Abstract
The human sensorimotor system readily adapts itself to altered relationships between visual appearances and physical reality. While adaptation of reaching movements has been extensively studied, it is unclear whether known features of reach adaptation can be generalized to grasp adaptation. In a series of experiments in which participants grasped objects that could appear larger or smaller than their physical sizes, we investigated multiple characteristics of grasp adaptation, including (1) error correction rates, (2) interference caused by interleaving positively perturbed (visual > physical) and negatively perturbed (visual < physical) targets at separate spatial locations, (3) functional asymmetries in adaptation and planning processes, (4) transfer to a cross-modal perceptual task (manual size estimation, MSE), and (5) effects on visual perception. In the single-perturbation experiments, the maximum grip aperture (MGA) gradually adapted to positive and negative perturbations. In the conflicting-perturbations experiment, interference was reduced when the distance between the two target locations was increased. However, participants were unable to fully adapt to both perturbations even in the increased-separation condition. Neither of these studies yielded clear evidence for an asymmetry in adaptation, as suggested previously, but they did reveal an asymmetry in the initial responses to perturbations: the initial MGA increase elicited by positive perturbation was greater than the initial MGA decrease elicited by negative perturbation. Finally, in the MSE experiment, we found a clear asymmetry in transfer of adaptation: MSEs increased following adaptation to a negative perturbation (requiring larger MGAs), but they did not decrease following adaptation to a positive perturbation. This transfer was slightly strengthened when MSEs were given in the same location as the grasp targets. We interpret these findings as evidence that reach and grasp adaptation are generally similar processes relying on flexible visuomotor mappings, but they differ due to their dependence on specific task constraints and movement feedback signals.
Meeting abstract presented at VSS 2017