How humans visually select where to grasp an object depends on many factors, including grasp stability and preferred grasp configuration. We examined how endpoints are selected when these two factors are brought into conflict: Do people favor stable grasps or do they prefer their natural grasp configurations? Participants reached to grasp one of three cuboids oriented so that its two corners were either aligned with, or rotated away from, each individual's natural grasp axis (NGA). All objects were made of brass (mass: 420 g) but the surfaces of their sides were manipulated to alter friction: 1) all-brass, 2) two opposing sides covered with wood, while the other two remained of brass, or 3) two opposing sides covered with sandpaper, and the two remaining brass sides smeared with vaseline. Grasps were evaluated as either clockwise (thumb to the left of finger in frontal plane) or counterclockwise of the NGA. Grasp endpoints depended on both object orientation and surface material. For the all-brass object, grasps were bimodally distributed in the NGA-aligned condition but predominantly clockwise in the NGA-unaligned condition. These data reflected participants' natural grasp configuration independently of surface material. When grasping objects with different surface materials, endpoint selection changed: Participants sacrificed their usual grasp configuration to choose the more stable object sides. A model in which surface material shifts participants' preferred grip angle proportionally to the perceived friction of the surfaces accounts for our results. Our findings demonstrate that a stable grasp is more important than a biomechanically comfortable grasp configuration.

中文翻译：

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在精确抓握中，摩擦优于抓握配置

人类如何在视觉上选择抓握物体的位置取决于许多因素，包括抓握稳定性和首选抓握配置。我们研究了当这两个因素发生冲突时如何选择端点：人们喜欢稳定的抓握还是他们更喜欢自然的抓握配置？参与者伸手抓住定向的三个长方体之一，使其两个角与每个人的自然抓握轴 (NGA) 对齐或旋转远离。所有物体均由黄铜制成（质量：420 克），但它们的侧面被操纵以改变摩擦力：1）全黄铜，2）两个相对的侧面覆盖着木头，而另外两个仍然是黄铜，或 3）两个相对的边用砂纸覆盖，剩下的两个黄铜边涂上凡士林。抓握被评估为顺时针（拇指在额平面中手指左侧）或逆时针方向的 NGA。抓取端点取决于对象方向和表面材料。对于全黄铜物体，在 NGA 对齐条件下抓握呈双峰分布，但在 NGA 未对齐条件下主要是顺时针分布。这些数据反映了参与者独立于表面材料的自然抓握配置。当抓取具有不同表面材料的物体时，端点选择发生了变化：参与者牺牲了他们通常的抓取配置来选择更稳定的物体侧面。我们的结果是一个模型，其中表面材料根据表面的感知摩擦成比例地改变参与者的首选抓握角度。