Anderson Andrew J, Stainer Matthew J, Brotchie Peter, Carpenter R H S
Department of Optometry and Vision Sciences, The University of Melbourne, Melbourne, 3010, Australia,
Exp Brain Res. 2014 Jul;232(7):2187-95. doi: 10.1007/s00221-014-3909-x. Epub 2014 Mar 25.
Saccadic latencies to targets appearing to the left and right of fixation in a repeating sequence are significantly increased when a target is presented out of sequence. Is this because the target is in the wrong position, the wrong direction, or both? To find out, we arranged for targets in a horizontal plane occasionally to appear with an unexpected eccentricity, though in the correct direction. This had no significant effect on latency, unlike what is observed when targets appeared in the unexpected direction. That subjects learnt sequences of directions rather than simply positions was further confirmed in an experiment where saccade direction was a repeating sequence, but eccentricity was randomised. Latency was elevated when a target was episodically presented in an unexpected direction. Latencies were also elevated when targets appeared in the correct hemifield but at an unexpected direction (35° polar angular displacement from the horizontal, a displacement roughly equivalent in collicular spacing to our unexpected eccentricity), although this elevation was of a smaller magnitude than when targets appeared in an unexpected direction along the horizontal. Finally, we confirmed that not all changes in the stimulus cause disruption: an unexpected change in the orientation or colour of the target did not alter latency. Our results show that in a repeating sequence, the oculomotor system is primarily concerned with predicting the direction of an upcoming eye movement rather than its position. This is consistent with models of oculomotor control developed for randomly appearing targets in which the direction and amplitude of saccades are programmed separately.
当目标以非顺序呈现时，在重复序列中向注视点左右两侧出现的目标的扫视潜伏期会显著增加。这是因为目标位置错误、方向错误，还是两者皆有？为了找出答案，我们安排水平面上的目标偶尔以意外的离心率出现，尽管方向正确。这对潜伏期没有显著影响，这与目标以意外方向出现时的观察结果不同。在一项实验中，扫视方向是重复序列，但离心率是随机的，这进一步证实了受试者学习的是方向序列而非简单的位置序列。当目标偶尔以意外方向呈现时，潜伏期会升高。当目标出现在正确的半视野但方向意外时（与水平方向呈35°极角位移，这种位移在视丘间距上大致相当于我们的意外离心率），潜伏期也会升高，尽管这种升高的幅度小于目标沿水平方向以意外方向出现时的情况。最后，我们证实并非所有刺激变化都会导致干扰：目标的方向或颜色的意外变化不会改变潜伏期。我们的结果表明，在重复序列中，动眼系统主要关注预测即将到来的眼动方向而非其位置。这与为随机出现的目标开发的动眼控制模型一致，在该模型中，扫视的方向和幅度是分别编程的。
