Prediction of auditory spatial acuity from neural images on the owl's auditory space map

The owl can discriminate changes in the location of sound sources as small as 3 degrees and can aim its head to within 2 degrees of a source. A typical neuron in its midbrain space map has a spatial receptive field that spans 40 degrees--a width that is many times the behavioural threshold. Here we have quantitatively examined the relationship between neuronal activity and perceptual acuity in the auditory space map in the barn owl midbrain. By analysing changes in firing rate resulting from small changes of stimulus azimuth, we show that most neurons can reliably signal changes in source location that are smaller than the behavioural threshold. Each source is represented in the space map by a focus of activity in a population of neurons. Displacement of the source causes the pattern of activity in this population to change. We show that this change predicts the owl's ability to detect a change in source location.     

Efficient auditory coding

The auditory neural code must serve a wide range of auditory tasks that require great sensitivity in time and frequency and be effective over the diverse array of sounds present in natural acoustic environments. It has been suggested that sensory systems might have evolved highly efficient coding strategies to maximize the information conveyed to the brain while minimizing the required energy and neural resources. Here we show that, for natural sounds, the complete acoustic waveform can be represented efficiently with a nonlinear model based on a population spike code. In this model, idealized spikes encode the precise temporal positions and magnitudes of underlying acoustic features. We find that when the features are optimized for coding either natural sounds or speech, they show striking similarities to time-domain cochlear filter estimates, have a frequency-bandwidth dependence similar to that of auditory nerve fibres, and yield significantly greater coding efficiency than conventional signal representations. These results indicate that the auditory code might approach an information theoretic optimum and that the acoustic structure of speech might be adapted to the coding capacity of the mammalian auditory system.     

年龄相关和空间扩散的半线性时变种群系统的最优控制

讨论了年龄相关和空间扩散的半线性时变种群系统的最优控制问题,证明了系统最优控制的存在性和控制为最优的必要条件,并得到了确定最优控制的最优性组,为种群实际控制问题的研究提供了严格的理论和方法。     

Adaptive coding of visual information in neural populations

Our perception of the environment relies on the capacity of neural networks to adapt rapidly to changes in incoming stimuli. It is increasingly being realized that the neural code is adaptive, that is, sensory neurons change their responses and selectivity in a dynamic manner to match the changes in input stimuli. Understanding how rapid exposure, or adaptation, to a stimulus of fixed structure changes information processing by cortical networks is essential for understanding the relationship between sensory coding and behaviour. Physiological investigations of adaptation have contributed greatly to our understanding of how individual sensory neurons change their responses to influence stimulus coding, yet whether and how adaptation affects information coding in neural populations is unknown. Here we examine how brief adaptation (on the timescale of visual fixation) influences the structure of interneuronal correlations and the accuracy of population coding in the macaque (Macaca mulatta) primary visual cortex (V1). We find that brief adaptation to a stimulus of fixed structure reorganizes the distribution of correlations across the entire network by selectively reducing their mean and variability. The post-adaptation changes in neuronal correlations are associated with specific, stimulus-dependent changes in the efficiency of the population code, and are consistent with changes in perceptual performance after adaptation. Our results have implications beyond the predictions of current theories of sensory coding, suggesting that brief adaptation improves the accuracy of population coding to optimize neuronal performance during natural viewing.     

Improved auditory spatial tuning in blind humans.

Despite reports of improved auditory discrimination capabilities in blind humans and visually deprived animals, there is no general agreement as to the nature or pervasiveness of such compensatory sensory enhancements. Neuroimaging studies have pointed out differences in cerebral organization between blind and sighted humans, but the relationship between these altered cortical activation patterns and auditory sensory acuity remains unclear. Here we compare behavioural and electrophysiological indices of spatial tuning within central and peripheral auditory space in congenitally blind and normally sighted but blindfolded adults to test the hypothesis (raised by earlier studies of the effects of auditory deprivation on visual processing) that the effects of visual deprivation might be more pronounced for processing peripheral sounds. We find that blind participants displayed localization abilities that were superior to those of sighted controls, but only when attending to sounds in peripheral auditory space. Electrophysiological recordings obtained at the same time revealed sharper tuning of early spatial attention mechanisms in the blind subjects. Differences in the scalp distribution of brain electrical activity between the two groups suggest a compensatory reorganization of brain areas in the blind that may contribute to the improved spatial resolution for peripheral sound sources.     

Optimal transsaccadic integration explains distorted spatial perception

We scan our surroundings with quick eye movements called saccades, and from the resulting sequence of images we build a unified percept by a process known as transsaccadic integration. This integration is often said to be flawed, because around the time of saccades, our perception is distorted and we show saccadic suppression of displacement (SSD): we fail to notice if objects change location during the eye movement. Here we show that transsaccadic integration works by optimal inference. We simulated a visuomotor system with realistic saccades, retinal acuity, motion detectors and eye-position sense, and programmed it to make optimal use of these imperfect data when interpreting scenes. This optimized model showed human-like SSD and distortions of spatial perception. It made new predictions, including tight correlations between perception and motor action (for example, more SSD in people with less-precise eye control) and a graded contraction of perceived jumps; we verified these predictions experimentally. Our results suggest that the brain constructs its evolving picture of the world by optimally integrating each new piece of sensory or motor information.     

Linear processing of spatial cues in primary auditory cortex.

To determine the direction of a sound source in space, animals must process a variety of auditory spatial cues, including interaural level and time differences, as well as changes in the sound spectrum caused by the direction-dependent filtering of sound by the outer ear. Behavioural deficits observed when primary auditory cortex (A1) is damaged have led to the widespread view that A1 may have an essential role in this complex computational task. Here we show, however, that the spatial selectivity exhibited by the large majority of A1 neurons is well predicted by a simple linear model, which assumes that neurons additively integrate sound levels in each frequency band and ear. The success of this linear model is surprising, given that computing sound source direction is a necessarily nonlinear operation. However, because linear operations preserve information, our results are consistent with the hypothesis that A1 may also form a gateway to higher, more specialized cortical areas.     

基于种群保护的最优税收策略

在两种群相互作用的Logistic模型的基础上,将税收考虑进去分析了一类食饵-捕食收获模型.讨论了正平衡点的存在性,利用Hurwitz判别法证明了正平衡点的局部渐近稳定性,利用Pontryagin最大值原则得到了最优税收策略,目的在于既保护生态系统又能使社会经济收益最大.     

时变种群系统的最优边界控制

讨论了与年龄相关的时变种群系统的最优边界控制,证明了最优控制的存在唯一性,得到了控制为最优的充分必要条件,给出了由积分一偏微分方程和变分不等式组成的最优性组．这些结果可为种群控制问题的研究提供严格的理论基础．     

用于犯罪空间聚集态研究的优化聚类算法

针对犯罪空间聚集态研究算法中有关窗宽优化选择问题,将动态优化窗宽算法与DENCLUE(DENsity-based CLUstEring)算法结合,提出一种新的聚类算法。以入室盗窃案件为例,研究了该算法在犯罪热点探测方面的应用。结果显示引入优化窗宽算法后,可得到较为精确的聚类中心位置及概率密度变化趋势,并且当格网边长与邻近格网距离阈值及邻近点距离阈值之比为2:3:1时会得到较好的热点分析结果。通过分析犯罪热点分布图,可协助公安机关调整警力配置,加强案件高发区警力巡逻。     

Bazooka provides an apical cue for Inscuteable localization in Drosophila neuroblasts

Asymmetric cell division generates daughter cells with different developmental fates from progenitor cells that contain localized determinants. During this division, the asymmetric localization of cell-fate determinants and the orientation of the mitotic spindle must be precisely coordinated. In Drosophila neuroblasts, inscuteable controls both spindle orientation and the asymmetric localization of the cell-fate determinants Prospero and Numb. Inscuteable itself is localized in an apical cortical crescent and thus reflects the intrinsic asymmetry of the neuroblast. Here we show that localization of Inscuteable depends on Bazooka, a protein containing three PDZ domains with overall sequence similarity to Par-3 of Caenorhabditis elegans. Bazooka and Inscuteable form a complex that also contains Staufen, a protein responsible for the asymmetric localization of prospero messenger RNA. We propose that, after delamination of the neuroblast from the neuroepithelium, Bazooka provides an asymmetric cue in the apical cytocortex that is required to anchor Inscuteable. As Bazooka is also responsible for the maintenance of apical-basal polarity in epithelial tissues, it may be the missing link between epithelial polarity and neuroblast polarity.     

时滞Logistic种群的控制问题:最优收获

研究一类带时滞的Logistic种群系统的最优收获问题.分析了状态系统的精确可控性,应用极大化序列法和Mazur定理证明了最优控制函数的存在性,利用Dubovitskii-Milyutin理论导出了最优性条件.     

污染环境中种群的最优收获问题

研究了污染环境中可再生资源的最优收获问题,利用Pontryagin极大值原理,得到了处理资源毒素的努力度与收获资源的努力度的一种最优分配方案,同时还得到次最优轨线,且此轨线最终趋近于最优解。     

基于神经网络的K－L变换及其在图象压缩中的应用

介绍了一种可用迭代方法实现Ｋ－Ｌ变换的神经网络及相应的算法（ＧＨＡ），采用该算法对网络的权作修正，可使网络唯一的收敛到一个稳定点，其ｍ个输出神经元对应的权依次为最大ｍ个特征值所对应的单位特征矢量．文章给出了网络实现中的改进结构，并把该网络用于图象压缩．结果表明它具有比ＤＣＴ变换更理想的压缩效果，而比常规Ｋ－Ｌ变换方法实现起来更容易、更快，特别是它便于计算多幅图象的公共变换基，因此具有较大的现实意义．     

陕西省生态人口容量时空差异性分析

基于生态足迹理论,提出了生态人口容量相关概念及其模型,并对陕西省人地系统资源供需态势及区域差异性进行实证研究。结果表明：1990年—2006年,陕西省各市人均生态足迹大幅增长,区域生态承载力微小波动,生态人口容量普遍下降。然而,人口数量日益增多,多数市区人口生态超载现象严重,人地关系日趋紧张。截止2006年底,各市生态超载率由高到低依次为西安市（82.8%）、咸阳市（68.9%）、渭南市（64.9%）、宝鸡市（61.1%）、榆林市（38.8%）;铜川市（27.6%）,汉中市（25.0%）、安康市（8.7%）。延安市和商洛市尚没有生态超载人口。     

基于Hopfield神经网络的燃气轮机可靠性分配

首先推导出了燃气轮机可靠性和造价之间的拟合函数;然后利用惩罚甬数法把有造价约束问题转化为无约束优化问题,基于Hopfield神经网络构造和最优可靠性分配相对应的网络优化计算的能量函数,建立了系统可靠性优化分配的数学模型;最后用适合刚性方程的ode15s算法给出了最优的数值解.得出了惩罚因子变化趋势对最优数值解的影响关系:当惩罚因子的值在一定范围内逐渐增加时,优化结果趋于稳定.即收敛于最优解.改变约束条件,得出了燃气轮机可靠性随总造价的优化后的变化趋势,为燃气轮机的优化设计和综合决策提供一定的参考.     

一种基于分类的改进BP神经网络图像压缩方法

探讨了神经网络用于图像压缩和解压缩技术,实现了一种基于分类的改进BP神经网络压缩方法:按图像各部分像素特征将图像分为平滑块、中间块和边缘块,不同的分类块采用不同的隐含层数,从而在保证重建图像丰富细节的同时,提高图像的压缩比.同时,对3层BP神经网络进行优化,提高了网络的收敛速率,实验结果证明本算法在取得较大的压缩比的同时能保证图像的恢复质量.     

Isolation of a cDNA clone coding for a possible neural nicotinic acetylcholine receptor alpha-subunit

We have isolated a complementary DNA clone containing sequences homologous to those encoding the alpha-subunit of a mouse muscle nicotinic acetylcholine receptor. Based on the structural similarities between the encoded protein and the muscle acetylcholine receptor alpha-subunit, and the presence of hybridizing RNA species in the brain, we propose that this clone codes for a neural nicotinic acetylcholine receptor alpha-subunit.