Abstract
We reach for and grasp different sized objects numerous times per day. Most of these movements are visually-guided, but some are guided by the sense of touch (i.e. haptically-guided), such as reaching for your keys in a bag, or for an object in a dark room. A marked right-hand preference has been reported during visually-guided grasping, particularly for small objects. However, little is known about hand preference for haptically-guided grasping. Recently, a study has shown a reduction in right-hand use in blindfolded individuals, and an absence of hand preference if grasping was preceded by a short haptic experience. These results suggest that vision plays a major role in hand preference for grasping. If this were the case, then one might expect congenitally blind (CB) individuals, who have never had a visual experience, to exhibit no hand preference. Two novel findings emerge from the current study: first, the results showed that contrary to our expectation, CB individuals used their right hand during haptically-guided grasping to the same extent as visually-unimpaired (VU) individuals did during visually-guided grasping. And second, object size affected hand use in an opposite manner for haptically- versus visually-guided grasping. Big objects were more often picked up with the right hand during haptically-guided, but less often during visually-guided grasping. This result highlights the different demands that object features pose on the two sensory systems. Overall the results demonstrate that hand preference for grasping is independent of visual experience, and they suggest a left-hemisphere specialization for the control of grasping that goes beyond sensory modality.
Highlights
We execute hundreds of reaching and grasping movements a day
In light of this evidence, we investigated if object size affects hand preference for those with lifelong deprivation of visual experience (CB individuals)
congenitally blind (CB) and visually unimpaired (VU: Sighted and Blindfolded/Matched controls) individuals were asked to replicate 3D models using small or large blocks scattered on a tabletop
Summary
We execute hundreds of reaching and grasping movements a day. Both vision and hapsis (i.e. sense of touch) play an integral role in guiding these movements. The results showed that participants used their right hand significantly more to grasp the blocks while sighted, but even so, a preference to grasp with the right hand persisted during the blindfolded trials If these blindfolded trials were preceded by five minutes of haptic experience (without vision), equal use of the right and left hands was observed [12]. Kinematic analyses have shown that when reaching for an object, blind individuals do display differences in movement (i.e. a double opening and closing of the hand towards the target), but they still accurately scale to the size of the unseen object (in a manner similar to sighted individuals) [32,33] In light of this evidence, we investigated if object size affects hand preference for those with lifelong deprivation of visual experience (CB individuals). Hand preference for grasping was documented in ipsilateral (same side as the hand) and contralateral (opposite side of the hand) space as studies have found that reaching across the midline is a powerful indicator of hand preference [6,8,34]
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