【作者】 汤勇；

【导师】 周逸峰；

【作者基本信息】 中国科学技术大学 ， 生物物理学， 2009， 博士

【摘要】 正常的视觉运动感知功能对人们的生活是至关重要的。视觉运动感知系统可以分析并预测出运动物体的运动轨迹以帮助本体做出正确的应对该运动的决策。大量的心理物理学和神经生物学研究表明视觉信息在运动感知系统中的分析过程可以分为两步。第一步可以在视觉皮层的较低级区域完成,它分析出映射在视网膜上图像中各个点的局部运动。第二步需要在视觉皮层的较高级区域完成,它将前一阶段分析出的所有局部运动按照一定的方式整合在一起,形成完整的物体运动知觉。然而,视觉运动感知功能会受到许多因素的影响。受损的视觉运动感知功能会影响人们的日常生活,降低人们的生活质量。毫无疑问,利用科学的方法改善这些受损的视觉功能进而提高人们的生活质量具有重大的现实意义。而寻找改善方法的第一步就是需要清楚地了解视觉运动感知系统在哪些方面、哪些部分受到了相应的影响。在众多的影响因素中,老化是常见的一种,许多视觉功能都随着老化的进行而逐步衰退。此外,与老化相对应的是发育,一些发育性的疾病也会导致视觉功能状况的紊乱。因而在这里,我们调查了正常老化和一种发育性疾病——弱视——对运动知觉能力的影响。由于以前与老化相关的研究在整体运动知觉能力方面阐述甚多而在局部运动知觉能力方面涉及很少,因此我们在与老化相关的研究中主要调查了其对局部运动知觉能力的影响。另一方面,由于人们对弱视患者的运动栅格知觉能力所知甚少,我们在与弱视相关的研究中主要调查了其对运动栅格知觉能力的影响。1.正常老化对一/二阶局部运动知觉的影响一阶和二阶视觉刺激很早就被用来研究视觉信息处理的机制。一般来说,一阶刺激的特征变化主要体现在亮度上,视觉系统也主要通过亮度上的变化来识别一阶刺激;而二阶刺激在平均亮度上没有显著性的差异,视觉系统主要通过其他的一些特征来识别它们,这些特征包括对比度、深度和纹理等。相关的研究已经表明:在我们的日常生活中存在着大量的一阶和二阶视觉信息;在充满噪音的环境中,有效地综合一阶和二阶信息能够显著地提高人们的知觉能力。因而对一阶和二阶视觉刺激的感知能力对人们的生活至关重要。然而到目前为止,人们对二阶视觉刺激感知能力受老化影响的状况知道得还很少。因而在这里我们使用一/二阶视觉刺激调查了老化对这两种局部运动感知能力的影响。此外,我们同时还调查了老化对静止的一/二阶视觉刺激感知能力的影响。我们测量了141名年龄在19到79岁之间具有正常视力的被试对一阶和二阶静止/运动刺激的对比敏感度,结果发现对这两种刺激的对比敏感度都随着年龄的增长而逐步下降。也就是说,老化对这两种局部运动都存在着显著性的影响。此外,为了更好地描述对一阶和二阶刺激的知觉能力和年龄之间的关系,我们提出了一个能很好地契合我们数据的分段线性函数模型。根据此模型,我们进一步发现:二阶刺激的对比敏感度在老化的过程中比一阶刺激的对比敏感度更早地发生明显的衰退。我们认为这种较早的衰退反映视觉系统对二阶信息具有更为复杂的处理过程。2.弱视对运动栅格知觉能力的影响与传统使用的随机点运动模式不同,运动的栅格是另外一种形式的整体运动,它由两个方位不同的子正弦光栅的运动叠加而形成。大量的研究表明视觉系统对运动栅格的处理分两个步骤:第一步是将运动的栅格拆分成两个独立的子成分正弦光栅的运动,这一步可以在V1区完成;第二步是将已经拆分好的两个独立的子运动重新整合成一个整体的运动,这一步主要在MT区完成。弱视对局部运动和随机点运动这种整体运动知觉能力的影响已经广为人们所知,但是有关弱视对运动栅格知觉能力影响的研究却很少。此外,由于随机点运动感知和运动栅格感知的生理学基础都是大脑皮层中颞叶区的神经元,有关弱视对运动栅格知觉能力影响的研究还将有助于人们对弱视损伤位点的进一步理解。因而在这里我们主要调查弱视对运动栅格知觉能力的影响。我们测量了10名正常人与13名屈光参差性弱视患者检测运动栅格和相应的运动的子成分正弦光栅的敏感度。结果发现:弱视眼检测这些运动栅格和正弦光栅的能力都明显地差于正常眼。但更重要的是,我们发现弱视眼和正常眼在检测运动正弦光栅能力上的差异与检测运动栅格能力上的差异是一致的。也就是说,在排除了包括局部运动感知能力在内的较低级的视觉信息处理能力上的差异之后,弱视眼和正常眼在观察整体运动的能力上相差无几。这意味着视觉系统在观察运动栅格时进行运动信息整合处理的能力没有受到弱视的影响。由于观察运动栅格时进行运动信息整合处理的生理学基础是视觉皮层的中颞叶区,因而我们的发现并不支持认为中颞叶区神经元的功能普遍受到了弱视影响的假说。更多还原

【Abstract】 The primate visual motion system performs numerous functions essential for survival in a dynamic visual world. Prominent among these functions is the ability to recover and represent the trajectories of objects in a form that facilitates behavioral responses to those movements. To achieve this goal, the visual motion information undergoes a two-step analysis, which has been suggested by a large amount of evidence from psychophysical and neurobiological studies. In the first step which may occur at an earlier cortical stage, the displacement of local retinal image features is detected; then in the second step which may occur at higher levels of visual cortical regions, such as MT and MST, all local retinal motion signals are selectively integrated according to the object of origin. By this way, the retina image motion gives rise to our perceptual experience of moving objects.However, the function of the visual motion system can be impaired by a lot of factors, which surely reduces the people’s life quality. The first step aimed to improving this reduced function is to outline the characterics of the influeced motion perception. Here, we explored the effect of normal aging and a type of development disorder, amblyopia, on the motion perception. In the first study, we put our emphasis on the local motion perception since the effect of aging on global motion perception has been widely investigated while this is not for local motion perception. In the second study, taking account of the fact that little is known about the perception of amblyopes on moving plaids, a kind of global motion, and the perceptual capbility of moving plaids may suggest more about the nature of global motion processing deficits in amblyopia, we investigated the effect of amblyopia on perceptual capbility of moving plaids.1. The effect of normal aging on first-/second-order local motion perception First- and second-order stimuli are two types of patterns which have been used to characterize early visual processing. The former are defined by modulation of luminance, and the latter are defined by changes in features, such as contrast or texture. It has been suggested that these two types of stimuli are ubiquitous in everyday visual scenes, and that natural images are rich in both kinds of information. In a noisy environment, first- and second-order stimuli can be combined to improve perceptual accuracy. Therefore, perception of these two types of stimuli plays an important role in people’s daily life.However, little is known about the effect of aging on second-order stimuli, both static and dynamic. The purpose of the present study is to make some progress in understanding this issue.We measured contrast sensitivity for both first- and second-order stimuli, both static and dynamic, in 141 subjects with normal visual acuity and aged from 19 to 79 years old. The results have shown no gender effect but an evident aging effect, i.e., a progressive decline during aging, for perception of both types of stimuli. We have also proposed a piecewise linear model to interpret our data. Based on this model, contrast sensitivity for second-order stimuli begins to decline significantly earlier than for first-order stimuli, but with a slower rate of progression. We suggest the earlier decline for the perception of second-order stimuli may be interpreted as reflecting a greater complexity of second-order processing,consistent with Jocelyn Faubert’s theory on visual perception and aging.2. The effect of amblyopia on moving plaid perceptionA moving plaid, composed of two moving gratings with different orientations which are physically superimposed, is a different type of global motion stimuli. It has suggested that a two-stage visual analysis underlying the moving plaid perception, a decomposition into two one-dimensional component motions which can be implemented by component-selective neurons such as those in V1 and a recombination of these component motions which may be implemented in MT.The effect of amblyopia on moving plaids perception is not as well known as that on the random dot kinematograms which are traditionally used in global motion perception research. Additionally, since the physiological basis for processing of moving plaids and random dot kinematograms are both neurons in MT, it can be used to test the hypothesis whether there is a general loss of MT functions in amblyopia. Therefore, we investigated the effect of amblyopia on moving plaid perception here. We measured contrast sensitivities for moving plaids and their corresponding component gratings over a range of stimuli durations, spatial and temporal frequencies in 10 normal subjects and 13 anisometropic amblyopes by using motion direction discrimination task. We found reduced contrast sensitivities for moving plaids and their corresponding component gratings in anisometropic amblyopia. Additionally, the reduction in sensitivity for plaids was statistically identical to that for their component gratings, suggesting the former can be almost completely accounted for by the latter. In other words, there are no residual deficits in plaid perception at the threshold level after excluding the influence of low-level processing deficits, suggesting the global processing for plaid perception, whose physiological bases are supposed to be MT neurons, is largely intact in anisometropic amblyopia. This is against the hypothesis that there is a general loss of MT functions in amblyopia.更多还原