Proceedings of The Physiological Society

Physiology 2016 (Dublin, Ireland) (2016) Proc Physiol Soc 37, PCB147

Poster Communications

Body ownership and representation when holding a fake finger

N. Bayle1, M. E. Héroux1,2, A. A. Butler1,2, S. C. Gandevia1,2

1. Neuroscience Research Australia, Randwick, New South Wales, Australia. 2. University of New South Wales, Sydney, New South Wales, Australia.

Grasping a hidden finger-like object induces perceived ownership of the object and a change in perceived position of the hands such that they appear much closer together (Héroux et al. 2013). We investigated whether object characteristics (shape, firmness, texture or temperature) influence this "grasp illusion". Thirty healthy subjects held a finger-like object (control finger) between their left index and thumb, and their right index finger was clamped, 12 cm directly below the left. After holding the object passively for 3 min, the perceived vertical spacing between the index fingers was only ~4 cm. The object was then changed to one with a different shape (rectangular or oddly shaped), firmness (squishy or firm), texture (smooth or rough) or temperature (hot or cold [55 or 12 deg C]). The order of presentations was randomised. Perceived ownership of the held object was assessed with a 7-point Likert scale. Perceived vertical spacing between the index fingers was also measured. Judgements were made immediately after the object was changed. Compared to when subjects held the control finger, perceived ownership decreased by 1.2 [0.6-1.8; mean, 95% CI] points with the cold finger, by 1.2 [0.6-1.7] points with the rough finger, and by 1.1 [0.5-1.7] points with the oddly shaped finger. Compared to holding the control finger, perceived vertical spacing was further reduced by 1.0 [0.2-1.9] cm with the smooth finger. There was no difference in perceived spacing when holding any of the other objects. In summary, once a grasp illusion has been induced by 3 min of holding a fake finger, changing the finger's physical characteristics can decrease the extent to which subjects feel it is part of their body. However, the distorted representation of the hands caused by the grasp illusion resists changes in object characteristics.

Where applicable, experiments conform with Society ethical requirements