Grouping of image fragments in primary visual cortex.

In the visual world, objects are partially occluded by nearer objects, separating them into image fragments. However, the image fragments of the object can easily be grouped and organized together by the visual system. Psychophysical data and theoretical analysis indicate that such perceptual grouping might be mediated in the early stages of visual processing. Here I show that some orientation-selective cells in the primary visual cortex (V1) have response properties that can mediate the grouping of image fragments. These cells stopped responding to a stimulus bar when it was partly occluded by a small patch. The cells also did not respond when the patch had uncrossed disparity so that it appeared to be behind the bar. However, the cells began responding again when the patch had crossed disparity so that it appeared to be in front of the bar. These results indicate that cells as early as V1 have the computational power to make inferences about the nature of partially invisible forms seen behind occluding structures.     

交通车辆轮廓跟踪算法研究及其工程应用

针对模式识别在智能交通领域的实际工程应用,提出了一种提取运动车辆轮廓线的精细跟踪算法．首先,通过冗余离散小波变换法提取运动区域,检测出相邻两帧图像内的运动变化从而确定运动对象的存在及其初始位置;其次,以当前帧运动区域为参考,通过改进的mean-shift算法在后续帧中跟踪运动对象的中心位置;最后,以mean—shift跟踪窗口作为目标初始轮廓线,采用自适应水平集法得到目标轮廓,从而精确定位运动对象位置．实验结果表明本文算法能够以轮廓线的方式以较高精确度跟踪运动车辆目标,目前已被市交通局科研单位采纳,具有一定的工程应用前景．     

Imaging cortical correlates of illusion in early visual cortex

Exploring visual illusions reveals fundamental principles of cortical processing. Illusory motion perception of non-moving stimuli was described almost a century ago by Gestalt psychologists. However, the underlying neuronal mechanisms remain unknown. To explore cortical mechanisms underlying the 'line-motion' illusion, we used real-time optical imaging, which is highly sensitive to subthreshold activity. We examined, in the visual cortex of the anaesthetized cat, responses to five stimuli: a stationary small square and a long bar; a moving square; a drawn-out bar; and the well-known line-motion illusion, a stationary square briefly preceding a long stationary bar presentation. Whereas flashing the bar alone evoked the expected localized, short latency and high amplitude activity patterns, presenting a square 60-100 ms before a bar induced the dynamic activity patterns resembling that of fast movement. The preceding square, even though physically non-moving, created gradually propagating subthreshold cortical activity that must contribute to illusory motion, because it was indistinguishable from cortical representations of real motion in this area. These findings demonstrate the effect of spatio-temporal patterns of subthreshold synaptic potentials on cortical processing and the shaping of perception.     

Motion-induced blindness in normal observers.

Cases in which salient visual stimuli do not register consciously are known to occur in special conditions, such as the presentation of dissimilar stimuli to the two eyes or when images are stabilized on the retina. Here, we report a striking phenomenon of 'visual disappearance' observed with normal-sighted observers under natural conditions. When a global moving pattern is superimposed on high-contrast stationary or slowly moving stimuli, the latter disappear and reappear alternately for periods of several seconds. We show that this motion-induced blindness (MIB) phenomenon is unlikely to reflect retinal suppression, sensory masking or adaptation. The phenomenology observed includes perceptual grouping effects, object rivalry and visual field anisotropy. This is very similar to that found in other types of visual disappearance, as well as in clinical cases of attention deficits, in which partial invisibility might occur despite the primary visual areas being intact. Disappearance might reflect a disruption of attentional processing, which shifts the system into a winner-takes-all mode, uncovering the dynamics of competition between object representations within the human visual system.     

Masking unveils pre-amodal completion representation in visual search

When one object is partly occluded by another, its occluded parts are perceptually 'filled in', that is, the occluded object appears to continue behind its occluder. This process is known as amodal completion. The completion of a partially occluded object takes about 200 ms, and pre-completion information (that is, information from before amodal completion has occurred) exists in the visual system for that duration. It has been suggested, however, that observers cannot make use of this information, even when it is beneficial to do so: visual search for a target that appears to be partly occluded, for example, is slower than for a target that does not undergo occlusion, despite both targets being physically identical. Here we show that visual search does have access to pre-completion representations, but only for a limited time that depends on the size of the occluded region.     

基于差分法和概率估计方法的运动目标检测

针对视频序列运动目标检测问题,提出根据灰度直方图概率密度函数特点自动确定阈值的方法,以准确地从背景中分割出运动目标.本文以差分法为基础,利用正态分布的经验法则确定阈值,对差分图像进行分割,并用方框标识运动目标.该方法省去了滤波、形态学处理等冗余步骤,缩短了图像处理的时间.实验表明,该方法实时性强,且对面积较大或较小的运动目标都能达到有效跟踪的目的.     

基于幂次变换和区域收缩算法的运动目标检测与定位

运动目标分割与跟踪是计算机视觉中的重要研究课题,而目标检测与定位是其中的必要步骤,对分割与跟踪效果影响很大.在此提出一种新的运动目标检测与定位方法,该方法在差分二值图像上,通过区域收缩定位到运动像素密度较大的区域,从而实现运动目标定位.在多目标情况下,先通过幂次变换突出不同位置的目标,然后再通过区域收缩实现目标定位,给出目标的特征矩形,便于进一步的跟踪与识别.该方法不需要任何关于目标数的先验知识,对噪声鲁棒性较强.文中给出的实验结果证明该算法的有效性.     

A back-propagation programmed network that simulates response properties of a subset of posterior parietal neurons

Neurons in area 7a of the posterior parietal cortex of monkeys respond to both the retinal location of a visual stimulus and the position of the eyes and by combining these signals represent the spatial location of external objects. A neural network model, programmed using back-propagation learning, can decode this spatial information from area 7a neurons and accounts for their observed response properties.     

fMRI evidence for objects as the units of attentional selection.

Contrasting theories of visual attention emphasize selection by spatial location, visual features (such as motion or colour) or whole objects. Here we used functional magnetic resonance imaging (fMRI) to test key predictions of the object-based theory, which proposes that pre-attentive mechanisms segment the visual array into discrete objects, groups, or surfaces, which serve as targets for visual attention. Subjects viewed stimuli consisting of a face transparently superimposed on a house, with one moving and the other stationary. In different conditions, subjects attended to the face, the house or the motion. The magnetic resonance signal from each subject's fusiform face area, parahippocampal place area and area MT/MST provided a measure of the processing of faces, houses and visual motion, respectively. Although all three attributes occupied the same location, attending to one attribute of an object (such as the motion of a moving face) enhanced the neural representation not only of that attribute but also of the other attribute of the same object (for example, the face), compared with attributes of the other object (for example, the house). These results cannot be explained by models in which attention selects locations or features, and provide physiological evidence that whole objects are selected even when only one visual attribute is relevant.     

LDCQ下的误差限制问题

提出了位置相关连续查询(LDCQ)中的误差限制的概念，误差可以是位置误差或者是时间误差．因为移动对象和查询边界实际相交的位置和时刻事先难以确定，所以一般采用预测相交点作为参照点．对选取合适的系统参数使之满足给定的误差限制进行了讨论，研究结果表明，可以选择预测相交时刻移动对象的位置和查询边界上预测相交点的实际位置到预测相交点的距离，或者选择它们之间的距离，使之满足给定的误差限制．     

Spatio-temporal correlations and visual signalling in a complete neuronal population

Statistical dependencies in the responses of sensory neurons govern both the amount of stimulus information conveyed and the means by which downstream neurons can extract it. Although a variety of measurements indicate the existence of such dependencies, their origin and importance for neural coding are poorly understood. Here we analyse the functional significance of correlated firing in a complete population of macaque parasol retinal ganglion cells using a model of multi-neuron spike responses. The model, with parameters fit directly to physiological data, simultaneously captures both the stimulus dependence and detailed spatio-temporal correlations in population responses, and provides two insights into the structure of the neural code. First, neural encoding at the population level is less noisy than one would expect from the variability of individual neurons: spike times are more precise, and can be predicted more accurately when the spiking of neighbouring neurons is taken into account. Second, correlations provide additional sensory information: optimal, model-based decoding that exploits the response correlation structure extracts 20% more information about the visual scene than decoding under the assumption of independence, and preserves 40% more visual information than optimal linear decoding. This model-based approach reveals the role of correlated activity in the retinal coding of visual stimuli, and provides a general framework for understanding the importance of correlated activity in populations of neurons.     

基于视频图像的运动目标检测与跟踪研究

实际生活中,每时每刻都有千万种物体在进行运动,而这些不同的运动物体对不同的群体传达着不一样的视觉信息,对于群体来说,这些视觉信息给他们带来了重要的现实意义。然而在人们用视觉捕捉到的信息里,往往只对对自己有存在价值的运动目标或物体感兴趣,研究基于视频图像的运动目标的检测与跟踪,有很大的现实意义和实际价值。目前在实验室环境中已实现了对运动目标的检测和跟踪。在运动目标检测方面,参考理论,用帧间差分法得到基本完整可靠的运动目标;在运动目标跟踪方面,利用一种低复杂度的分块搜索算法,能对其进行仿真实验与编程实现。     

基于序列图像的视觉定位

提出了一种静止摄像机条件下基于计算机视觉的工业机器人的定位算法。采用单目视觉系统,由线性摄像机模型推导出定位测量模型。通过序列图像,以一种改进的自适应混合高斯模型更新背景,运用背景差分法检测出运动目标,用CAMSHIFT算法实现对运动目标的跟踪,确定其位置和姿态,估计出运动参数,反馈给机器人指导其准确运动。实验结果表明,该方法快速、有效,能够满足视觉定位的实时性要求。     

一种快速运动目标检测算法

运动目标检测是智能视觉监控系统的重要组成部分,其主要功能是检测监控场景中的运动目标,为高层运动分析提供必要的信息。文章提出一种快速运动目标检测算法,以帧差法和背景减法为基础,快速实现背景提取、背景更新、运动目标检测的功能。实验结果表明,该算法计算量小,检测目标完整,能够满足实时监控系统的要求。     

Large adjustments in visually guided reaching do not depend on vision of the hand or perception of target displacement

When we reach towards an object that suddenly appears in our peripheral visual field, not only does our arm extend towards the object, but our eyes, head and body also move in such a way that the image of the object falls on the fovea. Popular models of how reaching movements are programmed have argued that while the first part of the limb movement is ballistic, subsequent corrections to the trajectory are made on the basis of dynamic feedback about the relative positions of the hand and the target provided by central vision. These models have assumed that the adjustments are dependent on seeing the hand moving with respect to the target. Here we present evidence that a change in the position of a visual target during a reaching movement can modify the trajectory even when vision of the hand is prevented. Moreover, these dynamic corrections to the trajectory of the moving limb occur without the subject perceiving the change in target location. These findings demonstrate that visual feedback about the relative position of the hand and target is not necessary for visually driven corrections in reaching to occur, and the mechanisms that maintain the apparent stability of a target in space are dissociable from those that mediate the visuomotor output directed at that target.     

基于单目运动摄像机的三维物体运动参数估计

针对单目视觉监测系统摄像机和目标物体同时运动时,如何有效测量物体三维运动参数的难题,提出一种基于单目序列图像对插入虚拟视点的算法确定运动物体位姿及运动参数的方法。动摄像机连续采集运动物体的图像序列,根据摄影几何原理对摄像机和运动物体进行分析,结合本质矩阵的特性,估算空间物体运动参数。实验结果表明,该方法能够在为摄像机与目标物体同时运动的情况下,有效地估测出物体三维运动参数,且该方法简单有效,具有较高的精确度和准确性。     

基于扩展Kalman滤波的声阵列定位数据融合算法

利用各阵元和目标相对于一中心阵元的几何关系建立目标运动方程，坐标变换方程和声阵列测量方程，并以此建立了声阵列目标定位模型。在此基础上提出了基于扩展Kalman滤波算法的目标定位数据融合算法。通过地面目标和空中目标的计算机仿真表明，本算法能够有效地克服由于智能雷布阵的随机性给智能雷定位数据估计带来的困难，对声阵列定位数据也能进行较好的融合，对提高定位精度有一定效果。     

Transparency and coherence in human motion perception

When confronted with moving images, the visual system often must decide whether the motion signals arise from a single object or from multiple objects. A special case of this problem arises when two independently moving gratings are superimposed. The gratings tend to cohere and move unambiguously in a single direction (pattern motion) instead of moving independently (component motion). Here we report that the tendency to see pattern motion depends very strongly on the luminance of the intersections (that is, to regions where the gratings overlap) relative to that of the gratings in a way that closely parallels the physics of transparency. When the luminance of these regions is chosen appropriately, pattern motion is destroyed and replaced by the appearance of two transparent gratings moving independently. The observations imply that motion detecting mechanisms in the visual system must have access to tacit 'knowledge' of the physics of transparency and that this knowledge can be used to segment the scene into different objects. The same knowledge could, in principle, be used to avoid confusing shadows with real object boundaries.     

一种改进的Hausdorff距离目标跟踪算法

在序列图像中进行目标跟踪是计算机视觉、图像处理和模式识别领域里非常活跃的课题。采用Hausdorff距离模板匹配的方法具有计算量小、适应性强的特点,为了能对复杂背景（包括运动背景或移动镜头）情况下的序列图像进行准确的跟踪,综合考虑了图像边缘的位置信息和方向信息,对模板匹配和模板更新的策略作了改进,与原有方法相比,目标跟踪的准确度和算法的效率有了显著提高。     

考虑运动对象位置不确定性的位置管理策略

以传统轨道模型为基础,观测构造运动对象历史信息统计样本并分析其特征,设计了基于样本统计的位置预测模型,更好地考虑了运动对象运动随机性的特点,提高了位置预测的准确性;然后在该模型的基础上设计了一种为管理运动对象位置不确定性而设定最佳阈值的方法,这种方法相对于传统的静态阈值策略减少了位置更新的信息代价开销;最后,采用一种基于时间和空间划分的Grid模型构造索引结构,给出了管理运动对象位置信息进行区域查询和kNN（k-Nearest Neighbor）查询的实现过程和算法,是一种进行运动对象位置相关查询的可行性方案.