Abstract
When we grasp and lift novel objects, we rely on visual cues and sensorimotor memories to predictively scale our finger forces and exert compensatory torques according to object properties. Recently, it was shown that object appearance, previous force scaling errors, and previous torque compensation errors strongly impact our percept. However, the influence of visual geometric cues on the perception of object torques and weights in a grasp to lift task is poorly understood. Moreover, little is known about how visual cues, prior expectations, sensory feedback, and sensorimotor memories are integrated for anticipatory torque control and object perception. Here, 12 young and 12 elderly participants repeatedly grasped and lifted an object while trying to prevent object tilt. Before each trial, we randomly repositioned both the object handle, providing a geometric cue on the upcoming torque, as well as a hidden weight, adding an unforeseeable torque variation. Before lifting, subjects indicated their torque expectations, as well as reporting their experience of torque and weight after each lift. Mixed-effect multiple regression models showed that visual shape cues governed anticipatory torque compensation, whereas sensorimotor memories played less of a role. In contrast, the external torque and committed compensation errors at lift-off mainly determined how object torques and weight were perceived. The modest effect of handle position differed for torque and weight perception. Explicit torque expectations were also correlated with anticipatory torque compensation and torque perception. Our main findings generalized across both age groups. Our results suggest distinct weighting of inputs for action and perception according to reliability.
Highlights
To dexterously grasp and lift objects, it is important to plan the grasp execution according to object properties before sensory feedback about these become available
We found no significant effect of the previous planning error within person variation (WP) on Tcom for the young and a positive significant correlation for the elderly group [young 0.033 (Nm/Nm), t(2209) = 1.534, CI − 0.009 to 0.076 (Nm/ Nm), p = 0.123, elderly 0.051 (Nm/Nm), t(2093) = 2.432, CI 0.010–0.092 (Nm/Nm), p = 0.01511, see Fig. 3b]
The interaction between the external torque induced by handle position and trial did not reach significance, indicating that the use of geometric cues did not improve in the course of the experiment
Summary
To dexterously grasp and lift objects, it is important to plan the grasp execution according to object properties before sensory feedback about these become available. It has been shown that subjects can successfully utilize the shape of objects to anticipate its torque (Fu and Santello 2012; LeeMiller et al 2016; Salimi et al 2003). Experimental Brain Research (2020) 238:395–409 the rapid formation of memory links between shapes and torques might have confounded the evaluation of the contribution of visual processing in sensorimotor control mechanisms and the reliance on sensorimotor memories after the first lift (Fu and Santello 2015). It is not known how the addition of random torque variation interacts with the utilization of visual cues. The position and orientation of the handle of a tea cup signals the torque direction, the exact torque magnitude can be uncertain if the level of liquid is not visible
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