Does it feel the same when you touch an object in Augmented Reality (AR) or in Virtual Reality (VR)? In this paper we study and compare the haptic perception of stiffness of a virtual object in two situations: (1) a purely virtual environment versus (2) a real and augmented environment. We have designed an experimental setup based on a Microsoft HoloLens and a haptic force-feedback device, enabling to press a virtual piston, and compare its stiffness successively in either Augmented Reality (the virtual piston is surrounded by several real objects all located inside a cardboard box) or in Virtual Reality (the same virtual piston is displayed in a fully virtual scene composed of the same other objects). We have conducted a psychophysical experiment with 12 participants. Our results show a surprising bias in perception between the two conditions. The virtual piston is on average perceived stiffer in the VR condition compared to the AR condition. For instance, when the piston had the same stiffness in AR and VR, participants would select the VR piston as the stiffer one in 60% of cases. This suggests a psychological effect as if objects in AR would feel "softer" than in pure VR. Taken together, our results open new perspectives on perception in AR versus VR, and pave the way to future studies aiming at characterizing potential perceptual biases.

3D interaction in virtual reality often requires to manipulate and feel virtual objects with our fingers. Although existing haptic interfaces can be used for this purpose (e.g. force-feedback exoskeleton gloves), they are still bulky and expensive. In this paper, we introduce a novel multi-finger device called "FlexiFingers" that constrains each digit individually and produces elastic forcefeedback. FlexiFingers leverages passive haptics in order to offer a lightweight, modular, and affordable alternative to active devices. Moreover, we combine Flexifingers with a pseudo-haptic approach that simulates different levels of stiffness when interacting with virtual objects. We illustrate how this combination of passive haptics and pseudo-haptics can benefit multi-finger interaction through several use cases related to music learning and medical training. Those examples suggest that our approach could find applications in various domains that require an accessible and portable way of providing haptic feedback to the fingers.

Haptic rendering of deformable phenomena remains computationally-demanding, especially when topology modifications are simulated. Within this context, the haptic rendering of tearing phenomena is under-explored as of today. In this paper we propose a fully-functional interaction pipeline for physically-based simulation of deformable surfaces tearing allowing to reach a haptic interactive rate. It relies on a high efficiency collision detection algorithm for deformable surface meshes, combined with an efficient FEM-based simulation of deformable surfaces enabling tearing process. We especially introduce a novel formulation based on clusters for the collision detection to improve the computation time performances. Our approach is illustrated through interactive use-cases of tearing phenomena with haptic feedback, showing its ability to handle realistic rendering of deformable surface tearing on consumergrade haptic devices.