An elasticity-curvature illusion decouples cutaneous and proprioceptive cues in softness exploration
A tactile illusion for softness perception
April 14, 2021
Chang Xu, Yuxiang Wang, Steven C. Hauser, and Gregory J. Gerling
How do we differentiate soft objects by touch, as we do in judging the ripeness of fruit? Our understanding of how material softness is perceptually encoded remains incomplete. This study investigates an illusion phenomenon that occurs in discriminating material compliances. We find that small-compliant and large-stiff spheres are naturally indistinguishable when pressed into a stationary finger, but readily discriminable when pressed upon. This phenomenon illuminates an interplay within our somatosensory system, in particular, between cutaneous responses from skin receptors and proprioceptive feedback traditionally tied to joint movements. It also reveals how our movements optimally evoke these cues to inform our percept of softness. Understanding how softness is encoded at skin contact is key to designing touch-enabled displays.
Pressing an object onto the finger does not reveal its softness, but pressing actively does, therefore our perception of softness is a product of both sensation and volition, and depends upon both afferents in skin and proprioception
Computational modeling of contact mechanics with compliant spheres
Experimental setup and biomechanical analysis of finger-stimulus contact
An active, force-control movement strategy is optimal for softness perception
Xu, C., Wang, Y., and Gerling, G.J., An elasticity-curvature illusion decouples cutaneous and proprioceptive cues in active exploration of soft objects [DOI]. PLoS Computational Biology, 2021.
Xu, C., Wang, Y., Hauser, S.C., and Gerling, G.J., In the tactile discrimination of compliance, perceptual cues in addition to contact area are required [DOI]. Proceedings of the Human Factors and Ergonomics Society Annual Meeting, 2018.
Wang, Y. and Gerling, G.J., Computational modeling reinforces that proprioceptive cues may augment compliance discrimination when elasticity is decoupled from radius of curvature [DOI]. EuroHaptics 2014: Haptics: Neuroscience, Devices, Modeling, and Applications, 2014.
Gregory J. Gerling
Professor, Systems Engineering
151 Engineer's Way Charlottesville, Virginia 22904 Phone: 434-924-0533