Task-Specific Stimulation Duration for fNIRS Brain-Computer Interface

In this paper, the most effective stimulation durations in the visual, somatosensory, and motor cortices are investigated. To evoke hemodynamic responses (HRs) for the purpose of brain-computer interface (BCI) with functional near-infrared spectroscopy (fNIRS), the best and the minimal durations for three tasks (visual, tapping, and poking) are presented. The examined tasks include the checkerboard, right-hand-index-finger poking, and the right-hand-index-finger tapping tasks in association with the visual, somatosensory, and motor cortices. Upon stimulations, the peak value, time to peak, and the full width at half maximum of the HRs are examined. Six different stimuli durations (i.e., 1, 3, 5, 7, 10 and 15 sec) were tested. Ten male subjects participated in the experiment. Three types of stimulations having the same duration were presented to the subjects randomly. The stimulation durations that showed the maximum peak values in the checkerboard, poking, and tapping tasks were 7, 5, and 10 sec, respectively. The peak value increased with the increase of stimulation duration. But beyond a certain period of time, the peak value did not increase anymore and sometimes it decreased when the stimulation period is too long. It is noted that 1-sec stimulation (for all three tasks) can generate a noticeable peak value. Instead, the initial dip upon poking occurred only with 1-sec poking (i.e., initial dip did not occur in all other poking periods). Conclusively, this work reveals the possibility of a BCI command generation within 1 sec.