Immersive 3D Virtual Reality Cancellation Task for Visual Neglect Assessment: A Pilot Study

Abstract

Background: Unilateral spatial neglectis an attention disorder frequently occurring after a right-hemispheric stroke. Neglect results in a reduction in qualityof life and performance in activities of daily living. With current technical improvements in virtual reality (VR) technology, trainingwith stereoscopic head-mounted displays (HMD) has become a promising new approach for the assessment and the rehabilitation of neglect. The focus of this pilot study was to develop and evaluate a simple visual search task in VR for HMD. The VR system was tested regarding feasibility, acceptance, and potential adverse effects in healthy controls and right-hemispheric stroke patients with and without neglect. Methods: The VR system consisted of two main components, a head-mounted display to present the virtual environment, and a hand-held controller for the interaction with the latter. The task followed the rationale of diagnostic paper-pencil cancellation tasks; i.e., the participants were asked to search targets among distractors. However, instead of a two-dimensional setup, the targets and distractors were arranged in three dimensions, in a sphere around the subject inside its field of view. Usability and acceptance of the task, as well as the performance in the latter, were tested in 15 right-hemispheric subacute stroke patients (10 of whom with and five of whom without unilateral spatial neglect; mean age: 67.1 ± 10.5 years) and 35 age-matched healthy controls. Results: System usability and acceptance were rated as high both in stroke patients and healthy controls, close to the maximum score of the questionnaire scale. No relevant adverse effects occurred. There was a high correlation (r = 0.854, p = 0.002) between the Center of Cancellation [an objective neglect measure) calculated from a paper-pencil cancellation task (Sensitive Neglect Test (SNT)] and the newly developed VR cancellation task. Conclusion: Overall, the developed visual search task in the tested VR system is feasible, well-accepted, enjoyable, and does not evoke any significant negative effects, both for healthy controls and for stroke patients. Findings for task performance show that the ability of the VR cancellation to detect neglect in stroke patients is similar to paper-pencil cancellation tasks.

Keywords: cancellation task; head-mounted display; immersive virtual reality; stroke; visual neglect.

Figure 1

Patient flow-chart from enrolment to analysis.

Figure 2

(A) Scheme of the subject wearing the head-mounted displays (HMD) and holding a virtual reality (VR) controller in the dominant hand overlaid with the targets and distractors. (B) Participant’s view, where not all objects were in the initial field of view but could be found by turning the head.

Figure 3

Overview and comparison of the questionnaire result from the System Usability Scale (SUS) and the Simulator Sickness Questionnaire (SSQ). The gray bars represent the mean values in the healthy controls, light gray represents the mean values for the stroke patients. No significant differences were found between the groups. The whiskers represent the mean standard error.

Figure 4

Center of Cancellation in the three groups (Neglect: dark-gray, No-Neglect: gray, Healthy: light-gray) in the paper-pencil (left side) and the VR cancellation task (right side). The asterisks represent the level of significance: **p < 0.01, ***p < 0.001. The whiskers represent the mean standard error. The Center of Cancellation represents the center of mass of the spatial distribution of detected targets and is standardized between plus and minus one (Rorden and Karnath, 2010).

Figure 5

Correlation plot with regression line (in red) of the Center of Cancellation calculated in the VR cancellation task and the paper-pencil cancellation task for all participants.

Figure 6

In-task performance data of the VR cancellation task of the three groups (Neglect: dark-gray, No-Neglect: gray, Healthy: light-gray). The top graph shows the number of targets per minute. The middle graph displays the mean solving time each group had. The bottom plot shows the percentage of found targets in each group. The asterisks represent the level of significance: *p < 0.05, ***p < 0.001. The whiskers represent the standard error.

Figure 7

In-task performance data of the VR cancellation task of the three groups (Neglect: dark-gray, No-Neglect: gray, Healthy: light-gray) of the first 5 s. In the top row, the number of targets found on the left and the right side is shown. In the bottom row, the total number of targets and the left vs. right difference is presented. The whiskers represent the standard error. The asterisks represent the level of significance after Bonferroni correction: ^•p < 0.1, **p < 0.01, ***p < 0.001.