Towards Brain-Computer Interface Speller with Movement-Related Cortical Potentials as Control Signals

Jose Jesus Hernandez-Gloria ^1,2 Andres Jaramillo Gonzalez ^1,2 Andrej M Savic ³ Natalie Mrachacz Kersting ^1,2,4*

• ¹ Department of Sport and Sport Science, Wirtschafts- und Verhaltenswissenschaftliche Fakultät, Albert Ludwigs Universität Freiburg, Freiburg, Germany
• ² Albert Ludwigs Universität Freiburg, Freiburg, Germany
• ³ School of Electrical Engineering, University of Belgrade, Belgrade, Serbia
• ⁴ BrainLinks-BrainTools Center, IMBIT, Albert-Ludwigs University of Freiburg, Freiburg im Breisgau, Germany

Brain Computer Interface spellers offer a promising alternative for individuals with Amyotrophic Lateral Sclerosis (ALS) by facilitating communication without relying on muscle activity. This study assessed the feasibility of using movement related cortical potentials (MRCPs) as a control signal for a Brain-Computer Interface speller in an offline setting. Unlike motor imagery-based BCIs, this study focused on executed movements. Fifteen healthy subjects performed Three spelling tasks that involved choosing specific letters displayed on a computer screen by performing a ballistic dorsiflexion of the dominant foot. Electroencephalographic signals were recorded from 10 sites centered around Cz. Three conditions were tested to evaluate MRCP performance under varying task demands: a control condition using repeated selections of the letter "O" to isolate movement-related brain activity; a phrase spelling condition with structured text ("HELLO IM FINE") to simulate a meaningful spelling task with moderate cognitive load; and a random condition using a randomized sequence of letters to introduce higher task complexity by removing linguistic or semantic context. The success rate, defined as the presence of an MRCP, was manually determined. It was approximately 69% for both the control and phrase conditions, with a slight decrease in the random condition, likely due to increased task complexity. Significant differences in MRCP features were observed between conditions with Laplacian filtering, whereas no significant differences were found in single-site Cz recordings. These results contribute to the development of MRCP-based BCI spellers by demonstrating their feasibility in a spelling task. However, further research is required to implement and validate real-time applications.