Age-related slowing, S-R compatibility, and stages of information processing

Previous work in this laboratory (Vercruyssen, Carlton & Diggles-Buckles, 1989) has found that older individuals are at a disproportional disadvantage when stimulus-response (S-R) compatibility were manipulated, age interacted with the S-R manipulation, suggesting in an additive factors framework that the locus of age-related slowing was the response selection stage. In that study S-R compatibility was manipulated by changing the S-R spatial map as well as changing the environment (subjects were required to cross their arms). The present study attempted to tease apart factors that might be contributing to that age x S-R compatibility relationship by using S-R maps of simple, moderate, and high difficulty as one factor and the arm position (crossed or uncrossed, a test of the Simon effect (Simon, Sly & Vilapakkam, 1981) as a different factor. In addition, stimulus quality was manipulated as a factor in this 4 factor design: age x stimulus quality x S-R map x arm position. Results revealed that both factors, S-R compatibility and arm position interacted with age. The conclusion from an additive factors perspective is that the stages of decision making (S-R compatibility) and response preparation (arm position) show age-dependent slowing whereas the stimulus encoding stage (stimulus quality) does not.