Abstract
Haptics provides information about the size and position of a handheld object. However, it is still unknown how haptics contributes to action correction if a sudden perturbation causes a change in the configuration of the handheld object. In this study, we have occasionally perturbed the size of an object that was the target of a right-hand reach-to-grasp movement. In some cases, participants were holding the target object with their left hand, which provided haptic information about the object perturbation. We compared the corrective responses to perturbations in three different sensory conditions: visual (participants had full vision of the object, but haptic information from the left hand was prevented), haptic (object size was sensed by the left hand and vision was prevented), and visuo-haptic (both visual and haptic information were available throughout the movement). We found that haptic inputs evoked faster contralateral corrections than visual inputs, although actions in haptic and visual conditions were similar in movement duration. Strikingly, the corrective responses in the visuo-haptic condition were as fast as those found in the haptic condition, a result that is contrary to that predicted by simple summation of unisensory signals. These results suggest the existence of a haptomotor reflex that can trigger automatic and efficient grasping corrections of the contralateral hand that are faster than those initiated by the well-known visuomotor reflex and the tactile-motor reflex.NEW & NOTEWORTHY We show that online grip aperture corrections during grasping actions are contingent on the sensory modality used to detect the object perturbation. We found that sensing perturbations with the contralateral hand only (haptics) leads to faster action corrections than when object perturbations are only visually sensed. Moreover, corrections following visuo-haptic perturbations were as fast as those to haptic perturbations. Thus a haptomotor reflex triggers faster automatic responses than the visuomotor reflex.
Highlights
In everyday life, object manipulations are constantly performed without the aid of vision
It is evident that haptic inputs can successfully trigger appropriate corrective responses of the contralateral hand during reaching movements (Pruszynski et al 2016) and in bimanual coordination tasks (Dimitriou et al 2012; Manson et al 2019; Mutha and Sainburg 2009; Omrani et al 2013), it is still unclear 1) whether haptic inputs can guide fast grip aperture adjustments, 2) how haptically triggered grasping corrections compare with those triggered by visual inputs, and 3) how the corrections elicited by the simultaneous combination of haptic and visual inputs compare with those triggered by each input separately
In this study we investigated whether grip aperture corrections are contingent on the sensory modality used to detect an object’s size perturbation
Summary
Object manipulations are constantly performed without the aid of vision. The simultaneous afferent tactile inputs from mechanoreceptors and proprioceptive inputs from the muscle spindles and tendons of the hand are integrated to signal a change in the object properties (Berryman et al 2006; Johansson and Flanagan 2009) and trigger a correction of the contralateral hand. How does this corrective process unfold? And, how do haptic corrections compare with the wellstudied corrections to visual perturbations? does the simultaneous availability of both visual and haptic inputs lead to a multisensory advantage with even faster corrections?
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