Perceptual And Motor Decisions In The Primate Brain

在感知和行动单元中，我们研究视觉输入如何转化为感知和行为。 我们的大部分研究都集中在额叶眼区（FEF），这是前额叶皮层中将视觉信息转换为眼动命令的区域。 我们已经表明，FEF结合视觉输入与认知知识，形成视觉空间的优先级地图，识别视觉场景中最重要的对象的位置，以引导注视。 在过去的一年中，我们扩展了这一发现，表明额叶皮层中的空间选择性信号增强了视觉处理，导致物体识别（参考文献1）和视觉皮层中复杂物体表征的形成（参考文献2）。 我们还描述了FEF神经元在视觉搜索过程中合作和竞争选择扫视目标的机制（参考文献3）。 在参考文献1中，我们研究了额叶眼区神经元活动与内隐空间注意相关的视觉处理增强之间的联系。 我们发现，FEF活动与性能的准确性和反应时间在猴子手动报告的视觉搜索目标的身份在没有眼球运动。 FEF的化学失活产生空间选择性的知觉缺陷，与失活的有效性和最强的试验，需要自愿注意力转移。这些结果表明，FEF活动和隐蔽空间注意力之间有很强的功能联系，并表明，从FEF的空间信号直接影响视觉处理的时间，待识别的刺激被视觉系统处理。 在参考文献2中，我们通过同时记录来自两个大脑区域的单个神经元来解决我们如何在复杂的自然环境中定位和识别物体的问题，这两个大脑区域在这种熟悉的活动中发挥着不同的作用：额叶眼区，前额叶皮层中参与视觉空间选择的区域，以及下颞叶皮层（IT），它参与了猴子在执行隐蔽视觉搜索任务时的物体识别。 虽然猴子报告的对象的身份，而不是位置，神经活动指定目标位置是明显的FEF神经活动指定的目标身份在IT。这两个不同的过程是时间相关的，这意味着在哪里和什么视觉处理的结束阶段之间的功能联系，并表明空间选择是必要的形成复杂的对象表示与视觉感知。 在参考文献3中，我们研究了在视觉目标选择过程中尖峰频率和尖峰时间的作用。 我们同时记录了多个额叶眼区神经元的活动，并询问它们是否在视觉搜索过程中相互作用以从干扰物中选择目标。 当一对神经元中的两个神经元都选择了目标，并且有重叠的感受野时，它们的合作比一个或两个神经元都不选择目标时更多。升高的尖峰时间巧合发生在两个神经元的目标的注意力选择的时间。减少尖峰时间的一致性发生在神经元之间的空间非重叠的感受野在时间的注意力选择的目标之一的神经元。这些结果为在视觉目标选择过程中额叶眼区神经元之间的动态和任务依赖的合作与竞争提供了证据。 这些研究扩展了我们对视觉处理的理解。 我们已经证明，额叶眼区提供自上而下的认知信号，调节正在进行的视觉处理。 我们还确定了两个独立的和可分离的认知过程中的额眼场，视觉选择和眼跳准备。 这两个过程对于正常视力和与世界互动都至关重要。 有了这些知识，我们可以设计实验来研究感觉信息在大脑中的流动，因为它被转化为感知和行动。这项工作有助于我们了解大脑如何集中注意力以做出感知决策和指导行为的机制，这对于理解和治疗人类的眼球运动和注意力相关疾病是必要的。

In the Unit on Perception and Action we investigate how visual inputs are transformed into perception and behavior. Most of our research has been focused on the frontal eye field (FEF), an area in the prefrontal cortex that converts visual information into eye movement commands. We have shown that FEF combines visual inputs with cognitive knowledge to form a priority map of visual space that identifies the location of the most important objects in the visual scene to guide gaze. During the past year we have extended this finding to show that spatially selective signals in the frontal cortex enhance visual processing leading to object recognition (ref. 1) and the formation of complex object representations in the visual cortex (ref. 2). We also described mechanisms by which FEF neurons cooperate and compete to select targets for saccades during visual search (ref. 3). In ref. 1 we investigated the link between neuronal activity in the frontal eye field and the enhancement of visual processing associated with covert spatial attention. We found that FEF activity was correlated with performance accuracy and reaction time in monkeys manually reporting the identity of a visual search target in the absence of eye movements. Chemical inactivation of FEF produced spatially selective perceptual deficits that were correlated with the effectiveness of the inactivation and were strongest on trials that require a voluntary attention shift. These results demonstrate a strong functional link between FEF activity and covert spatial attention, and suggest that spatial signals from FEF directly influence visual processing during the time that a stimulus to be identified is being processed by the visual system. In ref. 2 we addressed the question of how we locate and identify objects in complex natural environments by simultaneously recording single neurons from two brain regions that play different roles in this familiar activity the frontal eye field, an area in the prefrontal cortex that is involved in visual spatial selection, and the inferotemporal cortex (IT), which is involved in object recognition in monkeys performing a covert visual search task. Although the monkeys reported object identity, not location, neural activity specifying target location was evident in FEF before neural activity specifying target identity in IT. These two distinct processes were temporally correlated implying a functional linkage between the end-stages of where and what visual processing and indicating that spatial selection is necessary for the formation of complex object representations associated with visual perception. In ref. 3 we investigated the role of spike rate versus spike timing in visual target selection. We simultaneously recorded activity from multiple frontal eye field neurons and asked whether they interacted to select targets from distractors during visual search. When both neurons in a pair selected the target and had overlapping receptive fields, they cooperated more than when one or neither neuron in the pair selected the target. Elevated spike timing coincidences occurred at the time of attentional selection of the target by both neurons. Decreased spike timing coincidences occurred between neurons with spatially non-overlapping receptive fields at the time of attentional selection of the target by one of the neurons. These results provide evidence for dynamic and task-dependent cooperation and competition among frontal eye field neurons during visual target selection. These studies have extended our understanding of visual processing. We have shown that the frontal eye field provides top-down cognitively-derived signals that modulate ongoing visual processing. We also have identified two separate and dissociable cognitive processes within the frontal eye field, visual selection and saccade preparation. Both of these processes are crucial for normal vision and for interacting with the world. With this knowledge we can design experiments to investigate the flow of sensory information through the brain as it is transformed into perception and action. This work helps us understand the mechanisms of how the brain focuses attention to make perceptual decisions and guide behavior, which is necessary to be able to understand and treat eye movement and attention-related disorders in humans.