SUMMARY Three groups of patients who had suffered head injury were compared with matched control subjects on reaction time (RT) tasks. Group I consisted of outpatients previously hospitalised for head injury ofwide ranging degrees of severity, assessed at varying intervals after injury. Group II was composed of non-hospitalised mildly concussed patients. Group III was made up of head injured patients of varying degrees of severity assessed 7-10 months after initial hospitalisation for their injury. The reaction time tests were graded in difficulty, from a simple RT response to a complex choice RT test. In addition, subjects were compared in their ability to ignore redundant information during one of the choice RT tests. The findings indicate that traumatic brain injury causes slower information processing, deficits in divided attention, an impairment of focused attention, and inconsistency of performance.Reaction time (RT) tests have consistently revealed slowness ofinformation processing, a deficit in divided attention after head injury.' In this study, we addressed four specific issues concerning the effects of head injury on reaction time.The question of fatigue was examined by using the same simple RT test at the beginning and end of experimental sessions to see if head injured patients and normal control subjects changed their performance differently across the session.A second question addressed the nature of the attentional deficit. While "There can be no controversy... about the presence of DADs [divided attention deficit] in head injury",2 there has been less success in identifying a specific impairment in focused attention.< Focused attention is tested by evaluating the ability to ignore distracting stimuli. A selective involvement of frontal lobe areas has been suggested in head injury7"'1 and deficits in focused attention using

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