## Materials and Methods
### Experimental Design and Set-Up  
The pilot study as well as its experimental set-up were approved by the ethics committee of Ulm University, Germany ([[https://www.uni-ulm.de/einrichtungen/ethikkommission-der-universitaet-ulm/](https://www.uni-ulm.de/einrichtungen/ethikkommission-der-universitaet-ulm/)]([https://www.uni-ulm.de/einrichtungen/ethikkommission-der-universitaet-ulm/](https://www.uni-ulm.de/einrichtungen/ethikkommission-der-universitaet-ulm/))). The criteria for the inclusion of participants were defined as follows: Healthy young adults (e.g., students from Ulm University, Germany, or from Ulm University of Applied Sciences, Ulm, Germany) with no history of drug abuse, medication, somatic injuries, or somatic, physiological, or neurological diseases could take part in the pilot study. The participants had to fill in a pre-study questionnaire to confirm these parameters and give oral and written informed consent for voluntary participation. In total, three volunteers (three females, age: 22-24 years) were included for pilot testing. All participants wore glasses, since all three were short-sighted. Participants were asked to walk on the treadmill with bare feet. The experiment was conducted in the EEG-FNIRS Brain Imaging Lab of the Department of Applied Emotion and Motivation Psychology at Ulm University, Germany. Furthermore, the interface solutions were tested in the Motion Lab of the Research Group for Biomechatronics of Ulm University of Applied Sciences, Germany.  
Upon arrival at the laboratory, the participants received detailed instructions about the experiment and were debriefed about its purpose. They were accustomed to the treadmill and the EEG recording (see Figure 2 for an overview). They received practice trials to determine individual preferences for walking on the treadmill at their own preferred pace. Next, participants were familiarized with the procedure of the experimental psychological walking paradigm. The paradigm was developed to standardize and control the participants' gait cycles in different conditions of spontaneous and instructed treadmill walking. In total, seven different experimental conditions were created. These conditions were experimentally designed in a manner such that they manipulated the participants' selective attention to gait. This allowed us to produce reliable and reproducible alterations in the gait cycles and to explore gERP components across varying degrees of voluntary attention. While walking on the treadmill at the velocity of their own pace, the participants received detailed written instructions on the TV screen. They were told to walk spontaneously without any specific attention focus (task 1). Next, they received the instruction to take big steps (task 2), small steps (task 3), to concentrate on the left initial contact (task 4) or the right initial contact (task 5), on the left toe-off (task 6) or the right toe-off (task 7). Tasks and walking conditions were randomized, and they were counterbalanced across participants. Each task lasted about 30 s and was repeated four times in a randomized order. Between each task condition, 30 s of normal walking were included. At the start and the end of the experiment, the participants were asked to walk for about 4 min without any task to have additional data for the training of the artificial network (see Section 2.9). None of the three participants stated any problems with the tasks given. All participants independently chose to walk with a pace of 3.5 km/h.