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

Abstract

When interacting with an object, we use kinesthetic and tactile information to create our perception of the object's properties and to prevent its slippage using grip force control. We previously showed that applying artificial skin-stretch together with, and in the same direction as, kinesthetic force increases the perceived stiffness. Here, we investigated the effect of the direction of the artificial stretch on stiffness perception and grip force control. We presented participants with kinesthetic force together with negative or positive artificial stretch, in the opposite or the same direction of the natural stretch due to the kinesthetic force, respectively. Our results showed that artificial skin-stretch in both directions augmented the perceived stiffness; however, the augmentation caused by the negative stretch was consistently lower than that caused by the positive stretch. Additionally, we proposed a computational model that predicts the perceptual effects based on the preferred directions of the stimulated mechanoreceptors. When examining the grip force, we found that participants applied higher grip forces during the interactions with positive skin-stretch in comparison to the negative skin-stretch, which is consistent with the perceptual results. These results may be useful in tactile technologies for wearable haptic devices, teleoperation, and robot-assisted surgery.

Exploring the Relation Between Stiffness Perception and Action Using Models and Artificial Neural Networks

“…In this study, our goal was to assess the possibility of predicting participants' perception from their action signals. To do this, we used the data collected in the stiffness discrimination experiment In a stiffness discrimination task comprised of trials (Farajian et al, 2023), we recorded participants' action signals and perceptual responses. We used the perceptual responses from the trials to compute metrics describing participants' perception.…”

“…in our previous work (Farajian et al, 2023). The experiment was comprised of trials in which participants (N=40) interacted with two virtual objects (standard and comparison) and chose which of the two they perceived as stiffer.…”

“…Additionally, in some of the trials, the standard object also applied artificial skin stretch, which could be either in the same direction (positive stretch) or the opposite direction (negative stretch) as that of the force field. It has been well established that positive artificial stretch increases the perceived stiffness (Farajian et al, 2020;Quek et al, 2014;Farajian et al, 2023Farajian et al, , 2021.…”

“…Artificial skin stretch can be generated by devices that make use of a moving tactor, such as a pin with a flat high-friction top, which moves against the skin to create artificial skin deformation (Witney et al, 2004;Quek et al, 2014;Farajian et al, 2020;Prattichizzo et al, 2012). Artificial skin stretch has been shown to increase stiffness perception (Quek et al, 2014;Farajian et al, 2020Farajian et al, , 2023Farajian et al, , 2021, and affect aspects of the grip force (Farajian et al, 2020). Grip force is the perpendicular force applied between the fingers and an object, and it is comprised of a predictive and a reactive component.…”

“…Furthermore, we aim to explore the ability of artificial neural networks to predict perception from action signals. To do this, we use the data recorded in a stiffness discrimination task, which included experimental conditions with only force, and those with artificial skin stretch (Farajian et al, 2023). We design models, and train networks, to receive action information for each trial, and predict the participant's perceptual response in that trial.…”