**2. Research background**

For children with a development disorder, occupational therapy is usually performed. Occupational therapy for such children includes a variety of different therapies with many evaluation methods either proposed or existing. A suitable therapy provides individual therapy to treat the level of the disorder and the age of the child.

In the therapy for young children, the goal is to prepare them for elementary school. Of course, preparation requires many different actions. Occupational therapy is mainly focused on obtaining handwriting skills and self-reliance in daily life. Thus, the goals of therapy are enabling development of dexterous hand and visual perception. This means that hand-eye coordination is important.

In occupational therapy, many different tools are used, for example, toys, musical instruments, paper projects, mazes, and puzzles. Most of these tools are readily available in retail markets. Also, some are handmade by the therapist. These tools are used not only for therapy but also for evaluation the level of disorder. However, the evaluation of the effects are mostly based on the therapist's subjective observations and conventional pen-paper tests. At the present time, evidence-based occupational therapy is desirable. Therefore, establishment of quantitative evaluation methods are required. To meet this need, we apply computer technology and virtual reality to conventional therapy.

Additionally, therapists are interested in how to motivate patients and maintain the motivation for both children and adults. Virtual reality devices offering visual and sound experiences provide tactile and haptic sensations, which are interesting for patients, especially young patients. Therefore, we developed an effective haptic device system with training software that provides a haptic sensation on a hand grip held by the user. The sensation generated depends on the visual program.
