Prioritized Spatial Updating in the Intrinsic Frame of Reference

In order to maintain valid situation awareness, people need to update the spatial representations of their surroundings as objects, including themselves, move. The present study investigates the properties of spatial updating in the intrinsic frame of reference, where spatial relations are represented with respect to an external object (other than the viewer self) with an intrinsic reference direction. Three experiments were conducted using a task of direction pointing. It was found that given a relatively stable intrinsic reference direction, responses to a small number of salient objects were faster than responses to non-salient objects (Experiment 1 and Experiment 3). The salience effect disappeared when the intrinsic reference direction was no longer stable (Experiment 2). Furthermore, all three experiments revealed a type of orientation dependence similar to that found in egocentric spatial updating. Our results indicate that spatial updating in the intrinsic reference system can be easy only if a fixed reference direction is maintained and the number of objects that need to be tracked is limited.     

Path Integration During a Neighborhood Walk

In three experiments, we contrast two accounts of path integration processes that track direction and distance of movement. Moment-to-moment updating involves the continuous sensing of motion; automatic calculations constantly produce an estimate of position and orientation of self to an anchor point for travel. In contrast, configural updating can be accomplished using episodic memories; a representation of the traveled path is periodically revised and the bearing to the origin of a route can be estimated by connecting the endpoint of the current leg to the starting point of the first leg. Experiments 1 and 3 indicate that people encode the number and direction of turns but have difficulty configuring more gradually curved legs. In Experiment 2, we find that blindfolded people show better than chance performance in estimating the origin of outdoor routes when they are unexpectedly asked to point. It appears that, in addition to episodic memories that allow configural updating, we have available a moment-to-moment representation of our position and heading based on the cues that accompany self-movement.     

Spatial updating and common misinterpretations of spatial reference frames

Spatial memory plays an important role in everyday life, and a large amount of research has been devoted to understanding spatial coding and reference frames across many areas. The popular research paradigms to study spatial reference frames include novel shortcut, perspective change, and landmark control tests. However, the growing research on spatial updating challenges the logical foundation of these classical paradigms, and suggests that the experimental findings using these paradigms have usually been misinterpreted. That is, performance in these tasks is generally unrelated to whether the spatial representations themselves are egocentric or allocentric. This article reviews the traditional paradigms and their logic, summarizes the theories of spatial updating, analyzes the logical flaws in these popular paradigms, and discusses their implications.     

基于SAR景象不变特征点的匹配定位技术研究

针对精确制导领域中的SAR景象匹配定位技术中由于实时图与基准图可能存在形变、分辨率不一致,图像旋转及雷达视角变化及噪声的影响下差异较大情况时直接利用基于灰度的规则正交二维信息匹配算法适应性差的问题,将不变特征点匹配方法(Scale Invariant Feature Transform,SIFT)应用到SAR景象匹配中,通过仿真实验取得了满意的效果,试验结果表明SIFT特征是图像的局部特征,其对旋转、尺度缩放、亮度变化保持不变性,对视角变化、噪声也保持一定程度的稳定性,对提高匹配概率和对不同图像的适应性,降低应用风险具有借鉴意义。     

Why do speakers mix perspectives?

Although considerations of discourse coherence and cognitive processing suggest that communicators should adopt consistent perspectives when describing spatial scenes, in many cases they switch perspectives. Ongoing research examining cognitive costs indicates that these are small and exacted in establishing a mental model of a scene but not in retrieving information from a well-known scene. A perspective entails a point of view, a referent object, and terms of reference. These may change within a perspective, exacting cognitive costs, so that the costs of switching perspective may not be greater than the costs of maintaining the same perspective. Another project investigating perspective choice for self and other demonstrates effects of salience of referent object and ease of terms of reference. Perspective is mixed not just in verbal communications but also in pictorial ones, suggesting that at times, switching perspective is more effective than maintaining a consistent one.     

基于图像自匹配性的景象匹配区的选定淮则

定义了图像的自匹配性，并用自匹配系数作为光景象匹配区的选定准则，和以前提出的相关长度、独立像元素准则进行了分析对比，说明了这两个准则的实质，通过分析和实验得出了相对相于关匹配算法而言，自匹配系统准则效更佳的结论，对于光学景象匹配区的选择具有一定的实用价值。     

Structural damage detection from transient responses using square-root unscented filtering

Health monitoring of large structures is inherently difficult due to the relatively small number of available sensors/measurements that can be made within budgetary constraints. To accurately detect the presence of damage in a structure requires a reliable model, or at least a good representation of the structure prior to damage. Approaches to detecting and localizing damage are predominantly based on either frequency changes or transient responses. Transient or closed-loop responses are available more readily during operation and appear to be more suitable for online damage detection than approaches based on frequency changes. In order to detect damage in a large structure, the structural characteristics such as mass matrices and stiffness matrices need to be estimated. This paper utilizes an implementation of the unscented Kalman filter in square-root form to estimate changes to the system mass/stiffness. The damage detection problem is solved online by updating the structural parameter estimates using a limited amount of measurement data. Example results are presented for spring–mass, beam and truss structures where the only measurements are accelerometer data from a limited number of nodes. The numerical results show that the approach is capable of detecting changes in the structure from the outputs online.     

互相关景象匹配系统的正确匹配概率研究

首先阐述了景象可导航性分析的定义，指出正确匹配概率是评价景象可导航性的重要指标；接着假定预处理后的基准图和附加噪声是零均值随机场。然后从图像的内容性质和其统计特性两个方面出发进行了，给出了基于景象灰度相关匹配的自主导航系统的正确匹配概率的一个估计模型。通过遥感图像的大量试验结果表明：该匹配概率的估计模型优于一般的仿真模型，从而为景象匹配自主导航系统的设计提供理论和应用基础。     

The physical price of a ticket into space

As a direct consequence of exposure to microgravity astronauts experience a number of physiological changes, which can have serious medical implications when they return to Earth. Most immediate and significant are the head-ward shift of body fluids and the removal of gravitational loading from bone and muscles, which lead to progressive changes in the cardiovascular and musculoskeletal systems. Cardiovascular adaptations result in an increased incidence of orthostatic intolerance (fainting) post-flight, decreased cardiac output and reduced exercise capacity. Changes in the musculoskeletal system contribute significantly to the impaired functions experienced in the post-flight period. The underlying factor producing these changes is the absence of gravity. Countermeasures, therefore, are designed primarily to simulate Earth-like movements, stresses and system interactions. Exercise is one approach that has received wide operational use and acceptance in both the US and Russian space programmes, and has enabled humans to stay relatively healthy in space for well over a year. Although it remains the most effective countermeasure currently available, significant physiological degradation still occurs. The development of other countermeasures will therefore be necessary for longer duration missions, such as the human exploration of Mars.     

结构有限元模型的综合修正方法

本文的方法是针对像卫星这样的大型复杂结构而提出的。它既包含了对物理参数的修正又包含了对矩阵元素的修正。除了可以修正刚度矩阵[K]和质量矩阵[M]外,它还可以修正阻尼矩阵[C]。该方法最大限度地利用了实验数据,包括固有频率、模态和频响函数。在对许多模态和固有频率进行修正的基础上,首先保证了前几阶固有频率的修正精度。本文的计算方法不需要实验频响函数是满秩的,只需要在做实验时得到频响函数的一行或一列、几行或几列,而且避免了对阻抗矩阵求逆。本文提出的方法可以进行较大误差的修正。     

基于离散分数布朗随机场模型的景象适配性分析方法

首先阐述了在自然景象的齐次平稳高斯随机场模型下进行景象适配性分析的不足；然后建立了景象的离散分数布朗随机场模型，在小波多分辨率分析的基础上提取了分形特征；接着推导了景象的分形特征与基准子图的二维相关性之间的关系，并提出了基于分形特征的景象适配性分析方法；最后通过大量仿真试验验证了分形特征和基准图的正确匹配概率之间的关系，对于景象匹配区的选择具有一定的实用价值。     

Design of transfer trajectories between resonant orbits in the Earth–Moon restricted problem

The application of dynamical systems techniques to mission design has demonstrated that employing invariant manifolds and resonant flybys enables previously unknown trajectory options and potentially reduces the ΔV$\mathrm{\Delta }V$ requirements. In this investigation, planar and three-dimensional resonant orbits are analyzed and cataloged in the Earth–Moon system and the associated invariant manifold structures are computed and visualized with the aid of higher-dimensional Poincaré maps. The relationship between the manifold trajectories associated with multiple resonant orbits is explored through the maps with the objective of constructing resonant transfer arcs. As a result, planar and three-dimensional homoclinic- and heteroclinic-type trajectories between unstable periodic resonant orbits are identified in the Earth–Moon system. To further illustrate the applicability of 2D and 3D resonant orbits in preliminary trajectory design, planar transfers to the vicinity of L₅ and an out-of-plane transfer to a 3D periodic orbit, one that tours the entire Earth–Moon system, are constructed. The design process exploits the invariant manifolds associated with orbits in resonance with the Moon as transfer mechanisms.     

Spatial Memory Organized by Environmental Geometry

We investigated the simultaneous effects of different reference systems on spatial memory. Participants studied a configuration of objects surrounding them. During retrieval, they imagined themselves in the center of the object configuration facing a particular object, and then indicated the directions of other objects relative to this imagined heading. Besides strong effects of egocentric retrieval direction, retrieval was enhanced for objects and headings aligned with an object-centered reference system (triangular object configuration within a neutrally-shaped room), or with a sufficiently salient environmental reference system (triangular room surrounding a neutrally-shaped object configuration). Moreover, remembered object positions were spatially distorted by the object-centered reference system. Results suggest that object positions are accessed by imagining oneself within a topographical representation of objects which is preorganized in terms of both environmental and object-centered reference systems.     

Learning Routes from Visualizations for Indoor Wayfinding: Presentation Modes and Individual Differences

Abstract

Participants (N = 78) studied a visualization of a route through a complex building and walked that route in the real building without further assistance. Erroneous turns on the route as well as indicators of uncertainty such as hesitations were assessed. Three types of route visualizations were compared: (1) an allocentric, map-based visualization with the route indicated in floor maps, (2) an ordered sequence of pictures of decision points shown from the egocentric perspective, and (3) an animation showing a virtual walk of the route from the egocentric perspective. In addition to the experimental variation, gender differences, differences in visual-spatial abilities and differences in self-reported wayfinding strategies were considered as predictor variables. Wayfinding performance did not differ between allocentric (map) and egocentric (decision point pictures and animation) visualizations. However, wayfinding performance was better with animated than with static egocentric visualizations. Individual differences in the ability to encode visual-spatial information from the visualization played a critical role for route learning. Self-reported sense of direction related to egocentric wayfinding strategies also predicted wayfinding performance. Gender differences were attributable to differences in visual-spatial abilities and egocentric wayfinding strategies. Interactions between visualizations and individual differences were not found. It is concluded that animations of virtual walks are suitable to convey route information in complex buildings. Successful acquisition of route knowledge from maps is possible but might depend on the comprehensibility of the structure of the building.     

基于组字典学习的逆合成孔径雷达成像方法

基于压缩感知(compressive sensing, CS)的逆合成孔径雷达(inverse synthetic aperture radar, ISAR)成像方法可以使用非常少的数据来获得高质量的图像。但基于CS的ISAR成像方法中目标场景不准确的稀疏表示限制了成像方法的性能。结合字典学习(dictionary learning, DL)技术的CS ISAR成像方法能够寻找到目标场景图像块的最优稀疏表示,提高成像质量,但每一个图像块被单独考虑,而忽略了彼此之间的相互依赖关系。为了实现进一步提高成像质量的目标,针对ISAR图像分块重建的问题,首次提出一种基于组字典学习(group dictionary learning,GDL)的ISAR成像方法。将具有相似结构的图像块聚类并构建出多个图像块组,利用奇异值分解(singular value decomposition, SVD)从图像块组中学习出最优组稀疏变换字典。学习好的组稀疏变换字典可以寻找到待重建图像块组的最优稀疏表示,进而重建出高质量的目标场景图像。实验结果表明:与现有的CS ISAR成像方法相比,基于GDL的ISAR成像方法能获得更好的成像效果,并具有更高的计算效率。     

一种适用于大场景圆迹环扫SAR的改进CS成像算法

在宽测绘带圆迹环扫合成孔径雷达(CSSAR)中,目标斜距表示形式复杂,测绘带内距离徙动(RCM)变化剧烈均给成像处理引入难点。针对上述问题,根据圆迹环扫SAR平台的运动特性,使用高阶逼近的方法建立圆弧曲线模型下的回波信号斜距方程,并以导出的二维频谱高阶近似解析表达式为基础,考虑大场景下的距离徙动空变问题,对空变的斜距历程进行详细的分析,并提出了一种适用于大场景圆迹环扫SAR的改进线性调频变标(CS)成像算法。仿真结果说明,曲线模型的斜距方程精度较高,该算法能够精确校正空变的距离徙动,对较大场景取得了较好的成像效果。     

Mental Object Rotation and Egocentric Body Transformation: Two Dissociable Processes?

An important question in studies on mental rotation is whether the mental object rotation and the egocentric body transformation rely on dissociable mechanisms. We tested non-dancers and professional dancers as experts in the mental object rotation task (MORT, 3D-cubes used by Shepard & Metzler, 1971) and the mental body transformation task (MBRT, line drawings of human bodies similar to those used by Parsons, 1987). The cubes and body figures were presented in exactly the same rotation conditions; in the picture plane, 0 degree, 45 degrees, 90 degrees, 135 degrees, and 180 degrees, and in combination with a rotation in depth, 0 degree (the stimuli are rotated in the picture plane only) and 180 degrees. We could replicate the linear increase in RT with increasing angle for the cubes whereas the RT for rotated body figures increased for not depth-rotated bodies only (back view). Though, the RTs for inverted body figures were faster when they were rotated in depth (front view) compared to when they were rotated in the picture plane only (back view). This finding suggests that participants use different strategies depending on the perceived orientation of the stimulus. The results indicate impaired performance in the MORT for the experts.     

连续景象匹配的后处理算法

下视景象匹配是各类巡航飞行器实现导航误差修正的关键技术。由于基准图和实时图存在差异，配准点往往落在相关阵的次峰上，导致匹配的失败。提出了N帧连续景象匹配决策的图论算法。该算法利用单帧匹配后形成的相关阵中的主次峰信息以及惯导的位移信息，进行多帧景象匹配的一致性决策。由于引入了相关阵中的次峰信息并结合惯导位移的一致性判断，使得匹配算法能有效剔除误匹配点，从而提高算法的鲁棒性和匹配概率。     

Navigating in a Virtual 3D Maze: Body and Gravity,Two Possible Reference Frames for Perceiving and Memorizing

Although recent studies have brought new insight into the mechanisms of spatial memory and cognitive strategies during navigation, most of these studies have concerned two-dimensional navigation and little is known regarding the problem of three-dimensional (3D) spatial memory. We found previously that memorizing complex 3D-structured corridors was easier with natural self-motion that included only yaw turns, and vertical translations facing the walls at vertical sections. This suggests that when only sideways (yaw) mental rotations had to be performed in order to shift from the experienced egocentric to the allocentric reference frame where recognition was tested, memorization of such corridors was improved. In the present investigation we studied the effect of tilting separately subject's body axis and self-motion's rotation axis relative to gravity. With a computerized 3D reconstruction task of the maze, we examined whether having any single rotation axis was enough to facilitate this reference shift or, if not, what aspect of the terrestrial condition-where visual displacement rotation, gravity and body axes were aligned-led to better performance. Field dependent (FD) and independent (FI) subjects, as determined by the rod and frame test, showed distinct effects of the navigation conditions. The FD group performance was markedly impaired when gravity and body axis were in conflict, independently of the rotation axis, whereas FI performance only slightly worsened when the body was tilted and the rotation axis remained aligned with gravity. Moreover, tilting the body in the control condition only worsened performance for the FD group.     

最小二乘支持向量机的在线学习算法研究

针对最小二乘支持向量机在线逼近过程中求解矩阵维数逐渐扩大的问题,提出了一种最小二乘支持向量机的在线学习算法。借助滚动窗口的思想,建立一个随时间滑动的建模数据区间,在线逼近中通过接受新数据删除旧数据来保持数据区间长度不变,同时数据不断更新,从而实现模型的在线学习。仿真结果表明了这种学习算法的有效性。