猫纹状皮层神经元整合野的形状和范围

用正弦调制的移动光栅测量了１２０个猫纹状皮层神经元在长度和宽度方向上的空间整合特性。结果表明：（１）大多数细胞的传统感受野具有长宽相近的结构,然而它们的整合野多数是宽而短或者窄而长的长条形。（２）整合野大小为传统感受野的２—７倍,平均为３．７倍。简单细胞与复杂细胞整合野的大小没有显著差别。（３）随着感受野的视网膜偏心度的增加,整合野大小有逐渐增大的趋势。（４）感受野靠近视网膜垂直中线的细胞,其整合野可以跨越中线进入同侧视野;在两半视野中整合野的范围没有显著差异,但是同侧视野整合野的作用强度明显弱于对侧视野。以上结果提示,初级视皮层神经元能够对大范围内的图形特征进行整合,这种整合作用来自两侧视野。     

用脑光学成像精确测定猫初级视皮层视野拓扑投射关系

利用基于脑内源信号的光学成像和二维互相关分析的方法,对猫初级视皮层17区的视野拓扑离心度(即视网膜-皮层拓扑关系)进行了精确测量。当采用在同一屏幕内处于上下视野的、方位互相垂直的两个相邻光栅刺激时,皮层中一部分区域的绝大部分细胞因同时兴奋而导致方位功能图模糊不清。将这种方位功能图和用单一方位(水平或垂直)全屏光栅刺激所得到的功能图进行比较,通过计算每一像素的互相关系数,从而获得皮层的精确视野拓扑离心度。同时用电生理的方法测量了同一视皮层内的单细胞的感受野位置,证明这种方法得到的视野离心度和光学记录方法得到的相同。因此,本研究为大面积地确定视皮层细胞感受野在视野中的位置提供了一种快速和较准确的方法。     

中间锦鸡儿的生长及生态化学计量学特征与基质稳定性关系初探

选取半流动沙丘、半固定沙丘和丘间低地3种生境条件下的中间锦鸡儿为对象,研究了灌丛群落学特征、叶片化学计量学特征及其与土壤基质条件的关系。结果表明：(1)中间锦鸡儿灌丛在3种生境下的基质特征差异明显,半流动沙丘土壤相对贫瘠、土质疏松,半固定沙丘和丘间低地土壤紧实度较大;(2)灌丛当年枝长度、枝干重、叶干重以及叶干物质含量均与土壤紧实度呈显著负相关关系,而叶片N∶P及C∶P与土壤紧实度均呈显著正相关,但叶片C∶N与土壤紧实度的相关性并不显著;(3)中间锦鸡儿灌丛的灌幅、密度和盖度在不同沙丘生境间差异显著,这可能是由于土壤紧实度的差异引起的。土壤紧实度对中间锦鸡儿生长状况的影响不仅表现在地上生物量和当年枝生长量上,而且也表现在叶片C:N:P化学计量学特征以及叶片对营养物质的保持效率上。     

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.     

青光眼病人的心理治疗及护理

青光眼是眼科的常见病,是一种以眼压病理性增高、视乳头血液灌注不良、视乳头凹陷扩大和萎缩、视野缺损、视力下降为主要特征的眼病.目前,我国人群中青光眼发病率为0.5%～2.6%.青光眼致盲人数在全盲中占有10%～21%.做好青光眼的早期诊断和及时治疗是当前防盲工作中的重要任务.本文报道我科1989～2002年收治的200例青光眼病人的临床心理治疗与护理体会.     

不同尺度下城市景观综合指数的空间变异特征研究

在GIS与RS技术支持下,采用5 m分辨率的SPOT遥感图像数据,从城市土地利用角度,利用半变异函数对不同尺度的景观多样性、聚集度与分维数的空间变异进行了定量分析.结果表明,不同尺度下3种指数的空间变异具有相似特征,各个尺度上都具有空间依赖性,尺度越小,空间依赖性越大,空间变异的细节更显著,空间自相关性对总体变异的贡献逐渐增加,但尺度过小,有时会破坏景观内部结构.不同指数的半变异函数模型在相同尺度上差异显著,说明不同景观指数在不同尺度下的半变异函数模型不具可比性.就研究上海市内部土地利用结构而言,1 km的幅度是较合适的空间尺度.景观指数空间变异特征是尺度的函数,尺度对景观格局的影响不能忽视.景观综合指数对尺度响应的生态过程揭示了上海城市空间结构的规律性:在小尺度上的复杂无规律性,中尺度上的多中心性和大尺度上的圈层结构性,但各个尺度是相互依赖的,没有绝对界限.     

中国树鼩下丘脑视上核和室旁核内加压素和催产素能神经元的比较分布

应用PAP-PAAP双重免疫组化染色程序在同一切片上进行两种肽能物质的定位,观察了中国树鼩下丘脑视上核和室旁核内VP能和OT能神经元的比较解剖学分布,发现:视上核被视束分成主部和交叉后部。在视上核主部,其头侧部几乎仅含OT能神经元胞体,中间部VP能胞体出现并逐渐增多,尾侧部VP能胞体数目明显超过OT能胞体。在明显含有两种胞体的中间部和尾侧部,OT能胞体多位于背内侧,VP能胞体多位于腹外侧;在视上核交叉后部,其头侧部以VP能胞体为主,且多位于背外侧,OT能胞体多位于腹内侧。中间部OT能胞体多位于内侧,VP能胞体多位于外侧。尾侧部OT能胞体多位于背、腹两侧,VP能胞体则多位于中间;在室旁核,其头侧部几乎全由OT能胞体构成。中间部,VP能胞体出现并逐渐增多,OT和VP能胞体分别主要位于内、外侧。尾侧部两种神经元胞体较明显地分为内、外两群,内侧群主要为OT能胞体,外侧群几乎全为VP能胞体,该群的头侧半又可分为背腹两个亚群,至尾侧半,此二亚群渐合并。本文讨论了OT和VP能神经元在中国树鼩和大鼠视上核和室旁核内的比较分布。     

桂西北喀斯特区域生态环境脆弱性

以桂西北喀斯特区域--广西环江县为研究区,基于景观结构信息对研究区的生态环境脆弱度进行评价.将灰关联分析法应用于指标体系的构建,选取破碎度、分维数、聚集度、土壤侵蚀指数、植被覆盖指数和喀斯特地貌面积比作为评价指标,计算了研究区的景观类型脆弱度和区域生态环境脆弱度,并对结果进行半变异函数分析和空间插值分析,揭示了研究区生态环境脆弱度的空间分布特征.研究结果表明:(1)研究区林地景观脆弱度最高,其次为未利用地和耕地;(2)半变异函数分析表明,区域生态环境脆弱度指数具有明显的空间相关性,相关距离在25km左右,区域脆弱度的空间变异在15km以内表现出明显的各向同性,15km以外表现出各向异性;(3)区域生态环境脆弱度整体上表现出从东北到西南逐渐增大的趋势,局部随着高程的增加表现出"高-中-低-中-高"的变化特征,地质和地形是该区生态环境脆弱度空间格局的两大控制因素.     

指甲油简易制片封藏法

中学生物制片(永久或半永久的)最后封藏时可直接用市售的无色或浅色透明指甲油作为封藏剂,不需要稀释,方法简便,快速,观察效果好.具体方法:1.视标本需保存长短决定是否脱水,如长久保存需脱水.2.在洁净的载玻片中央,滴上指甲油,所需指甲油多少视     

景观生态学中的尺度分析方法

多尺度空间分析法是发现和识别景观特征尺度的主要方法.当前这类方法很多,缺乏归类和对比分析评价.基于空间类型变量和数值变量,对多尺度空间分析方法进行了重新梳理.同时对当前常用的尺度分析方法:半方差分析、尺度方差分析、小波分析和孔隙度指数分析,以中国三北防护林为例,对比了各种尺度分析方法的特点和优劣.结果表明,在特征尺度的识别上:小波方差方法清晰明了;半方差分析法灵活简捷,结果明显;尺度方差分析法和孔隙度指数法在本研究中的判识结果不甚明显.在计算速度上:半方差分析法计算量最大、耗时最长,尺度方差次之,小波方差速度最快,孔隙度指数法计算速度快于前两种,慢于小波方差分析方法.半方差分析方法简单灵活,而且相关理论方法成熟,但缺乏对大尺度格局的整体把握,而小波分析恰恰能很好的弥补这一不足.最后提出,半方差分析和小波变换相结合将会是最优的尺度分析方法.     

Bilateral field advantage in visual enumeration

A number of recent studies have demonstrated superior visual processing when the information is distributed across the left and right visual fields than if the information is presented in a single hemifield (the bilateral field advantage). This effect is thought to reflect independent attentional resources in the two hemifields and the capacity of the neural responses to the left and right hemifields to process visual information in parallel. Here, we examined whether a bilateral field advantage can also be observed in a high-level visual task that requires the information from both hemifields to be combined. To this end, we used a visual enumeration task--a task that requires the assimilation of separate visual items into a single quantity--where the to-be-enumerated items were either presented in one hemifield or distributed between the two visual fields. We found that enumerating large number (>4 items), but not small number (<4 items), exhibited the bilateral field advantage: enumeration was more accurate when the visual items were split between the left and right hemifields than when they were all presented within the same hemifield. Control experiments further showed that this effect could not be attributed to a horizontal alignment advantage of the items in the visual field, or to a retinal stimulation difference between the unilateral and bilateral displays. These results suggest that a bilateral field advantage can arise when the visual task involves inter-hemispheric integration. This is in line with previous research and theory indicating that, when the visual task is attentionally demanding, parallel processing by the neural responses to the left and right hemifields can expand the capacity of visual information processing.     

Category learning induces position invariance of pattern recognition across the visual field

Human object recognition is considered to be largely invariant to translation across the visual field. However, the origin of this invariance to positional changes has remained elusive, since numerous studies found that the ability to discriminate between visual patterns develops in a largely location-specific manner, with only a limited transfer to novel visual field positions. In order to reconcile these contradicting observations, we traced the acquisition of categories of unfamiliar grey-level patterns within an interleaved learning and testing paradigm that involved either the same or different retinal locations. Our results show that position invariance is an emergent property of category learning. Pattern categories acquired over several hours at a fixed location in either the peripheral or central visual field gradually become accessible at new locations without any position-specific feedback. Furthermore, categories of novel patterns presented in the left hemifield are distinctly faster learnt and better generalized to other locations than those learnt in the right hemifield. Our results suggest that during learning initially position-specific representations of categories based on spatial pattern structure become encoded in a relational, position-invariant format. Such representational shifts may provide a generic mechanism to achieve perceptual invariance in object recognition.     

Recognition of visual images by separate hemispheres in conditions of masked blocking of interhemispheric transmission

The subjects learned to recognize three figures presented in the left visual hemifield and three figures presented in the right visual hemifield. During presentation of a stimulus, the contralateral hemifield was overlapped by a mask. After the training, recognition of all six figures presented in the right and left visual hemifields, was compared. Each hemisphere recognizes figures which were learned in the corresponding visual hemifield, but the recognition of figures learned in the opposite visual hemifield was poor. Thus, the ability of the hemispheres to act separately in recognizing different sets of visual images, was established.     

Distractor-target interactions during directed visual attention

The spatial extent of directed visual attention (DVA) was examined in a series of experiments using precuing in a suprathreshold luminance detection (reaction time) paradigm. Previous findings (Hughes, H. C. and Zimba, L. D. J. Exp. Psychol.; Human Percept Perf., 1985, 11, 409-430) indicated that, in an empty visual field, the effects of DVA were primarily manifest as a uniform elevation of response times to all probe targets in the hemifield contralateral to the observer's expectancy. The present experiments were designed to determine whether increased spatial selectivity could be found when luminous markers indicated the exact location of the expected visual target. To maintain equivalent states of adaptation in both hemifields, luminous markers were also present at the same location in the contralateral hemifield. In general, hemifield effects were again obtained, but with two notable exceptions. First, marking locations in the unattended hemifield produced a local increase (enhanced interference) in RTs above the level characteristic of other locations within that hemifield. Second, when multiple locations were indicated with identical luminous markers, graded costs were obtained in both hemifields. However, scaling the markers according to estimates of cortical magnification factor (M) substantially reduced the slope of these inhibitory gradients, and the results once again approached those characteristic of an unstructured visual field. The findings suggest that when attention is directed to a marked location along the horizontal meridian, a transition in performance typically occurs at the vertical meridian. In addition, irrelevant stimuli some distance from the attentional focus interfere with detection times to unexpected targets that appear in the same vicinity. This interference may relate to an enhanced susceptibility to spatial interactions between the distractors and target away from the attentional focus. The interference appears to extend over a constant area of visual cortex, since it is reduced when the markers are M-scaled.     

Effect of the loci of visual cues on ability of polyrhythmic bimanual movement

Abstract

The present study investigated whether the deviation of the performed movement cycle from the required cycle during polyrhythmic bimanual (BM) movement depends on the loci of the visual cues that guide the rhythm of finger movements. Twelve healthy right-handed males rhythmically abducted and adducted the index finger or index fingers with the rhythm of the visual cues. During UM movement, the visual cue guiding the rhythm of finger movement was provided in the left or right visual hemifield. During 2:3 polyrhythmic BM movement, two visual cues, one guiding the rhythm of the left finger movement and another guiding the rhythm of the right finger movement, were provided in a single visual hemifield, or each visual cue guiding each finger movement was provided in each visual hemifield. During polyrhythmic BM movement, the cycle duration of the slower side of the movement guided by the rhythm of the visual cues provided in one visual hemifield was shorter than the required cycle duration, and the magnitude of the shortage in this condition was greater than that guided by each visual cue provided in each visual hemifield. Slower side of the movement is more precisely performed by each visual cue guiding each finger movement in each visual hemifield rather than that guided by visual cues provided in one visual hemifield during polyrhythmic BM movement. This may be explained by bottle-neck model in which visual information overflows the processing capacity when two visual processes are simultaneously provided in a single visual cortex.     

Optic Flow Stimuli in and Near the Visual Field Centre: A Group fMRI Study of Motion Sensitive Regions

Motion stimuli in one visual hemifield activate human primary visual areas of the contralateral side, but suppress activity of the corresponding ipsilateral regions. While hemifield motion is rare in everyday life, motion in both hemifields occurs regularly whenever we move. Consequently, during motion primary visual regions should simultaneously receive excitatory and inhibitory inputs. A comparison of primary and higher visual cortex activations induced by bilateral and unilateral motion stimuli is missing up to now. Many motion studies focused on the MT+ complex in the parieto-occipito-temporal cortex. In single human subjects MT+ has been subdivided in area MT, which was activated by motion stimuli in the contralateral visual field, and area MST, which responded to motion in both the contra- and ipsilateral field. In this study we investigated the cortical activation when excitatory and inhibitory inputs interfere with each other in primary visual regions and we present for the first time group results of the MT+ subregions, allowing for comparisons with the group results of other motion processing studies. Using functional magnetic resonance imaging (fMRI), we investigated whole brain activations in a large group of healthy humans by applying optic flow stimuli in and near the visual field centre and performed a second level analysis. Primary visual areas were activated exclusively by motion in the contralateral field but to our surprise not by central flow fields. Inhibitory inputs to primary visual regions appear to cancel simultaneously occurring excitatory inputs during central flow field stimulation. Within MT+ we identified two subregions. Putative area MST (pMST) was activated by ipsi- and contralateral stimulation and located in the anterior part of MT+. The second subregion was located in the more posterior part of MT+ (putative area MT, pMT).     

Visual hemifield differences in recognition of kanji and hiragana and its relation to hemispheric cerebral asymmetries

Visual hemifield differences in recognition of kanji and hiragana were studied on forty male right handers. A letter of kanji or hiragana was presented unilaterally to the right or left visual hemifield on a CRT display for 123 msec. A hundred and twenty recognition trials were performed for each subject using 20 well-acquainted kanji, 20 unfamiliar kanji and 20 hiragana. Kanji was more accurately recognized in the left visual hemifield than in the right hemifield. This tendency was more prominent in unfamiliar kanji compared with well-acquainted kanji. There were no visual hemifield differences in recognition of hiragana. Learning effects were observed for the right hemifield on kanji and both hemifields on hiragana. The results were discussed in relation to cerebral asymmetries of function. Kanji might be processed in the right cerebral hemisphere as geometric forms. The results on hiragana may be explained by mental set. It is suggested that modes of processing may be different between kanji and hiragana.     

Cortical Contributions to Saccadic Suppression

The stability of visual perception is partly maintained by saccadic suppression: the selective reduction of visual sensitivity that accompanies rapid eye movements. The neural mechanisms responsible for this reduced perisaccadic visibility remain unknown, but the Lateral Geniculate Nucleus (LGN) has been proposed as a likely site. Our data show, however, that the saccadic suppression of a target flashed in the right visual hemifield increased with an increase in background luminance in the left visual hemifield. Because each LGN only receives retinal input from a single hemifield, this hemifield interaction cannot be explained solely on the basis of neural mechanisms operating in the LGN. Instead, this suggests that saccadic suppression must involve processing in higher level cortical areas that have access to a considerable part of the ipsilateral hemifield.     

Single cell responses from the optic tectum of the zebra finch (Taeniopygia guttata castanotis Gould)

Responses of neurons of the optic tectum, the prominent, highly laminated mesencephalic station of the tectofugal visual pathway in birds, to computer-generated and other visual stimuli were examined in zebra finches. Our study shows that the contralateral retina projects to the tectum in topographic order. The representation of the visual field is tilted against the horizon by 22°. The representation of the contralateral hemifield extends to the ipsilateral side by 15°. Most neurons have receptive fields with excitatory centres of different shapes and inhibitory surround. A new type of neuronal receptive field is described which has an excitatory centre and a surround which is movement sensitive and preferably excited by very small spots. The first type of neurons is mostly located in upper tectal layers, the latter only in deeper layers. Excitatory centre sizes increase with depth, and there is a tendency of smaller receptive fields in the foveal region. The representation of the frontal visual field does not show specializations which could be expected if it were used for fixation of grain during pecking. Our results are in accordance with previous behavioural experiments. Accepted: 30 April 1999     

Crossmodal spatial influences of touch on extrastriate visual areas take current gaze direction into account

Recent results indicate that crossmodal interactions can affect activity in cortical regions traditionally regarded as "unimodal." Previously we found that combining touch on one hand with visual stimulation in the anatomically corresponding hemifield could boost responses in contralateral visual cortex. Here we manipulated which visual hemifield corresponded to the location of the stimulated hand, by changing gaze direction such that right-hand touch could now arise in either the left or right visual field. Crossmodal effects on visual cortex switched from one hemisphere to the other, depending on gaze direction, regardless of whether the hand was seen. This indicates that crossmodal influences of touch upon visual cortex depend on spatial alignment for the multimodal stimuli, with gaze posture taken into account.