title: Individually adapted imagery improves brain-computer interface performance in end-users with disability.
abstract: Brain-computer interfaces (BCIs) translate oscillatory electroencephalogram (EEG) patterns into action. Different mental activities modulate spontaneous EEG rhythms in various ways. Non-stationarity and inherent variability of EEG signals, however, make reliable recognition of modulated EEG patterns challenging. Able-bodied individuals who use a BCI for the first time achieve - on average - binary classification performance of about 75%. Performance in users with central nervous system (CNS) tissue damage is typically lower. User training generally enhances reliability of EEG pattern generation and thus also robustness of pattern recognition. In this study, we investigated the impact of mental tasks on binary classification performance in BCI users with central nervous system (CNS) tissue damage such as persons with stroke or spinal cord injury (SCI). Motor imagery (MI), that is the kinesthetic imagination of movement (e.g. squeezing a rubber ball with the right hand), is the "gold standard" and mainly used to modulate EEG patterns. Based on our recent results in able-bodied users, we hypothesized that pair-wise combination of "brain-teaser" (e.g. mental subtraction and mental word association) and "dynamic imagery" (e.g. hand and feet MI) tasks significantly increases classification performance of induced EEG patterns in the selected end-user group. Within-day (How stable is the classification within a day?) and between-day (How well does a model trained on day one perform on unseen data of day two?) analysis of variability of mental task pair classification in nine individuals confirmed the hypothesis. We found that the use of the classical MI task pair hand vs. feed leads to significantly lower classification accuracy - in average up to 15% less - in most users with stroke or SCI. User-specific selection of task pairs was again essential to enhance performance. We expect that the gained evidence will significantly contribute to make imagery-based BCI technology become accessible to a larger population of users including individuals with special needs due to CNS damage.
authors.affiliation: Institute for Knowledge Discovery, Graz University of Technology, 8010 Graz, Austria; BioTechMed-Graz, Austria; Clinic Judendorf-Straßengel, 8111 Gratwein-Straßengel, Austria.
authors.forename: Reinhold
authors.initials: R
authors.lastname: Scherer
authors.affiliation: Institute for Knowledge Discovery, Graz University of Technology, 8010 Graz, Austria; BioTechMed-Graz, Austria.
authors.forename: Josef
authors.initials: J
authors.lastname: Faller
authors.affiliation: Institute for Knowledge Discovery, Graz University of Technology, 8010 Graz, Austria; BioTechMed-Graz, Austria; Department of Cognitive Science, University of California, San Diego, La Jolla, CA, 92093, USA.
authors.forename: Elisabeth V C
authors.initials: EV
authors.lastname: Friedrich
authors.affiliation: Institut Guttmann, Institut Universitari de Neurorehabilitació adscrit a la UAB, 08916 Badalona, Barcelona, Spain.
authors.forename: Eloy
authors.initials: E
authors.lastname: Opisso
authors.affiliation: Institut Guttmann, Institut Universitari de Neurorehabilitació adscrit a la UAB, 08916 Badalona, Barcelona, Spain.
authors.forename: Ursula
authors.initials: U
authors.lastname: Costa
authors.affiliation: Institute of Psychology, University of Würzburg, 97070 Würzburg, Germany.
authors.forename: Andrea
authors.initials: A
authors.lastname: Kübler
authors.affiliation: Institute for Knowledge Discovery, Graz University of Technology, 8010 Graz, Austria; BioTechMed-Graz, Austria.
authors.forename: Gernot R
authors.initials: GR
authors.lastname: Müller-Putz
mesh_terms: D000328:Adult; D001921:Brain / Q000503:physiopathology; D062207:Brain-Computer Interfaces / Q000523:psychology; D004569:Electroencephalography; D005260:Female; D006801:Humans; D019018:Imagery, Psychotherapy; D007092:Imagination; D008297:Male; D008875:Middle Aged; D009068:Movement; D011782:Quadriplegia / Q000503:physiopathology / Q000523:psychology / Q000534:rehabilitation; D015203:Reproducibility of Results; D013119:Spinal Cord Injuries / Q000503:physiopathology / Q000523:psychology / Q000534:rehabilitation*; D020521:Stroke / Q000503:physiopathology / Q000523:psychology; D000071939:Stroke Rehabilitation; D014584:User-Computer Interface; D055815:Young Adult