Saccadic reaction time in the monkey: Advanced preparation of oculomotor programs is primarily responsible for express saccade occurrence
Saccadic reaction time in the monkey: Advanced preparation of oculomotor programs is primarily responsible for express saccade occurrence
复制标题
DOI：
10.1152/jn.1996.76.6.3666
复制
发表时间：
1996-12-01
影响因子：
2.5
通讯作者：
Munoz, DP
中科院分区：
文献类型：
--
作者：
Pare, M;Munoz, DP
1.在最初的注视目标消失和外围眼跳目标出现之间引入一段黑暗时间会导致眼跳反应时间(SRT)的普遍缩短--称为GNP效应--而且通常潜伏期很短的快速眼跳。为了解释这些现象，运动前过程可以通过释放视觉注视和提前准备眼跳程序来促进。本文所描述的实验旨在通过确定不同因素对SRT的影响以及猴子快速眼跳的发生来检验眼睛注视、脱离和动眼准备假说之间的相关性。用两种行为范式测量了两只猴子的SRT。在无间隙任务中，在中央注视靶消失时出现外围眼跳靶，而在间隙任务中，在注视靶消失和眼跳靶出现之间有一个200ms的无刺激周期。SRT在这些任务中的分布一般为双峰分布，第一和第二模式分别由快速眼跳和规则眼跳组成。我们测量了两个任务中的平均SRT、平均规则眼跳潜伏期、平均快速眼跳潜伏期和快速眼跳百分比。我们还估计了GAP效应，即无GAP试验中的SRT与GAP试验中的SRT之间的差异。一旦训练动物对单个目标位置进行扫视并产生快速扫视，当目标位置在一组试验中随机变化时，无间隙和间隙试验中的SRT都显示出相对于训练目标的空间位置的广泛调整。快速扫视只对训练过的目标位置周围的有限视野区域进行。几乎所有被测试的目标位置都存在间隙效应，而不考虑快速扫视的发生。最后，随着目标位置不确定性的引入，在训练的目标位置产生快速扫视的概率降低。快速眼跳的发生随着动物的视觉和非视觉(GAP)注视时间的延长而增加，而视觉和非视觉(GAP)注视是动物在扫视靶点开始之前被要求保持的。对于小于或等于300ms的间隙，间隙持续时间对降低平均SRT是有效的，并且其对视觉注视持续时间的影响比可比变化更大。当最初的眼睛注视位置向与扫视方向相反的方向偏心时，对相同偏心目标的快速眼跳的发生增加。同时，初始注视位置每改变1度，平均SRT降低约2毫秒。快速眼跳的发生取决于语境因素，即猴子在前一次实验中对同一目标执行的眼跳的行为任务(无间隙或间隙)和潜伏期。在无缝隙试验中，快速眼跳后的快速眼跳百分比最高，而在GAP试验中，快速眼跳后的快速眼跳百分比最低。这些发现表明，训练依赖的快速眼跳被限制在训练目标所决定的特定空间位置，其发生受到目标呈现的高预测性、持续时间长、没有视觉注视、眼球初始位置与眼跳方向相反的偏心以及先前试验中发生的快速眼跳的促进。间隙提供的注视释放解释了一般的间隙效应，但对快速眼跳的产生只有调制影响。我们得出结论，眼跳程序的高级运动准备通常会降低SRT，并是快速眼跳发生的主要原因，因此，这可能主要是由于限制在眼跳神经图谱中特定位置的神经元变化--编码训练的动作--所致。
1. The introduction of a period of darkness between the disappearance of an initial fixation target and the appearance of a peripheral saccade target produces a general reduction in saccadic reaction time (SRT) -known as the gnp effect-and often very short latency express saccades. To account for these phenomena, premotor processes may be facilitated by release of visual fixation and advanced preparation of saccadic programs. The experiments described in this paper were designed to test the relevance of the ocular fixation disengagement and oculomotor preparation hypotheses by identifying the influence of different factors on SRTs and the occurrence of express saccades in the monkey.2. The SRTs of two monkeys were measured in two behavioral paradigms. A peripheral saccade target appeared at the time of disappearance of a central fixation target in the no-gap task, whereas a 200-ms period of no stimuli was interposed between the fixation target disappearance and the saccade target appearance in the gap task. The distribution of SRTs in these tasks was generally bimodal; the first and second mode was composed of express and regular saccades, respectively. We measured the mean SRT, mean regular saccade latency, mean express saccade latency, and percentage of express saccades in both tasks. We also estimated the gap effect, i.e., the difference between the SRTs in no-gap trial and the SRTs in gap trials.3. Once the animals were trained to make saccades to a single target location and produce express saccades, SRTs in both no-gap and gap trials displayed a broad tuning with respect to the spatial location of the trained target when the target location was varied randomly in a block of trials. Express saccades were made only to a restricted region of the visual field surrounding the trained target location. A gap effect was present for nearly all target locations tested, irrespective of express saccade occurrence. Finally, the probability of generating an express saccade at the trained target location decreased with the introduction of uncertainty about target location.4. The occurrence of express saccades increased with the duration of the visual and nonvisual (gap) fixation that the animal was required to maintain before the onset of a saccade target. The gap duration was effective in reducing the mean SRT for gaps less than or equal to 300 ms, and it was more influential than comparable variation in the visual fixation duration.5. The occurrence of express saccades made to targets of identical eccentricity increased when the initial eye fixation position was shifted eccentric in a direction opposite to the saccade direction. Concomitantly, mean SRT decreased by similar to 2 ms for each 1-deg change in initial eye fixation position.6. The occurrence of express saccades depended upon contextual factors, i.e., on both the behavioral task (no-gap or gap) and the latency of the saccade that the monkey executed to the same target in the preceding trial. The highest percentage of express saccades was observed after an express saccade in a no-gap trial, whereas the lowest percentage was obtained after a regular saccade in a gap trial.7. These findings indicate that training-dependent express saccades are restricted to a specific spatial location dictated by the training target, and their incidence is facilitated by high predictability of target presentation, long-duration foreperiod, absence of visual fixation, eccentric initial eye position opposite to the saccade direction, and express saccade occurrence in the previous trial. The release of fixation afforded by the gap accounts for the general gap effect, but has only a modulatory influence on express saccade generation. We conclude that advanced motor preparation of saccadic programs generally reduces SRT and is primarily responsible for the occurrence of express saccades, which therefore may be caused mainly by neuronal changes restricted to a specific locus-coding for the trained movements-in a neural map of saccades.