NEURAL MECHANISMS OF VISUAL PERCEPTION

这个子项目是利用由NIH/NCRR资助的中心拨款提供的资源的许多研究子项目之一。子项目和调查员(PI)可能从另一个NIH来源获得了主要资金，因此可能会出现在其他CRISE条目中。列出的机构是针对中心的，而不一定是针对调查员的机构。我们提出了三个实验，以测试有关大脑决策能力所依据的神经机制的假设。我们的实验建立在大脑如何表示视觉中物体运动信息的知识基础上。我们的实验考察了视觉皮层中的感觉证据转化为关于运动方向的决定。我们表明，猕猴大脑皮质中的神经元代表了这种证据的积累，支持一种选择，反对另一种选择。今年，我们证明了神经计算类似于积分，即作为输入发射率的时间函数的累积(Huk等人，2005年)。我们还发现，这些神经元能够代表时间的流逝(Janssen和Shadlen，2005)，我们现在相信，时间、证据和关于决策结果的先前偏见由联合皮质中的神经元组合成一个连贯的量。我们目前正在使用多种方法来测试这些想法：心理物理学、神经记录和刺激以及计算建模。我们最近在两个重要方面扩展了我们的实验。我们研究了当有两个以上的选择时的决策过程，我们开发了一个概率分类任务来直接测试大脑用概率进行推理的能力。这些研究已在摘要中发表(Yang和Shadlen，2004；Churchland等人，2005)。决策是感觉和行为之间的桥梁。几乎所有的非反射性行为都需要大脑利用其感觉皮质来指导未来的行为。因此，我们研究的简单决定的神经机制可能会让我们对更复杂的认知策略有更深入的了解。我们的实验最终为影响感知、计划和推理的精神障碍的原因和治疗提供了新的见解。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. We proposed three experiments that test hypotheses about the neural mechanisms that underlie the brain's ability to make decisions. Our experiments build on knowledge about how the brain represents information about the movement of objects in vision. Our experiments examine the conversion of sensory evidence in visual cortex to a decision about the direction of motion. We showed that neurons in the association cortex of the macaque represent the accumulation of this evidence for one choice and against an alternative. This year, we demonstrated that the neural computations resemble integration, that is, the accumulation as a function of time of the input firing rates (Huk et al, 2005). We also discovered that these neurons are capable of representing the passage of time (Janssen and Shadlen, 2005), and we now believe that time and evidence and prior biases about the decision outcome are combined by neurons in the association cortex into a single coherent quantity. We are currently testing these ideas using a combination of approaches: psychophysics, neural recording and stimulation, and computational modeling. We have recently extended our experiments in two important ways. We examine the process of decision making when there are more than two options, and we have developed a probabilistic classification task to directly test the brain's ability to 'reason' with probabilities. These studies have been reported in abstracts (Yang and Shadlen, 2004; Churchland et al, 2005). Decision-making bridges the gap between sensation and behavior. Nearly all non-reflexive behaviors require the brain to draw upon its sensory cortex to guide future behavior. Thus, the neural mechanisms for the simple decisions we study are likely to lend insight into more complex cognitive strategies. Our experiments ultimately furnish new insights into the causes and treatments of mental disorders affecting perception, planning and reasoning.