用显示器测量办公亮度环境下的人眼对比度敏感视觉特性

对比度敏感是描述人眼视觉系统空间特性的主要指标之一,对比度敏感函数是反映不同条件下的对比度敏感与空间频率之间的关系。人眼对比度敏感数据的测量受到环境亮度较大的影响,为了研究常用办公环境条件下的人眼对比度敏感情况,对6位青年在环境亮度分别为153,312,470 cd/m2和暗室条件下,在距离为2米处观测11种空间频率的矩形光栅进行测量,光栅用显示器进行显示,其平均亮度分别为60和90 cd/m2。实验结果表明,对于相同频率的光栅,人眼对比度敏感程度随着环境亮度的增加而减小,而且人眼在暗室环境下比在办公环境条件下对亮度光栅更敏感;但是在观测平均亮度为60cd/m2的光栅时,人眼特殊地对在环境亮度为312 cd/m2的条件下更敏感。     

综述: 初级视皮层的亮度信息加工

亮度(luminance)是最基本的视觉信息.与其他视觉特征相比,由于视神经元对亮度刺激的反应较弱,并且许多神经元对均匀亮度无反应,对亮度信息编码的神经机制知之甚少.初级视皮层部分神经元对亮度的反应要慢于对比度反应,被认为是由边界对比度诱导的亮度知觉(brightness)的神经基础.我们的研究表明,初级视皮层许多神经元的亮度反应要快于对比度反应,并且这些神经元偏好低的空间频率、高的时间频率和高的运动速度,提示皮层下具有低空间频率和高运动速度通路的信息输入对产生初级视皮层神经元的亮度反应有贡献.已经知道初级视皮层神经元对空间频率反应的时间过程是从低空间频率到高空间频率,我们发现的早期亮度反应是对极低空间频率的反应,与这一时间过程是一致的,是这一从粗到细的视觉信息加工过程的第一步,揭示了处理最早的粗的视觉信息的神经基础.另外,初级视皮层含有偏好亮度下降和高运动速度的神经元,这群神经元的活动有助于在光照差的环境中检测高速运动的低亮度物体.     

初级视皮层的亮度信息加工

亮度(luminance)是最基本的视觉信息.与其他视觉特征相比,由于视神经元对亮度刺激的反应较弱,并且许多神经元对均匀亮度无反应,对亮度信息编码的神经机制知之甚少.初级视皮层部分神经元对亮度的反应要慢于对比度反应,被认为是由边界对比度诱导的亮度知觉(brightness)的神经基础.我们的研究表明,初级视皮层许多神经元的亮度反应要快于对比度反应,并且这些神经元偏好低的空间频率、高的时间频率和高的运动速度,提示皮层下具有低空间频率和高运动速度通路的信息输入对产生初级视皮层神经元的亮度反应有贡献.已经知道初级视皮层神经元对空间频率反应的时间过程是从低空间频率到高空间频率,我们发现的早期亮度反应是对极低空间频率的反应,与这一时间过程是一致的,是这一从粗到细的视觉信息加工过程的第一步,揭示了处理最早的粗的视觉信息的神经基础.另外,初级视皮层含有偏好亮度下降和高运动速度的神经元,这群神经元的活动有助于在光照差的环境中检测高速运动的低亮度物体.     

视觉图形诱发的瞳孔反应

以图形变化刺激进行瞳孔反应研究,实验表明：（１）空间平均亮度守恒的光栅或棋盘格图形翻转能激发起瞳孔反应,为瞬态收缩波形,与ｐｕｐｉｌｌａｒｙ ｅｓｃａｐｅ相似;（２）光栅或棋盘格的空间频率的变化也能引起瞳孔反应,且反应幅度随空间频率差别增大而变大;（３）从均匀亮背景变化到棋盘格图形或者从棋盘格图形变化到黑暗背景,虽然不存在任何局部亮度增强,皆能引起瞳孔反应。实验结果明确证明了人的瞳孔反应系统除接收     

不同运动速度下人眼的阈上调制特性

本文报道了在光栅的三种恒定运动速度(0°/S,10°/S,30°/S)下,阈值对比敏感度函数CSF(V)和阈上对比度比配函数CMF(V,C)的测试数据.计算机拟合结果表明,在各个不同的恒定运动速度下,人眼的阈上对比度比配函数CMF(V,C)和阈值对比敏感度函数CSF(V),可以由静止目标的阈值对比敏感函数CSF近似地预测出来.本文给出了预测方法的数学描述及有关经验公式.     

弱稳恒磁场环境下基于BiFeO_3@TiO_2复合纳米颗粒体外光动力疗法灭活HL60细胞试验研究

本文通过溶胶-凝胶法制备了BiFeO_3@TiO_2复合纳米颗粒,利用透射电镜(TEM)、X射线衍射(XRD)、荧光发光光谱等对纳米颗粒进行表征。研究采用Cell Counting Kit-8(CCK-8)法分别检测了在暗室条件、光照条件以及不同强度的弱稳恒磁场作用下,用终值质量浓度为50μg/mL纳米颗粒处理HL60细胞活性,试验结果表明:在暗室条件下,药物质量浓度为50μg/mL,与HL60细胞共同孵育12 h后,BiFeO_3@TiO_2复合纳米颗粒随着TiO_2外壳厚度增加,细胞的暗室相对存活率从78%增加到85%;在光照条件下,有弱稳恒磁场作用的BiFeO_3与TiO_2质量比为1∶2的BiFeO_3@TiO_2复合纳米颗粒对HL60细胞的PDT灭活效率最高达到78%,弱稳恒磁场环境增强了对HL60细胞的PDT灭活效率,这为对弱稳恒磁场环境下的光动力疗法治疗白血病肿瘤细胞的临床应用提供了参考。     

恒河猴和树鼩角膜内皮细胞的比较分析

目的对比分析恒河猴和树鼩角膜内皮细胞的特点和差异。方法利用非接触式自动角膜内皮细胞仪SP3000P分别对6只恒河猴(12眼)和20只树鼩(40眼)进行角膜内皮细胞测量,并获得角膜的8个相关参数:中央角膜厚度(CCT)、最小细胞面积(Smin)、最大细胞面积(Smax)、平均细胞面积(Savg)、细胞面积标准差(SSD)、细胞面积变异系数(CV)、细胞密度(CD)和六边形细胞百分比(HG),并结合文献与人眼的相关参数进行对比分析。结果 SP3000P角膜内皮细胞仪能在较短时间内完成恒河猴和树鼩角膜内皮的图像采集和参数的检查,耗时差异无显著性。恒河猴和树鼩CCT分别为(449.2±12.8)μm和(262.4±24.6)μm;Smin分别为(120.4±26.3)S/μm2和(153.2±42.9)S/μm2;Smax分别为(705.0±130.8)S/μm2和(468.7±109.3)S/μm2;Savg分别为(351.1±26.1)和(295.4±18.9)S/μm2;SSD分别为(113.1±27.4)和(75.9±27.3)S/μm2;CV分别为(31.9±6.0)和(25.3±8.3);CD分别为(2874.2±203.8)p/cell·mm-2和(3399.3±224.7)p/cell·mm-2;HG%分别为(58.6±9.1)和(94.0±9.7)。二者的上述参数差异均有显著性(P0.05)。树鼩角膜厚度比恒河猴小,内皮细胞面积、变异系数也较恒河猴小,但是角膜内皮细胞密度和六边形细胞比例显著高于恒河猴。恒河猴角膜厚度、角膜内皮细胞变异系数和六边形细胞比例与人眼高度相似,但内皮细胞密度低于人眼;树鼩角膜厚度为恒河猴的60%、人眼的50%,但角膜内皮细胞密度和平均细胞面积更接近于10~20岁人眼。结论恒河猴和树鼩角膜内皮细胞的形态和各项参数均有显著差异,各自与人眼角膜内皮细胞既有相似之处,也有不同点,恒河猴和树鼩均是研究人类角膜内皮疾病可以选择的合适实验动物。     

猫外膝体神经元对光栅刺激方位倾向性的一种分布特性

我们检测了猫外膝体(LGN)神经元对闪烁方波光栅的反应与光栅方位的关系。对一定对比度和空间频率的光栅,26个记录到的神经元的反应均随方位不同而变化,其最大反应和最小反应的比值平均为3.0±0.3(S.E.)。神经元的最优方位(即引起最大反应的光栅方位)随其感受野中心在视网膜上的位置而异,具有平行于其各自感受野中心与视网膜中央区(area cen-sralis)的连接线的倾向。     

视觉诱发电位(VEP)方位效应与刺激位置的关系

以人视觉诱发电位(VEP)反应为指标,在视野的不同位置测定了VEP对四个方位的闪烁方波光栅刺激(时间频率2.9Hz,空间频率1.4c/deg,对比度0.94)的反应幅度。在距中央凹20°视角同心圆的八个刺激位置上,VEP反应幅度对与向心线垂直方位的光栅刺激(同心圆的切线方向),有统计意义上的优势。这一规律在垂直、水平向心线上尤为明显。从总体上未发现VEP反应幅度与刺激光栅方位有着明显的关系。这说明在人视野周边区,VEP反应幅度与光栅方位和向心线的夹角(偏向角)相关,而与光栅的绝对方位无关。在相同的刺激条件下,中央区的VEP反应幅度与刺激光栅方位之间也未发现明显关系。     

图形视网膜电图研究的新进展

图形视网膜电图(PERG)是视网膜的综合电反应,是用亮度呈周期变化的光栅或周期翻转的黑白相间的图形诱发。其幅度是图形的空间频率和时间频率的函数,也受图形的对比度及清晰度影响。基础和临床研究都提示PERG可能起源于神经节细胞。一旦神经节细胞的活动发生异常,PERG明显减小或消失。PERG为人的视网膜细胞活动的分层分析提供了一种有效的手段,具有广泛的应用前景。     

Visual sensitivity of ground squirrels to spatial and temporal luminance variations

Summary We have investigated the visual sensitivity of the California ground squirrel (Speromphilus beecheyi) to spatial and temporal luminance patterns. Spatial contrast sensitivity functions were determined in behavioral discrimination experiments in which the stimuli were sinusoidally-modulated luminance gratings. These squirrels were found to be maximally sensitive to spatial frequencies of about 0.7 cycles/ degree (c/d), and they are unable to discriminate gratings whose frequencies exceed 4 c/d. Similar results were obtained in electrophysiological experiments when the visually evoked cortical potential (VECP) was recorded from anesthetized squirrels. A third experiment involved tests of the ability of ground squirrels to discriminate square-wave gratings of much higher luminance (340 cd/m²). The finest gratings which were discriminable at this luminance level did not exceed 3.9–4.3 c/d and, thus, we conclude that the maximal spatial resolution of the California ground squirrel is about 4 c/d (corresponding to a bar separation of 7.5). In another behavioral experiment the abilities of ground squirrels to discriminate sinusoidally flickering lights (mean luminance = 3.4 cd/m²) was measured. The results show that ground squirrels are maximally sensitive to lights flickering at a rate of about 18 Hz, and that the highest rates that are still discriminable are slightly above 60 Hz.Abbreviations c/d cycles/degree - CFF critical flicker frequency - VECP visually evoked cortical potential This research was supported by Grant EY 00105 from the National Eye Institute. We thank David Birch who participated in some preliminary behavioral experiments and Kenneth Long who provided the histological material from which measurements of receptor spacing were made.     

Visual acuity and spatial contrast sensitivity in tree squirrels

The visual sensitivity of tree squirrels from three different species (two western gray squirrels, Sciurus griseus; three fox squirrels, Sciurus niger; and an eastern gray squirrel, Sciurus carolinensis) was measured for spatial patterns defined by luminance differences. Spatial contrast sensitivity functions were determined in behavioral discrimination experiments in which the stimuli were sinusoidally-modulated gratings. At an average luminance level of 3.4 cd/m² these squirrels were maximally sensitive to spatial frequencies of about 0.5 cycles/degree (c/d). These experiments, in conjunction with additional measurements involving discrimination of square-wave grating patterns, also indicate that the finest gratings these squirrels can discriminate average 2.2 c/d (SD = 0.42 c/d). There are no obvious differences in resolution acuity among the three species. Grating acuity also was measured at a much higher luminance level (340 cd/m²). The results of this experiment indicate that the spatial acuity of the tree squirrel increases with luminance level, reaching a maximum of 3.9 c/d at 340 cd/m².     

Contrast sensitivity in a harbor seal (<Emphasis Type="Italic">Phoca vitulina</Emphasis>)

In this study, the contrast sensitivity function (CSF) of one harbor seal was determined behaviorally in a go-/no-go-experiment at an ambient light of 0.9 lx in air. Contrast sensitivity was assessed as the reciprocal value of the threshold contrast for spatial frequencies varying between 0.03 and 1.5 cycles/deg, which were displayed with contrast ranging from 0.02 to 1 on a TFT monitor with a mean luminance of 3.8 cd/m2. The CSF of the harbor seal shows the general characteristics described for other species with a peak at an intermediate frequency, a low frequency roll-off and a high frequency cut-off towards the harbor seal’s resolution limit determined in a previous study. The position of the CSF’s peak lies at approximately 0.5 cycles/deg and adopts an absolute height of 40. These results compare well with the cat’s CSF assessed at a comparable adaptation light which might reflect similarities in lifestyle and optics.     

Spatiotemporal frequency responses of cat retinal ganglion cells

Spatiotemporal frequency responses were measured at different levels of light adaptation for cat X and Y retinal ganglion cells. Stationary sinusoidal luminance gratings whose contrast was modulated sinusoidally in time or drifting gratings were used as stimuli. Under photopic illumination, when the spatial frequency was held constant at or above its optimum value, an X cell's responsivity was essentially constant as the temporal frequency was changed from 1.5 to 30 Hz. At lower temporal frequencies, responsivity rolled off gradually, and at higher ones it rolled off rapidly. In contrast, when the spatial frequency was held constant at a low value, an X cell's responsivity increased continuously with temporal frequency from a very low value at 0.1 Hz to substantial values at temporal frequencies higher than 30 Hz, from which responsivity rolled off again. Thus, 0 cycles X deg-1 became the optimal spatial frequency above 30 Hz. For Y cells under photopic illumination, the spatiotemporal interaction was even more complex. When the spatial frequency was held constant at or above its optimal value, the temporal frequency range over which responsivity was constant was shorter than that of X cells. At lower spatial frequencies, this range was not appreciably different. As for X cells, 0 cycles X deg-1 was the optimal spatial frequency above 30 Hz. Temporal resolution (defined as the high temporal frequency at which responsivity had fallen to 10 impulses X s-1) for a uniform field was approximately 95 Hz for X cells and approximately 120 Hz for Y cells under photopic illumination. Temporal resolution was lower at lower adaptation levels. The results were interpreted in terms of a Gaussian center-surround model. For X cells, the surround and center strengths were nearly equal at low and moderate temporal frequencies, but the surround strength exceeded the center strength above 30 Hz. Thus, the response to a spatially uniform stimulus at high temporal frequencies was dominated by the surround. In addition, at temporal frequencies above 30 Hz, the center radius increased.     

Spatial properties of goldfish ganglion cells

We systematically classified goldfish ganglion cells according to their spatial summation properties using the same techniques and criteria used in cat and monkey research. Results show that goldfish ganglion cells can be classified as X-, Y-, or W-like based on their responses to contrast-reversal gratings. Like cat X cells, goldfish X-like cells display linear spatial summation. Goldfish Y-like cells, like cat Y cells, respond with frequency doubling at all spatial positions when the contrast-reversal grating consists of high spatial frequencies. There is also a third class of neurons, which is neither X- nor Y-like; many of these cells' properties are similar to those of the "not-X" cells found in the eel retina. Spatial filtering characteristics were obtained for each cell by drifting sinusoidal gratings of various spatial frequencies and contrasts across the receptive field of the cell at a constant temporal rate. The spatial tuning curves of the cell depend on the temporal parameters of the stimulus; at high drift rates, the tuning curves lose their low spatial frequency attenuation. To explore this phenomenon, temporal contrast response functions were derived from the cells' responses to a spatially uniform field whose luminance varied sinusoidally in time. These functions were obtained for the center, the surround, and the entire receptive field. The results suggest that differences in the cells' spatial filtering across stimulus drift rate are due to changes in the interaction of the center and surround mechanisms; at low temporal frequencies, the center and surround responses are out-of-phase and mutually antagonistic, but at higher temporal rates their responses are in-phase and their interaction actually enhances the cell's responsiveness.     

Psychophysical measure of visual luminance contrast during a daily rhythm

ABSTRACT

This study evaluated visual sensitivity to luminance contrast during a daily period. Twenty-eight young male adults (M = 24.85; SD = 2.4) with normal color vision and 20/20 visual acuity participated in this study. The circadian pattern was assessed using the Karolinska Sleepiness Scale (KSS), the Pittsburgh Sleep Quality Index (PSQI), and a sleep diary. To measure the luminance contrast, we used version 11.0 of the Metropsis software with sine-element frequency stimuli for spatial frequencies of 0.2, 0.6, 1, 3.1, 6.1, 8.8, 13.2, and 15.6 cycles per degree of visual angle (cpd). The stimuli were presented on a 19-inch color cathode ray tube (CRT) video monitor with a resolution of 1024 × 786 pixels, an update rate of 100 Hz, and a photopic luminance of 39.6 cd/m2. There was a significant difference in KSS on the weekdays [χ2₍₂₎ = 20.27; p = .001] and in the luminance contrast for frequencies of 13.2 cpd [χ2₍₂₎ = 8.27; p = .001] and 15.6 cpd [χ2₍₂₎ = 13.72; p = .041]. The results showed greater stability of the measurement during the afternoon and a reduction in the visual sensitivity in the high spatial frequencies during the night.     

Critical flicker detection frequency and double pulse recognition threshold do not depend on the spectral properties of stimuli

We have measured the critical flicker detection frequency (CFDF) and double pulse recognition threshold (DPT) using three LEDs with power peaks at 460, 525 and 625 nm for target illumination. Brightness equalization was performed by customized heterochromatic flicker photometry (cHFP). Reference luminance levels were 170 cd/m² (blue LED, 60 subjects), 4 cd/m² (green LED, 20 subjects), and 1 cd/m² (green LED, 20 subjects). The measurement at 1 cd/m² was preceded by 15 min of dark adaptation. The angle of view for the target was 3°, and the duration of stimuli was 1 ms. An experimental pulse generator with three channels and a projector was used. No differences in CFDF at different spectral properties of stimulus were observed at all three levels of luminance. Thus, it is concluded that temporal vision resolution does not depend on the spectral properties of visual stimuli.     

同心圆感受野去抑制特性的数学模拟

以感受野外周区内各亚区之间的抑制性相互作用为基础,提出了一个能描述视网膜神经节细胞传输特性的数学模型,此模型能很好地解释传统感受野外大范围去抑制区产生的机制。当用来处理亮度对比边缘时,它既能很好地增强边缘对比,又可有效地提升被传统感受野中心／外周拮抗机制所滤除了的区域亮度对比和亮度梯度信息。本文也用不同空间频率的光栅和真实图像检验了模型的空间频率传递特性,并与其它模型进行了比较。     

Anisotropy in the chromatic channel: a horizontal-vertical effect

We compared the chromatic contrast thresholds of drifting (2Hz) red-green sine-wave gratings of horizontal, vertical, and two oblique orientations at three spatial frequencies (2, 4, 8 cpd). Luminance contrast thresholds for yellow-black gratings were also obtained. The classic oblique effect was found for high spatial frequency luminance and chromatic stimuli. For chromatic thresholds, a significant difference was found between the horizontal and vertical thresholds of all observers. One observer was retested with her head tilted 45 deg and demonstrated that the anisotropy was specific to retinal coordinates. These results give evidence for orientation selectivity in the chromatic channel which is at least partially independent of that in the luminance channel. We estimated the degree of lateral chromatic aberration in our observers' eyes and discuss the possible contribution of this aberration to the horizontal-vertical difference in the chromatic channel.