Neural correlates of perceptual motion coherence.

The motions of overlapping contours in a visual scene may arise from the physical motion(s) of either a single or multiple surface(s). A central problem facing the visual motion system is that of assigning the most likely interpretation. The rules underlying this perceptual decision can be explored using a visual stimulus formed by superimposing two moving gratings. The resultant percept is either that of a single coherently moving 'plaid pattern' (coherent motion) or of the two component gratings sliding noncoherently across one another (noncoherent motion). When plaid patterns are configured to mimic one transparent grating overlying another, the percept of noncoherent motion dominates. We now report that neurons in the visual cortex of rhesus monkeys exhibit changes in direction tuning that parallel this perceptual phenomenon: sensitivity to the motions of the component gratings is enhanced under conditions that favour the perception of noncoherent motion. These results challenge models of cortical visual processing that fail to take into account the contribution of figural image segmentation cues to the analysis of visual motion.     

Transparency and the uniqueness constraint in human and computer stereo vision

The sensation of depth that is obtained with human binocular vision results from the differences in the projection of the world onto the two retinae. The process entails solving the problem of stereo correspondence, which involves choosing the correct matches between left and right image features. Many computational models of stereo vision assume a uniqueness constraint on stereo matching-that is, each feature identified in one image should eventually be matched with only one feature in the other image. This constraint would seem to be justified, as allowing non-unique matches would be tantamount to supposing that the scene entities to which matches relate are in two places at once. The value of the uniqueness constraint for eliminating false matches has been demonstrated in a variety of stereo algorithms. Yet on the basis of psychophysical results Weinshall concluded that it was not used by humans in dealing with certain types of ambiguous random-dot stereograms. We have now tested how Weinshall's stereograms are dealt with by PMF, a stereo algorithm which uses a unique-matches selection procedure in conjunction with a purely local similar-disparity support scheme. We found that PMF produces results that are closely analogous to the psychophysical results. This suggests that Weinshall's experiments should not be interpreted as evidence that the human stereo mechanism establishes non-unique matches.     

Neuronal synchrony does not correlate with motion coherence in cortical area MT

Natural visual scenes are cluttered with multiple objects whose individual features must somehow be selectively linked (or 'bound') if perception is to coincide with reality. Recent neurophysiological evidence supports a 'binding-by-synchrony' hypothesis: neurons excited by features of the same object fire synchronously, while neurons excited by features of different objects do not. Moving plaid patterns offer a straightforward means to test this idea. By appropriate manipulations of apparent transparency, the component gratings of a plaid pattern can be seen as parts of a single coherently moving surface or as two non-coherently moving surfaces. We examined directional tuning and synchrony of area-MT neurons in awake, fixating primates in response to perceptually coherent and non-coherent plaid patterns. Here we show that directional tuning correlated highly with perceptual coherence, which is consistent with an earlier study. Although we found stimulus-dependent synchrony, coherent plaids elicited significantly less synchrony than did non-coherent plaids. Our data therefore do not support the binding-by-synchrony hypothesis as applied to this class of motion stimuli in area MT.     

Hysteresis in the perception of motion direction as evidence for neural cooperativity

When elements of a parallel network, such as the human brain, are extensively interconnected, the network can exhibit 'cooperative behaviour'. Such behaviour, which is characterized by order-disorder transitions, multi-stable states, and a form of memory called 'hysteresis', has been observed in human stereopsis and has motivated models of stereopsis that incorporate cooperative networks. More recently, cooperative phenomena have also been observed in human visual motion perception. This report strongly supports a cooperative interpretation of motion perception by demonstrating hysteresis in the perception of motion direction. The results agree quantitatively with a mathematical model incorporating nonlinear excitatory and inhibitory interactions among direction-selective elements.     

A computational theory for the perception of coherent visual motion

When we see motion, our perception of how one image feature moves depends on the behaviour of other features nearby. In particular, the Gestaltists proposed the law of shared common fate, in which features tend to be perceived as moving together, that is, coherently. Recent psychophysical findings, such as the cooperativity of the motion system and motion capture, support this law. Computationally, coherence is a sensible assumption, because if two features are close then they probably belong to the same object and thus tend to move together. Moreover, the measurement of local motion may be inaccurate and so the integration of motion information over large areas may help to improve the performance. Present theories of visual motion, however, do not account fully for these coherent motion percepts. We propose here a theory that does account for these phenomena and also provides a solution to the aperture problem, where the local information in the image flow is insufficient to specify the motion uniquely.     

Interaction between colour and motion in human vision

There is a wealth of anatomical and psychological evidence which suggests that when people look at an object in the visual world, its various attributes such as colour, 'form', motion and depth are analysed by separate channels in the visual system. If so, how are these attributes put back together again to create a unified picture of the object? And if the object moves rapidly, how is perfect perceptual synchrony maintained between different features on its surface, if it is indeed true that they are being processed separately? Our evidence suggests that the visual system extracts certain conspicuous image features based on luminance contrast, and that the signals derived from these are then attributed to other features on the object, a process that we call 'capture'. Specifically, we find that when either illusory contours or random-dot patterns are moved in the vicinity of a colour-border, the colour border will also seem to move in the same direction even though it is physically stationary.     

人手柔性触觉感知特性

提出了一种新颖的基于弹性梁有效变形长度控制的柔性触觉感知再现方法,并研制了柔性触觉感知装置.通过在该柔性触觉装置上进行实验,对人手的柔性触觉感知特性进行了研究,得出一些结论.刚度越大,分辨率越低,随着刚度的增大,相比较的2个物体间需具有更大的刚度差异才能够分辨.当人们触摸物体时,习惯的次数为2～6次,按压频率主要分布在0.3～1.3 Hz.实验点的刚度越大越难记忆.连续感知的正确率要明显高于不连续感知的正确率.本实验方法简单有效,得出的实验结论不仅可用来改进触觉再现装置的设计,而且为触觉再现技术的研究提供了生理学依据.     

Motion speed modulates walking direction discrimination: The role of the feet in biological motion perception

The human visual system is tuned to the motions of biological entities, which provide potentially vital information for survival. The current study examines the interplay between motion speed and motion direction perception. Following a brief presentation of a point-light walker walking straight ahead or slightly leftward or rightward, observers were asked to quickly judge the walking direction (left or right). Participants showed better direction discrimination when the walker walked at a fast pace compared to a natural or slow pace, and this was not simply due to a difference in motion cycles. Moreover, walking direction sensitivity could be enhanced by increasing the feet motion speed alone, so long as the direction of feet movement was consistent with that of the other body parts. These findings demonstrate that our perception of walking direction is influenced by local motion speed, and highlight the role of the feet in biological motion perception.     

党务公开理论探析

逐步推进党务公开,对于构建和谐社会、发展党内民主、提高党的执政能力、加强党的监督具有十分重大的现实意义。当前,推行党务公开需处理好党内公开与党外公开、公开内容与公开形式、党务公开和党务保密、党务公开与政务公开的关系。而克服思想障碍、明确公开内容、创新公开形式、健全公开机制,则是稳步推进党务公开的几个重要环节。     

关于过程调用中的透明性和可靠性

以反例的形式指出了Ｂｉｊｌｓｍａ等人提出的过程调用中透明性引理证明中的错误，并且分别给出了透明性引理和可靠性定理的新的证明方法。     

Genetic variation in a human odorant receptor alters odour perception

Human olfactory perception differs enormously between individuals, with large reported perceptual variations in the intensity and pleasantness of a given odour. For instance, androstenone (5alpha-androst-16-en-3-one), an odorous steroid derived from testosterone, is variously perceived by different individuals as offensive ("sweaty, urinous"), pleasant ("sweet, floral") or odourless. Similar variation in odour perception has been observed for several other odours. The mechanistic basis of variation in odour perception between individuals is unknown. We investigated whether genetic variation in human odorant receptor genes accounts in part for variation in odour perception between individuals. Here we show that a human odorant receptor, OR7D4, is selectively activated in vitro by androstenone and the related odorous steroid androstadienone (androsta-4,16-dien-3-one) and does not respond to a panel of 64 other odours and two solvents. A common variant of this receptor (OR7D4 WM) contains two non-synonymous single nucleotide polymorphisms (SNPs), resulting in two amino acid substitutions (R88W, T133M; hence 'RT') that severely impair function in vitro. Human subjects with RT/WM or WM/WM genotypes as a group were less sensitive to androstenone and androstadienone and found both odours less unpleasant than the RT/RT group. Genotypic variation in OR7D4 accounts for a significant proportion of the valence (pleasantness or unpleasantness) and intensity variance in perception of these steroidal odours. Our results demonstrate the first link between the function of a human odorant receptor in vitro and odour perception.     

虚拟人手臂无碰撞运动规划

针对基于虚拟人进行维修可达性分析中的手臂的无碰撞运动规划问题,在建立虚拟人手臂模型的基础上,采用双向RRTs(快速搜索随机树)算法对9自由度虚拟人手臂进行运动规划,并对算法中的抽样、距离定义和差值函数分别做了阐述.规划过程还考虑了手臂关节角度的生理限制,结合碰撞检测得到虚拟人手臂无碰撞运动路径.通过在Jack软件平台上开发的实验环境验证了所用方法的有效性,且此方法可以扩展应用于更多自由度虚拟人的运动规划.     

WTO透明度原则与中国行政审判

WTO透明度原则是世贸组织增加各成员方法律的可预见性、可计算性而提出的基本要求。透明度原则对中国立法、执法和司法都会产生重大影响。透明度原则与司法所蕴涵的审判公开有着异曲同工之妙，其制度设计都是为了避免因“暗箱操作”带来腐败、滥用权力等不利后果。审判公开在中国一直贯彻了几十年，目前仍然是司法改革的关键。可见，无论是透明度原则还是公开审判制度并非一蹴而就。WTO透明度原则对中国行政审判的影响深远，不仅体现在观念上，也体现在审判程序、文书制作和司法解释上。这种影响是逐步的，潜移默化的，需要一个过程。     

我国财政透明度现状及对策分析——兼论纳税人知情权、参与权和监督权

财政透明度是建立公共财政体系的必然要求。我国的财政透明度进程大致是从上个世纪90年代末开始启动,目前来看虽然已有改观,但是在财政资金筹集以及分配和使用上离国际规范做法尚有较大差距,不但造成财政资金使用效率低下的后果,同时还使纳税人的知情权、参与权和监督权受到侵害。为此,应当在商品零售环节中实行价税分离的标价方法,同时在财政资金分配上应当改革现有预算制度,加强政府信息公开,完善财政资金使用的决策机制,以保障纳税人知情权、参与权和监督权。     

智能虚拟人Agent行为建模与运动控制

针对虚拟环境中人的行为分析,研究了井下智能虚拟人Agent的行为建模和运动控制技术.基于人工智能/人工生命方法,构建了集成感知、运动、行为、认知、内部属性等组件的井下智能虚拟人Agent的体系结构;研究了基于简化包容结构的智能虚拟人Agent行为控制模型及其行为选择机制,并基于A*算法,实现了智能虚拟人Agent的路径规划;初步构建了井下虚拟人Agent行为仿真系统,实现了虚拟人Agent的复杂行为控制,为进一步构建具有行为真实感的井下虚拟环境提供技术参考.     

超冷玻色气体中的电磁感应透明

研究了超冷玻色气体中的电磁感应透明现象.利用平均场理论,考虑处于所有能级的原子被光势阱所囚禁,本文导出了系统的色散关系并计算了在超冷原子气体中传播的慢光的群速.     

肢体运动微型监测系统研究

人体肢体运动的动态检测和模拟具有极大的医学应用价值。介绍一种采用微机电传感器(加速度计和磁强计)集成制作的微型监测装置,可以用于人体姿态和运动的测量。在姿态和运动的表示方面,采用单次转动和空间转轴结合的方式,计算简便,姿态反映直观,运动特征突出。此外对人体头部运动进行了实际测量和运动模拟。实验证明:该装置能够动态检测肢体的姿态和速度等运动信息,并可快速地进行体态模拟。     

基于微型传感器的虚拟人运动控制

利用传感器数据和相邻肢体段相互关联的特点,根据人体运动特征建立了层次化结构的虚拟人运动模型,通过微型传感器采集的数据驱动虚拟人每个关节旋转,计算出关节的旋转角度,给出基于下肢运动的人体位移的计算方法。最后采用微型传感器数据和前向动力学相结合的方法对虚拟人运动进行控制,实现人体运动的重现。