Ma Zheng, Watamaniuk Scott N J, Heinen Stephen J
Smith-Kettlewell Eye Research Institute, San Francisco, CA, USA.
Psychology Department, Wright State University, Dayton, OH, USA.
J Vis. 2017 Oct 1;17(12):20. doi: 10.1167/17.12.20.
When small objects move in a scene, we keep them foveated with smooth pursuit eye movements. Although large objects such as people and animals are common, it is nonetheless unknown how we pursue them since they cannot be foveated. It might be that the brain calculates an object's centroid, and then centers the eyes on it during pursuit as a foveation mechanism might. Alternatively, the brain merely matches the velocity by motion integration. We test these alternatives with an illusory motion stimulus that translates at a speed different from its retinal motion. The stimulus was a Gabor array that translated at a fixed velocity, with component Gabors that drifted with motion consistent or inconsistent with the translation. Velocity matching predicts different pursuit behaviors across drift conditions, while centroid matching predicts no difference. We also tested whether pursuit can segregate and ignore irrelevant local drifts when motion and centroid information are consistent by surrounding the Gabors with solid frames. Finally, observers judged the global translational speed of the Gabors to determine whether smooth pursuit and motion perception share mechanisms. We found that consistent Gabor motion enhanced pursuit gain while inconsistent, opposite motion diminished it, drawing the eyes away from the center of the stimulus and supporting a motion-based pursuit drive. Catch-up saccades tended to counter the position offset, directing the eyes opposite to the deviation caused by the pursuit gain change. Surrounding the Gabors with visible frames canceled both the gain increase and the compensatory saccades. Perceived speed was modulated analogous to pursuit gain. The results suggest that smooth pursuit of large stimuli depends on the magnitude of integrated retinal motion information, not its retinal location, and that the position system might be unnecessary for generating smooth velocity to large pursuit targets.
当小物体在场景中移动时，我们通过平滑跟踪眼动使它们始终位于中央凹。尽管人和动物等大物体很常见，但我们如何跟踪它们仍不清楚，因为它们无法被中央凹注视。可能是大脑计算物体的质心，然后在跟踪过程中将眼睛对准质心，就像中央凹注视机制那样。或者，大脑只是通过运动积分来匹配速度。我们用一种以不同于视网膜运动速度平移的视错觉运动刺激来测试这些可能性。刺激物是一个以固定速度平移的加博尔阵列，其组成部分的加博尔条纹以与平移一致或不一致的方向漂移。速度匹配预测在不同漂移条件下会有不同的跟踪行为，而质心匹配预测没有差异。我们还测试了在运动和质心信息一致时，通过用实心边框包围加博尔条纹，跟踪是否能分离并忽略无关的局部漂移。最后，观察者判断加博尔条纹的整体平移速度，以确定平滑跟踪和运动感知是否共享机制。我们发现，一致的加博尔条纹运动会提高跟踪增益，而不一致的、相反的运动会降低跟踪增益，使眼睛从刺激中心移开，并支持基于运动的跟踪驱动。追赶扫视倾向于抵消位置偏移，将眼睛引导至与跟踪增益变化引起的偏差相反的方向。用可见边框包围加博尔条纹会消除增益增加和补偿性扫视。感知速度的调制与跟踪增益类似。结果表明，对大刺激的平滑跟踪取决于视网膜运动信息积分的大小，而不是其在视网膜上的位置，并且位置系统对于生成对大跟踪目标的平滑速度可能是不必要的。
