The role of area V4 in the perception and recognition of visual objects

 描述(申请人提供)：人类视觉系统将到达我们眼睛的信息解析成有意义的区域和对象的排列。这一过程被称为图像分割，是灵长类动物大脑完成的最具挑战性的计算之一。为了发现其神经基础，我们将研究猕猴V4和前额叶皮质(PFC)两个脑区的神经元过程，V4是沿枕颞部通路进行形态处理的基本阶段，前额叶皮质对执行控制非常重要。这两个区域的功能障碍损害了需要识别分割对象的显示器中的形状辨别行为，强烈地表明它们对于图像分割是重要的。我们的实验技术将包括单电极和多电极记录、行为操纵、微扰方法和计算机模型。在目标1中，我们将识别反映视觉皮质分割的神经信号。使用各种具有遮挡、杂波和阴影的参数刺激-已知的在自然视觉中挑战分割的刺激特征-我们将评估分割是通过对具有相似表面属性的区域进行分组来实现的，还是通过对可能形成对象边界的轮廓段进行分组来实现的，或者通过这两种策略之间的某种相互作用来实现。我们将检验这一假设，即轮廓分组机制在低杂乱和靠近中心凹的情况下最有效。在目标2中，我们将研究来自PFC的反馈如何调节V4中的形状反应并促进分割：我们将检验长期存在的假设，即在较高皮质阶段的物体识别先于并促进视觉形式处理的中层的分割。我们将同时研究动物参与形状辨别行为时V4和PFC神经元的群体。我们将使用单次尝试解码方法和相关分析来将这两个区域的神经元反应的内容和时间联系起来。为了因果检验来自PFC的反馈的作用，我们将通过冷却和研究V4神经元来可逆地使PFC失活。我们的结果将提供第一个详细的V4神经元反应动力学的分析模型，在存在遮挡和杂乱的情况下，并促进我们对复杂视觉场景在V4区如何处理的理解。他们还将揭示V4和PFC如何共同调节复杂形状辨别任务的表现，执行功能和中层视觉如何在行为过程中协调，以及反馈如何用于大脑皮层计算。视觉失认症、枕颞部通路功能障碍和前额叶功能障碍(如精神分裂症)都会损害物体识别。这些实验的结果将是我们对大脑计算的理解的重大进步，大脑计算是分割和对象识别的基础，并将使我们更接近于设计策略，以缓解和治疗这些能力受损的大脑疾病。

 DESCRIPTION (provided by applicant): The human visual system parses the information that reaches our eyes into a meaningful arrangement of regions and objects. This process, called image segmentation, is one of the most challenging computations accomplished by the primate brain. To discover its neural basis we will study neuronal processes in two brain areas in the macaque monkey-V4, a fundamental stage of form processing along the occipito-temporal pathway, and the prefrontal cortex (PFC), important for executive control. Dysfunctions of both areas impair shape discrimination behavior in displays that require the identification of segmented objects, strongly suggesting that they are important for image segmentation. Our experimental techniques will include single and multielectrode recordings, behavioral manipulations, perturbation methods and computer models. In Aim 1 we will identify the neural signals that reflect segmentation in visual cortex. Using a variety of parametric stimuli with occlusion, clutter and shadows-stimulus features known to challenge segmentation in natural vision-we will evaluate whether segmentation is achieved by grouping regions with similar surface properties, such as surface color, texture and depth, or by grouping contour segments that are likely to form the boundary of an object or some interplay between these two strategies. We will test the hypothesis that contour grouping mechanisms are most effective under low clutter and close to the fovea. In Aim 2, we will investigate how feedback from PFC modulates shape responses in V4 and facilitates segmentation: we will test the longstanding hypothesis that object recognition in higher cortical stages precedes and facilitates segmentation in the midlevels of visual form processing. We will simultaneously study populations of V4 and PFC neurons while animals engage in shape discrimination behavior. We will use single-trial decoding methods and correlation analyses to relate the content and timing of neuronal responses in the two areas. To causally test the role of feedback from PFC, we will reversibly inactivate PFC by cooling and study V4 neurons. Our results will provide the first detailed, analytical models of V4 neuronal response dynamics in the presence of occlusion and clutter and advance our understanding of how complex visual scenes are processed in area V4. They will also reveal how V4 and PFC together mediate performance on a complex shape discrimination task, how executive function and midlevel vision may be coordinated during behavior and how feedback is used in cortical computation. Object recognition is impaired in visual agnosia, a dysfunction of the occipito-temporal pathway, and in dysfunctions of the PFC (e.g. schizophrenia). Results from these experiments will constitute a major advance in our understanding of the brain computations that underlie segmentation and object recognition and will bring us closer to devising strategies to alleviate and treat brain disorders in which these capacities are impaired.