Information about the future trajectory of a visual target is contained not only in the history of target motion but also in static visual cues, e.g., the street provides information about the car's future trajectory. For most natural moving targets, this information imposes strong constraints on the relation between velocity and acceleration which can be exploited by predictive smooth pursuit mechanisms. We questioned how cue-induced predictive changes in pursuit direction depend on target speed and how cue- and target-induced pursuit interact. Subjects pursued a target entering a +/-90 degrees curve and moving on either a homogeneous background or on a low contrast static band indicating the future trajectory. The cue induced a predictive change of pursuit direction, which occurred before curve onset of the target. The predictive velocity component orthogonal to the initial pursuit direction started later and became faster with increasing target velocity. The predictive eye acceleration increased quadratically with target velocity and was independent of the initial target direction. After curve onset, cue- and target-induced pursuit velocity components were not linearly superimposed. The quadratic increase of eye acceleration with target velocity is consistent with the natural velocity scaling implied by the two-thirds power law, which is a characteristic of biological controlled movements. Comparison with linear pursuit models reveals that the ratio between eye acceleration and actual or expected retinal slip cannot be considered a constant gain factor. To obey a natural velocity scaling, this acceleration gain must linearly increase with target or pursuit velocity. We suggest that gain control mechanisms, which affect target-induced changes of pursuit velocity, act similarly on predictive changes of pursuit induced by static visual cues.

译文

有关视觉目标的未来轨迹的信息不仅包含在目标运动的历史中,而且还包含在静态视觉提示中,例如,街道提供有关汽车未来轨迹的信息。对于大多数自然运动目标,此信息对速度与加速度之间的关系施加了严格的约束,可以通过预测性平滑追踪机制加以利用。我们质疑线索诱导的追踪方向的预测变化如何取决于目标速度,以及线索和目标诱导的追踪如何相互作用。受试者追求目标,进入90度曲线并在均匀背景或低对比度静态带上移动,指示未来轨迹。提示引起了追踪方向的预测性变化,该变化发生在目标曲线开始之前。与初始追踪方向正交的预测速度分量稍后开始,并且随着目标速度的增加而变得更快。预测眼加速度随目标速度呈二次增加,并且与初始目标方向无关。曲线开始后,提示和目标诱导的追踪速度分量没有线性叠加。眼睛加速度随目标速度的二次增加与3分之2幂定律所隐含的自然速度标度一致,这是生物控制运动的特征。与线性追踪模型的比较表明,眼睛加速度与实际或预期的视网膜滑动之间的比率不能被视为恒定的增益因子。要服从自然速度缩放,此加速度增益必须随目标或追踪速度线性增加。我们建议影响目标引起的追踪速度变化的增益控制机制对静态视觉提示引起的追踪预测变化具有类似的作用。

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