This study used speed-accuracy trade-off (SAT) methodology to test competing explanations for processing speed deficits due to traumatic brain injury (TBI): fixed limited capacity and volition. Twenty TBI participants and 20 comparison participants performed a visual scanning task with processing times controlled by the experimenter using a response deadline procedure. Results of the study demonstrated marked differences in SAT functions between the two groups. Participants who had TBIs were significantly slower on information accrual across processing deadlines (supporting a fixed limit explanation), but when early responding was allowed they chose to hold off responding despite being no more accurate in their responses with the additional time (a finding supporting a volitional explanation). Results of the study are discussed in terms of a resource allocation model that incorporates the influences of both processing capacity and volitional processes for individuals who suffer from brain injuries.