Haarmeier T, Thier P
Department of Neurology, University of Tübingen, Tübingen, Germany.
Brain. 1999 Aug;122 ( Pt 8):1495-505. doi: 10.1093/brain/122.8.1495.
It is usually assumed that the raison d'être for smooth pursuit eye movements is an advantage in the visual analysis of moving objects due to the stabilization of the retinal image on the fovea. Although such benefits resulting from foveal pursuit are plausible, there have been few attempts to demonstrate them rigorously. Moreover, it is unknown whether and to what extent pursuit deficits due to neurological disease impair vision. In this study, therefore, we measured psychophysical thresholds for two different discrimination tasks assessing the visual analysis of moving objects as a function of smooth pursuit performance. Results from a group of healthy subjects were compared with those obtained from patients exhibiting catch-up saccades (n = 9) or saccadic intrusions in the form of square-wave jerks (n = 2). In a first set of experiments we measured acuity thresholds for Landolt optotypes moving horizontally at velocities of up to 14 degrees /s (dynamic visual acuity, DVA). In the control group (n = 20), DVA thresholds were indistinguishable from thresholds observed under stationary fixation due to efficient pursuit eye movements allowing continuous foveal stabilization of the retinal Landolt image. In contrast, all patients with catch-up saccades showed pursuit gains that decreased with increasing velocity, paralleled by a dramatic rise in DVA thresholds. Patients with square-wave jerks in turn revealed sufficient pursuit velocity but impaired foveation due to the involuntary saccades that occurred at similar frequencies independent of target velocity. In these patients, thresholds were more or less independent of the Landolt velocity but significantly raised compared with controls. Similar results were obtained in a test determining the sensitivity for vertical position steps of a given pursuit target. In summary, our results indicate that the lack of adequate pursuit eye movements is indeed deleterious for the visual analysis of moving objects.
通常认为，平稳跟踪眼球运动存在的理由是，由于视网膜图像在中央凹上的稳定，这在对移动物体的视觉分析中具有优势。尽管中央凹跟踪所带来的这些益处看似合理，但很少有人尝试严格地证明它们。此外，尚不清楚由于神经疾病导致的跟踪缺陷是否以及在多大程度上会损害视力。因此，在本研究中，我们测量了两种不同辨别任务的心理物理学阈值，这些任务评估了作为平稳跟踪性能函数的移动物体的视觉分析。将一组健康受试者的结果与从表现出追赶性扫视（n = 9）或以方波急跳形式出现的扫视侵入（n = 2）的患者那里获得的结果进行了比较。在第一组实验中，我们测量了以高达14度/秒的速度水平移动的兰多尔特视标（动态视敏度，DVA）的视敏度阈值。在对照组（n = 20）中，由于有效的跟踪眼球运动允许视网膜兰多尔特图像在中央凹持续稳定，DVA阈值与在固定注视下观察到的阈值没有区别。相比之下，所有有追赶性扫视的患者都表现出随着速度增加跟踪增益下降，同时DVA阈值急剧上升。有方形波急跳的患者则显示出足够的跟踪速度，但由于与目标速度无关的相似频率下发生的不自主扫视，导致中央凹注视受损。在这些患者中，阈值或多或少与兰多尔特视标的速度无关，但与对照组相比显著升高。在确定给定跟踪目标垂直位置步长的敏感性的测试中也获得了类似的结果。总之，我们的结果表明，缺乏足够的跟踪眼球运动确实对移动物体的视觉分析有害。
