Bimanual grasping does not adhere to Weber’s law

Abstract

According to Weber’s law, a fundamental principle of perception, visual resolution decreases in a linear fashion with an increase in object size. Previous studies have shown, however, that unlike for perception, grasping does not adhere to Weber’s law. Yet, this research was limited by the fact that perception and grasping were examined for a restricted range of stimulus sizes bounded by the maximum fingers span. The purpose of the current study was to test the generality of the dissociation between perception and action across a different type of visuomotor task, that of bimanual grasping. Bimanual grasping also allows to effectively measure visual resolution during perception and action across a wide range of stimulus sizes compared to unimanual grasps. Participants grasped or estimated the sizes of large objects using both their hands. The results showed that bimanual grasps violated Weber’s law throughout the entire movement trajectory. In contrast, Just Noticeable Differences (JNDs) for perceptual estimations of the objects increased linearly with size, in agreement with Weber’s law. The findings suggest that visuomotor control, across different types of actions and for a large range of size, is based on absolute rather than on relative representation of object size.

Dissociable effects of irrelevant context on 2D and 3D grasping

“…Such constraints could lead to ceiling effects when looking at the varaiblity of the responses for consderably large obejcts, beyond the limit of one's reach (Bruno, Uccelli, Viviani, & De'Sperati, 2016;Heath, Manzone, Khan, & Jazi, 2017). Researches should be conscious, therefore to possible ceiling effects when designing experiments that tap visual resolution during grasping (Ganel, Namdar, & Mirsky, 2017). We note, however, that biomechanical constraints could not have affected the results of the current study because the target objects were similar in size (40 mm) across the two ranges.…”

Object complexity modulates the association between action and perception in childhood

“…Weber's law as a tool to measure the dissociation between perception and action-In the last decade, Weber's law has been used extensively to measure the dissociation between action and perception under different conditions (e.g., Ganel, Chajut, et al, 2008;Ganel et al, 2014;Ganel, Namdar, & Mirsky, 2017;Heath, Holmes, Mulla, & Binsted, 2012;Holmes & Heath, 2013;Holmes et al, 2011;Ozana & Ganel, 2017). However, it has been argued, that the violation of Weber's law by grasping movements, reflects biomechanical constraints rather than the nature of visuomotor representations.…”

Mental Size Scaling of Three-Dimensional Objects Perceived Visually or Tactilely

“…Perhaps also for bimanual estimation, the imagery representation used by the participants was underestimated, but it was correlated with an overestimation error committed for a manual estimation that occurred in previous studies on size estimation (c.f. Ganel, Namdar, & Mirsky, 2017).…”