Moore Tirin, Fallah Mazyar
Department of Psychology, Princeton University, Princeton, New Jersey 08544-1010, USA.
J Neurophysiol. 2004 Jan;91(1):152-62. doi: 10.1152/jn.00741.2002. Epub 2003 Sep 17.
Many studies have established that the strength of visual perception and the strength of visual representations within visual cortex vary according to the focus of covert spatial attention. While it is clear that attention can modulate visual signals, the source of this modulation remains unknown. We have examined the possibility that saccade related mechanisms provide a source of spatial attention by studying the effects of electrical microstimulation of the frontal eye fields (FEF) on spatial attention. Monkeys performed a task in which they had to detect luminance changes of a peripheral target while ignoring a flashing distracter. The target luminance change could be preceded by stimulation of the FEF at current levels below that which evoked saccadic eye movements. We found that when the target change was preceded by stimulation of FEF, the monkey could detect smaller changes in target luminance. The increased sensitivity to the target change only occurred when the target was placed in the part of the visual field represented by neurons at the stimulation site. The magnitude of improvement depended on the temporal asynchrony of the stimulation onset and the target event. No significant effect of stimulation was observed when long intervals (>300 ms) between stimulation and the target event were used, and the magnitude of the increased sensitivity decreased systematically with increasing asynchrony. At the shortest asynchrony, FEF stimulation temporally overlapped the target event and the magnitude of the improvement was comparable to that of removing the distracter from the task. These results demonstrate that transient, but potent improvements in the deployment of covert spatial attention can be obtained by microstimulation of FEF sites from which saccadic eye movements are also evoked.
许多研究已经证实，视觉皮层内视觉感知的强度和视觉表征的强度会根据隐蔽空间注意力的焦点而变化。虽然很明显注意力可以调节视觉信号，但这种调节的来源仍然未知。我们通过研究额叶眼区（FEF）的电微刺激对空间注意力的影响，来检验扫视相关机制是否提供了空间注意力的来源。猴子执行一项任务，它们必须检测周边目标的亮度变化，同时忽略一个闪烁的干扰物。在当前水平低于诱发眼球扫视运动的水平下，对FEF进行刺激后，目标亮度可能会发生变化。我们发现，当在目标变化之前刺激FEF时，猴子能够检测到目标亮度更小的变化。对目标变化的敏感性增加仅在目标位于刺激部位神经元所代表的视野部分时才会出现。改善的程度取决于刺激开始与目标事件之间的时间异步性。当刺激与目标事件之间的间隔时间较长（>300毫秒）时，未观察到刺激的显著效果，并且随着异步性增加，敏感性增加的幅度会系统性地降低。在最短的异步情况下，FEF刺激在时间上与目标事件重叠，并且改善的幅度与从任务中移除干扰物的幅度相当。这些结果表明，通过对也能诱发眼球扫视运动的FEF部位进行微刺激，可以获得隐蔽空间注意力部署的短暂但有效的改善。
