Perturbing gaze shifts reveals new visuo-motor encoding mechanisms

人类擅长做出快速、准确的动作，这些动作涉及到同时运动的功能耦合的身体部分。大脑如何协调这种复杂的运动一直是我实验室的主要焦点，作为一个实验模型，我们研究了眼+头部的协调运动，这种运动通常会产生视觉轴的快速定向运动，称为凝视扫视。***中脑上丘（SC）是注视控制的关键结构。经典的假设是，SC包含一个根据编码方案驱动快速（眼动）凝视转移的运动地图，其中地图上的一个位点编码一个凝视转移向量。我们称之为“一个地点，一个扫视”假说。我们有初步的证据表明，当一个人用一系列快速的目光扫视来观察环境时，这种假设就失效了。在这种情况下，SC编码的是整体位移，而不是单个扫视。这种与SC函数的主导假设的关键突破需要得到验证，我们在这里建议这样做。如果我们确认失败，那么这将要求对大脑如何控制我们对环境的看法的当前模型进行批判性的重新评估。“观察周围环境的目的显然是为了看到”。这个简单的日常术语隐藏了一个极其复杂的大脑功能集合，这些功能是感知的基础。首先，我们需要把视觉和眼睛的运动联系起来。这种联系是必要的，因为：1)当我们每秒钟扫视3-5次时，尽管感知到的物体在视网膜上的位置发生了变化，但我们的视觉世界在扫视过程中看起来是稳定的；2)每次扫视后，一个空间固定的注意点在视网膜上占据不同的位置，但必须在内部被认为是空间固定的。*** ***有趣的是，大脑的视觉系统以视觉地图的方式组织，类似于SC的运动地图。因此，视觉地图上的一个站点编码了视觉空间中的一个小位置。这被称为“一个地点，一个接受场”假说。与凝视运动系统类似，有证据表明这一假设可能会失败。事实上，视觉地图中的神经元可以根据即将到来的扫视的方向和幅度，对视觉世界中任何地方出现的视觉刺激做出反应。因此，视觉地图上的一个站点可以编码无限数量的空间位置！这种与经典思维的彻底决裂需要被理解才能理解视觉。我们计划在这里通过研究当预期的注视跳动受到干扰时，视觉神经元如何对视觉刺激作出反应来做到这一点。***运动和视觉系统中大脑组织的关键原理可以统称为“一处一功能”假说。我们有这些系统如何工作的模型，但当它们不起作用时，如果我们要了解大脑的功能以及我们在扫描环境时是如何看到的，那么理解其中的原因是至关重要的

Humans are skilled at making rapid, accurate movements that involve functionally coupled body segments that move simultaneously. How the brain orchestrates such complex movements has been a major focus of my lab and, as an experimental model, we have studied coordinated eye + head movements that routinely generate rapid orienting movements of the visual axis called gaze saccades. ***The midbrain's superior colliculus (SC) is a critical structure in gaze control. The classic hypothesis is that the SC contains a motor map which drives rapid (saccadic) gaze shifts according to a coding scheme wherein one-site on the map encodes one gaze shift vector. We call this the “one-site, one- saccade” hypothesis. We have preliminary evidence that this hypothesis fails when one looks about the environment using a sequence of rapid gaze saccades separated by periods of fixation. In this context the SC encodes the overall displacement not individual saccades. This critical break with the dominant hypothesis of SC function needs to be verified which we propose to do here. If we confirm failure then this will call for a critical re-evaluation of current models of how the brain controls how we look about the environment. ***The objective of looking about the environment is obviously to see'. This simple day to day term hides an extraordinarily complex ensemble of brain functions that underlie perception. For one thing we need to link vision with movements of the eyes. Such a link is necessary because: 1) our visual world appears stable across saccadic gaze shifts despite a perceived object changing position on the retina as we make saccades 3-5 times/sec; and 2) a spatially-fixed locus of attention occupies a different position on the retina after each saccade but must internally be perceived as spatially immobile. *** ***Interestingly, the brain's visual system is organized in visual maps in a manner analogous to the SC's motor map. Thus, one site on a visual map encodes one small location in visual space. This is called the “one-site, one-receptive-field” hypothesis. Similar to the gaze motor system there is evidence that this hypothesis can fail. Indeed, a neuron in a visual map can respond to a visual stimulus presented anywhere in the visual world depending on the direction and amplitude of the upcoming saccade. Thus one site on a visual map can encode an infinite number of spatial positions! This radical break with classic thinking needs to be understood to understand vision. We plan to do this here by studying how visual neurons respond to visual stimuli when the intended gaze saccade is perturbed. ***Together, the key principles of brain organization in the motor and visual system can be referred to as the “one-site, one-function” hypotheses. We have models of how these systems work but when they don't work, it is critical to understand why if we are to understand brain function and how we see when we scan our environment.**