Stimulus preprocessing, response selection, and motor adjustment in the elderly: An additive factor analysis

Old adults are slower in reaction time (RT) tasks than young adults. Howeve r, it is not clear whether aging affects all stages of information processi ng or only some of them. In the present study, this question was addressed using the additive factor method. Eight old adults (aged 68-91, M = 80) and eight young adults (aged 22-33, M = 27) performed a two-choice visual RT t ask. Signal intensity, stimulus-response mapping, and foreperiod duration w ere manipulated. The effects of these three variables were found to be addi tive on RT, indicating that the three stages manipulated - namely, stimulus preprocessing, response selection, and motor adjustment - were independent . Importantly, this stage structure was robust across age conditions. This demonstrates the merits of the additive factor method in aging research. Th e old subjects' RT was expressed as a function of the young subjects' RT th rough a regression function. An analysis of variance on the transformed dat a yielded no interactions between age group and any of the manipulated fact ors. This lends support to the idea that aging affects stimulus preprocessi ng, response selection, and motor adjustment to the same proportional degre e.