Random-dot Stereograms Stimuli Research Articles

Effect of disparity and viewing ambient illumination on stereoscopic viewing: An eye movement approach

AbstractResearchers have found that factors related to viewing content and viewing environment could influence viewers' stereoscopic viewing experiences. In this paper, the effect of both disparity and viewing ambient illumination condition on stereoscopic viewing was investigated by using an eye movement approach. The eye movement responses to random dot stereograms (RDS) stimuli in stereoscopic viewing were studied by performing a fusion range measurement experiment involving a judgment task. The fusion ranges under two ambient illumination conditions, eye movement responses to RDS stimuli and effects of disparity on eye movement parameters, were analyzed, respectively. The experimental results showed that fusion range under two ambient illumination conditions were different, and changes of eye movement parameters were different among various disparities when ambient illumination conditions varied. As a result, in order to improve viewers' viewing experiences when viewing different 3D contents, the arrangement of viewing ambient illumination conditions and the selection of disparity should be appropriately considered. The findings in this paper provide guidelines to reasonably arrange the viewing ambient illumination condition and efficiently produce healthy disparity in stereoscopic viewing.

Imaging of Convergence Insufficiency Treatment Effects (ICITE) Pilot Study: Design and Methods

Background: The blood-oxygen-level-dependent (BOLD) signal from functional magnetic resonance imaging (fMRI) identifies brain activation during specific tasks.1,2 This paper describes the design and methodology of the Imaging of Convergence Insufficiency Treatment Effects (ICITE) Study, a two-phase study comparing BOLD activations during vergence eye movements in symptomatic convergence insufficiency (CI) subjects (1) to those with normal binocular vision (NBV) and (2) after office-based vergence/accommodative therapy (OBVAT) versus office-based placebo therapy (OBPT). Methods: Young adults, 18 to 30 years, with NBV or symptomatic CI (near exophoria at least 4Δ [prism diopters] greater than at distance, receded near point of convergence [NPC], and insufficient positive fusional vergence [PFV]) were enrolled. During fMRI scanning, subjects were instructed to fuse a random-dot stereogram stimulus with vergence demands ranging from -3Δ to +25Δ. CI subjects were then randomized to 12 weeks of OBVAT or OBPT. Vision and fMRI examination at outcome were performed by a masked examiner. BOLD signal at baseline was compared between NBV and CI patients. Later, the BOLD response at baseline was compared to that following vision therapy for those with CI. Conclusion: The imaging results are expected to advance understanding of neurological mechanisms of CI and the effects of therapy on the vergence system, which in turn may guide development of future research that could lead to new treatment strategies.

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.

Stereoscopic depth perception varies with hues

The contribution of color information to stereopsis is controversial, and whether the stereoscopic depth perception varies with chromaticity is ambiguous. This study examined the changes in depth perception caused by hue variations. Based on the fact that a greater disparity range indicates more efficient stereoscopic perception, the effect of hue variations on depth perception was evaluated through the disparity range with random-dot stereogram stimuli. The disparity range was obtained by constant-stimulus method for eight chromaticity points sampled from the CIE 1931 chromaticity diagram. Eight sample points include four main color hues: red, yellow, green, and blue at two levels of chroma. The results show that the disparity range for the yellow hue is greater than the red hue, the latter being greater than the blue hue and the disparity range for green hue is smallest. We conclude that the perceived depth is not the same for different hues for a given size of disparity. We suggest that the stereoscopic depth perception can vary with chromaticity.

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.

Spatial scale of stereomotion speed processing

To examine the spatial scale of the mechanisms supporting the perception of motion in depth defined by binocular cues, we measured stereomotion speed discrimination thresholds as a function of stimulus size using a two-interval speed comparison task. Stimuli were either random dot stereogram (RDS) bars featuring both the changing disparity (CD) and the interocular velocity difference (IOVD) cues to motion in depth or dynamic random dot stereogram (DRDS) bars featuring the CD cue alone. Monocular speed discrimination performance was also assessed, using half-images of the RDS stimulus. In addition, subjects' stereoacuity for stationary versions of the binocular stimuli was measured. Stimuli ranged in vertical extent from 1.25 to 40 min. Sensitivity to speed differences was strongly related to stimulus height for DRDS stimuli. Performance decreased rapidly as stimulus size was reduced, becoming nearly random for heights below 5 min. However, for RDS stimuli, speed discrimination performance declined with reductions in stimulus size at a far slower rate, providing superior performance at every stimulus size used. Monocular performance was superior still for the majority of subjects, yet showed a similar rate of decline to binocular RDS stimuli. We conclude that the spatial resolution of the CD mechanism and its static disparity inputs is, on average, nearly nine times more coarse than the IOVD system and its monocular motion inputs. Static stereoacuity controls show that this finding cannot be explained by differences in the disparity signals available in our RDS and DRDS stimuli.

Stereomotion speed perception: Contributions from both changing disparity and interocular velocity difference over a range of relative disparities

The role of two binocular cues to motion in depth-changing disparity (CD) and interocular velocity difference (IOVD)- was investigated by measuring stereomotion speed discrimination and static disparity discrimination performance (stereoacuity). Speed discrimination thresholds were assessed both for random dot stereograms (RDS), and for their temporally uncorrelated equivalents, dynamic random dot stereograms (DRDS), at relative disparity pedestals of -19, 0, and +19 arcmin. While RDS stimuli contain both CD and IOVD cues, DRDS stimuli carry only CD information. On average, thresholds were a factor of 1.7 higher for DRDS than for RDS stimuli with no clear effect of relative disparity pedestal. Results were similar for approaching and receding targets. Variations in stimulus duration had no significant effect on thresholds, and there was no observed correlation between stimulus displacement and perceived speed, confirming that subjects responded to stimulus speed in each condition. Stereoacuity was equally good for our RDS and DRDS stimuli, showing that the difference in stereomotion speed discrimination performance for these stimuli was not due to any difference in the precision of the disparity cue. In addition, when we altered stereomotion stimulus trajectory by independently manipulating the speeds and directions of its monocular half-images, perceived stereomotion speed remained accurate. This finding is inconsistent with response strategies based on properties of either monocular half-image motion, or any ad hoc combination of the monocular speeds. We conclude that although subjects are able to discriminate stereomotion speed reliably on the basis of CD information alone, IOVD provides a precise additional cue to stereomotion speed perception.

Interocular velocity difference contributes to stereomotion speed perception.

Two experiments are presented assessing the contributions of the rate of change of disparity (CD) and interocular velocity difference (IOVD) cues to stereomotion speed perception. Using a two-interval forced-choice paradigm, the perceived speed of directly approaching and receding stereomotion and of monocular lateral motion in random dot stereogram (RDS) targets was measured. Prior adaptation using dysjunctively moving random dot stimuli induced a velocity aftereffect (VAE). The degree of interocular correlation in the adapting images was manipulated to assess the effectiveness of each cue. While correlated adaptation involved a conventional RDS stimulus, containing both IOVD and CD cues, uncorrelated adaptation featured an independent dot array in each monocular half-image, and hence lacked a coherent disparity signal. Adaptation produced a larger VAE for stereomotion than for monocular lateral motion, implying effects at neural sites beyond that of binocular combination. For motion passing through the horopter, correlated and uncorrelated adaptation stimuli produced equivalent stereomotion VAEs. The possibility that these results were due to the adaptation of a CD mechanism through random matches in the uncorrelated stimulus was discounted in a control experiment. Here both simultaneous and sequential adaptation of left and right eyes produced similar stereomotion VAEs. Motion at uncrossed disparities was also affected by both correlated and uncorrelated adaptation stimuli, but showed a significantly greater VAE in response to the former. These results show that (1) there are two separate, specialised mechanisms for encoding stereomotion: one through IOVD, the other through CD; (2) the IOVD cue dominates the perception of stereomotion speed for stimuli passing through the horopter; and (3) at a disparity pedestal both the IOVD and the CD cues have a significant influence.

Modeling V1 neuronal responses to orientation disparity

The contribution of interocular orientation differences to depth perception, at either the neuronal or the psychophysical level, is unclear. To understand the responses of binocular neurons to orientation disparity, we extended the energy model of Ohzawa et al. (1990) to incorporate binocular differences in receptive-field orientation. The responses of the model to grating stimuli with interocular orientation differences were examined, along with the responses to random dot stereograms (RDS) depicting slanted surfaces. The responses to combinations of stimulus orientations in the two eyes were left-right separable, which means there was no consistent response to the binocular orientation difference. All existing neuronal data concerning orientation disparity can be well described by this type of model (even a version with no disparity selectivity). The disparity sensitive model is nonetheless sensitive to changes in RDS slant, although it requires narrow orientation bandwidth to produce substantial modulation. The disparity-insensitive model shows no selectivity to slant in this stimulus. Several modifications to the model were attempted to improve its selectivity for orientation disparity and/or slant. A model built by summing several disparity-sensitive models showed left-right inseparable responses, responding maximally to a consistent orientation difference. Despite this property, the selectivity for slant in RDS stimuli was no better than the simple disparity-selective model. The range of models evaluated here demonstrate that interocular orientation differences are neither necessary nor sufficient for signaling slant. In contrast, within the framework of the energy model, positional disparity sensitivity appears to be both necessary and sufficient.

Contrast and stereoscopic visual stimuli yield lateralized scalp potential fields associated with different neural generators

The use of dynamic random-dot stereograms (RDS) allows to investigate evoked potential components generated exclusively by cortical structures. We analyzed the scalp distribution of stereoscopically evoked or contrast evoked potential fields by recording electrical brain activity in 20 channels simultaneously from an electrode array covering the occipital scalp areas. Evoked brain activity was obtained from 13 healthy adults with dynamic RDS stimuli presented as a stereoscopic checkerboard pattern in the center, or in the right or left visual half-field. Such stereoscopically evoked scalp potential distributions were compared to those elicited by a conventional 2-dimensional checkerboard reversal stimulus of the same mean luminance and retinal extent. We found that the latencies of the major evoked components were similar for contrast and stereoscopic stimuli, while significant differences were observed when we compared the strength of the evoked potential fields or the topographical pattern elicited by lateralized stereoscopic and contrast stimuli. The functional relation of evoked electrical brain activity to the retinal stimulus location was significantly different for stereoscopic and contrast stimuli. We present evidence that stereoscopic perception relies on the activation of cortical structures in the human visual system that are different from those activated by comparable contrast stimuli, supporting the conclusions derived from our earlier electrophysiological experiments on stereoscopic vision. These data on the physiological correlates of processing of stereoscopic information in humans are in line with the results obtained with single neuron recordings from the cat and monkey visual cortex.

New phenomena linking depth and luminance in stereoscopic motion

A novel random-dot stereogram (RDS) was used to study stereoscopic motion. For this RDS stimulus, the direction of luminance motion and the direction of the moving cyclopean pattern can be independently controlled. The perceived cyclopean motion was examined under five different conditions, in which the cyclopean pattern was moving either up or down, the luminant dots were: (1) moving in the cyclopean direction; (2) moving opposite to the cyclopean direction; (3) moving orthogonal to the cyclopean direction, (4) stationary; or (5) dynamic (dots uncorrelated in successive frames). The study showed that luminance direction dominated cyclopean direction and that smooth and coherent cyclopean motion is seen only if luminance motion is present. The results suggest that stereoscopic motion is processed by interactions between separate binocular disparity units and luminance motion units, and not by a single binocular motion system, in which binocular units are tuned to both disparity and direction of motion.

Visual persistence of stereoscopic stimuli: Electric brain activity without perceptual correlate

Dynamic random-dot stereograms (RDS) were used to study cortical neuronal mechanisms related to visual persistence in nine subjects. Electric brain potential components evoked by stereoscopic stimuli were compared to those evoked by conventional checkerboard stimuli with contrast borders. In a pattern-onset/offset presentation visual persistence thresholds were significantly lower for stereoscopic than for contrast stimuli: with temporally modulated patterns stereoscopic stimuli appeared to visually persist at much shorter interstimulus intervals than contrast stimuli. With stereoscopic stimuli all subjects reported not seeing changes of the RDS pattern, while the corresponding evoked potentials showed components related to the stimulus changes indicating a consistent discrepancy between psychophysical and electrophysiological data. The electrical brain activity was not caused by vergence eye movements elicited by the stereoscopic stimulus. In addition, for dynamic RDS stimuli a significant inverse linear relationship between temporal modulation frequency and evoked potential amplitude was found which was not observed with comparable contrast stimuli.