Kossowsky, H. | bioRxiv Science

bioRxiv2020

Visual Feedback Weakens the Augmentation of Perceived Stiffness by Artificial Skin Stretch

Tactile stimulation devices are gaining popularity in haptic science and technology - they are lightweight, low-cost, can be easily made wearable, and do not suffer from instability during closed loop interactions with users. Applying tactile stimulation in the form of stretching the skin of the fingerpads, concurrently with kinesthetic force feedback, has been shown to augment the perceived stiffness during interactions with elastic objects. However, all of the studies to date have investigated the perceptual augmentation effects of artificial skin-stretch in the absence of visual feedback. We investigated how visual displacement feedback affects the augmentation of perceived stiffness caused by the skin-stretch. We used a forced-choice paradigm stiffness discrimination task with four different conditions: force feedback, force feedback with artificial skin-stretch, force and visual feedback, and force and visual feedback with artificial skin-stretch. We found that visual displacement feedback weakens the skin-stretch induced perceptual augmentation and improves the stiffness discrimination sensitivity.

bioengineering↗

bioRxiv2020

The Effect of Between-Probe Variability in Haptic Feedback on Stiffness Perception and Grip Force Adjustment

When interacting with objects, haptic information is used to create perception of the object stiffness and to regulate grip force. Studies have shown that introducing noise into sensory inputs can create uncertainty in those sensory channels, yet a method of creating haptic uncertainty without distorting the haptic information has yet to be discovered. Toward this end, we investigated the effect of between-probe haptic variability on stiffness perception and grip force control. In a stiffness discrimination task, we added different levels of between-probe haptic variability by changing the stiffness of the force fields between consecutive probes. Unlike the low and high variability levels, the medium level created perceptual haptic uncertainty. Additionally, we ascertained that participants calculated a weighted average of the different stiffness levels applied by a given force field. Examining participants grip force showed that the modulation of the grip force with the load force decreased with repeated exposure to the force field, whereas no change in the baseline was observed. These results were observed in all the variability levels and suggest that between-probe variability created haptic uncertainty that affected the grip force control. Overall, the medium variability level can be effective in inducing uncertainty in both perception and action.

neuroscience↗