Visual uncertainty unveils the distinct role of haptic cues in multisensory grasping

Abstract

Human multisensory grasping movements (i.e., seeing and feeling a handheld object while grasping it with the contralateral hand) are superior to movements guided by each separate modality. This multisensory advantage might be driven by the integration of vision with either the haptic position only or with both position and size cues. To contrast these two hypotheses, we manipulated visual uncertainty (central vs. peripheral vision) and the availability of haptic cues during multisensory grasping. We showed a multisensory benefit irrespective of the degree of visual uncertainty suggesting that the integration process involved in multisensory grasping can be flexibly modulated by the contribution of each modality. Increasing visual uncertainty revealed the role of the distinct haptic cues. The haptic position cue was sufficient to promote multisensory benefits evidenced by faster actions with smaller grip apertures, whereas the haptic size was fundamental in fine-tuning the grip aperture scaling. These results support the hypothesis that, in multisensory grasping, vision is integrated with all haptic cues, with the haptic position cue playing the key part. Our findings highlight the important role of non-visual sensory inputs in sensorimotor control and hint at the potential contributions of the haptic modality in developing and maintaining visuomotor functions.Significance statementThe longstanding view that vision is considered the primary sense we rely on to guide grasping movements relegates the equally important haptic inputs, such as touch and proprioception, to a secondary role. Here we show that by increasing visual uncertainty during visuo-haptic grasping, the central nervous system exploits distinct haptic inputs about the object position and size to optimize grasping performance. Specifically, we demonstrate that haptic inputs about the object position are fundamental to support vision in enhancing grasping performance, whereas haptic size inputs can further refine hand shaping. Our results provide strong evidence that non-visual inputs serve an important, previously under-appreciated, functional role in grasping.

Keywords: Multisensory integration; grasping; haptics; peripheral vision; visual uncertainty.