When boosting preparation sets older adults free from central bottlenecking: Evidence for dual-task automaticity

Younger adults can, in certain conditions, select two responses in parallel, thereby bypassing the central attentional bottleneck that constrains their dual-task performance. Older adults, meanwhile, have never been found to attain such parallel central processing (i.e., dual-task automaticity), even with highly practiced or extremely easy tasks. Here we asked whether older adults do not bypass the central bottleneck because they apply extra attention to one or both tasks as a strategy to compensate for cognitive deficits. In Experiment 1, we used the traditional psychological refractory period (PRP) procedure and replicated the typical finding: even though Task 2 was extremely easy, it suffered from large dual-task interference (353 ms) due to a central bottleneck. Because the PRP paradigm prioritizes Task 1, we hypothesized that this central bottleneck is strategic: older adults strategically over-prepare Task 1 at the expense of Task 2. So, in Experiment 2, we induced older adults to more evenly balance preparation between the two tasks. We did so by randomly intermixing single-task trials of each task amongst the dual-task PRP trials. This rebalancing of preparation allowed most older adults (20 out of 24) to consistently select the two responses in parallel, as evidenced by a close match between the observed distribution of inter-response intervals and that predicted by bottleneck bypassing, as well as by surprisingly little dual-task interference on Task 2 (85 ms). We conclude that older adults' processing mode is governed by the preparatory state, which can be modified to enable dual-task automaticity.