Barnes G R, Donelan S F
MRC Human Movement and Balance Unit, Institute of Neurology, 23 Queen Sq., London WC1N 3BG, UK.
Exp Brain Res. 1999 Nov;129(1):57-67. doi: 10.1007/s002210050936.
Regular, repeated presentation of identical constant-velocity target motion stimuli (ramps) appears to allow build up of an internal store, release of which can be used to generate anticipatory smooth pursuit prior to subsequent target onset. Here, we examine whether release of the anticipatory response can be controlled by timing cues unrelated to the motion stimulus itself. In experiment 1, the target moved in alternate directions and was exposed for 480 ms as it passed through centre; otherwise subjects were in darkness. Inter-stimulus interval (ISI) was either regular (3.6 s) or randomized (2.7-4.3 s). Presentations were given with or without audio cues that occurred at a constant cue time (CT) prior to target appearance. Even when ISI was randomized, cues could be used to generate anticipatory smooth pursuit. Eye velocity (V100) measured 100 ms after target onset (just prior to visual feedback influence) was greater with cues than without and decreased significantly as CT increased from 240-960 ms. In experiment 2, we assessed the effects of fixation between presentations and eccentricity of target starting position, using unidirectional ramps. The target was visible for 400 ms and started on, ended on or straddled the midline. Subjects held fixation on the midline until an audio cue signalled that preparation for ensuing target appearance could begin. There was no difference in V100 between starting positions or between presence/absence of fixation. In experiment 3, we compared the effects of using audio, visual or tactile cues. All types of cue evoked anticipatory smooth pursuit, but the response to the visual cue was significantly delayed compared with the others. However, V100 was not significantly different between cues. In all experiments, V100 was scaled in proportion to target velocity over the range 12.5-50 degrees /s, showing that this was a truly predictive response. The results provide evidence that timing and velocity storage can be independently controlled through different sensory channels and suggest that the two functions are probably carried out by separate neural mechanisms.
定期、重复呈现相同的匀速目标运动刺激（斜坡）似乎能使一种内部存储得以建立，该存储的释放可用于在后续目标出现之前产生预期的平滑追踪。在此，我们研究预期反应的释放是否可由与运动刺激本身无关的时间线索控制。在实验1中，目标向交替方向移动，当它经过中心时暴露480毫秒；否则受试者处于黑暗中。刺激间隔（ISI）要么是规则的（3.6秒），要么是随机的（2.7 - 4.3秒）。呈现刺激时伴有或不伴有在目标出现之前固定时间（CT）出现的音频线索。即使ISI是随机的，线索也可用于产生预期的平滑追踪。在目标开始后100毫秒（恰好在视觉反馈影响之前）测量的眼速度（V100），有线索时比无线索时更大，并且随着CT从240毫秒增加到960毫秒而显著降低。在实验2中，我们使用单向斜坡评估了两次呈现之间的注视以及目标起始位置的偏心度的影响。目标可见400毫秒，起始于中线、结束于中线或跨越中线。受试者保持注视中线，直到音频线索表明可以开始为随后的目标出现做准备。起始位置之间或有无注视之间的V100没有差异。在实验3中，我们比较了使用音频、视觉或触觉线索的效果。所有类型的线索都引发了预期的平滑追踪，但与其他线索相比，对视觉线索的反应显著延迟。然而，不同线索之间的V100没有显著差异。在所有实验中，V100在12.5 - 50度/秒的范围内与目标速度成比例缩放，表明这是一种真正的预测性反应。结果提供了证据，表明时间和速度存储可通过不同的感觉通道独立控制，并表明这两种功能可能由不同的神经机制执行。
