Virtual reality as a tool for evaluation of repetitive rhythmic movements in the elderly and Parkinson's disease patients

Abstract

This work presents an immersive Virtual Reality (VR) system to evaluate, and potentially treat, the alterations in rhythmic hand movements seen in Parkinson's disease (PD) and the elderly (EC), by comparison with healthy young controls (YC). The system integrates the subjects into a VR environment by means of a Head Mounted Display, such that subjects perceive themselves in a virtual world consisting of a table within a room. In this experiment, subjects are presented in 1(st) person perspective, so that the avatar reproduces finger tapping movements performed by the subjects. The task, known as the finger tapping test (FT), was performed by all three subject groups, PD, EC and YC. FT was carried out by each subject on two different days (sessions), one week apart. In each FT session all subjects performed FT in the real world (FT(REAL)) and in the VR (FT(VR)); each mode was repeated three times in randomized order. During FT both the tapping frequency and the coefficient of variation of inter-tap interval were registered. FT(VR) was a valid test to detect differences in rhythm formation between the three groups. Intra-class correlation coefficients (ICC) and mean difference between days for FT(VR) (for each group) showed reliable results. Finally, the analysis of ICC and mean difference between FT(VR) vs FT(REAL), for each variable and group, also showed high reliability. This shows that FT evaluation in VR environments is valid as real world alternative, as VR evaluation did not distort movement execution and detects alteration in rhythm formation. These results support the use of VR as a promising tool to study alterations and the control of movement in different subject groups in unusual environments, such as during fMRI or other imaging studies.

Figure 1. Virtual Reality System.

Representation of the different elements in the system: movement of reflective markers at the Patient/Subject's anatomical points (1.1) are captured by IR cameras (1.2, 1.3, 1.4) and the cameras send information to the main computer, which integrates subjects movements into the virtual experience. An acquisition module (1.5) connects reciprocally to the main computer, so that different analogue and digital input/outputs can be controlled. The Subject wears the HMD, and the display is also shown on the main computer for experimenter to supervise the experience. The figure represents the virtual environment and the avatar's forearms in 1^st person perspective. The HMD is provided with tri-axial accelerometer tracking head movements and has been modified with black foam in order to isolate subjects completely from the real environment. The foam adapts to the subjects' face thereby “removing” the subject from the real world environment.

Figure 2. Motor behavior in the different days during VR testing.

The figure represents the motor behavior on the first and second days of evaluation (blue and green respectively) for the different variables. Pair-wise comparisons after Bonferroni correction show that PD had larger variability that EC and YC on both days.

Figure 3. Scatter plot comparing execution between days in the VR environment.

The figure illustrates the motor behavior on the first and second days of evaluation for each group and for both variables (Tapping Frequency left panel, CV right panel). ICC values between days, and 95% CI for the mean difference between days for each group and variable, are presented in tables.

Figure 4. Scatter plot comparing execution in Real and VR environments.

The figure shows the behavior in both conditions for each group and for both variables (Tapping Frequency left panel, CV right panel). ICC values and 95% CI for the mean difference between conditions (VR and Real), for each group and variable, are presented in tables.