Perceptual And Motor Decisions In The Primate Brain

我的研究兴趣是了解感知和行动如何从大脑活动中产生。我的主要方法是记录猴子在执行各种视觉搜索和强迫选择辨别任务时大脑中的神经活动。我的大部分研究都集中在额叶眼场（FEF）上，它位于前额叶皮层，参与将视觉信息转化为移动眼睛的命令。我最近的研究可以分为两个相关的项目，（1）视觉搜索，（2）信号检测。视觉搜索实验的目的是了解大脑如何从许多可能的视觉对象中选择哪一个来引导眼球运动。信号检测实验旨在了解近阈值知觉判断的神经机制。 我的工作假设是，FEF功能作为一个视觉显着性地图，结合视觉输入和认知的影响到地形图的视觉显着性，或显着性，在视觉场景中的每一个位置。显著图是定向空间注意和眼跳目标选择的许多理论模型的显著特征。我推测，内隐空间注意和眼跳是针对空间位置所代表的最高活动的FEF。我和我的同事已经证明，在视觉搜索任务中，在干扰物中寻找一个古怪的目标时，视觉响应的FEF神经元在将目光引导到目标的扫视之前指定目标。我们最近的工作与猴子执行各种视觉搜索任务的结果强烈表明，在额眼场的目标识别过程索引的视觉处理的结果，而不是眼跳准备。在Sato等人的研究中，2001年，我们增加了猴子的反应时间，使目标类似于分心物，或偶尔改变一个容易区分的目标的位置，并要求猴子停止眼跳到第一个位置，并作出一个单一的眼跳到新的目标位置。扫视反应时间增加，在这两个任务条件下，但只有在歧视难度的变化增加了额眼区神经元识别扫视目标所需的时间。在Murthy等人中，2001年，我们分析了这些试验上的目标改变位置之前扫视。额叶眼区视觉神经元的活动非常可靠地识别了目标刺激位置的变化，而不管是否对该刺激进行了扫视。最近，我们已经调查了目标识别过程中的先验知识的影响，通过操纵的相似性的干扰，一个不变的目标在视觉搜索。我们发现，与目标更相似的干扰物的神经表征大于与目标不太相似的干扰物的神经表征，即使没有目标存在。这表明，在前眼区对物体的神经表征是图像的物理属性和对正在寻找的东西的自上而下的知识的组合。错误试验的FEF视觉活动的分析表明，当代表的干扰超过目标，即使是一个很小的数额，眼跳是对该干扰。 这些研究扩展了我们对额叶眼场的理解，远远超出了它在控制眼球运动中的熟悉作用。总之，他们通过识别具有理论显着图的所有特征的神经元群体来验证选择性注意的计算模型。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。

My research interest is to understand how perception and action emerge from brain activity. My main approach is to record neural activity in the brains of monkeys performing various visual search and forced-choice discrimination tasks. Most of my research has focused on the frontal eye field (FEF), which is located in the prefrontal cortex, and participates in the transformation of visual information into commands to move the eyes. My recent research can be divided into two related projects, (1) Visual Search, and (2) Signal Detection. The goal of the visual search experiments is to understand how the brain chooses which of many possible visual objects will be used to guide eye movements. The signal detection experiments aim to understand the neural mechanisms of near-threshold perceptual judgments. My working hypothesis is that the FEF functions as a visual salience map that combines visual input and cognitive influences into a topographic map of visual conspicuity, or salience, at every location in the visual scene. The salience map is a prominent feature of many theoretical models of directed spatial attention and saccade target selection. I hypothesize that covert spatial attention and saccades are directed to the spatial location represented by the highest activity in the FEF. My coworkers and I have shown that during a visual search task for an oddball target among distractors, visually responsive FEF neurons specify the target before the saccade that directs gaze to the target. The results from our recent work with monkeys performing various visual search tasks strongly suggests that the target discrimination process in the frontal eye field indexes the outcome of visual processing, not saccade preparation. In Sato et al., 2001, we increased the monkeys' reaction times by making the target similar to the distractor or by occasionally changing the location of an easily discriminated target and requiring the monkey to withhold the saccade to the first location and make a single saccade to the new target location. Saccadic reaction time increased in both task conditions, but only the change in discrimination difficulty increased the amount of time it took for frontal eye field neurons to identify the saccade target. In Murthy et al., 2001, we analyzed those trials on which the target changed locations before the saccade. The activity of frontal eye field visual neurons very reliably identified the change in the target stimulus location regardless of whether or not the saccade was made to that stimulus. Recently we have investigated the effect of prior knowledge on the target discrimination process by manipulating the similarity of the distractors to an unchanging target during visual search. We found that the neural representation of the distractors that were more similar to the target was greater than the neural representation of the distractors that were less similar to the target, even when no target was present. This shows that the neural representation of objects in the frontal eye field is a combination of the physical properties of the image and a top-down knowledge of what is being looked for. An analysis of FEF visual activity on error trials showed that when the representation of the distractor exceeds that of the target, even by a small amount, the saccade is made to that distractor. These studies have extended our understanding about the frontal eye field far beyond its familiar role in controlling eye movements. Taken together, they validate computational models of selective attention by identifying a population of neurons that have all of the characteristics of a theoretical salience map. 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.