Using Sternberg's (1969) Additive Factors Method (AFM), previous investigations in search of the locus of age-related slowing in reactive capacity have found conflicting results possibly due to inconsistencies in research methodologies. This experiment was conducted to examine age differences in the performance of AFM intratask manipulations of a reaction time task using both fixed and variable foreperiod conditions with subject testing at both naive and practiced skill levels. Twenty male subjects, ten young and ten old, performed a visual four-choice RT task with intratask manipulations of stimulus-degradation, stimulus-response compatibility, and response-stimulus intervals (RSIs were fixed at 0, 2, and 5 sec and variable with random presentations at 0, 2, and 5 sec), once when subjects were naive and again when practiced. The results varied by level of practice and RSI, but clearly the older subjects had difficulty with the intratask manipulations. The older subjects took twice as long, on the average, to respond. Interactions of age by compatibility suggest that, according to the AFM, with age comes inordinately long delays in the response selection stage of information processing. Conclusions are made with caution since this research points to limitations and methodological confounds which serve to explain many of the equivocal findings in previous studies.
Neurophysiological modulations in the (pre)motor-motor network and the role of GABA+ levels underlying age-related reaction time slowing
