Department of Neurobiology, David Geffen School of Medicine at University of California (UCLA), Los Angeles, CA 90095, USA.
Proc Natl Acad Sci U S A. 2012 Jun 19;109(25):10083-8. doi: 10.1073/pnas.1120763109. Epub 2012 Jun 5.
We make decisions about where to look approximately three times per second in normal viewing. It has been suggested that eye movements may be guided by activity in the lateral intraparietal area (LIP), which is thought to represent the relative value of objects in space. However, it is not clear how values for saccade goal selection are prioritized while free-viewing in a cluttered visual environment. To address this question, we compared the neural responses of LIP neurons in two subjects with their saccadic behavior and three estimates of stimulus value. These measures were extracted from the subjects' performance in a visual foraging task, in which we parametrically controlled the number of objects on the screen. We found that the firing rates of LIP neurons did not correlate well with the animals' behavior or any of our estimated measures of value. However, if the LIP activity was further normalized, it became highly correlated with the animals' decisions. These data suggest that LIP activity does not represent value in complex environments, but that the value can easily be extracted with one further step of processing. We propose that activity in LIP represents attentional priority and that the downstream normalization of this activity is an essential process in guiding action.
我们在正常观看时，大约每三秒钟就会做出一次注视点转移的决定。有研究表明，眼球运动可能受到顶内沟外侧区（LIP）活动的引导，该区域被认为代表了空间中物体的相对价值。然而，在杂乱的视觉环境中自由观看时，如何对扫视目标选择的价值进行优先级排序尚不清楚。为了解决这个问题，我们比较了两名被试的 LIP 神经元的神经反应与其扫视行为和三种刺激价值估计值。这些测量值是从被试在视觉搜索任务中的表现中提取出来的，我们在该任务中参数化地控制了屏幕上的物体数量。我们发现，LIP 神经元的放电率与动物的行为或我们估计的任何价值测量值都没有很好的相关性。然而，如果进一步对 LIP 活动进行归一化，它就会与动物的决策高度相关。这些数据表明，LIP 活动在复杂环境中并不代表价值，但是通过进一步的处理步骤，很容易提取出价值。我们提出，LIP 中的活动代表了注意力的优先级，而对这种活动的下游归一化是指导行动的一个重要过程。
