiological data about adult 3-D vision.

Algorithms↗
PubMed1992

Quantitative analysis of associated and disassociated phorias: linear and nonlinear static models.

Ogle proposed two measures of oculomotor balance, called associated and disassociated phorias, which he assumed were equivalent. However, experimentally determined values of these phorias do not show a close correspondence. To analyze the rationale behind Ogle's assumption of equality, a linear static model was evaluated. It was found that indeed the linear model predicts an exact correspondence between associated and disassociated phorias. Thus, his assumption depended on the presence of a linear model. To account for the discrepancy between these two measures, a nonlinear static model, containing the dead space operators depth of field and Panum's fusional area, was evaluated. Four equations for fixation disparity were derived corresponding to the four combinations of deadspace operator outputs. It was found that only one of these four equally possible solutions for associated phoria corresponded to the disassociated phoria. This suggests that the variability in the four solutions may account for the scatter in the experimental data. The nonlinear model was analyzed further to determine its sensitivity to parameter changes and to show how such a model could generate the classical shape of the fixation disparity curve.

Accommodation, Ocular↗
PubMed1990

[Neurons in monkey parietal association cortex sensitive to depth movement].

We recorded neurons sensitive to depth movement from the inferior parietal lobule (area 7a) of alert behaving monkeys, and studied their response to changing sizes of retinal images and to changing binocular disparity. The size of the stimulus was changed by changing both the height and width of a slit in the same way, and the disparity change was produced by varying distances between a pair of polarized stimuli on a screen. Of 227 purely visual neurons recorded from 11 hemispheres of 7 monkeys, 32 neurons responded to the change of either the size or disparity, or both. Some of the neurons sensitive to size change could be activated by changing length on only one axis, but the optimal stimulus for most of them was a uniform change of size in all directions. The neurons sensitive to disparity change responded weakly to monocular stimuli, but showed clear selectivity in the direction of change of disparity when binocular stimuli were applied. We also found a group of depth movement sensitive neurons that responded maximally to the simultaneous change of size and disparity. This type of neurons may signal real depth movement by integrating the signals of size change and disparity change.

Animals↗
PubMed2000

Spatial frequency tuning for 3-D corrugations from motion parallax.

We provide evidence for the existence of multiple channels tuned to the spatial frequency of depth modulations defined by motion parallax. By linking the distortion of a random dot pattern to the horizontal position of an observer's head horizontally oriented 3-D corrugations were simulated in which the depth function consisted of a range of frequencies. In a baseline experiment thresholds were obtained for detecting depth modulations of single sinewaves for a range of spatial frequencies. In a masking experiment threshold signal strength was determined for detecting a signal frequency in the presence of noise with frequencies restricted to two bands around the signal component ('notched noise'). Threshold elevation was found to decrease with an increase in the spectral difference between signal and noise. By determining thresholds at various noise levels it was further established that the channel responded linearly in the tested range. Estimates of the bandwidth for spatial frequencies of 0.33 and 0.87 cycles/deg were both found to be 1.4 octaves. The results show that motion parallax processing is mediated by a series of narrowly tuned channels with bandwidths similar to those found for processing depth modulations defined by binocular disparity.

Depth Perception↗
PubMed2001

3D after-effects are due to shape and not disparity adaptation.

There are a variety of stereoscopic after-effects in which exposure to a stimulus with a particular slant or curvature affects the perceived slant or curvature of a subsequently presented stimulus. These after-effects have been explained as a consequence of fatigue (a decrease in responsiveness) among neural mechanisms that are tuned to particular disparities or patterns of disparity. In fact, a given disparity pattern is consistent with numerous slants or curvatures; to determine slant or curvature, the visual system must take the viewing distance into account. We took advantage of this property to examine whether the mechanisms underlying the stereoscopic curvature after-effect are tuned to particular disparity patterns or to some other property such as surface curvature. The results clearly support the second hypothesis. Thus, 3D after-effects appear to be caused by adaptation among mechanisms specifying surface shape rather than among mechanisms signaling the disparity pattern.

Adaptation, Physiological↗
PubMed1997

Spatial limitation of vertical-size disparity processing.

We investigated the upper limit of horizontal spatial modulation of vertical-size disparity in a textured surface for the perception of depth. In Experiment 1 subjects matched the appearance of a surface with modulated horizontal-size disparity to that of a surface with modulated vertical-size disparity. In Experiment 2 we determined the threshold amplitude of modulation of vertical-size disparity required for the perception of depth as a function of the spatial frequency of disparity modulation. The results indicate that sensations of depth are not elicited by modulations of vertical-size disparity of any amplitude at spatial frequencies higher than about 0.04 c/deg. We conclude that vertical disparities are averaged within about 20 deg-wide areas and suggest that this global measurement is used to scale local horizontal disparities for the perception of surface slant.

Depth Perception↗
PubMed2000

The effect of disparity on the very earliest ocular following responses and the initial neuronal activity in monkey cortical area MST.

Movement of the visual scene evokes tracking movement with the eyes (ocular following response, OFR) at short latency (Miles, F.A., Kawano, K., Optican, L.M., 1986. Short-latency ocular following responses of monkey. I. Dependence on temporospatial properties of visual input. J. Neurophysiol. 56, 1321-1354). We examined the effect of binocular disparity on the initial OFR. The dependence of the OFR on horizontal disparity steps was studied in three monkeys (Macaca fuscata), and the associated unit discharges in the medial superior temporal area (MST) were studied in two of these. Based on the changes in eye position over the period 50-83 ms (measured from stimulus onset), the initial OFR showed clear dependence on the disparity imposed during the preceding centering saccade. The disparity tuning curves were S-shaped with a peak at a small crossed disparity and a trough at uncrossed disparities. Based on the changes in discharge rate over the period 40-73 ms (measured from stimulus onset), almost all OFR-related MST neurons (80/83, 96.4%) showed significant dependence on the disparity step (Student's t-test, P < 0.05). The early neuronal responses of the majority of units (41/75, 55%) had disparity tuning curves resembling those for the OFR, which peaked at small crossed disparities. These findings suggest that the neurons in the MST contain information on binocular disparity in their short-latency discharges, and are involved in the neural basis of the OFR's dependence on horizontal disparity.

Action Potentials↗
PubMed1997

Stereopsis: how the brain sees depth.

Recent studies show how single neurons detect binocular disparities. But how these signals are used for stereoscopic perception remains a puzzle.

Animals↗
PubMed1998

Depth interactions between inclined and slanted surfaces in vertical and horizontal orientations.

Depth interactions between a frontal test surface and an adjacent induction surface were measured as a function of the type of disparity in the induction surface and of the vertical/horizontal orientation of the boundary between the surfaces. The types of disparity were 4 degrees horizontal-shear disparity, 4 degrees vertical-shear disparity, and 4 degrees rotation disparity; 4% horizontal-size disparity, 4% vertical-size disparity, and 4% overall-size disparity. Depth contrast in a frontal surface was produced by surfaces containing horizontal-size disparity but not by those containing horizontal-shear disparity. Vertical-shear and vertical-size disparities produced induced effects in both the induction and the test surface, which is here explained in terms of deformation-disparity processing. Effects of rotation disparity on the test surface can be accounted for in terms of cyclovergence, deformation disparity, and perhaps also depth contrast. The fact that horizontal-size disparity produced more depth contrast than horizontal-shear disparity is due to an anisotropy of disparity processing rather than the relative orientation of the surfaces. Ground surfaces appeared more slanted than ceiling surfaces. Surfaces containing horizontal disparities produced a sharp boundary with the test surface because horizontal disparities are processed locally. Surfaces with vertical disparities produced a gradual boundary with the test surface because vertical disparities are processed over a wider area.

Depth Perception↗
PubMed1989

Stereoscopic depth perception by static stereo-deficient observers in dynamic displays with constant and changing disparity.

The performance of 11 static stereo-deficient subjects and 11 static stereo-normal subjects was compared on two types of dynamic stereo displays--one where disparities were constant during motion and one where disparities changed continuously. Computer-generated displays simulating horizontal motion of figures at different depths or rotation of figures about a vertical axis were viewed through a Brewster stereoscope. About one-half of the subjects in our static stereo-deficient sample were able to make depth judgments on the basis of disparity in both types of dynamic displays. The clinical feature which appeared to distinguish those static stereo-deficient subjects who could use disparity information in dynamic displays from those who could not was early onset constant strabismus. These results indicate that a complete evaluation of stereo ability should include tests with dynamic displays, possibly including both constant and changing disparities.

Adult↗
PubMed2003

Interocular orientation disparity and the stereoscopic perception of slanted surfaces.

The orientation threshold for two-dimensional filtered noise stimuli was estimated using forced-choice procedures with both dioptic and dichoptic viewing. In the dioptic case the two patterns were co-rotated. In the dichoptic case the stimuli were counter-rotated to produce an orientation disparity, which yields a percept of slant about the horizontal axis orthogonal to the cyclopean line of sight. Dioptic thresholds increased with the orientation bandwidth of the stimuli. In contrast, dichoptic thresholds were essentially constant across a wide range of conditions. In all cases, dichoptic orientation acuity was much finer than conventional estimates. In a second experiment, the dichoptic threshold was estimated for patterns superimposed on a depth pedestal. Acuity was affected significantly by the presence of the pedestal, and was an inverse function of pedestal amplitude. The results suggest that stereoscopic slant caused by dichoptic counter-rotation arises because of neural processing of the overall pattern of disparities of position produced by counter-rotation, rather than specialised encoding of orientation disparity.

Depth Perception↗