人的体视超视锐度阈值

体视超视(?)象是视觉系统中(?)度的超(?)在一些特殊的(?)图形下,它的阈值可达2秒以下.考虑到人眼的一般体(?)锐度的60(?),(?)未超视度现象就是一个很有意义并值得注意研究的问题.对于如此精细的分辨能力,视(?)膜细胞可以说是很粗糙的(其直径约24秒)我们想了解,这么粗糙的视网膜是如何分辨出仅为其直径1/10的目标位差的呢?本文对人眼体视超视锐度现象做了一此研究,测定出体视超视锐度(?)值,并研究了低通滤波后对其影响.     

精神分裂症视觉周边抑制异常及其神经机制

精神分裂症患者普遍存在视觉信息处理异常,这些视知觉功能紊乱涉及视通路的高级以及低级视区,表明在部分精神分裂症患者中,视觉系统早期或晚期的不同信息处理阶段均可能存在损伤.阐明这些感知觉信息处理紊乱的神经机制对理解精神分裂症神经病理生理学机制有重大意义.视觉周边抑制(surround suppression)是一种广泛存在的视觉现象,指在神经生理水平或视知觉水平上外周对中央视觉目标的抑制作用.精神分裂症的视觉周边抑制发生异常改变,然而其损伤状况并不完全一致,且其具体神经机制目前仍不清楚.本文以周边抑制为对象,从精神分裂症周边抑制改变状况及其神经机制两个层面简述了国内外精神分裂症视觉周边抑制的研究进展.未来研究方向需要系统全面地调查精神分裂症周边抑制损伤状况,综合脑科学研究技术共同探究精神分裂症患者周边抑制异常的具体神经环路.     

蝗虫复眼光谱敏感性的比较研究——Ⅰ.屏蔽色素显微分光光谱的测量

用显微分光光谱法,测定了9种蝗虫复眼两类屏蔽色素的光密度。咖啡色屏蔽色素在400—520nm 波段密度最高,在深红区密度最低。反光屏蔽色素在365—390nm 波段的密度最高,在深红区最低。此外还测定了9种蝗虫之一的黄脊蝗复眼的光屏蔽色素的反射光谱,结果显示在近紫外和橙红区反光率最高。关于屏蔽色素对蝗虫视觉功能如光谱敏感性、明适应、视锐度、视色素和间视紫红之间的转化等问题曾加以讨论。     

Organization and postembryonic development of glial cells in the visual system of the Chinese honeybee, Apis cerana cerana (Hymenoptera:Apidae )

神经胶质作为视觉系统的重要成分之一,对视觉系统的发育及功能起着重要的作用.本研究通过组织解剖观察、免疫组织化学等技术,对中华蜜蜂Apis cerana cerana幼虫和蛹的视觉系统中神经胶质的类型和发育过程进行了比较研究.研究表明:在中华蜜蜂视觉系统中,根据神经胶质的位置和形态主要分为表面神经胶质、皮层神经胶质和神经纤维网神经胶质3种类型;神经胶质主要来源于视柄和视叶中的神经胶质前体中心;神经胶质细胞数量的增加一方面来自于细胞的迁移,另一方面来自于神经胶质细胞自身的分裂增殖.本研究为昆虫神经胶质的发育以及功能研究提供理论基础.     

老年猫视皮层细胞对刺激反应的对比敏感度下降伴随皮层内抑制作用减弱(英文)

对人类和动物的心理学研究证实,老年个体的视觉对比敏感度相对青年个体显著下降。为揭示其可能的神经机制,采用在体细胞外单细胞记录技术研究青、老年猫(Felis catus)初级视皮层(primary visual cortex,V1)细胞对不同视觉刺激对比度的调谐反应。结果显示,老年猫V1细胞对视觉刺激反应的平均对比敏感度比青年猫显著下降,这与灵长类报道的研究结果相一致,表明衰老影响视皮层细胞对视觉刺激反应的对比敏感度是灵长类和非灵长类哺乳动物中普遍存在的现象,并可能是介导老年性视觉对比敏感度下降的神经基础。另外,与青年猫相比,老年猫初级视皮层细胞对视觉刺激的反应性显著增强,信噪比下降,感受野显著增大,表明衰老导致的初级视皮层细胞对视觉刺激反应的对比敏感度下降伴随着皮层内抑制性作用减弱。     

Vax基因与视觉神经系统的早期发育

视觉神经系统的发育与形成是一个相当复杂的过程,其基因调控机理是神经发育生物学领域的研究热点.Vax基因家族是新近发现的一类与视觉神经系统发育密切相关的同源异型盒基因,调控前脑、眼原基、视泡、视柄以及视网膜的发育.Vax-1参与色素上皮和视柄的分化;Vax-2则在视网膜及视神经背腹轴建立方面起重要作用.Vax基因的研究将对阐明视觉神经系统发育调控机制提供新的认识.     

不同视觉经验中zif268基因的表达模式

zif268基因编码一转录因子ZIF268. 在发育的视皮层中,zif268基因的表达模式受发育的调节. 在具有正常视觉经验的视皮层中,zif268基因有较高水平的表达. 视觉废置后,视皮层内该基因的表达水平显著降低. 通过视觉刺激可显著增强该基因的表达. 有关zif268基因表达模式的研究对于阐明该基因在哺乳动物视觉系统中的生理功能起到借鉴的作用.     

宽周边视视网膜皮层映射的核磁共振研究

目的:人类视觉皮层的组织方式是视网膜皮层映射组织,先前研究已经证实视觉皮层在中心视采用这种组织方式,本文主要研究宽周边视的视觉皮层组织方式.方法:本文采用一种可以在核磁共振室中使用的光纤设备,设计了30度、40度、50度、60度的类圆环block刺激,使用1.5T的功能性核磁共振仪器,T1高分辨率图像分辨率为1*1*5.5mm,T2加权图像分辨率为4*4*5.5mm,TR反应时间为60,矩阵大小为64*64.核磁共振数据分析使用了SPM2和Brain voyager软件.结果:通过对试验者的数据处理分析,周边视的刺激的反应区域在枕叶上,主要分布在枕叶的前部,刺激反应区域随着偏心率的增大而沿着距状沟从距状沟的后部向前部移动.结论:周边视的视网膜皮层映射组织特性和中心视的特性非常相似.     

视觉学习与成人大脑的可塑性

我们对视觉特征和客体的分辨与识别能力会随着训练提高,这种现象被称为视知觉学习。对其神经机制的研究使我们更好地理解成人大脑可塑性。回顾了该研究领域的两大核心问题:(1)视知觉学习发生的皮层位置:学习发生在早期信息加工的视皮层,或是涉及决策等认知功能的高级额顶叶区域,抑或是视觉区域到高级认知区域的连接;(2)视知觉学习发生的形式:包括表征增强、表征锐化、易化等多种机制。最后,讨论了神经干预手段在知觉学习领域的应用,并展望该领域未来的研究方向。     

GABA神经元在金黄地鼠视觉中枢的分布

本文用免疫细胞化学技术研究了GABA在金黄地鼠视觉中枢的分布特征,同时用统计学方法作了定量分析,结果表明:GABA阳性神经元分布在整个视皮层和上丘中,呈不均匀分布,外膝体中GABA阳性神经元密度较低.视皮层中GABA阳性神经元密度为781mm~2,占视皮层细胞总数的19.7%,上丘中其密度为812/mm~2,占22.3%,视皮层Ⅰ层中GABA阳性神经元为52%,上丘表层(浅灰层及视觉层GABA阳性神经元为56%,GABA阳性神经元包括不同类型的细胞.在视皮层中可观察到GABA免疫疫应阳性的锥体细胞.     

Contrast and duration of exposure differentially affect vernier and stereoscopic acuity

Although stereoacuity and vernier acuity both yield comparable thresholds well below the eye's resolution limit, the neural circuits for these two classes of visual responses do not process the signals in an identical manner. It had previously been demonstrated that hyperacuity is more resistant to image blur than stereoacuity and that the zones within which two targets must be placed to achieve the lowest thresholds differ quite radically. Two further differences are reported here: reduced contrast affects stereoacuity more severely than hyperacuity, as also does shortening of exposure into a range of tens of milliseconds, even when the Bunsen-Roscoe-Bloch law has been factored out.     

The role of stimulus structure in spatial hyperacuity

In spatial hyperacuity the subjects discriminate a stimulus feature relative to a reference, with an accuracy significantly better than the grain of the retinal mosaic. We show that the normalized thresholds have a dichotomous behavior; they are either insensitive to the spatial parameter in the experiment or increase very steeply with it. This behavior is explained by the involvement in the processing of pixel (receptor) accuracy information about the structure of the stimulus. A computational model employing optimal filtering reproduces the experimental data and suggests that processing of spatial hyperacuity tasks in the human visual system is optimal.     

一种感知视觉运动信息的简化脑模型

视觉运动信息的感知过程,包括从局域运动检测到对模式整体运动的感知过程.我们以蝇视觉系统的图形-背景相对运动分辨的神经回路网络为基本框架,采用初级运动检测器的六角形阵列作为输入层,构造了一种感知视觉运动信息的简化脑模型,模拟了运动信息应该神经计算模型各个层次上的处理.该模型对差分行为实验结果作出了正确预测.本文并对空间生理整合的神经机制作了讨论.     

High Accuracy Decoding of Dynamical Motion from a Large Retinal Population

Motion tracking is a challenge the visual system has to solve by reading out the retinal population. It is still unclear how the information from different neurons can be combined together to estimate the position of an object. Here we recorded a large population of ganglion cells in a dense patch of salamander and guinea pig retinas while displaying a bar moving diffusively. We show that the bar’s position can be reconstructed from retinal activity with a precision in the hyperacuity regime using a linear decoder acting on 100+ cells. We then took advantage of this unprecedented precision to explore the spatial structure of the retina’s population code. The classical view would have suggested that the firing rates of the cells form a moving hill of activity tracking the bar’s position. Instead, we found that most ganglion cells in the salamander fired sparsely and idiosyncratically, so that their neural image did not track the bar. Furthermore, ganglion cell activity spanned an area much larger than predicted by their receptive fields, with cells coding for motion far in their surround. As a result, population redundancy was high, and we could find multiple, disjoint subsets of neurons that encoded the trajectory with high precision. This organization allows for diverse collections of ganglion cells to represent high-accuracy motion information in a form easily read out by downstream neural circuits.     

Visual acuity and hyperacuity in 11- to 17-year-old secondary school students

Visual acuity and hyperacuity of 11- to 17-year-old secondary school students with normal vision were measured and compared. The estimations of hyperacuity and acuity were made using the vernier stimuli, Landolt Cs, and Tumbling Es. When test stimuli were located in the tables, visual acuity estimations measured using Landolt Cs were significantly higher by a factor of 1.1 than that measured using Tumbling Es. Visual hyperacuity was 1.25?C4.1 times higher than visual acuity. The estimations of visual hyperacuity were almost 2 times higher in 16-year-old than 13-year-old secondary school students, in contrast to the estimations of visual acuity that did not change with age. The binocular visual acuity estimations were 1.05 times higher than the monocular ones and did not depend on the age. The ratio of binocular visual hyperacuity to monocular visual hyperacuity in 13-year-old secondary school students was 1.9, whereas, in senior secondary school students, it was 1.2. The contribution of binocular vision to the development of the mechanisms of visual acuity and hyperacuity in ontogenesis and the differences between the mechanisms of visual acuity and hyperacuity are discussed.     

Complex predictive eye pursuit in monkey: a model system for cerebellar studies of skilled movement

Smooth pursuit eye movements provide a good model system for cerebellar studies of complex motor control in monkeys. First, the pursuit system exhibits predictive control along complex trajectories and this control improves with training. Second, the flocculus/paraflocculus region of the cerebellum appears to generate this control. Lesions impair pursuit and neural activity patterns are closely related to eye motion during complex pursuit. Importantly, neural responses lead eye motion during predictive pursuit and lag eye motion during non-predictable target motions that require visual control. The idea that flocculus/paraflocculus predictive control is non-visual is also supported by a lack of correlation between neural activity and retinal image motion during pursuit. Third, biologically accurate neural network models of the flocculus/paraflocculus allow the exploration and testing of pursuit mechanisms. Our current model can generate predictive control without visual input in a manner that is compatible with the extensive experimental data available for this cerebellar system. Similar types of non-visual cerebellar control are likely to facilitate the wide range of other skilled movements that are observed.     

Motion-based prediction explains the role of tracking in motion extrapolation

During normal viewing, the continuous stream of visual input is regularly interrupted, for instance by blinks of the eye. Despite these frequents blanks (that is the transient absence of a raw sensory source), the visual system is most often able to maintain a continuous representation of motion. For instance, it maintains the movement of the eye such as to stabilize the image of an object. This ability suggests the existence of a generic neural mechanism of motion extrapolation to deal with fragmented inputs. In this paper, we have modeled how the visual system may extrapolate the trajectory of an object during a blank using motion-based prediction. This implies that using a prior on the coherency of motion, the system may integrate previous motion information even in the absence of a stimulus. In order to compare with experimental results, we simulated tracking velocity responses. We found that the response of the motion integration process to a blanked trajectory pauses at the onset of the blank, but that it quickly recovers the information on the trajectory after reappearance. This is compatible with behavioral and neural observations on motion extrapolation. To understand these mechanisms, we have recorded the response of the model to a noisy stimulus. Crucially, we found that motion-based prediction acted at the global level as a gain control mechanism and that we could switch from a smooth regime to a binary tracking behavior where the dot is tracked or lost. Our results imply that a local prior implementing motion-based prediction is sufficient to explain a large range of neural and behavioral results at a more global level. We show that the tracking behavior deteriorates for sensory noise levels higher than a certain value, where motion coherency and predictability fail to hold longer. In particular, we found that motion-based prediction leads to the emergence of a tracking behavior only when enough information from the trajectory has been accumulated. Then, during tracking, trajectory estimation is robust to blanks even in the presence of relatively high levels of noise. Moreover, we found that tracking is necessary for motion extrapolation, this calls for further experimental work exploring the role of noise in motion extrapolation.     

Acuity and hyperacuity for pupils of 11-17 years old

Estimations of hyperacuity and visual acuity (VA) have been compared in schoolchildren aged 11-17 years with normal vision. VA was measured using Landolt Cs and Tumbling Es. Hyperacuity was measured by vernier stimuli. Acuity estimations depended on the test stimuli. They were in 1.1 times over for Landolt Cs than for Tumbling Es. Hyperacuity estimations exceeded VA in 1.25-4.1 times. They were almost twice as high among pupils of 16 years compared to 13-year-olds, in contrast to estimates of VA, which practically did not change with age. Binocular VA was significantly higher monocular VA in 1.05 times regardless of age. The ratio between the binocular and monocular hyperacuity estimates for thirteen years pupils in average was equal to 1.9, while for sixteen years pupils--1.2. We discuss the contribution of binocular vision in the development of mechanisms of VA and hyperacuity in ontogenesis and the difference between these mechanisms.     

Discrimination thresholds for channel-coded systems

We present an analytical ideal observer model to predict discrimination thresholds for stimuli that are processed by arrays of noise-perturbed receptors that have smooth and overlapping tuning functions. We show that hyperacuity phenomena are natural properties of these systems. A comparison of thresholds for a number of discrimination tasks allows a psychophysically derived estimate of parameters of the receptor array involved. We note the consistency of this scheme with data from a number of visual subfields.