Weber's law states that our ability to detect changes in stimulus attributes decreases linearly with their magnitude. This principle holds true for many attributes across sensory modalities but appears to be violated in grasping. One explanation for the failure to observe Weber's law in grasping is that its effect is masked by biomechanical constraints of the hand. We tested this hypothesis using a bimanual task that eliminates biomechanical constraints. Participants either grasped differently sized boxes that were comfortably within their arm span (action task) or estimated their width (perceptual task). Within each task, there were two conditions: One where the hands’ start positions remained fixed for all object sizes (meaning the distance between the initial and final hand-positions varied with object size), and one in which the hands’ start positions adapted with object size (such that the distance between the initial and final hand-position remained constant). We observed adherence to Weber's law in bimanual estimation and grasping across both conditions. Our results conflict with a previous study that reported the absence of Weber's law in bimanual grasping. We discuss potential explanations for these divergent findings and encourage further research on whether Weber's law persists when biomechanical constraints are reduced.

韦伯定律指出，我们检测刺激属性变化的能力随着其强度线性下降。这一原则对于跨感官模式的许多属性都适用，但在抓取过程中似乎被违反了。对抓取过程中未能遵守韦伯定律的一种解释是，其效果被手的生物力学约束所掩盖。我们使用消除生物力学约束的双手任务测试了这一假设。参与者要么抓住在他们的臂展范围内舒适的不同大小的盒子（动作任务），要么估计它们的宽度（感知任务）。在每项任务中，有两种条件：一种是手的起始位置对于所有物体大小都保持固定（这意味着初始和最终手位置之间的距离随对象大小而变化），另一种是手的起始位置进行调整与物体大小（使得初始和最终手位置之间的距离保持恒定）。我们观察到在两种情况下双手估计和抓握都遵循韦伯定律。我们的结果与之前的一项研究相冲突，该研究报告了双手抓取中不存在韦伯定律。我们讨论了这些不同发现的潜在解释，并鼓励进一步研究当生物力学约束减少时韦伯定律是否仍然存在。