Age differences in letter and color matching: selective attention or internal noise?

We tested healthy young and older adults on a letter-matching task that varied letter identity and letter color (Experiment 1) and on a color matching task that varied letter color and letter identity (Experiment 2). The goal of this investigation was to empirically disentangle the theoretical concepts of internal noise and selective attention. The results from Experiment 1 indicated that both young and older adults exhibited "fast-same" effects for reaction time and "false-different" effects for errors, and older adults exhibited a relatively larger "false-different" effect. However, letter color did not affect performance. The data from Experiment 2 indicated that older adults, compared with young adults, evidenced greater interference from "different-similar" letter pairs than "different-dissimilar" letter pairs even though the task was color matching. These data suggest that older adults evidenced greater levels of internal noise, and that this factor may modulate age differences in selective attention.