The endless visuomotor calibration of reach-to-grasp actions

2020

Preprint

Self Cite

Grasping actions are directed not only toward objects we see but also toward objects we both see and touch (multisensory grasping). In this latter case, the integration of visual and haptic inputs improves movement performance compared to each sense alone. This performance advantage could be due to the integration of all the redundant positional and size cues or to the integration of only a subset of these cues. Here we selectively provided specific cues to tease apart how these different sensory sources contribute to visuo-haptic multisensory grasping. We demonstrate that the availability of the haptic positional cue together with the visual cues is sufficient to achieve the same grasping performance as when all cues are available. These findings provide strong evidence that the human sensorimotor system relies on non-visual sensory inputs and open new perspectives on their role in supporting vision during both development and adulthood.

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Integration of haptics and vision in human multisensory grasping

2020

Preprint

Self Cite

“…However, one open question concerns the contribution of the different haptic and visual signals. Visual estimates of size are tightly linked to visual estimates of distance: we can properly scale retinal information only if our visual distance estimates are approximately correct 61–67 . On the other hand, two signals supply us with independent haptic information.…”

Section: Discussionmentioning

confidence: 99%

Grasping movements toward seen and handheld objects

2019

Sci Rep

Self Cite

Grasping movements are typically performed toward visually sensed objects. However, planning and execution of grasping movements can be supported also by haptic information when we grasp objects held in the other hand. In the present study we investigated this sensorimotor integration process by comparing grasping movements towards objects sensed through visual, haptic or visuo-haptic signals. When movements were based on haptic information only, hand preshaping was initiated earlier, the digits closed on the object more slowly, and the final phase was more cautious compared to movements based on only visual information. Importantly, the simultaneous availability of vision and haptics led to faster movements and to an overall decrease of the grip aperture. Our findings also show that each modality contributes to a different extent in different phases of the movement, with haptics being more crucial in the initial phases and vision being more important for the final on-line control. Thus, vision and haptics can be flexibly combined to optimize the execution of grasping movement.

“…The difference in MGA between V and VH previously reported (Camponogara and Volcic 2019) was now probably masked by the mixture of unperturbed and perturbed trials. It is, in fact, known that grasping actions can be directly affected by increased uncertainty and by preceding actions (Bozzacchi et al 2016;Volcic and Domini 2018;Whitwell et al 2008). With regard to the factor perturbation, MGA was larger in the perturbed than in the unperturbed trials (perturbed: 123 Ϯ 1.28 mm, unperturbed: 118 Ϯ 1.48 mm).…”

Section: Kinematic Variablesmentioning

confidence: 96%

Grasping adjustments to haptic, visual, and visuo-haptic object perturbations are contingent on the sensory modality

Journal of Neurophysiology

2019

Self Cite

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.