Reaction time indicators of attention deficits in closed head injury.

The nature of deficits in attention in closed head injury (CHI) was studied by three reaction time (RT) paradigms given to 20 patients who had a CHI 2 or more years previously and to 25 controls. We studied the effects of temporal uncertainty by varying the length and regularity of the preparatory interval, the effects of stimulus modality uncertainty on simple RT to tones and lights, and the effects of response selection in choice RT. The CHI group showed slower and more variable RT than controls under all conditions. In addition, a long preparatory interval on the preceding trial retarded RT more in the CHI group, and they showed greater effects of stimulus modality uncertainty. Both of these findings suggest a difficulty in shifting attention to unexpected stimuli. These greater effects on RT of variations of attention or preparation in CHI may account for their greater within-subject variability possibly due to frontal lobe damage.