内容和运动方向感知计算模型

对视野中的物体及运动方向进行感知是视觉感知的基本问题之一,较高级视皮层从V1区的简单细胞开始分为两个通路：“What通路”和“Where通路”．前者对物体的形状、颜色、纹理等内容感知,后者对空间运动速度和方向等感知．本文利用仿脑视觉信息处理计算结构,研究视觉内容和运动方向上的感知计算模型、计算机理和学习算法．该计算模型是一个三层的神经网络,第一层是视觉信号输入层,用于接收外界图像刺激．第二层是神经信息内部表象层,与第一层的网络联结是通过神经元稀疏表象原理自适应形成神经元的感受野．为此,引入Kullback_Leibler散度描述神经元响应的独立性,极小化该代价函数导出网络联结权值的学习算法．从自然图像块中学习得到图像基函数,这些基函数具有局部性、朝向性和带通滤波性．这些性质与生理实验结果中的V1区简单细胞感受野特征相吻合．将这些基函数作为神经元的感受野,并在第三层对较高级视皮层的内容感知和运动感知神经元进行建模．在理想刺激中加入一定量的噪声后,该模型对内容和运动方向的感知仍有较高的准确率和较好的鲁棒性．最后给出的实验仿真结果说明模型的可行性和学习算法的简单有效性．     

基于EMDs阵列和BP网络的视觉运动感知过程

以Ｒｅｉｃｈａｒｄｔ的相关型初级运动检测器阵列和Ｒｕｍｅｌｈａｒｔ的误差反传学习（ｌｅａｒｎｉｎｇｂｙｂａｃｋ－ｐｒｏｐａｇａｔｉｎｇｅｒｒｏｒｓ,ＢＰ）网络相结合构成了一个视觉运动感知神经网络,探讨了视觉运动信息的感知过程。试图从计算神经科学的观点来阐明从一推运动分量的检测到二维模式运动感知的神经原理,从而回答运动矢量在脑内如何表征。计算机仿真表明,在有监督学习的条件下,网络可以学会解决局城运动检测所带来的多义性问题,给出模式的真实朝向、运动方向和运动速度。     

蝇视觉运动信息的神经计算原理

本文基于理论、实验和计算三大研究方法,遵循计算神经科学的认识路线,以蝇视觉系统为研究对象,通过建立简化的脑模型,探讨蝇视觉运动信息的神经计算原理。本文系统地综述了蝇初级运动检测器、图形-背景分辨系统的提出及其演化,介绍了图形-背景相对运动分辨的行为实验和相应的计算机仿真,给出了蝇视觉系统的模型及算法,并对有关问题进行了讨论。     

视觉运动图象滤波模型及其实时模拟

在充满生存竞争的动物世界,视觉的伪装与反伪装现象随处可见,视觉反伪装的原理是什么？本文对Ｒｅｉｃｈａｒｄｔ的图形－背景相对运动分辨模型加以发展,提出了视觉反伪装功能的运动图象滤波器模型。为了检验此模型,我们建立了一个生物学似真的实时运动信息加工神经网络电子装置,实现了实时、高分辨运动目标图象滤波。与Ｍｅａｄ的人工视网膜的运动目标图象检测功能相比,检测的运动目标图象的分辨率有很大提高,而噪声水平显著降低,克服了人工视网膜的一些局限性。     

蝇视觉运动信息的神经计算原理(续)

3.蝇眼视觉运动计算模型的神经基础 在细胞水平上,蝇眼初级运动检测器得到了电生理记录实验的支持。同时,行为实验分析证实了存在两个平行的不同时空整合特性的控制系统——SF和LF系统。神经生理学的     

不同视觉通道中频差所引起的深度感知

为了解体视倾斜效应(Stereoscopic tilt effect)是否能在视觉系统的不同空间频率通道中由双眼频差(Binocular diffrequency)所引起,我们设计了二组心理物理实验.观察到了Wilson频率调制曲线的第二及第四峰值的二个频道(1.7周 度和4.0周 度)中双眼频差所引起的倾斜感知.它们在同样频差率(频率和中心频率之比)下,引起相等倾斜感知.在一定频差率范围内(0.070-1.30),倾斜感知和频差率成正比关系.     

运动延缓脑衰老的实验研究

运动是延缓脑衰老的重要手段之一。以“跑转笼”方式建立运动动物模型,用行为学、形态学和生物学研究方法,研究从青年开始的长期运动（８ｍｏ,１９ｍｏ）对运动相关中枢随年龄增加而出现的退行性变化的作用及作用机制。结果表明,长期适量运动能够延缓运动相关中枢随年龄增加而出现的形态结构和功能的退行性变化,通过促进神经元结构代偿而改善神经元功能。     

几种幼鱼视觉运动反应研究

对鲻鱼(Mugit cephalus)、鲈鱼(Lateolabrax japonicus)、黄鳍鲷(Sparus latus)、鲤鱼(Cyprinus carpio)和草鱼(Ctenopharyngodon idellus)5种幼鱼进行了视觉运动反应实验。反应率随照度的降低或屏幕转速的提高而下降。高限可跟刺激频率随照度而提高,在10^2 1x下,鲻鱼达37次／秒,鲈鱼26次／秒,黄鳍鲷27次／秒,鲤鱼24次／秒,草鱼29次／秒。明暗视过渡照度值：鲻鱼10^0-10^1 1x,鲤鱼和草鱼10^-1—10^01x,鲈鱼和黄鳍鲷10^-2-10^-1 1x。照度和刺激频率对反应潜伏期有一定影响。跟随角速度普遍落后于屏幕角速度,即跟随率低于100％,并且随屏幕转速提高而下降。照度对跟随率无明显影响。几种幼鱼对运动条纹的反应可分为三阶段：跟随、活泼运动、无反应。     

基于初级视觉皮层的同步振荡目标检测模型

提出一种基于初级视觉皮层的目标检测模型,该模型只采用方位选择性细胞和皮层内水平连接等Ｖ１基本单元,它以链码表示的目标轮廓作为知识,允许该知识以时间脉冲的形式控制Ｖ１区内神经细胞的动态活动,使与知识轮廓形状相符合的轮廓内的细胞进入同步振荡状态,实现对视野中特定目标轮廓的识别。计算机仿真结果表明,在较高级皮层的“知识”控制之下,初级视觉皮层结构上实现简单的目标检测是可行的。     

一种基于可穿戴器件触觉感知信息的盲人虚拟视觉导航系统

目的 全球视力受损或失明人数已超2亿,长期以来各类人工视觉系统被广泛研究。人工视觉系统的研发主要有两种技术路径,第一种是各类植入式人工视觉装置,第二种是各类非植入式、可穿戴装置。本文展示了一种非植入式、基于可穿戴头部触觉激发装置的系统原型,能够帮助盲人和视觉障碍者完成行走等复杂任务。方法 该系统采集受试者周边环境图像信息并无线传输到后台,操作人员分析处理图像信息后,将指令以触觉编码形式无线传输到头套等可穿戴装置,由驱动电路激发多点位头部触觉,从而为受试者提供准确的行动指令。系统并辅助以语音信息,让其了解更多道路状况和环境信息。结果 用原型系统对5名（2男3女）在读大学生健康志愿者和1名年轻盲症患者（男）进行实验。结果表明,原型系统充分利用了头部对前后左右的天然区分能力和对触觉的快速反应,具备直行、左右调整、转弯等明确指令功能。受试者对指令的响应时间约0.5 s,直线行走约7 m距离的偏差量标准差平均值相比未佩戴装置的情况下降低到（16±10）cm。结论 该系统可隐蔽、准确地提供环境图像信息,有效帮助视觉障碍人士完成行走、避让障碍物、上台阶、进入咖啡厅等公共场所、桌上取物等日常活动,达到了预期目标。今后对原型系统作进一步完善,特别是小型化、智能芯片化,把触觉装置制成颈环、腰带、手环、脚环等,将能够广泛应用于盲人出行辅助、夜间野外旅行、深海潜水等多种工作场景。     

Stochastic growth and extinction in a spatial geometric Brownian population model with migration and correlated noise

A continuous spatial model for populations that are not density-regulated is analyzed. The model is a generalization of the geometric Brownian motion often used to describe populations at a single location. The locations are linked by migration and spatial correlation in the noise. At any point of time, the population size at a given location is log normally distributed so the log population size constitutes a Gaussian field. The model is homogeneous in space but not in time. In particular, we analyze the case when the stochastic growth rate is negative and the total population approaches extinction. The properties of the extinction process is studied by considering local quasi-extinctions. A major conclusion is that migration tends to increase the time to extinction provided that there is no cost of migration. However, as the area occupied by the species starts to decrease, the decrease is faster for populations with larger migration.     

脑机融合系统综述

脑机接口是生物脑与电脑或机器之间的一种直接连接通路。脑机融合计算系统是一种基于脑机接口技术,综合利用生物智能和机器智能的新型智能融合系统,其在医疗康复、生活娱乐和军事侦查等方面具有巨大的应用开发潜力。首先从信息传输的角度简述由脑机接口到脑机融合的发展趋势;其次重点阐述脑机融合系统的概念及其研究所面临的挑战,并分三个层次介绍当前若干典型相关工作;最后介绍吴朝晖课题组在脑机融合计算系统方面的相关工作。     

Collective motion from local attraction

Many animal groups, for example schools of fish or flocks of birds, exhibit complex dynamic patterns while moving cohesively in the same direction. These flocking patterns have been studied using self-propelled particle models, most of which assume that collective motion arises from individuals aligning with their neighbours. Here, we propose a self-propelled particle model in which the only social force between individuals is attraction. We show that this model generates three different phases: swarms, undirected mills and moving aligned groups. By studying our model in the zero noise limit, we show how these phases depend on the relative strength of attraction and individual inertia. Moreover, by restricting the field of vision of the individuals and increasing the degree of noise in the system, we find that the groups generate both directed mills and three dynamically moving, ‘rotating chain’ structures. A rich diversity of patterns is generated by social attraction alone, which may provide insight into the dynamics of natural flocks.     

The visual processing of motion-defined transparency

Our understanding of how the visual system processes motion transparency, the phenomenon by which multiple directions of motion are perceived to coexist in the same spatial region, has grown considerably in the past decade. There is compelling evidence that the process is driven by global-motion mechanisms. Consequently, although transparently moving surfaces are readily segmented over an extended space, the visual system cannot separate two motion signals that coexist in the same local region. A related issue is whether the visual system can detect transparently moving surfaces simultaneously or whether the component signals encounter a serial 'bottleneck' during their processing. Our initial results show that, at sufficiently short stimulus durations, observers cannot accurately detect two superimposed directions; yet they have no difficulty in detecting one pattern direction in noise, supporting the serial-bottleneck scenario. However, in a second experiment, the difference in performance between the two tasks disappears when the component patterns are segregated. This discrepancy between the processing of transparent and non-overlapping patterns may be a consequence of suppressed activity of global-motion mechanisms when the transparent surfaces are presented in the same depth plane. To test this explanation, we repeated our initial experiment while separating the motion components in depth. The marked improvement in performance leads us to conclude that transparent motion signals are represented simultaneously.     

The Intrinsic Electrophysiological Characteristics of Fly Lobula Plate Tangential Cells: III. Visual Response Properties

In this last paper in a series (Borst and Haag, 1996; Haag et al., 1997) about the lobula plate tangential cells of the fly visual system (CH, HS, and VS cells), the visual response properties were examined using intracellular recordings and computer simulations. In response to visual motion stimuli, all cells responded mainly by a graded shift of their axonal membrane potential. While ipsilateral motion resulted in a graded membrane potential shift, contralateral motion led to distinct EPSPs. For HS cells, simultaneous extracellular recorded action potentials of a spiking interneuron, presumably the H2 cell, corresponded to the EPSPs in the HS cell in a one-to-one fashion. When HS cells were hyperpolarized during ipsilateral motion, they mainly produced action potentials, but when they were hyperpolarized during contralateral motion only a slight increase of EPSP amplitude, could be observed. Intracellular application of the sodium channel blocker QX 314 abolished action potentials of HS cells while having little effect on the graded membrane response to ipsilateral motion. HS and CH cells were also studied with respect to their spatial integration properties. For both cell types, their graded membrane response was found to increase less than linearly with the size of the ipsilateral motion pattern. However, while for HS cells various amounts of hyperpolarizing current injected during motion stimulation led to different saturation levels, this was not the case for CH cells. In response to a sinusoidal velocity modulation, CH cells followed pattern motion only up to 10 Hz modulation frequency, but HS cells still revealed significant membrane depolarizations up to about 40 Hz.In the computer simulations, the compartmental models of tangential cells, as derived in the previous papers, were linked to an array of local motion detectors. The model cells revealed the same basic response features as their natural counterparts. They showed a response saturation as a function of stimulus size. In CH-models, however, the saturation was less pronounced than in real CH-cells, indicating spatially nonuniform membrane resistances with higher values in the dendrite. As in the experiments, HS models responded to high-frequency velocity modulation with a higher amplitude than did CH models.     

蟋蟀脑的解剖结构与生理机能

蟋蟀脑由前脑、中脑和后脑三部分组成。前脑由1对蕈形体、中央复合体和视叶构成;每个蕈形体由2个冠、柄及与柄相连的α叶和β叶组成,是信息联络整合部位;中央复合体由中央体和脑桥组成,主要参与感觉信息的加工过程;视叶由神经节层、外髓和内髓组成,是视觉系统的中心。中脑由主要组成成分为嗅觉纤维球的嗅叶组成,是嗅觉系统的中心。后脑向后与食道下神经节相连。     

Spatial integration using a 3D virtual environment with humans

Spatial integration refers to the superimposition of two separate spatial relationships between cues (C1–C2 and C2–C3) by a common linking element (C2). This linkage creates a new spatial relationship between cues that were never paired together (C1–C3). Several authors obtained conflicting results on spatial integration in both humans and animals. Using a dynamic 3D virtual environment, we provide the first clear evidence that humans can integrate two spatial relationships into a new spatial relationship that guides spatial navigation. This research is discussed in light of a spatial version of the temporal coding hypothesis (Savastano and Miller, 1998).