A novel technology has been developed at the University of South Dakota that uses pupil diameter as the physiological input for brain computer interfaces. Since this invention uses pupil diameter as a secondary input (EEG being the primary input), patients suffering from severe motor disabilities can utilize this technology. To date, known hBCI systems have not taken advantage of pupil diameter as an input, and USD investigators have created an algorithm to verify pupil diameter use in target letter selection in a BCI speller. Incorporating pupillometry into new and existing commercially available products can be used to increase spelling performance and usability than by EEG detection alone. For some individuals, eye tracking is not an option for them to communicate; for example, locked-in ALS patients are unable to utilize eye tracking technology.