Neural mechanisms of long-range spatial vision: an investigation of perceptive, integrative and association fields across the lifespan

入射光由视网膜感受器处理。从彼此邻近的物体反射的光线会落到相邻的视网膜位置，并被馈送到视觉皮质中相应位置的神经元。在视觉皮质中，不同复杂程度的单位将进一步处理这些信息，最终产生我们日常的视觉体验。视网膜上视觉皮层单位对其作出反应的空间区域称为视野。自20世纪60年代胡贝尔和威塞尔的开创性研究以来，视场的概念在视觉知觉研究中起着至关重要的作用。视野决定了哪些信息将被绑定在一起，哪些信息将被个性化。离开视网膜中心，视野会增大，但这种大小是灵活的，有些令人惊讶的是，这取决于接收到的信号的强度(颜色或亮度)以及附近物体的存在或不存在，这些物体激活了邻近的神经单位。也有不同复杂程度的视野：初级视觉皮质的神经元简单地整合其范围内的亮度或颜色对比度，而其以外的神经元整合或个性化物体的更复杂属性，例如方向，以识别物体的形状。因此，视野决定了跨空间的信息处理，特别是相对较远距离的空间信息的处理，一旦我们离开视网膜中心，这些信息就会彼此相距一段距离。这个项目的目标是建立一个统一的框架，在整个生命周期内，将不同复杂程度的视野内的神经处理包括在内。尽管进行了多年的研究，但这样一个统一的框架仍然缺乏：尽管我们知道许多关于初级视觉皮质神经元支持的颜色和亮度的“低水平”加工，但视觉加工的中间阶段更难探索，这种“中等水平”视觉的不同方面往往是单独研究的。我们的方法的独特之处在于，我们将使用相同的范式，探索不同复杂程度的视野，包括“低级”和“中级”视野。这种范式简单而强大：它依赖于相同的刺激，由可以形成不同字母的多个定向元素(称为Gabor补丁的黑白栅格)组成，通过简单地改变参与者执行的任务来探测不同复杂程度的视野：a)检测目标元素的存在或不存在，b)判断其属性，或c)判断整个字母的身份。我们将确定视野如何处理由亮度、颜色或两者定义的刺激，从而整合人眼可见的所有类型的对比度。最后，我们将在一个由20岁到80岁的参与者组成的大样本上进行实验。我们的实验将结合行为学和神经科学技术，使用新的、最先进的脑电(EEG)技术来确定视觉处理中与年龄相关的变化背后的神经机制。我们将确定神经噪音增加在多大程度上导致与年龄相关的缺陷，并将其与更基本的对比敏感度变化联系起来。这种与年龄相关的差异分析将为人类视觉中维持信息处理的神经机制提供一个令人兴奋的窗口。这样，该项目不仅将为视觉感知的理论发展提供基础，而且还将极大地影响我们对感觉机制老化的理解。这些信息可以用来提高老年人的生活质量。

Incoming light is processed by retinal receptors. Light reflected from objects that are nearby each other will fall onto adjacent retinal locations, and will be fed to correspondingly located neurons in the visual cortex. In the visual cortex, units of different complexity will process this information further, ultimately giving rise to our everyday visual experience. The area of space on the retina to which a visual cortex unit responds is called a visual field. The concept of visual fields has played a crucial role in the study of visual perception since the pioneering studies of Hubel and Wiesel in the 1960s. Visual fields determine which information will be bound together and which will be individuated. Away from the centre of the retina, visual fields increase in size, but this size is flexible and, somewhat surprisingly, depends on the strength of the received signals (colour or brightness) as well as the presence or absence of nearby objects, which activate neighbouring neural units. There are also visual fields of different complexity: while neurons in the primary visual cortex simply integrate the amount of brightness or colour contrast that fall within their scope, neurons beyond it integrate or individuate more complex attributes of objects, e.g. orientation, to identify the object's shape. Therefore, visual fields determine information processing across space, especially processing of relatively long-range spatial information, which will be at some distance from each other once we move away from the centre of the retina. The aim of this project is to build a unitary framework that would encompass neural processing within visual fields of different complexity across the lifespan. Despite years of research, such a unitary framework is still lacking: while we know a lot about "low-level" processing of colour and luminance supported by neurons in the primary visual cortex, the intermediate stages of visual processing are more difficult to probe and distinct aspects of such "mid-level" vision are often studied separately. The uniqueness of our approach is that we will probe visual fields of different complexity, covering both "low" and "mid-level" vision, using the same paradigm. This paradigm is simple yet powerful: it relies on the same stimulus, consisting of multiple oriented elements (black and white gratings known as Gabor patches) that can form different letters, to probe visual fields of different complexity by simply changing the task that the participants are performing: a) detecting the presence or absence of a target element, b) judging its properties, or c) judging the identity of the whole letter. We will establish how visual fields process stimuli defined by brightness, colour, or both, thus integrating all types of contrast visible to the human eye. Finally, we will conduct our experiments on a large sample that consists of participants that are between 20 and 80 years of age. Our experiments will combine behavioural and neuroscientific techniques, using new, state-of-the-art electroencephalographic (EEG) techniques to ascertain which neural mechanisms underlie age-related changes in visual processing. We will determine the degree to which age-related deficits are driven by an increase in neural noise, and relate it to more basic changes in contrast sensitivity. Such analyses of age-related differences will offer an exciting window into the neural mechanisms that sustain information processing in human vision. In this way, this project will not only provide a basis for theoretical developments in visual perception, but will also considerably affect our understanding of the aging of sensory mechanisms. Such information can be used to improve the quality of life for the elderly.