Abstract
Haptic exploration produces mental object representations that can be memorized for subsequent object-directed behaviour. Storage of haptically-acquired object images (HOIs), engages, besides canonical somatosensory areas, the early visual cortex (EVC). Clear evidence for a causal contribution of EVC to HOI representation is still lacking. The use of visual information by the grasping system undergoes necessarily a frame of reference shift by integrating eye-position. We hypothesize that if the motor system uses HOIs stored in a retinotopic coding in the visual cortex, then its use is likely to depend at least in part on eye position. We measured the kinematics of 4 fingers in the right hand of 15 healthy participants during the task of grasping different unseen objects behind an opaque panel, that had been previously explored haptically. The participants never saw the object and operated exclusively based on haptic information. The position of the object was fixed, in front of the participant, but the subject’s gaze varied from trial to trial between 3 possible positions, towards the unseen object or away from it, on either side. Results showed that the middle and little fingers’ kinematics during reaching for the unseen object changed significantly according to gaze position. In a control experiment we showed that intransitive hand movements were not modulated by gaze direction. Manipulating eye-position produces small but significant configuration errors, (behavioural errors due to shifts in frame of reference) possibly related to an eye-centered frame of reference, despite the absence of visual information, indicating sharing of resources between the haptic and the visual/oculomotor system to delayed haptic grasping.
Highlights
Haptic exploration produces mental object representations that can be memorized for subsequent object-directed behaviour
These results show evidence that the early visual cortex (EVC) is involved in haptic exploration of objects, but it is reactivated dur
While previous studies have investigated the effect of gaze direction on maximum grip aperture of the thumb and index finger, as in a precision grip[36], we examined the influence of gaze on all fingers involved in a precision whole-hand grasp in order to provide a comprehensive view of the kinematics of all fingers that participate in hand actions
Summary
Haptic exploration produces mental object representations that can be memorized for subsequent object-directed behaviour. Neuroimaging evidence in humans shows that gaze direction modulates the activity in the parieto-frontal network, which is known to be crucial for motor behaviour, during reaching movements towards visual targets[25,26,27]. Haptic information of objects, acquired in a hand-centred frame of reference is stored in “visual” buffer in the EVC and information in the EVC needs to integrate gaze position to be used in grasping movements. Such a “visual” storage, albeit temporary, could be useful for the genesis of movement towards objects, after appropriate integration of object information in a more complex spatial map that includes other coordinate systems, such as hand-, body- or head-centred ones
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