Near-infrared spectroscopy (NIRS) brain-computer interfaces (BCIs) enable individuals to interact with their environment using only cognitive activities. This thesis investigates the development of a more user-friendly, intuitive, and easy to use NIRS-BCI through six research objectives:​ exploring prescribed and personalized mental task frameworks offline, using researcher-selected tasks to move beyond the binary paradigm, exploring correlations of user characteristics with accuracy, comparing user-selected personalized tasks to prescribed tasks online, weaning off mental tasks to achieve voluntary self-regulation, and applying personalized frameworks to a client case study.

Firstly, personalized tasks outperformed prescribed tasks in a five-session offline study conducted on ten able-bodied participants. Specifically, user-selected tasks resulted in significantly higher ease-of-use, while researcher-selected tasks resulted in significantly higher accuracies. The same data were used to show that researcher-selected personalized mental tasks enabled classification in some users beyond a binary BCI paradigm. Accuracy was strongly positively correlated with perceived ease of session, ease of concentration, and enjoyment, but strongly negatively correlated with verbal IQ. In a second study, when comparing two able-bodied groups online (N = 9 and N = 10), the usability of user-selected personalized mental tasks exceeded prescribed mental tasks without a decrease in accuracy. Expanding on this study, the nine able-bodied subjects who used user-selected tasks took part in an additional ten sessions and were weaned off mental tasks to achieve online voluntary self-regulatory control of a BCI using a neurofeedback-based paradigm. Participants indicated that they found self-regulation to be more intuitive and easier to use than mental tasks. Finally, user- and researcher-selected frameworks were applied to a client with undiagnosed motor impairments, unveiling a host of neuropsychological challenges to BCI control. Overall, this thesis advances the field of knowledge of NIRS-BCIs, specifically with respect to usability