Miller J M
Smith-Kettlewell Eye Research Institute, San Francisco, CA 94115, USA.
Vision Res. 1996 Mar;36(6):837-51. doi: 10.1016/0042-6989(95)00184-0.
Reaching towards a visual object in the absence of visual referents relies on a chain of information, from the sensory signals encoding the object's image on the retina, to the motor signals driving the hand. One link in this chain is an extraretinal eye position signal (EEPS), which specifies the position of the eye in the head. EEPS must be updated in precise coordination with the eye's rapidly changing position, or perisaccadic visual targets will be mislocalized. There have been conflicting reports about the existence and nature of mislocalizations associated with saccades. We measured perisaccadic visual localization by presenting brief (250 microseconds), bright (6000 cd/m2), binocular, gaze-point (foveal) probe flashes in an otherwise dark field to normal human subjects instructed to point to them with an unseen hand. Saccade and fixation targets were auditory, making intravisual comparison impossible. Saccades, elicited randomly to left and right of straight ahead, had a mean magnitude of 8.9 deg. Control trials, employing only non-perisaccadic probes and providing feedback of pointing errors, were randomly interspersed, to monitor and control drift of hand-eye coordination. On average, localization began to shift for probes presented 2 msec after the eye began to move, reaching a stable post-saccadic value with time constant tau = 71 msec. A second experiment was similar, except that viewing was monocular, and probes were presented randomly, at gaze (on fovea), 6 deg left of gaze (right of fovea) and 6 deg right of gaze (left of fovea). The main analysis treated saccades larger than 8 deg: their mean magnitude was 12.9 deg. Flashes left of gaze were relocalized faster (tau = 65 msec) than flashes right of gaze (tau = 129 msec) around the time of leftward saccades. In contrast, flashes right of gaze were relocalized faster (tau = 62 msec) than flashes left of gaze (tau = 90 msec) around the time of rightward saccades. Time constant was independent of saccade size. Updating began for probes presented within 4 msec of the beginning of saccades, and was not a function of saccade or flash direction. Thus, there were no systematic mislocalizations of probes presented before eye movement, and large mislocalizations of probes presented during and after. Mislocalizations were, on average, always in the direction opposite the saccade, and were maximal (about half the magnitude of the completed saccade) near the end of the saccade. Stable post-saccadic localization was not achieved until about 100-300 msec after completion of a saccade; EEPS was updated slowly, compared to eye position itself. The visual field was not remapped uniformly: the side that would normally contain the target of a visually evoked saccade (and usually the target of a corrective saccade), was updated with a shorter time constant.
在没有视觉参照的情况下伸手去够一个视觉物体，依赖于一系列信息，从编码视网膜上物体图像的感觉信号，到驱动手部的运动信号。这条信息链中的一个环节是视网膜外眼位置信号（EEPS），它指明眼睛在头部的位置。EEPS必须与眼睛快速变化的位置精确协调更新，否则扫视期间的视觉目标将会定位错误。关于与扫视相关的定位错误的存在和性质，一直存在相互矛盾的报道。我们通过在其他方面均为黑暗的视野中向正常人类受试者呈现短暂（250微秒）、明亮（6000坎德拉每平方米）、双眼、注视点（中央凹）探测闪光，并指示他们用一只看不见的手指向这些闪光，来测量扫视期间的视觉定位。扫视和注视目标是听觉的，使得视觉内比较不可能进行。随机诱发的向左和向右的扫视，平均幅度为8.9度。仅使用非扫视期间探测并提供指向误差反馈的对照试验被随机穿插进行，以监测和控制手眼协调的漂移。平均而言，对于在眼睛开始移动后2毫秒呈现的探测，定位开始偏移，随着时间常数τ = 71毫秒达到稳定的扫视后值。第二个实验类似，只是观看是单眼的，并且探测随机呈现，在注视点（中央凹上）、注视点左侧6度（中央凹右侧）和注视点右侧6度（中央凹左侧）。主要分析针对幅度大于8度的扫视：其平均幅度为12.9度。在向左扫视期间，注视点左侧的闪光比注视点右侧的闪光重新定位得更快（τ = 65毫秒）。相比之下，在向右扫视期间，注视点右侧的闪光比注视点左侧的闪光重新定位得更快（τ = 62毫秒）。时间常数与扫视大小无关。对于在扫视开始后4毫秒内呈现的探测，更新开始，并且不是扫视或闪光方向的函数。因此，在眼睛运动之前呈现的探测没有系统性的定位错误，而在眼睛运动期间和之后呈现的探测有较大的定位错误。定位错误平均而言总是与扫视方向相反，并且在扫视接近结束时最大（约为完成扫视幅度的一半）。直到扫视完成后约100 - 300毫秒才实现稳定的扫视后定位；与眼睛位置本身相比，EEPS更新缓慢。视野不是均匀重新映射的：通常包含视觉诱发扫视目标（以及通常是矫正性扫视目标）的那一侧，以较短的时间常数进行更新。
