University of Leeds, Leeds, UK.
Exp Brain Res. 2011 May;211(1):145-60. doi: 10.1007/s00221-011-2659-2. Epub 2011 Apr 12.
Extensive research has identified the affordances used to guide actions, as originally conceived by Gibson (Perceiving, acting, and knowing: towards an ecological psychology. Erlbaum, Hillsdale, 1977; The ecological approach to visual perception. Erlbaum, Hillsdale, 1979/1986). We sought to discover the object affordance properties that determine the spatial structure of reach-to-grasp movements--movements that entail both collision avoidance and targeting. First, we constructed objects that presented a significant collision hazard and varied properties relevant to targeting, namely, object width and size of contact surface. Participants reached-to-grasp objects at three speeds (slow, normal, and fast). In Experiment 1, we explored a "stop" task where participants grasped the objects without moving them. In Experiment 2, we studied "fly-through" movements where the objects were lifted. We discovered the object affordance properties that produced covariance in the spatial structure of reaches-to-grasp. Maximum grasp aperture (MGA) reflected affordances determined by collision avoidance. Terminal grasp aperture (TGA)--when the hand stops moving but prior to finger contact--reflected affordances relevant to targeting accuracy. A model with a single free parameter predicted the prehensile spatial structure and provided a functional affordance-based account of that structure. In Experiment 3, we investigated a "slam" task where participants reached-to-grasp flat rectangular objects on a tabletop. The affordance structure of this task was found to eliminate the collision risk and thus reduced safety margins in MGA and TGA to zero for larger objects. The results emphasize the role of affordances in determining the structure and scaling of reach-to-grasp actions. Finally, we report evidence supporting the opposition vector as an appropriate unit of analysis in the study of grasping and a unit of action that maps directly to affordance properties.
大量研究已经确定了用于指导行动的可供性，这些可供性最初是由 Gibson 提出的（Perceiving, acting, and knowing: towards an ecological psychology. Erlbaum, Hillsdale, 1977; The ecological approach to visual perception. Erlbaum, Hillsdale, 1979/1986）。我们试图发现决定伸手抓握动作空间结构的物体可供性属性，这些动作既涉及避免碰撞，也涉及目标定位。首先，我们构建了具有显著碰撞危险的物体，并改变了与目标定位相关的属性，即物体的宽度和接触面的大小。参与者以三种速度（慢、正常和快）伸手抓握物体。在实验 1 中，我们探索了一个“停止”任务，参与者在不移动物体的情况下抓住物体。在实验 2 中，我们研究了“飞过”动作，物体被抬起。我们发现了产生伸手抓握空间结构协变的物体可供性属性。最大抓握孔径（MGA）反映了由避免碰撞决定的可供性。终端抓握孔径（TGA）——当手停止移动但在手指接触之前——反映了与目标定位精度相关的可供性。具有单个自由参数的模型预测了抓握的空间结构，并提供了对该结构的功能可供性基础解释。在实验 3 中，我们研究了一个“猛击”任务，参与者伸手抓握放在桌面上的扁平矩形物体。发现这个任务的可供性结构消除了碰撞风险，从而使较大物体的 MGA 和 TGA 的安全裕度降低到零。结果强调了可供性在确定伸手抓握动作的结构和比例中的作用。最后，我们报告了支持反对向量作为抓握研究中适当分析单位的证据，以及直接映射到可供性属性的行动单位。
