Interocular Velocity Differences Research Articles

Neural population models for perception of motion in depth.

Changing disparity (CD) and interocular velocity difference (IOVD) are two possible mechanisms for stereomotion perception. We propose two neurally plausible models for the representation of motion-in-depth (MID) via the CD and IOVD mechanisms. These models create distributed representations of MID velocity as the responses from a population of neurons selective to different MID velocity. Estimates of perceived MID velocity can be computed from the population response. They can be applied directly to binocular image sequences commonly used to characterize MID perception in psychophysical experiments. Contrary to common assumptions, we find that the CD and IOVD mechanisms cannot be distinguished easily by random dot stereograms that disrupt correlations between the two eyes or through time. We also demonstrate that the assumed spatial connectivity between the units in these models can be learned through exposure to natural binocular stimuli. Our experiments with these developmental models of MID selectivity suggest that neurons selective to MID are more likely to develop via the CD mechanism than the IOVD mechanism.

Motion in depth cued by chromatic interocular velocity differences and changing disparity

Motion in depth cued by chromatic interocular velocity differences and changing disparity

The Interaction of Changing Disparity and Interocular Velocity Difference in Motion in Depth Perception

The Interaction of Changing Disparity and Interocular Velocity Difference in Motion in Depth Perception

Evidence for speed sensitivity to motion in depth from binocular cues

Motion in depth can be perceived from binocular cues alone, yet it is unclear whether these cues support speed sensitivity in the absence of the monocular cues that normally co-occur in natural viewing. We measure threshold contours in space-time for the discrimination of three-dimensional (3D) motion to determine whether observers use speed to discriminate a test 3D motion from two identical standards. We compare thresholds for random-dot stereograms (RDS) containing both binocular cues to 3D motion-interocular velocity difference and changing disparity over time-with performance for dynamic random-dot stereograms (DRDS), which contain only the second cue. Threshold contours are tilted along the axis of constant velocity in space-time for RDS stimuli at slow speeds (0.5 m/s), evidence for speed sensitivity. However, for higher speeds (1.5 m/s) and DRDS stimuli, observers rely on the component cues of duration and disparity. In a second experiment, noise of constant velocity is added to the standards to degrade the reliability of these separate components. Again there is evidence for speed tuning for RDS, but not for DRDS. Considerable variation is observed in the ability of individual observers to use the different cues in both experiments, however, in general the results emphasize the importance of interocular velocity difference as a critical cue for speed sensitivity to motion in depth, and suggest that speed sensitivity to stereomotion from binocular cues is restricted to relatively slow speeds.

Straight or curved? From deterministic to probabilistic models of 3D motion perception

Straight or curved? From deterministic to probabilistic models of 3D motion perception

Motion in depth cued by chromatic interocular velocity differences and changing disparity

Motion in depth cued by chromatic interocular velocity differences and changing disparity

Disparity-based stereomotion detectors are poorly suited to track 2D motion

A study was conducted to examine the time required to process lateral motion and motion-in-depth for luminance- and disparity-defined stimuli. In a 2 × 2 design, visual stimuli oscillated sinusoidally in either 2D (moving left to right at a constant disparity of 9 arcmin) or 3D (looming and receding in depth between 6 and 12 arcmin) and were defined either purely by disparity (change of disparity over time [CDOT]) or by a combination of disparity and luminance (providing CDOT and interocular velocity differences [IOVD]). Visual stimuli were accompanied by an amplitude-modulated auditory tone that oscillated at the same rate and whose phase was varied to find the latency producing synchronous perception of the auditory and visual oscillations. In separate sessions, oscillations of 0.7 and 1.4 Hz were compared. For the combined CDOT + IOVD stimuli (disparity and luminance [DL] conditions), audiovisual synchrony required a 50 ms auditory lag, regardless of whether the motion was 2D or 3D. For the CDOT-only stimuli (disparity-only [DO] conditions), we found that a similar lag (~60 ms) was needed to produce synchrony for the 3D motion condition. However, when the CDOT-only stimuli oscillated along a 2D path, the auditory lags required for audiovisual synchrony were much longer: 170 ms for the 0.7 Hz condition, and 90 ms for the 1.4 Hz condition. These results suggest that stereomotion detectors based on CDOT are well suited to tracking 3D motion, but are poorly suited to tracking 2D motion.

Cyclovergence is controlled by both interocular correlation and interocular velocity difference mechanisms.

Cyclovergence is controlled by both interocular correlation and interocular velocity difference mechanisms.

Low-level motion analysis of color and luminance for perception of 2D and 3D motion

We investigated the low-level motion mechanisms for color and luminance and their integration process using 2D and 3D motion aftereffects (MAEs). The 2D and 3D MAEs obtained in equiluminant color gratings showed that the visual system has the low-level motion mechanism for color motion as well as for luminance motion. The 3D MAE is an MAE for motion in depth after monocular motion adaptation. Apparent 3D motion can be perceived after prolonged exposure of one eye to lateral motion because the difference in motion signal between the adapted and unadapted eyes generates interocular velocity differences (IOVDs). Since IOVDs cannot be analyzed by the high-level motion mechanism of feature tracking, we conclude that a low-level motion mechanism is responsible for the 3D MAE. Since we found different temporal frequency characteristics between the color and luminance stimuli, MAEs in the equiluminant color stimuli cannot be attributed to a residual luminance component in the color stimulus. Although a similar MAE was found with a luminance and a color test both for 2D and 3D motion judgments after adapting to either color or luminance motion, temporal frequency characteristics were different between the color and luminance adaptation. The visual system must have a low-level motion mechanism for color signals as for luminance ones. We also found that color and luminance motion signals are integrated monocularly before IOVD analysis, showing a cross adaptation effect between color and luminance stimuli. This was supported by an experiment with dichoptic presentations of color and luminance tests. In the experiment, color and luminance tests were presented in the different eyes dichoptically with four different combinations of test and adaptation: color or luminance test in the adapted eye after color or luminance adaptation. Findings of little or no influence of the adaptation/test combinations indicate the integration of color and luminance motion signals prior to the binocular IOVD process.

Isolation of two binocular mechanisms for motion in depth: A model and psychophysics1

AbstractRandom dot patterns (RDPs) have been used to stimulate in isolation either of two binocular mechanisms for motion in depth: interocular velocity difference (IOVD), and changing disparity over time (CDOT). First, we examined how these stimuli isolate either mechanism using models based on motion/disparity energy detection. In the model, the IOVD mechanism calculates the difference in motion signal between the two eyes, and the CDOT mechanism calculates the difference in disparity signal between sequential stereo images. The simulation revealed that uncorrelated (0% correlation) RDPs are useful to isolate either of the two mechanisms, while the contrast‐reversed version (anticorrelation) of RDPs may not. Second, we compared the IOVD model predictions with experimental data from a previous study for motion in depth with various contrasts, displacements and vertical shifts between the two eyes. The simulation showed that the model predicts the general trends of the effects of contrast, displacement and vertical shift shown in the data. This suggests the physiological plausibility of the energy‐based model of motion in depth.

Motion aftereffect in depth based on binocular information

We examined whether a negative motion aftereffect occurs in the depth direction following adaptation to motion in depth based on changing disparity and/or interocular velocity differences. To dissociate these cues, we used three types of adapters: random-element stereograms that were correlated (1) temporally and binocularly, (2) temporally but not binocularly, and (3) binocularly but not temporally. Only the temporally correlated adapters contained coherent interocular velocity differences while only the binocularly correlated adapters contained coherent changing disparity. A motion aftereffect in depth occurred after adaptation to the temporally correlated stereograms while little or no aftereffect occurred following adaptation to the temporally uncorrelated stereograms. Interestingly, a monocular test pattern also showed a comparable motion aftereffect in a diagonal direction in depth after adaptation to the temporally correlated stereograms. The lack of the aftereffect following adaptation to pure changing disparity was also confirmed using spatially separated random-dot patterns. These results are consistent with the existence of a mechanism sensitive to interocular velocity differences, which is adaptable (at least in part) at binocular stages of motion-in-depth processing. We did not find any evidence for the existence of an "adaptable" mechanism specialized to see motion in depth based on changing disparity.

Isolation of Binocular Cues for Motion in Depth

There are two binocular cues of motion in depth: the interocular velocity difference (IOVD) and changing disparity over time (CDOT). Psychophysical evidence for the contribution to perceiving motion in depth has been accumulated for both of the two cues, using techniques to isolate each cue. However, no study estimated seriously how reliably each cue is isolated in the techniques. In this study, we apply a model of motion in depth to estimate how each type of stimuli isolates each of IOVD and CDOT cues. The model consists of the motion energy and the disparity energy detectors as subunits and adds their outputs to built the IOVD and CDOT detectors. Simulations show that some, but not all of stimuli used in the literature are appropriate for isolating cues. The temporally uncorrelated randomdot stereogram isolates CDOT cue and the binocularly uncorrelated randomdot kinematogram isolates IOVD cues. However, temporally anticorreated version of randomdot stereogram has influence of reverse motion components of IOVD and binocularly anticorreated version of randomdot kinematogram has influence of reverse motion components of CDOT. Gratings with opposite orientation between the eyes are also good for isolation of IOVD. We performed psychophysical experiments to examine the plausibility of the model prediction.

Accuracy of Stereomotion Speed Perception with Persisting and Dynamic Textures

It has been established that the motion in depth of stimuli visible to both eyes may be signalled binocularly either by a change of disparity over time or by the difference in the velocity of the images projected on each retina, known as an interocular velocity difference. A two-interval forced-choice stereomotion speed discrimination experiment was performed on four participants to ascertain the relative speed of a persistent random dot stereogram (RDS) and a dynamic RDS undergoing directly approaching or receding motion in depth. While the persistent RDS pattern involved identical dot patterns translating in opposite directions in each eye, and hence included both changing disparity and interocular velocity difference cues, the dynamic RDS pattern (which contains no coherent monocular motion signals) specified motion in depth through changing disparity, but no motion through interocular velocity difference. Despite an interocular velocity difference speed signal of zero motion in depth, the dynamic RDS stimulus appeared to move more rapidly. These observations are consistent with a scheme in which cues that rely on coherent monocular motion signals (such as looming and the interocular velocity difference cue) are less influential in dynamic stimuli due to their lack of reliability (i.e., increased noise). While dynamic RDS stimuli may be relatively unaffected by the contributions of such cues when they signal that the stimulus did not move in depth, the persistent RDS stimulus may retain a significant and conflicting contribution from the looming cue, resulting in a lower perceived speed.

On the Inverse Problem of Binocular 3D Motion Perception

It is shown that existing processing schemes of 3D motion perception such as interocular velocity difference, changing disparity over time, as well as joint encoding of motion and disparity, do not offer a general solution to the inverse optics problem of local binocular 3D motion. Instead we suggest that local velocity constraints in combination with binocular disparity and other depth cues provide a more flexible framework for the solution of the inverse problem. In the context of the aperture problem we derive predictions from two plausible default strategies: (1) the vector normal prefers slow motion in 3D whereas (2) the cyclopean average is based on slow motion in 2D. Predicting perceived motion directions for ambiguous line motion provides an opportunity to distinguish between these strategies of 3D motion processing. Our theoretical results suggest that velocity constraints and disparity from feature tracking are needed to solve the inverse problem of 3D motion perception. It seems plausible that motion and disparity input is processed in parallel and integrated late in the visual processing hierarchy.

Speed and Eccentricity Tuning Reveal a Central Role for the Velocity-Based Cue to 3D Visual Motion

Two binocular cues are thought to underlie the visual perception of three-dimensional (3D) motion: a disparity-based cue, which relies on changes in disparity over time, and a velocity-based cue, which relies on interocular velocity differences. The respective building blocks of these cues, instantaneous disparity and retinal motion, exhibit very distinct spatial and temporal signatures. Although these two cues are synchronous in naturally moving objects, disparity-based and velocity-based mechanisms can be dissociated experimentally. We therefore investigated how the relative contributions of these two cues change across a range of viewing conditions. We measured direction-discrimination sensitivity for motion though depth across a wide range of eccentricities and speeds for disparity-based stimuli, velocity-based stimuli, and "full cue" stimuli containing both changing disparities and interocular velocity differences. Surprisingly, the pattern of sensitivity for velocity-based stimuli was nearly identical to that for full cue stimuli across the entire extent of the measured spatiotemporal surface and both were clearly distinct from those for the disparity-based stimuli. These results suggest that for direction discrimination outside the fovea, 3D motion perception primarily relies on the velocity-based cue with little, if any, contribution from the disparity-based cue.

What Visual Information is Used for Stereoscopic Depth Displacement Discrimination?

There are two ways to detect a displacement in stereoscopic depth, namely by monitoring the change in disparity over time (CDOT) or by monitoring the interocular velocity difference (IOVD). Though previous studies have attempted to understand which cue is most significant for the visual system, none has designed stimuli that provide a comparison in terms of relative efficiency between them. Here we used two-frame motion and random-dot noise to deliver equivalent strengths of CDOT and IOVD information to the visual system. Using three kinds of random-dot stimuli, we were able to isolate CDOT or IOVD or deliver both simultaneously. The proportion of dots delivering CDOT or IOVD signals could be varied, and we defined the discrimination threshold as the proportion needed to detect the direction of displacement (towards or away). Thresholds were similar for stimuli containing CDOT only, and containing both CDOT and IOVD, but only one participant was able to consistently perceive the displacement for stimuli containing only IOVD. We also investigated the effect of disparity pedestals on discrimination. Performance was best when the displacement crossed the reference plane, but was not significantly different for stimuli containing CDOT only and those containing both CDOT and IOVD. When stimuli are specifically designed to provide equivalent two-frame motion or disparity-change, few participants can reliably detect displacement when IOVD is the only cue. This challenges the notion that IOVD is involved in the discrimination of direction of displacement in two-frame motion displays.

Two Independent Mechanisms for Motion-In-Depth Perception: Evidence from Individual Differences

Our forward-facing eyes allow us the advantage of binocular visual information: using the tiny differences between right and left eye views to learn about depth and location in three dimensions. Our visual systems also contain specialized mechanisms to detect motion-in-depth from binocular vision, but the nature of these mechanisms remains controversial. Binocular motion-in-depth perception could theoretically be based on first detecting binocular disparity and then monitoring how it changes over time. The alternative is to monitor the motion in the right and left eye separately and then compare these motion signals. Here we used an individual differences approach to test whether the two sources of information are processed via dissociated mechanisms, and to measure the relative importance of those mechanisms. Our results suggest the existence of two distinct mechanisms, each contributing to the perception of motion-in-depth in most observers. Additionally, for the first time, we demonstrate the relative prevalence of the two mechanisms within a normal population. In general, visual systems appear to rely mostly on the mechanism sensitive to changing binocular disparity, but perception of motion-in-depth is augmented by the presence of a less sensitive mechanism that uses interocular velocity differences. Occasionally, we find observers with the opposite pattern of sensitivity. More generally this work showcases the power of the individual differences approach in studying the functional organization of cognitive systems.

Integration of monocular motion signals and the analysis of interocular velocity differences for the perception of motion-in-depth

We investigated how the mechanism for perceiving motion-in-depth based on interocular velocity differences (IOVDs) integrates signals from the motion spatial frequency (SF) channels. We focused on the question whether this integration is implemented before or after the comparison of the velocity signals from the two eyes. We measured spatial frequency selectivity of the MAE of motion in depth (3D MAE). The 3D MAE showed little spatial frequency selectivity, whereas the 2D lateral MAE showed clear spatial frequency selectivity in the same condition. This indicates that the outputs of the monocular motion SF channels are combined before analyzing the IOVD. The presumption was confirmed by the disappearance of the 3D MAE after exposure to superimposed gratings with different spatial frequencies moving in opposite directions. The direction of the 2D MAE depended on the test spatial frequency in the same condition. These results suggest that the IOVD is calculated at a relatively later stage of the motion analysis, and that some monocular information is preserved even after the integration of the motion SF channel outputs.

The changing disparity energy model

Changing disparity is a possible cue for stereomotion perception. We propose the changing disparity energy model, a physiologically plausible model for neurons tuned to changing disparity. This model combines the disparity and motion energy models commonly used to model cortical neuron outputs. The model outputs are consistent with psychophysical experiments indicating that stereomotion speed discrimination thresholds for dynamic random dot stereograms are higher than for random dot stereograms. Thus, these experimental results are not necessarily strong evidence for the existence of an inter-ocular velocity difference cue. The model also predicts a relationship between the speed discrimination threshold ratio and the dot density.

Differences in temporal frequency tuning between the two binocular mechanisms for seeing motion in depth

There are two types of binocular cues available for perception of motion in depth. One is the binocular disparity change in time and the other is the velocity difference between the left and the right retinal images (inter-ocular velocity differences). We measured the luminance contrast threshold for seeing motion in depth while isolating either of the cues at various temporal modulations of velocity in the stimulus. To isolate disparity cues, dynamic random-dot stereograms were used (the disparity condition) while binocularly uncorrelated random-dot kinematograms were used to isolate velocity cues (the velocity condition). Results showed that sensitivity peaked at a temporal frequency (approximately 1 cps) in the velocity condition while the peak in the disparity condition was at the lowest frequency (0.35 cps) or at least at a frequency lower than that in the velocity condition. This suggests that the visual system has different temporal frequency properties for the velocity and disparity cues for motion in depth.