Thaler Lore, Goodale Melvyn A
Department of Psychology, The University of Western Ontario, London, ON, Canada.
J Vis. 2010 Mar 23;10(3):3.1-27. doi: 10.1167/10.3.3.
In their day-to-day activities human beings are constantly generating behavior, such as pointing, grasping or verbal reports, on the basis of visible target locations. The question arises how the brain represents target locations. One possibility is that the brain represents them metrically, i.e. in terms of distance and direction. Another equally plausible possibility is that the brain represents locations non-metrically, using for example ordered geometry or topology. Here we report two experiments that were designed to test if the brain represents locations metrically or non-metrically. We measured accuracy and variability of visually guided reach-to-point movements (Experiment 1) and probe-stimulus adjustments (Experiment 2). The specific procedure of informing subjects about the relevant response on each trial enabled us to dissociate the use of non-metric target location from the use of metric distance and direction in head/eye-centered, hand-centered and externally defined (allocentric) coordinates. The behavioral data show that subjects' responses are least variable when they can direct their response at a visible target location, the only condition that permitted the use of non-metric information about target location in our experiments. Data from Experiments 1 and 2 correspond well quantitatively. Response variability in non-metric conditions cannot be predicted based on response variability in metric conditions. We conclude that the brain uses non-metric geometrical structure to represent locations.
在日常活动中，人类不断基于可见目标位置产生行为，比如指向、抓握或言语报告。于是问题出现了：大脑如何表征目标位置？一种可能性是大脑以度量方式表征它们，即根据距离和方向。另一种同样合理的可能性是大脑以非度量方式表征位置，例如使用有序几何或拓扑结构。在此我们报告两项实验，旨在测试大脑是以度量方式还是非度量方式表征位置。我们测量了视觉引导的指向运动（实验1）和探测刺激调整（实验2）的准确性和变异性。在每次试验中告知受试者相关反应的具体程序，使我们能够区分在以头部/眼睛为中心、以手部为中心和外部定义（以体为中心）的坐标中，非度量目标位置的使用与度量距离和方向的使用。行为数据表明，当受试者能够将反应指向可见目标位置时，他们的反应变异性最小，这是我们实验中唯一允许使用关于目标位置的非度量信息的条件。实验1和实验2的数据在数量上吻合得很好。非度量条件下的反应变异性无法根据度量条件下的反应变异性来预测。我们得出结论，大脑使用非度量几何结构来表征位置。
