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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. [ABSTRACT FROM AUTHOR]

Predicting instead of only reacting to the properties of objects we grasp is crucial to dexterous object manipulation. Although we normally plan our grasps according to well-learned associations, we rely on implicit sensorimotor memories when we learn to interact with novel or ambiguous objects. However, little is known about the influence of sensorimotor predictions on subsequent perception and action. Here, young and elderly subjects repeatedly lifted an object in which the center of mass (CoM) was randomly varied between trials straight upward with the aim of preventing object tilts. After each lift, subjects indicated the location of the perceived CoM and reported how heavy the object felt. Surprisingly, we found that sensorimotor torque memories eventually causing initial lifting errors had substantial effects on the perception of torques, weight, and the torque planning for the next lift. Whereas subjects tended to partly retain their previous erroneous sensorimotor memories (instead of solely relying on the previously encountered torque for the upcoming motor plan), they perceived encountered torques to be stronger when they erroneously predicted them. Additionally, we found that torque prediction errors, as well as the actual torques, made the object feel heavier. By contrast, perception did not influence upcoming motor control. There were no major differences observed between the age groups. The sensorimotor impact on torque perception can be explained by internal feedforward prediction highlighting task-relevant errors, while the partial retention and adaptation of sensorimotor torque memories is reconciled with the trial-to-trial learning rule for motor adaptation. [ABSTRACT FROM AUTHOR]

With the emergence of pen-enabled tablets and mobile devices, stylus-based interaction has been receiving increasing attention. Unfortunately, styluses available on the market today are all passive instruments that are primarily used for writing and pointing. The article describes a novel stylus, HaptiStylus, which is capable of conveying certain vibrotactile and inertial haptic effects to the user. The stylus is equipped with two vibration actuators at each end that are used to create a tactile sensation of up and down movement along the stylus. The stylus is also embedded with a DC motor, which helps create a sense of bidirectional rotational torque along the pen. Psychophysical experimental results and practical application use-case studies show that the proposed device can effectively convey movement and rotational torque information to the user. [ABSTRACT FROM AUTHOR]

The brain receives input from multiple sensory modalities simultaneously, yet we experience the outside world as a single integrated percept. This integration process must overcome instances where perceptual information conflicts across sensory modalities. Under such conflicts, the relative weighting of information from each modality typically depends on the given task. For conflicts between visual and haptic modalities, visual information has been shown to influence haptic judgments of object identity, spatial features (eg location, size), texture, and heaviness. Here we test a novel instance of haptic–visual conflict in the perception of torque. We asked participants to hold a left–right unbalanced object while viewing a potentially left-right mirror-reversed image of the object. Despite the intuition that the more proximal haptic information should dominate the perception of torque, we find that visual information exerts substantial influences on torque perception even when participants know that visual information is unreliable. [ABSTRACT FROM AUTHOR]

To make the prosthetic hand move faster with less vibration and smaller than adult thumb, a prosthetic thumb has been designed on the basis of underacutuated mechanism. To make the hand more intelligentized, torque and position perception devices have been integrated. The thumb consists of three joints and is actuated by one motor. And the motor, gearhead and bevel device are all embedded in palm. Planar four-bar linkage and spatial four-bar linkage are adopted between metacarpal anti proximal phalanx to make the appearance anti track more humanoid. It is verified from experiment that the thumb has faster grasping speed without vibration at the beginning and end of grasping. It is more humanoid when grasping and can accomplish the prehension by subterminal opposition, tridigital grip, cylindrical palmar prehension, and can meet the basic life needs of the handicapped. [ABSTRACT FROM AUTHOR]