Keller Edward L, McPeek Robert M
The Smith-Kettlewell Eye Research Institute, 2318 Fillmore Street, San Francisco, California 94115, USA.
Ann N Y Acad Sci. 2002 Apr;956:130-42. doi: 10.1111/j.1749-6632.2002.tb02814.x.
Neural studies of oculomotor function in the past have been conducted with the use of very simple visual stimuli. More recently there has been a new emphasis on using more natural stimuli to extend our knowledge of oculomotor organization. Visual search paradigms are an example of the use of these more natural visual surrounds. In search a subject must locate and saccade to a target that appears simultaneously with an array of distractors. When monkeys are used in this paradigm, it is possible to record from neurons located in various central structures in the brain while the initial visual response, subsequent discrimination processes and final saccadic movement unfold. In the present study we used an array of four visual stimuli, and the target was distinguished by its odd color from three distractors of uniform color. Location of the target within the array and its color were randomly selected on each trial. Neurons located in the deeper layers of the superior colliculus (SC) were recorded by standard methods in blocks of search trials. We found several new features in the discharge of SC neurons using this search paradigm that have not previously been reported in studies using single-target visual displays. (1) In contrast to the "winner take all" behavior previously reported for the SC, we found evidence of concurrent processing of alternative movement vectors. When incorrect movements were made to distractor locations, this concurrent activity was associated with significantly shorter intersaccadic intervals. (2) The discharge profile of the visual response in many units was modified by the appearance of a second prominent peak which followed the initial phasic visual response, but which was clearly differentiated from a third burst in activity associated with a saccade into the cell's response field. In some neurons, the activity in this second peak was discriminatory for the impending saccade vector. That is, it was larger when the target appeared in the response field of the cell than when it contained a distractor. This target selection signal was thus distinct from the burst normally associated with saccades into the movement fields of SC neurons. (3) Some saccades in search had a curved trajectory bowing toward the location of a distractor. These saccades were accompanied by an elevated discharge of neurons coding that distractor.
过去对眼球运动功能的神经学研究一直使用非常简单的视觉刺激。最近，人们开始重新强调使用更自然的刺激来拓展我们对眼球运动组织的认识。视觉搜索范式就是使用这些更自然视觉环境的一个例子。在搜索过程中，受试者必须定位并向与一系列干扰物同时出现的目标进行扫视。当在这个范式中使用猴子时，就有可能在最初的视觉反应、随后的辨别过程以及最后的扫视运动展开时，记录位于大脑各种中枢结构中的神经元活动。在本研究中，我们使用了一组四个视觉刺激，目标通过其奇特的颜色与三个颜色一致的干扰物区分开来。每次试验中，目标在阵列中的位置及其颜色都是随机选择的。通过标准方法在搜索试验块中记录位于上丘（SC）深层的神经元。我们使用这种搜索范式在SC神经元的放电中发现了几个新特征，这些特征在以前使用单目标视觉显示的研究中尚未报道过。（1）与之前报道的SC的“胜者通吃”行为相反，我们发现了替代运动向量并行处理的证据。当向干扰物位置做出错误运动时，这种并行活动与明显更短的扫视间隔相关。（2）许多单元中视觉反应的放电特征因第二个突出峰值的出现而改变，该峰值跟随最初的相位视觉反应，但与与扫视进入细胞反应场相关的第三次活动爆发明显不同。在一些神经元中，这个第二个峰值的活动对即将到来的扫视向量具有辨别性。也就是说，当目标出现在细胞的反应场中时，它比当它包含一个干扰物时更大。因此，这个目标选择信号与通常与扫视进入SC神经元运动场相关的爆发不同。（3）搜索中的一些扫视有一条向干扰物位置弯曲的轨迹。这些扫视伴随着编码该干扰物的神经元放电增加。
