Thompson Aidan A, Henriques Denise Y P
Centre for Vision Research, York University, 4700 Keele Street, Toronto, ON, Canada.
Vision Res. 2010 Dec;50(24):2651-60. doi: 10.1016/j.visres.2010.09.013. Epub 2010 Sep 17.
Previous work from our lab, and elsewhere, has demonstrated that remembered target locations are stored and updated in an eye-fixed reference frame. That is, reach errors systematically vary as a function of gaze direction relative to a remembered target location, not only when the target is viewed in the periphery (Bock, 1986, known as the retinal magnification effect), but also when the target has been foveated, and the eyes subsequently move after the target has disappeared but prior to reaching (e.g., Henriques, Klier, Smith, Lowy, & Crawford, 1998; Sorrento & Henriques, 2008; Thompson & Henriques, 2008). These gaze-dependent errors, following intervening eye movements, cannot be explained by representations whose frame is fixed to the head, body or even the world. However, it is unknown whether targets presented sequentially would all be coded relative to gaze (i.e., egocentrically/absolutely), or if they would be coded relative to the previous target (i.e., allocentrically/relatively). It might be expected that the reaching movements to two targets separated by 5° would differ by that distance. But, if gaze were to shift between the first and second reaches, would the movement amplitude between the targets differ? If the target locations are coded allocentrically (i.e., the location of the second target coded relative to the first) then the movement amplitude should be about 5°. But, if the second target is coded egocentrically (i.e., relative to current gaze direction), then the reaches to this target and the distances between the subsequent movements should vary systematically with gaze as described above. We found that requiring an intervening saccade to the opposite side of 2 briefly presented targets between reaches to them resulted in a pattern of reaching error that systematically varied as a function of the distance between current gaze and target, and led to a systematic change in the distance between the sequential reach endpoints as predicted by an egocentric frame anchored to the eye. However, the amount of change in this distance was smaller than predicted by a pure eye-fixed representation, suggesting that relative positions of the targets or allocentric coding was also used in sequential reach planning. The spatial coding and updating of sequential reach target locations seems to rely on a combined weighting of multiple reference frames, with one of them centered on the eye.
我们实验室及其他地方之前的研究表明，记忆中的目标位置是在眼睛固定的参考系中存储和更新的。也就是说，到达误差会根据相对于记忆中目标位置的注视方向而系统地变化，不仅当目标在外围视野中被观察时（博克，1986年，即视网膜放大效应），而且当目标被中央凹注视，且在目标消失后但在伸手抓取之前眼睛随后移动时也是如此（例如，恩里克斯、克利尔、史密斯、洛伊和克劳福德，1998年；索伦托和恩里克斯，2008年；汤普森和恩里克斯，2008年）。这些在中间有眼球运动后的注视依赖误差，无法用固定于头部、身体甚至世界的参考系的表征来解释。然而，尚不清楚依次呈现的目标是否都相对于注视进行编码（即以自我为中心/绝对地），或者它们是否相对于前一个目标进行编码（即以他为中心/相对地）。可以预期，向相隔5°的两个目标的伸手动作在距离上会相差5°。但是，如果在第一次和第二次伸手之间注视发生了转移，那么目标之间的动作幅度会有所不同吗？如果目标位置是以他为中心编码的（即第二个目标的位置相对于第一个目标进行编码），那么动作幅度应该约为5°。但是，如果第二个目标是以自我为中心编码的（即相对于当前注视方向），那么向这个目标的伸手动作以及后续动作之间的距离应该如上述那样根据注视而系统地变化。我们发现，在伸手抓取两个短暂呈现的目标之间，要求进行一次向相反侧的扫视，这导致了一种到达误差模式，该模式根据当前注视与目标之间的距离而系统地变化，并导致相继的到达终点之间的距离如以眼睛为锚点的自我中心参考系所预测的那样发生系统变化。然而，这个距离的变化量比纯粹的眼睛固定表征所预测的要小，这表明在相继的伸手动作规划中也使用了目标的相对位置或以他为中心的编码。相继的伸手抓取目标位置的空间编码和更新似乎依赖于多个参考系的综合加权，其中一个以眼睛为中心。
