Motion Segregation Research Articles

Adaptive Trade-off between Sensitivity and Spatial Resolution and its Implications for Motion Discrimination and Segregation

Adaptive Trade-off between Sensitivity and Spatial Resolution and its Implications for Motion Discrimination and Segregation

Spatial suppression promotes rapid figure-ground segmentation of moving objects

Segregation of objects from their backgrounds is a fundamental visual function and one that is particularly effective when objects are in motion. Theoretically, suppressive center-surround mechanisms are well suited for accomplishing motion segregation. This longstanding hypothesis, however, has received limited empirical support. We report converging correlational and causal evidence that spatial suppression of background motion signals is critical for rapid segmentation of moving objects. Motion segregation ability is strongly predicted by both individual and stimulus-driven variations in spatial suppression strength. Moreover, aging-related superiority in perceiving background motion is associated with profound impairments in motion segregation. This segregation deficit is alleviated via perceptual learning, but only when motion segregation training also causes decreased sensitivity to background motion. We argue that perceptual insensitivity to large moving stimuli effectively implements background subtraction, which, in turn, enhances the visibility of moving objects and accounts for the observed link between spatial suppression and motion segregation.

Suppressive mechanisms in visual motion processing: From perception to intelligence

Perception operates on an immense amount of incoming information that greatly exceeds the brain’s processing capacity. Because of this fundamental limitation, the ability to suppress irrelevant information is a key determinant of perceptual efficiency. Here, I will review a series of studies investigating suppressive mechanisms in visual motion processing, namely perceptual suppression of large, background-like motions. These spatial suppression mechanisms are adaptive, operating only when sensory inputs are sufficiently robust to guarantee visibility. Converging correlational and causal evidence links these behavioral results with inhibitory center-surround mechanisms, namely those in cortical area MT. Spatial suppression is abnormally weak in several special populations, including the elderly and individuals with schizophrenia—a deficit that is evidenced by better-than-normal direction discriminations of large moving stimuli. Theoretical work shows that this abnormal weakening of spatial suppression should result in motion segregation deficits, but direct behavioral support of this hypothesis is lacking. Finally, I will argue that the ability to suppress information is a fundamental neural process that applies not only to perception but also to cognition in general. Supporting this argument, I will discuss recent research that shows individual differences in spatial suppression of motion signals strongly predict individual variations in IQ scores.

Background subtraction as a mechanism for efficient motion segregation

Background subtraction as a mechanism for efficient motion segregation

Motion integration for pursuit does not hinder attentive motion segregation

Motion integration for pursuit does not hinder attentive motion segregation

Motion integration and segregation modulated by surrounding motion

Motion integration and segregation modulated by surrounding motion

Direction repulsion facilitates motion segregation

Direction repulsion facilitates motion segregation

Smooth pursuit eye movements and the segregation of coherent motion

Coherent motion has been used extensively as a research tool to study human motion sensitivity and the properties of motion sensitive neurons, but it has been rarely used to study smooth pursuit eye movements. Here we measured smooth pursuit eye movements in response to coherent motion. The stimulus consisted of random dots that moved at a speed of 10 deg/sec within a circular aperture of 10 deg radius. The dot density amounted to 2 dots/deg, the dot lifetime was 200 ms. We varied the percentage of coherent moving dots from 20 to 100%. The coherent motion was always horizontal, either leftward or rightward. In the first experiment, subjects were instructed to initiate smooth pursuit eye movements immediately after motion onset. We found that the amount of coherence had only minor influence on the latency of smooth pursuit initiation, but a strong influence on the acceleration during the initiation period, with faster acceleration for higher coherence levels. Steady-state pursuit gain, however, was similar for all coherence levels. To test if the dependency on coherence is an intrinsic property of smooth pursuit initiation or a result of incomplete motion segregation, we performed a second experiment. Subjects were initially required to hold fixation on a fixation point for 500 ms after motion onset. After fixation offset, they had to pursue the coherent motion for another 1000 ms. Again we found a strong influence of motion coherence: number and magnitude of fixation errors were higher for higher coherence levels. However, we did not find a strong relationship between coherence level and pursuit acceleration after the offset of the fixation point. The results indicate that smooth pursuit acceleration depends crucially on the segregation of motion signals. If this segregation is completed before pursuit onset, pursuit acceleration is rather immune to noisy motion signals.

Simulation of multiple functions of the retinal circuitry: a computational and a hardware model

Experimental findings showed that retinal signal process-ing is not a linear light-to-spike conversion mechanismbut is composed of nonlinear computations that realizecomplex visual functions. However, even before lighttransduction at the photoreceptor (PR) layer, the image iscomplicated by sudden saccadic eye movements. It waspreviously shown that certain retinal ganglion cells (GC)alleviate this problem by segregating motion fromglobal motion [1]. Even for a stationary scene, due tothose saccades, a different image impinges on the retinafor short periods, thus complicating retinal computation.Previous reports showed that a class of GCs can encodevisual stimulation based on the latencies of the first spikesrather than complex features of the spike train [2], so thatwithin those short periods, neural can berealized efficiently. Although and rapidneural coding mechanisms are observed at GC layer, itwas shown that those mechanisms arised from inter-reti-nal neurons such as horizontal cells (HC), bipolar cells(BC) and amacrine cells (AC) [1,2]. Specifically, wide-field amacrine cells (wfAC) are believed to play an impor-tant role in mechanism by providing timedinhibition to blank out excitatory signals produced by glo-bal movements [1]. The latency between On- and Off- BCpathways are found to be critical for rapid neural codingmechanisms [2]. Although separate models can realizethose mechanisms by means of GC responses, each classof retinal neurons were largely omitted in those models[1,2]. Here, we present a spatio-temporal model of the ret-inal circuit [3], combining temporal cellular responsefunctions and anatomical inter-cellular connections. Themodel was constructed in a two-dimensional grid andeach pixel of the grid was composed of eight cell elementsrepresenting PR, HC, On- and Off- BCs, On- and Off- ACs,On-Off wfAC and On-Off GC. For each of the cell ele-ments, the response function was governed by push-pulldifferential equations [4] in which chemical/electricalsynaptic inputs as well as intrinsic membrane dynamicswere implemented. Additionally, same retinal circuitrywas re-designed by using CMOS elements and the modelresponse tested by a SPICE simulator [5]. In the presentstudy, not only center-surround antagonistic receptivefields of BCs and GC, but also complex visual functionssuch as object motion segregation from a backgroundmotion (Figure 1, left panel) and rapid neural coding

A Fast Biologically Inspired Algorithm for Recurrent Motion Estimation

We have previously developed a neurodynamical model of motion segregation in cortical visual area V1 and MT of the dorsal stream. The model explains how motion ambiguities caused by the motion aperture problem can be solved for coherently moving objects of arbitrary size by means of cortical mechanisms. The major bottleneck in the development of a reliable biologically inspired technical system with real-time motion analysis capabilities based on this neural model is the amount of memory necessary for the representation of neural activation in velocity space. We propose a sparse coding framework for neural motion activity patterns and suggest a means by which initial activities are detected efficiently. We realize neural mechanisms such as shunting inhibition and feedback modulation in the sparse framework to implement an efficient algorithmic version of our neural model of cortical motion segregation. We demonstrate that the algorithm behaves similarly to the original neural model and is able to extract image motion from real world image sequences. Our investigation transfers a neuroscience model of cortical motion computation to achieve technologically demanding constraints such as real-time performance and hardware implementation. In addition, the proposed biologically inspired algorithm provides a tool for modeling investigations to achieve acceptable simulation time.

Disambiguating Visual Motion by Form-Motion Interaction—a Computational Model

The neural mechanisms underlying motion segregation and integration still remain unclear to a large extent. Local motion estimates often are ambiguous in the lack of form features, such as corners or junctions. Furthermore, even in the presence of such features, local motion estimates may be wrong if they were generated near occlusions or from transparent objects. Here, a neural model of visual motion processing is presented that involves early stages of the cortical dorsal and ventral pathways. We investigate the computational mechanisms of V1-MT feedforward and feedback processing in the perception of coherent shape motion. In particular, we demonstrate how modulatory MT-V1 feedback helps to stabilize localized feature signals at, e.g. corners, and to disambiguate initial flow estimates that signal ambiguous movement due to the aperture problem for single shapes. In cluttered environments with multiple moving objects partial occlusions may occur which, in turn, generate erroneous motion signals at points of overlapping form. Intrinsic-extrinsic region boundaries are indicated by local T-junctions of possibly any orientation and spatial configuration. Such junctions generate strong localized feature tracking signals that inject erroneous motion directions into the integration process. We describe a simple local mechanism of excitatory form-motion interaction that modifies spurious motion cues at T-junctions. In concert with local competitive-cooperative mechanisms of the motion pathway the motion signals are subsequently segregated into coherent representations of moving shapes. Computer simulations demonstrate the competency of the proposed neural model.

Colour, Polarity, Disparity, and Texture Contributions to Motion Segregation

We measured how different cues are combined in motion-segregation processes by using motion stimuli where randomly distributed target dots were organised in global revolving motion while the remaining noise dots performed random motion. Target dots were cued with a different colour, polarity, disparity depth, or texture orientation than the noise dots, or they were the same as the noise dots. The stimuli were presented with a prolonged static cue preview which provided position cues to target dots or, briefly with static pre-target and post-target noise frames, which provided false position cues (no preview). All cues efficiently facilitated global motion segregation in cued-preview conditions. Colour completely failed to facilitate global motion segregation in no-preview conditions. Polarity and disparity facilitated segregation in no-preview conditions, although sensitivities were lower than in the preview conditions. Remarkably, texture orientation largely facilitated motion segregation by the same amount in both cued-preview and no-preview conditions. So, colour provides only position cues to the motion-segregation task whereas texture orientation, disparity, and to a lesser extent polarity are integrated with the segregation process.

In-Situ Electron Microscopy Studies of the Effect of Solute Segregation on Grain Boundary Anisotropy and Mobility in an Al-Zr Alloy

ABSTRACTThe presence of impurities in aluminum alloys is of great interest with respect to microstructural properties, specifically, the effect of solute on texture and anisotropy. This paper presents new evidence of the pronounced effect of solute drag based on in-situ annealing and Electron Backscatter Diffraction experiments of Zr-rich Al alloys subject to prior strain. A compensation effect was found for grain boundary mobility maxima for specific boundary types. Trends in activation energy as a function of boundary type support the observations of a compensation effect with respect to temperature. Evidence for irregular motion of boundaries from in-situ observations is discussed in reference to new theoretical results that suggest that boundaries migrating in the presence of solutes should move sporadically provided that the length scale at which observations are made is small enough. A study of both boundary motion and solute segregation to specific boundary types using Scanning Transmission Electron Microscopy and in-situ TEM is presented.

Auditory motion segregation: a limited analogy with vision.

Interaural time delay (ITD) is the dominant cue to sound-source location. When one component of a complex sound changes rapidly but smoothly in ITD, it perceptually segregates from the complex. When different components were changed in ITD in succession, a recognizable melody was heard. Each note was more detectable from the transition than from a distinct ITD with respect to the complex. However, a transition relative to a coherently changing complex produced no segregation, whereas cyclic modulation of ITD, too rapid to be perceived as movement, did produce segregation. These two results suggest that the relevant cue is not movement per se but rather the lack of a well-defined ITD during the transition. Segregation largely disappeared when the transition in ITD was replaced by a temporal gap in the complex of the order of 100 ms. The effect seems similar to visual motion segregation but is best explained by the mechanism of binaural unmasking.

Auditory motion segregation: A limited analogy with vision.

Auditory motion segregation: A limited analogy with vision.

A global process in motion segregation.

Observers viewed sparse random dot cinematograms in which the moving dots were confined to eight windows. The motions in seven of the windows were consistent with a global flow pattern, while the direction of motion in the eighth window deviated from this pattern. The observer's task was to determine which of the eight windows contained the inconsistent motion. The task was performed on two types of global flow patterns: spirals, which appear rigid, and deformations, which appear highly non-rigid. Although these patterns produce qualitatively different global percepts, they are exactly matched in their local velocities and velocity differences. Observers were better able to locate an inconsistent motion in spiral patterns than in deformation patterns, indicating that they were using more than just local motion information to find the target. This result is taken as indirect support for a segregation process that involves fitting the stimulus with a global motion pattern and segregating motions inconsistent with this pattern.

Discussions of the internal motions and mass segregation of M67 on the basis of accurate proper motions

The radius and virial mass of the old open cluster M67 are presented. The internal motion and mass segregation of the cluster are also discussed on the basis of accurate stellar proper motions obtained combining three independent proper motion catalogues of the cluster. Increases of the mean proper motion and the intrinsic dispersion of member stars with radial distance from the cluster center might suggest that the stars are escaping from the cluster. The stars in both inner and outer regions appear to be in isotropic orbits. At last, it is found that both space and velocity mass segregations exist for the old open cluster due to the dynamical evolution.

Motion detectors and motion segregation.

The response of motion detectors necessarily confound image velocity with image structure. In particular, even a rigidly moving image (with a uniform velocity field) will give rise to non-uniform detector responses. A mathematical framework has been proposed on how to intrinsically compare motion detectors' responses so that their differences will reflect the true differences in image velocity (Zhang and Wu, Proc. Natl. Acad. Sci. USA 87, 7819-7823, 1990). Here, this notion of 'intrinsic differentiation' was implemented by introducing a gamma-matrix determined by the image spatial gradients. The perceptual phenomenon of random-dot motion segregation was successfully simulated.

Motion segregation from speed differences: Evidence for nonlinear processing

This paper examines observers' ability to detect regions delimited by speed differences. Several types of translational motion stimuli, of varying task difficulty, were tested over a wide range of base speeds. The observer's task was to decide whether a region of dots moving at a different speed from the base speed was located to the left or right of the display's center. Both increments (dots within the test region moving faster than the base speed) and decrements (dots within the test region moving slower than the base speed) were examined. When the task was relatively difficult the following asymmetries were found: at slow base speeds, incremental thresholds were lower than decremental thresholds; at fast base speeds, the reverse pattern occurred. When the task was relatively easy, no consistent asymmetries were found. It is proposed that the visual system encodes speed through a sigmoidal nonlinear response function, and it is shown that this one nonlinearity can be used to explain results for both easy and difficult tasks.

Charge motion in a semi-autogenous grinding mill

In order to develop more accurate procedures for scale-up and design of semi-autogenous grinding mills through detailed mathematical models, a better understanding of the charge motion and rock/ball segregation is needed. To achieve this a 0.61 m (2.0 ft) diam by 0.305 m (1.0 ft) length plexiglas mill was constructed as a scale model of a commercial SAG mill. Rock motion in the rotating mill was simulated using various sizes of ceramic balls. Quantitative measurements of dynamic angle of repose, water and slurry motion, holdup and size segregation of the charge were taken. In addition, a video presentation (available to the public) was prepared to elucidate charge and water motion at various mill speeds, charge volumes, rock size distribution, and flow rates.