Current knowledge about how spatial vision guides everyday actions is still quite limited, despite much excellent research on a variety of details. By combining many approaches, some consensus may be achieved about whether and how certain attributes are used. The emphasis here is on determining which spatial attributes are used to guide common ongoing movements. Sometimes it may be clear that certain attributes are not suitable for performing a task because they are altogether irrelevant for that task or take too long to process to be of any use in a task in which the situation is rapidly changing. Thus, the way in which ongoing movements are controlled may depend on details such as the speed of the movement. Before presenting two examples of the complexity of studying how spatial vision guides our actions, reaching out to grasp an object and intercepting a moving object, the aspects of spatial vision that are likely to be important for guiding actions are briefly introduced, and the evidence against the two assumptions that were mentioned in the first paragraph of this section are presented.
Figure 1. How implicit assumptions influence spatial judgments. (A) The items are assumed to be identical and symmetrical, so the textured surface created by these gray disks is perceived as slanted. (B) The gray items that share a border with the black square are perceived as partially occluded disks. (C) Even if one of the disks is completely occluded one is likely to infer its presence, probably because it would be quite coincidental for precisely the disk that is completely hidden by the square to be missing. (D) This is even so when the square itself is inferred from occlusion (Kanizsa, 1976; van Lier, 1999). (E) The presence of partially occluded disks may not even be essential. (F) However, there must be some reason to believe that there might be an occluded disk. 2b1af7f3a8