Attention allocation in the dual-task paradigm as measured through behavioral and psychophysiological responses

We investigated attention allocation in a dual-task paradigm using behavioral and pupillary measures. We used an auditory digit span (DS) and a simple visual response time (RT) task. Participants were administered four conditions in which they performed neither task (no-task), a single task (DS or RT only), or both tasks (dual). Dependent variables were DS accuracy, RT, and task-evoked pupillary responses (TEPRs) to digits as estimates of mental effort. Participants maintained almost the same level of DS accuracy on dual as on DS only and sacrificed speed on the RT task. As expected, TEPRs increased linearly with memory load in both DS only and dual. Although TEPRs were initially higher in dual than in DS only, the slope of the increase was shallower in dual. Results suggest that TEPRs can elucidate mechanisms of attention allocation by distinguishing between effectiveness (level of behavioral performance) and efficiency (the costs of that performance in mental effort).