A stimulus is displayed in a visual field on a stimulus side (e.g., right or left) of a subject. An input is received from an input side of the subject. Where the input side is contralateral to the first stimulus side, a crossed reaction time is determined as a span of time between displaying the stimulus and receiving the input. Where the input side is ipsilateral to the stimulus side, an uncrossed reaction time is determined as a span of time between displaying the stimulus and receiving the input. A crossed-uncrossed difference time can be determined as a difference between the crossed reaction time and the uncrossed reaction time. The crossed reaction time, the uncrossed reaction time, and/or the crossed-uncrossed difference time can be used to determine a severity of Traumatic Brain Injury of the subject.