The Neurophysiology of Visual Search: Oculomotor and Visual Mechanisms

视觉搜索是动物的基本行为，它们必须觅食以维持生计或繁殖。下 在普通情况下，人类和非人类灵长类动物通过眼球运动探索他们的视觉世界， 人类视觉搜索的效率与这些眼球运动的数量和准确性有关。 视觉搜索的基础过程包括纯视觉加工、视觉注意的产生和视觉搜索。 一般来说，是眼球运动的产生。大脑的视觉、注意力和眼动区域网络， 参与视觉搜索，但对灵长类动物大脑的神经过程知之甚少。 完成这个关键的过程。这个项目的目标是了解大脑的机制， 视觉搜索通过研究网络中的3个节点的活动，即外侧顶内区（LIP），额叶皮层（LIP）， 视野（FEF）和纹前视区V4。 我们最近发现，在视觉搜索过程中，LIP中的神经元表现出3种不同的信号 我们所研究的几乎每一个神经元的活动中都可以辨别出：1）自下而上的视觉信号 描述对象在其响应场中突然出现，但没有关于 即将发生的扫视的方向或感受野中的刺激的性质（例如，它是否是 搜索目标或干扰物）; 2）扫视信号，其预测即将出现的搜索目标的目标和反应时间。 眼动;以及3）描述对象在其响应场中的性质的认知信号 而不管即将发生的眼睛运动的方向如何。这些信号以一种可预测的方式相加， 大脑在视觉搜索中使用的显著图。LIP连接到眼区，它可以 发送和接收对产生眼球运动有用的信息，并发送和接收到视觉区域， 相同的信息可用于指定视觉注意力的位置。 V4和FEF项目的LIP，大概有助于不同的4。在这些实验中，我们 研究视觉搜索中所有3个区域的活动，并研究每个区域贡献的信息类型 另外两个。我们将训练恒河猴进行两项视觉搜索任务， 移动他们的眼睛，其中一个必须保持他们的眼睛不动，固定一个中心点。神经活动将 记录下猴子执行任务的过程。该项目的目的是首先研究 神经元LIP，V4和FEF，比较自由观看和固定任务中的活动以及它们在 简单的视觉引导延迟扫视任务。第二个是研究电刺激在 每个区域对猴子在搜索任务中的表现。三是研究瞬态效应 每个区域的失活对任务的执行和其余区域的神经元的活动的影响。 这些实验将提供洞察大脑如何决定在视觉过程中看哪里。 搜索，以及它如何将视觉信息转化为运动。项目叙述 顶叶和额叶病变患者的视觉搜索受损。 解决这些具体目标中提出的问题将导致更大的 了解大脑皮层如何安排视觉搜索的基本过程。 这反过来又会导致洞察到视觉和眼科赤字， 对额叶和顶叶皮层损伤的人来说是毁灭性的， 设计诊断、预后和康复策略。

Visual search is a basic behavior in animals that must forage for sustenance or reproduction. Under ordinary circumstances humans and non-human primates explore their visual world using eye movements, and the efficiency of visual search in humans is related to the number of and accuracy of those eye movements. The processes underlying visual search involve pure visual processing, the generation of visual attention, and ordinarily, the generation of eye movements. A brain network of visual, attentional, and oculomotor areas is involved in visual search, but little is known about the neural processes by which the primate brain accomplishes this critical process. The goal of this project is to understand the brain mechanisms underlying visual search by studying the activity of 3 nodes in the network, the lateral intraparietal area (LIP), the frontal eye field (FEF) and prestriate visual area V4. We have recently discovered that neurons in the LIP exhibit 3 different signals during visual search which are discernable in the activity of almost every neuron we have studied: 1) a bottom-up visual signal describing the abrupt appearance of an object in its response field but bearing no information about the direction of the impending saccade or the nature of the stimulus in the receptive field (e.g. whether it is the search target or a distractor); 2) a saccadic signal which predicts the goal and reaction time of an impending eye movement; and 3) a cognitive signal which describes the nature of the object in its response field regardless of the direction of the impending eye movement. These signals sum in a predictable way to create a salience map used by the brain in visual search. LIP is connected both to oculomotor areas, to which it can send and receive information useful for the generation of eye movements, and to visual areas, to which the same information can be used to specify the locus of visual attention. V4 and the FEF project to LIP, and presumably contribute differently to 4. In these experiments we will study the activity of all 3 areas in visual search, and study what types of information each area contributes to the other two. We will train Rhesus monkeys on two visual search tasks, one in which they which they are free to move their eyes, and one in which must hold their eyes still, fixating a central point. Neural activity will be recorded while the monkeys perform the tasks.. The aims of the project are first to study the activity of neurons LIP, V4, and FEF, comparing activity in the free-viewing and fixation tasks as well as their activity in a simple visually guided delayed-saccade task.. The second is to study the effects of electrical stimulation in each area on the performance of the monkeys in the search tasks. The third is to study the effects of transient inactivation of each area on the performance of the tasks and the activity of neurons in the remaining areas. These experiments will provide insight into how the brain makes decisions about where to look during visual search, and how it transforms visual information into movement. Project Narrative Visual search is impaired in human patients with parietal and frontal lesions. Answering the questions posed in these specific aims will lead to a greater understanding of how the cerebral cortex orders the processes underlying visual search. This in turn will lead to insight into the visual and oculomotor deficits that are so devastating in humans with lesions of frontal and parietal cortex, and will aid the designing of diagnostic, prognostic, and rehabilitative strategies.