1. Introduction
Serious games (SG) can improve gait rehabilitation. [1] In an augmented reality environment, the real time visual feedback modalities can be multiple [2]. This study aims to test the feasibility of the protocol to compare the effect of three visual feedback modalities on reaching and exceeding a target walking speed.

2. Research Question
Is the study design adapted to test if there is a feedback modality that optimize the control of gait speed?

3. Methods
The SG has been developed for Microsoft Hololens Augmented Reality (AR) headset. The target speed (mean maximum walking velocity on 20 meters) of fifteen participants was recorded during a calibration trial. Each participant then tested randomly four mini games plus the control on 30 meters (Fig. 1). Displacement of the participant was recorded (100 Hz) with the Hololens. [3] Time spent above the target speed and mean speed were compared between feedback modalities.

4. Results
There was a significant difference between feedback modalities for the difference between mean speed and target speed (p < 0.001). The combination of Knowledge of Result, World-locked content, and challenging game seemed to be the best way to exceed the target speed (percent of time spent above target speed of 78%+/-18%). The distance difference between the calibration trial and the test trials is not enough, all the participants succeed in reaching their target speed with the control condition (without feedback).

5. Discussion
Visual feedback modalities in AR have a real time effect on the controllability of the walking speed. The future study should include a harder task of walking speed. It should be interested to calibrate the target speed using the Muscle-Power-Sprint-Test [4] and to test the feedback modalities on 30 meters.

References
[1] S. Lopes, et al., Games Used With Serious Purposes: A Systematic Review of Interventions in Patients With Cerebral Palsy, Frontiers in Psychology 9 (2018).
[2] A. MacIntosh, E. Lam, V. Vigneron, N. Vignais, E. Biddiss, Biofeedback interventions for individuals with cerebral palsy: a systematic review, Disability and Rehabilitation (2018) 1–23.
[3] A.L. Guinet, G. Bouyer, S. Otmane, E. Desailly, Reliability of the head tracking measured by Microsoft Hololens during different walking conditions, Comput Methods Biomech Biomed Engin (2019).
[4] O. Verschuren, T. Tak