Response slowing of older adults: effects of time-limit contingencies on single- and dual-task performances.

Younger and older men (18-25 vs. 65-76 years of age) were given extended practice (44 hr) with a memory scanning procedure in which lists of visual and auditory items were presented singly (single-task condition) or together with a second visual or auditory list (dual-task condition). For both age groups, identification of test items was slower with the dual-task procedure, and experience with the tasks produced only small changes in response latencies. When time limits were placed on responding, latencies decreased substantially, and the difference between single and divided tasks was reduced. Although the older men were slower throughout the experiment, the time limit contingency reduced age differences in responses to both tasks. The task effect was larger for the older men, but this age difference also was reduced by the time limit procedures.