Henriques D Y, Klier E M, Smith M A, Lowy D, Crawford J D
Psychology, York University, Toronto, Ontario, Canada, M3J 1P3.
J Neurosci. 1998 Feb 15;18(4):1583-94. doi: 10.1523/JNEUROSCI.18-04-01583.1998.
Establishing a coherent internal reference frame for visuospatial representation and maintaining the integrity of this frame during eye movements are thought to be crucial for both perception and motor control. A stable headcentric representation could be constructed by internally comparing retinal signals with eye position. Alternatively, visual memory traces could be actively remapped within an oculocentric frame to compensate for each eye movement. We tested these models by measuring errors in manual pointing (in complete darkness) toward briefly flashed central targets during three oculomotor paradigms; subjects pointed accurately when gaze was maintained on the target location (control paradigm). However, when steadily fixating peripheral locations (static paradigm), subjects exaggerated the retinal eccentricity of the central target by 13.4 +/- 5.1%. In the key "dynamic" paradigm, subjects briefly foveated the central target and then saccaded peripherally before pointing toward the remembered location of the target. Our headcentric model predicted accurate pointing (as seen in the control paradigm) independent of the saccade, whereas our oculocentric model predicted misestimation (as seen in the static paradigm) of an internally shifted retinotopic trace. In fact, pointing errors were significantly larger than were control errors (p </= 0.003) and were indistinguishable (p >/= 0.25) from the static paradigm errors. Scatter plots of pointing errors (dynamic vs static paradigm) for various final fixation directions showed an overall slope of 0.97, contradicting the headcentric prediction (0. 0) and supporting the oculocentric prediction (1.0). Varying both fixation and pointing-target direction confirmed that these errors were a function of retinotopically shifted memory traces rather than eye position per se. To reconcile these results with previous pointing experiments, we propose a "conversion-on-demand" model of visuomotor control in which multiple visual targets are stored and rotated (noncommutatively) within the oculocentric frame, whereas only select targets are transformed further into head- or bodycentric frames for motor execution.
为视觉空间表征建立一个连贯的内部参考框架，并在眼球运动过程中保持该框架的完整性，被认为对感知和运动控制都至关重要。通过在内部将视网膜信号与眼睛位置进行比较，可以构建一个稳定的以头部为中心的表征。或者，视觉记忆痕迹可以在以眼为中心的框架内被主动重新映射，以补偿每次眼球运动。我们通过在三种眼动范式中测量（在完全黑暗中）手动指向短暂闪烁的中央目标时的误差来测试这些模型；当注视保持在目标位置时（控制范式），受试者指向准确。然而，当稳定注视周边位置时（静态范式），受试者将中央目标的视网膜离心率夸大了13.4±5.1%。在关键的“动态”范式中，受试者短暂地注视中央目标，然后向周边扫视，之后指向目标的记忆位置。我们的以头部为中心的模型预测，无论扫视情况如何，指向都是准确的（如在控制范式中所见），而我们的以眼为中心的模型预测，内部移位的视网膜拓扑痕迹会被错误估计（如在静态范式中所见）。事实上，指向误差显著大于控制误差（p≤0.003），并且与静态范式误差无显著差异（p≥0.25）。针对各种最终注视方向的指向误差（动态范式与静态范式）散点图显示，总体斜率为0.97，这与以头部为中心的预测（0.0）相矛盾，而支持以眼为中心的预测（1.0）。改变注视和指向目标方向均证实，这些误差是视网膜拓扑移位的记忆痕迹的函数，而非眼睛位置本身的函数。为了使这些结果与之前的指向实验结果相协调，我们提出了一种“按需转换”的视觉运动控制模型，其中多个视觉目标在以眼为中心的框架内被存储并（非可交换地）旋转，而只有选定的目标会进一步转换为以头部或身体为中心的框架以进行运动执行。
