Preparing to react in the absence of uncertainty: I. New perspectives on simple reaction time

Almost from the inception of psychological enquiry into reaction time (RT), a broad distinction has been drawn between two types of process-serving performance in RT tasks, namely, the on-line processes initiated by the arrival of the imperative signal and preparatory processes, which precede the imperative signal and may contribute to performance efficiency. Restriction of attention to on-line processing fosters the conclusion that the processes serving simple RT are no more than a subset of those involved in choice reactions. If, however, latencies can be reduced by specific preparation then the certitudes of the simple reaction task may invest it with distinctive properties. The possibility of preparation being sensory as well as motor needs to be considered. Until recently, attempts to study preparedness have failed to make controlled comparisons across simple and choice RT. However, recent work has shown that simple reactions have distinctive characteristics that set them apart from minimal choice reactions. The optimization of simple RT seems to depend upon attention-demanding processes which are probably preparatory in nature. When attention has to be shared with a concurrent task, much of the normal advantage of the simple reaction is lost. Neuropsychological studies suggest that patients may be found with abnormally extended simple RT but spared choice reactions. In these patients, the simple reactions are prolonged relative to those of controls but less vulnerable to imposition of a secondary task. Evidence is beginning to accrue to the effect that some distinctive processing features of simple reactions may be mediated by activity in the frontal lobes.