Simple and choice reaction time to visual signals were recorded in persons having sustained a closed head injury. The results show a disproportional effect of task complexity in comparison to the performance of a normal group. Moreover, an interaction was demonstrated between complexity of the reaction task and length of coma after the injury. Finally it was shown that this interaction was still visible 22 months after the concussion. At that time, there is no longer a difference in simple reaction time between groups with different lengths of coma, while there is still a significant difference in the choice reaction task.