This paper presents a novel multimodal virtual rehabilitation environment. Its design and implementation are based on principles related to intrinsic motivation and game design. The system consists of visual, acoustic, and haptic modalities. Elements contributing to intrinsic motivation are carefully joined in the three modalities to increase patients' motivation during the long process of rehabilitation. The message in a bottle (MIB) virtual scenario is designed to allow interplay between motor and cognitive challenges in the exercising patient. The user first needs to perform a motor action to receive a cognitive challenge that is finally solved by a second motor action. Visual feedback provides the most relevant information related to the task. Acoustic feedback consists of environmental sounds, music, and spoken instructions or encouraging statements for the patient. The haptic modality generates tactile information related to the environment and provides various modes of assistance for the patient's arm movements. The MIB scenario was evaluated with 16 stroke patients, who rated it positively using the Intrinsic Motivation Inventory questionnaire. Additionally, the MIB scenario seems to elicit higher motivation than a simpler pick-and-place training task.

In this article we present a new isometric input device for multi-fingered grasping in virtual environments. The device was designed to simultaneously assess forces applied by the thumb, index, and middle finger. A mathematical model of grasping, adopted from the analysis of multi-fingered robot hands, was applied to achieve multi-fingered interaction with virtual objects. We used the concept of visual haptic feedback where the user was presented with visual cues to acquire haptic information from the virtual environment. The virtual object corresponded dynamically to the forces and torques applied by the three fingers. The application of the isometric finger device for multi-fingered interaction is demonstrated in four tasks aimed at the rehabilitation of hand function in stroke patients. The tasks include opening the combination lock on a safe, filling and pouring water from a glass, muscle strength training with an elastic torus, and a force tracking task. The training tasks were designed to train patients' grip force coordination and increase muscle strength through repetitive exercises. The presented virtual reality system was evaluated in a group of healthy subjects and two post-stroke patients (early post-stroke and chronic) to obtain overall performance results. The healthy subjects demonstrated consistent performance with the finger device after the first few trials. The two post-stroke patients completed all four tasks, however, with much lower performance scores as compared to healthy subjects. The results of the preliminary assessment suggest that the patients could further improve their performance through virtual reality training.