-This paper proposes a novel pseudo-haptics soft object stiffness simulation technique which is a marked improvement to currently used simulation methods and an effective low-cost alternative to expensive 3-DOF haptic devices. Soft object stiffness simulation is achieved by maneuvering an indenter avatar over the surface of a virtual soft object by means of an input device, such as a mouse, a joystick, or a touch-sensitive tablet. The alterations to the indenter avatar behavior produced by the proposed technique create for the user the illusion of interaction with a hard inclusion embedded in the soft object. The proposed pseudo-haptics technique is validated with a series of experiments conducted by employing three types of 2-DOF force-sensitive haptic surfaces, including a touchpad, a tablet with an S-pen input, and a tablet with a bare finger input. It is found that both the sensitivity and the positive predictive value of hard inclusion detection can be significantly improved by 33.3% and 13.9% respectively by employing tablet computers. Using tablet computers could produce results comparable to direct hand touch in detecting hard inclusions in a soft object. The experimental results presented here confirm the potential of the proposed technique for conveying haptic information in rigid tool / soft object interaction in virtual environments.

This paper proposes a pseudo-haptic feedback method conveying simulated soft surface stiffness information through a visual interface. The method exploits a combination of two feedback techniques, namely visual feedback of soft surface deformation and control of the indenter avatar speed, to convey stiffness information of a simulated surface of a soft object in virtual environments. The proposed method was effective in distinguishing different sizes of virtual hard nodules integrated into the simulated soft bodies. To further improve the interactive experience, the approach was extended creating a multi-point pseudo-haptic feedback system. A comparison with regards to (a) nodule detection sensitivity and (b) elapsed time as performance indicators in hard nodule detection experiments to a tablet computer incorporating vibration feedback was conducted. The multi-point pseudo-haptic interaction is shown to be more time-efficient than the single-point pseudo-haptic interaction. It is noted that multi-point pseudo-haptic feedback performs similarly well when compared to a vibration-based feedback method based on both performance measures elapsed time and nodule detection sensitivity. This proves that the proposed method can be used to convey detailed haptic information for virtual environmental tasks, even subtle ones, using either a computer mouse or a pressure sensitive device as an input device. This pseudo-haptic feedback method provides an opportunity for low-cost simulation of objects with soft surfaces and hard inclusions, as, for example, occurring in ever more realistic video games with increasing emphasis on interaction with the physical environment and minimally invasive surgery in the form of soft tissue organs with embedded cancer nodules. Hence, the method can be used in many low-budget applications where haptic sensation is required, such as surgeon training or video games, either using desktop computers or portable devices, showing reasonably high fidelity in conveying stiffness perception to the user.

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