Compensating for the mobile menace with extra effort: A pupillometry investigation of the mere presence effect of smartphones

Previous research suggests that the mere presence of a smartphone can detrimentally affect performance. However, other studies failed to observe such detrimental effects. A limitation of existing studies is that no indexes of (potentially compensating) effort were included. Further, time-on-task effects have been unexplored. Here, we address these limitations by investigating the mere-presence effect of a smartphone on performance in two continuous-performance experiments (Experiment 1 using an n-back and a number judgement task at two difficulty levels, and Experiment 2 using a pure, challenging n-back task), measuring pupil size to assess invested effort, and taking into account time-on-task effects. Finally, contrary to previous studies that predominantly used between-subject designs, we utilized within-subject designs in both experiments. Contrary to expectations, Experiment 1 largely yielded no significant effects of smartphone presence on performance. Nonetheless, the presence of a smartphone triggered larger tonic pupil size in the more difficult task, and a more rapid decrease over time. Experiment 2 similarly failed to demonstrate smartphone effects on performance, but replicated the finding of larger tonic pupil size in the presence of a smartphone. In addition, tonic pupil size showed a slower decrease over time when a smartphone was present. In Experiment 2, we could furthermore look at phasic pupil size, which decreased over time in the absence of a phone but not in its presence. These findings suggest a complex relationship between smartphone presence, effort, and time-on-task, which does not necessarily express itself behaviorally, highlighting in particular the need to also explore potential contributions of (compensatory) effort.