Perceptual And Motor Decisions In The Primate Brain

我的研究兴趣是了解感知和行动是如何从大脑活动中产生的。我的主要方法是记录执行各种视觉搜索和强迫选择辨别任务的猴子大脑中的神经活动。我的大部分研究都集中在位于前额叶皮质的额叶眼场(FEF)，它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。视觉搜索实验的目标是了解大脑如何从许多可能的视觉对象中选择将被用来指导眼睛运动的视觉对象。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起着视觉显著图的作用，它将视觉输入和认知影响结合到视觉场景中每个位置的视觉显著或显著的地形图中。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一个显著特征。我假设，隐蔽的空间注意和扫视被引导到FEF中最高活动所代表的空间位置。我和我的同事们已经证明，在分心物中寻找古怪目标的视觉搜索任务中，视觉响应型FEF神经元在将目光引导到目标的扫视之前指定目标。我们最近对执行各种视觉搜索任务的猴子的研究结果强烈表明，前视视野中的目标辨别过程索引的是视觉处理的结果，而不是眼跳准备。在2001年的Sato等人中，我们通过使目标类似于分心物体，或者偶尔改变一个容易辨别的目标的位置，并要求猴子将眼跳暂停到第一个位置，并向新的目标位置进行一次扫视，从而增加了猴子的反应时间。在两种任务条件下，眼跳反应时间都增加了，但只有辨别难度的改变增加了额叶眼场神经元识别眼跳目标的时间。在Murthy等人，2001年，我们分析了目标在扫视前改变位置的试验。额叶视野视神经元的活动非常可靠地识别了目标刺激位置的变化，无论眼跳是否对该刺激进行了。最近，我们通过在视觉搜索过程中操纵干扰物与不变目标的相似性来研究先验知识对目标辨别过程的影响。我们发现，即使在没有目标的情况下，与目标更相似的干扰物的神经表征也比与目标不太相似的干扰物的神经表征更大。这表明，前视视野中物体的神经表示是图像的物理属性和对正在寻找的东西的自上而下知识的组合。一项对错误试验中FEF视觉活动的分析表明，当分心物体的表征超过目标时，即使只有很小的量，眼跳也会发生在该分心物体上。 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常见作用。综上所述，他们通过识别一组具有理论显著图所有特征的神经元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.