**3. The Human Computer Interface**

The HCI provides a natural interface suitable for subjects with limited computer skills and with motor impairments. It is implemented through a Graphical User Interface (GUI) and an interactive menu based on choice icons (Figure 3). During the interaction with the system, the user is guided by video and textual support. The 3D position of HandR joint, output by SDK, is tracked and re-projected onto the GUI screen, and the user selection is confirmed by considering the hand closure information provided by the SDK (Figures 1b, 2a and 3). At any time during an assessment session, the user can stop it and quit, for example when tired, to avoid the onset of stress and/or anxiety.

**Figure 3.** Gesture-based HCI: (**a**) GUI for the selection of lower limbs and postural tasks; (**b**) GUI for the selection of left/right leg before starting LA task.
