CC BY 4.0Vorreuther, AnnaAnnaVorreutherBastian, LisaLisaBastianBenitez Andonegui, AmaiaAmaiaBenitez AndoneguiEvenblij, DanielleDanielleEvenblijRiecke, LarsLarsRieckeLührs, MichaelMichaelLührsSorger, BettinaBettinaSorger2024-01-152024-01-152023-10-01https://publica.fraunhofer.de/handle/publica/458744https://doi.org/10.24406/publica-243110.1117/1.NPh.10.4.04500510.24406/publica-24312-s2.0-85181506675Significance: Brain computer interfaces (BCIs) can provide severely motorimpaired patients with a motor-independent communication channel. Functional near-infrared spectroscopy (fNIRS) constitutes a promising BCI-input modality given its high mobility, safety, user comfort, cost-efficiency, and relatively low motion sensitivity. Aim: The present study aimed at developing an efficient and convenient two-choice fNIRS communication BCI by implementing a relatively short encoding time (2 s), considerably increasing communication speed, and decreasing the cognitive load of BCI users. Approach: To encode binary answers to 10 biographical questions, 10 healthy adults repeatedly performed a combined motor-speech imagery task within 2 different time windows guided by auditory instructions. Each answer-encoding run consisted of 10 trials. Answers were decoded during the ongoing experiment from the time course of the individually identified most-informative fNIRS channel-bychromophore combination. Results: The answers of participants were decoded online with an accuracy of 85.8% (run-based group mean). Post-hoc analysis yielded an average single-Trial accuracy of 68.1%. Analysis of the effect of number of trial repetitions showed that the best information-Transfer rate could be obtained by combining four encoding trials. Conclusions: The study demonstrates that an encoding time as short as 2 s can enable immediate, efficient, and convenient fNIRS-BCI communication.enMotor disability"locked-in" syndromeBrain-based communicationBrain-computer interfacefNIRSMental imageryOnline data analysisjournal article