Van Gelder P, Lebedev S, Tsui W H
Nathan S. Kline Institute for Psychiatric Research, Orangeburg, NY 10962, USA.
Exp Brain Res. 1997 Sep;116(2):201-15. doi: 10.1007/pl00005750.
Smooth pursuit typically includes corrective catch-up saccades, but may also include such intrusive saccades away from the target as anticipatory or large overshooting saccades. We sought to differentiate catch-up from anticipatory and overshooting saccades by their peak velocities, to see whether the higher velocities of visually rather than nonvisually guided saccades in saccadic tasks may be found also in saccades in pursuit. In experiment 1, 12 subjects showed catch-up, anticipatory, and overshooting saccades to comprise 70.4% of all saccades in pursuit of periodic, 30 degrees/s constant-velocity targets. Catch-up saccades were faster than the others. Saccadic tasks were run as well, on 19 subjects, including the 12 whose pursuit data were analyzed, with target-onset, target-remaining (saccade to the remaining target when the other three extinguish), and antisaccade tasks. For 17 of the 19 subjects, antisaccade velocities were lower than for either target-onset or target-remaining tasks. Velocities for the target-remaining task were near those for target onset, indicating that target presence, not its onset, defines visually guided saccades. Error and reaction-time data suggest greater cognitive difficulty for target remaining than for target onset, so that the cognitive difficulty of typical nonvisually guided saccade tasks is not sufficient to produce their lowered velocity. To produce reliably, in each subject, catch-up and anticipatory saccades with comparable amplitude distributions, nine new subjects were asked in experiment 2 to make intentional catch-up and anticipatory saccades in pursuit, and were presented with embedded target jumps to elicit catch-up saccades, all with periodic target trajectories of 15 degrees/s and 30 degrees/s. Velocities of intentional anticipatory saccades were lower than velocities of intentional catch-up saccades, while velocities of intentional and embedded catch-up saccades were similar. Target-onset and remembered-target saccadic tasks were run, showing the expected higher velocity for the target-onset task in each subject. Both experiments demonstrate higher peak velocities for catch-up saccades than for anticipatory saccades, suggesting that cortical structures preferentially involved in nonvisually guided saccades may initiate the anticipatory and overshooting saccades in pursuit.
平稳跟踪通常包括矫正性的追赶扫视，但也可能包括远离目标的侵入性扫视，如预期性或大幅超射性扫视。我们试图通过峰值速度来区分追赶扫视与预期性和超射性扫视，以观察在扫视任务中视觉引导而非非视觉引导的扫视具有更高速度这一现象，在跟踪扫视中是否也会出现。在实验1中，12名受试者在跟踪以30度/秒的恒定速度做周期性运动的目标时，其追赶、预期性和超射性扫视占所有扫视的70.4%。追赶扫视比其他扫视更快。还对19名受试者进行了扫视任务，其中包括分析了其跟踪数据的12名受试者，任务包括目标起始、目标留存（当其他三个目标熄灭时扫视到留存的目标）和反扫视任务。在19名受试者中的17名身上，反扫视速度低于目标起始或目标留存任务的速度。目标留存任务的速度与目标起始任务的速度相近，这表明目标的存在而非其起始，决定了视觉引导的扫视。误差和反应时间数据表明，目标留存任务比目标起始任务具有更大的认知难度，所以典型的非视觉引导扫视任务的认知难度不足以导致其速度降低。为了在每个受试者身上可靠地产生具有可比幅度分布的追赶和预期性扫视，在实验2中，9名新受试者被要求在跟踪中故意做出追赶和预期性扫视，并呈现嵌入式目标跳跃以引发追赶扫视，所有目标轨迹的周期性速度均为15度/秒和30度/秒。故意预期性扫视的速度低于故意追赶扫视的速度，而故意和嵌入式追赶扫视的速度相似。进行了目标起始和记忆目标的扫视任务，结果显示每个受试者的目标起始任务速度符合预期更高。两个实验均表明，追赶扫视的峰值速度高于预期性扫视，这表明优先参与非视觉引导扫视的皮质结构可能引发了跟踪中的预期性和超射性扫视。
