FIXATION DISPARITY WITH AND WITHOUT FOVEAL FUSION CONTOURS.
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Fovea Centralis↗
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Studies of fixation disparity. II. Apparatus, procedure and the problem of constant error.
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Humans↗
Binocular disparity in tonometry in normal eyes.
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Humans↗
Neurons that respond to more than one depth cue.
The 3D orientation of a surface can be specified by perspective, motion parallax or binocular disparity. Tsutsui et al. have found cells in the monkey intraparietal sulcus that responded to surface orientation defined only by a texture gradient. Most of these cells also responded to orientation defined only by binocular disparity.
Animals↗
Does binocular disparity or familiar size information override effects of relative size on judgements of time to contact?
Previous studies indicate that non-tau sources of depth information, such as pictorial depth cues, can influence judgements of time to contact (TTC). The effect of relative size on such judgements, the size-arrival effect, is particularly robust. However, earlier studies of the size-arrival effect did not include binocular disparity or familiar size information. The effects of these cues on relative TTC judgements were measured. Results suggested that disparity can eliminate the size-arrival effect but that the amount of disparity needed to do so is greater than typical stereoacuity thresholds. In contrast, familiar size eliminated the size-arrival effect even when disparity information was not available. Furthermore, disparity contributed more to performance when familiar size was present than when it was absent. Consistent with previous studies, TTC judgements were influenced by multiple sources of information. The present results suggested further that familiar size is one such source of information and that familiar size moderates the influence of binocular disparity information.
Female↗
[Motor and sensory responses in fusion of vertical disparities in different convergence places].
UNLABELLED: To study motor and sensory responses in vertical fusion at different angles of horizontal vergence in normal humans. METHODS: The study included 12 normal subjects. A cross (+) extending 3.4 degrees x3.2 degrees was presented dichoptically. Vertical disparity was introduced by changing the vertical position of the cross in front of one eye. The disparity was incremented by 0.08 degrees every 8 s. Distance viewing was tested with 1 degrees of convergence demand, near vision with 6-15 degrees convergence demand. Eye movements were recorded using three-axis search coils. RESULTS: Vertical fusion capability was larger at near vision than at distance in 9 of 12 subjects. For the entire group, total vertical fusion capability (motor plus sensory response) differed between distance (mean 1.68 degrees ) and near (mean 2.39 degrees ). The motor component differed significantly between distance (mean 1.42 degrees ) and near (mean 2.13 degrees ). No difference in the sensory component was seen between distance (mean 0.26 degrees ) and near (mean 0.27 degrees ). CONCLUSIONS: Vertical fusion capability increases with convergence. This increase is mainly due to an increase of the motor response.
Accommodation, Ocular↗
Fixation disparity under open- and closed-loop accommodation.
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Accommodation, Ocular↗
Direct extraction of curvature-based metric shape from stereo by view-modulated receptive fields.
Any computation of metric surface structure from horizontal disparities depends on the viewing geometry, and analysing this dependence allows us to narrow down the choice of viable schemes. For example, all depth-based or slant-based schemes (i.e. nearly all existing models) are found to be unrealistically sensitive to natural errors in vergence. Curvature-based schemes avoid these problems and require only moderate, more robust view-dependent corrections to yield local object shape, without any depth coding. This fits the fact that humans are strikingly insensitive to global depth but accurate in discriminating surface curvature. The latter also excludes coding only affine structure. In view of new adaptation results, our goal becomes to directly extract retinotopic fields of metric surface curvatures (i.e. avoiding intermediate disparity curvature). To find a robust neural realisation, we combine new exact analysis with basic neural and psychophysical constraints. Systematic, step-by-step 'design' leads to neural operators which employ a novel family of 'dynamic' receptive fields (RFs), tuned to specific (bi-)local disparity structure. The required RF family is dictated by the non-Euclidean geometry that we identify as inherent in cyclopean vision. The dynamic RF-subfield patterns are controlled via gain modulation by binocular vergence and version, and parameterised by a cell-specific tuning to slant. Our full characterisation of the neural operators invites a range of new neurophysiological tests. Regarding shape perception, the model inverts widely accepted interpretations: It predicts the various types of errors that have often been mistaken for evidence against metric shape extraction.
Animals↗
Directional discrimination of motion in depth based on changing target vergence.
Difference limens for the apparent direction of motion in depth were measured in eight observers. Two points of light were presented dichoptically in an otherwise dark field. Their lateral motion (changing target-vergence stimulus) mimicked the oscillation of an object in depth along different paths. All seven paths of 100 cm length had a common distant position in the median plane 150 cm from the observer. The directions of the paths were equidistant; the second and sixth paths were directed toward the left and right eye of the observer, respectively. Discrimination of direction was best for motion along the median plane and deteriorated toward the periphery. There was no indication of local minima of the difference limen for motions toward the eyes as has been observed with changing-disparity stimuli.
Adult↗
Depth cue integration: stereopsis and image blur.
Depth-of-focus limitations introduce spatial blur in images of three-dimensional scenes. It is not clear how the visual system combines depth information derived from image blur with information from other depth cues. Stereoscopic disparity is the pre-eminent depth cue, so experiments were conducted to investigate interactions between image blur and stereoscopic disparity. Observers viewed two random dot stereograms (RDSs) in a 2AFC task, and were required to identify the RDS depicting the greatest depth. In control observations, all dots in both RDSs were sharply defined. In experimental observations, one RDS contained only sharply defined dots, but the other contained differential spatial blur to introduce an additional depth cue. Results showed that the addition of differential blur made only a marginal difference to apparent depth separation, and only when the blur difference was consistent with the sign of disparity. Cue combination between blur and disparity cues is thus weighted very heavily in favour of the latter. It is shown that blur and disparity cues co-vary according to geometric optics. Since the two cues are effective over different distances, the visual system is not normally called upon to integrate them, and is most likely to make use of blur cues over distances beyond the range of disparity mechanisms.
Cues↗
The relationship between stereoacuity and stereomotion thresholds.
There are in principle at least two binocular sources of information that could be used to determine the motion of an object towards or away from an observer; such motion produces changes in binocular disparities over time and also generates different image velocities in the two eyes. It has been argued in the past that stereomotion is detected by a mechanism that is independent of that which detects static disparities. More recently this conclusion has been questioned. If stereomotion detection in fact depends upon detecting disparities, there should be a clear correlation between static stereo-detection thresholds and stereomotion thresholds. If the systems are separate, there need be no such correlation. Four types of threshold measurement were performed by means of random-dot stereograms: (1) static stereo detection/discrimination; (2) stereomotion detection in random-dot stereograms (temporally uncorrelated); (3) stereomotion detection in temporally correlated random-dot stereograms; and (4) binocular detection of frontoparallel motion. Three normal subjects and five subjects with unusually high stereoacuities were studied. In addition, two manipulations were performed that altered stereomotion thresholds: changes in mean disparity, and image defocus produced by positive spectacle lenses. Across subjects and conditions, stereomotion thresholds were well correlated with stereo-discrimination thresholds. Stereomotion was poorly correlated with binocular frontoparallel-motion thresholds. These results suggest that stereomotion is detected by means of registering changes in the output of the same disparity detectors that are used to detect static disparities.
Cues↗
Aftereffects and the representation of stereoscopic surfaces.
The structure of human disparity representation is examined through (i) adaptation experiments and (ii) model simulations of the data. Section 3 presents results of adaptation experiments designed to illuminate the structure of human disparity representation. Section 4 presents model simulations of three different disparity representation schemes. In the experiments, participants adapted to a 0.133 cycle deg-1 sinusoidally corrugated surface with 10 min of arc peak-to-trough disparity. A flat test surface was briefly presented, in which the aftereffect surface was perceived. Adapt and test surfaces were placed on disparity pedestals and thus presented in front of or behind the plane of fixation. The adapt surface could be offset from the fixation plane by +/- 8 to 24 min of arc. The test surface could be offset from the fixation plane by +/- 8 to 48 min of arc. The depth aftereffect was measured in different disparity planes by a nulling method and 'topping-up' procedure. Aftereffect tuning functions were obtained whose bandwidths, magnitudes, and tuning depended on the disparity planes of both the adapt and test surfaces. These parameters were used to constrain the models tested in section 4. On the basis of the two studies, it is argued that the human stereoscopic system encodes spatial changes of disparity using channels localised within disparity planes. A localised disparity-gradient model of the human representation of disparity is proposed.
Adaptation, Psychological↗
Neural mechanisms for encoding binocular disparity: receptive field position versus phase.
The visual system uses binocular disparity to discriminate the relative depth of objects in space. Because the striate cortex is the first site along the central visual pathways at which signals from the left and right eyes converge onto a single neuron, encoding of binocular disparity is thought to begin in this region. There are two possible mechanisms for encoding binocular disparity through simple cells in the striate cortex: a difference in receptive field (RF) position between the two eyes (RF position disparity) and a difference in RF profiles between the two eyes (RF phase disparity). Although there is evidence that supports each of these schemes, both mechanisms have not been examined in a single study to determine their relative roles. In this study, we have measured RF position and phase disparities of individual simple cells in the cat's striate cortex to address this issue. Using a sophisticated RF mapping technique that employs binary m-sequences, we have obtained left and right eye RF profiles of two or more cells recorded simultaneously. A version of the reference-cell method was used to estimate RF position disparity. We find that RF position disparities generally are limited to values that are not sufficient to encode large binocular disparities. In contrast, RF phase disparities cover a wide range of binocular disparities and exhibit dependencies on RF orientation and spatial frequency in a manner expected for a mechanism that encodes binocular disparity. These results suggest that binocular disparity is encoded mainly through RF phase disparity. However, RF position disparity may play a significant role for cells with high spatial frequency selectivity that are constrained to have only small RF phase disparities.
Animals↗
[Perceived depth produced by luminance differences in the two eyes with zero disparity].
We examined Kaufman, Bacon, and Barroso's (1973) finding that perceived depth covaries with relative luminance of the two half-fields of the stereogram. Five subjects were shown two sets of stereograms: one with three lines and another with random dots. In each trial, they reported the apparent depth plane produced by one of 15 different relative luminances of the lines or the mid portions of the random dots. The direction and the magnitude of perceived depth as a function of the relative luminance varied across subjects. It is argued that the stimulus should be considered as being Wheatstone-Panum's Limiting Case rather than that requires processing of binocular retinal disparity.
Adult↗
[Apparent size of stereoscopic images with disparity in relation to the function of accommodation].
PURPOSE: We investigated experimentally the relationship between the apparent size of stereoscopic images with disparity and the accommodative function. METHODS: The judgement of the apparent stereoscopic image size used the subject reply. The size of the forward image, which was produced by crossed visual lines with binocular disparity and by a time-sharing type stereoscopic three-dimensional display using liquid crystal shutter glasses, was compared with the size of the plane image. The size of the backward image produced by uncrossed visual lines was also compared with the size of the plane image. Sixteen normal volunteers were requested to subjectively compare each image with the original plane image on the display screen in relation to its size. Accommodation was measured using an infrared optometer to record the step responses (from far to near, and near to far). The subjects were divided into two groups, a fast response group and slow response group. RESULTS: It was found that the forward image was smaller than the plane image and the backward image was larger than the plane image, and this tendency was remarkable in the fast response group. CONCLUSION: From these results, it appears that the state of accommodation affects the perceived size of stereoscopic images with disparity.
Accommodation, Ocular↗
Unilateral paralytic strabismus in the adult cat induces plastic changes in interocular disparity along the visual midline: contribution of the corpus callosum.
Neurones activated through the corpus callosum (CC) in the cat visual cortex are known to be almost entirely located at the 17/18 border. They are orientation selective and display receptive fields (RFs) distributed along the central vertical meridian of the visual field ("visual midline"). Most of these cells are binocular, and many of them are activated both from the contralateral eye through the CC, and from the ipsilateral eye via the direct retino-geniculo-cortical (GC) pathway. These two pathways do not carry exactly the same information, leading to interocular disparity between pairs of RFs along the visual midline. Recently, we have demonstrated that a few weeks of unilateral paralytic strabismus surgically induced at adulthood does not alter the cortical distribution of these units but leads to a loss of their orientation selectivity and an increase of their RF size, mainly toward the ipsilateral hemifield when transcallosally activated (Watroba et al., 2001). To investigate interocular disparity, here we compared these RF changes to those occurring in the same neurones when activated through the ipsilateral direct GC route. The 17/18 transition zone and the bordering medial region within A17 were distinguished, as they display different interhemispheric connectivity. In these strabismics, some changes were noticed, but were basically identical in both recording zones. Ocular dominance was not altered, nor was the spatial distribution of the RFs with respect to the visual midline, nor the amplitude of position disparity between pairs of RFs. On the other hand, strabismus induced a loss of orientation selectivity regardless of whether neurones were activated directly or through the CC. Both types of RFs also widened, but in opposite directions with respect to the visual midline. This led to changes in incidences of the different types of position disparity. The overlap between pairs of RFs also increased. Based on these differences, we suggest that the contribution of the CC to binocular vision along the midline in the adult might be modulated through several intrinsic cortical mechanisms.
Action Potentials↗
Mechanisms of vertical phoria adaptation revealed by time-course and two-dimensional spatiotopic maps.
The spatial spread of short term phoria adaptation was measured in response to either a single vertical disparity presented at a single eye position, or, vertical disparities of opposite sign presented at two different locations along either the primary vertical or horizontal meridians or along an oblique axis. The spread of adaptation to eye positions not specifically adapted was assessed by measuring phoria across a two-dimensional surface. The change in phoria was uniform across the field in response to a single disparity. With two disparities, adaptation conformed to the stimulus demand in the direction in which the disparity varied but was uniform in the orthogonal direction. The time-course of the adaptation indicated the presence of two mechanisms, a global one which shifted the phoria uniformly across the field and a local one which selectively adjusted the phoria to the position dependent demands of the disparity stimulus.
Adaptation, Ocular↗
Spatial interactions minimize relative disparity between adjacent surfaces.
Computational models of stereopsis employ a number of algorithms that constrain stereo matches to produce the smallest absolute disparity and to minimize the relative disparity between nearby features. In some natural scenes, such as large slanted textured surfaces, these two constraints lead to different matching solutions. The current study utilized a stimulus in which there was a large discrepancy in both the magnitude and direction of matches that solved for minimum absolute and minimum relative disparity. This discrepancy revealed a dominance for the minimum relative disparity over the minimum absolute disparity matching solution that increased with spatial proximity, spatial frequency and width of adjacent features. The likelihood of a minimum-relative-disparity matching solution also increased when the difference between the amplitudes of the alternative relative disparities was large. When alternative relative disparity matching solutions had similar amplitudes but opposite signs (crossed vs. uncrossed), an idiosyncratic depth bias served as a tie-breaker. The present results show that absolute disparity matches are constrained to minimize relative disparity between adjacent features.
Depth Perception↗