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

Abstract

Tactile stimulation devices are gaining popularity in haptic science and technologythey 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 skinstretch. We found that visual displacement feedback weakens the skin-stretch induced perceptual augmentation and improves the stiffness discrimination sensitivity.

Direction-Specific Effects of Artificial Skin-Stretch on Stiffness Perception and Grip Force Control

“…The standard virtual object always had a stiffness value of 85 N/m, and in trials with artificial skinstretch stimulation the skin-stretch gain was +80 mm/m in the positive stretch session, and -80 mm/m in the negative stretch session. This artificial skin-stretch gain was chosen because in our previous studies [27], [29] a clear augmentation in the perceived stiffness was demonstrated due to this level of positive artificial stretch. The stiffness level of the comparison virtual object was selected in each trial from a range of 12 values, evenly spaced between 30-140 N/m.…”

“…Recent studies showed that applying artificial skin-stretch in the same direction as kinesthetic load force augments the perceived stiffness linearly to the amount of stretch [27]- [29]. Additionally, this skin stretch increases the predictive grip force modulation in anticipation of the load force [27].…”

“…In the current study, we use a similar experimental setup and methodologies to two of our previous works [27], [29]. Despite the technical similarities, the research questions addressed in these three studies are different.…”

“…We reported the magnitude of the increase in perceived stiffness and the timeline of its creation, as well as the effect on the predictive and reactive grip force control. Next, in [29], we studied if the perceptual augmentation caused by the positive artificial skin-stretch is impaired when visual displacement information is presented to the participants, and found that the presence of visual information weakens the augmentation. Hence, in both of these studies the artificial stretch was applied in the same direction as the natural stretch caused by kinesthetic forces.…”

Highlights from the 30th Annual Meeting of the Society for the Neural Control of Movement

“…According to Ilana Nisky, 2021 Early Career Award winner, robot-assisted surgery can bridge the gap between laboratory-based research and real-life applications. Currently, surgical training is not optimized, partly due to a lack of haptic feedback and partly due to limited knowledge on how to measure surgical skills (4,11,23,30,45,45). Nisky's research used a teleoperated needle driving task and integrated data measuring the dynamics of the robotic manipulandum and modeling human kinematics to describe the quality of surgical skill throughout the learning process.…”