Cabel D W, Armstrong I T, Reingold E, Munoz D P
Department of Physiology, Queen's University, Kingston, Ontario, Canada.
Exp Brain Res. 2000 Aug;133(4):431-41. doi: 10.1007/s002210000440.
We examined inhibitory control in an oculomotor countermanding task, where the primary task required a saccadic eye movement be made to a target and a less-frequent secondary task required that the movement be halted. Previous studies have used a visual stimulus presented centrally on the fovea as the signal to stop or countermand a saccade. In these previous studies, there are at least two possible sources of saccadic inhibition: (1) sensory stimulation at the fovea can elicit a bottom-up mechanism, where a visual transient signal can delay or inhibit the developing saccade command; and (2) information based on the task instruction can be used to initiate a top-down mechanism to halt the movement. In the present study, we used both visual and auditory stop signals to test the hypothesis that the bottom-up mechanism is activated only after presentation of a foveal visual stop signal. Subjects were instructed first to look at a central spot and then to look to an eccentric visual target that appeared randomly to the left or right of center. On about one-third of the trials, a stop signal was presented. Three types of stop signals were used with equal probability: a broad-band noise burst (auditory), a central fixation spot (visual), and a combination of the auditory and visual stimuli (combined). Saccadic reaction time and stop-signal accuracy were used to calculate stop signal reaction time (SSRT), an estimate of the time required to inhibit the eye movement. Mean SSRT was longer for the auditory stop signals (201 ms) than for the signals with a foveal visual component (visual 113 ms; combined 91 ms). We conclude that a foveal visual stop signal in an oculomotor countermanding task changes the measure of inhibitory control to reflect not only inhibitory processes but also the sensory information afforded by stimulation at the fovea.
我们在一项眼动反指令任务中研究了抑制控制，其中主要任务要求进行一次眼跳运动看向一个目标，而较不频繁的次要任务则要求停止该运动。先前的研究使用中央凹处呈现的视觉刺激作为停止或取消眼跳的信号。在这些先前的研究中，至少有两种可能的眼跳抑制来源：（1）中央凹处的感觉刺激可引发自下而上的机制，其中视觉瞬态信号可延迟或抑制正在形成的眼跳指令；（2）基于任务指令的信息可用于启动自上而下的机制来停止运动。在本研究中，我们使用视觉和听觉停止信号来检验以下假设：仅在呈现中央凹视觉停止信号后自下而上的机制才被激活。受试者首先被指示看向中央点，然后看向中心左侧或右侧随机出现的偏心视觉目标。在大约三分之一的试验中，会呈现一个停止信号。以相等的概率使用三种类型的停止信号：宽带噪声突发（听觉）、中央注视点（视觉）以及听觉和视觉刺激的组合（组合）。使用眼跳反应时间和停止信号准确性来计算停止信号反应时间（SSRT），这是对抑制眼动所需时间的估计。听觉停止信号的平均SSRT（201毫秒）比具有中央凹视觉成分的信号（视觉113毫秒；组合91毫秒）更长。我们得出结论，在眼动反指令任务中，中央凹视觉停止信号改变了抑制控制的测量方式，不仅反映抑制过程，还反映中央凹处刺激提供的感觉信息。
