经直接与间接通路的视动震颤(OKN)眼动反应

采用鼻向及颞光栅图形刺激猫的半侧视网膜,以探讨鼻侧半神网膜至视束核的视动震颤直接通路及颞侧半视网膜经皮层至ＮＯＴ的间接通路对ＯＫＮ眼动反应的神经控制特性。实验结果显示：高速度刺激的闭环ＯＫＮ反应及开环ＯＫＮ反应均对鼻向运动刺激有明显的方向选择性;半侧视网膜刺激时,鼻侧半视网膜的鼻向ＯＫＮ增益明显高于颞侧半视网膜的鼻向增益,说明猫的ＫＯＮ眼动反应以跟踪鼻向运动为主,并且这种对鼻向运动刺激选择性主要来     

运动图形刺激时家兔的视动震颤反应

旨在用实验方法研究家兔的视动震颤（ＯＫＮ）眼动特点以及单侧前庭迷路损伤对ＯＫＮ的影响,结果表明：单眼刺激时,家兔的ＯＫＮ反应存在着从颞侧到鼻侧方向的方向优势;恒定速度刺激时,刺激开始后,家兔的ＯＫＮ眼动跟踪速度具有从小到大最后趋于稳态的建立过程,刺激消失后,存在眼动速度由大到小直到消失的视动后震颤（ＯＫＡＮ）反应,这两个过程反应了ＯＫＮ系统中可能存在速度存储机制及其对ＯＫＮ眼动的控制作用;单侧前庭     

两种等亮度不同运动图形刺激下的交替OKN眼动

等亮度彩色运动条纹产生视动震颤（ＯＫＮ）眼动反应揭示了ＯＫＮ眼动控制系统中存在颜色通道;而在两个相反方向运动的等亮度彩色运动条纹图象同时显示刺激时能引起交替的两个方向的ＯＫＮ跟踪眼动。故表明了在ＯＫＮ眼动控制系统中各个颜色通道交替地控制产生ＯＫＮ眼动反应。     

正常及异常双眼视觉的视动震颤（OKN）反应特性研究

为探讨不同双眼视觉状态下ＯＫＮ反应的特性,对正常人和不同类型的双眼视觉异常者的单眼鼻向及颞向ＯＫＮ反应进行了研究。实验发现：单眼视觉抑制者表现出鼻向与颞向ＯＫＮ反应不对称特性;两眼皆因视剥夺造成双眼视觉异常者主要以ＯＫＮ眼动增益降低为特点;双眼视觉正常者鼻、颞向ＯＫＮ反应是对称的。结果表明：单眼ＯＫＮ眼动反应的不对称特性及增益改变对探讨双眼视觉异常机制有重要意义,为视皮层双眼细胞异常导致单眼ＯＫＮ不对称的假设提供了支持性证据,并对弱视早期诊断及其分类有重要价值。     

家兔视动震颤(OKN)眼动反应的方向特性

采用两维方向上运动的光栅作为刺激并以电磁感应眼动测量方法对家兔ＯＫＮ方向特性进行研究。结果表明：水平单一方向运动的图形刺激时,只有鼻向刺激引起ＯＫＮ反应,且ＯＫＮ反应的慢相方向接近于刺激方向,说明水平刺激时,家兔ＯＫＮ反应方向与刺激方向基本一致;其它方向上运动图形刺激时,家兔ＯＫＮ反应方向并没有随刺激方向的改变作相应变化,而基本集中在三个方向：水平鼻向、垂直向上及垂直向下附近,表明家兔ＯＫＮ的反应方向随不同刺激方向呈非线性的变化特性。     

复合运动条纹刺激下的视动震颤（OKN）眼动反应

研究视动震颤眼动系统在同时包含两个二维运动的复合运动条纹刺激下的反应特性,并探讨两种子条纹运动方向的夹角和运动速度的影响。实验结果发现,在一定参数范围内,复合运动条纹引起了双重交替ＯＫＮ反应,即ＫＯＮ交替地跟踪合成运动和分别运动;在跟踪分别运动中,又是交替地跟踪两种子条纹的运动。     

分眼刺激时家兔的交替OKN眼动跟踪特性

本工作用不同运动图形分别同时刺激家兔左右眼,通过检测正常及单侧前庭迷路损伤后家兔的ＯＫＮ反应,证明在这种刺激情况下,正常家兔的眼动反应为交替的ＯＫＮ反应,为进一步探讨交替ＯＫＮ的控制机制及控制部位建立了动物模型。     

不同运动图象同时刺激左右眼时的交替视动震颤(OKN)现象

采用了同时对左右眼分别以不同的运动图象刺激的实验方法,来测量及分析其OKN眼动反应,探索在OKN反映中两眼之间的输入关系以及眼动控制机制。实验结果发现在两眼的刺激图象不一致时,眼动反应为交替的OKN反应,即中枢神经系统根据各眼的刺激速度,交替地控制产生OKN眼动反应。本文还从闭环控制上讨论了视网膜上速度误差信号的作用。     

不同运动图象同时刺激左右眼时的交替视动震颤(OKN)现象

采用了同时对左右眼分别以不同的运动图象刺激的实验方法,来测量及分析其OKN眼动反应,探索在OKN反映中两眼之间的输入关系以及眼动控制机制。实验结果发现在两眼的刺激图象不一致时,眼动反应为交替的OKN反应,即中枢神经系统根据各眼的刺激速度,交替地控制产生OKN眼动反应。本文还从闭环控制上讨论了视网膜上速度误差信号的作用。     

运图象刺动激的视动振颤(OKN)眼动反应的速度跟踪特性

本文用传统的转筒式运动条纹刺激及电视运动条纹图形刺激两种方法进行了OKN实验,对所引起的OKN反应进行了定量比较,结果证明两者的刺激效果是相似的;用电视运动图象刺激方法,分别在中心视场和周边视场进行刺激实验,阐明了OKN主要是由作用于视网膜中央区域的运动图象刺激所引起的;并对OKN的动态反应进行了实验分析,在正弦速度刺激下,OKN增益主要取决于刺激运动的加速度,而不是单纯取决于刺激运动的速度或频率,并在脉冲速度刺激的OKN实验中,用动态反应时间阐明了这一结论.     

Lack of homogeneity of receptive fields of visual neurons in the cortical area 18 of the cat

The receptive fields of complex neurons within area 18 of the cerebral cortex of the cat were determined by a computer-assisted method using a moving light bar substantially shorter than the long diameter of the receptive field as a visual stimulus. The visual cells repeatedly generated nerve impulses when the stimulus crossed well-defined active points within their receptive fields. Outside of these active points, the cells remained silent. It is suggested that the receptive fields are formed by a discontinuous accumulation of such active points. When the electrical activities of two neighbouring visual neurons are recorded simultaneously, their active points do not coincide. In addition, some active points were located outside the most prominent excitatory part of the receptive field of the studied cells. Individual visual cells typically differ in the number and distribution of active points. Since these cells best respond to a stimulus moving in a certain direction, it is suggested that they may act as direction of movement and/or velocity detectors. Alternate firing of a number of neighboring cells connected to a distributed pattern of peripheral receptors may form a system which is able to code for velocity and direction of the moving stimulus.     

OKN眼动跟踪在运动文字识别中的作用

用运动文字的阅读眼动实验来研究运动图像识别与眼动控制的关系,并与一般OKN眼动及一般正常阅读进行对比,探讨了速度及位置信息处理与内容信息处理的关系.实验结果表明;(1)一般正常文字阅读的眼动是Saccades眼动与注视停顿;运动文字识别阅读的眼动中没有注视停顿,而是快、慢交替的OKN眼动,在其慢相期间即运动文字与视网膜相对静止期间采集内容信息进行处理,慢相期间既处理文字内容信息又处理运动速度信息,说明对运动速度与内容信息的处理是并行的.(2)在运动文字运动速度高达80°/s以上时,已不能阅读甚至不能识别单字意义,但仍可产生OKN眼动;这一方面证实阅读速度的受限不在于眼球运动的跟踪能力,而在于高级识别中枢的解码速度,另一方面也说明OKN眼动不是在识别后才产生,而是进行运动图象识别的必要条件.(3)运动文字识别阅读的速度不低于一般正常文字阅读的速度.本文的结果还证实OKN眼动的快相眼动有别于Foveating Saccades.     

Visual control of cursorial prey pursuit by tiger beetles (Cicindelidae)

Target detection poses problems for moving animals, such as tiger beetles, that track targets visually. The pursuer's movements degrade target image contrast and induce reafferent image movement that confounds continuous detection of prey. In nature, beetles pursue prey discontinuously with several iterations of stop-and-go running. The beetle's dynamics were analyzed by filming pursuits of prey or experimenter-controlled dummies. Durations of stops are inversely related to prey visual angular velocity; as the prey image moves between neighboring ommatidial fields, the beetle relocalizes it and renews running. During subsequent runs, translation and rotation depend upon prey visual angular velocity and position, respectively, seen during the previous stop. The beetle runs, then stops, while prey continues moving. After two to three iterations of stop-and-go the beetle catches its prey, suggesting open-loop control of running. Computational model simulations produce good qualitative spatio-temporal fit with actual pursuits. However, when pursuing prey dummies, beetles track continuously and quickly follow changes in target position, suggesting closed-loop control using a position-sensitive servo mechanism. Differences between these types of pursuit control system are discussed with respect to limitations in signal detection, particularly spatio-temporal contrast, that may force beetles to use an open-loop system. Accepted: 7 April 1997     

Optokinetic behavior is reversed in achiasmatic mutant zebrafish larvae

The vertebrate optokinetic nystagmus (OKN) is a compensatory oculomotor behavior that is evoked by movement of the visual environment. It functions to stabilize visual images on the retina. The OKN can be experimentally evoked by rotating a drum fitted with stripes around the animal and has been studied extensively in many vertebrate species, including teleosts. This simple behavior has earlier been used to screen for mutations affecting visual system development in the vertebrate model organism zebrafish. In such a screen, we have found a significant number of homozygous belladonna (bel) mutant larvae to be defective in the correct execution of the OKN [1]. We now show that about 40% of homozygous bel larvae display a curious reversal of the OKN upon visual stimulation. Monocular stimulation leads to primary activation of ipsilateral eye movements in larvae that behave like the wild type. In contrast, affected larvae display contralateral activation of eye movements upon monocular stimulation. Anatomical analysis of retinal ganglion cell axon projections reveal a morphological basis for the observed behavioral defect. All animals with OKN reversal are achiasmatic. Further behavioral examination of affected larvae show that OKN-reversed animals execute this behavior in a stimulus-velocity-independent manner. Our data support a parsimonious model of optokinetic reversal by the opening of a controlling feedback loop at the level of the optic chiasm that is solely responsible for the observed behavioral abnormality in mutant belladonna larvae.