Stretching the skin of the fingertip creates a perceptual and motor illusion of touching a harder spring

Abstract

We investigated how artificial tactile feedback in the form of a skin-stretch affects perception of stiffness and grip force adjustment. During interactions with objects, information from kinesthetic and tactile sensors is used to estimate the forces acting on the limbs. These enable the perception of the mechanical properties of objects to form, and the creation of internal models to predict the consequences of interactions with these objects, such as feedforward grip-force adjustments to prevent slippage. Previous studies showed that an artificial stretch of the skin of the fingertips can produce a linear additive effect on stiffness perception, but it remains unclear how such stretch affects the control of grip force. Here, we used a robotic device and a custom-built skin-stretch device to manipulate kinesthetic and tactile information. Using a stiffness discrimination task, we found that adding artificial tactile feedback to a kinesthetic force can create the illusion of touching a harder spring which affects both perception and action. The magnitude of the illusion is linearly related to the amplitude of the applied stretch. We also isolated the contribution of tactile stimulation to the predictive and reactive components of grip force adjustment, and found that unlike in other cases of perceptual illusions, the predictive grip force is . CC-BY-NC-ND4.0 International license peer-reviewed) is the author/funder. It is made available under aThe copyright holder for this preprint (which was not . http://dx.doi.org/10.1101/203604 doi: bioRxiv preprint first posted online Oct. 15, 2017; 2 modulated consistently with the perceptual tactile-induced illusion. These results have major implications for the design of tactile interfaces across a variety of touch applications such as wearable haptic devices, teleoperations, robot-assisted surgery, and prosthetics.Keywords: grip force control, stiffness perception, skin-stretch, sensory augmentation, predictive control, reactive control. Significance StatementSensing forces, using kinesthetic and tactile modalities, is important for assessing the mechanical properties of objects, and for acting the objects while stabilizing grasp against slippage. A major challenge in understanding the internal representations that allow for a predictive grip force control during contact with objects is to dissociate the contribution of tactile and kinesthetic stimuli. To date, this contribution was investigated only in impaired cases either through local anesthesia or in patients with sensory impairment. Our study demonstrates using a programmable mechatronic device that artificially applied skinstretch creates an illusion of a greater load force that affects grip force control and stiffness perception. These results are applicable in tactile technologies for wearable haptic devices, teleoperation, robot-assisted surgery, and prosthetics.

The Effect of Dissociation between Proprioception and Vision on Perception and Grip Force Control in a Stiffness Judgment Task

“…However, we observed a smaller increase in the lag. One possible explanation is that the dominant peaks in the grip force were of a reactive nature and not of a predictive nature [16]. In such case, the calculation of the lag would show smaller value than 50 ms.…”

Smart switching in feedforward control of grip force during manipulation of elastic objects

“…Another proposed measure is Extended Rate Hardness, a measure of the perceived hardness of a surface based on rate of force change and penetration velocity (Han and Choi, 2010). Skin deformation accompanying the probing also likely plays a role in perception of stiffness (Quek et al, 2014, Quek et al, 2015, Farajian et al, 2017). Here, we do not attempt to spill more light on this matter, but it is possible that the estimated stiffness is used in the process of the switching.…”

The effect of tactile augmentation on manipulation and grip force control during force-field adaptation

“…Aiming to understand the integration between tactile and kinesthetic information during adaptation to a force perturbation, we built a 1 DOF skin-stretch device similar to the one that was used in [4], with several modifications to fit the needs of the current study. We modified the configuration of the device such that the skin-stretch will be applied in the horizontal plane and perpendicularly to the desired movement direction ( Fig.…”

“…Manipulation forces are the forces and torques that we exert against the held object to translate and rotate it. In contrast, grip forces stabilize the grasped object to prevent its slippage without resulting in any other motion [2][3][4]. Previously, studies showed that sensory information can be used differently to form internal representation for manipulation and grip force control [5][6][7].…”

“…In the recent years, new devices were developed that can stimulate the tactile mechanoreceptors by deforming the skin, and thereby augment the tactile sensation [37]. Using these devices, it was shown that artificial skin deformation can increase the perceived mechanical properties [4,[38][39][40][41][42][43], possibly due to an increase in the perceived forces, and substitute and augment kinesthetic information in some motor tasks [44][45][46][47][48]. The effect of artificial skin deformation on the integration of kinesthetic and tactile information for the control of grip force was recently examined in the case of a stiffness perception task [39].…”