The interaction of binocular disparity and motion parallax in determining perceived depth and perceived size.

Although binocular disparity and motion parallax are powerful cues for depth, neither, in isolation, can specify information about both object size and depth. It has been shown that information from both cues can be combined to specify the size, depth, and distance of an object in a scene (Richards, 1985 Journal of the Optical Society of America A 2 343-349). Experiments are reported in which natural viewing and physical stimuli have been used to investigate the nature of size and depth perception on the basis of disparity and parallax presented separately and together at a range of viewing distances. Observers adjusted the relative position of three bright LEDs, which were constrained to form a triangle in plan view with the apex pointing toward the observer, so its dimensions matched that of a standard held by the subject. With static monocular viewing, depth settings were inaccurate and erratic. When both cues were present together accuracy increased and the perceptual outcome was consistent with an averaging of the information provided by both cues. When an apparent bias evident in the observers' responses (the tendency to under-estimate the size of the standard) was taken into account, accuracy was high and size and depth constancy were close to 100%. In addition, given this assumption, the same estimate of viewing distance was used to scale size and depth estimates.     

Relationship between binocular disparity and motion parallax in surface detection

The ability to detect surfaces was studied in a multiple-cue condition in which binocular disparity and motion parallax could specify independent depth configurations. On trials on which binocular disparity and motion parallax were presented together, either binocular disparity or motion parallax could indicate a surface in one of two intervals; in the other interval, both sources indicated a volume of random points. Surface detection when the two sources of information were present and compatible was not better than detection in baseline conditions, in which only one source of information was present. When binocular disparity and motion specified incompatible depths, observers’ ability to detect a surface was severely impaired if motion indicated a surface but binocular disparity did not. Performance was not as severely degraded when binocular disparity indicated a surface and motion did not. This dominance of binocular disparity persisted in the presence of foreknowledge about which source of information would be relevant.     

Independence of sampling of motion parallax and binocular disparity in discrimination of depth1

Abstract: The sampling strategy of the visual system in binocular disparity and motion parallax to discriminate depth was investigated. Human observers were asked to discriminate between the depths of two surfaces defined by both cues. Gaussian noise was added to the depths represented by each cue, and the correlation in noise was manipulated. Human performance was compared with two types of likelihood models. The first was based on independent sampling, in which data from the two cues were gathered from independent sets of points in the display. The second was based on paired sampling, in which data from these cues were gathered from the same set of points. The former model yielded a better fit with human performance. This suggests that the visual system is more likely to adopt independent sampling.     

Effect of disparity and viewing distance on perceived depth

It is shown that veridical depth perception presupposes the processing of both the magnitude of retinal disparity and observation distance according to a square-law function specified by the underlying geometrical stimulus relations. In the present study, after testing its existence, this constancy of depth perception was investigated by measuring perceived depth as a function of retinal disparity and observation distance. In addition, the relative effectiveness of convergence and accommodation as possible indicators of distance was examined through a conflicting-cues paradigm. It was shown that in the perception of depth the visual system computes distance by taking into account the convergence parameter only, rather than that of accommodation or of both.     

The effects of age upon the perception of depth and 3-D shape from differential motion and binocular disparity

The ability of younger and older adults to perceive the 3-D shape, depth, and curvature of smooth surfaces defined by differential motion and binocular disparity was evaluated in six experiments. The number of points defining the surfaces and their spatial and temporal correspondences were manipulated. For stereoscopic sinusoidal surfaces, the spatial frequency of the corrugations was also varied. For surfaces defined by motion, the lifetimes of the individual points in the patterns were varied, and comparisons were made between the perception of surfaces defined by points and that of more ecologically valid textured surfaces. In all experiments, the older observers were less sensitive to the depths and curvatures of the surfaces, although the deficits were much larger for motion-defined surfaces. The results demonstrate that older adults can extract depth and shape from optical patterns containing only differential motion or binocular disparity, but these abilities are often manifested at reduced levels of performance.     

Binocular disparity magnitude affects perceived depth magnitude despite inversion of depth order

The hollow-face illusion involves a misperception of depth order: our perception follows our top-down knowledge that faces are convex, even though bottom-up depth information reflects the actual concave surface structure. While pictorial cues can be ambiguous, stereopsis should unambiguously indicate the actual depth order. We used computer-generated stereo images to investigate how, if at all, the sign and magnitude of binocular disparities affect the perceived depth of the illusory convex face. In experiment 1 participants adjusted the disparity of a convex comparison face until it matched a reference face. The reference face was either convex or hollow and had binocular disparities consistent with an average face or had disparities exaggerated, consistent with a face stretched in depth. We observed that apparent depth increased with disparity magnitude, even when the hollow faces were seen as convex (ie when perceived depth order was inconsistent with disparity sign). As expected, concave faces appeared flatter than convex faces, suggesting that disparity sign also affects perceived depth. In experiment 2, participants were presented with pairs of real and illusory convex faces. In each case, their task was to judge which of the two stimuli appeared to have the greater depth. Hollow faces with exaggerated disparities were again perceived as deeper.     

The appearance of surfaces specified by motion parallax and binocular disparity

The experiments reported in this paper were designed to investigate how depth information from binocular disparity and motion parallax cues is integrated in the human visual system. Observers viewed simulated 3-D corrugated surfaces that translated to and fro across their line of sight. The depth of the corrugations was specified by either motion parallax, or binocular disparities, or some combination of the two. The amount of perceived depth in the corrugations was measured using a matching technique.

A monocularly viewed surface specified by parallax alone was seen as a rigid, corrugated surface translating along a fronto-parallel path. The perceived depth of the corrugations increased monotonically with the amount of parallax motion, just as if observers were viewing an equivalent real surface that produced the same parallax transformation. With binocular viewing and zero disparities between the images seen by the two eyes, the perceived depth was only about half of that predicted by the monocular cue. In addition, this binocularly viewed surface appeared to rotate about a vertical axis as it translated to and fro. With other combinations of motion parallax and binocular disparity, parallax only affected the perceived depth when the disparity gradients of the corrugations were shallow. The discrepancy between the parallax and disparity signals was typically resolved by an apparent rotation of the surface as it translated to and fro. The results are consistent with the idea that the visual system attempts to minimize the discrepancies between (1) the depth signalled by disparity and that required by a particular interpretation of the parallax transformation and (2) the amount of rotation required by that interpretation and the amount of rotation signalled by other cues in the display.     

Effects of different motion characteristics on perceived motion in depth

Abstract.— The effect of different velocity characteristics on type of perceived motion were tested with three different stimulus patterns, each representing a certain case of relative motion vectors derived from a vector model for perceived motion in space. The oscilloscope generated patterns, displayed onto a translucent screen, consisted of two dots moving back and forth in their motion paths. The subjects described the perceived motion verbally. The reports were classified into four response categories, i.e. perceived translation in depth, rotation in depth, translation and rotation in depth, and finally, perceived motion in a frontoparallel plane. It was found, first, that no type of relative motion vectors consistently yielded the same distribution of responses for the different velocity conditions. Second, there were no main effects of type of velocity functions (sinusoidal, hyperbolical, and constant) on perceived motion. Third, the position of maximum velocity of the dots affected perceived motion, maximum velocity at the center of the motion path favoring perceived rotation in depth and maximum velocity at the end points of the paths favoring perceived translation in depth. Finally, patterns with continuously repeated motion cycles favored perceived rotation in depth. When the continuity was broken down by pauses at the center and the end points of the motion paths and a small spatial gap at the center of the path, perceived translation in depth was favored.     

Recovery of 3-D shape from binocular disparity and structure from motion

Four experiments were conducted to examine the integration of depth information from binocular stereopsis and structure from motion (SFM), using stereograms simulating transparent cylindrical objects. We found that the judged depth increased when either rotational or translational motion was added to a display, but the increase was greater for rotating (SFM) displays. Judged depth decreased as texture element density increased for static and translating stereo displays, but it stayed relatively constant for rotating displays. This result indicates that SFM may facilitate stereo processing by helping to resolve the stereo correspondence problem. Overall, the results from these experiments provide evidence for a cooperative relationship between. SFM and binocular disparity in the recovery of 3-D relationships from 2-D images. These findings indicate that the processing of depth information from SFM and binocular disparity is not strictly modular, and thus theories of combining visual information that assume strong modularity-or-independence cannot accurately characterize all instances of depth perception from multiple sources.     

Integration of motion parallax with binocular disparity specifying different surface shapes

We investigated the interaction between motion parallax and binocular disparity cues in the perception of surface shape and depth magnitude by the use of the random dot stimuli in which these cues specified sinusoidal depth surfaces undulating with different spatial frequencies. When ambiguous motion parallax is inconsistent with unambiguous disparity cue, the reasonable solution for the visual system is to convert the motion signal to the flow on the surface specified by disparity. Two experiments, however, found that the visual system did not always use this reasonable solution; observers often perceived the surface specified by a composite of the two cues, or the surface specified by parallax alone. In the perception of this composite of the two cues, the apparent depth magnitude increased with the increase of the depth magnitude specified by both cues. This indicates that the visual system can combine the depth magnitude information from parallax and disparity in an additive fashion. The interference with parallax by disparity implies that the parallax processing is not independent of the disparity processing.     

Depth interval estimates from motion parallax and binocular disparity beyond interaction space

Static and dynamic observers provided binocular and monocular estimates of the depths between real objects lying well beyond interaction space. On each trial, pairs of LEDs were presented inside a dark railway tunnel. The nearest LED was always 40 m from the observer, with the depth separation between LED pairs ranging from 0 up to 248 m. Dynamic binocular viewing was found to produce the greatest (ie most veridical) estimates of depth magnitude, followed next by static binocular viewing, and then by dynamic monocular viewing. (No significant depth was seen with static monocular viewing.) We found evidence that both binocular and monocular dynamic estimates of depth were scaled for the observation distance when the ground plane and walls of the tunnel were visible up to the nearest LED. We conclude that both motion parallax and stereopsis provide useful long-distance depth information and that motion-parallax information can enhance the degree of stereoscopic depth seen.     

Matching perceived depth from disparity and from velocity: Modeling and psychophysics

We asked observers to match in depth a disparity-only stimulus with a velocity-only stimulus. The observers’ responses revealed systematic biases: the two stimuli appeared to be matched in depth when they were produced by the projection of different distal depth extents. We discuss two alternative models of depth recovery that could account for these results. (1) Depth matches could be obtained by scaling the image signals by constants not specified by optical information, and (2) depth matches could be obtained by equating the stimuli in terms of their signal-to-noise ratios (see Domini & Caudek, 2009). We show that the systematic failures of shape constancy revealed by observers’ judgments are well accounted for by the hypothesis that the apparent depth of a stimulus is determined by the magnitude of the retinal signals relative to the uncertainty (i.e., internal noise) arising from the measurement of those signals.     

Aging and the discrimination of 3-D shape from motion and binocular disparity

Two experiments evaluated the ability of younger and older adults to visually discriminate 3-D shape as a function of surface coherence. The coherence was manipulated by embedding the 3-D surfaces in volumetric noise (e.g., for a 55?% coherent surface, 55?% of the stimulus points fell on a 3-D surface, while 45?% of the points occupied random locations within the same volume of space). The 3-D surfaces were defined by static binocular disparity, dynamic binocular disparity, and motion. The results of both experiments demonstrated significant effects of age: Older adults required more coherence (tolerated volumetric noise less) for reliable shape discrimination than did younger adults. Motion-defined and static-binocular-disparity-defined surfaces resulted in similar coherence thresholds. However, performance for dynamic-binocular-disparity-defined surfaces was superior (i.e., the observers?? surface coherence thresholds were lowest for these stimuli). The results of both experiments showed that younger and older adults possess considerable tolerance to the disrupting effects of volumetric noise; the observers could reliably discriminate 3-D surface shape even when 45?% of the stimulus points (or more) constituted noise.     

Intersubject variability in perceived oscillation as a function of threshold for binocular disparity.

Four groups of 15 female subjects each were classified along a quantitative dimension for proportion of perceived oscillation and threshold for binocular disparity. Analyses of variance showed that significant differences in proportion of perceived oscillation were accompanied by significant differences in threshold for binocular disparity for perceivers of "high" and "low" oscillation (p less than .05). For perceivers of "intermediate" oscillation significant differences in proportion of perceived oscillation but not threshold for binocular disparity were found. It was suggested that: (1) intersubject variability in perceived oscillation may be governed by the threshold for binocular disparity, (2) "low" perceivers may be especially sensitive to the magnitude of the cue, (3) "intermediate" perceivers' subjective reports may be primarily dependent on response criteria and the multiplicity of subjective factors which constitute it, (4) "high" perceivers apparently have least response sensitivity and they cannot maintain a consistent response criterion.     

The visual control of reaching and grasping: binocular disparity and motion parallax

The primary visual sources of depth and size information are binocular cues and motion parallax. Here, the authors determine the efficacy of these cues to control prehension by presenting them in isolation from other visual cues. When only binocular cues were available, reaches showed normal scaling of the transport and grasp components with object distance and size. However, when only motion parallax was available, only the transport component scaled reliably. No additional increase in scaling was found when both cues were available simultaneously. Therefore, although equivalent information is available from binocular and motion parallax information, the latter may be of relatively limited use for the control of the grasp. Binocular disparity appears selectively important for the control of the grasp.     

The temporal course of the relationship between retinal disparity and the equidistance tendency in the determination of perceived depth

Changes in perceived depth as a function of exposure duration were compared for two stimulus conditions. In one. a depth interval between two points of light was produced by the retinal disparity cue, and in the other condition, otherwise identical to the first, the light points were connected by a thin luminous line. The principle finding was that the perceived depth interval between the light points increased as a function of exposure durations greater than 1 sec, while no change in the perceived depth interval between the end points of the line occurred. The results were interpreted in terms of a greater equidistance tendency (ET) operating for the line than for the point condition. It was concluded that both the ET and the retinal disparity cue increase in strength as a function of exposure duration.     

Interrelation of the effects of binocular disparity and perspective cues on judgments of depth and height

The effects of binocular disparity (aniseikonia) and perspective cues operating together on judgments of depth and height were studied, both when these stimulus variables operated in the same direction and when they were in conflict. Both depth cues were effective upon the perception of depth and height. The effects of binocular disparity and perspective cues upon perceived depth were found to be additive. The effects of these depth cues upon perceived height showed some interaction in the sense that, operating together, the effect of the perspective cue was stronger than the separate effect of the perspective cue, both when binocular disparity and perspective cues operated in the same direction and when they were in conflict. This interactive effect increased with increasing strength of the perspective cues. The size-distance invariance hypothesis was confirmed under the present experimental conditions. By a causal analysis of inference, this invariant relation could be explained in the following way: both the perceived depth and the perceived height of the sides of the patterns were directly determined by binocular disparity and perspective cues, but the perceived height was also indirectly determined through change of perceived depth. A direct causal relation between perceived depth and perceived height was found.     

Seeing stereoscopic depth from disparity between kinetic edges

Traditionally, it is assumed that stereovision operates only on the positional difference (disparity) between luminance-defined features in the images in the left and the right eye. Here, I show that stereoscopic depth can be seen from disparity between edges created by relative motion of texture elements, and between edges created by correlated flicker of stationary texture elements. Luminance-based stereopsis was impossible since the texture was binocularly uncorrelated. Positional disparity of the centre of revolving patterns was not an efficient depth cue. Stereopsis from the stimuli presented here was possible even without binocular overlap of textured areas. The results provide evidence that positional disparity of kinetic edges, defined by correlated flicker or motion contrast alone, can be used as matching features to recover stereoscopic depth.     

Visually perceived motion in depth resulting from proximal changes. I

According to a model for form and motion perception proposed by Johansson (1964), every two-dimensional change in the proximal stimulation is projected out as a motion in depth. The amount of perceived depth motion can then be predicted from the projective relationship between the proximal change and the projected motion. This prediction was tested in a series of experiments by using squares that continuously changed their sizes as stimuli, and measuring perceived distance of motion in depth. The obtained relationship between perceived and predicted distance of motion was curvilinear for all Ss. Furthermore, the majority of the Ss underestimated the motion systematically, the remainder overestimated it. Thus, the prediction given in the model could not be verified. However, an alternative projective relation based on the assumption that a fixed proportion of the change is not projected out as a motion but perceived as a change of size agreed quite well with the data, both with distance judgments and with judgments of perceived change of size.     

Independent effects of local and global binocular disparity on the perceived convexity of stereoscopically presented faces in scenes

Evidence suggests that experiencing the hollow-face illusion involves perceptual reversal of the binocular disparities associated with the face even though the rest of the scene appears unchanged. This suggests stereoscopic processing of object shape may be independent of scene-based processing of the layout of objects in depth. We investigated the effects of global scene-based and local object-based disparity on the compellingness of the perceived convexity of the face. We took stereoscopic photographs of people in scenes, and independently reversed the binocular disparities associated with the head and scene. Participants rated perceived convexity of a natural disparity ("convex") or reversed disparity ("concave") face shown either in its original context with reversed or natural disparities or against a black background. Faces with natural disparity were rated as more convincingly convex independent of the background, showing that the local disparities can affect perceived convexity independent of disparities across the rest of the image. However, the apparent convexity of the faces was also greater in natural disparity scenes compared to either a reversed disparity scene or a zero disparity black background. This independent effect of natural scene disparity suggests that the 'solidity' associated with natural scene disparities spread to enhance the perceived convexity of the face itself. Together, these findings suggest that global and local disparity exert independent and additive effects upon the perceived convexity of the face.