Direction Of Motion In Depth Research Articles

Enhancing Motion-In-Depth Perception of Random-Dot Stereograms.

Random-dot stereograms have been widely used to explore the neural mechanisms underlying binocular vision. Although they are a powerful tool to stimulate motion-in-depth (MID) perception, published results report some difficulties in the capacity to perceive MID generated by random-dot stereograms. The purpose of this study was to investigate whether the performance of MID perception could be improved using an appropriate stimulus design. Sixteen inexperienced observers participated in the experiment. A training session was carried out to improve the accuracy of MID detection before the experiment. Four aspects of stimulus design were investigated: presence of a static reference, background texture, relative disparity, and stimulus contrast. Participants' performance in MID direction discrimination was recorded and compared to evaluate whether varying these factors helped MID perception. Results showed that only the presence of background texture had a significant effect on MID direction perception. This study provides suggestions for the design of 3D stimuli in order to facilitate MID perception.

Sensory uncertainty leads to systematic misperception of the direction of motion in depth.

Although we have made major advances in understanding motion perception based on the processing of lateral (2D) motion signals on computer displays, the majority of motion in the real (3D) world occurs outside of the plane of fixation, and motion directly toward or away from observers has particular behavioral relevance. Previous work has reported a systematic lateral bias in the perception of 3D motion, such that an object on a collision course with an observer's head is frequently judged to miss it, with obvious negative consequences. To better understand this bias, we systematically investigated the accuracy of 3D motion perception while manipulating sensory noise by varying the contrast of a moving target and its position in depth relative to fixation. Inconsistent with previous work, we found little bias under low sensory noise conditions. With increased sensory noise, however, we revealed a novel perceptual phenomenon: observers demonstrated a surprising tendency to confuse the direction of motion-in-depth, such that approaching objects were reported to be receding and vice versa. Subsequent analysis revealed that the lateral and motion-in-depth components of observers' reports are similarly affected, but that the effects on the motion-in-depth component (i.e., the motion-in-depth confusions) are much more apparent than those on the lateral component. In addition to revealing this novel visual phenomenon, these results shed new light on errors that can occur in motion perception and provide a basis for continued development of motion perception models. Finally, our findings suggest methods to evaluate the effectiveness of 3D visualization environments, such as 3D movies and virtual reality devices.

Neural representation of motion-in-depth in area MT.

Neural processing of 2D visual motion has been studied extensively, but relatively little is known about how visual cortical neurons represent visual motion trajectories that include a component toward or away from the observer (motion in depth). Psychophysical studies have demonstrated that humans perceive motion in depth based on both changes in binocular disparity over time (CD cue) and interocular velocity differences (IOVD cue). However, evidence for neurons that represent motion in depth has been limited, especially in primates, and it is unknown whether such neurons make use of CD or IOVD cues. We show that approximately one-half of neurons in macaque area MT are selective for the direction of motion in depth, and that this selectivity is driven primarily by IOVD cues, with a small contribution from the CD cue. Our results establish that area MT, a central hub of the primate visual motion processing system, contains a 3D representation of visual motion.

Vision and cricket

This review discusses the hypothesis that hitting a cricket ball depends on predicting the instant that the ball will be located in the volume of space within which it can be successfully hit, and that this prediction is based on retinal image correlates of the direction of motion in depth and the time to collision (or time to passage). The performance of top cricket players allows an estimation of their accuracy in this spatio-temporal prediction. The bowler challenges the batsman's skill by (1) causing the ball to change direction in flight and/or after bouncing and (2) causing linked variations in the speed and trajectory of the ball. I suggest that the linked variations of speed and trajectory exploit a visual inadequacy of the batsman, namely poor sensitivity to the instantaneous absolute distance and speed of the ball. Two alternative hypothese are also discussed, one based on eye movements, the other based on continuous coupling between perception and action.

Binocular processing of motion: some unresolved questions

The unresolved questions relating to binocular processing of motion include: Is the perceived speed of the motion in depth (MID) of an approaching object inversely proportional to the time to collision?; What visual information supports judgements of the direction of MID?; What is the relation between binocular and monocular processing in the perception of MID? We review whether the perception of stereomotion in depth of a monocularly visible object is caused entirely by a rate of change of disparity, and conclude that the difference between the horizontal velocities of the object's left and right retinal images makes at most only a small contribution to speed discrimination, but conclusions may be different for detection, perceived speed and directional discrimination. We review laboratory evidence on the relative importance of binocular and monocular information for interceptive action and collision avoidance and conclude that, in addition to the effect of considerable intersubject variability, the relative importance depends on the physical size of the approaching object, its distance and, if nonspherical, its direction of motion and whether it is rotating. We compare attempts to find whether the human visual system contains a mechanism specialized for the speed of cyclopean motion within a frontoparallel plane, and find the question ill-posed.

Whether radial receptive field organization of the fourth extrastriate crescent (area V4A) gives special advantage for analysis of the optic flow. Comparison with the first crescent (area V2)

Recently, elongated comet-shaped receptive fields were discovered in the fourth extrastriate crescent (area V4A) of cats and monkeys. It was shown that the long axes of these receptive fields were oriented radially toward the centre of the retina. Such unusual "radial" organization of this extrastriate area led to the assumption that these neurons may contribute to the analysis of optic flow. To investigate this assumption we recorded activity of neurons in the V4A of cats during real motion in depth toward or away from a stationary visual scene. Responses of neurons in area V4A were compared with activity of neurons in area V2 under similar conditions of stimulation. Area V2 is known to be sensitive to motion but does not have radial organization. It was found that a substantial number of visual neurons in both areas did not fire at all when cats were exposed to motion in depth. Nevertheless, neurons with selective activation to direction of motion in depth were identified, but comparable numbers were found in both areas studied. We conclude that radial organization of the fourth extrastriate crescent does not provide any special advantage for the analysis of optic flow information.

Unconfounding the direction of motion in depth, time to passage and rotation rate of an approaching object

Observers were presented with a set of 216 simulated approaching textured baseballs in random order. In Experiment 1 each had a different combination of time to passage (TTP), direction of motion in depth (dMID) in the vertical plane and total change in angular size (Δ θ). In Experiments 2 and 3 each had a different combination of TTP, dMID and rate of ball rotation (RR). When required to discriminate TTP and dMID in separate experimental blocks for a non-rotating baseball (Experiment 1), observers could not discriminate dMID independently of variations in TTP but instead showed a bias towards perceiving objects approaching on a trajectory close to the nose as having a shorter TTP than objects approaching on a trajectory that would miss the face. When required to discriminate TTP, dMID and RR in separate experimental blocks (Experiment 2), TTP judgments were again influenced by dMID but could be made independently of RR. Judgments of the relative dMID were affected by variations in RR and rotation direction: for simulated overspin the (i.e., the top of the ball spins towards the observer) perceived ball trajectory was biased towards the ground whereas for simulated underspin the perceived ball trajectory was biased towards the sky. RR could be discriminated independently of both TTP and dMID. When required to make all three of these judgments simultaneously on each trial (Experiment 3) discrimination thresholds were not appreciably different from those found in Experiment 2. We conclude that TTP, dMID and RR can be estimated in parallel but not completely independently within the human visual system.

Seeing motion in depth using inter-ocular velocity differences

An object moving in depth produces retinal images that change in position over time by different amounts in the two eyes. This allows stereoscopic perception of motion in depth to be based on either one or both of two different visual signals: inter-ocular velocity differences, and binocular disparity change over time. Disparity change over time can produce the perception of motion in depth. However, demonstrating the same for inter-ocular velocity differences has proved elusive because of the difficulty of isolating this cue from disparity change (the inverse can easily be done). No physiological data are available, and existing psychophysical data are inconclusive as to whether inter-ocular velocity differences are used in primate vision. Here, we use motion adaptation to assess the contribution of inter-ocular velocity differences to the perception of motion in depth. If inter-ocular velocity differences contribute to motion in depth, we would expect that discriminability of direction of motion in depth should be improved after adaptation to frontoparallel motion. This is because an inter-ocular velocity difference is a comparison between two monocular frontoparallel motion signals, and because frontoparallel speed discrimination improves after motion adaptation. We show that adapting to frontoparallel motion does improve both frontoparallel speed discrimination and motion-in-depth direction discrimination. No improvement would be expected if only disparity change over time contributes to motion in depth. Furthermore, we found that frontoparallel motion adaptation diminishes discrimination of both speed and direction of motion in depth in dynamic random dot stereograms, in which changing disparity is the only cue available. The results provide strong evidence that inter-ocular velocity differences contribute to the perception of motion in depth and thus that the human visual system contains mechanisms for detecting differences in velocity between the two eyes’ retinal images.

Spatial and temporal tuning of motion in depth

We used the Pulfrich effect to investigate perception of motion in depth. Independent manipulation of spatial and temporal frequency content in stereoscopic motion stimuli revealed the tuning characteristics of motion-in-depth perception. Sensitivity to interocular phase difference between sinusoidally oscillating sine-wave gratings was measured in four observers who judged direction of motion in depth. Discrimination thresholds in terms of interocular phase difference were determined to investigate spatial and temporal tuning characteristics of a system that is based on interocular phase difference, interocular delay, binocular disparity and velocity difference. Temporal frequency tuning of interocular phase difference thresholds was band pass and relatively dependent on spatial frequency variation. These results together with evidence from two control experiments support the idea that sensitivity to direction of motion in depth is limited by a stereo-motion system that monitors binocular horizontal disparity and motion rather than interocular phase difference, interocular delay, or interocular velocity difference.

Development of a Human-like Head Robot for Emotional Communication with Human. 1 st Report. Development of Facial Expressions and Visual Sensation.

The authors developed a human-like head robot WE-3 RV (W__-aseda E__-ye No. 3__- R__-efined V__-). It realized the pursuing motion in 3 D space using coordinated head-eye motion with V.O.R. (Vestibular-Ocular Reflex) as well as pursuing a motion in depth direction psing the angle of convergence between the two eyes. Moreover, it can express human like facial expressions using eyebrows, eyelids, lips, jaw, facial color and voice.

フレッシュパーソン9-4 奥行き方向の運動の方向知覚における輻輳運動と焦点調節の役割

フレッシュパーソン9-4 奥行き方向の運動の方向知覚における輻輳運動と焦点調節の役割

Discrimination of the direction and speed of motion in depth of a monocularly visible target from binocular information alone.

Thresholds for discriminating a monocularly visible object's direction of motion in depth and speed of motion in depth were measured using only binocular cues. Observers could discriminate the direction of motion in depth while totally ignoring speed and discriminate the speed of motion in depth while totally ignoring direction. Direction discrimination thresholds were the same for motion in depth within the vertical and horizontal meridians, even though a cue to trajectory was available for motion within the horizontal meridian that is not available for motion within the vertical meridian. Speed discrimination thresholds also were the same for motion in depth within the vertical and horizontal meridians. For the 3 observers the lowest direction discrimination thresholds were 0.14 degree, 0.18 degree, and 0.22 degree (means of horizontal and vertical thresholds).

Visual factors in hitting and catching

To hit or catch an approaching ball, it is necessary to move a bat or hand to the right place at the right time. The performance of top sports players is remarkable: positional errors of less than 5 cm and temporal errors of less than 2 or 3 ms are reliably maintained. There are three schools of thought about how this is achieved. One holds that predictive visual information about where the ball will be at some future instance (when) is used to achieve the hit or catch. The second holds that the bat or hand is moved to the correct position by exploiting some relation between visual information and the required movement. The third focuses on the use of prior knowledge to supplement inadequate visual information. For a rigid spherical ball travelling at constant speed along or close to the line of sight, the retinal images contain both binocular and monocular correlates of the ball's instantaneous direction of motion in depth. Also, the retinal images contain both binocular and monocular information about time of arrival. Humans can unconfound and use this visual information, but they are unable to estimate the absolute distance of the ball or its approach speed other than crudely. In cricket, this visual inadequacy allows a slow bowler to cause the batsman to misjudge where the ball will hit the ground. Such a bowler uses a three-pronged strategy: first, to deliver the ball in such a way as to prevent the batsman from obtaining the necessary visual information until it is too late to react; secondly, to force the batsman to rely entirely on inadequate retinal image information; thirdly, to allow the batsman to learn a particular relationship between the early part of the ball's flight and the point where the ball hits the ground, and then to change the relationship with such skill that the batsman does not detect the change.

Cyclopean Discrimination Thresholds for the Direction and Speed of Motion in Depth

We measured just-noticeable differences in the direction and speed of motion in depth of cyclopean and monocularly visible targets. Our stimulus set comprised different combinations of (dφ/dt)/(dδ/dt), dδ/dt, dφ/dt and Δδ, where dφ/dt was the angular frontal plane speed of the binocularly-fused target, dδ/dt was its rate of change of disparity and Δδ was its disparity displacement. Our three subjects based their direction discriminations entirely on the task-relevant variable (dφ/dt)/(dδ/dt), and based their speed discriminations entirely on the task-relevant variable dδ/dt. They ignored all task-irrelevant variables in both tasks. Performance on both tasks was the same for motion within the horizontal and vertical meridians. Direction discrimination threshold rose significantly as the reference direction grew more oblique with respect to a line passing midway between the eyes and perpendicular to the frontal plane. Performance on the direction discrimination task was significantly better for the noncyclopean than for the cyclopean target, but the difference was not great. For the cyclopean target, the lowest value of the direction discrimination threshold was 0.70 deg (mean of three observers and two meridians). The Weber fraction for discriminating speed was not significantly different for the cyclopean and monocularly visible targets, and did not depend on the direction of motion in depth. The lowest values (mean of three observers and two meridians) were 0.12 (cyclopean) and 0.10 (noncyclopean). Findings did not scale for viewing distance. We propose that the human visual pathway contains: (a) a cyclopean mechanism sensitive to variations in the ratio (dφ/dt)/(dδ/dt) that is comparatively insensitive to both dφ/dt and dδ/dt; and (b) a speed-sensitive cyclopean mechanism that responds to variations in the value of dδ/dt, but is comparatively insensitive to dφ/dt. We also propose that a single speed-sensitive mechanism determines speed discrimination thresholds for both cyclopean and monocularly visible targets. Copyright © 1996 Elsevier Science Ltd.

The Hierarchical nature of perceiving direction of motion in depth from optic flow

Monocular adaptation to flow fields of optic expansion and contraction juxtaposed on either side of fixation influenced subsequently perceived rotation direction of a figure rotating in depth (kinetic depth effect) about its vertical axis with a normally ambiguous direction. This influence was shown to be asymmetric since adapting to optic expansion produced significantly more aftereffects of translation in depth than did adapting to perceived rotation in depth when viewing a neutral test stimulus. The results are evidence for a hierarchical processing model for the perception of motion in depth from optic flow. Serendipitously, we discovered a new aftereffect from viewing kinetic depth rotation with direction specified by proximity-luminance covariation (PLC). The results and other research are discussed in terms of neural network models with synergistic interactions between levels.

Visual processing of the motion of an object in three dimensions for a stationary or a moving observer.

A rate of change of relatively disparity is a sufficient binocular stimulus for the perception of motion in depth. For motion within the meridian that contains the eyes, disparity change associated with approaching motion is processed through four channels, each tuned to a different direction of motion in depth. Directional discrimination is most acute but detection sensitivity falls to a minimum for a trajectory passing approximately midway between the eyes. This can be explained if discrimination depends on the relatively of the four channels. Two binocular retinal-image correlates of the direction of the motion of an object in depth are the ratio between the velocities of the retinal images of the object in the left and right eyes [(d phi/dt)R/(d phi/dt)L], and the ratio between the translational velocity of the binocularly fused images and the rates of change of disparity [(d phi/dt)/(d gamma/dt)]. Directional discrimination is possible by using the second cue alone. An isotropic rate of expansion of the retinal image is a sufficient monocular stimulus for the perception of motion in depth. There is no evidence that expansion is processed through channels tuned to the direction of motion in depth. Two monocular correlates of the direction of the motion of an object in depth are the ratio between the translational velocity and the rate of expansion of the retinal image of the object [(d phi/dt)/(d theta/dt)], and the ratio between the velocities of opposite edges of the retinal image [(d alpha 1/dt)/(d alpha 2/dt)]. Subjects are able monocularly to discriminate the direction of motion in depth with high acuity (better than 0.1 deg threshold) in the vertical, horizontal, or oblique meridians, even when the direction and the speed of translational motion are removed as cues. Visual discrimination of time to contact with an approaching object can be disconfounded from discrimination of its rate of expansion and vice versa with a threshold separation ratio of as much as 100:1.

Monocular discrimination of the direction of motion in depth

The direction of motion in depth of a monocularly-viewed rigid sphere can be quantified in terms of the distance by which the sphere's centre will miss the centre of the pupil of the observing eye. If we express this distance as ns (where s is the sphere's radius and n is a scaling factor), then n approximates the ratio (d Φ/d t)(d θ/d t) between the translational velocity (d Φ/d t) and the rate of expansion (d θ/d t) of the object's retinal image. To use this monocular information alone as a basis for motor action, prior knowledge of 5 would be necessary. (However, the value of s is available from binocular information, so that die distance by which the sphere's centre would miss the eye is, in principle, available from retinal image information alone and, in particular, without knowing the object's size or distance from the eye.) We measured the just-discriminable difference in the direction of motion in depth for a monocularly-viewed simulated object. Thresholds were measured for trajectories contained within the horizontal, vertical and two oblique mendia. The translational speed of the retinal image was removed as a reliable cue to the direction of motion in depth by randomly varying the simulated object's speed on a trial to trial basis. The direction of translational motion was also removed as a reliable cue. Discrimination threshold for the simulated direction of motion ranged from 0.03 to 0.12 deg for our seven subjects, and did not vary appreciably with the direction of motion relative to the Une of sight over the range investigated, nor did it depend on whether trajectory was contained within the horizontal, vertical or oblique meridia. We conclude that subjects are able monocidarly to discriminate differences in the direction of motion in depth, even when both the direction and speed of retinal image translation are removed as reliable cues.

Binocular correlates of the direction of motion in depth.

Two binocular cues to the direction of an object's motion in depth are the ratio (phi R/phi L) between the velocities of the object's retinal images in the right and left eyes and the ratio (phi/gamma) between the velocity of the binocularly-fused image of the object and the rate of change of disparity. We report that the apparent direction of motion in depth of a monocularly-camouflaged target can be varied by altering the ratio phi/gamma. Because no monocular motion signal is available in this case, we conclude that the ratio phi/gamma is a sufficient cue to the direction of motion in depth. This is not to deny that the phi R/phi L cue might be used in the everyday visual situation where monocular velocities phi R and phi L are available to the brain.

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 tight 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 die difference limen for motions toward the eyes as has been observed with changing-disparity stimuli.

Motion parallax information for direction of rotation in depth: order and direction components.

The work of Hershberger and his associates has demonstrated the effectiveness for judging direction of rotation in depth of several components of motion parallax. Confounding and conflicting results have made the status of two of these transformations, labeled Direction and Order, unclear. A study is reported in which the problems encountered in previous studies have been eliminated. College students correctly judged the direction of rotation of horizontal rows of dots which appeared to rotate in depth, which demonstrates that Direction and Order can, in fact, provide useful information about direction of motion in depth.