Depth Motion Research Articles

Interruption of visually perceived forward motion in depth evokes a cortical activation shift from spatial to intentional motor regions

Forward locomotion generates a radially expanding flow of visual motion which supports goal-directed walking. In stationary mode, wide-field visual presentation of optic flow stimuli evokes the illusion of forward self-motion. These effects illustrate an intimate relation between visual and motor processing. In the present fMRI study, we applied optic flow to identify distinct interfaces between circuitries implicated in vision and movement. The dorsal premotor cortex (PMd) was expected to contribute to wide-field forward motion flow (FFw), reflecting a pathway for externally triggered motor control. Medial prefrontal activation was expected to follow interrupted optic flow urging internally generated action. Data of 15 healthy subjects were analyzed with Statistical Parametric Mapping and confirmed this hypothesis. Right PMd activation was seen in FFw, together with activations of posterior parietal cortex, ventral V5, and the right fusiform gyrus. Conjunction analysis of the transition from wide to narrow forward flow and reversed wide-field flow revealed selective dorsal medial prefrontal activation. These findings point at equivalent visuomotor transformations in locomotion and goal-directed hand movement, in which parietal–premotor circuitry is crucially implicated. Possible implications of an activation shift from spatial to intentional motor regions for understanding freezing of gait in Parkinson's disease are discussed: impaired medial prefrontal function in Parkinson's disease may reflect an insufficient internal motor drive when visual support from optic flow is reduced at the entrance of a narrow corridor.

Brain areas involved in perception of motion in depth: a human fMRI study

Brain areas involved in perception of motion in depth: a human fMRI study

Contributions of vergence, looming, and relative disparity to the perception of motion in depth

Contributions of vergence, looming, and relative disparity to the perception of motion in depth

Cortical regions for the processing of stereoscopic motion in depth as revealed by fMRI in the alert rhesus monkey

Cortical regions for the processing of stereoscopic motion in depth as revealed by fMRI in the alert rhesus monkey

Human perception of image speed derived from the simultaneous extraction and analysis of visual information in two- and three-dimensional space

An important task of the visual system is to extract speed estimates from the two-dimensional image plane (2D) and from motion in depth (3D), or, as in the majority of scenes, from a combination of both. However, it remains unclear from available research how 2D and 3D speeds are combined. We addressed this issue using a square (5×5deg) Global Dot Motion (GDM) stimulus consisting of 100 circular dots (radius: 8minarc, 90 cd/m2) undergoing random motion on a grey computer screen (45cd/m2). Concurrently, the entire GDM stimulus was displaced in depth (by systematically changing binocular disparity) towards the observer. Using this stimulus, we determined how the 3D speed of the dot-defined square is affected by systematic manipulation of 2D dot speed. A two-interval forced-choice procedure was used. One interval presented the reference stimulus: a dot defined square moving in depth at speeds of 4, 6 and 9cm/sec with no 2D motion, while the other presented the test stimulus: an identical dot defined square, but containing dots moving randomly at speeds of: 0 0.4, 0.8, 1.6 and 3.2cm/sec on the image plane. The task of the observer was to adjust the test stimulus 3D speed to match the reference stimulus. Results show that increasing 2D speed increased the apparent 3D speed of the dot-defined square in a manner consistent with the vector sum of 2D and 3D velocities. We discuss our findings in light of the functional properties of global motion detectors tuned for speed information.

Slant stereomotion: A new kind of depth motion from modulation of interocular spatial frequency difference

Slant stereomotion: A new kind of depth motion from modulation of interocular spatial frequency difference

Interaction of scene background, size change, direction and velocity in determining perceived motion in depth

Interaction of scene background, size change, direction and velocity in determining perceived motion in depth

Visual velocity aftereffects in radial flow: Inherited and unique features

A realistic radial flow field contains a range of local velocities, yet global movement is perceived at a single speed. The present experiments explore the contribution of complex motion sensors to this velocity percept, by recording changes in speed perception and speed sensitivity after adaptation to or to coherently expanding/contracting radial flow. A large-scale drifting concentric sine grating, conveying motion in depth, was confined to non-abutting display sectors, defining different global patterns of flow. After adapting to a flow pattern in one display region, observers compared its speed to that in a non-adapted region. Velocity aftereffects (VAEs) from continuous unchanging motion were independent of the pattern of flow: apparent speed was reduced and speed discrimination improved in inverse proportion to the speed of the test. Sensitivity to speed differences, however, was pattern specific, and superior for expansion. Also, adapted expansion recovered its apparent speed when tested against non-adapted contraction, and direction reversals of the adapter attenuated scrambled, but not coherent VAEs. No VAEs were recorded for test motions opposite to the adapted direction. It is concluded that higher-order optic flow mechanisms are not uniquely involved in velocity estimation per se, but modulate velocity judgments in response to changes in the ongoing flow. Independent expanding and contracting velocities rival and do not suppress one another when juxtaposed in space or over time. This unique motion opponency appears to be transient and depends on the 3D quality of the flow. It ensures that the speed of approaching objects is correctly perceived, regardless of stimulus history.

Investigating perception of motion in depth using monocular motion aftereffect

Investigating perception of motion in depth using monocular motion aftereffect

Diminished discriminability of motion in depth after adaptation to frontoparallel motion

Diminished discriminability of motion in depth after adaptation to frontoparallel motion

Comparing real world and computer generated motion in depth

Comparing real world and computer generated motion in depth

Neural correlates of stimulus-invariant decisions about motion in depth

Perceptual decision-making is a complicated, multi-stage process. Recently human neuroimaging studies implicated a set of regions, extending from the medial frontal cortex to the inferior parietal lobule that are involved in various steps of perceptual judgments. However, relatively little is known about the dependence of perceptual decisions on the visual stimulus itself. In the current study, we used functional magnetic resonance imaging to map neural activations while subjects performed a demanding 3D heading estimation task (heading slightly to the left or right of fixation). Subjects (n=13) were presented a constantly expanding optic-flow stimulus, composed of disparate red–blue spheres, viewed stereoscopically through red–blue glasses. We varied task difficulty either by adding incoherently moving spheres to the stimuli, hence reducing the strength of the motion signal and thereby increasing the amount of noise or by reducing the relevant differential information by decreasing the deviation of the average trajectory of the spheres from straight ahead. BOLD signals were compared during “easy” and “hard” trials in both stimulation conditions to isolate the neural mechanisms underlying the decision process. We hypothesized that areas involved in perceptual decisions about motion should exhibit significantly different activation across both stimulus conditions. Our results indicate that during earlier, sensory-stimulation-related phases of decision-making the left dorsolateral prefrontal cortex, posterior cingulate and inferior parietal cortex showed more activation for the “easy” compared to the “hard” trials, while during later, response-related phases the bilateral precuneus and inferior parietal cortex, as well as the bilateral superior medial gyrus showed this pattern of activation. Our results suggest that a large, non-overlapping network of areas is involved in various steps of decisions regarding 3D motion.

The effect of changing size on vergence is mediated by changing disparity

In this study, we investigated the effect of changing size on vergence. Erkelens and Regan (1986) proposed that this cue to motion in depth affects vergence in a similar way as it affects perception. The measured effect on vergence was small and we wondered why the vergence system would use changing size as an additional cue to changing disparity. To elucidate the effect of changing size on vergence, we used an annulus carrying both changing size and changing disparity signals to motion in depth. The cues were either congruent or signaled a different depth. The results showed that vergence was affected by changing size, however in an opposite way than that perception was affected. These results were incongruent with those reported by Erkelens and Regan (1986). We therefore additionally measured the effects on vergence of the individual parameters associated with changing size, i.e., stimulus area, retinal eccentricity, and luminance. Stimulus (retinal) eccentricity was inversely related to vergence gain. Luminance, on the other hand, had a smaller but positive relation to vergence gain. Thus, changing size affected the disparity signal two-fold: it changed the retinal location of the disparity signal and it changed the strength of the disparity signal (luminance change). These effects of changing size on disparity can explain both our results (change in retinal location of the disparity signal) and those of Erkelens and Regan (1986; change in luminance). We thus conclude that changing size did not in itself contribute to vergence, rather its effect on vergence was mediated by disparity.

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.

Visual fields, eye movements, and scanning behavior of a sit-and-wait predator, the black phoebe (Sayornis nigricans)

Foraging mode influences the dominant sensory modality used by a forager and likely the strategies of information gathering used in foraging and anti-predator contexts. We assessed three components of visual information gathering in a sit-and-wait avian predator, the black phoebe (Sayornis nigricans): configuration of the visual field, degree of eye movement, and scanning behavior through head-movement rates. We found that black phoebes have larger lateral visual fields than similarly sized ground-foraging passerines, as well as relatively narrower binocular and blind areas. Black phoebes moved their eyes, but eye movement amplitude was relatively smaller than in other passerines. Black phoebes may compensate for eye movement constraints with head movements. The rate of head movements increased before attacking prey in comparison to non-foraging contexts and before movements between perches. These findings suggest that black phoebes use their lateral visual fields, likely subtended by areas of high acuity in the retina, to track prey items in a three-dimensional space through active head movements. These head movements may increase depth perception, motion detection and tracking. Studying information gathering through head movement changes, rather than body posture changes (head-up, head-down) as generally presented in the literature, may allow us to better understand the mechanisms of information gathering from a comparative perspective.

Cue conflict between disparity change and looming in the perception of motion in depth

We hypothesized that it is the conflict between various cues to distance that have produced results purportedly showing that vergence eye movements induced by disparity change are not an effective cue for depth. Single and compound stimuli were used to examine the perceived motion in depth (MID) produced by simulated motion oscillations specified by disparity, relative disparity, and/or looming. Estimations of the extent of MID and binocularly recorded eye movements showed that the vergence induced by disparity change is indeed an effective cue for motion in depth in conditions where looming information does not conflict with it. When looming and disparity are in conflict, looming is the stronger cue.

Position Correction Using Echoes From a Navigation Fix for Synthetic Aperture Sonar Imaging

In synthetic aperture sonar (SAS), the platform position must be known sufficiently accurately for signals to be added coherently along the synthetic aperture. Often, the onboard navigation system is insufficiently accurate by itself, so corrections are needed. A well-known method is the displaced phase center antenna (DPCA) procedure for correcting platform position using seabed echoes. DPCA methods have the advantage of insensitivity to changing interference patterns, moving specular reflection, and changing occlusion, with aspect. However, when seabed echoes are unusable, either because they are too weak, or because they are corrupted by multipath, the seabed DCPA method may fail. Therefore, we present an alternative DPCA method using sonar echoes from a suitable navigation fix, based on an object detected after standard beamforming. In our proposed system, look angle is obtained by tracking the centroid of the rectified image of the fix object. When the standard DPCA correction equations are modified for a fixed reflector, it turns out that they provide incremental range and look-angle errors, precisely the values required when the target itself is used as the navigation fix. Moreover, the values obtained are then self-compensating for errors in estimating seabed depth or forward motion of the platform. The navigation fix is selected by bracketing in range, and beamforming overlapping subsets of the receiver array. In this paper, we present experimental results at transmitter frequencies of 25 and 100 kHz where our method enabled well-focused SAS images to be generated with little recourse to other navigation information. Hence, SAS can be carried out, even when a sophisticated inertial navigation system (INS) is not available.

Robotic Cell Injection System With Position and Force Control: Toward Automatic Batch Biomanipulation

Biological cell injection is laborious work that requires lengthy training and suffers from a low success rate. In this paper, a robotic cell-injection system for automatic injection of batch-suspended cells is proposed. To facilitate the process, these suspended cells are held and fixed to a cell array by a specially designed cell-holding device, and injected one by one through an ldquoout-of-planerdquo cell-injection process. A micropipette equipped with a polyvinylidene fluoride microforce sensor to measure real-time injection force is integrated in the proposed system. Through calibration, an empirical relationship between the cell-injection force and the desired injector pipette trajectory is obtained in advance. Then, after decoupling the out-of-plane cell injection into a position control in the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">X</i> - <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Y</i> horizontal plane and an impedance control in the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Z</i> -axis, a position and force control algorithm is developed to control the injection pipette. The depth motion of the injector pipette, which cannot be observed by microscope, is indirectly controlled via the impedance control, and the desired force is determined from the online <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">X</i> - <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Y</i> position control and cell calibration results. Finally, experimental results demonstrate the effectiveness of the proposed approach.

Latent Stereopsis for Motion in Depth in Strabismic Amblyopia

To investigate the residual stereo function of a group of 15 patients with strabismic amblyopia, by using motion-in-depth stimuli that allow discrimination of contributions from local disparity as opposed to those from local velocity mechanisms as a function of the rate of depth change. The stereo performance (percentage correct) was measured as a function of the rate of depth change for dynamic random dot stimuli that were either temporally correlated or uncorrelated. Residual stereoscopic function was demonstrated for motion in depth based on local disparity information in 2 of the 15 observers with strabismic amblyopia. The use of a neutral-density (ND) filter in front of the fixing eye enhanced motion-in-depth performance in four subjects randomly selected from the group that originally displayed only chance performance. This finding was true across temporal rate and for correlated and uncorrelated stimuli, suggesting that it was disparity based. The opposite occurred in a group of normal subjects. In a separate experiment, the hypothesis was that the beneficial effect of the ND filter is due to its contrast and/or mean luminance-reducing effects rather than any interocular time delay that it may introduce and that it is specific to motion-in-depth performance, as similar improvements were not found for static stereopsis. A small proportion of observers with strabismic amblyopia exhibit residual performance for motion in depth, and it is disparity based. Furthermore, some observers with strabismic amblyopia who do not display any significant stereo performance for motion in depth under normal binocular viewing may display above-chance stereo performance if the degree of interocular suppression is reduced. The authors term this phenomenon latent stereopsis.

Illusory temporal order for stimuli at different depth positions

We used four experiments to examine how the perceived temporal order of two visual stimuli depends on the depth position of the stimuli specified by a binocular disparity cue. When two stimuli were presented simultaneously at different depth positions in front of or around a fixation point, the observer perceived the more distant stimulus before the nearer stimulus (Experiments 1 and 2). This illusory temporal order was found only for sudden stimulus presentation (Experiment 3). These results suggest that a common processing, which is triggered by sudden luminance change, underlies this illusion. The strength of the illusion increased with the disparity gradient and the disparity size (Experiment 4). We propose that this illusion has a basis in the processing of motion in depth, which would alert the observer to a potential collision with an object that suddenly emerges in front of the observer.