Proceedings of The Physiological Society

Physiology 2014 (London, UK) (2014) Proc Physiol Soc 31, C48

Oral Communications

Judgements of lifted objects and grasp aperture

A. A. Butler1, S. C. Gandevia1

1. Neuroscience Research Australia, Sydney, New South Wales, Australia.

Accurate proprioceptive information and body representations are required to accomplish even simple tasks, such as lifting a cup (1-3). However it is unclear how the properties of lifted objects affect the ‘representation' of the hand involved in the task. Specifically, is the perceived grasp aperture of the human hand influenced by the size and weight of lifted objects? Vision was excluded in all experiments. In experiment 1, 14 subjects reported the perceived weight of lifted canisters that were of different sizes (5.2, 6.6, 10 cm width) but the same weight (600 g). In experiment 2, these subjects reported perceived grasp aperture while lifting canisters that were of the same size (width 6.6 cm) but varied weights (300, 600, 900, 1200 g). In experiment 3, 16 subjects reported perceived grasp aperture as they grasped a stationary canister at varied force levels. This investigated the role of both efferent and afferent inputs in grasp aperture perception (4). When canisters of the same weight but different widths were lifted (experiment 1), perceived weight decreased by ~50% from the narrowest to the widest (p < 0.001). When canisters of the same width but different weights were lifted (experiment 2), perceived grasp aperture decreased as the weight of the canister increased. However this decrease was only 5% across the range of weights (p < 0.001). In experiment 3, perceived grasp aperture did not change with the level of grasp force (p > 0.05). The effect of object properties on hand representation was much smaller than its effect on weight perception. This small effect is not the result of varied grasp forces. Overall, despite a distorted perception of the weight of a grasped object, the central nervous system maintains a reasonably accurate perception of the posture and representation of the grasping hand over a four-fold range of object weights. Presumably this accuracy in perception of grasp aperture derives from peripheral proprioceptive signals.

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