Effects of performance feedback on P300 and reaction time in closed head-injured outpatients.

In an earlier study, we have demonstrated that the choice reaction times (RTs) of closed head-injured patients may be reduced significantly by instructions which emphasize speed, thus indicating that this portion of the RT delay was not due to a motor deficit. Despite the reduction in patient RTs, however, they remained significantly longer than those of controls. Furthermore, the RTs of patients were 56 msec longer than their P300 latencies, whereas those of controls occurred at about the same time as P300. The delay which remained in patient RTs was thus not entirely due to longer stimulus evaluation times. The goal of the present study was to further reduce patient RTs using feedback (FB) on response speed and time windows within which subjects were required to respond. When FB on speed and a 'narrow' time window were used, patient RTs occurred at about the same time as P300 latency (as was also the case with controls) indicating that the longer RTs of these patients in our earlier study, and in the other conditions of the present study, could not have been exaggerated beyond P300 latency due to a motor deficit. It was suggested that CHI patients may not be able to internally monitor their responses to the same degree as controls. The provision of external cues may have compensated for this deficit.