It is well known that old people respond more slowly than young but it is not known whether these changes occur because some elements in control processes which are responsible for choice and execution of responses are impaired more than others by advancing age. In order to control response speed and accuracy human beings must be able to exercise control of three parameters: (1) they must detect errors when they occur; (2) they must be able to monitor and vary response speed so as to recognize, and avoid, faster RT bands at which errors are intolerably frequent; (3) they must be able to adaptively control response speeds so as to select optimal RT bands and avoid others which may be too fast or too slow.

In two serial, self-paced C.RT experiments groups of old people were found to detect and correct their errors as efficiently as young. With increasing age RTs for error and for error correction responses remained relatively constant while RTs for correct responses and for other, arbitrary, error-signalling responses markedly increased. It seems that efficiency of error detection and maximal response speed are relatively unimpaired with age. It seems likely that slowing of C.RT with age is related to loss of precise control over speed at which responses can be made, or to loss of fine differentiation between ‘fast’ and ‘slow’ responses.